68 



ALASKA GLACIERS 



flotation. If the glacier rested on a solid support there 

 would be retardation from the friction on its bed, and this 

 resistance would tend, under the laws of glacier motion, 

 to produce a surface gradient. 



If it be true that the ice is floated, then the sea water 

 has access to its under surface, and the rate of melting is 

 greater than would obtain if the front only were exposed. 

 Should an increase take place in the supply of ice from 

 the neve, and consequently in the size and speed of the 

 ice stream, the end of the glacier would be thrust farther 

 out on the water of the bay, but this extension would in- 

 crease the surface exposed to melting, and the loss thus 

 occasioned would soon check the enlargement. The op- 

 posite result would follow a diminution in the supply of 

 ice, and the equilibrium between supply and waste would 

 thus be maintained without great modification of the form 

 and extent of the ice front. There would of course be 

 progressive modification from the silting up of the bay. 

 Direct melting of the under surface of the glacier before 

 the mass is broken up into bergs would tend to localize 

 the deposit of drift, so that the accumulation under the ice 

 would be quite rapid, and eventually the drift floor would 



reach up to the ice 



and subglacial melt- 

 ing would be 

 checked. 



If the glacier 

 floats, its thickness 

 can be estimated 

 from the measure- 

 ment of the visible portion. In water of such density 

 as Reid observed in Glacier Bay, the ice of glaciers 

 floats with about seven-eighths of its mass submerged; 

 and the thickness of the visible portion of the tabular 

 mass in question would be one-eighth of the total thick- 



FIG. 36. 



HYPOTHETIC LONGITUDINAL SECTION OF 

 TURNER GLACIER. 



