Short answer
A glacier is a persistent, moving mass of ice on land. An iceberg is a detached piece of land-origin ice floating in water, often after calving from a glacier or ice shelf. Where the ice is connected and supported, versus detached and afloat, is the useful distinction. 1 2 3
An iceberg often begins as part of a glacier or ice shelf, then becomes a detached floating body through calving.
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At a glance
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| Question | Glacier | Iceberg |
|---|---|---|
| Setting | Originates on land and flows | Detached and floating in water |
| Movement | Flows under gravity as a mass | Drifts with water and wind |
| Typical transition | May calve at its edge | May be produced by calving |
The table summarizes the cited definitions and the article’s stated scope. 1 2 3
What each thing is
Glacier. A persistent mass of land ice formed from accumulated snow that moves under its own weight. 1
Iceberg. A large piece of land-origin ice detached from a glacier or ice shelf and floating in water. 3
Key differences
Glaciers form as snow accumulates and compacts over time. Some reach the coast or feed floating ice shelves. When a sufficiently large piece breaks away into water, it can be called an iceberg. An iceberg remains freshwater ice even while floating in salty ocean water. 1 2 3
Snow persists on land, compresses into ice and flows slowly under gravity as a glacier. Where the flowing ice reaches water or feeds an ice shelf, pieces can break away in a process called calving. Once a detached piece floats separately, ocean currents can carry it far from its original glacier. 1 2 3
How to tell them apart
Ask whether the ice is still part of the flowing land-ice system or has broken free and floats independently. A detached chunk that drifts away is an iceberg; a continuous mass flowing from a mountain valley is a glacier. 1 2 3
Where they overlap
They can be made of the same ice. An iceberg can literally have been part of a glacier shortly before it detached. 1 2 3
Edge cases
An ice shelf floats but remains attached to land ice; that is different from an iceberg. Sea ice freezes from ocean water and is not an iceberg merely because it floats. Naming very small calved pieces may use other terms. 1 2 3
An attached ice shelf is already afloat but still part of a larger land-ice system. Sea ice instead forms by freezing seawater and is not reclassified as an iceberg when it breaks into floes. For very small fragments of calved ice, specialist naming can differ from the ordinary “iceberg” label. 1 2 3
Why the distinction exists
The terms track origin and physical state. That separation helps describe ice flow, calving and hazards at sea. 1 2 3
Common misconceptions
An iceberg is not simply any frozen ocean surface. Sea ice and calved land ice have different origins. 1 2 3
Examples
A coastal glacier reaches water; a large fragment breaks off and drifts away. Before separation it belonged to the glacier system; afterward it is an iceberg. 1 2 3
Sources
Sources checked October 3, 2026.
- U.S. Geological Survey — What is a glacier?. Main definition.
- National Snow and Ice Data Center — Glacier Quick Facts. Quick facts.
- National Snow and Ice Data Center — The Science of Ice Shelves. Calving and floating ice.