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rapid slipping of a mass of earth or rockrock,
aggregation of solid matter composed of one or more of the minerals forming the earth's crust. The scientific study of rocks is called petrology. Rocks are commonly divided, according to their origin, into three major classes—igneous, sedimentary, and metamorphic.
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 from a higher elevation to a lower level under the influence of gravity and water lubrication. More specifically, rockslides are the rapid downhill movement of large masses of rock with little or no hydraulic flow, similar to an avalancheavalanche,
rapidly descending large mass of snow, ice, soil, rock, or mixtures of these materials, sliding or falling in response to the force of gravity. Avalanches, which are natural forms of erosion and often seasonal, are usually classified by their content such as a debris
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. Water-saturated soil or clay on a slope may slide downhill over a period of several hours. Earthflows of this type are usually not serious threats to life because of their slow movement, yet they can cause blockage of roads and do extensive damage to property. Mudflows are more spectacular streams of mud that pour down canyons in mountainous regions during major rainstorms where there is little vegetation to protect hillsides from erosion. The runoff from the storm and mud becomes a thin slurry that funnels down the canyons until it thickens and stops. Earthquakesearthquake,
trembling or shaking movement of the earth's surface. Most earthquakes are minor tremors. Larger earthquakes usually begin with slight tremors but rapidly take the form of one or more violent shocks, and end in vibrations of gradually diminishing force called
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 also may cause landslides by shaking unconsolidated or weathered material from slopes. Rockslides triggered by an earthquake in Montana in 1959 caused an entire mountainside to slide into the Madison River gorge, killing 27 people in its path, damming the gorge, and forming a new lake. Humans have triggered a number of tragic landslides that have caused great damage and loss of life. In the Los Angeles area of California, extensive real estate development carried out on hillsides has resulted in widespread mudflows after winter rains have saturated the over-steepened embankments of soil. In some areas, slow-moving earthflows have been initiated by the lubrication of certain types of underlying clays by septic tank effluent. Submarine slides, or a sliding mix of seawater and sediment, are called turbidity currents. Undersea landslides can travel several hundred miles across very gradual slopes, riding on a thin film of water that reduces friction.



the sliding movement of rock masses down a slope under the action of the force of gravity. Landslides occur on particular segments of an incline or slope as a result of unbalance of the rocks caused by an increase in the steepness of the slope through erosion by water, weakening of the rock by weathering or supersaturation by precipitation and groundwater, seismic shocks, or construction and economic activity carried out without consideration for the geological conditions of the terrain (breaking up slopes by road excavation, excessive watering of gardens and orchards on slopes, and so on).

Landslides most often occur on slopes composed of alternating impervious (clayey) and water-bearing rock (for example, sand and gravel or fissured limestone). The development of landslides is also promoted by types of bedding in which layers are inclined in the direction of the slope or are crossed by fissures going in the same direction. Landslides assume the form of a flow in strongly moistened clayey rock. A landslide is often semicircular in cross section (see Figure 1), forming a depression in the slope that is called the landslide cirque.

Figure 1. Cross section of a landslide

Landslides cause great damage to farmland, industrial enterprises, and populated areas. Reinforcement works and drainage structures are constructed to combat landslides, piles are driven to secure the slopes, and vegetation is planted.


Knorre, M. E., S. K. Abramov, and I. S. Rogozin. Opolzni i mery bor’by s nimi. Moscow, 1951.


The perceptible downward sliding or falling of a relatively dry mass of earth, rock, or combination of the two under the influence of gravity. Also known as landslip.


a. the sliding of a large mass of rock material, soil, etc., down the side of a mountain or cliff
b. the material dislodged in this way
a. an overwhelming electoral victory
b. (as modifier): a landslide win