Motion and change define a glacier's life. Glacial ice advances, then retreats. Glaciers grow and shrink in response to changing climate. Typically glacier movement and shape shifting occur over long periods of time hundreds to thousands of years), but within historic memory such transformations in fewer than 100 years are not unknown.
Not all glaciers move slowly. For example, surging glaciers experience dramatic increases in flow rate, sometimes traveling as much as ten to one hundred times faster than the normal rate of movement.
By their movement, glaciers mark change and for this reason—among others—scientists study glaciers. By monitoring glaciers over time and around the world, researchers construct valuable records of glacial activity and their response to climate variation.
By comparing contemporary observations with historical and environmental records, such as agricultural records, pre-historic temperature or climate profiles, glaciologists acquire and provide an enhanced understanding of global processes and change.
NSIDC Glacier Photograph Collection - NSIDC archives a Glacier Photograph Collection of historical photos, which includes both aerial and terrestrial photos for the 1880s to 1975. The photos are primarily of Alaskan glaciers, but coverage also includes the Pacific Northwest and Europe.