摘要
Both topography and meteorology control snow avalanching around Svalbard's main settlement Longyearbyen in the High Arctic. Extensive plateau mountains in combination with wind activity in this barren landscape lead to significant cornice accretion preferably on west-facing slopes. These cornices deform, detach and eventually breaking down as cornice fall avalanches, the most observed avalanche type with 45.2 % of the total, in the 2006?009 observation period. Slab avalanches as the second most dominant type (32.6 % ) accounted for the largest observed avalanches (up to 250,000 m3 debris), releasing equally in all aspects. The main triggering mechanism for slab avalanches seems to be additional snow loading as well as distinctive cooling or warming of the upper snow layers. Both mechanisms were caused by daily or weekly air temperature fluctuations, mainly due to winter storm activity, when frequent low-pressure systems passed the islands. These snowstorms resulted in 19 major avalanche cycles, in which 80 % of all observed avalanches released. These avalanche cycles had a minimum of five releases per day, lasting between 1 and 12 days. In total we observed 423 avalanches with an avalanche debris volume of 100 m3 or larger. The majority released between March to May, due to the slow onset of the snow cover in the early snow season, and a lack of direct insolation during the polar night. Cold and stable high-pressure periods, often occurring during the spring months, however, reduced the avalanche activity. We also use our results from this first systematic avalanche quantification to assess how future climate variability will affect the avalanche regime around Longyearbyen. As almost 50 % of all avalanches were cornice fall avalanches, which are topographically controlled, we expect the same avalanche type distribution in the future. As the rest of the avalanches are controlled mainly by the frequency of low-pressure systems, which is projected to decrease in a warming climate, these avalanche occurrences will most likely decrease in amount. Thus cornice fall avalanches will become a more pronounced natural hazard to the infrastructure in Longyearbyen. This first comprehensive analysis of the recent avalanche regime in Svalbard provides an important first step towards the development of an avalanche forecasting service.