Dirt on Snow Patches

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Abstract
The surfaces of late snow patches in arctic and alpine regions often bear a certain amount of dirt. This dirt varies in character from wholly mineral to largely organic. The constitution of the organic fraction (moss, dead flowers, bulbils, etc.) varies according to the character of the vegetation in the region concerned. The dirt is usually deposited in spring, after general snow melt has set in; it is transported by wind, or rarely by water. Highly organic dirt deposits may have been separated out by winnowing or flotation. The surface of a snow patch shrinks during melting, and this movement carries much of the dirt towards the center of the late snow area. This region therefore receives an especially heavy deposit when the snow patch finally melts. Repeated deposition of dirt in late snow areas affects the vegetation there by burying plants, and by building up a fine, organic soil. The dirt may contain sufficient nitrogen to be of importance under the nitrogen-deficient conditions of arctic lands. Also dirt affects the rate of ablation of the underlying snow, and hence the growing season of the plants.