Download
1 / 60
640 likes | 982 Vues
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
E N D
Bedrock • Solid, unweathered rock that lies beneath regolith
Soil and Climate • Climate is most important factor influencing soil formation
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: • 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: • 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 • Forms soils from mechanical weathering • Soil is thin and mostly of regolith
Various forces move weathered fragments of rock away from where the weathering
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 • 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 • 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
When soil is washed away by rainfall, furrows become larger forming gullies (gravity and water at work)
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
Severe soil erosion from wind in the 1930's was a result of drought coupled with unsound farming practices.
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.
constant erosion reduces the fertility of the soil by removing the A horizon, which is rich in humus (unable to grow crops)
Soil Conservation contour plowing: soil is plowed in circular bands that follow the shape of the land (prevents water from flowing directly down slope)
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.
terracing: construction of step-like ridges that follow the contours of a sloped field
During heavy rain storms terraces catch water and lead it slowly off the field. Slowing down the speed of flowing water reduces soil erosion.
crop rotation: farmers plant one type of crop one year and a different type of crop the next year
<> 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, through its downward pull, causes rock fragments to move down inclines • mass movement is the movement of fragments down a slope (rapid or slow)
Rapid mass movements • rockfall: the fall of rock from a steep cliff • is the most rapid • can be from tiny fragments to large boulders
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.
landslide: sudden movement of masses of loose rock and soil down the slope of a hill
Slumgullion landslide Hinsdale County, Colorado 700 years old and still moving
