question

PT 1- What Is Science?

answer

- Science is a discipline that tries to explain the world around us (religion, philosophy, and other fields do the same thing, but they use different tools) - Science is based on facts- things you can repeatedly demonstrate as true

question

The Scientific Method

answer

- The process used by scientists to test explanations - Step 0- Make an observation (Ex: you notice one type of flower is bigger than another) - Step 1- Ask a question (Ex: 'Why is Flower A bigger than Flower B?)

question

Scientific Method continued

answer

- Step 2- Form a hypothesis- An 'educated guess' based on preliminary data ;/or observations (Ex: you know plants need water, so maybe Flower A has been getting more water than Flower B)

question

Scientific Method continued

answer

- A good hypothesis is testable - You must be able to gather facts to determine if your hypothesis is correct - Note- you do not have to re-create an event to study it! (Ex- dinosaurs went extinct long ago, but we can still develop and test hypotheses about why they went extinct) - Some hypotheses are hard to test, but that's ok

question

Scientific Method continued

answer

- Step 3- Gather information (data) - Do an experiment to get some facts that will test your hypothesis

question

Scientific Method continued

answer

- Step 4- Use your data to evaluate your hypothesis - Do the data support your hypothesis? If so, you still have to repeat your experiment to make sure it's not a one-time fluke

question

Scientific Method continued

answer

- Theory- A hypothesis that has withstood repeated testing over a long time There is a lot of data, collected over a long time, by many different people, that supports the idea Saying "that's just a theory" = a good thing in science! That phrase is often meant in a negative way outside of science - Principle- an important concept treated as a fact The idea is so well established we do not have to test it any more - Law- A theory that seems irrefutable

question

Scientific Method continued

answer

- Theories and laws are sometimes tested and revised - It is fine to disagree with a hypothesis, but if you want to disprove it, you must come up with a new hypothesis that better explains the data. - You can't just say, 'I don't like that hypothesis so it's wrong", That's just your opinion, not a fact. - You must have scientific data to challenge scientific ideas

question

PT 2- What is Geology?

answer

- Geology = "study of the Earth" - Q: Why do we care about Geology? - A: Earth is the only planet we can live on at this time, so we need to understand it. - Geology was devised in the early 1800s.

question

Q: How did people study the Earth before Geology?

answer

- Other ideas existed - Ex: Catastrophism (1600s-1700s) stated that the Earth formed by a few big, catastrophic events, like Noah's flood

question

Who Invented Geology?

answer

- James Hutton (1795, Scotland) - He noticed that small, slow changes could add up over time to create a big change (Ex- an entire mountain could be worn down by eroding it little by little over a long time) - This idea became the Principle of Uniformitarianism (Natural processes observed today are identical to those that operated in the past, so "the present is the key to the past").

question

Uniforimitarianism continued

answer

- Uniformitarianism replaced Catastrophism - Catastrophic events do play a role in Earth history (Ex: when an asteroid strikes the Earth) - Uniformitarianism is the rule, and catastrophes are exceptions to that rule

question

PT 3- How Did Earth Form?

answer

- > 6 billion years ago (= 6 Ga): No solar system existed, just a nebula of Hydrogen (H) atoms - Nebula- giant cloud of rotating gas - Nebular Hypothesis- the hypothesis with the most support currently - Step A- Gravity pulled H atoms together, forming a dense, hot core - Step B- gas around the core formed a flattened, rotating disk (Solar Disk Model)

question

Nebular Hypothesis con't

answer

- Step C- About 6 Ga: the core reached millions of degrees and becomes a protostar - To become a star, the temp had to increase more so fusion could begin - Fusion- combining 2 atoms into 1 larger atom (Ex: H + H = Helium (He)) - Step D- Once fusion began, the protostar became our Sun The surrounding disk began to cool down

question

Forming the Planets

answer

- At first, only dust-sized particles existed in the cooling disk, but those particles were moving very fast. - Collisions made them begin to stick together - Planetary accretion-build-up of larger bodies via collisions of smaller particles (Go from small chunks of rock and ice to meteorites, asteroids, and eventually planets) - By ~ 4.5 Ga Earth was mostly assembled - Planetary accretion still happens today! (Ex: the meteorite in the picture landed in Kansas)

question

Forming the Earth continued

answer

- The impacts produced heat (Remember the practice exercise form earlier? Lots of heat energy gets released during high-speed collisions) - About 4.5 Ga: Earth impacted a Mars-sized object - The impactor formed the moon - The temp increase melted the solid, outer Earth, creating a magma ocean

question

Density Stratification of the Earth

answer

- After the 'moon impact' everything was liquid Dense materials, like Iron (Fe) and Ni, sank Less dense elements (like O and Si) rose to Earth's surface - This created distinct chemical layers within the Earth - Eventually surface materials cooled down and became solid again. - The density stratification remained, creating distinct chemical layers within the Earth (continued after the next slide)....

question

Density Review

answer

- In case you don't remember... - Density- mass per unit volume. D = M/V (Ex: g/cm3 or pounds/gallon) - Rocks, minerals, elements, etc all have different densities - Materials with different densities tend to separate (Ex: oil and water separate in a test tube b/c they have different densities)

question

Compositional Layers of the Earth

answer

- 4 layers, defined by chemistry (aka composition) 1-Crust (goes down 8-45 km) (Contains lots of low-density elements (Si, O, Al)) - 2-Mantle (from 45-2900 km) (Denser elements more common (Fe, Mg, Mn)) The Core (Densest, mostly Fe & Ni) - 3-Outer core- some O & S - 4-Inner Core- just Fe & Ni-

question

Types of Crust

answer

- There are 2 types of crust - Continental crust differs from oceanic crust in that it is less dense - Denser oceanic crust is limited to the seafloor

question

Physical Layers of the Earth

answer

- Earth can also be divided up into a different layering system defined by physical (aka mechanical) strength of the rocks. 2 general strengths: - Brittle- at low temp, rocks are strong and hard to break. When they break, they shatter. Ex- Put a candy bar in the freezer, then take it out and break it- it's hard and shatters (don't actually try this at home!) - Ductile (aka Plastic)- at higher temp, solids start to become 'gooey' and can start to flow. Ex: leave a candy bar on your dashboard for an hour on a hot, sunny day. When you pick it up it will bend very easily

question

Physical Layers of the Earth

answer

- 1-Lithosphere (About 100 km thick, brittle rocks) - 2-Asthenosphere (A few hundred km thick, rocks become ductile but flow slowly (like peanut butter). Not a fluid!) - 3-Mesosphere (lower mantle) (Rocks switch back to more brittle behavior, The temp is higher, but so is the Pressure, which counteracts the temperature effect) - 4-Outer Core (Rocks become ductile again, flow easily (like ketchup)) - 5- Inner Core (Rocks become brittle again, essentially solid Fe)

question

The 2 Layering Systems

answer

- Note: the layers in the 2 systems do not all line up! (see the diagram) Ex: Crust ? Lithosphere Ex: Mantle ? Asthenosphere - You cannot use the names interchangeably (The systems are based on different things and have different thicknesses)

question

Q: How Do We Know What's Within the Earth?

answer

- Drilling only goes down a few miles at best - We study Earth's interior with other tools: 1- Volcanoes. Eruptions bring material to the surface 2- Earthquakes. Seismic waves tell us about density within the Earth (we'll come back to this in a later lecture) 3- Meteorites. Earth formed via accretion of meteorites, and their composition reflects Earth's overall composition

question

PT 1- Plate Tectonics

answer

- Q: Why do we care about this topic? - A: almost all Earth processes relate back to plate tectonics (Ex: climate, flora & fauna, volcanoes, earthquakes, rock and mineral distribution, fossil fuel deposits, etc etc etc)

question

Example: Climate in Antarctica

answer

- Today: Antarctica is at the South Pole, surrounded by a cold, oceanic current - 90 million years ago (= 90 Ma): Antarctica was farther north and had a climate like Canada's, with lots of plants & animals living there. - Tectonics changed the continent's location, which affected it's climate, flora, & fauna.

question

What is Plate Tectonics?

answer

- The lithosphere is divided into several pieces (plates) that move around Earth's surface - Often described as 'floating' on the ductile asthenosphere (Ex: icebergs moving around the surface of the ocean)

question

Plate Tectonics continued

answer

- Note: plate boundaries do not correspond to continent and ocean boundaries (see the map on the next slide). - Some plates contain just oceanic crust, some contain just continental crust, and some contain both - Remember: the crust is equal to just the upper part of the lithosphere

question

PT 2- Discovering Plate Tectonics

answer

- Early cartographers (map-makers) noticed that the continents looked like puzzle pieces that could fit together

question

Discovering Plate Tectonics

answer

- Early 20th century: Alfred Wegener developed the Continental Drift hypothesis - Thought that continents moved (drifted) over time. His evidence: (Continental boundaries fit together, Some fossil species were found on opposite sides of the ocean, Ex; mesosaurs were small reptiles whose fossils are found in Africa and South America)

question

Discovering Plate Tectonics

answer

- Continental Drift did not get much support right away. - The problem: Wegner could not explain HOW the continents moved. - So the idea was dismissed until the 1940s....

question

Discovering Plate Tectonics

answer

- WWII: lots of submarine warfare necessitated detailed maps of the ocean floor Scientists already knew there was a Mid-Ocean - Ridge- a long mountain chain that runs throughout the world's oceans (Ex: like the seam on a baseball)

question

Seafloor Anomalies

answer

- Scientists found some unusual features on the seafloor while mapping it during the 1940s-1960s - Found magnetic anomalies in seafloor rocks - Rocks close to the MOR record Normal magnetic polarity The magnetic mineral grains point North - But moving farther from the MOR, rocks begin alternating btwn Normal & Reverse polarity (see fig next slide)

question

Seafloor Anomalies continued

answer

- This meant that Earth's magnetic field changed through time, and the seafloor rocks were not all the same age

question

Seafloor Anomalies continued

answer

- Dating seafloor rocks confirmed this. - On the map, hot colors = young rocks, cool colors = old rocks - So rks are youngest near the MOR & get progressively older as you move away from the MOR

question

Explaining the Anomalies

answer

- Notice that the magnetic & age anomalies produce mirror images to the east & west of the MOR - Led to the Seafloor spreading hypothesis-lava rises to the surface at the MOR, cools to form new rocks, then the rocks get pushed aside as more lava comes up to the surface.

question

Explaining the Anomalies

answer

- Seafloor spreading revived Wegner's Continental drift hypothesis - This provided the mechanism for making continents move

question

How Do Plates Move?

answer

- Seafloor spreading is driven, in part, by convection- hot, low-density material moves upward displacing cooler, higher density material - Convection within the ductile asthenosphere helps move the brittle lithospheric plates - A simple convection system. The flame heats water that then rises. Then it is pushed aside, cools, and sinks closer to the flame, where it starts the process over

question

New Hypotheses

answer

- We now know that convection is only one process that makes plates move - Ridge Push Model- buoyant material near the MOR pushes the plates apart & they slide downhill away from the MOR

question

New Hypotheses

answer

- Slab Pull Model- as one end of the plate sinks, it pulls the rest of the plate down behind it - Slab Suction Model- The descending plate sucks down some asthenosphere, helping 'stir' the convection cell

question

Practice Exercise: How Fast Do Plates Move?

answer

- A fast-moving plate might cover 10 cm per year. - Q: Los Angeles & San Francisco actually sit on different tectonic plates. If LA and SF are 300 miles apart and moving towards each other at 10 cm per year, how many years until they're side by side?

question

Practice Exercise: How Fast Do Plates Move?

answer

- A: About 4.75 million years - Thus, plates move very slowly

question

PT 3-Plate Boundaries

answer

- Look back at the tectonic plate map (slide 7). There are no gaps between the plates. - When a plate moves, it affects the other plates next to it. - Q: What happens at the boundaries where 2 plates meet? 3 basic options: 1- They pull away from each other 2- They run into each other 3- They slide past each other

question

1- Divergent Margins

answer

- At a divergent boundary, two plates are moving away from each other. 2 types: - 1a- Seafloor spreading- occurs when a divergent boundary exists between 2 plates with oceanic crust (see pic below) - Characterized by undersea volcanic activity

question

Divergent Margins continued

answer

- 1b- Rift valleys- form when a divergent boundary starts forming in continental crust Ex: East Africa Rift Valley - Triple Junction- often get a Y-shaped split. - 1 arm may become an active plate boundary, other 2 arms become 'failed' rifts

question

2- Convergent Margins

answer

- At these boundaries, 2 plates collide head-on. 2 types: - 2a- Subduction zone- 1 plate contains oceanic crust, the other contains continental crust (sometimes both plates have oceanic crust) - The plate w/ oceanic crust is forced down (subducted) - Q: why is that plate subducted instead of the other one?

question

Subduction Zones continued

answer

- A: Because oceanic crust is denser than continental crust - Subduction zones are characterized by volcanic activity & big earthquakes

question

Convergent Margins continued

answer

- 2b- Collision zone- In this case both plates contain continental crust. But continental crust's low density makes it hard to subduct Ex: try getting a cork to stay under water - So instead of being pushed down, the rocks are pushed up - Collision boundaries are thus where mountain belts form

question

3- Transform Margins

answer

- At this type of boundary, 2 plates slide past one another (Ex: cars going past each other in opposite directions on a road) - The plates must overcome a lot of friction in order to move - Thus, transform boundaries have lots of earthquakes occur along them

question

Transform Margins continued

answer

- The San Andreas Fault marks a transform boundary between the North American Plate & the Pacific Plate. - This is why San Francisco & LA are on different plates - It also means part of California really is separating from North America, as shown in some sci-fi /disaster movies

question

Rocks & Minerals

answer

- Why do we care about minerals & rocks? 1- They're the raw materials for construction materials, gemstones, and mining resources 2- They're also the basic building blocks of the Earth

question

PT 1- Basic Chemistry

answer

- To understand minerals, we need to remember some basic chemistry: - Atoms- are the basic building blocks of matter. They have 3 main particles: 1- Protons (p+) have a positive charge 2- Neutrons (n0) have no electrical charge. Protons & neutrons make up the core (nucleus) of an atom 3- Electrons (e-) have a negative charge and exist outside the nucleus

question

Basic Chemistry continued

answer

- Element- A substance comprised of only one type of atom. (Ex: a bar of pure gold contains ONLY gold atoms) - Q: What makes the atoms of one element different from those of another element? - A: The # of p+ . This is the Atomic Number , which is used to place it on the Periodic Table (PT). (Ex: The atom pictured on the previous slide has 2 protons. Thus, it is a He atom. He is #2 on the PT.) -If you change the # of p+ present, you change the element the atom represents!

question

Chemistry of Earth's Crust

answer

- ...but most of Earth's crust is made up of only 8 elements! - Oxygen comprises almost half the crust! It and silicon account for almost 75% of the crust!

question

Building Molecules

answer

- To build a mineral, we need to combine atoms into larger structures. - Atoms bond with each other due to properties of the electrons. - Electrons exist in shells

question

Building Molecules continued

answer

- Each shell can hold a certain # of electrons - Atoms want to fill their shells, starting with the shell closest to the nucleus. - If there are 'vacancies' in the outermost shell, the atom is not stable.

question

Building Molecules continued

answer

- Some atoms fill vacancies by taking an e- from another atom that has only 1 e- in its outer shell - Anion (has a - charge since it gained an e-) - Cation (has a + charge since it lost an e-) - This is called an ionic bond. These are common in many rocks & minerals

question

PT 2- What is a Mineral?

answer

- 'Rock' and 'mineral' are two very different things in geology! - Minerals are the building blocks of rocks - Mineral- a naturally occurring, inorganic, crystalline solid possessing a set chemical composition.

