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Short answer

A glacier is a large, long-lasting mass of ice, snow, rock, sediment and often liquid water that starts on land and moves downslope under its own weight. It forms where snow piles up faster than it melts, so the weight of the snow compresses it into ice. [S1][S2]

Key points

• Glaciers need cold average temperatures, heavy winter snow, and summers that do not melt it all. [S1]
• Ice sheets are glaciers covering more than 50,000 square kilometers. [S2]
• The Greenland ice sheet averages almost a mile thick. [S2]

Claims

• id: C1 claim: A glacier is a large, perennial accumulation of ice and snow on land. source: S1 evidence: "A glacier is a large, perennial accumulation of crystalline ice, snow, rock"
• id: C2 claim: Glaciers form where winter precipitation accumulates significant snow. source: S1 evidence: "winter precipitation produces significant accumulations of snow"
• id: C3 claim: Ice sheets are glaciers covering more than 50,000 square kilometers. source: S2 evidence: "Ice sheets are glaciers that have spread outward to cover an area larger than 50,000"
• id: C4 claim: The Greenland ice sheet averages almost a mile thick. source: S2 evidence: "The Greenland ice sheet averages almost a mile in thickness"

Sources

• [S1] What is a glacier?. USGS. https://www.usgs.gov/faqs/what-a-glacier . License: US government work, public domain. Accessed 2026-11-04.
• [S2] Ice, Snow, and Glaciers and the Water Cycle. USGS. https://www.usgs.gov/special-topics/water-science-school/science/ice-snow-and-glaciers-and-water-cycle . License: US government work, public domain. Accessed 2026-11-04.

License: this note is CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Summary by iinventedlight (AI-assisted).

@misc{iil_note_7ma2tbs7,
  author = {{iinventedlight}},
  title = {{What is a glacier?}},
  howpublished = {iinventedlight Library},
  year = {2026},
  date = {2026-11-04},
  url = {https://iinventedlight.com/library/notes/glacier-basics/},
  note = {Permanent ID iil:note:7ma2tbs7. License: CC-BY-4.0.},
}

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