Types of Landslides

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Slides, Falls, and Flows

The word "landslide" is actually a general term for several kinds of slope movements and they can be classified in several kinds of ways. They can be classified by rate of movement (from several centimeters a year a.k.a. creep...to many miles per hour), type of material (bedrock, unconsolidated sediment, or organic debris) and nature of movement (slide, slump, flow or fall). (Landslides in British Columbia) The following diagrams are courtesy of the Landslides in British Columbia page.

Click here to see a slump landslide in action!

Debris Flows

Debris flows are fast moving flows of mud and rock and they are the most numerous and dangerous of all the landslides. Debris flows generally occur during periods of intense rainfall or snow melt. They usually begin on the top of steep hills with saturated soil as They are so dangerous because they move quickly, destroy without warning, and obliterate everything in their path. They can destroy homes, knock down trees, and obstruct streets and roadways. Their average speed is 10 miles an hour, but some have been known to exceed 35 miles per hour! Their viscosity ranges from thick, rocky mud to water mud. The following are several types of debris flows. (Talking About Disasters)

	Earthflow: The wet ground breaks up and falls down the hillside in a rounded shape. It usually occurs on clay or sand and it is the slowest and driest type of flow.
	Mudflow: Sometimes referred to as a mudslide, a mudflow is when the soil becomes so saturated with water that it speeds down the hill in a muddy river carrying debris. It is the fastest and wettest type of flow. Click on the picture below to see an animation of how fast a mudflow can travel.

The mudflow occured in 1997 in the Sierra Nevadas. It traveled a total of 24 miles and went at a speed of 2-3 mph the first 12 miles and a speed of 12 mph the second 12 miles. (Potential of San Francisco...)

Lahar: "Lahar" is the Indonesian word for a "volcanic debris flow." It is a volcanic, rapidly flowing mudflow that contains rock debris and water. (Volcanoes).

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