What makes good soil? Air Water Organic Material (Nutrients) Rock particles

Soil Formation & Mass Movement Soil is formed mainly because of biologic activity and weathering Physical weathering is dominant in cold, moist regions, while chemical weathering is dominant in warm, moist regions Soil horizons are layers of soil with distinct characteristics

Soil Horizons in a Soil ProfileSoil Profile O Horizon – thin layer of leaf mold A Horizon – the topsoil, organically rich (humus) One inch = 500 years B Horizon – subsoil, composed of clays C Horizon – zone of partially weathered rock Bedrock – solid rock

Soil Horizons The C horizon is first to form and contains only partly weathered rock

Soil Horizons As humus and other minerals are deposited the A layer forms. This layer is called Topsoil

Soil Horizons The B horizon is a combination of the A horizon and the C horizon The B horizon forms when clay and other particles wash down. This layer is called the subsoil.

Soil Types

Dust Bowl Near the end of 1800s the prairies were settled by the “Sod busters” (Sod is thick grass & topsoil).

New settlers moved to the Great Plains. The Great Plains soil was fertile but the climate was dryer

Dust Bowl Plowing removed the grass from the Great Plains

Dust Bowl 1931 was the first year of a drought that lasted till 1938.

Dust Bowl As the soil dried out the topsoil turned to dust and blew away.

Dust Bowl Many people abandoned their homes & farms and moved away.

Lessons learned Soil conservation was adopted George Washington Carver taught farmers how to restore soil fertility by planting peanuts Wind breaks were planted Contour plowing and Conservation plowing were introduced

Contour Plowing Slows runoff by plowing fields along the curves of a slope.

Conservation Plowing Also called low-till or no- till plowing. Disturbs the soil as little as possible.

Mass Movement The most dominant force of erosion is gravity Some types of mass movement are: Slump – occurs when loose rock layers slip down a slopeSlump

Creep – sediments slowly inch their way down slope Rockslides – large blocks of rocks fall suddenly and quickly down slope Mudslides – mixture of sediments and water quickly moving down slope

Mass Movement Gravity is a force that can move rock and sediment down hill. This movement is called Mass Movement.

Landslides Occurs when rock & soil move quickly down hill Most destructive type of mass movement

Mudflow Similar to a landslide but triggered by addition of water In some cases the mud may be 60% water

Slump A mass of rock or soil suddenly slips down hill as a single unit.

Slump

Creep Very slow downhill movement Is noticed by its effects on poles or trees

Creep