Landslides are a type of "mass wasting," where soil and rock move down-slope due to gravity.
Landslides can be caused by a combination of factors, such as rainfall, snowmelt, changes in water level, and human activities.
There are five modes of slope movement, including falls, topples, slides, spreads, and flows, which vary depending on the type of geologic material.
Debris flows and rock falls are common types of landslides.
Landslides can also occur underwater, known as submarine landslides, and sometimes cause tsunamis.
Landslides occur when down-slope forces exceed the strength of the earth materials that compose the slope.
Slopes already on the verge of movement are more susceptible to landslides, which can be induced by earthquakes, volcanic activity, and stream erosion.
There are four main types of movement: falls, topples, slides (rotational and translational), and flows.
Landslides can involve just one of these movements or a combination of several.
Geologists also consider the type of material involved in the movement, such as rock, debris, or earth.
Falls are landslides that involve the collapse of material from a cliff or steep slope.
Falls usually involve a mixture of free fall through the air, bouncing, or rolling.
Topple failures involve the forward rotation and movement of a mass of rock, earth, or debris out of a slope.
A topple often results in the formation of a debris cone at the base of the slope, called a talus cone.
A slide-type landslide is a downslope movement of material that occurs along a distinctive rupture or slip surface.
The slip surface in a slide-type landslide tends to be deeper than that of other types of landslides and not structurally controlled.
Slides can be either rotational or translational in nature.
Rotational slides occur when the slip surface is listric (curved or spoon-shaped).
Translational slides occur along a distinctive planar surface of weakness such as a fault, joint, or bedding plane.
Flows are landslides that involve the movement of material down a slope in the form of a fluid.
Different types of flows include mud, debris, and rock (rock avalanches.
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