question

Mineral Definition pts 1-2

answer

- 1- naturally occurring This means minerals have to form by natural processes. They cannot be man-made (synthetic) - 2- inorganic This means minerals do not contain molecules such as proteins, lipids, DNA, amino acids, or other building blocks of living organisms

question

Mineral Definition pt 3

answer

- 3- Crystalline This means that the atoms composing the mineral are bonded in very fixed, orderly, geometric arrays. - Amorphous- materials with no set internal structure. Minerals are not amorphous. (Ex: glass) - Crystalline structure of the mineral halite (aka salt). The green and red balls represent the 2 types of atoms found in halite, Na and Cl.

question

Definition pt 4

answer

- 4- Solid - Liquids & gases are not minerals. - Remember: State is determined by Temp & Pressure (T/P)

question

Definition pt 5

answer

- 5- Set chemical composition - Minerals are always made of the same types of atoms - You can write a chemical formula to represent each mineral Ex: Halite = NaCl Ex: quartz = SiO2 - Some substitutions may occur Ex: Calcite = CaCO3 but some Mg atoms may replace some Ca atoms

question

Q: How do you identify different minerals?

answer

- There are est 4,000-5,000 different minerals on Earth - We identify them based on their chemical and physical properties - These properties relate to the mineral's chemical composition & crystal structure

question

Property 1- Color

answer

- Some minerals always come in one, diagnostic color (Ex: Olivine is always light green) - Many minerals come in a variety of colors, so be careful!

question

Property 2- Hardness

answer

- Resistance to being scratched - Measured using Moh's Scale - Ea. # 1-10 gets progressively harder - Can also use simple tools instead of mineral samples: Fingernail = 2.5 Penny = 3.5 Tack/pin = 5 Glass = 6

question

Property 3- Luster

answer

- How the mineral reflects light. - i.e., how shiny is it?

question

Property 4- Effervescence

answer

- It means 'bubbly' - Some minerals react w/ weak acids (like hydrochloric acid, HCl) and release CO2 - The mineral fizzes, like opening a new can of soda. HCl + CaCO3 = CO2 + Ca + OH + Cl

question

Property 5- Crystal Form & Growth Habit

answer

- Remember: the atoms are bonded in fixed, geometric patterns. - The crystal shape reflects the internal structure. - Many minerals don't grow into a nice crystal b/c they have to squeeze into whatever space is available

question

Property 6- Breakage Pattern

answer

- Fracture -the mineral breaks into random pieces (Ex: quartz) - Cleavage- the mineral breaks along flat, smooth surfaces (Ex: halite) - Different minerals split into different numbers of cleavage planes that meet each other at different angles

question

Other Properties

answer

- Some minerals are magnetic. (Ex: magnetite) - Sulfur-bearing minerals may smell like rotten eggs (Ex: sphalerite) - Halides have a strong, salty taste (Ex: halite tastes like french fries (but don't lick it; it's concentrated salt!))

question

PT 3- Six Common Mineral Groups

answer

- Minerals are organized into groups by the anion they have in common - Group 1- Silicates- They contain SiO44- anions This is the most common group of minerals at Earth's surface - Q: Why are silicates so common? (hint: look at the anion's formula)

question

Silicates continued

answer

- A: the anion is comprised of Si and O, which are the 2 most abundant elements in Earth's crust (see the table on slide 6). - Thus, it makes sense that there will be lots of silicate minerals in Earth's crust

question

SiO4

answer

- Tetrahedron = 1 Si atom + four O atoms - Tetrahedra bond w/ cations or other tetrahedra - Polymerization- bonding of multiple tetrahedra - 2 tetrahedra never share more than 1 oxygen atom

question

Types of Silicates

answer

- Sub-groups depend on how tetrahedra polymerize - 1a- Island Silicates - Isolated tetrahedra + a cation(s) Ex- Olivine (L) & Garnet (R )

question

Types of Silicates

answer

- 1b- Chain Silicates- 1+ chains of tetrahedra & cations - Chains form by ea. tetrahedron sharing 2 of its oxygen atoms (w/ 2 different tetrahedra) Ex- Pyroxenes (single-chain) & Amphiboles (dbl-chain)

question

Types of Silicates

answer

- 1c- Sheet Silicates - Each Tetrahedron shares 3 oxygen atoms to form a sheet of tetrahedra - A layer of cations forms on top of this sheet - The cations are covered by another tetrahedra sheet Ex: think of building a sandwich

question

Sheet Silicates continued

answer

- Cation-oxygen bonds are weaker than Si-O bonds - Thus, the layers peel apart easily along a cleavage plane - Like lifting the top bun off the sandwich shown on the previous slide (Ex- Mica minerals, like biotite and muscovite)

question

Types of Silicates

answer

- 1d- Framework Silicates - Fully polymerized, forming a 3-D framework of tetrahedra (hard to show in a picture) - Cations worked into fixed places within the structure S- ome of the most common minerals are framework silicates (Ex- quartz & feldspars)

question

Group 2- Carbonates

answer

- Anion = (CO3)2- (Ex- calcite, dolomite, aragonite Carbonates are easy to differentiate from other mineral groups b/c they effervesce) - Many invertebrates make their shells out of carbonate minerals - Even microscopic plankton make carbonate shells; these shells create lots of carbonate deposits on the ocean floor

question

Group 3- Phosphates

answer

- Anion is (PO4)3- (Ex- apatite) - Importance: - 1- vertebrates make bones & teeth out of phosphate minerals - 2- some invertebrates make shells out of phosphates - 3- we mine phosphates to put in fertilizer Phosphorus is a nutrient plants need

question

Group 4- Sulfates

answer

- Anion is (SO4)2- (Ex- gypsum) - Importance: - 1- used in construction Drywall is made of sulfate minerals - 2- Used in plaster

question

Group 5- Sulfides & Group 6- Oxides

answer

- Anion = S- and O2- respectively - Both commonly bond with metal cations - Simple formulae (ex: PbS, FeO) - Both mined for metals

question

PT 4- The Rock Cycle

answer

- Rocks- non-living substance comprised of 1+ minerals and possibly other materials (e.g., fossils, natural glass) - Only three types of rocks form on Earth - Differentiated based on how they form - Linked together via the Rock Cycle

question

Rock Cycle

answer

- Cycles don't have a set beginning or end - Lets just start w/ Magma-' liquid rock' - Magma has a lower density than solid rock, so it tries to rise to Earth's surface - Closer to the surface the temp drops, so magma freezes to form igneous rocks

question

Rock Cycle continued

answer

- Rocks on Earth's surface are acted upon by surface processes (wind, rain, waves, etc) - Weathering - breaking down of pre-existing rocks into rubble (sediment) - Erosion- Transporting the sediment to a new location - Ex: step on a potato chip and it crumbles (weathers) into pieces. Then you sweep up the crumbs to move (erode) them to the trash can

question

Rock Cycle continued

answer

- Deposition- stop eroding the sediments and deposit them - The potato chip crumbs are put in a trash can - Lithification- combine the loose sediments into a new type of solid rock called sedimentary rocks

question

Rock Cycle continued

answer

- If lots of sediment get deposited in one place, those at the bottom can be buried deep below the surface - Every mineral is only stable at a certain temp & press (T/P) range - During burial, T/P changes can affect mineral stability - If you destabilize some minerals and replace them with new, stable minerals, you create metamorphic rocks

question

Rock Cycle continued

answer

- Increase T to the melting point, and you're back to magma, the cycle is complete! - The picture on the next slide shows the complete cycle - Note the 'shortcut' arrows in the middle of the cycle ... you can skip steps - Ex: igneous rock may get buried and turned into metamorphic rock, instead of getting weathered & eroded

question

PT 1- Magmas

answer

Why do we care? We need to understand magma in order to know how volcanoes erupt Igneous rocks, which form from cooling magma, are an important building material Ex: granite

question

PT 1- Magmas

answer

Magma vs Lava Both words refer to molten rock. When it's below ground, we call it magma. When in erupts onto the surface, it's called lava.

question

How does Magma Form?

answer

Have to melt rocks Requires temperature of at least several hundred degrees Celsius Problem: rocks contain many different minerals, each with its own melting point At a given temp, some minerals melt, but others do not. Produces a mix of solid crystals and liquid magma Ex: think of a slurpee/icee drink This is called Partial melting The magma's initial chemistry is different from the rock's chemistry since the whole rock does not melt all at once

question

How to Melt Rocks

answer

3 things can help melt a rock 1- Increase Temp No surprise there 2- Add Water Wet Melting- adding water lowers the melting point of minerals You can melt a 'wet' rock at a much lower temp than a 'dry' rock 3- Lower the Pressure Decompression Melting- removing press lowers the melting point of minerals

question

What's In Magma?

answer

There are some gases dissolved in magma Ex: CO2 + H2O = 98% Gas is < 3 wgt % of magma, but still important when studying volcanoes (we'll come back to this later) SiO2 is a primary component. There are 3 main types of magma that are formed in different ways The categories are based on how much silica is present

question

Type 1- Basaltic

answer

Basaltic magma contains 50% silica; the other 50% is various elements 80% of all magma is basaltic magma Hottest type of magma (>1100°C) Q: what's that in Fahrenheit? F = (9*C / 5) +32

question

Basaltic Magma continued

answer

A: over 2,000 degrees Fahrenheit! Forms in the mantle, moves up through both types of crust Contains little water (= dry magma) Common along mid-ocean ridge system. So, new seafloor made at divergent boundaries comes from basaltic magma

question

Type 2- Andesitic Magma

answer

Contains about 60% silica Cooler temp: 800-1000°C Notice that the temp went down as the silica content went up Forms only in specific places Andesite Line aka Ring of Fire

question

Andesitic Magma continued

answer

The Andesite Line corresponds to a lot of subduction zones. Subduction zones are where andesitic magma forms Different processes can form it Ex: melted oceanic crust rises but mixes with continental material

question

Type 3- Rhyolitic Magma

answer

Contains about 70% silica Coolest magma: 700-800 C Only forms in continental crust Contains a lot of water (= 'wet' magma)

question

How Does Magma Form a Rock?

answer

Partial Freezing- Diff minerals crystallize (aka freeze) at diff. temperatures. Each new crystal removes certain elements from the magma Ex: olivine uses Fe, Mg, Si, O If crystals remain in contact with the magma, they may get altered Crystal Settling- dense mins sink as magma rises, so they're not in contact with ea other Thus, the magma changes composition (magma differentiation)

question

Freezing Magma continued

answer

As magma cools, the minerals will form in a set sequence Ex: olivine has the highest freezing point, so it forms first Ex: quartz has a low freezing point, so it forms last This sequence is known as Bowen's Reaction Series

question

Bowen's Reaction Series continued

answer

Discontinuous Series (the left branch)- each of these minerals forms at a distinct temp. When the temp drops, that mineral stops forming i.e., it's production is discontinued Ex: Manufacturing of cars is discontinued at the end of each year, and the cars are replaced with next year's models

question

Bowen's Reaction Series continued

answer

Continuous Series (right branch)- the mineral plagioclase forms over a wide range of temp As the temp lowers, more Na and less Ca is included in its crystals Remember that minerals can have some substitutions in their chemical formula. Thus, there is a continuous change in plagioclase crystals' chemistry as temp drops

question

Bowen's Reaction Series continued

answer

The terms on the right side of the diagram refer to the silica content of the minerals Ultramafic- very low silica content Ex: olivine Mafic- low silica content Ex: pyroxene, amphibole Intermediate - intermediate silica content Ex: biotite Felsic- high silica content Ex: feldsapr, quartz

question

**Quick Clarification**

answer

Note that terms like 'mafic' and 'ultramafic' are not applied to plagioclase & the continuous reaction

question

Trends in Bowen's Series

answer

1- As temp drops, you get minerals with higher silica content Saw the same trend with magmas! 2- The first minerals to form have simple polymerized structures Ex: olivine = island silicate 3- The last minerals to form have 'big' polymerized structures Ex: quartz = framework silicate Q; What does this tell you....?

question

Bowens Reaction series continued

answer

The first minerals to crystallize require little silica and lots of other elements The other elements get used up rapidly, so at lower temps, the magma contains a lot of silica and small amounts of other elements Thus, at lower temps there is plenty of silica to make the large sheets & framework silicate structures

question

**Study Hint**

answer

Bowen's series often gives students trouble. Animation file 4c 'fractional crystallization' is a good example of how magma freezes Learn the Reaction Series diagram. You might see an exam question like this one.....

question

Practice Question Which of the following minerals is considered ultramafic? A- olivine B- quartz C- biotite D- muscovite E- None of the above

answer

If you know learn the diagram, the question is easy If you don't know the diagram, you just have a 1 in 5 chance of guessing correctly *** Study Hint #2 *** I often use "None of the Above" and "All of the Above" as the correct answer! So don't dismiss them as viable answer options!

question

PT 2- Igneous Rocks

answer

There are two types of igneous (ig) rocks: 1-Plutonic aka Intrusive- form below Earth's surface 2- Volcanic aka Extrusive- form above Earth's surface You need 2 properties to ID an ig rock: 1- Texture - size/shape of mineral grains 2- Composition -the minerals present

question

Type 1- Plutonic Rocks

answer

Sometimes magma freezes before it reaches the surface Plutons are any body of plutonic igneous rock. There are several specific types of plutons. They are basically classified by shape

question

Types of Plutons

answer

Batholith- large, amorphous plutonic bodies Dike- magma frozen in ~ vertical 'pipes'

question

Types of Plutons continued

answer

Sill- magma frozen in ~ horizontal layers Laccolith- resembles a sill that is swollen with magma; the resulting pluton warps the rock/sediment layers above it

question

Practice Question What type of pluton is the dark layer of rock in the center of the picture?

answer

A: A dike. The dark layer of rock is cutting near-vertically through the other layers of rock. The dark rock thus used to be magma trying to flow to the surface, but it froze and formed plutonic igneous rock before it made it above ground.

question

Textures of Intrusive Rocks

answer

To identify a specific plutonic rock, we first need to ID its texture. There are 2 basic textures: Phaneritic- grains large enough to see, ca. 1 mm - 3 cm Pegmatite- really big grains (> 3 cm)

question

Composition

answer

To finish the identification, we just need the composition Silica content is the key Categories: Felsic- many silica-rich minerals Intermediate- some silica-rich minerals Mafic few silica-rich minerals Ultramafic silica-poor minerals

question

Composition continued

answer

Instead of identifying every mineral & measuring its silica content, you can go by the rock's Color Index Rocks with an overall light color (white, pink) are felsic Grey rks are intermediate Dark rks are mafic Green-yellow rks are ultramafic The Color Index is a short-cut that works most of the time, but not always

question

Color Index continued

answer

Most rocks are not just one color. Use the dominant color for identifying the color index Ex: this rock has some dark mineral crystals & some gray crystals, but most of the minerals are pink-white. So it is a felsic rock.

question

Type 2- Volcanic Rocks

answer

2nd type of igneous rocks Form when lava freezes above ground ID with same traits- texture & composition

question

Textures of Extrusive Rocks

answer

Composition again based on Si content color index still works Common volcanic textures: 1- Porphyritic- a mix of large and small grains Ex: think of a chocolate chip cookie. Chips = large grains, dough = small grains The large grains (white & black squares) are called phenocrysts. They're mixed in the rock with very tiny gray-brown crystals

question

Textures of Extrusive Rocks continued

answer

Other common volcanic textures: Aphanitic- most grains are too small to see without magnification Glassy- natural glass In general- the smaller the grains, the faster the magma cooled down Note: Even though this glassy rock is dark colored, it has a high silica content and is thus felsic! It's one of the rare exceptions to the Color Index rule

question

Ig Rock ID

answer

Once you know the texture & composition, you can read the name of the rock right off a chart Ex: phaneritic + felsic = Granite Ex: aphanitic + mafic = Basalt

question

Case Study: Krakatoa

answer

Indonesian island volcano Erupted Aug 26, 1883 Force = 200 million tons of TNT = 13,000x > the Hiroshima atomic bomb 25 cubic km of material ejected Heard >3,000 miles away Air pressure waves circled the globe for 5 days Caused waves in the English Channel Over 30,000 dead, several languages went extinct 2/3 of the island destroyed

question

PT 1- Explosive vs Non-Explosive Eruptions

answer

But not all eruptions are explosive Compare the pictures below: L- Mt St Helens R- Mauna Loa Q: Why are some eruptions explosive but others aren't?....

