AVALANCHES, the name given to those im mense masses -of snow Which are precipitated from the Alps, and which villages in'their destrukive course. When . the snow begins to melt by the heat of summer, the water which is produced runs 'below, and deitrbys adhesion between the snow. and the -earth, and -a new snow sometimes falling upon the older Mass, increases its weight and determines its fall. These masses are-often detached by the impulse of the wind; .and the inha bitants of the Alps are so convinced that the least sound will produce their fall, -that they take •off the bells from their mules ; -and when the avalanches are too slow in falling- at places where -they are.precipi tated annually, the inhabitants endeavour to accele rate their fall by the report of their muskets. 'These avalanches sometimes occasion dreadful hurricanes. In the winter of 1769, 1.770, an avalanche produced by the immense quantity of snow .which 'had fallen, rolled down 'upon the pastures on the mountain of Sixt in the -Alps. The impulse which was given to the air by the fall of this huge mass was so dreadful, that it levelled with the ground a forest of beeches and firs, which covered the declivity of the mountain, stopped the course of the river Gipre which runs through the subjacent valley, and overthrew a num ber of trees and barns on the opposite shore of the stream.
" The snow which falls above the superior li mit of congelation," says Mr Leslie, " from its powdery and incohcsive quality, is incapable of much accumulation: loosened by the imprcssiou of the sun, it slides down, and, gathering force in its i descent, it often precipitates itself in those danger But I consider glaciers themselves as formed only by avalanches of a rarer and more formidable ,kind. The icy zone will accumulate till its weight at last overcomes its cohesion ; then giving way, it will rush down the side of the mountain with irresistible sweep, and spread its shi vered fragments. This statement agrees with the phenomena, and explains the reason why glaciers are not observed among -the Andes." Experimental In gdiry, &c. note xxv.p..537, 510. See GLACIER. (o)