Swift Creek Landslide - Cause

Cause

Landslides in the Pacific Northwest are caused by a number of reasons. One is the geology of the area; layers of loosely consolidated sediments, such as sand, overlay strongly consolidated (less permeable) layers of sediments such as clays. That, in addition to the large amount of precipitation received in Washington state each year, makes for prime landsliding conditions. Earthquakes are thought to help trigger landslides in the Puget Sound, as well as things such as logging and wave erosion. The Swift Creek Landslide is thought to be a smaller reactivation of an older and larger landslide in that area; perhaps an earthquake set the older, then static landslide into motion.