question

Eruptions & Viscosity

answer

A: The type of eruption depends on the magma's viscosity Viscosity (V)- resistance to flow Low V = thin, flows easily Ex: water High V = thick, flows slowly Ex: peanut butter

question

Eruptions & Viscosity

answer

A magma's viscosity depends on: 1- Temp: As magma cools, V increases b/c the magma is starting to transition from liquid to solid 2- Silica content: Higher silica content means large silicate polymers, which make magma's V increase Summary: cooler, Si-rich magma has a higher V than hotter, Si-poor magma

question

Eruptions & Viscosity

answer

Q: Why is V important? A: Viscosity controls the gas content of the magma Remember: magmas contain some dissolved gas Gas has a low density, so this gas is trying to move upward faster than the magma

question

Eruptions & Viscosity

answer

Low V: the gas can escape easily, so little gas pressure builds up in the magma, and the eruption is non-explosive Ex: open a bottle of flat soda High V: the gas cannot escape the magma, so gas pressure builds as the magma moves slowly upward Close to the surface, the gas forces its way upward, causing an explosive eruption Ex: shake a new bottle of soda & open it quickly

question

Non-Explosive Eruptions

answer

Magma is very hot, so V is low Surface of the lava will freeze quickly

question

Non-Explosive Features

answer

Initially the lava still moves pretty fast; it's still hot & fluid. Pahoehoe- name for the stringy/ropey appearance of the cooling lava's surface

question

Non-Explosive Features

answer

As cooling continues, the lava becomes more viscous as it becomes more solid. This harder, brittle structure is called Aa Some gas still trapped may burst out, leaving tiny holes honeycombed through the rock. These are called vesicles.

question

Non-Explosive Features

answer

Pillow lavas- if the lava quickly flows into cold water, it cools to form bulbous, pillow-shaped mounds This trait is a good indicator of past volcanic eruptions that occurred near/under water

question

Practice Exercise: Can You Outrun Lava?

answer

How fast does lava flow? A 'fast' lava might flow @ ~ 16 km/hr Q: what is that in mi/hr? A: about 10 mph Higher speeds (100+ km/hr) are possible, but are rare Thus, being caught in a lava flow is not the most dangerous aspect of eruptions Greater danger comes from hot, toxic gases, landslides, and airborne debris

question

Explosive Eruption Features

answer

Viscous magma prevents gas from easily escaping Phreatic eruption- if magma encounters water near the surface of the ground, the water is converted to steam This creates more gas pressure, resulting in very explosive eruptions

question

Explosive Eruption Features

answer

Lots of solid material becomes airborne, which can be dangerous. These solid materials are called pyroclasts Divided by size: Bombs > 64 mm Lapilli 64-2 mm Ash < 2 mm Note: ash is not from burning things with lava. It's just fine-grained solid material blown out of the volcano

question

Explosive Eruption Features

answer

Pyroclastic Flow -Mix of pyroclasts & gas Erupted upward, but they're denser than air & thus quickly come back down 100s of degrees & move fast ( 100s km/hr) Watch: https://www.youtube.com/watch?v=Cvjwt9nnwXY

question

Case Study: Vesuvius

answer

August 24, 79. Italy Town of Pompeii buried by pyroclasts & pyroclastic flows Most victims killed by falling debris or inhalating ash & toxic gases; dead long before lava reached the area Bodies preserved in the ash layers that buried them

question

PT 2- Types of Volcanoes

answer

A volcano is basically a vent through which magma reaches the surface Built during eruptions The diff types thus depend on what materials are typically erupted

question

The Top of the Volcano

answer

Crater Present before an eruption Vent for gases & other materials Caldera Sometimes form after eruptions when the top collapses inward after all the magma/pyroclastics have been removed Larger than the crater, often several km across

question

Type 1- Shield Volcanoes

answer

Low domes (see pics below) Form when low viscosity magma commonly erupts Flows easily, so it spreads far out, creating a large volcano w/ gentle slopes

question

Type 2- Tephra (Cinder) Cones

answer

Steep-sided volcanoes, but relatively short (see pic on R) Form when lots of pyroclastic material erupts. Pyroclasts can only pile up so much Ex: try to build a sand castle out of dry sand

question

Type 3- Stratocones

answer

aka composite volcanoes, aka stratovolcanoes Erupt a combination of pyroclasts & relatively viscous lava. The lava helps weld the pyroclasts together, creating large, steep-sided volcanoes

question

Type 4- Supervolcano

answer

Not really a volcano type Refers to eruptions large enough to affect global climate due to amount of material erupted

question

Supervolcano Case Study

answer

Tambora erupted in Indonesia in 1815 100 km3 ejecta, 1816 = 'Year Without A Summer' in northern hemisphere Frost in New England on July 4 Famine in Ireland from crop failure

question

Supervolcano Case Study

answer

The Yellowstone caldera has had several super eruptions in the past few million years Ex: Huckleberry Ridge eruption (2 Ma), 2500 km3 ejecta, covered the entire middle of N America

question

Supervolcano Case Study

answer

Toba erupted in Indonesia 75 ka 2800 km3 ejecta, largest eruption in the last 2 my est 60% of the entire human race was killed Based on genetic evidence

question

Indonesian Volcanism

answer

Q: Why does Indonesia have so many volcanoes? A: It's near a lot of subduction zones. Remember that subduction zones often have a lot of volcanic & seismic activity

question

PT 3- Hot Spots

answer

Q: If volcanoes usually form at plate boundaries, then why are there volcanoes on Hawaii? Hawaii couldn't be farther from the edges of the Pacific plate!

question

Hot Spots continued

answer

Hot Spot- a body of magma below that lithosphere that sends magma to the surface over millions of years As magma rises through the lithosphere, a volcano is formed above. When the lithospheric plate moves, the volcano is carried away and becomes dormant. A new volcano then forms over the hot spot Watch the animation file noted above

question

Hot Spots continued

answer

This fits other data about the Hawaiian Islands 1- All the active volcaones are on the Big Island 2- Moving away from the Big Island, the volcanoes get older

question

Sedimentary (Sed) Processes

answer

Q: Why do we care about sediments & sed rks? Sed rocks are the most common rock type at Earth's surface Thus we, utilize them for numerous things: 1- construction sites & building materials 2- Almost all fossils are found in sed rks 3-Fossil fuels, like coal and natural gas, come from sed rocks 4- Soils are associated with sedimentary processes 5- landslides involve sedimentary processes

question

PT 1- Forming Sedimentary Rock

answer

Start with some pre-existing rock (Parent Rock) Does not matter what type: ig, sed, or metamorphic Have to destroy the parent rock to create raw material for building the new sed rk

question

PT 1A- Weathering

answer

Weathering- breakdown of rock into particles (sediment) Weathering can occur in two different general ways: 1- Physical weathering- mechanically or physically break the rock down Ex: roll it down a hill to make it break apart 2- Chemical weathering- chemically alter the rock in order to break it down Ex: dissolve it in acid

question

Causes of Physical Weathering

answer

1- Natural zones of weakness exist in some rocks (see planes in the rock layers pictured below) Rocks can thus easily break apart

question

Causes of Physical Weathering

answer

2- Biological activity Plant roots can force their way through solid rock, splitting the rock apart Ex: root cracks in sidewalks

question

Causes of Physical Weathering

answer

3- Frost Wedging- When water freezes, it expands, so the ice presses against the sides of the crack, making it wider. Each time water gets in the crack and freezes, the crack widens until it finally splits. Ex: pot holes. This is why many pot holes form in winter (it's cold) and why they seem to open overnight- the pressure has actually been building for a long time

question

Causes of Physical Weathering

answer

4- Exfoliation- some rocks seem to peel apart in thin sheets Like dry skin flakes when you wash your face These rocks used to be buried deep below the surface & were under high pressure 'squashing' them

question

Causes of Physical Weathering

answer

When overlying rocks eroded away, all the pressure was removed isostatic rebound- material rises when press is removed Ex: watch the marshmellow expand as pressure is lowered & compress as press is increased https://www.youtube.com/watch?v=NSa9-6ceV94 Rocks are brittle, not ductile like the marshmellow, so when they rebound, they start to crack, resulting in exfoliation

question

2- Chemical Weathering

answer

Instead of breaking, you dissolve or chemically break apart the rock More common than physical weathering in many environments Remember: different mins will react at different rates

question

2- Chemical Weathering

answer

Notice the last mins to form in Bowens Reaction Series are the most stable at earth's surface. They form at near-surface conditions, and are thus hard to break down.

question

2- Chemical Weathering

answer

Notice the first mins to form in Bowens Reaction Series are the least stable at Earth's surface. They form at T/P conditions very different from Earth's surface, so they are less stable & easier to alter.

question

Chem Weathering w/ Water

answer

Water is key for many chemical weathering reactions Rain isn't pure water Contains dissolved CO2, SO2, nitrates, etc CO2 + H2O H2CO3 (= Carbonic acid) Feldspar + H2O + H2CO3 kaolinite + dissolved ions So you can change feldspar (Hardness = 6) into kaolinite (Hardness = 1.5) with a little water and acid

question

Chemical Weathering w/ Air

answer

Atmospheric oxygen accepts electrons from other elements (oxidation) This can alter minerals within rocks Ex: Iron changing to iron oxide (= rust) The same process accounts for the reddish color of both the car door and the sediment

question

Controls on Weathering

answer

The speed & type of weathering that occurs depends on several factors 1- Parent rock type- some rocks break down easier than others. Ex: granite (L) is usually very resistant whereas shale (R ) can break apart pretty easily

question

Controls on Weathering continued

answer

2- Climate Wet = more chemical weathering occurs Dry = more physical weathering occurs

question

Controls on Weathering continued

answer

3- Soil Presence/Absence Soil- combo of rock fragments, weathered minerals, and organic matter Formed by weathering As soils build up, they promote more weathering Promoters chemical weathering b/c soils retain water & are slightly acidic Promotes physical weathering b/c plants grow in soils, and their roots can break through rocks

question

Controls on Weathering continued

answer

4- Length of Exposure- the longer the rock sits on the surface, the more altered it becomes Rind- outer, weathered portion of a rock. Can look very different than the unweathered interior

question

1B- Erosion

answer

Erosion - moving sediment from one place to another 4 things in nature commonly cause erosion Water Wind Gravity (landslides) Ice (glaciers) Erosion requires energy to lift and move the sediment

question

1C- Deposition

answer

As energy level drops, sediment can't be carried any farther. Must be put down (deposited) Basin- any natural depression that can hold sediment. Accommodation space- the amount of space available in a basin to hold sediment Subsidence- as sediment is deposited, its weight may cause the basin to sink. This can open new accommodation space at the top of the basin

question

Deposition

answer

Sediment is deposited in layers (aka strata, aka beds) Each bed can be named to help geologists communicate easier; they'll know exactly which bed other geologists are talking about

question

1D- Lithification

answer

Lithification - process of becoming solid rock Ex: the basilisk in Harry Potter lithified people when it looked at them This involves a couple of steps

question

Lithification continued

answer

Compaction- first, you have to squash the particles of sediment closer together. When first deposited, there is plenty of open space in-between the grains Ex: Time 1

question

Lithification continued

answer

As the stratum gets buried, the weight of overlying beds compacts the grains, so little space is left between them

question

Lithification con't

answer

Cementation- Second, the grains must be stuck together with natural cements. During compaction, water is squeezed out Dissolved materials in the water get left behind CaCO3 SiO2, Fe, etc These precipitates 'glue' sediment grains together

question

PT 2- Types of Sediments

answer

Sediments can be divided up into 3 basic types. The names for these categories vary somewhat depending on what book you use. Type 1- Clastic Seds- (aka detrital) Particles produced by physical weathering. Classified by grain size using common terms Ex: gravel, sand, etc

question

Traits of Clastic Sediments

answer

Certain traits of clastics are useful to determine the environment they were deposited in Ex: were the strata below deposited in an ancient lake or an ancient desert?

question

Trait 1- Sorting

answer

Measurement of how uniform the grain size is Well-sorted- grains are very similar in size Moderately sorted- some sizes mixed together Poorly sorted- lots of different sizes mixed together Better sorting = eroded farther

question

Trait 2- Roundness

answer

Measures how spherical the grains are Poorly rounded- grains are very jagged, angular, and blocky Moderately rounded- somewhat spherical Well rounded- very spherical Longer transport = more rounded

question

Trait 3- Maturity

answer

Combination of roundness & sorting Very mature = well rounded & well sorted Moderately mature Immature = poorly rounded + poorly sorted

question

Practice Exercise

answer

Describe the rounding, sorting, and maturity of both sediment samples (the penny is for scale)

question

Answers

answer

L- the grains are poorly rounded and poorly sorted, so the sample is immature R- the grains are well rounded and well sorted, thus the sample is very mature

question

Common Clastic Sed Rocks

answer

Formed by lithifying clastic sediments Classified by the primary grain size Gravels = Conglomerate (if gravels are moderately rounded) & Breccia (if gravels are poorly rounded)

question

More Clastic Rocks

answer

Sand = Sandstones Silt = Siltstone Clay = Shale (if layered) & Mudstone (if unlayered) Pics (L-R): sandstone, shale, & mudstone samples

question

Types of Sediments continued

answer

Type 2- Chemical Sediments Form via chemical reactions dissolution & re-precipitation saltwater evaporation Ex: watch salt deposits form as saltwater evaporates: http://www.youtube.com/watch?v=fB5Tq_eiKG4

question

Types of Sediments continued

answer

Can form thick layers of chemical seds Ex: Bonneville salt flats in Utah (pic below) Note: Maturity factors don't apply to chemical seds They are transported as dissolved ions, so they don't get rounded, sorted, etc.

question

Chemical Sedimentary Rocks

answer

Usually comprised of 1 major mineral type ID the minreal to ID the rock Ex: Halite = Rock Salt Ex: Gypsum = Rock Gypsum Ex: Quartz = Chert These layers can be economically important deposits

question

Types of Sediments continued

answer

Type 3- Biogenic Sediments Composed of plant & animal remains Ex- carbonates from shells (even tiny ones) Ex- compressed plant material

question

Biogenic Sedimentary Rocks

answer

Classified by the types of materials present Ex: Chalk = tiny carbonate shells poorly cemented together Ex: Limestone = carbonate particles (size varies) Ex: Coal = compressed plant remains

question

Mass Wasting (aka Landslides)

answer

Transport of sediment & assoc materials downhill via gravity Why do we care?- Damage Ex: the landslide below closed a section of Interstate 40 for months. That means higher fuel costs for everyone detoured, and thus higher prices for goods being shipped

question

Case Study: Huascaran

answer

4th highest peak in South America (Peru) 1970 earthquake disloged an ice block 1 mile long x 1/2 mile wide x 1/2 mile deep Covered ~11 miles in 5 minutes Q: How many MPH is that?

question

Case Study: Huascaran

answer

A: ~ 132 mph! Destroyed the town of Yunguay, 11 miles away, killing 20,000 people Thus, we need to understand mass wasting b/c it poses a hazard to us

question

PT 1- Why Do Landslides Occur?

answer

Slopes can become unstable for many reasons 1- Lack of Consolidation. Cohesive forces bind sediments together Ex: plant roots consolidate seds. That's why there's so much dirt stuck to roots when you pull a plant out of the ground Areas become unstable if such binding agents are removed Ex- clear-cutting (see pic)

question

Stability Factors continued

answer

2- Slope steepness is of course a factor Angle of Repose- the maximum angle at which a slope is stable. Often cited as ~ 35 degrees, but AoR can vary a lot depending on other factors Moisture, grain shape, etc Never just assume 35 degrees is the AoR!

question

Stability Factors continued

answer

3- Moisture level Too little water: dry grains roll downhill Ex: try building a sandcastle with dry sand Too much water: seds turn to mud & flow downhill easily Moderate amount of moisture: adds cohesive force that holds grains in place Thus, you want the water level to be just right

question

Stability Factors continued

answer

4- Amount of Vegetation Usually stabilizes, but can destabilize The slope in the pic has plenty of plants, but a landslide still happened. Q: Why?

