This image shows the remains of a lahar on the slopes of Mt. Akutan in Alaska.
Click on image for full size
Image from: U.S. Geological Survey, photo by Robert McGimsey
Lahars are mudslides caused by the mixing of volcanic ash and debris with water. They can occur when the heat from a volcano melts snow and ice on the volcano's summit, or if an eruption disturbs a crater lake.
Lahars can cause great environmental and economic damage. They can cover fertile fields and topple buildings. Trees, boulders, and other debris which lahars pick up can shear off anything they flow by at ground level.
Lahars are very dangerous, and anyone caught in the path of one is in great danger of death from severe crushing injuries.
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