The Snohomish County Council will consider an emergency moratorium on development in areas at risk of landslides.
Dave Somers, president of the council, said he’ll propose a vote on the six-month ban at a council meeting Wednesday.
Somers, who was in Arlington today during President Obama’s visit to the site of the March 22 mudslide, said the moratorium would apply to new construction throughout the county within a half-mile of landslide hazard areas mapped by the county.
The ban would not halt projects that already have received building permits, Somers said.
The hillside that gave way and destroyed the Steelhead Haven community in Oso had experienced numerous mudslides over the years. But geologists were surprised by the size and speed of the slide that buried the Oso community.
The county considered buying up and emptying property in the Steelhead Drive area — wiped out in the slide — but decided instead to stabilize the base of the slope and leave residents where they were.
While it’s fairly easy to identify landslide-prone slopes, it’s much harder to predict how far slides will travel, University of Washington geomorphologist David Montgomery told The Times earlier this month.
Geologists who analyzed slide risks along the North Fork of the Stillaguamish warned in 1999 that a “large catastrophic failure” was possible. But in the worst-case scenario they deemed most likely, the runout was estimated at less than a quarter of a mile.
“Any geologist who went out there would say, yes, this situation is ripe for a landslide,” said Richard Iverson of the U.S. Geological Survey’s Cascades Volcano Observatory and one of the world’s foremost experts on landslides. “But in my mind, the story isn’t that a landslide occurred, but the type of landslide that occurred.”
He blames the disaster on a combination of unusually wet weather, erosion at the toe of the slide and local geology.