question

Stability Factors continued

answer

A: Lots of vegetation = lots of roots soaking up lots of water Water intake dries out the seds & adds weight to the slope Roots also help water flow deeper into the slope and saturate it

question

PT 2- Types of Mass Wasting

answer

'Landslide' is a general, catch-all term Different categories based on several variables: 1- type of material moving. Is it rock, mud, snow, ice, loose debris, etc? 2- type of movement Is it falling, sliding, flowing, etc?

question

Types of Mass Wasting continued

answer

Ex: the picture below shows a Rockfall Type of material: solid rock Type of movement: fell straight down Falls move very fast, but stop once they hit the ground

question

Types of Mass Wasting continued

answer

Ex- The pic below shows a Rockslide Material: rock Movement: sliding downhill Slides move slower due to friction, but they can cover long distances Ex: from Tennessee http://www.youtube.com/watch?v=ZVYGJYnJTi0&feature=related Lots of other categories: snow avalanches, mudslides, mudflows, etc

question

Types of Mass Wasting continued

answer

Some mass wasting events move pretty slowly Creep- gradual downhill movement of seds due to gravity Ex: crooked fence lines often indicate creep is occurring. Fence is shifting downhill as the seds slowly move

question

Types of Mass Wasting continued

answer

Solifluction- Slow like creep, but caused by repeated freeze-thaw action in the sediment instead of gravity Ex: sediment is essentially undergoing frost wedging

question

PT 3- Causes of Mass Wasting

answer

Unstable slopes do not automatically have a landslide occur. They may be unstable for years with no movement Possible natural triggers: Earthquakes. Energy release & resulting ground shaking can put seds into motion Over-saturation. During strong storms and spring melting, lots of water can put seds in motion

question

Causes continued

answer

Possible anthropogenic (man-made) triggers: Grading slopes too steeply. Landscaping past the angle of repose can destabilize a slope. Removing vegetative cover. Clear-cutting exposes the soil, and the roots no longer help hold seds in place

question

Risk Assessment

answer

Can assess the risk along slopes Factors may change over short timescales, so areas must be re-evaluated regularly Ex: US Geological Survey map of slope stability in Washington

question

Prevention

answer

Several things can be done to avoid/decrease the chances of a landslide: 1- Building codes. Don't build heavy structures on steep slopes. Avoid building at the base of steep slopes 2- Drainage control. Draining water from slopes can increase their stability a lot 3- Decrease slope grades. Make sure to grade then at angles < AoR

question

Prevention continued

answer

4- Retaining walls Build walls that will block seds if they start moving (L pic) 5- Rock bolts Use large bolts to attach rocks to the hillside (R pic)

question

Prevention continued

answer

It's expensive to build/implement changes listed above, but damage is more costly Est return is $10-$2,000 in damage avoided per $1 spent on prevention!

question

Case Study: Thistle, Utah

answer

Town knew nearby slopes were unstable Didn't want to/couldn't pay the $0.5 million to install drainage systems 1983: slopes failed, resulting landslide caused $200 million in damage Money doesn't replace people & pets killed or family heirlooms destroyed It's easy to postpone needed changes, but if you wait too long, it will be too late

question

PT 1- Metamorphic Rocks

answer

Formed by altering rocks via heat, pressure, or fluid interaction Metamorphism (met) changes mineralogy and/or texture Slow process: million-year timescales to create met rocks Why do we care about met rks? They document changes in the Earth's crust through time Ex: Mountain formation, uplifts, collision zones, T/P at depth

question

Ex: Pilot Mt (NC)

answer

Odd b/c it's not part of a continuous mountain belt Analyzing the met rks that make up part of Pilot Mt help us determine how it formed

question

Forming Met Rks

answer

Method #1- Increase Temperature As temp rises, some minerals in the parent rock will become unstable Temperature increases the deeper below the surface you go Gradient = change over distance Geothermal (GT) gradient= temp change w/ depth in the Earth Avg GT gradient = 30 C / km Range = 20-60 C / km It depends on the crust's thickness: thicker = lower gradient

question

Metamorphism via Temp Change

answer

One way to do this is have magma come in contact with the rocks. Contact metamorphism Relatively small-scale events; only rocks close to the magma will be metamorphosed

question

Forming Met Rks continued

answer

Method 2- Increase the pressure on the parent rock Remember, mins are also sensitive to press changes Press is measured in bars and pascals 1 bar = atmospheric press @ earth's surface 1,000 bar = 1 kilobar (kbar) = 1,000 atmospheres Press gradient w/in the Earth ~300 bar / km depth Most met rks form at 10-30 km depth (mid-lower crust) Q: how many miles is that? (1 mile = 1.6 km)

question

Forming Met Rks continued

answer

A: 6-18 miles below the surface! This is why metamorphism takes so long to occur; you have to bury the rocks very deep before the process even begins Q: How do met rks get back to the surface? A: erosion of overlying rocks, plus uplift (watch the animation file)

question

Pressure continued

answer

2 kinds of pressure can be applied to rks: Confining press- squeeze evenly from all sides Ex: the pressure you feel swimming underwater in a pool Directed press- squeeze mainly from one direction Directed press causes the material to re-organize itself Ex: push down on a ball of play-dough and you flatten it In the animation, watch how the mineral grains get realigned as directed pressure is applied

question

Metamorphism via Pressure

answer

Regional metamorphism- Press is the main factor (T increase occurs too) These are large-scale events Ex: a convergent plate boundary. Lots of press is generated when the plates collide

question

Metamorphism via Pressure

answer

In some cases press can increase extremely rapidly. Shock Metamorphism. Ex: when asteroids hit earth, tremendous press (& temp) is generated at the impact site 10s - 100s of kbars + rapid temp increase Near-melting conditions can occur Creates metamorphic features

question

Forming Met Rks continued

answer

Method 3- Fluid Interactions. This is called Metasomatism Hot fluids move through the rocks below the surface. "hydrothermal metamorphism" Water is squeezed out of rocks/mins at depth The water can dissolve some mins, and deposit materials that form new mins This changes the chemistry of the rock

question

Metasomatism continued

answer

Often form ore deposits by this process since the water can deposit high concentrations of a certain material. Ore- rk with a higher than usual concentration of some mineral/element. These are economically important- can mine them. Pic: Molybdenum ore formed in a metamorphic rock

question

PT 2- Met Rks & Environments

answer

Q: What met rock will form? A: The parent rock's composition helps determine which specific met rk forms

question

Metamorphic Grade

answer

A measure of how much the rock was altered This is used to identify met rocks Ex: Low Grade = little T/P change, so met was minor Ex: High Grade = big T/P change, so met was major Diagenesis- pre-metamorphic changes (ex: sedimentary steps)

question

Metamorphic Grade continued

answer

Problem: each met grade covers a wide range of T/P changes Ex: 200 C+0 MPa and 0 C+500MPa both cause low-grade met, but those are very different sets of conditions! So we need another, more specific measurement...

question

Index Minerals

answer

B/c every mineral is stable at certain T/P conditions, you often see certain mins in each grade These index mins define categories Metamorphic Facies- a group of minerals that indicate specific T/P conditions Ex- Blueschist facies includes the minerals glaucophane, lawsonite, epidote Another example is on the next slide...

question

Examples of Index Minerals

answer

Index min names in red. The shorter the line under the name, the better it works as an index mineral Met rk names in bold Facies names in italics

question

Using Metamorphic Facies

answer

Met Facies provide more detail about T/P conditions than Met Grade This helps ID the tectonic setting / metamorphic environment in which the met rk formed You won't always find every mineral in the facies b/c the parent rk composition may not be suitable for creating some minerals

question

Using Met Facies continued

answer

The diagram on the next slide shows you the major met facies on a T/P chart, similar to the met grade chart a few slides back. Look at the 3 examples A-C (dotted lines on the diagram). Path A represents an area where temp increases fast but press does not (ex: contact metamorphic event). The main facies along this path is hornfels. Path C represents an area where press increases fast but temp does not (ex: subduction zone). The main facies along this path is blueschist

question

P-T Paths

answer

Q: How long did it take to form a given met rk? Can chart the rock's history on a P-T path. The graph shows how long the rock was exposed to higher Press and Temp.

question

P-T Paths continued

answer

Prograde- the portion of the rock's history when P/T was increasing Retrograde- the portion of the rock's history when P/T was decreasing

question

P-T Paths continued

answer

Changes w/in mins can record P/T changes Ex: you can measure the concentration of elements within a single min crystal The picture on the next slide is a garnet crystal color-coded by Ca concentration. Warm colors -= more Ca

question

P-T Paths continued

answer

Notice there is more Ca in the center (green) than at the edge (blue). This means that, as the grain grew bigger, the Ca content was steady & high for a long time, then suddenly dropped right before the crystal stopped growing. Remember Bowen's continuous series? Ca is incorporated at high T, but not at low T This grain grew at high T for a long time, then cooled quickly and stopped growing Long prograde period, short retrograde period

question

Types of Metamorphic Rocks

answer

1- Foliated Met Rocks- Form when differential pressure is applied to the parent rock. Causes the minerals to realign themselves into layers/sheets (= foliations). Remember the animation file from earlier?

question

Common Foliated Rocks

answer

Larger grain size = higher met grade L: low grade = tiny grains = Slate M: intermediate grade = bigger grains = Schist R: high grade = large grains in felsic-mafic 'stripes' = Gneiss (pronounced "nice")

question

Types of Met Rocks

answer

2- Non-foliated rocks. Formed when confining pressure is applied to the parent rk Minerals are not realigned into layers. ID these by mineral content instead of by met grade.

question

Common Nonfoliated Rocks

answer

L: Hornfels: hornblende commonly present high T/low P M: Quartzite: quartz commonly present Parent rk quartz sandstone R: Marble: calcite present Parent rock limestone/biogenic sed rk

question

Practice Exercise: Q: how can you tell the difference between quartzite and marble? They look very similar & come in the same colors.

answer

Answer: 2 ways to tell: 1- Hardness. Quartz has a much higher hardness on Mohs Scale than calcite does. 2- Effervescence. Calcite is a carbonate, so marble, which contains lots of calcite, fizzes when you put weak acid on it. Quartz is not a carbonate, so the acid does not affect it.

question

PT 1- Structural Geology

answer

A sub-field of geology that studies deformation of rocks Strata obviously form as flat, horizontal layers, but they often get altered This deformation is the result of forces acting upon rocks

question

Tectonic Forces

answer

Deformation often occurs b/c force is being applied to rks via tectonics As plates try to move, they exert force on rocks. 3 main tectonic forces: Tensional- pulling something apart Compressional- squeezing things together Shearing- sliding things past each other

question

Tectonic Forces

answer

Notice that these 3 forces correspond with the 3 major types of plate boundaries: Tensional force reflects divergent boundary behavior Compressional force corresponds with convergent boundaries Shearing force equates with transform motion If this does not make sense, go back and review the plate boundaries before you continue.

question

Responses to Force

answer

Rocks deform due to tectonic forces in 2 main ways: Brittle- the rocks resist change until the force is too great, and then they shatter Ductile- the rocks show little resistance to change, and begin to twist & bend, acting like a plastic material

question

Responses to Force continued

answer

Q: What determines how the rock deforms? Response can vary based on several things: 1- Rock type. Some rks are prone to ductile behavior, some are prone to brittle behavior 2- Temp. Low temp promotes brittle behavior, high temp = ductile behavior Ex: the lithosphere vs the asthemosphere

question

Responses to Force continued

answer

3- Speed of deformation. Quick change = brittle response, slow change = ductile more likely Ex: Glass hit with a baseball shatters (brittle response). Ex: Glass in old windowpanes gets streaky b/c it starts flowing downward via gravity = ductile.

question

PT 2- Types of Structures

answer

A- Folds- bending of strata Folds are a ductile response to compressional force

question

Fold Terminology

answer

Hinge- the area where the folding actually occurred. Ex: the hinge of a door is where the movement occurs Limbs- the two relatively straight sections of strata on either side of the hinge.

question

Classifying Folds

answer

Classified based on 3 things: 1- Shape (in Cross-Section view) Antiform- arch/rainbow shape. The limbs point down. Synform- basin/smiley face shape. The limbs point up.

question

Fold Shapes continued

answer

If slightly tilted, add 'overturned' to the name Ex: an overturned anticline If completely on its side, just call it Overturned Ex: can't tell whether this was antiformal or synformal, so just call it an overturned fold

question

Classifying Folds continued

answer

2- Age of the folded strata. Anticline The oldest layers are in the center of the fold Syncline The youngest layers are in the center of the fold Note: not all anticlines are antiforms, and not all synclines are synforms. Evaluate each part separately

question

Practice Exercise:

answer

Q: How can an antiform be a syncline instead of an anticline? That seems illogical A: Remember that folds can get overturned. Some get flipped completely upside down! This flips the youngest layters to the bottom & the oldest layers to the top

question

Classifying Folds continued

answer

3- the geometry of the fold/fold axis. Horizontal- When compressed, the strata are not tilted. Plunging- When compressed, the strata are tilted. Watch the animation, it is very helpful in illustrating the difference

question

Fold Geometry continued

answer

In cross section, horizontal & plunging folds look identical. Must see them from above or from the other cross-section in order to differentiate them

question

Fold Geometry continued

answer

Map view: Horizontal folds show the end of the limbs, and not the hinge. Get a striped pattern Plunging folds reveal part of the hinge

question

Fold Geometry continued

answer

2nd cross section view: Horizontal folds have no tilting, so layers are just flat, stacked strata Plunging folds are tilted, so the strata are inclined

question

Types of Structures

answer

Part B- Joints Cracks in rock representing a brittle reaction to tectonic force. The rocks break, but there is no movement of rocks along the break. Occur in sets Very common structural feature

question

Types of Structures

answer

Part C: Fault- Break in a body of rock along which rock layers are displaced (slip/offset) Like a joint, but with movement on either side of the break Offset varies Inches to 100s of miles Classified by slip direction

question

1- Dip-Slip faults

answer

These faults have an inclined fault plane Vertical movement- 1 side moves up, the other moves down (fault line in black)

question

Dip-Slip faults continued

answer

The two sides are labeled based on shape/orientation Hanging wall (HW)- 'hangs above' the fault line Foot wall (FW) - 'below' the fault line

question

Dip-Slip faults continued

answer

If the HW moves down and the FW moves up, you have a Normal Fault

question

Dip-Slip Faults continued

answer

If the HW moved up and the FW moved down, you have a Reverse (dip slip) fault

question

Dip-Slip Faults continued

answer

1c- Thrust faults are just reverse faults where the fault plane is almost horizontal to ground level Ex: the dotted line below traces a thrust fault between the purple and white rocks

question

Type 2- Strike-Slip Faults

answer

The fault plane is vertical, not inclined Thus, the movement is lateral, not vertical Usually looking at a map view instead of a cross section view

question

Strike-Slip Faults continued

answer

There is no HW or FW to ID since the blocks of rock on each side are the same shape Instead, look at how surface features are offset on either side

question

Strike-Slip faults continued

answer

Left-Lateral fault- from one side, the other side appears to have shifted to the left

question

Strike-Slip faults continued

answer

Right lateral- from one side, the other side appears to have shifted to the right

question

Strike-Slip faults continued

answer

The key with strike-slip faults is to imagine you are on one side of the fault line, then look across the fault line to see how things have shifted It doesn't matter which side you stand on

question

Faults & Tectonic Forces

answer

The type of fault that forms depends on the type of tectonic force applied In full-screen mode, the faults below are animated

question

Earthquakes

answer

Q: Why do we care? A: Damage

question

Ex: Haitian Earthquake 2010

answer

7.0 magnitude, w/ 52 aftershocks > 4.5 Occurred near a transform boundary with left-lateral motion between the Caribbean plate and North American plate (see map)

question

Ex: Haitian Earthquake 2010

answer

Scientists predicted this quake in 2007-8 Even with their prediction, 100,000+ died, and 1 million + were left homeless. Why was this disaster so bad if we knew it was coming? We'll come back to this question later in this lecture

question

PT 1- Earthquake Basics

answer

Earthquake- Release of energy that built up as rocks try to move past one another along a fault (or plate margin)

question

Basics continued

answer

Time 2: tectonic force keeps pushing, so the rocks are building up a lot of stress. No slipping yet, but the strain is causing elastic deformation of some features (ex: the black line is getting bent)

question

Basics continued

answer

Time 3: Once the stress is > the frictional force, the rocks along that section of the fault quickly slip, releasing the stored energy as seismic waves. If the tectonic force is still applied, stress will start to build up again This is why some places regularly have earthquakes

question

The Point of Movement

answer

Focus- the spot on the fault where movement actually occurs Below the surface The entire fault will not move during every quake, just sections of it Epicenter- The point on the surface directly above the focus More useful as a reference point to describe where an earthquake occurred

question

Focus continued

answer

Many foci are 2-20 km deep in continental crust Some occur deeper, but they are relatively rare

question

Q: Why are deeper quakes rare?

