[ l a n d s l i d e s   :   g l o s s a r y ]

Below are definitions of important landslide terms.

• angle of rest: angle at which material will remain stable
• angle of repose: angle at which material will remain stable
• avalanche: a massive fall of ice and snow
• debris basin: a concrete, bowl-shaped pit built on a mountainside to catch debris from mud and rock slides
• earthflow: when the wet ground breaks up and falls down a mountainside, making a rounded, tongue-like shape; usually occurs on clay, silt, or sand; the slowest, driest flow of weathered material down a hillside
• erosion: the natural wearing away or weathering of rocks or soil
• quicksand: a mass of loose, wet sand that becomes fluid when suddenly vibrated; heavy objects will sink into it
• landslide: a sudden collapse of a large mass of hillside; the falling of masses of earth or rock
• mass movement: the downhill movement of rock and weathered material
• mudflow: when a slope is so heavily saturated with water that it rushes downhill as a muddy river, carrying down debris and spreading out at the base of the slope; the fastest, wettest flow of weathered material down a hillside
• rock fall: when fragments break away from the face of a steep slope and fall
• rock slide: similar to rock falls, except they take place on lower slopes, closer to inhabited areas, and are thus more dangerous
• sinkholes: rapid and sudden manifestations of subsidence most frequently experienced in areas underlain by gypsum or limestone substrata
• slumping: the slow and gradual slippage of all layers of soil so that the bottom of a hillside becomes level with the lowlands or even tipped upward
• soil creep: the gradual downhill slide of weathered material; the slow, gradual movement of a hill’s upper layers caused by the pull of gravity on loose stones, gravel, and soft topsoil
• subsidence: the vertical fall of earth, usually caused by the loss of underground water or gas support, sometimes resulting from man-made pumping and sometimes from seismic action

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