MASS MOVEMENT (WASTING)

MASS MOVEMENT (WASTING)

Mass Movement (wasting) is the spontaneous downhill movement of weathered rock particles and other materials under the force of gravity. Everywhere on earth, gravity pulls continually on all materials. Such materials include clay, silt, sand particles which are collectively referred to as residual overburden or regolith. There are the topsoil or solum upon the overburden where the grasses, shrubs and trees grows which also move along during the process of mass movement.

Gravity is very important in mass movement, but it can play its role only when the material overcomes its initial resistance to movement. The materials that are involved in the process of mass movement (wasting) are usually variable and the larger these materials are the more immediate and pronounced the effect of the movement.
Movements may be slow and gradual or sudden and rapid. The sudden and rapid movement of materials down slope are catastrophic in effect because they may lead to the devastation to human life and property. Plummer and his team, (staff of the U.S. Geological survey department) maintained that more people died from landslides in the year 1985 alone than the number that was lost during the previous twenty years from other geological hazards.

Facilitators (factors) of Mass Movement (Wasting)
There are conditions which must prevail before mass movement can take place. It is these conditions that are termed facilitators because they facilitate the processes of the mass movements. These conditions (facilitators) include:

Water
Water as a facilitator plays the role of a lubricant in mass movement. Sudden accession of water could be through heavy rainfall as the case in the tropical lands and owing rapid melting of snow in temperate lands. This water is capable of fluiding the debris sufficiently to move downhill. The water reduces cohesion of the materials and add weight to it. Water therefore plays three vital roles of lubrication, weight addition to the debris and loss in the degree of cohesion of material. These roles therefore facilitate down-slope movement of the materials.

Tectonic instability
Weathered material arid even bedrocks lie upon tectonic plates. Crustal disturbance such as earth quake, earth tremor, volcanic eruption and regional tilting create instability of the tectonic plates. These cause the overlying material to shake and become loose. This loose material therefore moves as mass down slope.

The Structure and Types of Material
Some geological structures are particularly conducive to mass movement. For example, areas which consist of flat-lying sediments and which have strata that are permeable, water accumulates above the impermeable layers and the depth of the regolith. This water lubricates the impermeable layer surface and the weathered material upon it and these leads to a downward movement of the mass along the slope.

Relief and Slope
The relief of an area is another factor that facilitates mass movement. Elevated areas normally create a slope and where such a slope is gentle, the
chances of mass movement occurrence is less. But with a steeper slope, the chances of slope failure which causes movement are greater. As such, steep slopes are prone to mass movement. The only possible stability which a steep slope could offer is when there is the presence of vegetation cover along such a slope. The vegetation checks the downward movement of the overlying regolith along the slope by fixing the individual particles together because the roots serve as a wedge.

Ground ice
In the temperate latitudes, water percolates into shallow surfaces in the soil and this is where it freezes. The soil and other rock fragments that overly this frozen water become frozen during the winter periods. When warmer conditions set in during summer, the ice sheets melt. Instability is created in the overlying mass and it begins to move vertically under the influence of gravity as solifluction.
Micro and micro-organisms
Vegetation cover