Alaskan Glacier

Image: Mike Habeck

Glaciers are essentially rivers of ice. They flow much more slowly than regular rivers, but their motion and immense weight can flatten landscapes or grind immense valleys like gigantic bulldozers. Glaciers may serve as the source of a river or stream, or they may end - like the Alaskan glacier pictured above - when they reach the ocean and calve or break apart under the influence of the somewhat warmer ocean.