wasting refers to the transfer, sliding, falling, creeping or flowing of rock
materials produced by the agents of denudation (weathering and erosion down
slope) under the influence of gravity. It is a link between weathering and
transport by agents of erosion. The force of gravity acts constantly on all
rocks and debris. Mass wasting is the downward movement of soil and rock under
the influence of gravity. It is most frequent on slopes above 25 degrees with
little vegetation and annual rainfall over 900mm and often occurs after heavy
storms when soil becomes waterlogged and heavy.
Land Slide A
landslide is the sliding down under force of gravity of a mass of land on a
mountain or hillside. This takes place when large quantities of loosened
surface rocks and soil suddenly slide down a cliff face or valley side. A
landslide may either take the form of sliding or slumping. The latter is common
on slopes made of clay A number of actions may trigger the occurrence of a
landslide. The undercutting of the base of a steep slope by a river or by the
sea and the steeping of a slope by human activities such as quarrying or
clearing up vegetation from a steep slope. An earthquake or prolonged heavy
rains in mountainous areas such as in the Sumatra cause landslides. Buildings
and roads can be buried. When landslides occur in a populated area, loss of
life and property may take place.
Soil Creep This
is the slow downward movement of soil under force of gravity common on all
sloping land. Rainwater enables soil particles slide over each other. Boulders
and stones in the soil, or resting on it, are carried down the slope by the
soil. Other factors, which influence soil creep, include heating and cooling of
soil, alternate wetting and drying of the soil, tramping of grazing animals and
burrowing of animals in the soil. Soil creep can be recognized by fences and
trees that lean down the slope.
is a moving mass of soil made fluid by continued heavy rains on a slope.
Mudflows can take place on desert slopes that are unprotected by vegetation
cover. Other places where mudflows take place are on the slopes of an erupting
volcano when heavy rains fall on the volcanic ash.
is a fast-moving body of sediment particles with water or air or both that
often has the consistency of wet cement. Debris flows occur as a series of
surges lasting from a few seconds to several hours that move at 1 to 20 m/s.
They may flow several kilometers beyond their source areas. Some are powerful
enough to destroy buildings and snap off trees that lie in their path. Mudflows
triggered by water saturating the debris on the sides of volcanoes are called
lahars e.g the debris flow on the volcanic mountain Pinatubo of the