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Causes the loss of topsoil.

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Presentation on theme: "Causes the loss of topsoil."— Presentation transcript:

1 Causes the loss of topsoil.
Erosion This is the process that moves weathered sediments from one location to another. Causes the loss of topsoil.

2 Where is erosion more common?.
More common on steep slopes than on gentle slopes. More common in areas where there is little vegetation.

3 What are the agents of erosion?
1. Gravity 2. Running water 3. Glaciers 4. Wind

4 What do the agents of erosion have in common?
They only carry the sediments as long as they have enough energy of motion. They all drop their load when the energy of motion decreases. – the dropping of sediments is called deposition.

5 1. Gravity Causes loose material to move down a slope. This is caused mass movement. Mass movement can be slow or rapid

6 Types of mass movement. Slump Creep Rockslide Mudflow

7 Slump Type of mass movement that takes place on steep slopes.
Loose material or rock layers slip downward as one large mass. Usually leaves a scar where the material originally rested. Occurs because the material under the slump weakens.

8 Creep Sediments slowly move down a hill. Very common is areas where there is freezing and thawing. As the ground freezes small sediments are pushed up be expanding water in the soil. When the soil thaws, the sediments fall downslope. This happens slowly about a millimeter each period.

9 When creep occurs along a roadway, fenceposts and telephone poles, on the other hand, don't grow vertically and merely tilt on creeping slopes.

10 Rockslide A rockslide happens when large blocks of rock break loose from steep slopes and tumble quickly to the bottom

11 Mudflows Usually occurs in relatively dry area. Have a thick layer of dry sediments. When you have heavy rain, the water mixes with the soil and forms mud. Gravity pulls this substance downhill.

12 Running Water Water moves more sediments than any other agent of erosion. Running water has a great deal of energy. Water usually moves down hill under the influence of gravity. When water looses its energy it deposits its sediments.

13 What happens to water when it rains?
Soaks into the ground. Evaporates. Runs over the ground. – Runoff Eventually enters streams, lakes or the ocean. Affected by the amount of rainfall and the length of time over which it falls. Affected by steepness of land. Affected by amount of vegetation present.

14 Types of water erosion. Rill and Gully Erosion
Groove or small ditch on the side of a slope left behind by running water. Begins when a small stream forms during heavy rain. As stream flows it has enough energy to carry away some soil Groove created is called a channel. If the rill channel becomes broader and deeper it forms a gully.




18 Sheet erosion Sometimes water erodes without being in a channel ex. Flowing out from a river, flowing down a gentle slope, fanning out after flowing down a mountain. Sheet erosion occurs when water that is flowing like a sheet picks up and carries away sediments. When the water looses its energy the sediments left behind cover the area like a sheet.


20 Stream erosion As water in a stream moves along, it picks up sediment from the bottom and sides of its channel. This makes the stream deeper and wider. Sediment carried along is called the load. The lightweight sediments carried along are the suspended load The heavier sediments rolls along the bottom, called the bed load. Acts like sandpaper, wears away other rocks by abrasion.


22 Water deposition. Sediments are deposited at different locations as the stream moves. Alluvial fan- shaped like a triangle. If sediments are deposited when water empties into a larger water body (ocean, gulf, lake) the alluvial fan is called a delta.


24 Here the alluvial fans are called deltas.

25 3. Glaciers Snows Snow does not get a chance to melt so it piles up.
Weight of the snow compresses the bottom layer into ice. Pile of snow is so large that ice on the bottom melts forming a putty-like mass. When the whole mass of snow begins to slide on this putty-like mass and moves downhill- this is a glacier.

26 Continental glacier – huge mass of ice and snow found near the polar regions - covers about 10% of Earth’s surface - found in Greenland and Antarctica

27 Valley glacier Found in mountainous areas where temperature is low enough so that snow does not melt over the summer season. -Glaciers in the glacier national park in Montana.

28 How do glaciers cause erosion?
As they move they act like a bulldozer pushing loose material out of their path. This material can be added to the mass of the glacier or piled up along the side. They weather and erode rock and soil that was not loose.

