How do lahars move so fast down a volcano’s slopes?
Quick Answer
Lahars are fast-moving flows of water, ash, rock, and debris that rush down valleys like wet concrete. They can travel tens of kilometers and be triggered by rain, melting snow, or eruptions.
The Full Story
A lahar is a volcanic mudflow made from water mixed with loose volcanic material. Once it starts, it can behave like a dense slurry that follows river valleys and sweeps away bridges, roads, and buildings. Lahars can form during eruptions when heat melts snow and ice, or later when heavy rain reworks ash deposits. The 1985 Nevado del Ruiz disaster in Colombia showed how deadly they can be, with the lahar burying the town of Armero. Because they move through channels, valleys near volcanoes are especially vulnerable.
Key Facts
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