GEOL 120 Exam 1

Shield Volcanoes are composed primarily of __________ lava flow

The existence of a potentially dangerous situation or event (ex. potential landslide of a steep slope or lava flow erupting from a volcano)

An assessment of whether the hazard might have some social impact (ex. loss of life, damage to property, etc.)

What is erupted by volcanoes?
Ash, Pumice, Lava

A composite cone would be expected to have a _________ slope than a shield volcano

Eruption Styles
1. Lava flow- least explosive, magma erupts onto surface and flows away from a vent.
2. Lava fountains- medium explosive, caused from high initial gas content and less vicious lava-> the gas propels the lava and separates it into discrete pieces
3. Eruption Column- most explosive, Tephra (magma that is blown apart by volcanic gases), erupts high into the atmosphere then falls back to Earth as solidified and cooled pieces of rock
4. Pyroclastic flow- most explosive, some ash does not jet straight up but collapses down the side of the volcano as a dense, hot cloud of ash particles and gas (ash flow) – devastating because of high speed and high temp.

Characteristics of actively erupting volcanoes:
billowing clouds of ash rising into the air, fragments of molten rock blasting into the air, glowing orange lava flowing down hill

Scoria Cone
Steep-sided cone shaped hill hundreds of meters high, with a small crater at the summit; composed of cinders (scoria) and volcanic bombs – basaltic or andesitic composition

Shield Volcano
Broad, gently sloping conical hill or mountain with fissures along its summit; composed mainly of basaltic flow

Composite Volcano
Moderately steep, cone-shaped mountains thousands of meters high with a crater at the top; composed of interlayered lava flows, pyroclastics, and volcanic mudflow- mostly composed of intermediate rocks (ex. andesite) but can have felsic or mafic rocks

Volcanic Dome
Steep-sided dome-shaped hill hundreds of meters high; composed of felsic lava- consist solidified lava

What kind of volcanoes produced pyroclastic flows that killed tens of thousands of people at Pompeii & St. Pierre?

Most composite volcanoes are found along ___________ plate boundaries
convergent –> subduction zones (ex. Ring of Fire)

Rocks found typically in calderas
Top: volcanic tuff
Middle: Hard, welded volcanic rock
Bottom: finely crystalline granite

Typical shape of most volcanoes is

Hazards of Scoria Cones
falling volcanic cinders and bombs, volcanic ash and gases

Hazards of lava flow
burial of roads, bulldozing and crushing of houses and other structures

Felsic Magma
-high gas pressure commonly lead to highly explosive eruptions
– high viscosities
– do not allow gas bubbles to escape –> hence build up of gas & explosions

Formation of Crater Lake:
1. Massive ash column eruption of a composite volcano empties the magma chamber
2. Overlying volcano collapses into the resulting void
3. Scoria cone forms in the caldera
4. Rain & snowmelt fill the caldera, producing a large and deep lake

Characteristics of volcanic domes:
-viscous silicic magma
-often occur in clusters
-rubble covered surface

Basaltic Magmas
fluid lava, flows from shield volcanoes; low viscosity

Felsic Magmas
explosive eruptions from composite volcanoes; high viscosity

Rock Type associated with Volcanic Domes
rhyolite & andesite

Events of 1980 Mount St. Helens eruption
order from 1st event to last:
1. Earthquake
2. Landslide
3. Lateral blast & eruption column

Flood basalts
represent the largest igneous eruption on Earth, with some covering tens of thousands of square kilometers

How do we assess the danger posed by a volcano?
Shape- steep slopes indicate high viscosity, explosive magma; gentle slopes indicate less explosive volcanoes

Rock Type- chemical analysis determines magma composition and potential for explosiveness

History- The sequence of layers and isotopic dating can indicate the timing and frequency of eruptions

Ways volcanic domes are destroyed
1. collapse of steep flanks into block and ash flow
2. internally derived explosions from trapped gas pressure

Monitoring volcanoes/ preceeding eruptions
– steam eruptions from the volcanic crater
– increase in seismic activity
– increased in gas flow from volcano
– increased heat flow from the volcano

Formation of a Caldera
1. Magma erupts as ash column, emptying a shallow magma chamber
2. Overlying material collapses into emptied chamber in a series of fault blocks
3. Ash and other pyroclastics fill the subsiding crater
4. Small rhyolite domes form form in caldera

Majority of transform boundaries are found ______________
in conjunction with mid-ocean ridges

Characteristics of continental rifting:
-stretching of the crust causes crustal blocks to drop down
– if rifting continues the continent can be split in two pieces
– rifting begins with a broad uplift as magma ascends

