Snow that falls on Antarctica is gradually compressed, by the weight of the snow that accumulates above it, into ice. This ice flows toward the coast, where it eventually melts or calves (breaks) off into the ocean as icebergs. Most of the ice flows in the form of a large, continuous, slowly moving ice sheet, but in many places drainage basins occur in the ice sheet that contain faster-moving ice streams and their tributaries. The flow dynamics of these systems can be monitored and the findings used to shed light on many phenomena, including global climate change.