Landslides occur in all U.S. states and territories. In a landslide, masses of rock, earth or debris move down a slope. Landslides may be small or large, slow or rapid. They are activated by storms, earthquakes, volcanic eruptions, fires and human modification of land.
Debris and mud flows are rivers of rock, earth, and other debris saturated with water. They develop when water rapidly accumulates in the ground, during heavy rainfall or rapid snowmelt, changing the earth into a flowing river of mud or “slurry.” They can flow rapidly, striking with little or no warning at avalanche speeds. They can also travel several miles from their source, growing in size as they pick up trees, boulders, cars, and other materials.
Landslide problems can be caused by land mismanagement, particularly in mountain, canyon, and coastal regions. Land-use zoning, professional inspections and proper design can minimize many landslide, mudflow and debris flow problems.