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A lahar travels down a river valley in Guatemala near the Santa Maria volcano, 1989. A lahar (/ ˈ l ɑː h ɑːr /, from Javanese: ꦮ꧀ꦭꦲꦂ) is a violent type of mudflow or debris flow composed of a slurry of pyroclastic material, rocky debris and water.
A lahar is a debris flow related in some way to volcanic activity, either directly as a result of an eruption, or indirectly by the collapse of loose material on the flanks of a volcano. A variety of phenomena may trigger a lahar, including melting of glacial ice, sector collapse , intense rainfall on loose pyroclastic material, or the outburst ...
The high temperatures can burn flammable materials in the flow's path, including wood, vegetation, and buildings. Alternately, when an eruption has contact with snow, crater lakes, or wet soil in large amounts, water mixing into the flow can create lahars, [4] which pose significant known risks worldwide.
Lahars can result from heavy rainfall during or before the eruption or interaction with ice and snow. Meltwater mixes with volcanic debris causing a fast moving mudflow. Lahars are typically about 60% sediment and 40% water. [40] Depending on the abundance of volcanic debris the lahar can be fluid or thick like concrete. [41]
Other types of mudflows include lahars (involving fine-grained pyroclastic deposits on the flanks of volcanoes) and jökulhlaups (outbursts from under glaciers or icecaps). [6] A statutory definition of "flood-related mudslide" appears in the United States' National Flood Insurance Act of 1968, as amended, codified at 42 USC Sections 4001 and ...
A lahar is a volcanic mudflow or landslide. The 1953 Tangiwai disaster was caused by a lahar, as was the 1985 Armero tragedy in which the town of Armero was buried and an estimated 23,000 people were killed. [citation needed] Volcanoes rated at 8 (the highest level) on the volcanic explosivity index are known as supervolcanoes.
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Tephra is a generalized word for the various bits of debris launched out of a volcano during an eruption, regardless of their size. [4] Pyroclastic materials are generally categorized according to size: dust measures at <1/8 mm, ash is 1/8–2 mm, cinders are 2–64 mm, and bombs and blocks are both >64 mm. [5] Different hazards are associated with the different kinds of pyroclastic materials.