Fig. 317.—Tidewater cliff at the front of a glacier tongue from which icebergs are born.
The Antarctic shelf ice.—It has been already pointed out that the inland ice of Antarctica is in part at least surrounded by a thick snow and ice terrace floating upon the sea and rising to heights of more than 150 feet above it ([plate 15 B] and [Fig. 316]). The visible portions of this shelf-ice are of stratified compact snow, and the areas which have thus far been studied are found in bays from which dislodgment is less easily effected. The origin of the shelf ice is believed to be a sea-ice which because not easily detached at the time of the spring “break-up” is thickened in succeeding seasons chiefly by the deposition of precipitated and drifted snow upon its surface, so that it is bowed down under the weight and sunk to greater and greater depths in the water. To some extent, also, it is fed upon its inner margin by overflow of glacier ice from the inland ice masses.
Icebergs and snowbergs and the manner of their birth.—Greenland reveals in the character of its valleys the marks of a large subsidence of the continent—the serpentine inlets or fjords by which its coast is so deeply indented. Into the heads of these fjords the tongues from the inland ice descend generally to the sea level and below. The glacier ice is thus directly attacked by the waves as well as melted in the water, so that it terminates in the fjords in great cliffs of ice ([Fig. 317]). It is also believed to extend beneath the water surface as a long toe resting upon the bottom ([Fig. 319]).
Plate 15.
A. An Antarctic ice foot with boat party landing (after R. F. Scott).
B. A near view of the front of the Great Ross Barrier, Antarctica (after R. F. Scott).
