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The Oso Mudslides: Lessons For Oregon

Meeting Date: July 11, 2014

Air Date: July 14, 2014

Landslides are intrinsic to the geology of the Pacific Northwest. Many natural features of this region resulted from slides triggered by weather or seismic activity. Less than 4 months ago, about 350 miles from Eugene, a massive landslide was hard to miss.

The slide near Oso, Washington, took a hillside down to the North Fork of the Stillaguamish River and buried 49 houses above the riverbank. By the end of May, 42 fatalities had been confirmed, making it the deadliest single landslide in U.S. history that was unconnected to a volcanoes, earthquake, or dam collapse.

In 2006, looking at geological evidence of a hazard in the area, Snohomish County officials considered buying out residents, but did not. Home construction continued on the hillside. So did logging, which some say aggravated the risk.

Light radar (LIDAR) and other research methods have produced a wealth of landslide hazard information in recent decades. In 2001, in the aftermath of several fatal landslides, Oregon’s legislature rewrote Land Use Goal 7. This April, Oregon’s Department of Geology and Minerals released a comprehensive report mapping thousands of landslides statewide, including many in Lane County. Whether that report will lead to any further changes in development policy is so far unknown.

Landslides themselves are a hazard alone, and they are also a secondary hazard of earthquakes. An Anchorage neighborhood lost 75 houses in a slide triggered by the 1964 Alaska earthquake. A major earthquake in Oregon could trigger numerous landslides, many in urban areas, and create a need for emergency response greater than existing resources can provide.

Meghan O’Hara was at the Oso disaster for several weeks and will report on what it takes to respond to a landslide. She will also provide an overview of how the region’s disaster response resources stack up against the potential for multiple landslides, and advise of steps we can all take towards the goal of preparedness.

Josh Roering is the principal investigator at the UO’s Earth Surface Processes Laboratory, which studies landslides. He describes how scientists evaluate the data and assess the risk of landslides. His team’s investigations include several Lane County hazard areas. He is familiar with the 1996 Oregon landslides that led to the legislative revision of Goal 7.

copyright, 2014 KLCC