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Physical/Mechanical

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the disintegration- breakdown of rocks by mechanical forces -physical forces that break rock into smaller and smaller pieces without changing the rock's mineral composition -breaking the rock into smaller pieces increases surface area available for chemical weathering

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Frost wedging

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alternate freezing and thawing of water in fractures and cracks promotes the disintegration of rocks -most pronounced in mountainous regions. -causes great destruction to highways in the northern US and Canada-especially in the early spring

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mass wasting

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-the transfer of rock, regolith, and soil downslope under the direct influence of gravity -example- landslides

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chemical weathering

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- Breaks down rock components and the internal structures of minerals. -chemical transformation of rock into one or more New compounds. -decomposition of rock by chemical reactions occurs in water, especially soil water and groundwater are rich in dissolved carbon dioxide produced during the decomposition of plants. -most important agent involved is water. (responsible for transport of ions and molecules involved in chemical processes) -products of chemical weathering will remain essentially unchanged as long as they remain in an environment similar to the one in which they formed

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talus slope

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- accumulation of rock debris at the base of a cliff -frost wedging causes broken rock fragments to fall to the base of the cliff and create a cone-shaped accumulation -not changing chemical or mechanical composition of rock

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Frost Action/ frost shattering

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-the force of water in rock fractures as it freezes and expands, or is forced into the rock by the pressure of freezing water -most effective in temperature range -3 (26F) to -8C (17.7F)

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sheeting

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- large masses of igneous rock, particularly granite, are exposed to erosion, concentric slabs begin to break lose. This is the process generating these onionlike layers. -caused by expansion of crystalline rock as erosion removes the overlying material

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exfoliation domes

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-large, dome shaped structure, usually composed of granite, formed by sheeting -continued weathering eventually causes these slabs to separate and spall off -examples include, Stone Mountain, GA, and half dome; and Liberty Cap in Yosemite

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Unloading/Exfoliation

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-exfoliation of igneous and metamorphic rocks at the Earth's surface due to a Reduction in confining Pressure. -rock breaks off into leaves or sheets along joints which parallel the ground surface; caused by expansion of rock due to uplift and erosion; removal of pressure of deep burial. -decompression is a huge part -ex. stone mountain, GA

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Thermal expansion

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alternate expansion and contraction due to heating and cooling

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fracturing- joints

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-important rock structures that allow water to penetrate to depth and start the process of weathering long before the rock is exposed -form a definite pattern- can be created by expansion, contraction as igneous materials cool, and tectonic forces while mountain building

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Water and Carbonic Acid

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-pure water is nonreactive, but a small amount of dissolved material can activate it -oxygen dissolved in water will oxidize some materials. example; iron nail in moist soil produces iron oxide -carbonic acid- formed by carbon dioxide and water -ionizes to form very reactive H+ and bicarbonate ion - readily decompose many rocks and produce certain products that are water soluble -Carbonation: dissolving of calcium carbonate (limestone) in acidic groundwater -similar to hydroloysis but the all the products are ionic, there is no residue -dissolved load of most rivers -the carbonation of limestone results in karst topography: caves, sinkholes, etc.

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Weathering of Granite

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-consists mainly of feldspar and potassium -Hydrogen ions H+ attack and replace potassium ions in the feldspar structure, disrupting the crystalline network -once removed, potassium is available as a nutrient for plants or becomes the soluble salt potassium bicarbonate, KHCO3 (may be incorporated into other minerals or carried to the ocean in dissolved form by streams -most abundant products of chemical breakdown of feldspar are residual clay minerals. (end products of weathering-very stable) -weathering of potassium feldspar generates a residual clay mineral, soluble salt, and some silica (carried away by groundwater), which enters into solution -quartz (other component of granite) resistant to water and most resistant mineral to weathering; remains unaltered when attacked by weak acidic solutions -as granite weathers, feldspar crystals dull and slowly turn to clay, releasing interlocked quartz grains -some quartz remains in soil, much is transported to the sea/other where it becomes a constituent of sandy beaches and sand dunes- may lithify to become sandstone

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Weathering of Silicate Minerals

