500 GLACIER LAKES. 
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 
gradual advance of glaciers, and the accumulation of great 
masses of water above the obstructions. The ice is finally dis- 
solved 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 1595, about a hundred and fifty lives and a great amount of 
property were lost by the eruption of a lake formed by the 
descent of a glacier into the valley of the Drance, and a similar 
calamity laid waste a considerable extent of soil in the year 
1818. On this latter occasion, the barrier of ice and snow was 
8,000 feet long, 600 thick, and 400 high, and the lake which 
had formed above it contained not less than 800,000,000 cubie 
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 rapidly enlarged it, and before the 
lake was half drained, the barrier gave way and the remaining 
500,000,000 eubic feet of water were discharged in half an 
hour. The recurrence of these floods has since been prevented 
by directing streams of water, warmed by the sun, upon the ice 
in the bed of the valley, and thus thawing it before it aceumnu- 
lates in sufficient mass to form a new barrier and threaten seri- 
ous danger.* 
* In 1845 a similar lake was formed by the extension of the Vernagt glacier. 
When the ice barrier gave way, 3,000,000 cubic yards of water were discharged 
in an hour.—SonKLAR, Die Octathaler Gebirgsgruppe, § 167. 
