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Fact Sheet 0112–95
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Debris-Flow Hazards in the San Francisco Bay Region

Reducing Landslide Hazards in the United States

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Fast moving flows of mud and rock, called debris flows or mudslides, are among the most numerous and dangerous types of landslides in the San Francisco Bay region. When prolonged, intense rain falls on steep hillslopes, the saturated soils can become unstable and move rapidly downhill as debris flows. These catastrophic flows are capable of destroying homes, washing out roads and bridges, sweeping away cars, knocking down trees, and obstructing streams and roadways with thick deposits of mud and rocks.

Past storms that triggered damaging debris flows in the Bay region occurred in 1982, 1986, and 1995. In 1982 alone, thousands of debris flows and other fast-moving landslides caused $66 million in damage and 25 fatalities. As more and more people build in the hills around the Bay region, the potential impact of debris flows on life and property is increasing.

Because debris flows can begin suddenly with little or no warning, it is essential to be prepared. This fact sheet provides some basic information. Illustrations of hazardous areas can help residents assess hazards in their neighborhood. Understanding debris-flow hazards and keeping alert during intense storms can save lives!

Version 1.1 (Revised and abridged November 1997)

Posted 2000

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