Fig. 299.—Map of Greenland showing the area of inland-ice and the routes of different explorers.
The inland ice of Greenland.—In Greenland and in Antarctica the land is almost or quite buried under a cover of snow and ice—the so-called “inland ice”—which always assumes the surface of a very flat dome or shield. In Greenland there is found a marginal ribbon of land generally from five to twenty-five miles in width ([Fig. 299]), but in Antarctica all the land, with the exception of a few mountain peaks, is inwrapped in a mantle of ice which is also extended upon the sea in a broad shelf of snow and ice. Neither of these vast glaciers has been explored except in its marginal portion, yet such is the symmetry of the profiles along the routes traversed, and such the flatness and monotony of the snow surface within the margins, that there is little reason to doubt that the profile made along Nansen’s route in southern Greenland would, save only for magnitude, fairly represent a section across the middle of the continent ([Fig. 300]).
The mountain rampart and its portals.—As soon as we examine the coastal belt we observe that the “Great Ice” of Greenland is held in by a wall of mountains and so prevented from spreading out to its natural surface in the marginal portions. Through portals of the inclosing mountain ranges—the outlets—it sends out tongues of ice which in many respects resemble certain types of mountain glaciers.
Fig. 300.—Profile in natural proportions across the southern end of the continental glacier of Greenland, constructed upon an arc of the earth’s surface and based upon Nansen’s profile corrected by Hess. The marginal portions of the profile are represented below upon a magnified scale in order to bring out the characters of the marginal slopes.
Such measurements as have been made upon the inland ice of Greenland at points back from, but yet comparatively near to, the outlets, show that it has here a surface rate of motion amounting to less than an inch per day, and it is highly probable that at moderate distances from the margin this amount diminishes to zero. Upon the outlets, on the contrary, surface rates as high as 59 feet per day have been measured, and even 100 feet per day has been reported. We are thus justified in saying that glacier flow within the outlets is from 700 to 1000 times as great as it is upon the near-by inland ice, and that the glacier is in a measure drained through the portals of the inclosing ranges. Back from these outlet streams of ice, or tongues, the surface of the inland ice is depressed to form a dimple or “basin of exudation” as is the surface of a reservoir above the raceway when the water is being rapidly drawn away ([Fig. 301]).
Plate 13.
A. Precipitous front of the Bryant glacier outlet of the Greenland inland-ice (after Chamberlin).