7/2/2023 0 Comments Frozen bubble level 99Compression and geothermal energy sometimes cause the bottom of an ice sheet to be slightly warmer than the ice above it. An ice sheet flows, oozes, and slides over uneven surfaces until it covers everything in its path, including entire valleys, mountains, and plains. They behave plastically, or like a liquid. Ice sheets tend to be slightly dome-shaped and spread out from their center. At this point, the glacier begins to move under its own weight. When the ice grows thick enough-about 50 meters (165 feet)-the firn grains fuse into a huge mass of solid ice. As years go by, layers of firn build on top of each other. The hard snow underneath gets even denser. New snow falls and buries the grainy snow. It slowly changes texture from fluffy powder to a block of hard, round ice pellets. The slightly melted snow gets harder and compresses. Snow accumulates year after year, then melts. How Ice Sheets Form Ice sheets formed like other glaciers. During the last glacial period, however, much of Earth was covered by ice sheets. Today, there are only two ice sheets in the world: the Antarctic ice sheet and the Greenland ice sheet. Making up ice fields, ice caps, and eventually ice sheets are individual glaciers. A series of connected ice caps is called an ice field. A mass of glacial ice covering less area than an ice sheet is called an ice cap. As ice sheets extend to the coast and over the ocean, they become ice shelves. Ice sheets contain about 99% of the freshwater on Earth, and are sometimes called continental glaciers. An ice sheet is a mass of glacial ice more than 50,000 square kilometers (19,000 square miles).
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