Mudflows, which are like giant moving mud pies, happen when lots of water mixes with soil and rock. The water makes the slippery mass of mud flow quickly down. Mudflows happen most in mountainous places where a long dry season is followed by heavy rains.

How are mudflows caused?

Mudflows can be caused by unusually heavy rains or a sudden thaw. They consist mainly of mud and water plus fragments of rock and other debris, so they often behave like floods.

Where do mudflows commonly happen?

Mudflows can be generated in any climatic regime but are most common in arid and semiarid areas. They may rush down a mountainside at speeds as great as 100 km (60 miles) per hour and can cause great damage to life and property. Boulders as large as houses have been moved by mudflows.