valley glacier

Smaller than continental glaciers or ice caps, valley glaciers (also called mountain or alpine glaciers or ice streams) originate high in the mountains and, moving a foot or less per day, crawl down valleys, sometimes to the sea. When they retreat, these glaciers leave behind characteristically U-shaped valleys with extremely steep sides. In some valley glaciers, the ice is thousands of feet thick. Outlet valley glaciers, such as the Jakobshavn Isbrae in west Greenland and the Hubbard in Yakutat Bay, Alaska, formed when tongues of ice sheets or ice caps extruded through gaps in mountain ridgelines, then descended into valleys. Alpine valley glaciers, such as the Schwan Glacier in Alaska’s Chugach Mountains, are born in mountain cirques where old snow compacts to firn, then glacial ice, and slides down a valley. Snow avalanching from steep slopes is the chief nourishment of alpine valley glaciers. On a cruise with missionaries in the Chilkat country of southeastern Alaska, John Muir was awed by mountains carved by valley glaciers: “Gloriously arrayed in snow and ice, some of the largest and most river-like of the glaciers [flowed] through wide, high-walled valleys like Yosemite, their sources far back and concealed, others in plain sight, from their highest fountains to the level of the sea” (Travels in Alaska). Not all valley glaciers are riverlike in appearance. Muir describes the glacier named after him, in the east arm of Glacier Bay, Alaska, as “a broad undulating prairie streaked with medial moraines and gashed with crevasses.”

Eva Saulitis