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-make up most of earth's crust -when chemically weathered, yield sodium, calcium, potassium, and magnesium ions that form soluble products, which may be removed by groundwater. -iron combines with oxygen producing insoluble iron oxides -3 remaining elements-> aluminum, silicon, and oxygen join with water to produce residual clay minerals, that are very slowly removed by subsurface water -most common silicate minerals are quartz, feldspars, hornblende, and olivine

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Spheroidal weathering

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- gives the weathered rock a more rounded or spherical shape -angular rock masses chemically weather as water enters along joints, tend to take on spherical shape. The corners or the rocks are attacked most readily because of their greater surface area, compared to the edges and faces. -sometimes during this formation, successive shells separate from the rock's main body. eventually the outer shells break off, allowing chemical weathering activity to penetrate deeper into the boulder. -results because, as minerals in the rock weather to clay, they increase in size through the addition of water. the increased bulk exerts an outward force that cause concentric layers of rock to break and fall off. (not sheeting because it results from reduction in pressure and rock layers are unaltered when separated)

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Process of chemical weathering

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1-Hydrolysis 2-Dissolution 3-Oxidation 4-Chelation

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hydrolysis

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-never move locations -example: feldspars to clay minerals -The reaction of any substance with water -Hydrogen ion attacks and replaces other positive ions -mineral cations (e.g., Ca+, Fe+, Na+, K+, Al+) are replaced by hydrogen ions (H+) from acidic water -the most common weathering process. -pure water is a poor H+ donor, however biogenic CO2 dissolves in water to produce carbonic acid: -the weathering products are in solution or a residue is clay, the first stage of soil development. -the soil water solution becomes more basic as H+ is consumed -original minerals are gradually altered to produce clay and soluble salts

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dissolution

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-Aided by small amounts of acid in the water -Soluble ions are retained in the underground water supply

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oxidation

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-Any chemical reaction in which a compound or radical loses electrons -Important in decomposing ferromagnesian minerals -loss of an electron to dissolved oxygen -iron is the most commonly oxidized mineral element -other readily oxidized mineral elements include magnesium, sulfur, aluminum and chromium

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chelation

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-bonding of mineral cations and organic molecules produced by plants -are stable at a pH at which the cation would normally precipitate and thus they are leached in seeping soil water -H+ released during chelation from organic molecules is available for hydrolysis thus plants, such as the lichens on bare rocks, contribute to the decomposition of soil and rock

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Lateritic profile

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-develop an indurated surface layer of resistant duricrust, forming laterally extensive sheets. These lateritized surfaces are chemically and physically resistant and may extend over large areas. -tropical soils where original soluble materials were already removed by chemical weathering and harden to a bricklike consistency. Ex. Clearing vegetation I'n the amazon -impenetrable to water and crop roots; no longer cultivated -virtually insoluble and very stable

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Examples of products of weathering different minerals

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•Quartz •Ferromagnesian silicates (olivine/biotite) •Feldspars •Calcite

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Biological

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-when living materials assist in chemical or mechanical weathering. -intense in estuarine and coastal environments

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Combination of weathering

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-mechanical weathering increases surface area that can be attacked by chemical and biological weathering processes -chemical weathering weakens outer portions of some rocks which, in turn, makes them more susceptible to being broken by mechanical weathering

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Alteration

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-breaking a rock into smaller pieces increases surface area -Decomposition of unstable minerals -Generation or retention of materials that are stable -Physical changes such as the rounding of corners or edges

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Differential Weathering

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-Masses of rock do not weather uniformly due to regional and local factors -Results in many unusual and spectacular rock formations and landforms -the number of spacing or joints can be a significant factor

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rock characteristics

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-Rocks containing calcite (marble and limestone) readily dissolve in weakly acidic solutions -Silicate minerals weather in the same order as their order of crystallization

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Climate - Critical Role of Temperature and Moisture in Weathering Rates

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-Temperature and moisture are the most crucial factors to the rate of weathering. -Chemical weathering is most effective in areas of warm, moist climates -regions with lush vegetation have a thick mantle of soil rich in decayed organic matter which chemically active fluids are derived. -acid rain accelerates the chemical weathering of stone structures

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typical chemical weathering mantle

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- need water table but not all oxidation -palid zone- reduction is dominant- leaching of ferric iron). It is composed predominantly of kaolinite with residual quartz and small corestones towards base. Contains clay minerals. -weathering front-unweathered bedrock -Ferruginous zone with residual quartz, hydrated iron, and aluminum oxides and clays (at the very top)

