The avalanche services responsible for road safety are confronted with many questions when heavy snowfall occurs: Have the main avalanches already released? Was the avalanche control successful? Can roads be opened again? It’s also very important for the avalanche forecasters at SLF to receive near real-time information on avalanche occurrences.
If it is dark or the snowfall heavy, it is usually impossible to visually detect whether avalanches have released. While radar systems can automatically record avalanches under such conditions, only a relatively small area can be monitored. FOEN therefore commissioned SLF to evaluate Infrasound Detection of Avalanches (IDA) systems in Frutigen, in Leventina und in Goms. IDA systems have the advantage of being able to record signals up to several kilometers away.
Winters with little snow in 2015/16 and 2016/17
The Head of the Project, Alec van Herwijnen, says: “Avalanches produce low frequency sound waves that cannot be detected by the human ear, so-called infrasounds. It is not, however, easy to distinguish signals generated by avalanches from those with other infrasound sources, such as wind.” To verify the recorded signals, automatic cameras were installed to monitor the surrounding area. In addition, the local avalanche services also document avalanche occurrences.
The tests confirm the hypothesis: the likelihood of recording an avalanche with infrasound is greater the larger the avalanche is, but decreases with distance. Detection worked best with larger dry snow avalanches. Since little snow fell during the last two winters and only a few large avalanches occurred, further measurements are necessary to be able to make a more definite assessment of the performance of IDA systems. (Sara Niedermann, Diagonal 2/17)