29 Glacial erosion Plucking – When the ice melts, water flows into rocks. Later the water refreezes in the cracks, expands, and breaks the rock. The boulders, gravel, and sand that is plucked can then be added to the bottom or the sides of the glacier.

30 Abrasion - the material plucked by the glacier grinds into the bedrock like sandpaper across wood.
-If the sediments are large they leave grooves in the bedrock smaller grooves are called striations -if the sediments are fine they polish the rock.

31 Striations This picture depicts a boulder that has been subjected to abrasion by the bottom of a glacier riding over the top of it. The orientation of the striations suggest ice movement from the top of the picture to the bottom. 

32   This picture shows the bedrock of a glaciated valley that has been subjected to abrasion by the base section of the ice.  Fine materials such as silt and clay abrade very small striations to create "Polish". Polish has created a smooth surface that is seen here.

33 Glacial deposition When glaciers begin to melt they are unable to carry much sediment. The sediment is deposited on the land. When glaciers melt and begin to shrink back – retreat. As the glacier retreats a mixture of boulders, sand, clay and silt is left behind. This is called the till.

34 Glacial till

35 Till can also be deposited when the glacier stops moving forward
Till can also be deposited when the glacier stops moving forward. This does not cover as wide an area. Made up of the rocks and soil that the glacier had been pushing along. Looks like a ridge of material that a bulldozer left behind. Smaller ridges can be found along the sides of the glacier These mounds of material are called moraines.

36 Another form of glacial deposition is called outwash.
This is deposited from the glacier’s melted ice. Usually found beyond the end of the glacier. Outwash carries sediments like a river. Alluvial fan- fan shaped deposit - Esker – looks like a winding road.

37 How do you know if erosion was caused by a glacier?
Valley glaciers erode bowl shaped basins called cirques into the sides of the mountain If two valley glaciers side by side erode a mountain peak a long ridge (arete) forms between them If the valley glacier erodes the mountain from several direction , get a sharpened peak called a horn. Valleys eroded by glaciers have a U - shape, those eroded by a stream are V - shaped.

38 cirque U-shaped valley horn Aretes – sharp, thin ridges


40 4. Wind When air moves it picks up loose material and transports it to other places. Usually cannot pick up heavy sediments Carries sediments over large areas. Sandstorms Dust storms

41 How does wind cause erosion?
Deflation - Small particles are picked up by the wind and the heavier ones are left behind. Abrasion - When wind blown sediments strike rock and the surface gets scraped and worn away.

42 Wind removes smaller soil particles and leaves rocks exposed on the surface.
Dust storm

43 How deflation leads to the formation of a desert pavement

44 Wind deposition. Loess - fine (can be fine like talcum powder) grained sediments deposited by the wind. Dunes – a mound of sediments drifted by the wind

45 What can cause erosion? 1. Agricultural cultivation.
Increase use of farmland because of the increase in the population 2. Deforestation. Forests are constantly being cleared for lumber, farming, and grazing. 3. Overgrazing 4. Urban Construction Plowing mechanically turns and loosens the soil- this improves it for crops, but removes plant cover that holds soil particles in place. Soil is now vulnerable to erosion. Soil in rain forests are rich in nutrients but the soil can only be used for a few years before the nutrients are gone. Farmers then clear more forest to get new land for their plants. If the land is overgrazed then ground cover is removed. Here the soil can be easily eroded. Vegetation is constantly being cleared for roads and other construction projects. Once again soil is exposed.

46 How to prevent erosion? 1. Shelter belts of trees.
2. Grazing management. 3. No-till farming. 4. Contour farming 5. Terracing 6. Special steps at construction sites 7. Special steps when building on steep slopes. Shelter belts break the force of wind 7. Plants can be planted, their roots hold the soil in place. Plants also absorb large amounts of water. Drainage pipes or tiles can also be added.

47 Field shelterbelts reduce wind erosion and conserve soil moisture.
During construction covering exposed soil with plastic to reduce erosion Contour Farming Farming with row patterns nearly level around the hill—not up and down hill.

48 No-till farming of wheat
Terracing as a Means of Soil Conservation

49 Crop Rotation Changing the crops grown in a field, from year to year. Grazing management - farmers must make sure that cattle do not over graze a field, grass must be given time to recover.

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