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

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.

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.

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.

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.

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

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)

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

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

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.

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.