lahar
LAH-har
A fast-moving flow of volcanic debris and water — a slurry of mud, rock, ash, and meltwater that pours down the flanks of a volcano with the consistency of wet concrete and the speed of a river in flood. Lahars are triggered by eruptions melting glaciers and snow on a volcano's summit, by heavy rain mobilizing loose ash, or by the collapse of a crater lake. They follow river valleys, filling them wall to wall, and can travel 50 miles or more from the volcano. Lahars are among the deadliest volcanic hazards — more people have been killed by lahars than by lava flows.
Etymology
Javanese, meaning lava or volcanic mudflow. The word entered English through Dutch colonial geological reports from Indonesia.
Notes
Mount Rainier, visible from Seattle and Tacoma, is considered the most dangerous volcano in the United States primarily because of lahar risk — its glaciated flanks and proximity to dense population make a catastrophic lahar virtually certain at some point.
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