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examples of biological agents:

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•Piddock shells, bore into rocks for protection either by scraping away the grains or secreting acid to dissolve the rock. •A tree has grown out of a rock; but a crack for the seed or root had been created by mechanical or chemical weathering. •Feces and urine speeds up the decaying process, creating compost and new dirt. •Worms and beatles are natural helpers, by changing old leaves, bark, wind-fallen fruits, and such like into fertile soil, and allow the earth to support life. They mix the mineral and organic portions of a soil. •Termites: Produce huge amount of physical of the upper pert of the weathering profile/soils- Very intense activity in tropical areas -Trigger a variety of chemical reactions carrying to the surface mineral particles - cementing mineral particles into mounds by using their salivary secretion -alterating the content of organic matter in the soils - modifies the clay mineral composition of the soil materials

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-Bowen's Reaction Series (crystallization) and Goldich's Weathering Series (stable)

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-olivine crystalizes first, is least resistant to chemical weathering, and not stable -Quartz crystalizes last, is most resistant to chemical weathering, and very stable -Goldich: olivine, augite, hornblende, and biotite are very unstable and least resistant. Orthoclase, muscovite and quartz are very stable. -Bowen: olivine, pyroxene, amphibole, and biotite crystalize first. orthoclase, muscovite and quartz crystalize last (more resistant).

question

what controls mass wasting?

answer

gravity

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saturation of material with water

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•Saturation-of the material with water • Diminishes particle cohesion • reduces the internal resistance of materials • Water adds weight- may be enough to cause the material to slide or flow downslope. • Particle cohesion/ frictional forces -when pores in sediment become filled with water, cohesion among particles is destroyed, allowing them to slide past one another with relative ease. • Pore/water pressure o the key to monitoring landslides. Pore water pressure is the pressure that develops as water fills in the pore spaces in between particles. Shear strength, a resisting force, decreases and the weight, a driving force, increases. • trigger of mass wasting

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oversteepening of slopes

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-trigger of mass wasting -oversteepeneed slopes are unstable -can be caused by people, stream undercutting a valley wall, or waves pounding against base of a cliff -angle of repose is unconsolidated, granular particles that assume a stable slope. It is the steepest angle at which material can remain stable. The angle varies from 25° to 40°. The larger more angular particles maintain the steepest slope. (increases with increasing grain size). •Slightly wet unconsolidated materials exhibit a very high angle of repose because surface tension between the water and the grains tends to hold the grains in place. Example, sand • When the material becomes saturated with water, the angle of repose is reduced to very small values and the material tends to flow like a fluid because the water gets between the grains and eliminates grain to grain frictional contact.

question

removal of anchoring vegetation

answer

-trigger of mass wasting •Plants protect against erosion and contribute to the stability of slopes because their root systems bind soil and regolith together •Where plants are lacking, mass wasting is enhanced, especially if slopes are steep and water is plentiful •When vegetation is removed, surface materials move down slope •Forest fires can bake the ground, creating a water repellant layer at a shallow depth. The impermeable barrier prevents/slows infiltration of water causing increased runoff.

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ground vibrations from earthquakes

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-trigger of mass wasting •May cause expensive property damage •Can cause liquefaction - water saturated surface materials behave as fluid-like masses that flow

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classifications of mass-wasting processes

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-type of material -kind of motion -velocity of movement

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type of material

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-depends upon whether the descending mass began as unconsolidated material or as bedrock. -when soil and regolith dominate, debris, mud and earth are used to describe it. -when a mass of bedrock breaks lose and moves downslope, rock is used to describe it.

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type of motion

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1. Avalanche/Fall- freefall of detached individual pieces of any size. Common form of movement on steep slopes that loose material cannot remain on the surface. 2. Slide- material moves along a surface as a coherent mass 3. Flow- material moves as a chaotic mixture/ viscous fluid. Most are saturated with water and move as lobes or tongues.

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rate of movement

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-rock avalanches- rock and debris can travel downslope at speeds at 125 miles per hour -high velocities result when air becomes trapped and compressed beneath the falling mass of debris, allowing it to move as a buoyant, flexible sheet across the surface. - a great deal is slow moving

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Sediment flows

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-occur when sufficient force is applied to rocks and regolith that they begin to flow down slope. -A sediment flow is a mixture of rock, regolith with some water.