When divergent boundaries occur on continents the process is called:
continental rifting

a mountain beneath the ocean that never reaches the surface

Mid-Ocean ridges
broad symmetrical ridges that cross ocean basins

Tools used to measure to measure plate motion:
GPS satellites, lasers

The Pacific Ring of Fire is formed by…
a string of volcanos –> subduction on both sides

Oceanic fracture zones
cracks and steps that cross the seafloor and run mostly at right angles to mid-ocean ridges

List the 5 oceans
Arctic Ocean
Pacific Ocean
Atlantic Ocean
Southern Ocean
Indian Ocean

Island arcs
curving island chains across the seafloor that are mainly volcanic in origin

Oceans cover ________% of Earth’s surface

transform fault
a fault that accommodate the horizontal movement of one tectonic plate past another

continental collision
when two continental masses converge

Geological features of Earth include:
dramatic mountains, intricate coastlines, beautiful valleys & undersea trenches

For a plate to move, the driving force must exceed the the ________
resisting force

convergent boundary
2 plates coming together

Volcano distribution on Earth:
– there are many volcanoes along the edge of the Pacific Ocean are associated with earthquakes
– there is a large volcanic belt along the west coasts of North & South America
– Volcanism occurs along mid-ocean ridges

Along the boundary of oceanic-continental convergence…
the oceanic plate subducts beneath the continental plate (because it’s denser)

Continental shelves
when continents continue outward from shoreline under the seawater (submerged benches)

the process of one plate sliding beneath another

What type of plate movement occurs at transform faults?

Tectonic plates are composed of the _______ and move around on the _________
lithosphere; asthenosphere

Stages of continental rifting:
1. Ascension of magma causes uplift of the crust
2. Stretching of the crust causes crustal blocks to drop into faults, forming rifts
3. Continuation of rifting splits the continent into two; a narrow ocean forms as seafloor spreading takes place
4. Continuation of seafloor spreading increases the ocean basin as it becomes wider

Oceanic crust forms from upwelling of magma that spreads outwards from mid-ocean ridges-
– the oldest basalt should be farthest from the mid-ocean ridge
– the thickest sediment cover should be the farthest from the mid-ocean ridge

Tectonics is the study of __________
the origin and arrangement of the broad structural features of Earth’s surface

Convergent boundaries
when plates move towards eachother

Triple Junction
a place where three boundaries meet

Outer Core
The layer of Earth that behaves as a dynamo (electrical generator) –> producing the magnetic field (convection currents)

Abyssal Plains
relatively smooth surfaces on the ocean floor

Plates move _______ per year
1 to 15 cm

the scientific study of the Earth

the balance or equilibrium of adjacent blocks of brittle lithosphere floating on the ductile asthenosphere

2 main types of crust on Earth;
continental, oceanic

Breaking down of rocks either mechanically or chemically

Shield Volcanoes
mafic eruptions- (ex. Hawaii)

Moving pieces of rock by wind, ice or water

Occurs when the energy of transported material decreases

Upward movement of underground rocks to the surface

Process of sediments turning into rocks

the rigid portion of the Earth (crust and upper mantle)

Outer planets from the sun outward-

Why is geology important to everyday life
– we rely o it for energy resources
– it helps us make decisions regarding the environment
– we rely on it to locate raw materials for industry

located beneath lithosphere

Earth’s three major concentric zones:

igneous rock
rocks that have solidified from magma

what kind of crust is thicker?

Composite Volcanoes
intermediate eruptions- anywhere where there are subduction zones – convergent boundary- most common volcano (ex. ring of fire)

3 factors that directly shape the surface of the Earth
1. Atmosphere & it’s movement
2. Water & it’s movement (Hydrosphere)
3. Impact of diverse life forms (Biosphere)

Metamorphism involves:
– heat
– pressure
– deformation

molten rock underground
usually rich in silica & containing dissolved gases

Composition of Layers of the Earth
– continental crust: granite
– oceanic crust: basalt
– mantle: olivine
– core: iron & nickle

Twenty-eight thousand years ago the Earth was __________
colder than it is today
– continental ice sheets covered large areas of the land

Rock Cycle
the process in which a rock may move from one place to another or be converted into a new rock type

Flowing Water
most important agent in sculpting the landscape

three terrestrial planets
Venus, Mercury, Mars

huge flowing fields of compressed ice & snow that carry large amounts of rocks and sediment

The decay of radioactive elements such as uranium creates ___________
-in the Earth’s crust

Qualitative Data includes:
labels, images, sketches, descriptive words

Density Formula

Cenozoic Era
began 65 million years ago- most recent chapter in Earth history – continues to the present

