1. Erosion

2. Various forces move weathered fragments of rock away from where the weathering

3. 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

4. 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

6. 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

10. Gullying is when soil is washed away by rainfall becomes larger forming gullies (gravity and water at work)

11. 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

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

15. 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.

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

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

19. strip cropping: crops are planted in alternate bands

20. Contour cropping of corn, alfalfa and wheat.

21. 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.

22. terracing: construction of step-like ridges that follow the contours of a sloped field

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

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

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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.

26. 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)

27. talus: a pile of rock fragments that accumulates at the base of the slope in piles

28. rockfall: the fall of rock from a steep cliff is the most rapid
Rapid mass movements
rockfall: the fall of rock from a steep cliff
is the most rapid
can be from tiny fragments to large boulders

31. landslide: sudden movement of masses of loose rock and soil down the slope of a hill

32. Hinsdale County, Colorado 700 years old and still moving
Slumgullion landslide
Hinsdale County, Colorado
700 years old and still moving

33. mudflow: the rapid movement of a large mass of mud

34. slump: downhill movement of a large block of soil under the influence of gravity

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

38. Slow mass movements
solifluction “slow flow” : slow downslope flow of wet, muddy topsoil over frozen or clay-rich subsoil

40. creep: extremely slow downhill movement of weathered rock material