Dr. Da Riche Preller — Ice- Avalanche, Gemmi Pass. 105 



curve, while the opposite mountain ridge bears, up to its crest-line, 

 numerous traces of the avalanche having been dashed against it and 

 hurled up to its summit level. 



The remarkable features of this ice-avalanche, and the conclusions 

 which I have drawn from them, may be summed up as follows : — 



1. The rupture of the glacier appears to have been produced 

 by two separate cross-rents, which, during the hot and dry summer, 

 extended and finally joined. The altered condition and appearance 

 of the glacier was noticed from a distance the day before the ice- 

 avalanche. The lower part of the glacier was probably set in 

 motion by the unusually rapid melting of the ice due to the hot 

 southerly wind (Foehn) which blew during the night. The disaster 

 was thus produced essentially by meteorological causes. 



2. In its descent from Altels, the avalanche crashed through, and 

 carried bodily along with it, an extensive plantation, a fact which 

 shows once more, if proof were wanted, that forest plantations are 

 no effectual protection against avalanches. 



3. The avalanche, in its descent, completely cleared the 

 Schwartsbach torrent, which shows that it moved practically as a 

 solid mass. Moreover, in its rebound from the opposite mountain 

 ridge, and in its fall on the Spitalmatte, it buried the Gemmi bridle- 

 path, but stopped short of the torrent, thereby fortunately preventing 

 the formation of a temporary lake which would have endangered the 

 Kander valley below. 



4. The prodigious velocity of the avalanche and the pressure of 

 the column of air displaced by, and pushed in front of it, are attested 

 by a distinct blast-zone of debris, such as the remains of chalets, 

 human bodies, cattle, etc., blown to a considerable height and 

 distance. 



5. The volume of the detached glacier and rock debris, about 

 100,000 square metres and 40 metres in average depth, is about four 

 million cubic metres or tons, which estimate agrees pretty accurately 

 with the volume of debris deposited on the Spitalmatte, viz. about 

 two square kilometres to a depth of two metres. If we consider the 

 avalanche as a moving mass possessing momentum, its kinetic energy 

 is given by the formula — 



weight 



\ m v-, in which v 2 = 2 g h ; or v = V 2 g h ; and m = "To - 



The mean depth of fall (/«), measured vertically, being 3000— 1900m. 

 = 1100m., the kinetic energy was 4400 million metre-tons. Assum- 

 ing that half of this energy was expended in overcoming the various 

 resistances in the descent, the remainder was still more than ample 

 to raise the mass to a height of 400 metres on the other side of the 

 valley. 



6. The velocity of the fall, measured vertically, and without taking 

 into account the various retarding resistances, works out 148 m. 

 (485 ft.) per second, and that of the rise 90 m. (295 ft.) per second. 

 Hence the avalanche, in falling, covered a distance of three kilometres 

 (on an incline of 42 deg., or about 1 in 1) in 20 seconds ; in rising, 

 a distance of one kilometre in 10 seconds ; and in rebounding, also 



