Chapter 8: Mass Movements, Wind, and Glaciers

1. Chapter 8: Mass Movements, Wind, and Glaciers

2. The downslope movement of soil and weathered rock resulting from the force of gravity is called mass movement. • Climatic conditions determine the extent of mass movement.

3. All mass movements occur on slopes. Because few places on Earth are completely flat, almost all of Earth’s surface undergoes some degree of mass movement.

4. Factors that influence mass movements. • The material’s weight • The material’s resistance to sliding or flowing • Triggers that shake material loose, and • The presence of water.

5. Types of Mass Movements Creep • The slow, steady, downhill flow of loose, weathered Earth materials, especially soils, is called creep. • The effects of creep are usually noticeable only over long periods of time.

6. One way to way to tell whether creep has occurred is to observe the positions of structures and objects.

7. Flows • Earth flows are moderately slow movements of soils, whereas mudflows are swiftly moving mixtures of mud and water.

8. Mudflows

9. Types of Mass Movements Mudflows

10. Types of Mass Movements Mudflows

11. Flows • Mudflows are common in sloped, semi-arid regions that experience intense, short-lived rainstorms.

12. Flows • Mudflows can be triggered by earthquakes or similar vibrations. • Lahars are mudflows that occur in volcanic regions where the heat from a volcano melts snow on nearby slopes that have fine sediment and little vegetation.

13. Lahar - Flows

15. Types of Mass Movements Lahar - Flows

16. Slides • A rapid, downslope movement of Earth materials that occurs when a relatively thin block of soil, rock, and debris separates from the underlying bedrock is called a landslide.

17. Landslides are common on steep slopes, especially when soils and weathered bedrock are fully saturated by water. • A rockslide is a type of landslide that occurs when a sheet of rock moves downhill on a sliding surface. Rockslides are often triggered by earthquakes.

18. Landslides

19. Types of Mass Movements Slides • Landslides

20. Types of Mass Movements Slides • rockslides

21. Types of Mass Movements Slides • rockslides

22. Slides • When the mass of material in a landslide moves along a curved surface, a slump results. • Material at the top of the slump moves downhill, and slightly inward, while the material at the bottom of the slump moves outward.

23. slump

24. Landslides that occur in mountainous areas with thick accumulations of snow are called avalanches. • Avalanches occur when snow that falls on an icy crust builds up, becomes heavy, slips off, and slides downslope.

26. On high cliffs, rocks that are loosened by physical weathering processes or by plant growth can break up and fall directly downward. Rockfalls commonly occur at high elevations, in steep road cuts, and on rocky shorelines.

27. Limited precipitation leads to an increase in the amount of wind erosion because precipitation holds down sediments and allows plants to grow. Wind Erosion and Transport

28. Wind transport and erosion primarily occur in areas with little vegetative cover, such as deserts, semiarid areas, seashores, and some lakeshores.

29. The lowering of the land surface that results from the wind’s removal of surface particles is called deflation. Deflation

31. During the 1930s, portions of the Great Plains region experienced severe drought. Because large areas of natural vegetation had been removed, strong winds readily picked up the dry surface particles. The region became known as the Dust Bowl.

32. Another process of erosion, called abrasion, occurs when particles such as sand rub against the surface of rocks or other materials.

33. Because sand is often made of quartz, a hard mineral, wind abrasion can be an effective agent of erosion—windblown sand particles eventually wear away rocks.

34. Rocks shaped by windblown sediments are called ventifacts.

38. In windblown environments, sand particles tend to accumulate where an object, such as a rock, landform, or piece of vegetation, blocks the forward movement of the particles. Over time, the pile of windblown sand develops into a dune. Wind Deposition Dunes

39. The conditions under which a dune forms determine its shape and include the availability of sand, wind velocity, wind direction, and the amount of vegetation present.

40. Dune migration is caused when prevailing winds continue to move sand from the windward side of a dune to its leeward side, causing the dune to move slowly over time.

41. Thick, windblown silt deposits are known as loess. Loess soils are some of the most fertile soils because they contain abundant minerals and nutrients. Loess

42. This map shows the location of loess deposits in the continental United States.

43. A large mass of moving ice is called a glacier. Glaciers form near Earth’s poles and in mountainous areas at high elevations. They cover about 10 percent of Earth’s surface. Moving Masses of Ice

44. Glaciers that form in valleys in high, mountainous areas are called valley glaciers. As valley glaciers flow downslope, they carve V-shaped stream valleys into U-shaped glacial valleys.

45. Valley Glaciers  Bylot Island, Canada

46. Glaciers that cover broad, continent-sized areas are called continental glaciers. These glaciers form in cold climates where snow accumulates over many years.

47. Both valley glaciers and continental glaciers move outward when snow gathers at the zone of accumulation, a location in which more snow falls than melts, evaporates, or sublimates.

48. Of all the erosional agents, glaciers are the most powerful because of their great size and weight.

49. When a valley glacier moves, it breaks off pieces of rock through a process called plucking. When glaciers with embedded rocks move over bedrock, they act like grains on a piece of sandpaper, grinding parallel scratches into the bedrock.

50. At the high elevations where snow accumulates, valley glaciers scoop out deep, bowl-shaped depressions, called cirques.