Gradational processes Weathering = breakdown of material in ...

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Gradational processes

Weathering = breakdown of material in place

Gradation = leveling of land

degradation (erosion) = removal of highs

transportation = movement of material

aggradation (deposition) = filling in lows

Tectonic processes build up of roughen up the earthGradational forces level off highs and fill in lows.

Ultimate gradation --> level smooth plain at "base level"base level ≈ sea level, cannot erode farther downward

Principal agents of gradationgravitywaterwindice

Landforms are usually result of more than one of these

Before material can be moved by any gradational agent,it must be freed from its parent material or bedrock.

Mountains do not move “en masse” to the sea

Breakdown of rock material in place = WEATHERINGWeathering does not, by itself, move material.

500 year old gargoyle on the old well at the National Museum of the Middle Ages, Paris

Three types of weatheringPhysicalChemicalBiological

Processes not mutually exclusiveone or the other may dominate due to climate

or rock type

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Bedding planes, joints, fractures, make rock moresusceptible to weathering

Massive (non-jointed) rocks are slower to weather

Physical: makes smaller pieces from bigger piecesdoes not change chemical composition of rockdisintegration

Important because1. smaller pieces easier to move2. increases surface area for chemical attack

Examples of Physical Weathering1. Freezing water...expansion in cracks

most effective where daily freeze-thaw eventshigh elevations in mid-high latitudesnot very important in tropics or polar regions

Examples of Physical Weathering2. Salt weathering...salt crystal expansion

capillary water evaporates leaving salt behindsandstone especially susceptible

action similar to frost wedgingarid and semi arid regions

Examples of Physical Weathering3. Differential expansion

minerals expand and contract differently withheat and cold

granite especially susceptiblefire promotes thisdiurnal temperature changes may also be factor

Causes peeling of thin concentric shells

Examples of Physical Weathering4. Unloading...removing pressure of overlying rock

exfoliation...peeling of thick concentric layerscommon in granite(unloading causes rock bursts in mines)

Half-dome in Yosemite

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Exfoliation Evidence of physical weatheringDomesAngular debris and jagged formsTalus slopes (piles of broken rock)

Above tree line in the Sierra Nevada.

Physical weathering dominates

Chemical weathering: decays rock by chemical reactionsdecomposition

Operates in three ways by creating1. new materials less resistant to erosion2. new materials with greater volume expansion3. soluble materials which are easily dissolved

and transported in water

Most chemical weathering requires waterheat speeds up reaction

Chemical weathering is fastest in warm wet climates

Cold

Hot

Wet

Dry

Soil profile showing depth of chemical weathering ‘front”

Examples of Chemical Weathering

1. Oxidationchemical union with oxygen

usually creates softer andfiner material

increase in volume (expansion)

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Examples of Chemical Weathering2. Hydration...water attached without chemical change

expansion, solution

Examples of Chemical Weathering

3. Hydrolysis...water unites chemically new compounds expansion, soluble compounds

4. Carbonation...formation of soluble carbonates

Examples of Chemical Weathering5. Solution...dissolves minerals

water soluble...NaCl, CaSO4 (gypsum)

acid soluble carbonic acid, acid rain

can dissolve limestone and marble (CaCO3)

Evidence of chemical weatheringEdges and corners along joints and bedding planes areweathered more rapidly than flat surfaces rounded edges

Spheroidal weathering...in placeElephant Rocks State Park, Missouri,

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Chemical weathering niche where water seeps out

Chemically weathered niche, New Mexico

Biological weatheringliving organisms break down rockphysically and/or chemically

Physical examplesplant rootsburrowing animals

Chemical exampleslichen acid litter

Chemical weathering dominates in warm & wet climates rounded shapes

Physical weathering dominates in drier cooler climates angular, jagged shapes

Differential weathering

one material breaks down faster than another

therefore, one is slower to erode than the other

Examples of differential weathering in different climates

In warm wet climatesgranite...subject to chemical weathering

saprolite (rotten rock)

In cool dry climates, granite is resistantmountains

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In warm wet climates limestone dissolvesto yield topographic lows

