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Artificial avalanche triggering

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Artificial avalanche triggering plays a vital role in Switzerland in protecting transport routes, communities and winter sports resorts. By way of controlled explosions, the practice aims temporarily to safeguard possible starting zones, avalanche paths and deposition zones, and to prevent large avalanches and lengthy closures.

 

Numerous methods are employed to release avalanches artificially, including hand charge delivery, the dropping of charges from a helicopter, cannons and permanently installed triggering devices. In every case, the same principle applies – the avalanche is triggered by detonating an explosive charge or gas mixture in the starting zone, which induces a shock wave and thus imposes an additional load on the snowpack. The pressure can initiate a fracture in the weak layer of the snowpack. The fracture then propagates and the slab of snow above the fractured layer is released. Permanently installed explosive systems have become more and more popular in recent years and are now commonplace. They use a charge or gas to produce an explosion above the snowpack and thus initiate the fracture highly efficiently. These systems can be operated from a safe distance, at any time of day, and in any weather. Permanent explosive systems have undergone substantial refinement during the last decade. No fewer than 300 such systems are now installed in Switzerland. To an increasing extent they are being combined with new technologies, such as avalanche detection systems, or warning and alarm systems, for monitoring both the detonation and the endangered area. The choice of delivery method depends, in particular, on the tolerated closure period, residual risk, topographical conditions, timing of execution, required explosive effect and cost. We compare the various explosive techniques and publish our findings. This work helps safety authorities to select the system that best matches their needs.