Our Northwest

I-90 mudslide bad, but entire highway washed out in 1959

Thursday, February 16, 2017by  Jon Osterberg

Heavy rainfall has triggered mudslides that closed several roads Thursday around the Northwest, most notably westbound I-90 east of Issaquah.

Thirteen cars got stuck when trees, rocks, and mud flowed across all four westbound lanes. Other Thursday mudslides closed roads in Puyallup, Tacoma, Renton, and Seattle.

February is on pace to break rainfall records in Seattle. Residents busy dodging peril on our roadways also should note that mudslides generally are excluded from coverage by insurance companies. But we can offer tips for how to make your property less vulnerable.

Severe as the I-90 mudslide is, it pales when compared with the November 1959 deluge that swelled the South Fork Snoqualmie River and washed away all four lanes 10 miles east of North Bend.

Five inches of warm rain fell in one day, melting 14 inches of Cascades snow that gushed downhill and choked the river with uprooted trees and brush.

road washed out by Snoqualmie River The highway, newly widened to four lanes at the time, was called U.S. 10 in those pre-interstate years. It took emergency roadbuilders 18 days to reroute the river and construct a two-lane detour around the 1,400-foot washout.

Our family went skiing at Snoqualmie Summit in December 1959, and though I was just 5, I vividly recall the chaotic, messy scene and feeling tense as dad drove over the detour that included a wobbly bridge.

road washed out by Snoqualmie River Working nearly around the clock, contractors filled the washed-out chasm with riprap (large boulders) and permanently relocated the four-lane highway north of the old U.S. 10 roadbed. You can spot the area today, notable for a broad swath of riprap that shields I-90 from the river near exit 42.

Photos courtesy WSDOT

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