OCR Text |
Show It has been known for a long time that avalanche formation is caused by unstable snow conditions on the slope in consequence of overload or the weakening of internal bonds. Zdarsky ( 1929), Selig-man ( 1936), and Flaig ( 1955) have written about this. Tyshinskii and others ( 19^ 9, 1953) have thoroughly discussed this point. The original inhabitants of the Alps, Himalayas, Andes, Caucasus, Altai, Tien- Shan, and other mountain regions were acquainted with the most significant signs of an avalanche hazard such as a heavy snowfall or blizzard, an intense thaw, the appearance of dangerous snow stratigraphy, the formation of cracks in the snow, etc. However, all of these signs are only qualitative estimates of the avalanche hazard. For a quantitative expression of the avalanche hazard, different authors have used relationships for the internal characteristics of the snow. Their results were dependent on specific types of avalanches, peculiarities of the snow cover, and the methods of the study. The majority of the investigators has expressed the avalanche hazard in terms of a comparison of the actual strength of the snow cover with its critical value computed according to a particular formula. Generally, the variables of these formulae are: the critical thickness of the snow cover, the steepness of the slope, the physical-mechanical properties of the snow, the coefficients of friction, and sometimes the dimensions of the snow slab. G. G. Saatchan ( 1936), for example cites the following dependence h - • \ 7 < » where 6 is the snow density ( kg m ) f] is the height of the snow cover ( m) G is the bonding strength of the snow ( kg m ) 71 is the tensile strength of the snow ( kg m" ) y is the coefficient of friction cK is the slope angle ( deg.) I i s the length of the slab ( m) Holding C , " H , and 0 constant for a given type of snow and taking £ * \ oo VY\. , Saatchan constructed a series of equilibrium curves for the snow cover. - 1- |