Fig. 413.—Map of the Rotmoos glacier, a radiating glacier of Switzerland (after Sonklar).
The horseshoe glacier.—As the glacier draws near to its final extinction, it is crowded hard against the wall of the amphitheater in which it has so long been nourished. Up to this stage it has offered a swelling front outwardly convex as a direct consequence of the laws controlling its flow. No longer amply nourished, for the first time its front is hollowed, and it awaits its final dissolution curled up against the cirque wall ([Fig. 408], stage V, and [Fig. 414]). Practically all the glaciers of the United States and southern Canada are of this type.
The above classification is one depending directly upon glacier nourishment, and hence also upon size, and upon the stage of the glacial hemicycle. In order to determine the type of any glacier it is necessary to know the outlines of the mountain valley—its divide—and those of the glacier or glaciers within it. It is likely that the types of the advancing hemicycle of glaciation would be much the same, save only for the new-born or nivation glacier, which would be as different as possible from the horseshoe type, to which in size it corresponds. Upon the continent of Antarctica, where the absence of any general melting of the ice, even in the summer season and near the sea level, introduces special conditions, some additional glacier types are found, which, however, it is not necessary that we consider here.
Fig. 414.—Outline map of the Asulkan glacier in the Selkirks, a typical horseshoe glacier.
The inherited-basin glacier.—It may be, however, that glaciers have developed, not upon mountains shaped in a cycle of river erosion, nor yet in succession to an ice cap, as in the normal cases which we have considered. On the contrary, glaciers may develop where basins of one sort or another have been inherited from the preceding period. In such cases inherited depressions may become more important than the auto-sculpture of the glacier. Glaciers which develop under such conditions may be described as inherited-basin glaciers.
Fig. 415.—Outline map of the Illecillewaet glacier, an inherited-basin glacier in the Selkirks.