Glaciers are known as rivers of ice because of the way they slowly flow down mountains or across a landscape. Glaciers move because the ice deforms and flows due to the tug of gravity. As glaciers flow, they mold to the shape of land but also shape the land like an icy bulldozer. The downhill, forward motion grinds and erodes the rocky bed the glacier slides on, forming sediment. Glaciers in cold climates, such as Alaska, can flow all the way to the sea, carving fjords and producing iceberg in the process.

Likewise, ice sheets, which are dome-shaped glaciers larger than 50,000 square kilometers, are constantly flowing downhill propelled by gravity and their own weight. Ice sheets spread outward in all directions from their center which can be 4,000 meters high, causing them to flatten and spread. The speed of an ice sheet’s spread is typically slowest at its center peak—perhaps only a few centimeters a year—to as much as 15 kilometers per year where its edges near a coast.

Scientists study glaciers and ice sheets to understand how topography influence their dynamic movement, analyze ice cores for clues into Earth's past, present, and future, and to track their motion to measure the effects their fresh water and icebergs on wildlife and ocean circulation.

NASA glacier and ice sheet motion data, such as interferograms, allow scientists to visualize and measure the motion of glaciers and ice sheet.