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Bedrock - PowerPoint PPT Presentation


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Bedrock. Solid, unweathered rock that lies beneath regolith. Bedrock. Soil and Climate. Climate is most important factor influencing soil formation. Temperate climates. Temperatures range from cool to warm Rain fall is not excessive

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Presentation Transcript
bedrock
Bedrock
  • Solid, unweathered rock that lies beneath regolith
soil and climate
Soil and Climate
  • Climate is most important factor influencing soil formation
temperate climates
Temperate climates
  • Temperatures range from cool to warm
  • Rain fall is not excessive
  • Two types of soil are found dependent on amount of rainfall:
soil types in temperate climates
Soil types in temperate climates:
  • Pedalfer – soil formed if an area receives 65 cm or more of rain per year (clay, quartz, iron)

-found in eastern United States

2. Pedocal – soil formed if rainfall is less then 65 cm a year (calcium carbonate)

-found in western United States

tropical wet warm climate
Tropical (wet & warm) climate:
  • forms laterites (thick and infertile soil)

*rain always is washing away the A horizon but constant rotting vegetation covers the B Horizon

desert dry climate
Desert (dry) Climate
  • Forms soils from mechanical weathering
  • Soil is thin and mostly of regolith
slide19
erosion is the process by which the products of weathering are transported
  • agents of erosion are gravity, wind, glaciers, water, ocean waves, currents streams, groundwater
soil erosion
Soil Erosion
  • occurs world wide and is normally a slow process
  • ordinarily, new residual soil forms about as fast as the existing soil erodes
  • However, unwise use of the land and unusual climatic conditions can upset this natural balance
accelerated soil erosion
Accelerated Soil Erosion
  • unwise farming and ranching methods increase soil erosion
  • one example is clearing of trees,small plants, and animal overgrazing
  • another example is furrows plowed in land
slide26

When soil is washed away by rainfall, furrows become larger forming gullies (gravity and water at work)

slide28

Sheet erosion is another type of soil erosion that strips away parallel layers of topsoil

  • may occur when continuous rainfall evenly washes away the topsoil
  • can also be caused by wind during unusually dry periods
slide30

Severe soil erosion from wind in the 1930's was a result of drought coupled with unsound farming practices.

slide32

The photo on the right though, was taken at 10:00 AM, March 13, 1991 in downtown Topeka, Kansas, looking into the sun. There was so much soil in the air it darkened the sky. So the problem is not just something of the past.

slide34

constant erosion reduces the fertility of the soil by removing the A horizon, which is rich in humus (unable to grow crops)

slide35

Soil Conservation

contour plowing: soil is plowed in circular bands that follow the shape of the land (prevents water from flowing directly down slope)

slide39

Contour farming (planting crops along the slope of the land) and contour strip cropping (alternating different crops in the same field) reduces soil erosion. Traps soil on the field.

slide41

During heavy rain storms terraces catch water and lead it slowly off the field. Slowing down the speed of flowing water reduces soil erosion.

slide42

crop rotation: farmers plant one type of crop one year and a different type of crop the next year

slide43

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With the development site cleared of all vegetation, area is now prone to soil losses in excess of 70 tons per acre.

gravity and erosion
Gravity and Erosion
  • Gravity, through its downward pull, causes rock fragments to move down inclines
  • mass movement is the movement of fragments down a slope (rapid or slow)
slide45

Rapid mass movements

  • rockfall: the fall of rock from a steep cliff
  • is the most rapid
  • can be from tiny fragments to large boulders
slide48

Figure 21 Rockslide The scar on the side of this mountain in northwestern Wyoming was made by an enormous rockslide that happened more than 75years ago.The debris in the slide formed a dam 70 m high across the Gros Ventre River.

slide50

Slumgullion landslide

Hinsdale County, Colorado

700 years old and still moving

slide53

A slump is a type of slope failure which involves the rotational movement of soil or rock

slide59

erosion of mountains: weathering and erosion wear down rugged peaks to rounded peaks and gentle slopes

Rocky Mountains

Appalachian Mountains