Encyclopedia of Natural Hazards

2013 Edition
| Editors: Peter T. Bobrowsky


  • Richard B. Waitt
Reference work entry
DOI: https://doi.org/10.1007/978-1-4020-4399-4_206


Volcanic mudflow; Debris flow


A lahar is a flowing slurry of rock debris and water originating on the slopes of a volcano. The term may also mean the deposit of such a flow.


Characteristics: Lahars contain grains from clay to large boulders. The flowing material is water-lubricated sand or mud, but the whole mixture maybe more than half of incorporated cobbles and boulders. Volumes can reach 109 m3 and peak discharge may exceed 107 m3/s. Depending on proportions of freshly erupted volcanic debris and snow or water, temperatures range from nearly 100°C to 0°C but are typically below 50°C. Flowing lahars peak swiftly and wane more slowly, passing any one place within minutes to a couple hours but sometimes lasting several hours.

Origin: Lahars can originate by eruption of hot fragmental debris onto snow or ice. A melting mass then flows swiftly downslope, incorporating more and more ash and rock from the volcano’s slopes. Some large lahars initiate from...

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  1. Major, J. J., and Newhall, C. G., 1989. Snow and ice perturbation during historical volcanic eruptions and the formation of lahars and floods. Bulletin of Volcanology, 52, 1–27.CrossRefGoogle Scholar
  2. Pierson, T. C., and Scott, K. M., 1985. Downstream dilution of a lahar – transition from debris flow to hyperconcentrated streamflow. Water Resources Research, 21, 1511–1524.CrossRefGoogle Scholar
  3. Vallance, J. W., 2005. Volcanic debris flows. In Jakob, M., and Hungr, O. (eds.), Debris-Flow Hazards and Related Phenomena. Berlin: Springer, pp. 247–274.CrossRefGoogle Scholar

Copyright information

© Springer-Verlag Berlin Heidelberg 2013

Authors and Affiliations

  1. 1.Cascades Volcano ObservatoryU.S. Geological SurveyVancouverUSA