The Landslide Problem

Landslides pose serious threats to roads and structures that support fisheries, tourism, timber harvesting, mining, and energy production as well as general transportation.

Expansion of urban and recreational developments into hillside areas results in ever increasing numbers of residential and commercial properties that are threatened by landslides. Landslides commonly occur in connection with other major natural disasters such as earthquakes, volcanoes, wildfires, and floods.

Effects of these disasters exacerbate relief and reconstruction efforts. Growth of urban areas and expanded land use elsewhere have increased the incidence of landslide disasters.

Debris flows occur wherever lithology and weathering patterns produce ample loose material on steep slopes; periodic heavy rains or rapid snow melt trigger debris flows in these areas. Loss of vegetation and ground cover that occurs during wildfires further enhances debris-flow susceptibility.

Major storms cause widespread flooding and landslide events. Heavy rain (rain on snow at higher elevations) caused thousands of damaging landslides across Washington and Oregon in February 1996; several fatalities resulted from rapidly moving landslides in Oregon.