11.2.1 Slumps

It is a form of mass wasting that occurs when a coherent mass of loosely consolidated materials or rock layers moves a short distance down a slope. Movement in slumps, involves the movement of relatively intact masses of rock or sediment downslope along a curved concave upward failure plane, characterized by sliding along a concave-upward or planar surface (figure 1). The upper surface of each slump block remains relatively undisturbed. Causes of slumping include earthquake shocks, thorough wetting, freezing and thawing, undercutting, and loading of a slope. Heavy rains or earthquakes usually trigger slumps.

 

Translational slumps occur when a detached landmass moves along a planar surface. Common planar surfaces of failure include joints or bedding planes, especially where a permeable layer overrides an impermeable surface (figure 2). Block slumps are a type of translational slump, in which one or more related block units move downslope as a relatively coherent mass.

 

 

Figure 1: Damage of electrial line and movement of surface due to Slump failure

 

 

 

Figure 2: Movement of rock mass or sediment downslope along a curved or concave upward.