Fig. 318.—A Greenlandic iceberg after a long journey in warm latitudes.
The exposed cliff is notched and undercut by the waves in the same manner as a rock cliff, and the upper portions override the lower so that at frequent intervals small masses of ice from this front separate on crevasses, and toppling over, fall into the water with picturesque splashes. Such small bergs, whose birth may be often seen at the cliff front of both the Greenland and Alaskan glaciers, have little in common with those great floating islands of ice that are drifted by the winds until, wasted to a fraction only of their former proportions, they reach the lanes of transatlantic travel and become a serious menace to navigation ([Fig. 318]).
Fig. 319.—Diagram showing one way in which northern icebergs may be born from the glacier tongue (after Russell).
Northern icebergs of large dimensions are born either by the lifting of a separated portion of the extended glacier toe lying upon the bottom of the fjord, or else they separate bodily from the cliff itself, apparently where it reaches water sufficiently deep to float it. In either case the buoyancy of the sea water plays a large rôle in its separation.
If derived from the submerged glacier toe ([Fig. 319]), a loud noise is heard before any change is visible, and an instant later the great mass of ice rises out of the water some distance away from the cliff, lifting as it does so a great volume of water which pours off on all sides in thundering cascades and exposes at last a berg of the deepest sapphire blue. The commotion produced in the fjord is prodigious, and a vessel in close proximity is placed in jeopardy.
Even larger bergs are sometimes seen to separate from the ice cliff, in this case an instant before or simultaneously, with a loud report, but such bergs float away with comparatively little commotion in the water.
Fig. 320.—A northern iceberg surrounded by sea ice.
The icebergs of the south polar region are usually built upon a far grander scale than those of the Arctic regions, and are, further, both distinctly tabular in form and bounded by rectangular outlines ([Fig. 321]). Whereas the large bergs of Greenlandic origin are of ice and blue in color, the tabular bergs of Antarctica might better be described as snowbergs, since they are of a blinding whiteness and their visible portions are either compacted snow or alternating thick layers of compact snow and thin ribbons of blue ice, the latter thicker and more abundant toward the base. All such bergs have been derived from the shelf ice and not from the inland ice itself. Blue icebergs which have been derived from the inland ice have been described from the one Antarctic land that has been explored in which that ice descends directly to the sea.