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Vashon Highway, closed near Burton, likely won't reopen until Friday
A large mudslide swept across Vashon Highway just south of Burton early Sunday morning, closing the thoroughfare for nearly a full week while King County road crews clear the debris and stabilize the bank.
The mudslide was triggered by torrential rains all day Saturday and much of Sunday, an early warning of what some say may be in store for the region as it braces for a La Niña event — a weather pattern expected to lead to a particularly wet and stormy winter.
Jim Didricksen, a Vashon-based supervisor with the county’s Roads Division who was on the scene by 5 a.m. Sunday, said a slide of this magnitude is unusual in October. A 50-yard stretch of bank collapsed, bringing down more than 500 cubic yards of debris.
“I’d expect this in November,” he said.
Nearly two inches of rain fell Saturday and Sunday, not a record but still a considerable amount of precipitation, Didricksen added.
“Whenever that happens, something’s going to slide on Vashon,” he said.
The slide occurred on the stretch of Vashon Highway that skirts Quartermaster Harbor south of Burton and north of Shawnee Road.
The span is considered one of the most vulnerable in unincorporated King County. This summer, county road crews worked there for weeks, putting culverts under the road and installing gabion baskets — mesh retaining walls filled with rock — along the base of the bluff.
Debris from Sunday’s slide crushed a portion of the gabion baskets, which will now have to be replaced, Didricksen said.
The mesh walls, Didricksen added, cannot be expected to stop an event such as this one — a slide that began at the top of the bluff. The gabion baskets were installed to help relieve water pressure from springs at the base of the bluff. “They’re really not connected,” he said.
County officials say the road likely won’t reopen until Friday because of the number of trees and stumps that still need to be cleared. On Monday alone, Didricksen said, eight trees had to come down.
“It’s still sliding,” he said of the bank.
The slide is not unusual on Vashon, where clay topped by sand can make for very vulnerable slopes, Didricksen said. What made this slide particularly vexing, he said, are the numbere of trees that are now poised to come down.
“The stumps are bigger than our equipment,” he said. “It’s just a very slow process.”
To find out when the road will reopen, visit http://gismaps.kingcounty.gov/roadalert/PrintView.aspx.