Floods caused by the Bursting of Lakes. 26 



5thly, The bursting of lakes. This takes place in summer, 

 and in elevated regions. The lakes, which are liable to pro- 

 duce debacles*, are formed, 



a. By landslips, as already explained, (p. 4). 



b. By the advance of obtuse cones (p. 15). Every obtuse cone 

 truncated at the base indicates the previous existence of a lake 

 which has burst the barrier and produced a sudden inundation. 

 Above such cones, the traces of lakes are often very apparent. 

 In the verdant spot called the Combe cle Taconaz, situated at the 

 junction of the Taconaz glacier-water widi the Arve, we see ex- 

 tensive terraces which are nearly, if not altogether, upon a level, 

 and which indicate the former height of the water. 



c. By the advance of glaciers and their moraines. The base 

 of every glacier is continually subject either to recede or to ad- 

 vance. In many cases, we now see the glaciers protrude their 

 moraines so as to form mounds across the valleys, and, in some 

 instances, they detain the water flowing from above. This ap- 

 pearance is magnificently displayed before the traveller, who de- 

 scends on the southern side of Mont Blanc through the Allee 

 Blanche. The first glacier boldly throws its rejected earth and 

 stones, so as to meet the opposite mountain, a rapid and copious 

 stream passing underneath the barrier. Next comes the enor- 

 mous refuse of the glacier of Miage, itself a mountain, which, 

 by barring the streams from above, gives origin to the Lake 

 of Combal. Having passed this barrier, we see before us, in 

 the third place, the termination of the glacier of Brenva, whose 

 moraine also forms a vast mound across the valley, but admits 

 the river to pass under it. The well-known debacle in the 

 Valley of Bagnes, A. D. 1818, was the discharge of a lake, caused 

 by the accumulation of ice, which fell from the glacier of 

 Getroz f. The following summer, a similar inundation was oc- 



• It may be proper to observe, that I always use the word DibAcle in its 

 strict sense, and not to denote a great rush of water, however produced. A 

 Debacle is a ru.sli of water, produced by the sudden removal of a barrier. In 

 this sense the word is exjilained, and its etymology given, in Menage, Diet. 

 Etymologique de la Langue Frangaise, v. Bacler and Debacler ° and in 

 this sense it is, I believe, constantly used in those countries where French is 

 spoken. 



t S'jc Edinhuigh I'hil. .Journal, No. 1. A. D. 1810. 



