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Tree-ring dating in several avalanche tracks in Galena Creek valley, northern Absaroka Mountains, Wyoming, is used to determine the frequency of large snow avalanches that pass below the forest line. The following criteria are used: (1) datable scars on the trees, (2) changes in growth-ring pattern from concentric to eccentric, caused by tilting, (3) changes in growth rate due to increase in photosynthesis when adjacent trees are destroyed, and (4) age of trees within a given reforested avalanche track. The first two of these criteria are most reliable.

Many young trees within the avalanche tracks are protected by snow during avalanches, and they thus survive to reforest the track immediately following destruction of the larger trees.

Above the forest line, avalanche boulder tongues are one of the most reliable indicators of persistent activity in alpine regions, for they are formed over a period of many years by the accumulation of debris swept out of avalanche chutes. A peculiar linear feature on the surface of the tongues is the avalanche debris tail, which consists of fine debris that was deposited by large snow avalanches downslope 5 to 10 m from a large boulder. They are thought to be formed by a mechanism similar to that by which sand shadows are formed in the lee of obstacles in river channels or on desert dunes.

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