Mass movement is the downslope movement of surface material such as rocks, soil, or mud. These bulk movements are a response to the pull of gravity or the rapid or gradual sinking of the earth's surface. Mass wasting is classified into four main categories based on how quickly the rock and sediments move and how much water there is (Hutchinson, 1968). These include falls, slides, creeps, and flows.
Creeps are gradual mass movements that go on for years or even centuries. One cannot see it happen, but it can be seen from leaning fences and walls. A slide occurs when a section of soil and rock suddenly gives way and moves down a slope. Here, soil, rocks, and water move as a single mass along a slippery slope. Falls occur when rocks and other sediments fall through the air and land at the bottom of a hill. Flows comprise of a mixture of water, rock, and sediment that move very quickly.
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One of the primary causes of mass movements is gravity. It is the driving force of mass wasting since it pulls all things on earth towards the center of the planet. Another potential cause is regional climatic conditions. Humid climates are prone to slides, while drier climates tend to have rock falls (McColl, 2015). Furthermore, mass wasting is prone during springtime when the snow melts, causing massive runoff. The amount of water in the soil is a primary factor in the stability of slopes. The increase of water on the grounds lubricates individual grains decreasing friction, which contributes to mass wasting. Another cause is human activities such as mining and construction.
The threat of mass movement is ever-present since it can be caused by various factors such as human activity, earthquakes, or climate change. Nonetheless, most of the cases occur seasonally due to changes in climate. One region that is susceptible to ever-present mass wasting is California because it lies along various faults. An area prone to seasonal mass movement is Alaska, where the ice caps melt during the summer and spring.
References
Hutchinson, J. N. (1968). Mass movement. Geomorphology , 688-696.
McColl, S. T. (2015). Landslide causes and triggers. In Landslide Hazards, Risks and Disasters (pp. 17-42). Academic Press.
