National Geographic : 1892 Mar 21
H. F. Reid-Studies of Muir Glacier. been overturned so that it could not have arisen vertically out of the water. Let us picture to ourselves what takes place at the end of the glacier, noting first that there are three ways in which the ice breaks away: (a) a piece may break off and fall over-this is the usual way with small pinnacles; (b) a piece may shear off and sink into the water-this is the usual way with the larger masses ; or, again, (c) ice may become detached under water and rise to the surface. The diagrams in figure 2 illustrate what I conceive to be successive forms of the ice-front. They show how, after a number of pieces break off from above, one large piece will break off from below, but, in all probability, not from near the bottom. The broken line shows where the break occurs. The dotted lines show the form of the front just after the last break. n rYYY) c d }_ -I FI URE 2-End of a Tide-water Glacier. In addition to waste by breakage, there is the waste by melt ing. Above the water surface this is unimportant, for there the quantity of ice floated away is much greater than that melted; but near the bottom of the glacier, where the motion is very slow, the melting is the principal, probably the only, cause of waste, for the ice is in contact with water which is probably not very cold* and is, moreover, salt. That the ice does melt * Professor Wright found the surface water in Muir inlet to be 40° F. I did not take the temperature, but I was once much astonished on putting my hand into the water to find it not at all cold, although there was a large amount of ice floating about. This high temperature must be due to the tides and warm winds prevailing here, and to the compara tively warm sea near by.
1892 May 15
1892 Feb 19