Our Northwest

Avalanches less threatening to motorists today

Friday, January 20, 2017by  Jon Osterberg

workers installing snow netsCross-state drivers ran short on patience this past week when ice storms and avalanches closed sections of Interstate 90, I-84, and I-82. But a look back reveals just how safe winter travel has become in 80 years.

Wednesday's Seattle Times revisited the deadly 1936 Snoqualmie Pass avalanche that killed three people. Drivers were yet to benefit from three innovations, in particular, that make winter travel quite ordinary today.

The original road over Snoqualmie Pass was called the Sunset Highway, built atop an old Indian trail and wagon road. You can still drive it today, two narrow lanes of asphalt winding from Denny Creek Campground up to Alpental.

In 1915, the Milwaukee Road railway abandoned its old route over the pass when its 2.3-mile Snoqualmie Tunnel opened. Because the old railroad grade was gentle and less curvy, highway builders shifted the Sunset Highway across the valley to the abandoned rail bed. Today, it's home to the eastbound lanes of I-90.

In 1931, highway crews kept the highway plowed all winter for the first time, and three years later it was entirely paved from Seattle to the pass.

But the route was not risk-free. Decades earlier, lengthy wood snowsheds had protected trains from avalanches that tumbled down the slopes. But nothing shielded motorists that February day in 1936. More than a mile of the Sunset Highway lay buried beneath more than 10 feet of snow.

concrete snowshed Looking at an old photo of the 1936 avalanche, it appears to have pounded the highway near a steep slope just west of Snoqualmie Pass where, in 1950, roadbuilders constructed a concrete snowshed to protect traffic. (See color postcard.) It was torn down decades later. A smaller snowshed also was built in 1950 alongside Lake Keechelus; it came down in April 2014 as part of the I-90 expansion.

So, about those three innovations that give us safer passage today:

Explosives. When avalanche danger rises, Washington State Department of Highways (WSDOT) workers halt traffic and trigger pre-emptive slides, either with artillery in hard-to-reach snow chutes, or by placing explosives atop slide zones by hand or with trams.

snow nets Snow nets. Made of stout galvanized pipe and steel mesh, snow nets impede the momentum of sliding snow, either blocking it entirely or slowing it so an avalanche stops before reaching the roadway. Hi-Tech Rockfall Construction of Forest Grove, partnering with Atkinson Construction, began installing I-90's avalanche barriers in 2013.

avalanche bridge Avalanche bridges. Rather than build new snowsheds along Lake Keechelus, WSDOT opted to replace them with overpasses that safely carry traffic up and over risky avalanche chutes. The first bridge opened last Aug. 9, and its twin is currently under construction. Now when snow crashes down the mountain, it passes harmlessly underneath the roadway and into the lake.

Photos courtesy Hi-Tech Rockfall Construction, WSDOT

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