484 GLACIER LAKES. 



two parallel tunnels were cut througli tlie intervening rock, and 

 tlie river turned into them. The violence of the current burst 

 up the roof of the tunnels, and, in a very short time, wore the 

 new channel down not less than one hundred feet, and even 

 deepened the former bed at least fifty feet, for a distance of two 

 or tliree miles above the tunnel. The lake was two hundred feet 

 deep at the point where the river was conducted into it, but the 

 gravel and sand carried down by the Kander has formed at its 

 mouth a delta containing more than a hundred acres, which is 

 still advancing at the rate of several yards a year. The Linth, 

 which formerly sent its waters directly to the Lake of Zurich, 

 and often produced very destructive inundations, was turned into 

 the Wallensee about fifty years ago, and in both these cases a 

 great quantity of valuable land was rescued both from flood and 

 from insalubrity. 



Glacier Lakes. 



In Switzerland, the most terrible inundations often result 

 from the damming up of deep valleys by ice-slips or by the grad- 

 ual advance of glaciers, and the accumulation of great masses of 

 water above the obstructions. The ice is finally dissolved by the 

 heat of summer or the flow of warm waters, and when it bursts, 

 the lake formed above is discharged almost in an instant, and all 

 below is swept down to certain destruction. In 1695, about a 

 hundred and fifty lives and a great amount of property were lost 

 by the eru]3tion of a lake formed by the descent of a glacier into 

 the valley of the Drance, and a similar calamity laid waste a con- 

 siderable extent of soil in the year 1818. On this latter occa- 

 sion, the barrier of ice and snow was 3,000 feet long, 600 thick 

 and 400 high, and the lake which had formed above it contained 

 not less than 800,000,000 cubic feet. A tunnel was driven 

 through the ice, and about 300,000,000 cubic feet of water safely 

 drawn off by it ; but the thawing of the walls of the tunnel rap- 

 idly enlarged it, and before the lake was half drained, the bar- 

 rier gave way and the remaining 500,000,000 cubic feet of water 

 were discharged in haK an hour. The recurrence of these floods 

 has since been prevented by directing streams of water, warmed 

 hj the sun, upon the ice in the bed of the valley, and thus thaw* 



