Mass Wasting

A 300-meter long slump that occurred in an area of thawing permafrost (2004). Noatak National Preserve, Alaska.

Mass wasting is the movement of rock and soil down slope under the influence of gravity. Rock falls, slumps, and debris flows are all examples of mass wasting. Often lubricated by rainfall or agitated by seismic activity, these events may occur very rapidly and move as a flow. Landslide triggers may include:

• Intense rainfall
• Rapid snowmelt
• Earthquake
• Volcanic eruption
• Stream or coastal erosion

The runout of a mass wasting event depends on the volume of material, water content, and slope steepness.

Diagram of mass wasting processes.

Illustration by Trista L. Thornberry-Ehrlich, Colorado State University.

Rock Fall or Topple

Falling, bouncing, and rolling of debris down slope.

Land Slides and Rock Slides

Debris Flows

A Debris Flow is a type of landslide made up of a mixture of water-saturated rock debris and soil with a consistency similar to wet cement. Debris flows move rapidly downslope under the influence of gravity. Sometimes referred to as earth flows or mud flows.

Avalanche

An avalanche occurs when a mass of rock or ice falls or slides suddenly under the force of gravity.

Slope Creep