Aerial survey of the Washington mudslide aftermath (Credit: King County Sheriff's Office)
Experts with the U.S. Geological Survey say Washington state is more prone to landslides than other states because of a combination of factors, according to the New York Times.
Washington ranks alongside California and Oregon as one of the states with the most slides annually. USGS officials say the distinction comes from Washington’s steep terrain, its rain patterns and loose glacial sediment left behind from the last ice age.
Much of this sediment is found in the western part of Washington near Puget Sound, about 60 miles from Oso, Wash. where a slide occurred March 22. State officials believe that a layer of glacial sediment, mostly impermeable clay, kept rainwater trapped near the surface in Oso, making topsoil more prone to saturation and failure.
Image: Aerial survey of the Washington mudslide aftermath (Credit: King County Sheriff’s Office)