Soil and Topography

• Soils at the top and bottom of the slope tend to be thicker than the soil on the slope itself

Section 12.4: Erosion

• Erosion – the process by which the products of weathering are transported

• Most of the eroded soil is deposited elsewhere as transported soil

• Accelerated Soil Erosion – unwise farming and ranching practices increase soil erosion– Clearing forests, overgrazing, etc…

• Gullying – process of rainwater eroding soil to produce gullies

• Sheet Erosion – stripping away of parallel layers of topsoil to expose the surface of subsoil or bedrock

Soil Conservation– Terracing – creation

of steplike ridges that follow the contours of the land; prevent rapid erosion

– Crop rotation – rotating of crops planted on a yearly basis; stops erosion in its early stages and allows gullies formed during one season to be filled with soil in the next

Gravity and Erosion– Gravity causes rock

fragments to move down inclines

– Movement of fragments down an incline is called mass movement; can either be rapid or slow

– Talus – accumulation of fragments at the base of a slope• May be reduced to

smaller fragments through mechanical and chemical weathering

Mass Movements• Rapid Mass Movements

– Rockfall: fall of rock from a steep cliff– Landslide: sudden movement of masses of loose rock and soil

down the slope of a hill, mountain or cliff– Mudflow: movement of a large mass of mud– Slump: movement of a large piece of soil or rock down a slope

in a single piece• Slow Mass Movements

– Solifluction: occurs in the mountain and arctic climates where there is permafrost and soil that has thawed above the permafrost and flows down the slope– Solifluction means “soil flow”

– Creep: extremely slow downhill movement of rock fragments

Erosion and Landforms– Landform: physical features on the Earth’s surface– Three major landforms:

• Mountains• Plains• Plateaus

– Erosion of Mountains• Mountains are generally uplifted faster than they are eroded; mountains being uplifted are rugged with sharp peaks

• Peneplain: low almost featureless surface near sea level caused as a result of erosion– New England

• Monadnocks: knobs of hard rock (granite) that are resistant to erosion and protrude above the peneplain

Erosion of Plains and Plateaus

• Plain – flat landform that is generally not high above sea level• Plateau – flat landform, high elevation; subject to more erosion than a plain– Mesa – smaller fragments of a plateau created by erosion

– Buttes – smaller fragments of a mesa created by erosion