Valley Glacier

a glacier that moves down the valley of a mountain river, with the valley determining the shape of the glacier, its character, and the direction of its movement.

Valley glaciers are divided into two morphologically different parts: the upper part—alimentation area, or névé basin, in which the accumulation of matter exceeds ablation—and the lower part, in which ablation exceeds accumulation. The alimentation area usually encompasses the glacial cirque, a dish-shaped expanse at the head of the valley, and sometimes also the flat surfaces adjoining the cirque, the broad saddles of the crest, and the relatively gentle slopes. The ablation area of a valley glacier is also called the glacier tongue. Depending on what part of the valley is occupied by the glacier, valley glaciers are divided into cirque (corrie) glaciers; alpine glaciers, which descend beyond the cirque into one valley; compound, or polysynthetic, glaciers, which form when two or several glacier tongues with independent alimentation areas fuse; and dendritic glaciers, which form when many glaciers from the lateral gorges fuse with the glacier of the main valley. Valley glaciers without névé basins which are fed by avalanches and ice slides from the slopes are called Turkestan-type glaciers; valley glaciers that flow from the névé field on the divide down both sides of the mountain range are diffluent glaciers.

There are also transitional forms between mountain glaciers and ice sheets. These include reticulate or Spitsbergen-type glaciers, which fill a network of connected glacier valleys and have ice caps over the divides, and piedmont or Alaskan-type glaciers, which have separate alimentation and drainage areas and a common ice lobe on the piedmont plain or on the floor of a broad valley. Valley glaciers among ice sheets are termed outlet glaciers.