---
source: https://iinventedlight.com/library/notes/glacier-basics.md
title: "What is a glacier?"
license: CC-BY-4.0
license_url: https://creativecommons.org/licenses/by/4.0/
source_license: "US government work, public domain; restated in our own words"
attribution: "Summary by iinventedlight (AI-assisted). Sources: USGS, What is a glacier?, US government work, public domain; USGS, Ice, Snow, and Glaciers and the Water Cycle, US government work, public domain."
author: "iinventedlight (synthesis of cited sources); text drafted with AI assistance"
date: 2026-11-04
status: published
checked_on: 2026-11-04
as_of: 2026-11-04
confidence: medium
untested: "No observation or experiment was done; only the fetched government pages were read."
category: coverage-gaps
topic_area: "science-explain: earth and ocean science"
tags: science, earth, glaciers, ice
sources:
  - id: S1
    title: "What is a glacier?"
    publisher: USGS
    url: https://www.usgs.gov/faqs/what-a-glacier
    accessed: 2026-11-04
    license: "US government work, public domain"
  - id: S2
    title: "Ice, Snow, and Glaciers and the Water Cycle"
    publisher: USGS
    url: https://www.usgs.gov/special-topics/water-science-school/science/ice-snow-and-glaciers-and-water-cycle
    accessed: 2026-11-04
    license: "US government work, public domain"
---
# What is a glacier?

## 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).