Wright Glacier flows down a valley between the mountains bordering Alaska and British Columbia, Canada. —Credit: Photographer unknown. 1948. Wright Glacier: From the Glacier Photograph Collection. Boulder, Colorado USA: National Snow and Ice Data Center. Digital media.

Motion and change define a glacier's life. Glaciers grow and shrink in response to changing climate. Typically, glacier movement occurs 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 can flow quickly, sometimes traveling as much as ten to one hundred times faster than the normal rate of movement. Others may retreat within only a few decades, leaving once glaciated valleys blooming with vegetation again.

By their movement, glaciers mark change. 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 variations.

By comparing contemporary observations with historical and environmental records, such as agricultural records, and prehistoric temperature or climate profiles, glaciologists acquire and provide an enhanced understanding of global processes and change.