Posted: 30 April 2001

Descent of a mass of earth and rock down a mountain slope. Landslides may occur when water from rain and melting snow sinks through the earth on top of a slope, seeps through cracks and pore spaces in underlying sandstone, and encounters a bed of shale inclined towards the valley. The water collects along the upper surface of the shale, which it softens to form slippery clay. If the support is sufficiently weakened, a mass of earth and rock slides down along the well-lubricated bedding of shale. Some great landslide masses move slowly and spasmodically for years, causing little destruction."Landslide," Microsoft® Encarta® Online Encyclopedia 2001 © 1997-2001 Microsoft Corporation. All rights reserved.