AVALANCHE (adopted from a French dialect form, ava lance, descent), a mass of snow usually mingled with ice, soil, pebbles and boulders, which rushes down a mountain side destroy ing anything in its path. It often produces a strong wind which uproots trees on each side of its course. Above the snow line where the supply of snow exceeds the loss by evaporation the surplus, partly compacted to ice by pressure descends the moun tain sides either slowly in the form of glaciers, or more swiftly in ice-falls or in avalanches. On steep slopes the foundation easily gives way, owing to the loosening effect of spring rains, the blow ing of the folio or from other causes and the whole mass slides downward. Thunder or even a loud shout is said to be sufficient to set the overloaded snow in motion when the mass is just poised, and Swiss guides often enjoin absolute silence when crossing dangerous spots.