Tlic Glacier's Snout. 47 



edly reach deep water. The Taku glacier, close l^y, finds no 

 such support at the opening of its gorge, and therefore discharges 

 into the ^vater as a tide-water glacier. Davidson glacier, Lynn 

 canal, has a termination exactly like that of the Norris. The 

 great Malaspina glacier seems to be merely the united ends of the 

 man}^ large glaciers flowing from the St. Elias alps, expanded on 

 the great plateau which borders these mountains on the south.* 



Tide-water Glaciers.— The Muir glacier is an excellent ex- 

 ample of this class. The inlet into which it pours increases in 

 depth from the sides to not less than 720 feet near the middle ; 

 but the ice is so thick that even this depth is not sufficient to 

 float it. Here we have an entirely different method of waste. 

 The ice breaks ofi' and floats away in the water as icebergs. 

 What is it that regulates the rate at which the ice breaks off? 

 AVhat is the form of the glacier's end below the water ? Alcove, 

 it is practically vertical. I can only give a partial answer to 

 these questions. 



Suppose the end of Muir glacier \vere vertical from top to bot- 

 tom ; let us apply what we know of the motion of glaciers to 

 this case and see what would follow. The more rapid motion 

 of the ujjper part would result in its projection beyond the lower 

 part, and this Avould become greater and greater until its weight 

 was sufficient in itself to break it off. The extent of the projec- 

 tion before a break would occur depends evidently on the 

 strength of ice. The water supports the ice b}^ its buoyancy, so 

 that the weight tending to cause fracture is slightly less than the 

 Aveight of that portion of the ice which is above water. The line 

 of fracture is determined by the position of some crevasse or some 

 irregular melting below the surface. This form seems to be one 

 of stable equilibrium, for if the ice should jDroject too far it would 

 break off, and if it did not project far enough no break would 

 occur until its proper motion had carried it out further. That 

 the ice for several hundred feet below the surface does not in 

 general project further than that above is evident from the fact 

 that I have frequently seen large masses, extending to the very 

 top of the ice-front, shear off" and sink vertically into the water, 

 disappear for some seconds, and then rise again almost to their 

 original height before turning over. If there were any projection 

 within 300 feet of the surface, this mass would have struck it and 



*See Russell, Exp. to Mount St. Elias: Nat. Geog. Mag., vol. iii, 1891, 

 p. 121. 