Geologic map
uses various colors to show the distribution of various rock types/ages, and features exposed on the land surface

layers within sedimentary rock

Quantitative date may include:
age of rock, specific temperature data, chemistry of water in stream, size measurements of sediments

Geological time scale
the periods and subdivisions of Earth’s history arranged in proper order

Topographic Map
uses contour lines to indicate specific elevations and is useful for getting specific information about the shape of the land

Satellite image
uses measurements of different wavelengths of light reflecting from a land surface to create a computer processed image to show the distribution of different types of plants, rocks & other features

billions of years before present

millions of years before present

Paleozic Era
began with the appearance of many shelled creatures and ended with a widespread extinction event
– began 542 million years ago
– ended 251 million years ago

Relative Age
the age of a fossil, organism, rock, geologic feature, or event as defined relative to other geologic features or events

– a hypothesis that survives scientist scrutiny may become a theory
– a theory is an explanation supported by experimental or factual evidence
– theories encompass a larger body of knowledge than a hypothesis

a smaller, steep sided mountain that has had its edges eroded away

Shaded Relief Map
Simulates light and dark shading on hills and valleys

how much something changed divided by the time required for the change to occur

Contour Lines
indicate areas of equal elevation on a topographic map

When a fracture cuts across several layers of rocks we can determine that…
the fracture is younger than the layers it crosscuts

the mass per unit volume of a substance

the amount of downward force exerted by an object under the pull of gravity

Properties of Water
– water can dissolve materials by breaking apart ionic bonds as polar molecules attract individual ions away from each other
– Hydrogen bonds form between water molecules and are responsible for the high surface tension of water
– a water molecule is polar, and opposite ends of individual water molecules are attracted to anions and cations

There are more than 4,000 known minerals most of which are …
uncommon to rare

an imbalance of protons and electrons within atoms or molecules

a ion with a positive charge -> more protons than electrons

an ion with a negative charge- more electrons than protons

silicon-oxygen tetrahedron
– forms major building blocks for the vast majority of Earths minerals
– has one silicon atom bonded with 4 oxygen atoms
– may join with other tetrahedra or cations to form different types of silicates and a wide variety of minerals

Covalent Bonds
When two atoms share an electron.
Ex: water molecule
strength: strongest
mineral examples: diamond, bonds within sheets of graphite

Ionic Bond
forms because of the attraction of two oppositely charge ions, such as when one atom loans one or more electrons to another atom
strength: moderate
mineral examples: halite, fluorite

Metallic Bond
Electrons in a metallic bond are shared widely by many atoms; this holds the material together in a nonrigid way, which is why many metals are pliable
strength: low
Min. Examples: gold, copper

Intermolecular Force
attraction due to polarity of molecules, which are bonded combinations of atoms
strength: lowest (clay, mica)
mineral examples: water ice and bonds between sheets of mica, clay or graphite

Internal Atomic Arrangement
atoms in minerals are arranged in an ordered geometric pattern

geologist & other scientist who study minerals

Criterion required to be classified as mineral
crystalline solid, naturally occurring, inorganic

Quartz uses
may be used for chemical components; the element silicon is used to make computer chips & is mostly derived from this mineral

Hematite uses
may be used for chemical components; iron is the main ingredient in steel & is mined from minerals like this

Clay uses
may be used for its physical properties; used to produce bricks, cement and ceramics

Periodic Table
– grouped elements tend to have similar chemical properties (like the two different types of metals, nonmetals, noble gases, etc.)
– it begins with the lightest element and advances to higher atomic numbers and heavier elements from left to right and from top to bottom
– it includes a elements atomic number and atomic symbol

Factors that contribute to a water molecule having polarity…
– hydrogen atoms are grouped on one side of the oxygen atom
– oxygen more strongly attracts electrons than hydrogen does
– electrons spend more time around the oxygen atom and give the molecule a negative side and two positive ends on the other side

A compound containing only silicon and oxygen in a ration of 1:2 (SiO2)

the 14th element of the Periodic Table; term may also be used to describe synthetic material used to make computer chip (or fake titties)

A synthetic material (often used for grease or caulk) in which carbon is bonded to silicon atoms to keep the material in long chains

forms in low-temperature environments; at or near Earth’s surface

Forms in high-temperature environments; minerals are interlocking

Igneous Rocks

Geothermal Gradient
the temperature increase with depth

solidified magma chamber

a sheetlike intrusion that cuts across layers in a hot rock

an intrusion that is parallel to the layers in the host rock

an intrusion that can eventually form a dome

Pegmatic texture
forms deep within Earth in the presence of water

Vesicular texture
near Earth’s surface – as gas bubbles go through the lava

Porphyritic texture
first deep within the earth then later near the surface