Gradation and Mechanical Weathering Ms. Inden Geography 12

Gradation ams_basic.htm

What is Gradation? All activities of the earth's surface that build up some areas and wear down others –Rivers –Waves and currents –Glaciers –Wind –Biotic – roots, animals –Mass Wasting (gravity)

What is Base Level Gradational process are trying to erode the surface down to base level Plate tectonics keep the earth from becoming completely smooth. ation.htm

Wear down, fill in! Gradational processes are constantly trying to wear down high points on the earth and to fill in low points – like a grader moving along a gravel road Wear down, fill in!

Weathering Weathering is the breaking up of rock into smaller pieces (sometimes called regolith) and/or changing the rock chemically –Mechanical weathering –Chemical weathering –Biotic weathering

Erosion Weathering (decomposition of rocks) takes place without movement (in situ), by heat, water, ice, or pressure, and chemical reactions Erosion is weathering and transportation together (water, wind, ice and gravity)

Mechanical Weathering Frost Shattering Corrasion or Abrasion Hydraulic Action Exfolation Insolation

Frost shattering/frost wedging/frost action –Water seeps into rock cracks –Freezing water expands 9% –Forces rocks to break apart Talus or Scree Slope -eroded rock deposited at the bottom of the slope Frost Shattering

Freeze and thaw; repeat –Most common in temperate climates where freezing occurs overnight and thawing occurs during the day through much of the year –Not as common in the arctic where it stays frozen months at a time – no freeze/thaw, freeze/thaw Located on mountain tops in England, dating back to the last ice age. Rock breaks up in situ, forming blockfields or blockslopes

Link to blog showing frost shattering 06/10/frost-shattering.htmlhttp://kespilotgeography.blogspot.com/20 06/10/frost-shattering.html

Abrasion or corrasion Breaking down and grinding away of material by collisions of moving particles –Waves rubbing rocks against each other –Rivers tumbling rocks along stream beds –Glaciers scraping rocks along the ground or bedrock –Wind picking up sand and sandblasting landforms

Abrasion or corrasion Rocks and sand pounding against the cliffs have created this coastal arch (and the sand on the beach) on the Dorset Coast in England e_preview.html?image

Glacial Abrasion Glacial striations or scratches Glacier drags rocks and gravel along the surface of the bedrock

Hydraulic Action (water) Water currents rush into cracks Air is compressed as the water forces itself in Water leaves as the wave recedes Air releases with explosive force Cracks widen Explosive action increases as the crack widens

High water level Chemical, biological and mechanical weathering Note the spring – moss in March!

Hydraulic Action this can be as high as 6 tonnes/cm3 – the force of a bulldozer

Exfoliation When a granite or other igneous intrusion is exposed through erosion, the pressure comes off and the rock falls apart – it peels off like layers of an onion. Creates an exfoliation dome. Happens in the Canadian Shield, although this one is in Georgia

Onion Skin Weathering ion/ppfiles/Onion%20skin%20weathering. ppt#256,1,Onion skin weathering Insolation – caused by extremes of hot and cold over a 24 hour period

Silt – created by mechanical weathering Rock flour, stone dust Glaciers, sandblasting, river and wave action Aeolian (created by wind) deposition of silt called loess

Often all these processes are at work at once /geography/coastal/coastalprocessesrev3.sh tmlhttp:// /geography/coastal/coastalprocessesrev3.sh tml Example – water eroding a cliff –Hydraulic action –Chemical weathering –Attrition –Abrasion or corrasion