Mass Wasting

• Mass wasting is the process of downslope movement of rock, regolith, sand and soil under the influence of gravity.
• Volcanic eruptions are events that cause mass wasting processes.
• Volcanic eruptions produce shocks, causing the production of large volumes of water from melting of glaciers during eruption, resulting in mudflows and debris flows.
• Mass wasting is also known as mass movement or slope movement.
• Factors influencing mass wasting include shear force, shear resistance, normal force, and gravitational force.
• Excess moisture in soil increases pore pressure, reducing shear strength.
• Low moisture in soil also reduces shear strength.
• Grain flow forms in dry or nearly dry granular sediment with air filling the pore spaces such as sand flowing down the dune face.
• Granular flow contains low amounts of water, 0-20% water, and fluid-like behavior is possible by mixing with air.
• Earth flow involves fine-grained material such as clay and silt and is usually associated with heavy rains or snowmelt.
• Debris avalanche is a very high velocity flow involving huge masses of falling rocks, debris, soil, and trapped air racing down in very steep mountain ranges.
• Intermediate moisture in soil causes soil to stick together, resulting in highest shear strength.
• Debris flow results from heavy rains causing soil and regolith to be saturated with water, and is composed mostly of volcanic materials on the flanks of volcanoes are called lahars.
• Creep is the slowest type of mass wasting requiring several years of gradual movement to have a pronounced effect on the slope.
• Mud flow is a highly fluid, high velocity mixture of sediment and water, and can start as a muddy stream that becomes a moving dam of mud and rubble.
• Types of mass wasting include slope failures, slump, rock fall and debris fall, rock slide and debris slide, landslide, sediment flow, and debris avalanche.
• Slope failures are sudden failures of the slope that result in the transport of debris downhill by sliding, rolling, and slumping.
• Slump is a type of slide wherein downward rotation of rock or regolith occurs along a curved surface.
• Rock fall and debris fall are the result of free falling of bodies of rocks that break loose or a mixture of rock, regolith, and soil in the case of debris fall.
• Rock slide and debris slide involve the quick displacement of masses of rock or debris along an inclined surface.
• Landslide is a type of mass movement from a sudden rapid event in which large quantities of rock and soil plunge down steep slopes.
• Slurry flow is a water-saturated flow which contains 20-40% water; above 40% water content, slurry flows grade into streams.
• Solifluction is common wherever water cannot escape from the saturated surface layer by infiltrating to deeper levels; it creates lobes and sheets of debris.