Burns, of Portland State, would like to see the USGS gather that kind of baseline information and assess landslide hazards in Western Washington and Oregon in the same way the agency has sized up the risks posed by earthquakes.
“People can go to the computer and find out if they live in a flood plain or what the earthquake hazard is at their home,” Burns said. “But you can’t find out: ‘Where have the landslides occurred in the past? And how do I interpret that?’ ”
One of the key missing pieces is an understanding of why some slopes “go rogue” and fail catastrophically, as happened in Oso, said Stock, of the USGS.
But several studies are underway to help fill in that gap.
USGS scientists have been monitoring coastal bluffs in Oregon for nearly a decade and can now predict when those slopes will start to move based on groundwater levels. A similar project in Seattle led to a rainfall formula used to forecast when slides are likely.
State and local transportation departments across the Northwest regularly monitor unstable slopes above roadways, and can step in to improve drainage or reroute traffic when they see signs of trouble.
There’s also at least one landslide alarm system in Washington. Acoustic sensors along the Puyallup and Carbon River valleys are designed to sound the alert when they detect the ground shaking from a massive landslide called a lahar off the flanks of Mount Rainier.
For the most part, though, slide monitoring in Washington has come after the fact.
After a chunk of coastline peeled off Whidbey Island last year — threatening several homes, including one owned by former Microsoft CEO Steve Ballmer — Island County spent more than $300,000 to analyze the slope and install inclinometers and groundwater sensors.
The Oso slide is now swarming with state and federal geologists. At a cost yet to be determined, they’ve installed instruments to detect any motion that might signal another slide. But instead of protecting homes and residents, the instruments are meant to safeguard the hundreds of emergency responders sifting through the debris for victims.
©2014 The Seattle Times
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GRAPHIC (from MCT Graphics, 202-383-6064): Mudslide monitor