answer

A: As you get deeper in the lithosphere, rocks act less brittle and more ductile Movement on faults is a brittle behavior Thus, at depth rocks behave like plastics and bend rather than break & slip

question

Movements Before & After

answer

Foreshocks- smaller movements before the quake. Attempts to relieve some of the strain on the rocks Aftershocks- smaller movements after the quake. Attempts to relieve any residual strain, or rocks shifting to adjust to their new positions

question

PT 2- Seismic Waves

answer

The released energy moves out in all directions as seismic waves 3 different types of waves are produced

question

Type 1- Primary (P) Waves

answer

These are compressional waves, so they do not cause vertical or lateral movements Ex: stretch out a spring, then push on one end and watch the waves travel along its length Fastest seismic waves 6 km/s in the crust = 20x > sound waves in air! Move through solids & liquids

question

Type 2- Secondary (S) Waves

answer

Cause vertical displacement (see pic next slide) Slower, move at ~ half the speed of P-waves Cannot move through fluid materials Ex: cannot pass through the outer core of the Earth b/c it's too ductile Visit the website below to help you visualize the wave movements:

question

Type 3- L (long, surface) Waves

answer

Little slower than S-waves Restricted to near Earth's surface Cause vertical and horizontal movement See the animation above to compare wave movement types Note- some references divide L-waves into sub-categories (ex: Rayleigh waves). For this course we'll just use the P, S, and L categories

question

Seismic Waves & Earth's Interior

answer

Seismic waves are used to study Earth's interior Their speed is affected by the materials they pass through & come in contact with Ex: useful tool for oil exploration. Seismic waves can help ID deposits below ground Drilling is very expensive, so you have to know where to drill or you'll go bankrupt before you ever hit oil Big area of research for geologists, and a very lucrative career

question

Seismic Waves & Earth's Interior

answer

Waves bounce off things and change course Note their paths through the Earth are thus curved, not straight Only P-waves are observed on the side of the Earth opposite the focus. This defines the S wave shadow zone (see next slide)

question

Changes in Wave Speeds

answer

In general: waves move faster through denser materials BUT they may slow down in ductile materials In continental crust: P wave ~ 6 km/s, S-wave ~ 3 km/sec Slightly faster in oceanic crust b/c it's denser

question

Wave Speeds continued

answer

Moho- boundary between crust and mantle The density increase causes waves to speed up as they cross this boundary Mantle: P & S-waves speed up some Outer Core: S-waves dissipate (cannot move through fluid-like materials), P-waves slow down

question

PT 3- Measurement & Detection

answer

Seismometer- device used to record seismic waves. Deployed in sets of 3 1 calibrated for waves moving north-south 1 calibrated for waves moving east-west 1 calibrated for waves moving vertically

question

Seismometers continued

answer

Misconception- the needle does NOT swing back and forth during an earthquake! If the needle moves along with the rest of the machine, the line on the paper would not jerk back & forth The needle is on a pendulum so it stays still while the rest of the machine gets shaken Modern seismometers are digital, so there is no needle & paper

question

Seismometers

answer

The graph produced by the seismometer is used to determine exactly when each type of seismic wave reached the seismometer (see next slide)

question

Practice Exercise Q: On the graph on the previous slide, why are the P-wave peaks so much shorter than the S and L-wave peaks?

answer

P-waves are compressional; they don't cause any vertical movement of the ground. S-waves & L-waves cause some vertical movement, so those peaks are taller (i.e., they have a greater amplitude)

question

Where Did The Earthquake Happen?

answer

This is a critical question to answer when an earthquake occurs Need to know where to focus relief/rescue efforts The key to finding the focus is that the different seismic waves travel at different speeds Let's work through an example...

question

Example

answer

People felt an earthquake in SC. To discover the location of the focus, we need data from at least 3 seismometer stations (the colored boxes)

question

Example continued

answer

At each station, you record the exact time that the first P-wave and the first s-wave arrive The difference in arrival times can be plugged into a formula that calculates how far the seismometer is from the focus

question

Example continued

answer

Next, you can draw a circle around each station, using the distance from that station as the circle's radius (see next slide) Where the three circles overlap = the focus. In real life, the circles may not quite overlap at one exact point. Scientists use data from dozens-hundreds of stations to locate the focus very accurately

question

How Big Was the Quake?

answer

This is another critical question to help determine how much damage may have occurred and how much disaster relief will be needed 3 scales measure the magnitude/intensity of earthquakes

question

Magnitude continued

answer

1- Mercalli Index- measures the amount of property damage Uses Roman numerals Ex: II = very minor, XII = major Useful for insurance adjustors, construction issues, etc Not used by scientists Q: Why do scientists avoid this scale?

question

Magnitude continued

answer

A: Because the amount of property damage depends on the area hit, not the energy released. Ex: The exact same quake hits New York and the Sahara Desert. New York's Mercalli rating will be very high b/c property values are so high there The Sahara's Mercalli rating will be very low- there's no property there to damage!

question

Magnitude continued

answer

2- Richter Scale- Measures the amount of ground shaking as measured by the seismometer Named for Charles Richter Created in 1935 It's a logarithmic scale This is why each number on the scale really is a big deal Mag. 3 = 10x the ground motion of a Mag 2 Mag 5 = 1000x the ground motion of a Mag 2 Energy release increases by factor of 33 instead of 10!

question

Magnitude continued

answer

3- Moment (aka Moment magnitude) Measures the area of slip on the fault line = energy released This is the scale scientists use most often, not the Richter scale! Advantages: more accurate easier to calculate from seismographs can calculate from field measurements even when no seismometer data is available

question

Quakes & Plates continued

answer

1- Most quakes occur along plate boundaries 2- Quakes w/ deep foci often occur at subduction zones 3- Some quakes do occur far from the edges of the plates If you don't see these patterns, go back to the plate tectonic map and compare

question

Quakes & Plates continued

answer

Q: why are the deep plates at subduction zones? A: remember the metamorphic facies. Blueschist facies is associated w/ subduction zones & represents high press + low temp The subducted plate takes a long time to warm up, so it remains brittle while it is pushed down Brittle = can still have earthquakes

question

Risk Assessment

answer

Since we know where earthquakes are likely to occur, we can generate maps that indicate the likelihood of quakes Notice the yellow and orange spots within the North American plate on the next slide Yellow = Charleston, SC Orange = New Madrid, MO

question

Intraplate Quake

answer

These 2 spots are where large intraplate ("within plate") quakes have occurred New Madrid had a large quake/+aftershocks in 1811-1812 Est > 8.0 mag. Reports of damage as far away as Maine Parts of the Mississippi River changed course due to the quake The area overlies a failed rift valley system that is 750 Ma (see next slide) Similar to the Africa Rift Valley, but it never became a fully active divergent margin The remaining faults are still active, could cause another large quake in the future

question

Damage Control

answer

How can we minimize the damage caused by earthquakes 1- Land use policies Ex: Do not build directly on fault lines In 1972 California outlawed building on a fault 2- Follow safe building codes Ex: use reinforced concrete in high-risk areas

question

Damage Control continued

answer

3- Build on the right type of material Myth- Don't build on solid rock b/c the ground will open & swallow your house Fact- Solid rock is one of the safest things to build on Q: Why is solid rock safer than loose sediment?

question

Damage Control continued

answer

A: Solid rock is denser and thus will not move as much So seismic waves pass through rock quickly & don't disturb it much Loose sediment is less dense, and seismic waves cause it to move around a lot If the sediments contain lots of water, shaking them creates mud Most sinking of building during quakes is due to the ground getting liquified into mud

question

Earthquake Prediction

answer

Scientists have predicted some quakes, but we cannot do so consistently Difficult because every fault is different Ex: have to factor in length, depth, rock types, tectonic force type, amount of groundwater, amount of construction, etc etc We continue to test new predicitive tools Even NASA works on monitoring areas with satellites looking for any signs of elastic deformation

question

Prediction continued

answer

Q: if we can predict some quakes, like the Haitian quake, why do they still cause so much damage? A: Predictions are not guarantees, so some people don't take them seriously We can't stop the quake & we can't reinforce every building, so the area will still be damaged How do you relocate a large population? What happens if you relocate everyone and then the quake doesn't happen on schedule?

question

Quakes & Tsunamis

answer

Tsunamis are large waves often caused by undersea earthquakes Requires vertical displacement along the fault (see the animation) When one side of the fault shifts upward, it Forces the water above the fault to shift which creates the wave

question

Tsunami Case Study

answer

1960 Chile Most powerful quake recorded 9.3 Moment magnitude Tsunami affected areas as far away as Alaska and New Zealand Rescue workers expected no survivors along the Chilean coast

question

Tsunami Case Study

answer

When they arrived, they found the area was not as devastated as they had feared The locals had learned that, living in an area prone to large quakes, it was not safe to build right on the coast Structures are instead built on hills a little farther inland, so the tsunami caused relatively little damage in Chile Good example of using safe building practices to minimize damage & casualties

question

Lecture #13 Outline

answer

PT 1- Climate Basics PT 2- What Controls Climate? A- Orbital Controls B- The Atmosphere Note- this lecture is relatively long and includes some concepts that often give students trouble, so give yourself some extra time to work through it

question

Intro to Climatology

answer

Q: Why do we care? A: climate change. If conditions are changing on Earth, it may affect where we live, how much food and water are available, how severe natural hazards are, etc. Q: Why are we covering this in a geology class? A: geologists do a lot of climate research! Studying ancient climate helps predict future climate trends (remember uniformitarianism)

question

PT 1- Climate Basics

answer

Climate- Average surface conditions over some long period of time Ex: usually want at least a decade of data Often confused with Weather- Average surface conditions over some short period of time Ex: days-season Ex: Temp in Clemson during February 2012 was often in the 50s, but that is not Clemson's climate; that was just the weather that particular month

question

Climate Basics continued

answer

Q: Why does climate vary so much on Earth? i.e., why don't we have a desert planet or an ice planet like in Star Wars? Climate (cli) is determined by complex interactions among the lithosphere, atmosphere, biologic processes, ocean circulation, etc It's not just about atmospheric processes!

question

System Interactions

answer

Interactions among all these Earth systems are complicated to untangle Ex: how do the lithosphere and atmosphere interact to affect climate? Some interactions create feedbacks- a change in one component of system affects other things that then eventually affect the original component So you create a type of cycle

question

Positive Feedback

answer

Change in the 2nd component enhances the change in the 1st component When A increases... B changes... which causes A to increase again.... Ex- increasing the amount of soil causes more weathering to occur, which creates even more soil, which again causes weathering to increase, which again creates more soil...etc, etc etc

question

Positive Feedback continued

answer

Note: 'A' can decrease every time you come around the cycle too! This is still a positive feedback b/c you keep enhancing the initial change Ex: When temp drops, glaciers can get larger, which makes the temp drop even lower, which allows the glaciers to grow even larger, causing another temp drop...etc

question

Positive Feedback continued

answer

Positive feedbacks can be problematic b/c it can be hard to break out of the cycle; they just keep going until one component cannot change anymore or something else affects the system "runaway train" effect

question

Negative Feedback

answer

Change to 2nd component offsets the initial change in the 1st component. Steps in a negative feedback: 1- When A increases, B decreases 2- When B decreases, A decreases 3- When A decreases, B increases 4- When B increases, A increases (back to step 1)

question

Negative Feedback continued

answer

Each component goes through a 'see-saw' effect. First A goes up, then it goes down, then it goes back up, then it comes back down, etc Same for B. Negative feedbacks stabilize the two components; neither can get too high nor too low.

question

PT 2- What Controls Climate?

answer

Main energy source for Earth's surface is the Sun Insolation- INcoming SOLar radiATION. Solar energy that reaches earth Not insulation! Vary insolation and you vary the climate Several things affect how much insolation Earth receives

question

2A- Orbital Parameters

answer

Vary Earth's distance from the Sun and you vary how much insolation we receive. The Sun is not directly in the center of Earth's orbit Aphelion- farthest orbital point from the Sun 152 million km Perihelion- closest orbital point to the sun 147 million km The 5 million km difference has an effect on how much insolation reaches Earth Aphelion & perihelion do NOT control summer versus winter!

question

Orbital Parameters continued

answer

Milankovich cycles- cyclic changes in Earth's motions in space. 3 main ones: 1- Eccentricity- The shape of Earth's orbital path oscillates from more to less circular. Affects Earth's distance from the Sun

question

Eccentricity continued

answer

It takes about 100,000 yrs for one full cycle 50,000 to go from max to min, then another 50,000 to go back to max Influences warming-cooling trends during ice ages It takes 50,000 years to change from one extreme to the other

question

Milankovich Cycles continued

answer

2 Obliquity (Tilt)- Earth is tilted on it's axis and the tilt angle oscillates over time

question

Obliquity continued

answer

It takes ~ 41,000 yrs for one full cycle 20,500 years to go from min to max angle Q: why does such a small change in the tilt angle affect climate? A: Earth is large planet, so even a couple of degrees difference impacts how much insolation different areas receive. Obliquity affects the seasons

question

Obliquity continued

answer

Obliquity is why we have opposite seasons in the N and S hemispheres (NH & SH) January: NH is tilted away from the Sun, so it gets less insolation, = winter. SH is titled towards the sun, so it gets more insolation & experiences summer

question

Obliquity continued

answer

Changing the obliquity angle changes the seasonal contrast- The temp contrast btwn summer & winter Higher angle = each hemisphere is pointed more directly towards/away from the Sun, so summer is really warm & winter is really cool, creating a high seasonal contrast Lower angle = each hemisphere is pointed less directly towards/away from the Sun, so summer is less warm & winter is less cool, creating a low seasonal contrast

question

Obliquity continued

answer

Eccentricity also affects the seasonal contrast. Obliquity: NH tilted away from sun = winter BUT... Eccentricity: NH winter currently occurs near perihelion (see pic below) So the 2 cancel each other out some, & the seasonal contrast is relatively low Remember: the cycles are changing over time eventually NH winter will occur @ aphelion It can be difficult to track all 3 Milankovitch cycles at once to determine what their net affect on climate will be

question

Milankovich Cycles continued

answer

#3 - Earth not only 'rocks' on its axis, but it also 'wobbles'. The wobble is called precession. This causes the North Pole to point in different directions in space over time Watch the animation at this link; note how the red line (indicating the N Pole) points in different directions as the video runs. That motion represents the 'wobble' of the planet on its axis

question

Precession continued

answer

Q: How is precession different from obliquity? Students often get these 2 confused A: Obliquity is a rocking motion; precession is a spinning motion Ex: think of the difference between a rocking chair and spinning a toy top

question

Precession continued

answer

Precession takes about 22,000 years per cycle (= one full 'spin' through a complete circle) Precession affects climate because it determines which hemisphere is pointed towards the Sun at any given time of year (see pic on next slide)

