OCR Text |
Show four avalanche stations in the Kirgiz showed that snow did not fall on scores of occasions when the relative humidity achieved 75%, 80%, and even 90%. Thus, the cited relationship between the critical value of total deposition and old snow thickness is questionable and may have been derived by chance; observations in the Kirgiz do not detect such a relationship. Finally, it is incomprehensible how a weather forecast which can neither predict the intensity of the snowfall nor the expected total deposition can possibly determine the date of the critical deposition. Thus, a short survey of the existing methods for determining and forecasting the avalanche hazard shows that Akkouratov's scheme of forecasting by wind transport is the most reliable and accessible This method has almost completely solved the forecast problem in the Khibiny where 80% of all avalanches is caused by wind transport. The problem of avalanche forecasting for other regions in the Soviet Region is still not solved. According to our observations in the Kirgiz ( 1965), 60% of all avalanches is directly related to newly fallen snow and 80 to 85% is directly or indirectly related to periods of snowfall. Unfortunately, the method of Akkouratov is of limited use in the Kirgiz since wind transport accounts for only 10 to 13% of the total. Therefore, the first task of avalanche science in the Kirgiz is to develop methods for forecasting avalanches of freshly fallen snow. This present paper describes a method of avalanche forecasting from snowfall intensity developed by the author and based on observations from four avalanche stations in the Kirgiz over the period 1958 to 1964. M. I. Iveronova ( 1953, 1962) has repeatedly pointed out the role of snowfall intensity in avalanche formation at the crest of the Terskei- Ala- Too in the Tien- Shan. Observations conducted by us in the Tien- Shan and Altai confirmed this idea and an attempt was made to establish a quantitative dependence between snowfall intensity and the time of onset of the avalanche hazard. The following simple equation has been customary for the computation of snow slope stability F S - cS 4- rl S, ( li) where PI^ is the tangential component of force exerted by one square meter of the slab ( kg m " 2 ) , c is the shear strength of the snow ( kg- m *) , S is the area of the base of the slab ( rrr) , n is the • 7- |