Avalanche studies at Alpental

Glide avalanche detection

Rock Face site, Alpental Ski Area

John Stimberis (WDOT) and I are investigating glide avalanche processes at the Alpental Ski area, northwest of Snoqualmie Pass, Washington.

Glide avalanches involve the full release of the snow pack over a rock slab and are often difficult to forecast. This type of avalanche release is dependent on elevation, aspect, snow cover, weather conditions, and the presence of free water at the snow-rock interface. Glide rate and acceleration of the snow slab is another determining factor for the eventual release of the slab.

We are focusing our studies at a site known as Rock Face, a smooth NE-facing 35° rock slab that is exposed 2.5 km N-NW of Snoqualmie Pass, Washington adjacent to the Alpental Ski Area at an elevation of 1055 m.

Experiment design

 Glide avalanches and equipment installation
 2004 winter season at Rock Face, Alpental Ski area
 Rock Face survey, November, 2004, Alpental Ski area
 ISSW 2004 abstract, glide avalanche detection at Snoqualmie Pass, WA

Rock Face, Alpental Ski area

Due to a smooth, steep bed surface, discontinuities in the slope above and below the sliding surface, and ample precipitation (e.g., the presence of free water at the snow-rock interface), glide avalanches commonly occur at Rock Face. A rockstep along the right flank provides additional compressive support to the gliding snowpack. The support, however, is temporary and adds to the challenge of forecasting glide events on at Rock Face.

Aerial photograph showing the location of Rock Face,
ski area boundary, and charlifts.

The annual snowfall at Rock Face exceeds 1150 cm with total precipitation averaging 2300 mm during the winter period (October through May). With a maritime climate, rain-on-snow events average nearly 550 mm during the winter period, typical at an evevatioin of 1055m in the Central Cascade Mountains, Washington State.