question

Precession continued

answer

Top: Earth's orientation during January NH points away from the Sun, so NH has winter Bottom: 11,000 years from now, precession will have wobbled so that, during January, the NH is pointed towards the Sun, so January will be summer in the NH

question

2B- Atmosphere

answer

First thing insolation encounters is the atmosphere Troposphere- the lowermost layer of the atmosphere This is where most weather phenomena occur

question

Atmosphere continued

answer

Some insolation (ca 30%) is reflected back into space, so it provides little-no energy to earth. Albedo- a measurement of reflectivity. Varies with material. That 30% loss comes from 3 reflection off 3 main things (see pic on next slide): Ground = 4% Atmosphere = 6% Clouds = 20%

question

Atmospheric Gases

answer

Insolation also interacts w/ the different gases in the atmosphere Atmospheric composition: Nitrogen- 78% Oxygen- 21% CO2 , H2O, and all others < 1% Many gases are thus present in small amounts, but they are important as greenhouse gases- they trap insolation close to Earth's surface for longer periods of time

question

Greenhouse Gases continued

answer

When insolation reaches Earth's surface, some is absorbed as heat energy, the rest is re-radiated back into space. Greenhouse gases prevent that re-radiated energy from leaving as quickly as it should This allows Earth to absorb more of the energy, making it warmer

question

Greenhouse Gases continued

answer

This is the greenhouse effect- insolation comes in through the atmosphere, but can't easily leave Ex: this is why the inside of your car is much warmer than the outside air temp during a sunny day See the diagram on next slide and the animation

question

Greenhouse Effect continued

answer

Key point: even though greenhouse gases (GGs) make up a small % of the atmosphere, they trap a large amount of insolation If you were to remove all GGs from the atmosphere, Earth's surface temp would be 33 C lower!! This explains why scientists think that adding more GGs to the environment could cause Global Warming (we'll come back to this in lecture 15)

question

Atmosphere continued

answer

Next point: Insolation changes w/ latitude At the equator: a given amount of insolation covers a relatively small area b/c it strikes the Earth ~ perpendicular to the surface But closer to the poles, the same amount of insolation gets spread over a larger area b/c it strikes a curved surface (see pic on next slide)

question

Atmosphere continued

answer

Explains why the poles are colder than the tropics- there's less insolation per unit area

question

Latitudinal Insolation Distribution

answer

This means there's an energy imbalance on Earth (see graph on next slide): Equator absorbs a lot, loses a little Poles absorb little, lose a lot Nature doesn't like such gradients, so processes redistribute the energy Otherwise the equator would get extremely hot and the poles would get extremely cold

question

Heat Transport in the Atmosphere

answer

Several circulation cells help move heat energy away form the equator and towards the poles Hadley cells- Transport heat from equator to 30 degrees latitude

question

Hadley Cells continued

answer

Steps in the Hadley cells, starting at equator: 1- Insolation warms the air close to the ground Remember convection? When you heat something, its density decreases, causing it to rise 2- As it rises, it begins to cool and gets pushed aside by warmer air rising beneath it This creates low air pressure at the equator Thus, Hadley cells in the atmosphere work just like convection cells in the asthenosphere

question

Hadley Cells continued

answer

3- As the air mass cools down while rising, some water vapor cools into liquid water & falls as rain This is why the equator is associated with rainforests & lots of rain 4- Once the cooler air is pushed aside, some moves N and some moves S 5- as it moves N or S, the air mass continues to cool, so more water vapor is lost as rain along the way

question

Hadley Cells continued

answer

6- By the time the air mass reaches ~ 30 degrees latitude, it is cold enough that its density has increased, causing it to sink back to Earth's surface This creates high air pressure at the surface There is little water vapor left, so this area gets little rain 7- Once close to the surface, the air absorbs more insolation, heating it up as it moves across the surface as wind until it is warm enough to rise again Some of the wind blows N, moving the heat farther N Some of the wind blows S, completing the cell

question

Hadley Cells continued

answer

The Ferrel cells and polar cells operate in the same way, just at higher latitudes The three interlock, like gears, to keep moving heat away from the equator and towards the poles

question

Atmospheric Processes continued

answer

El Nino- periodic changes in wind strength over the Pacific Ocean during some winters Affect global weather patterns First, let's look at normal conditions in the Pacific... The map on the next slide is color-coded by water temperature. Notice that, near the equator, water temp is much higher in the western Pacific (near Australia) than in the eastern Pacific (near Peru)

question

Normal Pacific Conditions

answer

West Pacific Warm Pool (WPWP)- the area of warm water in the western Pacific

question

Normal Conditions:

answer

1- Trade winds push water to the W 2- The 'void' left is filled by cool water upwelling in the E

question

Normal continued:

answer

3- WPWP heats the air above it, causing the air to rise creates low atmospheric pressure above it 4- the rising air cools, creating lots of rain just like the beginning of the Hadley cell So in the western Pacific during normal conditions it's warm & wet In the Eastern Pacific it's cool & dry

question

El Nino Conditions:

answer

1- The trade winds weaken or even stop 2- This allows the WPWP to flow back to the east (remember, the winds were the only thing pushing the warm water west) 3- Eastern waters become warm, so upwelling stops

question

El Nino Winter continued:

answer

4- The low pressure area must follow the warm water b/c the warm water creates it Southern Oscillation- the resulting flip-flop in air pressure between west & east 4- The rain must follow the low pressure area So in the Western Pacific during El Nino conditions it becomes cool & dry And in the Eastern Pacific it becomes warmer & wetter Basically, everything switched

question

Study Hints

answer

The El Nino cycle can be tricky to understand. You have to keep in mind which location you are at, AND you have to determine whether normal or El Nino conditions are occurring The animation is a good illustration of the entire process

question

Practice Exercise: Q: During an El Nino year, water temperature & precipitation near New Zealand will change in which direction?

answer

A: NZ is in the western Pacific, near Australia. So the water temp will decrease during El Nino, and the amount of precipitation will decrease too You'll definitely see some questions like this on the next exam!

question

El Nino Effects

answer

Q: why do these changes affect weather in other parts of the world? A: The Pacific Ocean is huge. As the warm water & low pressure system move across the Pacific, they displace other air and water currents, like the Jet Stream If the Jet Stream moves, it affects weather across N America During El Nino: SC has a wet & cool winter, then a dry & warm summer

question

El Nino Effects

answer

El Nino does not occur like clockwork Quasi-periodicity of once every 4-7 years Scientists know what happens during an El Nino, but they still are not sure why the trade winds occasionally weaken and cause an El Nino

question

What is La Nina?

answer

In some years, the trade winds strengthen instead of weaken This pushes the WPWP farther west La Nina basically has the opposite effects from El Nino Ex: The eastern Pacific gets even cooler & drier than usual Ex: SC has a relatively warm & dry winter Winter 2011-2012 was a La Nina winter, which explains why it was so warm around Clemson

question

Lecture #14 Outline

answer

Last lecture we looked at how the atmosphere affects climate, so we'll continue by looking at how other Earth systems affect climate PT 1- Other Controls on Climate A- The Hydrosphere B- The Biosphere C- The Cryosphere D- The Lithosphere PT 2- Studying Climate Direct Measurements Climate Proxies

question

1A- Hydrosphere

answer

This is the total volume of water on Earth The ocean is the primary body of water that influences climate Water has a relatively high heat capacity, allowing it to move heat energy from the equator to the poles similar to atmospheric processes discussed last time

question

Hydrosphere continued

answer

Ex: The Gulf Stream (shown below) moves warm water from the Gulf of Mexico to higher latitudes off the European coast Take away the Gulf Stream, and western Europe would have a cooler climate The Gulf Stream is just part of a bigger current system...

question

Thermohaline Circulation

answer

This is a 'conveyer belt'-like current that circulates throughout the global ocean Red Arrows = warm, surface water flow Blue Arrows = cold, bottom water flow Watch the animation to see it in motion

question

Thermohaline Circulation continued

answer

This system is based on temp and salinity Thermo = heat Haline = halite (salt) 1- As water flows N, it delivers heat to higher latitudes, resulting in cooler water So it's density increases 2- Over the ocean, rainfall is low & evaporation is high. This combo makes the water saltier So its density increases more Near Greenland, the water is dense enough to sink

question

Thermohaline Circulation continued

answer

Problem: as temp have risen, the water does not cool down as fast as it used to as it flows north Melting glaciers in Greenland add freshwater to the ocean, keeping the water from getting saltier Thus, the thermohaline current has been slowing down in recent decades If it stops, temps in high latitudes will get colder b/c they will no longer get heat via the current

question

Thermohaline Circulation continued

answer

The Day After Tomorrow was based on the idea of thermohaline circulation coming to a halt The timescale & results were modified to make the movie exciting Gradual slowing over decades does now keep an audience on the edge of their seats

question

Ocean Interaction w/ Atmosphere

answer

Remember that each Earth system does not exist independently of the others Thus, we have to know how each system interacts with the others Ex: Oceans can store lots of dissolved gas form the atmosphere Ocean contains ca 60x more CO2 than the atmosphere does! This is why climate studies take so long & involve so many people- no one person understands all the different system interactions

question

1B- Biosphere & Climate

answer

Biosphere- all living things on earth Plants affect climate draws down CO2 for photosynthesis affect albedo Animals also affect climate release CO2 & methane One single organism doesn't have a big effect, but when you add up entire populations, the effect can be huge Ex: there are > 1.3 billion cows on Earth Ex: there are > 7 billion people on Earth

question

Biosphere continued

answer

The biosphere also interacts with other systems Biological Pump- Photosynthesis by phytoplankton in the ocean draws CO2 out of the atmosphere The CO2 is stored in biological tissues until the plankton die Their shells sink to the seafloor & become lithified into carbonate rock This interaction involves the biosphere, atmosphere, hydrosphere, and lithosphere!

question

1C- Cryosphere

answer

This is the total volume of snow & ice on Earth Ice covers ca 9% of all land surface (the % is higher during winter in the NH)

question

Cryosphere continued

answer

L: ice (gray) around Antarctica in SH summer R: ice around Antarctica in SH winter

question

Cryosphere continued

answer

The cryosphere affects Earth's albedo Most land surfaces albedo ~ 15-25% Snow/ice albedo ~ 40-90%

question

1D- Lithosphere

answer

Tectonics affects climate in several ways 1- Continental position When continents drift towards the poles, they have cooler climates

question

Lithosphere continued

answer

2- Continental configuration Large continents have dry interiors b/c there is relatively little coastline, and the shores are far away Very hard to get coastal water vapor all the way inland

question

Lithosphere continued

answer

3- Mountain/plateau uplift creates circulation barriers Winds have to move up to pass over the mts (see image on the next slide) When air rises, it gets cooler, and water vapor turns into rain So one side of the mt gets lots of rain, but the climate on the other side is much drier (rain shadow)

question

Lithosphere continued

answer

4- Weathering of rocks & minerals affects atmospheric composition Weathering silicates absorbs CO2 (remember the feldspar-kaolinite chemical weathering reaction from an earlier lecture) Weathering carbonates releases CO2 One rock is no big deal, but think about the total volume of rock pushed up along a collision zone Ex: the Himalayan Mts have changed global climate by exposing so many rocks to weathering

question

Lithosphere continued

answer

5- Creating & destroying land bridges i.e., opening & closing oceanic gateways Ex: 8 million years ago, N & S America were not connected, so ocean water flowed between them Once they were connected with a land bridge (Central America), the Gulf Stream formed since water could not flow east-west anymore Central America closed the oceanic gateway

question

PT 2- Recording Climate

answer

To predict future climate changes, we need to know as much as possible about how climate has changed in the past Q: what was climate like in the past?

question

PT 2- Recording Climate

answer

Instrument records provide most of our modern climate info We only have about a century's worth of instrument records In many parts of the world, we don't even have that much 100 years is a very short part of Earth's 4.5 billion year history

question

PT 2- Recording Climate

answer

Historical records can give us some climate info Ex: the pic below shows what water level was like when the photo was taken These records are not always detailed, and only go back a few centuries at best in most places Ideally, we need some way to directly measure ancient climate variables

question

Recording Climate

answer

We do have one way to directly measure samples of the ancient atmosphere Glaciers in Greenland & Antarctica contain air bubbles trapped as the ice formed Each bubble = a tiny pocket of atmosphere Analyze the bubble & we can learn things like how much CO2 was in the air at that time

question

Ice Cores continued

answer

Some of the glaciers on Greenland and Antarctica are > 2 miles thick The deepest ice cores from Antarctica span 1 million years (and we haven't reached the bottom yet!) Thus, we can directly analyze greenhouse gas fluctuations in the atmosphere over the past 1 million years

question

Ice Cores continued

answer

Q: how do you determine the age of each gas bubble? A: the ice also contains layers of ash from volcanic eruptions. Ash can be easily radiometrically dated, so you can determine the age of the bubble from the ash layers that are close to that bubble

question

Recording Climate

answer

Q: what if we want data about other climate variables, like temperature? A: We have to use different tools called proxies Proxies- a 'substitute' for the real thing. Ex: we do not have a 10 million year-old thermometer, but many natural processes are sensitive to temp changes. If they leave a record that we can analyze, we can derive temp information from that proxy

question

Proxies continued

answer

There are lots of climate proxy records Diff proxies record different aspects of climate on different timescales. General rules for using proxies: 1- Always ensure your data set represents the appropriate area & timescale for your conclusions Ex: Don't use five trees from Clemson Forest that are all < 100 years old to discuss climate along the entire East Coast over the past 1,000 years Always consider the nature of the specimen Remember the zombie clams form radiometric dating? You can't use everything as a climate proxy

question

Proxy #1- Tree Ring Width

answer

Indicates weather conditions during that year Wide rings = good growing conditions Narrow rings = little growth, something was wrong in the environment Diff species have diff optimal conditions Again, think about your specimen!

question

Tree Ring Width continued

answer

What makes a year good or bad depends on the type of tree (some need lots of water, some need little water, etc)

question

Proxy #2- Biogeography

answer

Studying the Faunal/floral distribution Ex- crocodiles only live in areas where mean annual temp is high Today thee are no crocs in Canada, but in 90 million year-old Canadian rocks we find lots of croc fossils Thus, Canada must have been much warmer at that time

question

Proxy #3- Stable Isotopes

answer

Unlike radioactive isotopes, these don't decay over time Isotopes' diff atomic weights result in diff amounts of ea isotope getting incorporated into some molecules We thus measure stable isotopes in a sample as a ratio Ex: 18O/16O for oxygen, 13C/12C for carbon, etc Key- the ratio in some materials changes as certain climate variables change

question

Proxy #3a- Stable Carbon Isotopes

answer

Different plants conduct photosynthesis differently Ex: Ford and Dodge both make pickup trucks, but they build them differently The different ways of doing photosynthesis are called C3 and C4 Note: 'C3' and 'C4' has nothing to do with carbon isotopes! C3 plants are typical woodland/forest plants C4 plants are plants more typical of open grassland habitats

question

Stable Carbon Isotopes continued

answer

2 stable carbon isotopes: 13C/12C Plants take in different amounts of each based on their photosynthetic style Thus, C3 and C4 plants have distinct carbon isotope compositions Analyze the carbon isotope ratio in a plant fossil and you can determine whether it was a C3 or C4 plant

question

Stable Carbon Isotopes continued

answer

Animals eat the plants and thus 'inherit' the plant's isotopic signature 13C/12C in animals' skeletons thus reflects the type of plants in the ecosystem Ex- did the fossil deer live in a forested area or an open, grassland area? This provides clues about climate change over time

question

#3b- Oxygen Isotopes

answer

18O/16O ratio in some materials depends on the temp when the material formed Ex: many invertebrate shells At cool temperatures, the shell takes in more of one particular isotope As temp increases, the shell takes in more of a different isotope Thus, the new shell has a different isotope ratio Oxygen isotopes thus provide quantitative temperature data; they're a thermometer proxy

question

Oxygen Isotopes continued

answer

Ex- A phytoplankton shell's 18O/16O reflects water temp when the shell was growing Ex- 18O/16O in fish bone reflects water temperature when the fish was alive T = 111.4 - 4.3*(Df - Dw) Df = oxygen isotope ratio in fish bone Dw = oxygen isotope ratio in seawater (often ~ 1.0) T = water temp (Celsius)

question

Practice Exercise Q: You study a fish fossil and its measured oxygen isotope ratio is 20.1. What was the water temp when that fish was alive?

