Lots of snow and lots of avalanches: this is what it was like in the Swiss Alps during the winter 2017/2018. During the heavy snowfalls in January 2018, the SLF issued the highest avalanche danger level warning, 5 (very high), for widespread areas in the Swiss Alps. At this danger level, many very large and extremely large spontaneous avalanches can be expected.
Up to now, information on avalanches that have occurred has come from observer reports or helicopter overflights, but for some areas no information is available. Some of the avalanche outlines have been digitized on the basis of photographs, but often only the number and size of the avalanches in an area have been recorded.
In January 2018, SLF researchers were able to use optical satellite data for the first time to document avalanche activity. The images cover an area almost one third the size of Switzerland. Elisabeth Hafner from SLF used the photos to map the outlines of all avalanches in the areas where the highest danger level prevailed, as well as in adjacent areas, recording a total of 18,737 individual avalanches. “The areas in the shade were a challenge in the satellite images. So too were wind structures in the snow, which can look similar to avalanches,” Elisabeth says. Despite these difficulties, no avalanche period has ever been recorded so completely and accurately before. The data is valuable because it allows avalanche warnings to be checked after the event to see whether the assessment of the avalanche danger was correct. The data is also used to validate danger zones and for research purposes. (Sara Niedermann, Diagonal 1/19)