Fig. 224.—Ice-caps of small size. The figure also shows some valley glaciers extending out from the main ice-sheet and from the local ice-caps. A portion of the North Greenland coast, north of Inglefield Gulf. Lat. about 78°. (Peary.)
Fig. 225.—Small ice-caps in the northwestern part of Iceland. (Thoraddsen’s geological map of Iceland.)
Fig. 226.—A glacial lobe, midway between an ice-cap and a valley glacier. A protrusion from a local ice-cap east of Cape York, Greenland.
If both the surface on which the ice-sheet develops and its surroundings be essentially plane, as may happen in high latitudes, and if the snow- and ice-field be symmetrical in shape, the outward movement will be approximately equal in all directions, and the area covered by the spreading ice-field will remain more or less circular. If the ice-field rests on a steeply inclined surface, like a mountain slope, the movement becomes one-sided in conformity to the slope. If the surface, otherwise plane, be affected by valleys parallel to the direction of movement, the ice in the valleys will be deeper than that on the divides between them, and its movement stronger. In the valleys, therefore, the ice will advance farther than elsewhere before being melted, and the outline of the ice will become lobate, the lobes occupying the depressions. These general relations are shown in Figs. [224] and [225]. If the depressions be wide and shallow, the lobes will be broad and short ([Fig. 226]); if the depressions be narrow and deep, the lobes will be relatively narrow and Long. If the snow and ice rest on a surface consisting chiefly of steep valleys and sharp ridges, as is common on mountain slopes, the snow and ice are chiefly gathered in the valleys, and take a linear form.
TYPES OF GLACIERS.
These different forms give rise to different terms. The ice which spreads with some approach to equality in all directions from a center is a glacier, is indeed the type of the greatest glaciers, but is commonly called an ice-cap. The same name is applied to any glacier in which there is movement in all directions from the center, even though its shape departs widely from a circle. The glacier covering the larger part of Greenland ([Fig. 222]) is a good example of a large ice-cap, and the glaciers on some of the flat-topped peninsular promontories of the same island are good examples of small ones ([Fig. 224]). If ice-caps cover a large part of a continent, as some of those of the past have done, they are often called continental glaciers.
Fig. 227.—Characteristic end of a North Greenland (Bryant) glacier.