SUDDEN CHANGES IN GLACIERS. 335 



glacier, named the Rofenthaler, and crossing the valley of the Rofen, where 

 it comes in contact with the opposing wall of rock. In this way a dam is 

 formed, by wliich the waters of the stream are kept back until they have 

 accumulated in sufficient quantity to burst the barrier and overwhelm the 

 valley below. Six such catastrophes are on record as having taken place 

 since about the year 1591). in four of which tlie damage caused by the 

 giving way of the lake barrier was very great. The average interval 

 between the more important oscillations has 1)een eighty-four years, the 

 interval between two of them varying from seventy-three to ninety-three 

 years. The rapidity of the movement of the Vernagt glacier at the time of 

 one of these periods of advance is very great, it having in one day (June 1, 

 1845) amounted to as much as 45.51 meters, or fully six feet per hour. 

 The total amount of motion from November 13, 1843, to June 1, 1845, was 

 1331.4 meters.* 



Another celebrated glacier is that of Devdorok, which descends from the 

 northeastern side of Kasbek, in the Caucasian Range. In this case it is the 

 lower portion of the glacier itself which gives way and rushes down in an 

 avalanche of ice, mud, and granite blocks, causing terrible devastation in the 

 valley below. These occurrences take place at irregular intervals, and there 

 appear to have been ten or more of them during the past hundred years. 

 In the case of the Devdorok glacier, the cause of the sudden descent of the 

 mass seems to be simply that it imbibes so much water from the small 

 streams which run into it in its lower portion, that the mixed ice and water 

 becomes so fluid as to be no longer able to hold up against the force of 

 gravity m'ging it downward.! 



That sudden movements of a similar kind take place in the glaciers of 

 other regions, and perhaps not unfrequently, is to be inferred from accounts 

 given by Nordenskjold of an extraordinarily rapid increase of one of the 

 ice masses on the island of Spitzbergen. This occurrence is thus described 

 by that author: ''In the winter of 1860 -1801 the previously unimportant 

 glacier [entering the Nordfiord] extended itself out over the moraines and 

 the Russian Hill [a low eminence to the northeast of the harbor in which 

 Nordenskjold frequently took refuge, and on which a Russian cross had been 

 set up, near a grave] filled up the harbor, and spread itself far out into the 



* See Dr. M. Stotter, Die Gletscht!r des Veniogttliales in Tirol und ihre Geschichte, Innsbruck, 1S46; and 

 also a very good risumi of the work hy F. F. Tuekett, in the Alpine Journal, Vol. VI. pp. 40, 41. 

 t See, on pp. 324, 325, what has been said in reference to the causes of glacier motion. 



