Sir,

I read your recent article on snow and avalanches in the Newsletter of the Chicago Mountaineering Club, Vol 13, No. 2, March 1959, and was very interested to note your suggestion that avalanche releases attributed to voices might actually have resulted from propagation of disturbances through the snow for long distances. This coincides with my own opinion, and I thought you might be interested to know that I have from time to time observed evidence of sympathetic or distant avalanche releases in this manner.

Early this winter we observed a striking example here at Alta. A shallow snow cover on north exposures was converted to depth hoar during fair weather in December, and then overloaded by a couple of heavy storms early in January. The avalanche slopes were very unstable, and in one particular case we released a large slab avalanche in the ski area by artillery fire. Adjacent slopes, though not connected ones, also slid with this release, and an observer located further up the valley reported that slides on the opposite side of the mountain also fell at the same time. We were Iater able to trace cracks in the snow through almost all the areas between these slides up to the farthest one about a mile away over the ridge. There seems little doubt that this single artillery shell initiated cracking and release of creep tension over this wide distance, and that wherever the cracks propagated across an open, steep slope, an avalanche was released.

Last winter we had a similar situation on another area, where a single artillery shell released a whole series of slides along about

5 March 1960