answer

A: 29.27 degrees Celsius Note: different materials have different equations Can't use the fish equation for phytoplankton The method will not work for every fish species Again, you must think about your specimen!

question

Proxy #4- Alkenones

answer

Type of organic molecule made by some types of phytoplankton Some of the carbon atoms are double bonded The number of double bonds changes with water temperature Thus, alkenones can produce quantitative water temperature, just like oxygen isotopes

question

Alkenones continued

answer

Alkenones can survive in sedimentary strata for tens of millions of years All this temp data came from alkenones

question

Proxy #5- Mg/Ca

answer

Some trace metals in shells also provide quantitative temp of the water in which the shell grew Ex- Mg can substitute for Ca in carbonate minerals' crystal structure. The likelihood of this occurring changes with ambient temp. Thus, Mg/Ca in a shell depends on temp Sr/Ca works the same way

question

Temp Proxies continued

answer

Q: Why do we need so many temp proxies? A: Temp is a key climate variable A: Some areas may not preserve alkenones, but may preserve shells for Mg/Ca analysis A: Using more than one proxy helps you check the accuracy of your data If you test one shell w/ 2 proxies and get the same temp, you are more confident that the temp is correct

question

Global Warming (GW)

answer

This is a big topic in society, and debates can get quite heated Sorry, bad pun intended Everyone has an opinion, but remember the difference between opinions & hypotheses? Hypotheses require facts to support them Opinions do not

question

GW continued

answer

Ex: IMO sushi is terrible. This is just my opinion, and it's not even based on many facts: I've only tried sushi 1-2x There are a lot of types I've never tried So why should you believe me if I tell you sushi is yucky?

question

GW continued

answer

Remember: people are always trying to convince you to agree with their opinion "Vote for this candidate, he/she's the best!" "Buy this product, it's better than other products!" But what are their opinions based on? Think about the issue for yourself & develop your own, informed opinion

question

GW continued

answer

One big source of confusion with GW is that there are 2 separate questions to deal with: Q#1- is the Earth warming up? Q#2- if so, why is it warming up? We have to address these issues separately. If Earth is not warming up, we don't even have to worry about #2

question

PT 1- Is Earth Warming Up?

answer

This is the first question we have to tackle It sounds simple, but temp calculations can get confusing You have to consider different locations, whether you're measuring daily, weekly, monthly, or seasonal temp, are you going by daytime highs or daytime lows, what statistical and graphing methods to use....yikes! Instead let's use a simple proxy: glaciers If Earth is warming up, then glaciers should be getting smaller. That's a simple hypothesis to test

question

Is Earth Warming continued

answer

To test the hypothesis, all we have to do is see if glaciers are getting smaller. All pictures show the same location in the same season 1980 vs 2002

question

Is Earth Warming continued

answer

North Cascades Natl Park, 1973 vs 2006 (2 km retreat)

question

Glaciers Around the World

answer

Orange/brown dot = a glacier that's shrinking Blue dot = a glacier that's getting bigger The bigger the dot, the more the size has changed

question

Glaciers Around the World

answer

Q #1- Is Earth warming up? A: Based on glaciers shrinking, we must conclude that yes, lots of places are getting warmer over the past several decades So now we can start to figure out WHY the Earth is warming up....

question

PT 2- Why is Earth Warming?

answer

There's more than one reason 1- Earth is currently naturally warming coming out of the most recent ice age Natural processes (ex- Milankovich cycles) account for ~ 50% of warming over the past few centuries

question

Unusual Warming Pattern

answer

2- But the warming is occurring faster and has a greater magnitude than other warming trends we have data for in recent history Notice that temps are higher now than at any time within the past 2,000 years, and they've risen very quickly since ~ 1850

question

GGs & Global Warming

answer

Humans have added a lot of GGs to the atmosphere since the Industrial Revolution began in the 1800s. Remember: GGs trap insolation, keeping more heat energy at Earth's surface (Greenhouse Effect) Q: is the amount of GG in the atmosphere increasing?

question

GGs & GW continued

answer

These 3 GGs have become much more abundant in the atmosphere, and the timing coincides with the Industrial Revolution

question

GGs & GW continued

answer

Q: Are the GGs really decreasing the amount of insolation that escapes from Earth? A: Yes. Satellites measure exiting insolation. It's been steadily decreasing for decade. The energy wavelengths that GGs trap are exactly the wavelengths that are escaping less and less easily.

question

GGs & GW continued

answer

Conclusion: Based on these facts, scientists calculate that ~ 50% of the temp increase of the last ~ 200 yrs is due to greenhouse gas buildup.

question

Humans and GGs

answer

Next question: are human-made GGs responsible, for the warming? i.e., is the GG buildup anthropogenic (man-made)? World population is now > 7 billion up almost 3 billion since 1970 That's a lot of people emitting a lot of GGs, but is it really enough to alte global climate? Let's look at the atmospheric GG uildup closer...

question

CO2 Buildup (50 yr record)

answer

This data clearly shows that carbon dioxide levels in the atmosphere have been rising, but the graph cannot tell us where the carbon dioxide is coming from

question

CO2 Buildup (1,000 yr record)

answer

Levels are higher now than any time for the past 1,000 years This still doesn't tell us where the CO2 is coming from

question

CO2 Buildup (400k yr record)

answer

Moden levels have no equal in the past 400,000 yrs But this still does not prove where the CO2 came from

question

CO2 Buildup continued

answer

So we have plenty of data demonstrating that CO2 levels are higher now than at any point in the past 400,000 years Next, we need a way to figure out where all this extra CO2 has come from For that, we'll examine carbon isotopes again Note: C-12 and 12C mean exactly the same thing; the notations are used interchangeably in this lecture

question

Finding the Carbon Source

answer

Different sources produce diff isotopic mixes of carbon Ex: volcanoes release C-13 Ex: Forest fires release C-12 & C-14 Ex: Burning fossil fuels release C-12

question

Finding the Carbon Source

answer

Seuss Effect- a decline in the atmospheric 14C / 12C ratio over the past 150+ years

question

The Suess Effect continued

answer

Q: Why would that ratio decrease? A: There are two ways to make a ratio smaller: 1: Make the numerator smaller So decrease the amount of C-14 in the air OR..... 2: Make the denominator bigger So increase the amount of C-12 in the air

question

Suess Effect continued

answer

Think of the isotope ratio like a mixed drink C-14 = rum and C-12 = Coke You put one shot of rum in each glass, so they have the same amount (= the numerator is the same) Next, fill the glasses with Coke. The small glass has a higher rum/coke ratio than the big glass b/c the big glass has more Coke (the denominator is larger)

question

Suess Effect continued

answer

So which happened, less C-14 or more C-12? Remember that C-14 is created in the atmosphere (we covered this during lecture 12) at a pretty constant rate Thus, the amount of C-14 in the atmosphere has not significantly changed So there must be more C-12 in the air than they're used to be

question

Suess Effect continued

answer

Q: So what can add C-12 to the air without adding any C-14 or C-13? It wasn't discussed herein, but the amount of C-13 has not changed Volcanoes would add C-13 to the atmosphere Other sources (ex- forest fires, cellular respiration) would add some C-14 Fossil fuel burning adds lots of 12C to atmosphere and adds no 14C

question

Suess Effect continued

answer

Q: Why doesn't fossil fuel burning produce C-12? Remember: It takes ~ 57,300 yrs for all the 14C to decay after an organism dies But It takes millions of years for organic remains to become fossil fuels So, fossil fuels contain no C-14, just C-12

question

Suess Effect continued

answer

Thus, the Seuss Effect strongly supports the anthropogenic hypothesis b/c burning fossil fuels is the only thing that accounts for the drop in the 14/12 ratio. Note: it's fine if people want to challenge the GW hypothesis, but that requires finding a better explanation for the Suess Effect, which GW skeptics have not been able to do. Remember: to challenge scientific ideas, you have to work with facts, not just some group's opinion

question

Summary

answer

Fact: humans are increasing atmospheric CO2 Fact: CO2 helps increase temperature Conclusion: humans are responsible for some of the current warming

question

Summary

answer

Even if someone remains unconvinced that humans are the cause of GW, remember that we have to deal with the changes GW causes regardless of what's causing it Possible effects of GW: ice sheet melting rising sea levels aridity in mid latitudes stronger hurricanes and El Ninos extinctions due to ecosystem changes These are all things that will adversely affect our society

question

PT 3- Seven Global Warming Myths

answer

Both sides exaggerate & twist the facts Remember: Think for yourself! Be skeptical but NOT paranoid If you don't make up your own mind, others will be glad to tell you what to think Let's examine 7 statements commonly made about GW to see if they're real or not.....

question

1- "The Coasts are About to Flood!"

answer

As glaciers melt, much of the water will flow into the oceans, so sea level will rise Some GW advocates claim coastal cities and beaches thus are in imminent danger of flooding Consider the timescale of the change Significant sea level will occur, but on decadal-century timescale Thus, the threat is real BUT it is not imminent

question

2- "The Planet is Burning Up"

answer

The map below was included in Al Gore's movie, An Inconvenient Truth, to make people realize how much GW is occurring The data are real, but about that map.....

question

Myth 2 continued

answer

When you project a 3-D world onto a flat map, things can get distorted. This type of map makes things near the poles look really big Thus, the worst warming appears to cover a bigger area

question

Myth 2 continued

answer

Also, the color scheme intentionally uses colors that we associate with danger signs/warnings

question

Myth 2 continued

answer

This map shows the same type of data in a less alarming manner Earth tone color scheme Different type of map that doesn't stretch the area near the poles Again, the data on the other map is fine, but that map was designed specifically to get you to agree with their message

question

3- "It Isn't Really Global"

answer

Some skeptics claim that 'Global' warming is an exaggeration b/c not every place is warming up It's true that different areas of the planet react differently to changes Some are warming, some are cooling, some are not changing However, the effects of climate change will be global Ex- changing thermohaline circulation in the North Atlantic messes up global oceanic circulation Ex: El Nino in the Pacific affects SC weather

question

4- "Record Low Temps Disprove GW"

answer

GW skeptics often make statements like this one: "1,100 record low temperatures were recorded in the US during summer 2009... so much for Global Warming!" Many people listen to this point b/c it sounds like a fact with lots of data supporting it. Q: is it accurate?....

question

Myth 4 continued

answer

The data re accurate, but the data do not support the conclusion The temps may be from just one small area They may reflect only one small length of time Data on record highs and norms is lacking We don't base climate trends on data from just one area Often, these people are talking about weather, not climate

question

Myth 4 continued

answer

Ex: Spring semester 2011 was very cold around Clemson We even missed the first day of class due to snow! GW skeptics were quick to use this as anti-GW fodder, But it was just one cold month in one place- that's not a global climate trend, that's just unusual local weather Spring semester 2012 we had unusually WARM conditions all semester

question

5- "It's Only 3, Who Cares!?"

answer

Skeptics dismiss GW b/c scientists predict global temps will increase about 3 over the next century, and that seems like a tiny temp change Scientists use Celsius, but most people use Farenheit 3o C = ~ 5.4o F, that's a bigger change Always check your units!

question

Myth 5 continued

answer

That number is a global average; temps will vary a lot form place to place During the last Ice Age: global average temp was only ~ 4.5o C lower than today So drop the temp 4.5o C and we get an ice age, so what will a 3o C increase do? Many organisms can't tolerate temp shifts of even a few degrees We rely on many species for food, medicine, etc

question

6- "Scientists Can't Decide Between Global Warming & Cooling!"

answer

This point goes back to 1975 National Academy of Science Report stated that warming or cooling was possible Data was inconclusive, so they could not determine how temperature would change

question

Myth 6 continued

answer

Also published in 1975: Newsweek- "The evidence in support [of global cooling] has now begun to accumulate so massively that meteorologists are hard-pressed to keep up with it." Reporters often make mistakes when trying to explain scientific studies Skeptics still use this 40+ year-old Newsweek issue to try and discredit scientists, even though it is clearly outdated AND make a huge reporting error in the first place

question

Myth 6 continued

answer

Lesson: Always consider the source & check the date! We often get our 'facts' from unreliable sources Ex: I can post a blog on the internet describing my life as a roadie for Metallica who has 3 arms..... but that's not even remotely true If you want reliable info, talk to experts Tooth aches? Talk to a dentist Car won't start? Talk to a mechanic Unsure about GW? Talk to scientists Bloggers post anything to get your attention Politicians say anything to get your vote

question

7- "It's a Hoax"

answer

Climategate- Fall 2009: hackers stole emails from a UK climate lab and gave to GW skeptics The emails were touted as proof that GW isn't just wrong, but is a deliberate hoax by scientists Disagreeing w/ a hypothesis is fine- it happens all the time in science Claiming scientists are lying and making things up is incredibly serious- you could ruin a person's career

question

Myth 7 continued

answer

Emails contain this data: discussions of work in progress Complaints about co-workers, colleagues, skeptics Phrases like "manipulating my data" and "tricky statistics" Q: do these data support the conclusion that scientists are faking GW?

question

Myth 7 continued

answer

1- discussions of work in progress You can't grade someone based on a rough draft 2- Complaints about co-workers, colleagues, skeptics This says nothing about GW at all, it's just gossipy

question

Myth 7 continued

answer

3- Phrases like "manipulating my data" and "tricky statistics" Statistics are tricky even for many scientists The sentence does not mean that scientists are trying to trick people "Manipulating my data" is slang in labs for "get it ready to publish" It does not mean scientists are changing numbers, altering results, etc

question

Myth 7 continued

answer

Conclusion: This data does not prove GW is a conspiracy The scientists who wrote the emails have been investigated and officially cleared of any wrongdoing

question

Myth 7 continued

answer

Lesson: Be very suspicious when people only provide short portions of quotes Ex: I could claim that students say "MATH 1080 is incredible" But maybe the original statement was "the heavy workload in MATH 1080 is incredible" I selected only part of the quote and deliberately took it out of context in order to make MATH 1080 sound good

question

Myth 7 continued

answer

Summary: It's fine to disagree with a hypothesis, but it is not ok to attempt to discredit scientists just b/c you disagree Climategate is a good example of the "kill the messenger" tactic Make people distrust scientists, and they won't listen even if scientists are telling them the truth That could have serious consequences; people might start ignoring their doctors, safety inspectors, and other similar professionals

question

PT 1- Deserts

answer

Q: Why do we care? A: Deserts cover extensive areas and are growing 20% of all land area is desert Another 15% of all land area is semi-arid So over 1/3 of all land is arid or semi arid!

question

The 10 Largest Deserts (km²)

answer

Note that many deserts are quite large! Antarctic (Antarctica) 14 000 000 Sahara (Africa) 9 000 000 Greenland (Arctic) 2 000 000 Gobi desert (Asia) 1 125 000 Empty Quarter (Middle East) 650 000 Kalahari desert (Africa) 580 000 Great Sandy Desert (Australia) 414 000 Karakum (Asia) 350 000 Taklamakan desert (Asia) 344 000 Namib desert (Africa) 310 000 Compare: South Carolina: 82,000 Texas: 678,000 USA: 9,800,000

question

What Defines a Desert?

answer

Some researchers say deserts must be hot, but others disagree That's why places like Antarctica & Greenland are on the list on the prvious slide Everyone agrees that lack of rainfall is the key trait Deserts receive < 10 inches of rain per year That's < 1 inch per month!

question

Distribution of Deserts

answer

They are found in certain latitudes Notice all the deserts in red fall along 30 latitude

question

Q: Why are so many at that latitude?

answer

A: Remember Hadley cells? 30 is the latitude where air masses sink back to the surface as part of the Hadley cell Those cold, dense air masses contain little water vapor, so there's little rain

question

Next Q: what about the deserts in yellow on the map? Why aren't they at 30 too?

