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Show I. ESTIMATION OF THE FORCES OF AVALANCHES FROM THEIR EFFECTS. Immediately after the avalanche catastrophe, which in January of 1954 had overrun the Vorarlberg, the firm Vobag AG., Adliswil, commissioned the EMPA to survey the specific instances of damage, with the objective of obtaining inferences as to the magnitude and direction of the forces operative during the impact of avalanches on obstacles and under the existing circumstances. The analyses were based predominantly upon building damage, in the evaluation of which, the structural engineering experience of the EMPA could be drawn upon. In accordance with the wishes of R. Tschudi, Director of Vobag AG., the knowledge collected and the conclusions drawn therefrom by the observers are reported below. The inspections and surveys, which took place on the 19th and 20th of February and the 2nd of March and their evaluation have been the concern, on behalf of the EMPA, especially of the technical expert, W. Rimathe, in addition to the author. 1. General Information Concerning the snow situation which led to the catastrophe, Forest Engineer Brantner, avalanche adviser for the Bludenz district construction authority for torrent and avalanche control, expressed himself as follows: " Since New Year's low temperatures had retarded a thorough consolidation of the snow cover deposited since 19 December. On 8 January its structure still was characterized by a very weak base layer and zones of loose or wind packed surface layers. On this base, between 9 and 12 January, up to 160 cm of new snow fell with stormy, snow- laden northwest winds. With rising temperature these enormous masses slid, mainly as loose snow avalanches for lack of cohesion to the existing base layer. Unfortunately, I am able to report only limiting values for the snow density. The density was between about 50 to 150 kg/ m3. Also I can report only a little information about the velocities and I can give you only indicative numbers. They might have moved between 20 and 60 meters/ sec." The details from eyewitness observations concerning the catastrophe are unreliable; because of darkness, restricted visibility and snowfall exact observations were not possible. According to the statements of Councilor Wagner in Bregenz, the release zones are not clearly determinable; nevertheless releases, evidently triggered by snowfall, may have occurred even in the timber and produced avalanches. In any case it has been established by the investigation that the avalanche ran through forest with relatively thick underbrush ( for example in Bings). Objective measurements to characterize the snow at the time of the catastrophe were not obtained later. Snow with very little cohesion was probably present at the time of the catastrophe. Figure 1 shows the terrain near Blons and gives a summary of the avalanche situation. The average slope is estimated to be about 30°. The slope of the zone of origin and fracture behind the Dalaas railstation is pictured in Figures 2 and 3. In view of the prevailing meteorological situation on the occasion of the avalanche catastrophe in the Vorarlberg it may be assumed that the snow conditions in the Dalaas district did not differ materially from those in the Gross- Walsertal. U^ VERSiTYOFUTAHUBBAB- ES |