Guided Notes for Mass Movements Section 8.1

Mass Movement Mass movement is the downslope movement of loose sediments and weathered rock resulting from the force of gravity.

All mass movements occur on slopes, and they can occur anywhere on Earth.

4 Variables can influence mass movements: The material’s weight resulting from gravity, which can pull it downslope. The material’s resistance to sliding or flowing (friction) A trigger, such as an earthquake, that shakes the material loose Water: too little increases potential for movement of loose sediment, and too much increases the weight of sediments.

There are 6 major types of mass movements: 1. Creep: The steady, slow downhill flow of loose, weathered Earth materials, especially soil. The effects of creep are only noticeable over long periods of time. Creep can cause the tilting of utility poles, fences, gravestones, the bending of trees, the cracking of walls, and the breaking of underground pipes.

There are 6 major types of mass movements: 2. Flows: when Earth materials flow as if they were a thick liquid. Earth flows are slow movements of soil, and mudflows are swiftly moving mixtures of mud and water. Mudflows can be triggered by earthquakes or volcanic eruptions, and they are common in sloped, semi-arid regions that experience short, intense rainstorms.

There are 6 major types of mass movements: 3. Slides: a rapid, downslope movement of Earth materials that occurs when a relatively thin block of loose soil, rock and debris separates from the underlying bedrock. Landslides are common on steep slopes. A rockslide is a type of landslide that occurs when a sheet of rock moves downhill on a sliding surface.

There are 6 major types of mass movements: 4. Slumps: when the mass of material in a landslide rotates and slides along a curved surface. Slumps are common after rains. They leave crescent-shaped scars on slopes.

There are 6 major types of mass movements: 5. Avalanches: landslides that occur in mountainous areas with thick accumulations of snow.

There are 6 major types of mass movements: 6. Rock falls: commonly occur at high elevations, in road cuts, and on rocky shorelines. On high cliffs, rocks are loosened by weathering, and fall directly downward, producing a cone-shaped pile of debris called a talus at the base of the cliff. Rock falls do not occur in humid regions.

Human Activity Human activities contribute to the factors that cause mass movements. Examples are constructing heavy buildings, roads, and other structures, especially on or near a steep slope.

Actions that can prevent mass movements include: Digging a series of trenches to divert running water around a slope Covering steep slopes with materials such as steel nets Constructing protective fences at the base of cliffs along highways Installing retaining walls to support the base of weakened slopes Educating people about the problems of building on steep slopes.