Mass wasting is the movement of the weathered materials downslope due to gravitational forces accompanied by rain action. Mass wasting also known as slope movement or mass movement. Mass wasting is caused by a number of factors which include the following:
1. Gradient or slope: When the gravitational force acting on a slope exceeds its resisting force, slope failure (mass wasting) occurs. Mass wasting is very common and severe in areas with steep lands as compared to flat or moderately flat lands.
2. Weathering: weathering processes weaken and loosen the rock, hence accelerating the process of mass wasting. For example, oxidation of metallic elements and hydration of the minerals in rocks create lines of fracture and, consequently, the onset of mass wasting.
3. Amount of water present in the rocks: Water can increase or decrease the stability of a slope depending on the amount present. Small amounts of water can strengthen soils because the surface tension of water increases soil cohesion. This allows the soil to resist erosion better than if it were dry. If too much water is present the water acts as lubricating agent, reducing friction, and accelerating the erosion process, resulting in different types of mass wasting (i.e. mudflows, landslides, etc.).
4. Vegetation: The roots of plants help bind the soil particles together making the soil resistant to agents of erosion and weathering. This makes the soil hard to break and hence resistant. Mass wasting processes, such as soil creep, cannot occur easily in soils well-covered with vegetation. Also the mass of vegetation cover blocks and prevents movement of the eroded material. Plants remove water from the ground through absorption. There for absence of vegetation accelerates mass wasting.
5. The nature or type of the rock materials: Clay soil is compact and resistant to various types of soil erosion agents and mass wasting as compared to sandy soil, which is normally loose and easy to remove and transport by water, gravity, wind, etc. Thus, mass wasting may be more severe on sandy soil than its counterpart clay soil under similar prevailing conditions.
6. Overloading: When the soil accumulates in one location as a heavy mass of the rock material, it can be moved either by action of gravitational force or application of just a little force. Landslides occur as a result of the soil accumulated on a sloping land to an extent of exceeding the resistant force of gravity. Movement occurs when the gravitational force exceeds the resistant force of soil material.
7. Earthquakes: Earthquakes cause sections of the mountains and hills to break off and slide down. Earthquake tremors tend to loosen the soil material and make it easy to be removed and transported. It can accelerate rock falls, landslides and soil creeps.
8. Human activities: The activities of man such as cultivation, burning, mining, transportation, animal grazing, etc, removes the soil cover or leads to shaking of the soil.
9. Climate: Climate has a great influence on mass wasting. Areas that receive heavy rains often experience mass movements, such as landslides and soil creep, more often compared to dry areas. On the other hand, a little amount of rainfall does not wet the soil and so cannot cause the soil to move. In cold regions, alternate freezing and thawing triggers mass wasting.
10. Vulcanicity: Volcanic activity often causes huge mudflows when the icy cover of a volcano melts and mixes with the soil to form mud as the magma in the volcano stirs preceding an eruption.