FLOODS IN SWITZERLAND. 153 



when heavy rains fall upon the less elevated portions 

 of the Alpine snow, they not only melt that snow 

 much more rapidly than the summer sun would do, 

 but they wash down large masses, which add largely 

 to the destructive power of the descending waters. 



The most destructive floods which have occurred in 

 Switzerland have usually been those which take place 

 in early summer. The floods which inundated the 

 plains of Martigny in 1818 were a remarkable instance 

 of the effects which result from the natural damming 

 up of large volumes of water in the upper parts of the 

 Alpine hill - country. The whole of the valley of 

 Bagnes, one of the largest of the lateral branches of 

 the main valley of the Rhone above Geneva, was con- 

 verted into a lake, in the spring of 1818, by the dam- 

 ming up of a narrow pass into which avalanches of 

 snow and ice had been precipitated from a lofty glacier 

 overhanging the bed of the river Dranse. The icy 

 barrier enclosed a lake no less than half a league in 

 length and an eighth of a mile wide, and in places 

 two hundred feet deep. The inhabitants of the neigh- 

 boring villages were terrified by the danger which was 

 to be apprehended from the bursting of the barrier. 

 They cut a gallery seven hundred feet long through 

 the ice, while the waters had as yet risen to but a 

 moderate height ; and when the waters began to flow 

 through this channel, its course was deepened by the 

 melting of the ice, and at length nearly half the con- 



