Item: Avalanche activity on us highway 12
Title: Avalanche activity on us highway 12
Proceedings: 2010 International Snow Science Workshop
Authors: Mick A. Riffie Idaho Transportation Dept., Cascade, ID, USA
Abstract: US 12 in Idaho runs east from Lewiston, Idaho to the Montana border at Lolo Pass and on to Missoula. Travelling east of the town of Kooskia, the highway goes eighty miles through largely uninhabited mountainous terrain in the Clearwater National Forest. The route is important for local traffic between Lewiston and Missoula and serves as an alternate for I-90. In February of 2008 several large avalanches released about 30 miles east of Kooskia, and covered both lanes of US 12 as much as 10’ deep, effectively halting traffic. A second storm a week later caused another round of avalanches, this time piling 23’ of debris on the closed road and bringing down several 50 year old trees. While not known as a corridor with great avalanche hazard, workers on US 12 deal with a short path near Lolo Pass that puts debris on the road almost annually. However, none of the highway maintenance personnel on highway 12 could recall any slides in the areas where they occurred in February 2008. Because the highway was not built in the historic travel corridor (Lewis and Clark traveled through this country on ridge-top trails north and west of the Lochsa River) few records of avalanches exist. This poster displays photos of avalanche terrain that had lain “dormant” for forty years, and newspaper articles detailing an event that trapped over forty people between avalanche debris in 1964, two years after the road was opened to the public.
Keywords: avalanche hazard, us highway 12, kooskia