Stress measurements from common snow slope stability tests

Abstract

In the majority of fatal snow avalanches, skiers and snowmobilers trigger the avalanche by applying load to the snow cover. The snow cover is often tested to learn information about its stability on surrounding slopes. This testing is normally performed by digging down into the snow cover, isolating a column of snow, dynamically loading the top of the column and observing fractures that occur in the column due to the loading. Understanding how stress from dynamic surface loads and from loading in common stability tests transmit through the snow cover can help people avoid situations in which they can trigger avalanches. Capacitive sensors were used within the mountain snow cover to measure peak stress below dynamic surface loads and in common stability tests. The sensors were used on 21 field days to collect over 1,605 measurements. We present measured stress data illustrating the effect of isolating a column in stability tests compared to skiing and snowmobiling over a largely undisturbed snow cover. We observed that adjusting the depth of stability tests to account for the penetration depth of snowmobiles loads the snow cover more similarly to the loading applied by snowmobiling. We found that the stress profile in stability tests more closely matched skiing and snowmobiling when the snow cover was softer compared to when the snow cover was harder. Similarly, the differences between the skier and snowmobile loading compared to the stability test loading were increased for a harder snow cover. Finally, in the Extended Column Test, a modern stability test, stress was only measured directly below the loading and not on the opposite side of the column.