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From Simple English Wikipedia, the free encyclopedia
A lahar from the 1982 eruption of Galunggung.
Mailboxes caught in a mudflow following the May 1980 Mount St. Helens volcanic eruption.

A mudflow or mudslide occurs when mud travels down a slope very quickly. Mudflows, which are like giant moving mud pies, happen when lots of water mixes with soil and rock. The water makes the slippery mass of mud flow quickly down. Mudflows happen most in mountainous places where a long dry season is followed by heavy rains.

Mudflows of volcanic eruptions are the most dangerous, and are called lahars. A lahar is a type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris, and water. The material flows down from a volcano, typically along a river valley.[1] Lahars can move as quickly as 80km/h and are as thick as liquid concrete.

Lahars have several possible causes:[2]

Lahars can occur without volcanic activity, if conditions are right for the collapse and movement of mud from existing volcanic ash deposits.

  • Snow and glaciers can melt during periods of mild weather
  • Earthquakes underneath or close to the volcano can shake material loose and cause it to collapse triggering a lahar avalanche.
  • Rainfall or typhoons can cause slabs of solidified mud to come rushing down the slopes, with devastating results.

References[change | change source]

  1. "Lahar". USGS Photo Glossary. Retrieved 2009-04-19.
  2. "Lahars and their effects". USGS Volcano Hazards Program. Archived from the original on 2007-08-24. Retrieved 2007-09-02.