Chapter 8Chapter 8Part 1Part 1

Weathering, Weathering, Soils and Soils and

Mass MovementMass Movement

GRB Pages 62 - 71GRB Pages 62 - 71

Weathering and Weathering and ErosionErosion

• WeatheringWeathering - - DefDef. - the break down . - the break down of rocks that have been exposed to of rocks that have been exposed to the atmosphere. the atmosphere.

• Once the rocks are broken down, the Once the rocks are broken down, the pieces are transported from one pieces are transported from one place to another. This process is place to another. This process is calledcalled erosionerosion. .

• Erosion is caused by Erosion is caused by windwind, , moving moving waterwater (streams, waves, ocean (streams, waves, ocean currents), currents), iceice (glaciers), and by (glaciers), and by gravitygravity. .

• VIF - Most erosion that takes place on VIF - Most erosion that takes place on Earth is caused by moving waterEarth is caused by moving water

2 Types of 2 Types of WeatheringWeathering

Chemical weatheringChemical weathering – rocks break down as their minerals change in composition (they become different substances).

    Mechanical Mechanical weatheringweathering – rocks are broken down into smaller pieces without changing their composition (what they’re made of).

AKA - physical weathering

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• Ice wedging/frost Ice wedging/frost actionaction – water enters small water enters small

cracks in the rock. cracks in the rock. – When it freezes, it When it freezes, it

expandsexpands and and forces the crack to forces the crack to open more. open more.

– The process The process repeats over again repeats over again until the rock until the rock breaks apart.breaks apart.

Mt. Brewster – looks solid, right?Mt. Brewster – looks solid, right?

Close up shows jagged rocks from Close up shows jagged rocks from FROST wedging!FROST wedging!

Eventually, the rock splits Eventually, the rock splits from repeated frost action!from repeated frost action!

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• AbrasionAbrasion – It is the physical It is the physical

wearing down of wearing down of rocks as they rub rocks as they rub or bounce against or bounce against each other. This each other. This process is most process is most common in windy common in windy areas, under areas, under glaciers, or in glaciers, or in stream channels.stream channels.

– It can also It can also happen during happen during rock slidesrock slides

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• Wetting and dryingWetting and drying – breaks up rocks that breaks up rocks that

are made from clay. are made from clay. – When they are wet When they are wet

they expand, and they expand, and they shrink as they they shrink as they dry. dry.

– As this repeats over As this repeats over and over, the clay and over, the clay becomes weak and becomes weak and cracks (think of all cracks (think of all the projects you the projects you have made out of have made out of clay…they all crack clay…they all crack and fall apart)!and fall apart)!

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• ExfoliationExfoliation – soil and rock is soil and rock is

removed removed (glaciers or (glaciers or uplifting), uplifting), exposing rock exposing rock found deep found deep underground. underground.

– This releases the This releases the pressure causing pressure causing the the surfacesurface of of the rock to the rock to expand and expand and eventually crack. eventually crack.

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• Plant Roots– The roots of

trees often wedge in between cracks in rocks and force apart rocks even further!