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- 
be 
FIG. 36. 
HYPOTHETIC LONGITUDINAL SECTION OF 
TURNER GLACIER. 
ing would 
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- 
