1. Erosion and Soil Depostion
Chapter 8

2. Section One: Changing Earth’s Surface

3. Erosion
“Erosion” moves sediment from one place to another

4. While “deposition” lays down sediment in new locations.

5. What are the forces which cause erosion?

6. The force of gravity.

7. The force of running water.

8. The force of glaciers.

9. The force of waves.

10. And the force of wind.

11. What Do You Remember? What does erosion do?
moves sediment from one place to another
What does deposition do?
lays down sediment in new locations.
What are the forces which cause erosion?
Gravity, water, glaciers, waves, and wind.

12. Section 2: Water Erosion
Moving water is the major cause of erosion on Earth’s surface.

13. Runoff and Erosion
Runoff is water which moves over the land, carrying soil particles with it.

14. The amount of erosion caused by runoff can depend on how much plant life is there to hold the soil. With very little plant life, a desert can have high runoff and erosion.

15. Because of gravity, runoff and the soil in it carve little grooves called rills.

16. As rills flow into one another, they grow larger and form gullies.

17. Gullies join together to form streams
Gullies join together to form streams. While gullies only flow when it rains, streams flow all the time.

18. A stream grows into a larger stream by receiving water from tributaries.

19. Together, all these streams, from tiny rills to great rivers, form a system that drains the land. A drainage basin is a land area where all this water collects.

20. What Do You Remember?
What is the major cause of erosion on Earth’s surface?
Moving water.
What is water which moves over the land, carrying soil particles with it?
Runoff
Describe the system by which water is moved from small to large.
Rills to Gullies to Streams which are Tributaries to Larger Streams, which run to a Drainage Basin.

21. Rivers have features which are caused by erosion.

22. Near its source, a river flows quickly and follows a straight, narrow course. The steep slopes along the river erode rapidly and we see a deep,
V-shaped valley

23. Waterfalls occur where a river meets an area of rock that is very hard, followed by softer rock. The soft rock wears away more quickly, creating a waterfall.

24. Lower down on its course, a river usually flows over more gently sloping land. It spreads out and erodes the land, forming a wide river valley.

25. A wide, flat area of land along a river is called a flood plain
A wide, flat area of land along a river is called a flood plain. A river can cover the flood plain during floods.

26. A river can have meanders, which are looplike bends in the river caused by uneven erosion.

27. Sometimes a meandering river forms an oxbow lake
Sometimes a meandering river forms an oxbow lake. This is a meander that has been cut off from the river when the water level drops.

28. Complete River System

29. What Features Do You Remember?
High in the mountains near the river’s source are…
deep, V-shaped valleys.
When the river runs over hard rock, then soft rock?
Waterfalls
When it flows over gently sloping land?
Wide river valleys
When it comes to a wide, flat area of land?
Flood plains
Looplike bends in the river caused by uneven erosion?
Meanders

30. River Deposits
As water moves, it carries sediments with it. Any time moving water slows down, it drops some of the sediment.

31. Soil deposition creates new landforms, such as alluvial fans, which is a wide, sloping deposit of sediment.

32. Sediment deposited where a river flows into an ocean or lake builds up a landform called a delta, which can take a variety of shapes, like this “birds foot” delta.

33. What Do You Remember? What happens when water flow slows down?
The water drops its sediment.
What are wide, sloping deposits of sediment?
Alluvial fans
When a river flows into an ocean or lake, sediment builds up at the mouth. What is this landform called?
A delta

34. Groundwater Erosion and Deposition

35. Not all rainwater goes to runoff or evaporates
Not all rainwater goes to runoff or evaporates. Some of it soaks into the ground. This underground water is called groundwater.

36. Underground water combines with carbon dioxide to form a weak acid, which can dissolve limestone. These hollowed out pockets in the underground stone become caves.

37. Inside the caves, water containing dissolved limestone drips from the roof, forming stalactites (which hang down) and stalagmites (which grow up from the cave floor).

38. Sometimes the ground above a cave can collapse, creating a depression called a sinkhole.

39. What Do You Remember? What is water that soaks into the ground?
Groundwater
How do caves form?
Water combines with carbon dioxide to form a weak acid, which dissolves limestone.
What are the deposits of dissolved limestone in caves called?
Stalactites (ceiling) and Stalagmites (floor).
What is the name for a collapsed cave?
Sinkhole

40. Section 3: The Force of Moving Water

41. A river’s moving water has energy, and we can use this energy to create power.

42. There are two kinds of energy: Potential Energy and Kinetic Energy.

43. .

