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

Sheet erosion

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 Slow 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

Rockfall

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