Avalanche studies at Alpental

2004 ISSW abstract

Glide avalanche detection on a smooth rock slope, Snoqualmie Pass, Washington

John Stimberis, Department of Transportation, Snowqualmie Pass, Washington and Charles Rubin, Department of Geological Sciences, Central Washington Univeristy, Ellensburg, Washtington

Glide avalanches involve the full release of the snow pack over a rock slab and are often difficult to forecast. This type ofavalanche release is dependent upon local factors such as elevation, aspect, snow cover, weather conditions, and the presence of free water. Glide rate and acceleration of the snow slab is another determining factor for the eventual release Of the slab. A smooth rock slab, known as Rock Face, is exposed 2.5 km north-northwest of Snoqualmie Pass, Washington adjacent to the Alpental Ski Area. Rock Face, at an elevation of 1055m, has a slope angle of approximately 35° and a northeast aspect.

During the winter of 2003-2004, a continuous recording station was installed at the top of the Rock Face slope. These data will characterize avalanche processes that control the formation and release of the glide avalanches.

Instrumentation includes air temperature, snow temperature, solar intensity, a cable-extension transducerfor measuring glide rate and a geophone that will record the precise time of an avalanche.

During the 2004 field season, preliminary data collection has been successful, although strain measurements of snowpack glide and failure were not obtained. Since two to three full release avalanches per winter occur at Rock Face, the continuous data collectors will record multiple avalanches. By combining observations of time-series of weather data and glide measurements, we will be able to characterize avalanche processes that influence the onset and eventual release of full-depth avalanches.