Debris flows are fast-moving mud and rock mixtures that rush down mountainsides. They can be incredibly destructive because they're thick, heavy, and move very quickly. These flows can pick up trees and cars and leave behind big, muddy deposits. Debris flows need steep slopes, loose soil or rock, and enough water to get everything wet and flowing. Heavy rain or melting snow is often the trigger. Sometimes, landslides or volcanic activity can start them too. The biggest disasters, like the ones in Colombia and Venezuela, show how deadly they can be. One type, called a lahar, comes from volcanoes. Another, a jökulhlaup, is a big flood from a glacier. Scientists study these flows to try and predict them, but it's tricky. People build special basins to catch the debris, but it's expensive and not always perfect.