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Debris flow (mudflow)

answer

o Consists of soil and regolith with a large amount of water o Often confined to channels(open channels are the most efficient land forms) -most common in semiarid mountainous regions. o Serious hazard in dry areas with heavy rains o Composed mostly of volcanic materials on the flanks of volcanoes are called lahars

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Earthfolw

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o Form on hillsides in humid regions o Water saturates the soil o Commonly involve materials rich in clay and silt

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slump

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-movement of a mass of rock or unconsolidated material as a unit along a curved surface. -slump material does not travel fast nor far, which is a common form especially in thick accumulations of cohesive materials, like clay. -surface of rupture- spoon-shaped and concave upward or outward. -crescent shaped scarp- as movement occurs, this forms at the head -often consists of multiple blocks -Occurs along oversteepened slopes -an example is a valley wall that becomes oversteepened by a meandering stream. -can also occur when a slope is overloaded, causing internal stress on the material below. Occurs where weak, clay-rich material underlies layers of stronger, more resistant rock, such as sandstone. The seepage of water through the upper layers reduces the strength of the clay below, causing slope failure.

question

creep

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-slow movements -Gradual movement of soil and regolith downhill -Aided by the alternate expansion and contraction of the surface material caused by freezing or wetting, which lifts particles at right angles to the slope, and thawing or drying, which allows particles to fall back to a lower level. -aided by anything that disturbs the soil -examples of disturbances include raindrop impact, plant roots, burrowing animals, or heavy rainfall/snowmelt -cannot be observed -causes fences and utility poles to tilt and retaining walls to be displaced.

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soliflucation

answer

-Promoted by a dense clay hardpan or impermeable bedrock layer -Common in regions underlain by permafrost -Can occur on gentle slopes

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bedding plane

answer

...

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slip surfaces

answer

...

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Hydrologic Cycle Processes

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-a balanced cycle because the total amount of water vapor in the atmosphere remains about the same, the average annual precipitation over Earth must be equal to the quantity of water evaporated. o Precipitation o Evaporation o Infiltration o Runoff o Transpiration

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Water Balance

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-the volume of water that passes through each part of the hydrologic cycle annually -each year, solar energy evaporates 320,000km of water from oceans, evaporation of land is 60,000km. of this 380,000km, 284,000km falls back into the ocean, and the remaining 96,000 falls on land. of that 96,000km, 60,000km evaporates from land, leaving 36,000km to erode the land.

question

Sources of water and relative volumes

answer

-oceans- 97.2% -glaciers- 2.15% -groundwater- .62% - freshwater lakes .009% -saline lakes and inland seas .008% -soil moisture- .005% -atmosphere- .001% -stream channels- .0001%

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Fluvial System Components- water

answer

• In studying a drainage basin unit it is necessary to relate input from precipitation to output in the form of river discharge.

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Fluvial System Components- sediment

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• The drainage basin also acts rather like a conveyor belt for material in solution (solutes) and for sediment

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Drainage basin

answer

-the land area that contributes water to a river system -The drainage pattern consists of the interconnected network of streams in an area -also called catchment, catchment area, catchment basin, drainage area, river basin, water basin and watershed (watershed refers to a divide that separates one drainage area from another drainage area)

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Hierarchical pattern

answer

• Drainage basins drain into other drainage basins in this pattern • With smaller sub-drainage basins combining into larger drainage basins.

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Exorheic basins

answer

•flow to the ocean in geologically defined drainage patterns. This frequently happen through watercourse or watercourse segments that are seasonal or perennial and independent of seasonal or annual variations in runoff, rainfall, or tides..

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Endorheic basins

answer

• inland basins that do not drain into an ocean; around 18% of all land drains to endorheic lakes or seas. • The largest of these consists of much of the interior of Asia, and drains into the Caspian Sea and the Aral Sea. • Evaporation is the primary means of water loss, the water is typically more saline than the oceans. An extreme example is the Dead Sea

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Arheic areas

answer

• An area lacking surface runoff or drainage, such as deserts, in which surficial drainage is almost completely lacking, or where rainfall is so infrequent that all water sinks into the ground or evaporates

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Dendritic

answer

• Tree-like arrangement of small streams that join to form a larger river. Typically found in a region that has adequate rainfall and no unusual geologic features.

