AVALANCHE HAZARD AND DAMAGE SCENARIOS Sample Clauses

AVALANCHE HAZARD AND DAMAGE SCENARIOS. Instabilities in the snow cover and external impacts can cause avalanches at slopes with an angle of Extreme weather situations with heavy snowfall during several days may lead to catastrophic avalanches threatening villages, access roads and railways. Different of avalanches occur depending on the characteristics of the snow pack, the snow volume involved, the slope angle or additional loading. Slab avalanches are most frequent and typically are of moderate size and involve snow masses in the order of a few up to some On a long year average, most fatalities are due to accidental snow slab avalanche releases, initiated locally by mountaineers, or similar leisure activities (in Switzerland 24 out of 26 fatalities). Especially in the last decade only very few people have been on open roads or in settlements (Tschirky, 1998). F Situation at in February 1999. Several dense flow avalanches from both valley sides threatened the Loetschberg railway, the access road and a temporary construction site for the tunnelling work. This annual statistic may drastically change during a winter period with exceptional meteorological and nivological conditions as experienced in January/ February Situations with return periods of several decades may threaten a whole country severely endangering people and their settlements, roads and railways, forest and agricultural landscape. The devastating avalanches of January/ February 1999 were big powder-snow and/or dense avalanches consisting mainly of dry, loose snow, which started to rupture spontaneously under their own The rupture often situated- the base of several snow layers, accumulating a 2 - 4 m thick snow pack. Huge snow masses up to more then 1 were sometimes involved and the resulting avalanches advancing down to vailey level, endangering settlements, roads and railways (Fig.2.1 and 2.2). In addition to direct damages in terms of fatalities, destroyed buildings, devastated forests and landscape, even much more important indirect costs result. These latter are costs due to interrupted roads and railways, failures in the electricity distribution and in communication, reduced accessibility of tourist resorts, and decrease in hotel reservations (Fig.2.3).