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 move rapidly down the slopes of a volcano as channelized flows and deliver large amounts of sediment to the rivers and streams that drain the volcano. The flow velocity of some lahars may be as high as 20 to 40 meters per second and sediment concentrations of greater than 750,000 parts per million are not uncommon. Large volume lahars can travel great distances if they have an appreciable clay content (greater than 3 to 5 percent), remain confined to a stream channel, and do not significantly gain sediment while losing water. Thus, they may affect areas many tens to hundreds of kilometers downstream from a volcano.
The Indonesian term for a debris flow or a mudflow originating on a volcano (Harris, 2000, p. 1301). Lahars are generally composed of volcanic materials, but can contain significant amounts of non-volcanic materials derived from erosion during flow. Most volcanologists prefer this term to be used for the process and not the sedimentary deposits that it forms, but unfortunately, this distinction has been largely ignored in the geological literature. Many lahars are composed of sand and coarser materials, and thus, can be distinguished from "mudflows" which predominantly contain silt- or clay-sized grains (Rodolfo, 2000, p. 973).
Lahar is an Indonesian word for a rapidly flowing mixture of rock debris and water that originates on the slopes of a volcano. Lahars are also referred to as volcanic mudflows or debris flows. They form in a variety of ways, chiefly by the rapid melting of snow and ice by pyroclastic flows, intense rainfall on loose volcanic rock deposits, breakout of a lake dammed by volcanic deposits, and as a consequence of debris avalanches.
Photograph by J.N. Marso on 14 August 1989
A small lahar triggered by rainfall rushes down the Nima II River near the town of El Palmar in Guatemala in the image shown here. The lahar developed on the slopes of Santiaguito volcano.

Glossary of volcanic terms. - University of Wisconsin Oshkosh. . 2001.

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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 — A light weight soft crepe made of fine cotton warp and silk weft in Bombay and Madras on hand looms, plain weave …   Dictionary of the English textile terms

  • 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 — 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… …   Wikipedia

  • 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

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