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rectangular

answer

-right-angle bends -develops when the bedrock is crisscrossed by a series of joints and/or faults

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radial

answer

• A circular arrangement of streams that flow outward in all directions, away from a central high area. • Common in the vicinity of volcanic cones, salt domes, granite intrusions, and other localized uplifts

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trellis

answer

• A squared off drainage pattern in which streams often flow directly toward each other from opposite directions and then make right angle turns when they meet. • Common in places where layered sedimentary rocks are tilted up from the horizontal • Usually follow the layers of less-resistant rock until they get big enough to break through the resistant layers

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pinnate

answer

...

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parallel

answer

• An elongated pattern, in which the tributary streams flow in the same general direction and usually join at small angles. • Occurs in areas with a regional slope, prevailing wind, or some other factor that causes streams to flow unusually far in one direction before merging with another

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centripetal

answer

• A circular arrangement of streams, where water flows inward from all directions toward the center of the area. • Centripetal drainage is likely in karst topography and in deserts where intermittent streams flow toward a temporary salt lake or basin.

question

karst topography

answer

• can favor chaotic and disorganized drainage. Water causes solution of the limestone along these cracks and over time a series of caves, sinkholes, and disappearing streams are formed.

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zone or erosion

answer

-dominant in the upstream area in large river systems -generally consist of mountainous or hilly topography -small tributary streams erode the channels in which they flow and carry material provided by weathering and mass wasting -examples include Rapids, whitewater

question

zone of transportation

answer

- also called the trunk stream -lies between the zones of erosion and zones of deposition -serves to transport sediments

question

zone of deposition

answer

-region within a river system -located where the stream enters a large body of water -sediments accumulate to form a delta, or are reworked by wave action to form a variety of coastal features -Meandering channels, natural levees -Delta and distributaries

question

rills

answer

-after flowing as a thin,unconfined sheet for a short distance, threads of current typically develop and tiny channels called rills begin to form and carry the water to a stream -at first the streams are small, but they start to intersect one another and they become larger. -More erosive than sheet wash -Large amounts of sediment transported -Detachment and transport of sediment -Small scale; up to ~10s cm wide and deep -Ephemeral; may be obliterated during next event -Often seasonal -May result in gullying

question

sheetflow/sheetwash

answer

-mainly transports sediment, not too erosive -runoff that initially flows in broad, thin sheets across the ground -the amount of water that runs off this way rather than sinking into the ground depends on the infiltration capacity -when soil becomes saturated, sheet flow begins as a layer only a few millimeters thick

question

gullies

answer

-occurs when a master rill enlarges to the point where it is relatively permanent, unless subtantial effort (usually earth-moving machinery) are employed. -does not always produce a river channel

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Conditions for river channel formation

answer

1. cut must be maintained and enlarged requires "certain" drainage area for sufficient energy! 2. subsurface flow routes 3. connection to channel network

question

Factors influencing streamflow velocity

answer

-along straight stretches, the highest velocities are near the center of the channel, below the surface, where friction is lowest. -when a stream curves, its zone of maximum speed shifts toward the outer bank. -factors that determine velocity of a stream include: 1. gradient 2. shape, size and roughness of the channel 3. discharge

question

Stream Gradient

answer

- slope of a stream channel expressed as the vertical drop of a stream over a specified distance -higher gradient equals higher velocity

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discharge

answer

• The volume of water moving past a given point in a certain amount of time

question

channel characteristics

answer

- larger channels have a more efficient flow because a smaller portion of water is in contact with the channel -smooth channel has a more uniform flow -irregular channel filled with boulders creates enough turbulence to slow the stream significantly

question

Changes from Upstream to Downstream

answer

-most typical feature of a profile is: constantly decreasing gradient from the head to the mouth. It is a smooth, concave, upward curve. The gradient decreases down stream. -Humid regions- discharge increases from the head to the mouth because of increased volume of water -mountainous areas then flow through arid regions- discharge decreases downstream due to water loss, infiltration and removal by irrigation.

