A lahar is a type of mudflow / landslide composed of pyroclastic material and water that flows down from a volcano, typically along a river valley.cite web|url=|title=Lahar|work=USGS Photo Glossary|accessdate=2007-09-02] The term 'lahar' originated in the Javanese language of Indonesia. In Hindi 'lahar' means 'wave'.

Lahars have the consistency of concrete: fluid when moving, then solid when stopped.cite web|url=|title=Lahars and Their Effects|work=USGS Volcano Hazards Program|accessdate=2007-09-02] Lahars can be huge: the Osceola lahar produced 5,600 years ago by Mount Rainier in Washington produced a wall of mud Convert|140|m|ft|-1 deep in the White River canyon and extends over an area of over Convert|330|km2|sqmi|-1 for a total volume of 2.3 cubic kilometers (0.55 cubic miles).cite journal|last=Crandall|first=D.R.|date=1971|title=Postglacial Lahars From Mount Rainier Volcano, Washington |journal=U.S. Geological Survey Professional Paper|volume=677|url=]

Lahars can be extremely dangerous, because of their energy and speed. Large lahars can flow several dozen meters per second and can flow for many kilometres, causing catastrophic destruction in their path.cite journal|url=|title=Volcanic Hazards with Regard to Siting Nuclear-Power Plants in the Pacific Northwest|last=Hoblitt|first=R.P.|coauthors=Miller, C.D., and Scott, W.E.|journal=U.S. Geological Survey Open-File Report|volume=87-297] The lahars from the Nevado del Ruiz eruption in Colombia in 1985 caused the Armero tragedy, which killed an estimated 23,000 when the city of Armero was buried under Convert|5|m|ft|0 of mud and debris. [cite web|url=|title=Deadly Lahars from Nevado del Ruiz, Colombia|work=USGS Volcano Hazards Program|accessdate=2007-09-02] New Zealand's Tangiwai disaster in 1953, where 151 people died after a Christmas Eve express train fell into the Whangaehu River, was caused by a lahar.

Lahars have several possible causes:
* Snow and glaciers can be melted by a pyroclastic flow during an eruption
* A flood caused by a glacier, lake breakout, or heavy rainfall can release a lahar, also called glacier run or jökulhlaup.In particular, although lahars are typically associated with the effects of volcanic activity, lahars can occur even without any current volcanic activity, as long as the conditions are right to cause the collapse and movement of mud originating from existing volcanic ash deposits.

Several mountains in the world, including Mount Rainier in the USA, Mount Ruapehu in New Zealand, and Galunggung in Indonesia, are considered particularly dangerous due to the risk of lahars. Several towns in the Puyallup River valley in Washington state, including Orting, the closest to Mount Rainier, are built on top of lahar deposits that are only about 500 years old. Lahars are predicted to flow through the valley every 500-1,000 years, so Orting, Sumner, Puyallup, Fife, and the Port of Tacoma face considerable risk. The USGS has set up lahar warning sirens in Pierce County, so that people can flee an approaching debris flow.

A lahar warning system has been set up at Mount Ruapehu by the New Zealand Department of Conservation and hailed a success after it successfully alerted officials to an impending lahar on 18 March 2007.

The 1991 Mount Pinatubo eruption caused lahar as well, but it was due to the passing of a major typhoon over the Philippines which resulted in a torrent of volcanic ash and water down to the rivers surrounding the volcano. The lahar was caused by the mixing of settled ash and water from the monsoon which occurred the day after the volcano finished erupting. Although the eruption only killed 6 people, 1500 were killed in the resulting lahar, showing the destructive nature of lahars.

ee also



External links

* [ Schools page about lahars and pyroclastic flows]
* [ USGS web page about lahars]
* [ Mount Rainier Volcano Lahar Warning System]
* [ USGS fact sheet - "Mount Rainier -- Learning to Live with Volcanic Risk"]

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  • Lahar — am Mount St. Helens (März 1982) Der ursprünglich indonesische Begriff Lahar bezeichnet Schlamm und Schuttströme, die von einem Vulkan ausgehen. Dabei mischen sich eruptives Material, zum Teil metergroße Blöcke, mit Lockersedimenten und Wasser. Je …   Deutsch Wikipedia

  • Lahar — sur les pentes du volcan Santa María, au Guatemala, le 14 août 1989. Un lahar est une coulée boueuse d’origine volcanique. Elle est principalement formée d’eau, de cendres volcaniques et de tephras et se rencontre donc le plus souvent sur les… …   Wikipédia en Français

  • lahar — lahár s. n., pl. laháre Trimis de siveco, 10.08.2004. Sursa: Dicţionar ortografic  LAHÁR s.n. (geol.) Curgere noroioasă care apare în cazul unor erupţii vulcanice însoţite de ploi abundente. [< fr. lahar < cuv. indonezian]. Trimis de… …   Dicționar Român

  • Lahar —   [malaiisch] der, s/ s, Mure aus einem Brei von vulkanischer Asche mit Regen oder Schmelzwasser, auch durch Entleerung eines Kratersees verursacht. * * * La|har, der; s s [malai. lahar] (Geol.): bei Vulkanausbrüchen austretender heißer Strom von …   Universal-Lexikon

  • lahar — ● lahar nom masculin (mot javanais) Coulée boueuse de flanc de volcan …   Encyclopédie Universelle

  • lahar — [lä′här΄, lä här′] n. 1. a mudflow down the side of a volcano, containing pieces of hardened lava, ash, etc. 2. the deposit of such a mudflow …   English World dictionary

  • Lahar — Para otros usos de este término, véase Lahar (desambiguación). Lahar tras una erupción, Monte Saint Helens …   Wikipedia Español

  • lahar —    The landform and sediments (i.e., lahar deposit) emplaced by, and the process associated with, a mudflow composed mainly of volcaniclastic debris on or near the flank of a volcano. Sediment composition includes pyroclastic material, primary… …   Glossary of landform and geologic terms

  • lahar — ALASKA VOLCANO OBSERVATORY GLOSSARY An Indonesian term for a debris flow containing angular clasts of volcanic material. For the purposes of this report, a lahar is any type of sedimentwater mixture originating on or from the volcano. Most lahars …   Glossary of volcanic terms

  • lahar — /lah hahr/, n. Geol. 1. a landslide of wet volcanic debris on the side of a volcano. 2. the deposit left by such a landslide. [1925 30; < Javanese: lahar, lava] * * * ▪ volcanic mudflow  mudflow of volcanic material. Lahars may carry all sizes of …   Universalium

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