answer

The Pacific Northwest is dry due to the rain shadow created by mountains along the Pacific coast Central Asia is so far from any oceans that it is difficult to transport water vapor to the region

question

Weathering in Deserts

answer

Little water means little chemical weathering can occur Thus, physical weathering is more common in deserts Thus, weathering is relatively slow in desert regions

question

Weathering continued

answer

Some chemical weathering does occur Remember that some minerals react with atmospheric oxygen Iron oxides produced by chemical weathering give many deserts their reddish coloration

question

Desert Erosion

answer

There are few plants to soak up water or root the soil in place Thus, water causes lots of erosion in deserts WHEN it is present Arroyo- small gullies/dry stream beds that quickly flood during thunderstorms (see pic)

question

Erosion continued

answer

Wind is the main erosive agent in deserts Catch: it can only move relatively small particles wind has low density and low viscosity particles > ca 0.06 mm in diameter are hard for wind to erode

question

Erosion continued

answer

Those tiny grains add up to a huge volume of eroded sediments Ex: Sahara Desert: 250-500 million tons of dust are transported to the Atlantic Ocean ea yr

question

Erosion continued

answer

Deflation- the process of constantly eroding the tiny grains, leaving the larger grains behind Pavements- relatively coarse-grained land surfaces formed by deflation

question

Erosion continued

answer

Deflation results in lots of deserts being gravelly, not sandy! Only ~ 20% of desert areas are covered in sand! L: the typical 'Hollywood' desert R: this is what most deserts actually look like

question

PT 2- Desert Features

answer

Ventifacts- features in deserts that get weathered ('polished') by the wind L: The wind blows the small grains around, essentially 'silt-blasting' objects R: One side thus gets highly polished

question

Desert Features continued

answer

Alluvial Fans- fan-shaped bodies of sediment that form at the ends of arroyos Water flushes through the arroyo, eroding lots of sediment At the end of the arroyo, the water dumps its sediment load as the water velocity slows down

question

Desert Features continued

answer

Playa Lakes- water pools up in small basins during thunderstorms, forming a small lake As the water evaporates, dissolved material in the water precipitates, forming chemical sediments

question

Desert Features continued

answer

Inselberg- resistant body of rock forming a 'standalone' mountain Was once surrounded by other strata that were weaker Those strata eroded away, leaving the inselberg

question

Desert Features continued

answer

Arches- bodies of rock where erosion has created a tunnel through the rock Result of localized erosion Ex: Arches National Park (Utah) contains over 2,000 arches (one is shown below)

question

Arches continued

answer

Steps to form an arch (see pic below): 1- start with cracks in a body of rock 2- erosion along the cracks separates the rock into 'fingers' 3- erosion at the base of each finger erodes through it

question

Dunes

answer

Wind-formed deposits of sand Saltation- grains often 'hop' across the land surface instead of being lifted up into the air Remember, wind has a hard time moving most grains Dunes are initiated by some object (e.g., a rock) on the surface that disrupts wind flow This object allows saltating grains to 'hide' behind it so the grains stop moving and start to pile up (see animation)....

question

Dunes continued

answer

...eventually the first grains deposited are exposed to the wind again They saltate up the pile, then slide down the protected, downwind side, and stop moving again Thus, dunes are constantly turning themselves over Like a slow-motion summersault This allows them to move across the surface

question

Types of Dunes

answer

There are 5 different types of sand dunes The type found in an area depends on 3 things: 1 variance in wind direction 2 sand availability 3 vegetation's presence/absence

question

Dune Types continued

answer

1- Barchan dunes- common type. Key features: C-shaped (like a crescent moon) Found in areas with lots of sand and no plants Key: the horns (ends of the dune) point downwind

question

Dune Types continued

answer

2- Transverse Dunes - form by linking barchan dunes together end-to-end Require LOTS of sand, no plants Wavy crests that are perpendicular to the wind direction

question

Dune Types continued

answer

3- Linear (aka Longitudinal) Dunes - dunes w/ straight crests running parallel to the main wind direction Form in places with limited sand supply & no plants Wind direction changes a little over time

question

Linear Dunes continued

answer

The big white arrows show the primary wind direction The small white arrows indicate how the wind direction slightly changes from time to time

question

Dune Types continued

answer

4- Star Dune - look like starfish from above Form where wind direction varies a lot Basically forming several small barchan dunes that are linked in the center of the star

question

Dune Types continued

answer

5- Parabolic Dune- similar to barchan dunes at first glance. Some differences: U- or V-shaped, not C-shaped Form near coasts where plants are present Common 'beach dunes' The horns point upwind, not downwind

question

Practice Exercise: Q: What type of dune is this, and which direction is the wind blowing in this area?

answer

A: Barchan dune. The arrow points in the direction the wind is blowing; it's the same direction the horns are pointing in

question

PT 3- Desertification

answer

Process of an area becoming a desert Many deserts are growing, so areas that used to be productive farmland are now too arid (see pic) This is a problem b/c deserts are obviously a difficult environment for people to live in

question

Desertification continued

answer

Ex: The Sahara desert is expanding south ~ 30 mi/yr! If the edge were located at USC, it would only take 3 years for the desert to reach Clemson :-o

question

Desertification continued

answer

~ 1 billion people live in areas at risk of experiencing desertification in the near future Many areas in the US are at risk too (see map next slide) This is not a problem that just happens in poor countries on the other side of the world

question

Causes of Desertification

answer

1- Tectonics- currently, lots of continents are close to 30, so there are going to be lots of deserts to start with 2- Climate- remember that global warming causes increased aridity in mid-latitudes That includes many of the red areas on the map (previous slide) 3- Humans- when we use too much water & remove plants from areas, it makes them susceptible to desertification

question

Preventing Desertification

answer

1- Not much we can do about tectonic plates' locations 2- Dealing with GG output will help slow global warming 3- We can be more careful about how we use land & water resources. prevent overgrazing by livestock cut down fewer trees Conserve water

question

Prevention continued

answer

Note that the ideas listed under #3 sound very easy to do, but in real life they may be difficult to implement Ex: how do you tell people that they have to use less water if they live in an area that is already semi-arid? Ex: how do you tell people they can't let their livestock graze in certain places?

question

Glaciers- Why Should We Care?

answer

Drinking water & irrigation ex- Washington gets ~ 470 billion gallons/yr from glaciers Hydroelectric Power glaciers add meltwater to streams & rivers Thermohaline circulation- melting glaciers slow down oceanic circulation Polar wildlife is being affected by habitat loss

question

Effects of glaciers continued

answer

Melt all glaciers = sea level rise of ~ 65 m (200+ ft) Notice how many coastal areas will eventually be affected by even HALF that amount of sea level rise

question

Glaciers & Sea Level Changes

answer

The graph below shows how much lower sea level was during the last Ice Age, when large glaciers trapped huge amounts of water

question

Glaciers & Sea Level Changes

answer

Most of the area in light blue was exposed above water during the Ice Age!

question

PT 1- Intro to Glaciers

answer

Glacier- A mass of ice on land that slowly moves downhill via gravity

question

Ice on Earth

answer

Currently glaciers cover ~9% of Earth's land area Most glacial ice is in Greenland (L; 10%) & Antarctica (R; 85%) Ice on Antarctica exceeds 4,200 m (2.5 miles) in thickness in some areas!

question

Effects of Glaciers

answer

The weight of the ice actually changes the elevation of the land! Isostatic depression- 'sinking' of the ground beneath a glacier The East Antarctic ice sheet is ~ 25 million km 3 & has caused up to 2.5 km of isostatic depression!

question

Effects of Glaciers continued

answer

Isostatic rebound- when the glacier melts, the land 'rebounds' back to its original elevation Similar to the exfoliation process we covered in the sedimentary lectures

question

Forming a Glacier

answer

Three basic things are needed to form a glacier 1- Requires a long time to build a large ice mass You must keep snow/ice from completely melting during summer so you can build new layers each winter 2- Thus, it must stay relatively cold year-round 3- You also must have winter precipitation "If it don't snow, the glacier don't grow"

question

Forming a Glacier continued

answer

Snow goes through several changes as you build the glacier Snow thaws/freezes, converted to granular snow Pressure from new snow layers compresses granular snow into firn (denser) Continue compacting firn layers = glacial ice Moves once massive enough ~ 50 m thick is the minimum size

question

Types of Glaciers

answer

Valley (aka Alpine aka Mountain) Glaciers Form at high elevations Usually fill one entire valley

question

Alpine Glaciers continued

answer

Alpine glaciers are found around the world, not just at the poles Ex- Mt Kilimanjaro is near the equator in Africa It's elevation (~20,000 ft) allows alpine glaciers to exist at its summit

question

Types of Glaciers continued

answer

Continental Glaciers aka ice sheets- these are much larger, covering most of the land surface Today, these are only in Greenland & Antarctica

question

Changing the Size of Glaciers

answer

Zone of Accumulation- portion of a glacier where there is a net gain in ice volume each year This is the 'uphill' end of the glacier, where temp remains the coldest

question

Changing the Size continued

answer

Zone of Ablation- area of the glacier where there is a net loss of ice each year This is the 'downhill end' where lots of melting may occur Firn Line- the boundary btwn the 2 zones The balance btwn the zones determines whether the glacier is advancing (= large Z. of Accumulation) or retreating (= large Z. of Ablation) Watch the animation for a good example

question

Glacial Movement

answer

Speed varies: mm's/yr to meters per day! Center moves faster than edges (arrows on pic) Ice near the valley walls experiences more friction, so it moves slower

question

Movement continued

answer

Anything stuck in the ice moves too Ex: the flag placed at the ice when explorers first reached the south Pole is no longer at the South Pole b/c the glacier has moved

question

Types of Movement

answer

Glaciers move via 2 gravity-driven processes 1- Plastic Flow- caused by tiny movements of each ice crystal slowly being pulled downhill

question

Plastic Flow continued

answer

Similar to creep (discussed in the Mass Wasting lecture) Glacier must be > 50 m thick for this to occur Only occurs near the base of the glacier where press is really high similar to ductile/plastic behavior of rocks Plastic flow cannot account for relatively fast movements, so we need another process for that

question

Types of Movement

answer

2- Basal slip- a layer of liquid water exists btwn the base of the glacier and the ground, allowing the glacier to 'slide' downhill Melt water lubricates the ice-ground contact The same principle is what makes ice skates and Slip 'n Slides work A thin layer of liquid water lets you move easily across the surface

question

Crevasses

answer

Large cracks in the surface of glaciers There's low pressure at the glacier's surface, so the ice reacts in a brittle fashion when it's moving Hazardous

question

PT 2- Erosive Actions

answer

Glaciers can move tremendous volumes of sediment Most of the sediment gets trapped within the glacier, not pushed along in front of it Ex: think of a dump truck, not a bulldozer

question

Glacial Erosion continued

answer

Several processes work to move the sediment 1- Abrasion- grinding of sediment between the glacier and the ground surface Produces fine-grained sediments

question

Glacial Erosion continued

answer

1- Plucking- as the glacier slides over bedrock outcrops, liquid water at its base can get into cracks and cause large chunks to break off via frost wedging This often affects the 'down-ice' side more than the 'up-ice side of the outcrop

question

Glacial Erosion continued

answer

3- Katabolic Winds- cold air over the glacier creates an area of high atmospheric pressure Like the descending arm of a Hadley cell Warmer surrounding areas have lower pressure Winds are generated to move air form the high press area to the low press are Nature wants to smooth out the press difference These winds blow across the area around the glacier and can transport lots of fine-grained sediment

question

Glacial Erosive Features

answer

Glacial erosion can significantly re-shape the landscape Striations- grooves scratched into exposed bedrock Remember: glaciers are carrying lots of sediment; jagged edges sticking out of the ice can create straitions The parallel, linear scratches are striations; they indicate that a glacier once moved across this area

question

Erosive Features continued

answer

Alpine glaciers re-shape the entire valley as they move through it, creating a U-shaped valley These are distinct from valleys carved by streams and rivers Those are V-shaped (gentler slopes, narrower bottom) Note the strong, U-shaped curvature. This tells you a glacier formed this valley

question

Erosive Features continued

answer

Hanging valleys form where 2 U-shaped valleys connect Remember that many mountains will have more than 1 glacier As both move downhill, they may link up

question

Hanging Valleys continued

answer

The large glacier carves a deeper valley than the small glacier. This means the floor of the smaller valley is 'hanging' above the main valley Creates a drop-off between the valley floors

question

Erosive Features continued

answer

Cirque- a bowl-shaped depression carved by the glacier, usually on the mountainside If the cirque fills with rain after the glacier is gone, it forms a lake called a tarn

question

Erosive Features continued

answer

Horn- When multiple glaciers move down a mountain they erode the sides, leaving a relatively tall, jagged peak in the center Ex- the Matterhorn Arete- these are the thin, sharp ridges that remain between the valley glaciers moving down the different sides of the mt (pic on next slide)

question

Erosive Features continued

answer

Roche Moutonnée (aka Moutonnee)- when glaciers move across bedrock outcrops, they cause lots of plucking on the downhill side This creates an asymmetrical hill The steep side is the side the glacier moved towards

question

Practice Exercise Q: Which direction did the glacier move in? North is towards the right side of the picture

answer

A: the glacier moved towards the steep side, which is the south side

question

Study Tip:

answer

One key to doing well on this lecture is to make sure you keep the erosional and depositional features of glaciers separate The features covered so far are all related to erosion caused by glaciers The next section deals with features formed when glaciers melt and deposit sediment Make sure you don't get the 2 sections mixed up!

question

PT 3- Glacial Sediment Deposits

answer

There are 4 general types of sedimentary deposits formed by glaciers. These form many distinct features that we'll get to in a few minutes #1 Till- deposited straight from the ice and dumped on the ground Unstratified & poorly sorted

question

Sediment Deposits continued

answer

#2 Outwash- deposits formed by melt water streams carrying sediment away from the glacier These are better stratified and sorted since they are moved by flowing water before being deposited #3 Erratics- huge boulders dropped out of the ice Stick out in their surroundings

question

Sediment Deposits con't

answer

#4 Loess- layers of fine-grained sed transported by wind after being freed from the glacier Can form very thick layers (see pic) Good for productive soils for agriculture Ex: the northern Great Plains

question

Depositional Features

answer

Moraines- ridges formed by till deposits along the glacial margins

question

Depositional Features continued

answer

Drumlin- these are mounds of sediment that form beneath the glacier and are left behind when the glacier moves on They are asymmetric like moutonnees, but the orientation is backwards The gentle slope points downhill

question

Drumlins vs Moutonnees

answer

How can you tell them apart? Same shape, but remember: Moutonnees are formed by erosion, drumlins are formed by deposition Moutonnees are solid rock, drumlins are loose sediments 1 of these 2 hints will always be in the question

question

Practice Exercise: Which glacial erosional feature is shown, and what direction did the glacier come from? North is towards the left edge of the picture

answer

A: the question said it is an erosional feature, so it must be a moutonnee That means the glacier came from the gentle sloping side, which is on the left side of the picture. Left is north on this picture, so the glacier came from the north.

question

Study Tip

answer

With drumlin vs moutonnee questions, make sure to read carefully! Is the feature described as erosional or depositional? Is the feature described as solid rock or loose sediment? Does the question ask which way the glacier went, or which way it came from? Make sure you don't get north, south, east, west mixed up

question

Depositional Features continued

answer

Eskers - Outwash deposits that form long, winding, ridges Can form under the ice if melt water is flowing through ice tunnels Note that moraines are usually straighter and formed from till, not outwash

question

Depositional Features continued

answer

Kames- small hills formed from till deposited in mounds Results from blocks of ice breaking off the glacier, then melting Kettle lakes (aka kettles)- small lakes formed in depressions around the melting glacier

Geology Final Exam – Flashcards

Unlock all answers in this set

Haven't found what you were looking for?

Search for samples, answers to your questions and flashcards