question

Channel longitudinal profiles

answer

- a cross-sectional view of a stream from its source area (or head) to its mouth, where the river empties into another body of water

question

dissolved load

answer

-rock material in solution -brought to a stream by groundwater and is dispersed throughout the flow -quantity of material carried in solution is highly variable and most abundant in humid areas where limestone and other soluble rocks form the bedrock -usually a small amount

question

suspended load

answer

-rock material in suspension -most rivers carry the largest part of their load in suspension -fine particles consisting of silt and clay can usually only be carried this way -during a flood, sand and gravel-sized particles are transported as well. the total quantity of material carried increases. -type and amount of material carried depends on the velocity of the water and settling velocity (speed at which a particle falls through a still fluid) of each sediment grain -the larger the particle, more rapidly it settles in the stream bed -flat grains sink through water slower than spherical grains -dense particles fall toward the bottom more than less dense particles

question

bed load

answer

-rock material sliding or rolling along the bottom -sediment that is too large to be carried in suspension -saltation- sediment that jumps or skips along the stream bed. occurs as particles are propelled upward by collison or lifted by the current and then carried downstream a short distance until gravity pulls them back to the bed of the stream. -doesn't exceed 10% of the stream's total load.

question

competence and capacity

answer

- competence- measures the maximum size of particles the stream is capable of transporting. Determined by the stream's velocity. If velocity doubles, competence increases four times. velocity triples, competence increases 9 times. -capacity- maximum load it can carry. Directly related to discharge. Greater volume of water flowing in a stream, greater its capacity for hauling the sediment.

question

point bars deposits

answer

(channel deposits) a crescent shaped accumulation of sand and gravel deposited on the inside of a meander

question

cut-bank erosions

answer

-outside of meander is a zone of active erosion

question

cutoff

answer

-a short channel segment created when a river erodes through a narrow neck of land between meanders

question

owbow lake

answer

-a curved lake produced when a stream cuts off a meander

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Natural levees

answer

-form parallel to the stream channel by successive floods over many years

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Alluvial fans

answer

• Develop where a high-gradient stream leaves a narrow valley in mountainous terrain and comes out onto a broad, flat plain or valley floor • Deltas- when a stream enters the still waters of an ocean or lake, its velocity drops, and the resulting deposits form a delta -Distributaries-the main channel diving into several smaller ones

question

braided streams

answer

-complex network of converging and diverging channels that thread their way among numerous islands or gravel bars -form where a large population of the stream's load consists of coarse material (sand and gravel) and the stream has a highly variable discharge -wide and shallow -can form at the end of glaciers

question

meandering streams

answer

-streams that transport much of their load in suspension generally move in sweeping bends -flow in deep, smooth channels and transport mainly mud (silt and clay) -tends to resist erosion; erosion occurs on the outside where velocity is greatest

question

base level

answer

the lowest elevation to which a stream can erode its channel

question

Effects of changing base level

answer

• Raising base level causes deposition • lowering base level causes erosion

question

V-shaped valleys

answer

-the stream's gradient is steep and the channel is well above the base level -abrasion caused by bed load and the power of fast moving water, lowers the stream bed, resulting in a V-shaped valley -narrow -are rapids and waterfalls

question

wide valleys

answer

-Stream is near base level -Stream energy is directed from side to side forming a floodplain -broader, flat valley floor covered with alluvium -meander streams

question

incised meanders

answer

-rivers exhibiting meandering channels that flow in steep, narrow valleys -caused by a base level drop or the land upon which the river was flowing was uplifted

question

terrances

answer

a flat, benchlike structure produced by a stream that was left elevated as the stream cut downward. Rennants of a former floodplain.

question

Regional floods

answer

-rapid melting of snow in spring and/or heavy spring rains can overwhelm a river -often caused by slow moving storm systems

question

flash floods

answer

-can occur with little warning and can be deadly because it produces a rapid rise in water levels and can have a devastating flow velocity -factors that influence it: are rainfall intensity and duration, surface conditions, and topography -mountainous areas and urban areas are susceptible

question

ice-jam floods

answer

- frozen rivers are susceptible -the level of a stream rises, it breaks up the ice and creates ice flows that pile up on channel obstructions. creating a dam across the channel. water upstream rises quickly and overflows the channel banks. when the ice dam fails, water stored behind the dam is released causing a flash flood.

question

dam floods

answer

-caused by human interference with a stream -if a larger flood occurs, it overtops the dam and the water behind it is released causing a flash flood.

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