Mass Movement Notes PDF

Mass Movement Notes What Happened Here? Mass Movement A mass movement is the downslope movement of soil and weathered rock resulting from the force of gravity. Climate has a major effect on the weathering activities that occur in a particular area, climatic conditions determine the size an...

Mass Movement Notes What Happened Here? Mass Movement A mass movement is the downslope movement of soil and weathered rock resulting from the force of gravity. Climate has a major effect on the weathering activities that occur in a particular area, climatic conditions determine the size and scale of mass movement. 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. Factors that influence Mass Movements 01 Material’s weight 02 Material’s resistance The material’s weight which Which depends on the amount works to pull the material of friction, how cohesive the downslope. material is, and whether the material is anchored to bedrock. 03 A Trigger 04 Water such as an earthquake, that Water increases the weight of shakes materials loose. soils and sediments, which pulls material downslope, and water reduces friction between grain molecules.  Types of Mass Movements Creep slow, steady, downhill flow of loose, weathered Earth materials, especially soils. The effects of creep are usually noticeable only over long periods of time. One way to tell whether or creep has occurred is to observe the positions of structures and objects. Types of Mass Movements Earthflows moderately slow movements of soils, whereas mudflows are swiftly moving mixtures of mud and water. Mudflows can be triggered by earthquakes or similar vibrations. common in sloped, semi-arid regions that experience intense, short-lived rainstorms. especially destructive in areas where urban development has spread to the bases of mountainous areas. 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.  Types of Mass Movements Landslide A rapid, downslope movement of Earth materials that occurs when a relatively thin block of soil, rock, and debris separates from the underlying bedrock 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. Types of Mass Movements Landslides A slump results when the mass of material in a landslide moves along a curved surface. Slumps are common after rains, when water reduces the frictional contact between grains of soil and it acts as a lubricant between layers. Avalanches are landslides that occur in mountainous areas with thick accumulations of snow. Occur when snow that falls on an icy crust builds up, becomes heavy, slips off, and slides downslope.  Types of Mass Movements Rockfalls Occur when rocks that are loosened by physical weathering, including plant growth, break up and fall directly downward. Commonly occur at high elevations, in steep road cuts, and on rocky shorelines.