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Gradation and Mechanical Weathering

Explore the processes of gradation, base level, weathering, erosion, and mechanical weathering like frost shattering, abrasion, and hydraulic action in geography. Learn how these natural forces shape the Earth's surface.

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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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