Chapter 8 – Mass movements, Wind and Glaciers

1. Chapter 8 – Mass movements, Wind and Glaciers NCES 2.1 Created Fall 2012

2. What are mass movements? • The downslope movement of loose sediment and weathered rock resulting from the force of gravity. • Recall that erosion is the step that follows weathering. • All mass movements take place on slopes. • There are VERY few places on Earth that are extremely flat. • Movement could be very slow to sudden.

3. Variables that affect mass movements • 1. weight of the material • 2. resistance of the material to sliding or flowing • 3. A trigger – ex. An earthquake • 4. Water • Too little water can prevent sediments from sticking together at all. • Too much water can make a slope unstable.

4. Types of Mass movements • 1. creep: slow, steady downhill flow of loose, weathered materials, especially soils. • 2. flows: Earth materials flow as if they are a thick liquid. Ex. Mudflow • 3. Landslide: rapid, downhill movement of Earth materials that occurs when a thin block of loose soil, rock, and debris separates from the underlying bedrock. • Another type of slide is a rockslide.

5. Still More • 4. slumps: mass of material in a landslide rotates and slides along a curved surface. • Leave crescent shaped scars on slopes. • 5. Avalanche: occur in mountainous areas, thick snow accumulations, and a slope of at least 35 degrees. • Radiation from sun can melt snow, which then refreezes. Snow that falls on top of this can build up, become heavy, slip off and slide causing an avalanche. • 6. Rockfalls: caused by mechanical weathering.

6. Preventing the Risks • Catastrophic mass movements are most common on slopes greater than 25 degrees that experience rainfall of over 90 cm. • Avoid building structures on the slopes. • Trenches to divert running water • Cover steep slopes with steel nets • Retaining walls

7. Wind Erosion and Transport • Wind generally cannot carry particles as big as water can unless it is a strong storm like a tornado or hurricane. • Most areas where wind transport and erosion take place are in areas of limited precipitation and little vegetation. • Ex. Deserts, semi arid areas, seashores • Deflation: lowering of the land surface by wind removal of surface particles. • Abrasion: friction from sand rubbing other materials- wears away (weathers)

8. Types of transport by wind • Suspension: small particles remain suspended in the air for long distances. • Saltation: bouncing motion of particles.

9. Wind deposition • Sand dunes: pile of windblown sand that accumulates on a rock or vegetation as winds blow from one general direction. • Gentler slope is on windward side, and steeper on leeward side. • Dunes average between 12 and 25 meters tall. • Loess: Thick, windblown silt deposits. Jockey’s Ridge in NC

10. Glaciers and erosion • A glacier is a large, moving mass of ice. • Currently cover about 10% of Earth’s surface (2005). • Valley glaciers (high mountains) and continental glaciers. • Glaciers can move rocks that cause abrasion. • Glaciers can cause erosion and make some characteristic features.

11. Glacial Erosion and Deposition features • 1. cirque: scooped out depression from a valley glacier (erosion) • 2. Moraines: ridges of till deposited by glaciers. • 3. Outwash plain: when a glacier melts and begins to recede, the meltwater deposits sediments. • 4. Drumlins:elongated moraine shaped by glacier • 5. Eskers: long winding ridge of sediments deposited by a stream flowing from a melting glacier.