Appalachian Ridge and Valley...limestone valleysand sandstone ridges

In cool or arid climates, limestone is resistant often forms topographic highs

At mineral level...silica (quartz) highly resistant to weatheringReleased from rock by decomposition of surrounding material, carried by streams to oceans beaches

Gulf Shores sand comes mainly from Appalachians via the Apalachicola River, deposited in offshore sand sheet. GRAVITY AS AN AGENT OF GRADATION

Gravity causes mass movement (mass wasting)

Mass as in "matter" NOT as in large volume

Mass movement = movement of material downslope under the influence of gravity

Factors influencing mass movement

1. Wateracts as a lubricantadds weightmay cause “fluid” flow

2. Shaking as in earthquakes, explosions, trains

3. Undercutting by streams or human activity

4. Freeze/thaw or wet/dry cycles

Kind of material

Rock(dry)

Regolith& water

Water &sediment

Kind of motion

Falling,rolling, sliding

Flowage within mass

Fluidflow

Slow|

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Speed|

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Fast

Taluscreep

Soil creep

Low Water HighContent

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Slow

1. Creep...

Slow

1. Creep... Related to freeze/thaw or wet/dry cycles

Creep: gradual displacement downhill, greatest at surface,most material moves by creep

Evidence of creep

Kind of material

Rock(dry)

Regolith& water

Water &sediment

Kind of motion

Falling,rolling, sliding

Flowage within mass

Fluidflow

Low Water HighContent

Slow|

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Speed|

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Fast

Taluscreep

Soil creep

Solifluction

2. Solifluction... water saturated soil, high latitudes or elevations, permafrost beneath surface

Kind of material

Rock(dry)

Regolith& water

Water &sediment

Kind of motion

Falling,rolling, sliding

Flowage within mass

Fluidflow

Low Water HighContent

Slow|

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Speed|

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Fast

Taluscreep

Soil creep

Solifluction

Land-slides

Earthflowsslumps

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Landslide...mass of material moves as a unitmoves regolith (all material above bedrock) sudden, moderately high speed

Earthflow...usually water soaked massclay rich soil on a slope

linear = earthflowrotational = slump

All of above related to over-steepened slopesstream (or construction) undercuttingearthquakesloss of vegetationwater that adds weight / lubricates

1994, landslide, McClure Pass, CO

http://www.ngdc.noaa.gov/seg/hazard/slideset/landslides

Landslide: slippage on straight plane

Earth flow: material mixes

Earth slump: slippage on a curved plane La Conchita, CA,

1995

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Slump has a rotational element, slide does not

Landslide

http://www.youtube.com/watch?v=qEbYpts0Onw&feature=related

Kind of material

Rock(dry)

Regolith& water

Water &sediment

Kind of motion

Falling,rolling, sliding

Flowage within mass

Fluidflow

Low Water HighContent

Slow|

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Speed|

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Fast

Taluscreep

Soil creep

Solifluction

Land-slides

Rock-fall Avalanche

Earthflowsslumps

Rockfall: dry material “falls” downhill, common in spring thaw

Avalanche on Mt. Denali, Alaska Kind of material

Rock(dry)

Regolith& water

Water &sediment

Kind of motion

Falling,rolling, sliding

Flowage within mass

Fluidflow

Low Water HighContent

Slow|

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Speed|

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Fast

Taluscreep

Soil creep

Solifluction

Land-slides

Rock-fall Avalanche

Debrisflow

Str

eam

flo

w

Earthflowsslumps

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Debris flow...water, mud, and rock debrismore fluid than earthflowmoves faster and follows valleys (channelized flow)associated with

heavy rainsteep poorly vegetated slopesarid and semi-arid regionscommon in California

Csa (Mediterranean) climates dry summersfire destroys vegetation wet winters

1980, San Bernadino, debris flood control basin overflowed

Debris flow

http://www.youtube.com/watch?v=X4JPxw578UE&feature=related

Moral of the story:BE CAREFUL WHERE YOU BUY YOUR HOUSE

Low Water HighContent

Slow|

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Speed|

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Fast

Taluscreep

Soil creep

Solifluction

Land-slides

Rock-fall Avalanche

Debrisflow

Str

eam

flo

w

Earthflowsslumps

Speed and water content are the main classification variables for mass movement