Landslides are a major force in weathering the planets of the
solar system. They are a type of erosion called mass movement or mass wasting. Probably
the first step in wearing away the land is mass movement. The pull of gravity enables
loose material to move down a slope. Some mass movements are slow while others are fast.
In either case, weathered fragments move from higher to lower elevations. Eventually,
these materials come to rest at the bottom of the slope. The material that accumulates at
the foot of the hill is called talus. In some areas, gravity works alone to make
material roll, fall, or slide down a slope. In other areas, water helps to move the
material. Water adds weight and makes the fragments slippery. Any process that makes a
slope steeper also aids mass movement.
Many terms are used to describe mass movement. Some terms classify the movements according to the size of material moved downward. Some terms refer to the speed of movement. Landslides are rapid movements of large amount of materials. Sometimes large blocks break away from steep mountain slopes. These masses then move down the slope as a unit or break up into smaller masse. Landslides often follow long periods of rain, or they may be started by earthquake or other types of vibrations. The gradual loosening of a mass of rock takes along time but, landslides can carry millions of metric tons of rock to lower elevations very quickly causing tremendous damage.
Landslides viewed from above have three distinct parts: a head, main body and toe.
The head of a landslide is the spot where the landslide begins and is at the highest elevation. At the head, there are cuts or scarps shaping the hillside. These scarps are curved (concentric) much like the shape of a fingernail clipping. Sometimes, the scarp forms a vertical cliff with a sharp drop off, sometime this cliff collapses leaving a small cliff.
The body of a landslide is between the head and toe. Mostly, it looks lumpy with rolling, bumpy ground, frequent benches (semi-flat spots) and depressions are scattered within it. Sometimes, if the rock and soil is really dry, the body can look like a smooth slope all the way to the toe.
The toe of a landslide is at the very bottom. This is where the landslide has covered over the original land. The toe can spread out thin over a large area if it is very dry or very wet. If it has a medium amount of water in it the toe can have the shape of ..... toes. That is that it can create short lobes which are relatively flat on the top with three steep sides
Diagrammatic sketch of a landslide by David J. Varnes (1978)
For more information on mass wasting look at the more "technical" descriptions of Translational/Rotational Sides; Debris Slides and Debris Flow.