702 
PROFESSOR PRESTWICH ON THE ORIGIN 
main Indus, by a vast landslip caused by an earthquake.'" He estimates the lake so 
formed to have been probably about 35 miles long by about 1 mile broad, with a depth 
at the lower end of about 300 feet. The whole was drained in a day. 
Colonel God win-Austen mentions another great flood of the Upper Indus, which 
was caused by the Biafo glacier crossing the transverse valley of the Braldoh, into which 
it descended and abutted on the cliffs on the opposite sided The river usually forces its 
way at the foot of the cliffs, although in places it is completely hidden by the ice; but 
its channel occasionally becomes entirely obstructed, when a broad expanse, extending 
several miles up the valley, is converted into a deep lake. When the waters break 
through their icy barrier, more or less of it is swept away, devastating floods ensue, 
and the lake is in a very brief space of time emptied of its contents. 
Some instances of the bursting of such glacier lakes are also recorded by Mr. Drew. 
The most important was the lake formed in 1850 by the advance of the Tarshing 
glacier across the valley of the Astor, till it abutted on the hill on the opposite side. 
At first the stream flowed under the glacier, but the passage becoming stopped up in 
that year, a lake was formed \\ mile long by mile wide, and with an average depth 
of 100 to 150 feet, and an extreme one of 300 feet. The water, on reaching the top 
of the barrier, burst through and escaped between the ice and the rock on the side, 
producing a disastrous flood which lasted three days. A point of interest to us in 
connexion with this glacier, as bearing upon the compactness which the ice-sheet must 
have acquired in the narrow pent-up Highland valleys, is mentioned by Mr. Drew. 
The glacier, which has now advanced again only part of the way across the valley, is so 
much crevassecl that it is difficult to find a road over it; but when it abutted against 
the opposite hill, the crevasses were closed up, and the glacier was so smooth that 
people used to walk and ride on its surface. 
It is very different with the discharge of lakes of lateral ravines abutting on the 
great glacier of a main valley. The discharge, though often quick, is at other times 
prolonged. A case is recorded by Mr. Drew of a lake of this description, ^ mile 
long, 300 yards wide, and 150 feet deep, which took three days to drain; j while 
another, noticed by Colonel Godwin-Austen, 2 miles long by mile broad, after 
lasting a year and a half, subsided gradually, and took a month to drain away. § 
It is not, however, with the destructive effects of the inundations caused by glacier 
lakes [| that we are at present concerned. The questions we have now to consider are 
the effects that would be produced within the area of the drained basin itself by 
the rapid discharge of the water; or in our case what, in an area recently exposed and 
* ‘ The Jumraoo and Kashmir Territories,’ 1875, p. 417. See also Yigne’s ‘ Travels,’ vol. ii., p. 362. 
t ! Glaciers of the Mustakh Range,’ p. 45. 
% Op. cit., p. 369. 
§ Op. cit., p. 48. 
|| With regard to some analogous phenomena in connexion with the old ice-sheet, see Jamieson in 
Quart. Journ, Geol. Soc., vol. xxx., p. 317, 1874; and ‘The Great Ice Age,’ pp. 230 and 231. 
