Glaciers are essentially giant rivers of ice that are formed over eons as fallen snow is compressed into layers of ice. Glaciers are found on about 10 percent of Earth's land area, with most of them found in the Arctic and Antarctica regions, but some occurring high up on mountains, even in tropical areas. Glacial ice makes up the ice sheets that cover Antarctica and Greenland, with glaciers flowing out to sea, where their ends float on the water as ice shelves. Eventually pieces of the ice shelves break off, or calve, to form icebergs. The movement of glaciers scours the underlying rock, and a glacier's movement can be affected by climate change, with worries that global warming could cause substantial glacial melt and impact global sea levels. For the latest news on glacier research and stunning views of these rivers of ice, see below.