Oso Slide Was No Outlier, UW Study Concludes

SEATTLE (AP) — A new study from the University of Washington finds that the devastating Oso landslide in 2014 wasn't an outlier.

The landslide wiped out neighborhood north of Seattle and left 43 people dead when it roared down a hillside above the north fork of the Stillaguamish River. It was the deadliest landslide in U.S. history.

University geologists used radiocarbon dating of woody debris buried in earlier slides as well as a review of erosion characteristics to help map the history of landslides in the area. They found that slopes in the area have collapsed every 500 years, and with even greater frequency in the past millennium: every 140 years or so.

The authors say the study disproves the notion that the previous slides in the area all occurred thousands of years ago after the ice sheets retreated.