The recent rains and snow melt continue to lead to more risks of landslides. A landslide is the movement of rock, soil and debris down a hillside or slope. Landslides take lives, destroy homes, businesses, and public buildings, interrupt transportation, undermine bridges, derail train cars, cover marine habitat and damage utilities.
Ground failures that result in landslides occur when gravity overcomes the strength of a slope. While gravity is the primary reason for a landslide, there can be other contributing factors, including:
Saturation, by snowmelt or heavy rains, that weaken rock or soils on slopes.
Erosion by rivers, glaciers, or ocean waves that create over-steepened slopes.
Topography of a slope – its shape, size, degree of slope and drainage.
Stress from earthquakes magnitude 4.0 and greater can cause weak slopes to fail.
Volcanic eruptions that produce loose ash deposits and debris flows.
Excess weight, from accumulation of rain or snow, from stockpiling of rock or ore, from waste piles, or from manmade structures, may stress weak slopes to failure.
Human action, such as construction, logging or road building that disturbs soils and slopes.
Washington is one of the most landslide-prone states in the country, with hundreds to thousands of events each year. The direct cost of landslide damage includes the repair of roads and property and the loss of life. Indirect costs, such as loss of property value and tax revenue, and environmental effects, such as the degradation of water quality, can exceed direct costs. The Washington Department of Transportation routinely budgets $15 million a year for cleanup of landslides on highways. Nationally, landslides exceed $2 billion in loss each year and result in an estimated 25–50 deaths (1996 estimate).
