Mass wasting is the downslope movement of rock and soils under the affect of gravity. Mass wasting can occur very slowly or very suddenly in a matter of seconds. A landslide is a general term that geologists use to describe this downslope movement.

What Triggers A Landslide?

Landslides are the result of several interrelated factors. Degree of slope, nature of the soils/rock, vegetation cover, but most especially excessive water play a role in their development. Water acts as the lubricant in the landslide equation as well as adding additional weight to the scene. A number of somewhat outside factors can trigger landslides. Earthquakes, heavy rains, mining or construction activities are all major agents that trigger landslides.

Types Of Landslides

Landslides are classified based mostly on their character of movement and degree of internal disruption. These landslide classes are rockfall, flow, slide, and creep. Although these are clear divisions, in the real world a landslide may have components of more than one type.

Rockfall

Occurs when a block of coherent material (sediment, soil, rock) falls freely from a steep or undercut bank. This type of landslides is most commonly seen in quarry highwalls, vertical roadcuts, bluffs, and stream cut banks.

Flows

The downslope displacement of incoherent soils or regolith in the manner of a viscous fluid. Flows are a common minor component of slides and falls but in a few cases dominate the mass wasting process. Flows tend to extend well beyond the boundaries of the site of failure.

Rockslides

The downslope displacement of coherent masses of earth material along one or more well-developed failure planes.

Rockslides can further be divided into:

• Rotational slump – where the units (coherent masses) of the slide are few and rotated backward toward the slope.
• Translational slumps are where there are several coherent units displaced in a step-like fashion.
• The carpet slide only involves the near surface upper layers of soil and displaces them like a rumpled rug.
• The block glide is the dislocation of a coherent units along a very shallow plane with little internal disruption or rotation of the blocks.