• An ice shelf is a thick floating platform of ice that forms where a glacier or ice sheet flows down to a coastline and onto the ocean surface.
• Ice shelves are only found in Antarctica, Greenland, Canada and the Russian Arctic.
• The boundary between the floating ice shelf and the grounded (resting on bedrock) ice that feeds it is called the grounding line.
• The thickness of ice shelves ranges from about 100 to 1000 meters.
• In contrast, sea ice is formed on water, is much thinner (typically less than 3m), and forms throughout the Arctic Ocean.
• It also is found in the Southern Ocean around the continent of Antarctica.
• Ice shelves are principally driven by gravity-driven pressure from the grounded ice. That flow continually moves ice from the grounding line to the seaward front of the shelf.
• The primary mechanism of mass loss from ice shelves was thought to have been iceberg calving, in which a chunk of ice breaks off from the seaward front of the shelf.
• A study by NASA and university researchers – published in the June 14, 2013 issue of Science – found however that ocean waters melting the undersides of Antarctic ice shelves are responsible for most of the continent’s ice shelf mass loss.
• Typically, a shelf front will extend forward for years or decades between major calving events.
• Snow accumulation on the upper surface and melting from the lower surface are also important to the mass balance of an ice shelf.
• Ice may also accrete onto the underside of the shelf.
• The density contrast between glacial ice, which is denser than normal ice, and liquid water means that only about 1/9 of the floating ice is above the ocean surface. The world’s largest ice shelves are the Ross Ice Shelf and the Filchner-Ronne Ice Shelf in Antarctica.
• The term captured ice shelf has been used for the ice over a subglacial lake, such as Lake Vostok.

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