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Show The existence of general avalanche conditions is proved "by the Greeley Hill slide one week earlier. Artificially released by the victim, this slide caused the only avalanche fatality in Altafs reincarnation as a ski area, It would be interesting to have more data, such as total snow depths, and the storm sequences and characteristics. But even without them a pattern begins to emerge which is confirmed by Coal Pit and Argenta. Argenta (Big Cottonwood) History: Prior to 19^8, very little information is available. On Februarys, 1899» 28 slides reached the bottom of Big Cottonwood canyon. It is logical to assume that Argenta was among them. After the 19*4-8 slide, a prospector who had lived in the vicinity for many years stated that he had seen Argenta r\in in even greater volume. However, no dates were given. Argenta ran on March 25, 19^8 at 4:00 p.m. covering the highway 30 feet deep and damming up the stream. A violent storm was in progress. Complete weather data are available for Alta, nearby. A climax avalanche occurred on Mt; Baldy, same exposure as Argenta, on the same date. Terrain data: The release point and accumulation zone of Argenta lie in a bowl near the top of the range which separates Big Cottonwood and Little Cottonwood. The exposure is north and northeast and the location has good vegetative and forest cover. The bowl retains annual slides. A climax avalanche overcoming this barrier forces its way down a winding gully and then issues on to a steep brushy slope which overlooks the highway, The slide path is over a mile long with a difference of nearly 2,000 feet in elevation. Weather data: The following information is taken from the Alta records. The Argenta avalanche took place during a month of excessive snowfall and violent southwest storms. Release came during the fourth major storm of the month. Of these, the last three came on southwesterly winds of critical force. Total snowfall for the month had been 130 inches. Snow depth was 112 inches. Conditions therefore promoted the formation of slabs and cornices on northerly exposures. Normal sloughing and consolidation of the snow pack had $ot taken place. Coal Pit ran exactly a week earlier. Baldy ran on the same day. It was plainly a case of accumulation of an abnormal amount of snow, its weight eventually fracturing the slabs lying one on top of the other. Photographs of the fracture plane of the Baldy avalanche reveal at least three slab layers. Argenta was a slab and dry snow avalanche which was predominantly damp by the time it reached the bottom of the canyon. This was the result of its long travel and the friction developed in the gully. |
