Earth Science: Origins and Geology – Mass Movements
Avalanches, earthflows, and rockfalls: all over the Earth where the angle of the natural ground slope is exceeded, gravity makes itself felt and starts to flatten, carry away, and level the landscape.
Massive ground movements belong to the processes of large-scale erosion or denudation. This term incorporates all movement initiated by gravity, of rocks, soil, and sediments along the Earth’s surface. Apart from the gradient of a slope, the type of material involved and its water content are also of significance.
Massive dry ground movements mainly occur along steep slopes, for instance in high mountain ranges. Masses of rocks can become loose and crash down into the valley as rockfalls or even as rockslides. Smaller pieces of rock that continue to break loose from rock walls are referred to as falling rocks, which lead to the formation of large taluses.
Mass movements are enhanced by the participation of water. Enormous mud and rubble slides occur in mountainous regions without adequate vegetation cover, especially after severe precipitation. These so-called alpine mudflows can reach speeds of several miles per hour and leave a wide strip of destruction along mountain slopes. In 1970, an earthquake in the Peruvian Andes triggered a major slide, burying 70,000 people under masses of rubble, ice, and mud. The devastating mud avalanches along volcanic cinder cones are referred to as lahars. Snow avalanches also present potential dangers.
They principally develop with the sudden onset of thawing after a particularly heavy snowfall. Soil creeping is the slowest form of mass movement. It is caused by modest precipitation along gentle slopes, which triggers barely noticeable ground displacement over large areas. Since the ground usually remains intact, this movement can only be recognized by minor indicators such as bent tree growth. In permafrost regions, ground movement is referred to as solifluction. This occurs when the onset of thawing weather conditions, brought about by the warming spring sun, causes the upper layers of the ground to lose adhesion to the still frozen layers below.
BASICS
HUMAN INTERFERENCE is partially to blame for the fact that natural events such as rockslides and mudflows increasingly turn into catastrophes.
Mountain regions are being developed for tourism at ever-higher altitudes. Land clearing and road construction have destroyed stabilizing root networks along many mountain slopes.