44. As water moves down from a higher slope, its potential energy is released into kinetic energy.

45. This released energy picks up sediment, pebbles, and even rocks, which wear the riverbed away with a grinding action. This is called abrasion.

46. The power of a river depends on how steep it is (slope), how much water is flowing (volume) and the shape of its streambed.

47. A streambed can be full of boulders and other obstacles
A streambed can be full of boulders and other obstacles. All these rough surfaces can increase friction, which causes the water to move every which way. This is called turbulence.

48. What Do You Remember? What are the two kinds of energy?
Potential and Kinetic
Water at a high place has which kind of energy?
Potential
Water flowing downhill has which kind of energy?
Kinetic
Moving water can be used to create…
Power
The grinding action of pebbles and rocks on the riverbed is called…
Abrasion
What are the three features which determine the power of a river?
Slope, volume, and shape
River obstcles like boulders create more friction, which increases…
Turbulence

49. Section 4: Glaciers

50. A glacier is any large mass of ice that moves slowly over land.

51. There are two kinds of glaciers:
Valley Glaciers, which are long, narrow glaciers which forms when snow and ice build up high in a mountain valley.

52. Continental Glaciers, which cover much of a continent or large island
Continental Glaciers, which cover much of a continent or large island. They cover 10% of the earth today.

53. Many times in the past, continental glaciers have covered large parts of Earth’s surface. These times are known as the ice ages.

54. Although glaciers move slowly, they are a major force of erosion.

55. The glacier flows over the land and picks up rocks
The glacier flows over the land and picks up rocks. This is called “plucking”. As the rocks are dragged across the land they gouge and scrape the bedrock. This is called “abrasion”.

56. When the glacier melts, it deposits the sediments, which are called “till”. The till at the edge of a glacier forms a ridge, which is called a “moraine” A “terminal moraine” is the farthest point reached by a glacier.

57. Continental glaciers can scoop out huge basins
Continental glaciers can scoop out huge basins. The Great Lakes were formed by glaciers of the past.

58. What Do You Remember? What is a glacier?
A large mass of ice which moves over the land.
What are the two kinds of glaciers?
Valley glaciers and Continental glaciers.
What is an ice age?
A time when glaciers covered huge amounts of Earth.
What are the two things glaciers do to change the surface of earth?
Plucking and Abrasion
What are sediments left by glaciers called?
Till
What is the ridge of sediment at the edge of a glacier?
Moraine
What is the farthest point of sediment left by a retreating glacier?
Terminal Moraine.

59. Section 5: Waves

60. The energy in waves comes from wind that blows across the water’s surface.

61. The energy from waves can break apart rocks
The energy from waves can break apart rocks. Over time, waves can make the small cracks in the rocks larger. Eventually, pieces of the rock break off.

62. Waves also erode land by abrasion
Waves also erode land by abrasion. When a wave hits land, the sediment in it is carried forward by the wave and wears away rock like sandpaper wearing away wood.

63. Waves not only erode the land, but they also deposit sediment.

64. As waves reach the shore, they drop the sediment they carry, forming a beach.

65. What Do You Remember? What causes waves?
The pressure of wind across the surface of water.
What causes waves to break on the beach?
The friction of the land slows down the bottom water, but the top water keeps moving forward.
What are the two ways that waves erode land?
They hit rocks and cause cracks, and they abrade the rocks with their sediment like sandpaper.
What deposits do waves leave?
Sandy beaches.

66. Section 6: Wind

67. Wind is actually the weakest force of erosion
Wind is actually the weakest force of erosion. Water, ice, and waves are much stronger agents. But wind can be a powerful shaping force if there are no plants to hold the soil in place.

68. Wind picks up the smallest particles of sediment
Wind picks up the smallest particles of sediment. The stronger the wind, the larger the particles it can pick up. This sweeping away of earth is called “deflation”.

69. When the wind slows down, or some obstacle traps the windblown material, sand dunes form. These are formed by the coarser particles blown by the wind.

70. The finer particles in the wind are carried very far away from their source. These are particles of clay and silt and can create rich farmland. This windblown material is called “loess”.

71. What Do You Remember?
When can wind be a powerful force for shaping earth?
When there are few or no plants to hold the soil.
What is the sweeping away of particles by wind?
Deflation
How are sand dunes formed?
The wind-carried particles are trapped by obstacles or the wind slows down and drops the particles.
What are the finer particles which can be carried long distances before they fall?
Loess