| OCR Text |
Show when the charge was increased to 200 kg. The effect was considerably increased by the simultaneous detonation of several charges set along the cornice front In this way it was possible to clear 200- 300 m of slope. The explosives, packed in bags, were set in holes drilled or dug into the cornice. During the winters of 1939- 41, the Apatit Branch of the Snow and Meteorological Service successfully set off avalanches by the bombardment of danger slopes. This method is particularly effective when pre- season trial shots from selected gun and mortar emplacements provide the range and other needed data for firing under any subsequent weather conditions when required, an important point in Chibin where winter visibility is very poor. However, artificial avalanches can be created with certainty only when one is well acquainted with local conditions, which means that this method requires the proper groundwork. Neither explosives or shellfire will set off an avalanche unless it is ready, by virtue of its own condition, to let go. Preventative measures taken beforehand where avalanche danger exists can avoid considerable damage. A prognostication method has been worked out at the Apatit Branch of the Snow and Meteorological Service by I. K. Zeleny, using observation data of the weather station. This method is based on the relationship of the majority of dry snow avalanches to windstorms. An increase in wind velocity to 10 m/ sec, with drifting, is a danger signal.* When an avalanche alarm is given, all outside work is stopped in the danger area; and where the danger is serious, rail traffic is closed down. The alarm is repeated when the windstorm is over, and observations are then made of the danger sites. The forecast percentage for avalanches without reference to exact site is reasonably high. Forecasts of avalanches of dry snow precipitated during still weather are less reliable, and no method has yet been devised for predicting wet snow avalanches. In spite of the multiplicity of defense measures against avalanches, dependent as these are on specific site conditions, none constitutes insurance for any and all districts. Such an insecure locality is Hackmann Gorge in the vicinity of Kirovsk, where avalanches are frequent in the closely adjacent gullies as well as on the slopes below, often overriding one another. The road at the bottom of this gorge is often covered by avalanches for its entire length; even during the summer, some years, avalanche snow reaches a height of 16 m on the road. Dry avalanche snow is usually cleared off a railroad line by snowsweeper. One- way sweepers of " Bull"- type can handle 0.7 m of snow; " Rhinoceros"- type sweepers, 2 m. Several runs have to be made by the sweeper when a considerable extent of track has been blocked. The practical difficulty here is possible derailment of the sweeper where avalanches have displaced or knocked out the rails. Deposits of dry snow are easily removed by Leslie rotary plows ( sweepers). The hazard here is breakage of the rotor fan blades by the stones found even in dumps of loose drifted snow. Snowsweepers have to be used with extreme caution on wet snow, after a thorough inspection of the avalanched snow and the slide slope, because such avalanches in particular are loaded with rock and rubble. * For exactness in forecasting for a given site it is necessary to know the accumulation period for the snow field with the drift direction for the site. - 63- |
