CONSIDERATION OF lIYPOTHESKS 28i 



at Yakutat, the nearest inhabited point, report long-continued, terrifying 

 shaking of the ground. Some prospectors ^dlo were in camp near 

 Variegated glacier made a similar report, adding to it the statement that 

 during the most violent shaking the air was filled with noises like thunder, 

 as huge avalanches of snow and rock descended the neighboring moun- 

 tain slopes. 



There can be little, if any, question that during these shocks immense 

 quantities of snow and rock were thrown down from the steep mountain 

 slopes. The snowline descends to within two or three thousand feet of 

 sealevel, and the mountains rise to elevations of from ten to fifteen thou- 

 sand feet, so that the snow-covered slopes occupy a great area (plate 11). 

 By glacial erosion and other forms of denudation the valley slopes 

 have been greatly steepened, and therefore over large areas the snow lies 

 in very unstable positions. Even under ordinary conditions snow ava- 

 lanches may be seen at almost any time among these lofty mountains. 

 This is especially true during and after snowstorms, which are frequent 

 in September, the month during which the earthquake of 1899 occurred. 

 When to this heavy snow blanket, which mantles the steep mountain 

 slopes, is added a repeated shaking of the mountains, it follows that a 

 great and sudden addition to the neve must in all probability have taken 

 place. 



A comparison of the present conditions with photographs taken by Pro- 

 fessor Eussell clearly shows that in some cases, at least, there was a down- 

 shaking of materials from the steep valley slopes, In two cases where 

 these comparisons were possible — the valleys of Black and Galiano gla- 

 ciers — there have been notable changes. In Black Glacier valley extensive 

 areas, which in 1890 were covered with vegetation, are now bare rock. 

 In Galiano valley large patches of snow and ice which clung to the steep 

 slopes in 1890 have now disappeared (compare figures 1 and 2, plate 13), 

 In this valley also the effects of recent great avalanches are still plainly 

 visible, and on Hayden glacier there is an enormous mass of debris which 

 evidently has fallen recently. 



That there was abundant cause for an unusual down-sliding of snow, ice, 

 and rock in 1899, and that this downfalling actually did occur, I believe 

 the above facts amply prove. A notable accession of supply in the neve 

 region, such as these facts indicate, must of necessity start a wave of ad- 

 vance in the glacier, and this wave would naturally be a great one — far 

 more powerful and sudden in its effects than is liable to be produced by 

 normal climatic variations. One possible difficulty in the way of accept- 

 ance of the explanation here proposed is the briefness of time for the 



