Avalanche (adopted from a French dialectic form, avalance, descent), a mass of snow and ice mingled with earth and stones, which rushes down a mountain side, carrying everything before it, and producing a strong wind which uproots trees on each side of its course. Where the supply of snow exceeds the loss by evaporation the surplus descends the mountain sides, slowly in the form of glaciers, or suddenly in ice-falls or in avalanches. A mass of snow may accumulate upon a steep slope and become compacted into ice by pressure, or remain loosely aggregated. When the foundation gives way, owing to the loosening effect of spring rains or from any other cause, the whole mass slides downward. A very small cause will sometimes set a mass of overloaded snow in motion. Thunder or even a loud shout is said to produce this effect when the mass is just poised, and Swiss guides often enjoin absolute silence when crossing dangerous spots.