Professor: Washington landslide was deep-seated slide

Aerial survey of the Washington mudslide aftermath (Credit: King County Sheriff's Office)

The type of landslide that occurred March 22 in Oso, Wash. appears to be a deep-seated slide, according to a release from Northeastern University.

Tom Sheahan, professor of civil and environmental engineering at the school, says this type of slide usually leaves a concave-shaped surface behind a large debris flow. Beyond that distinction, he says the slide worked much like others.

Sheahan says the driving force in most slides is gravity. Whenever this force overcomes the resistance of soil and rock, a slide occurs. The slide in Oso, he says, was a “perfect storm” because heavy rains soaking into the area’s unusually dry soil created more pull to make the earth unstable.

Image: Aerial survey of the Washington mudslide aftermath (Credit: King County Sheriff’s Office)