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Gradation and Mechanical Weathering

Gradation and Mechanical Weathering. Ms. Inden Geography 12. Gradation. http://myweb.cwpost.liu.edu/vdivener/notes/streams_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

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Gradation and Mechanical Weathering

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  1. Gradation and Mechanical Weathering Ms. Inden Geography 12

  2. Gradation http://myweb.cwpost.liu.edu/vdivener/notes/streams_basic.htm

  3. 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)

  4. 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. http://geography.sierra.cc.ca.us/Booth/Physical/chp15_gradation/denudation.htm

  5. 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!

  6. 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 http://www.goodearthgraphics.com/virtcave/staltite/staltite.html

  7. 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)

  8. Mechanical Weathering Frost Shattering Corrasion or Abrasion Hydraulic Action Exfolation Insolation

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

  10. 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

  11. Link to blog showing frost shattering • http://kespilotgeography.blogspot.com/2006/10/frost-shattering.html

  12. 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

  13. 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 http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/image_preview.html?image

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

  15. 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

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

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

  18. 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

  19. Onion Skin Weathering • http://www.geointeractive.co.uk/contribution/ppfiles/Onion%20skin%20weathering.ppt#256,1,Onion skin weathering • Insolation – caused by extremes of hot and cold over a 24 hour period

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

  21. Often all these processes are at work at once • http://www.bbc.co.uk/schools/gcsebitesize/geography/coastal/coastalprocessesrev3.shtml • Example – water eroding a cliff • Hydraulic action • Chemical weathering • Attrition • Abrasion or corrasion

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