Short answer
An ice sheet is enormous land-based glacial ice, such as the Greenland Ice Sheet. An ice shelf is thick floating ice at a coast, often supplied by a glacier or ice sheet as ice flows seaward. The boundary where grounded ice begins to float is crucial. 1 2
An ice sheet is grounded on land; an ice shelf is already floating on ocean water.
On this page
At a glance
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| Question | Ice sheet | Ice shelf |
|---|---|---|
| Support | Land or bedrock | Ocean water |
| Typical position | Continental interior and outlets | Coastal fringe over sea |
| Direct sea-level effect of melting | Land ice can add water to ocean | Floating ice melt has little direct displacement effect |
The table summarizes the cited definitions and the article’s stated scope. 1 2
What each thing is
Ice sheet. A vast mass of glacial ice resting on land and flowing outward under its own weight. 1
Ice shelf. A thick floating plate of ice along a coast, commonly fed by land ice flowing into the ocean. 2
Key differences
Because an ice shelf floats, its direct melting differs from land ice loss. Yet shelves can buttress upstream glaciers, so shelf retreat can indirectly speed land-ice flow into the sea. Grounding lines and flow relationships matter more than the word sheet versus shelf alone. 1 2
How to tell them apart
On a map or diagram, ask whether the ice rests on bedrock or floats over seawater. Thick ice attached to Antarctica that extends offshore can be a shelf; Greenland interior ice is sheet ice. 1 2
Where they overlap
They can be connected parts of one glacial system. Snowfall adds ice and gravity drives movement in both, while their responses to air and ocean warming differ. 1 2
Edge cases
Some ice shelves include sea ice and local snowfall in their formation. An ice tongue may be a narrower floating extension. “Ice shelf” is not the same as thin seasonal sea ice. 1 2
Why the distinction exists
The grounded-versus-floating boundary is central to ice dynamics and sea-level accounting. 1 2
Common misconceptions
Breaking up an ice shelf is not harmless: it can remove support for land ice even though the shelf itself floated before breakup. 1 2
Examples
The Antarctic Ice Sheet lies over the continent. The Ross Ice Shelf projects over the ocean from the Antarctic ice system. 1 2
Sources
Sources checked October 3, 2026.
- National Snow and Ice Data Center — Ice Sheet Science. Formation and movement.
- National Snow and Ice Data Center — Science of Ice Shelves. Formation and floating ice.