What is a glacier?

A glacier is a large, perennial accumulation of crystalline ice, snow, rock, sediment, and often liquid water that originates on land and moves down slope under the influence of its own weight and gravity. Typically, glaciers exist and may even form in areas where:

  1. mean annual temperatures are close to the freezing point
  2. winter precipitation produces significant accumulations of snow
  3. temperatures throughout the rest of the year do not result in the complete loss of the previous winter’s snow accumulation

Over multiple decades this continuing accumulation of snow results in the presence of a large enough mass of snow for the metamorphism from snow to glacier ice process to begin. Glaciers are classified by their size (i.e. ice sheet, ice cap, valley glacier, cirque glacier), location, and thermal regime (i.e., polar vs. temperate). Glaciers are sensitive indicators of changing climate.

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How would sea level change if glaciers melted?

If all of the glacier ice on Earth were to melt, sea level would rise ~ 80 m (~ 265 ft), flooding every coastal city on the planet. If all of Earth’s temperate glaciers melted, sea level would rise ~ 0.3–0.6 m (~ 1-2 ft). If all of Greenland’s glaciers melted, sea level would rise ~ 6 m (~ 20 ft). If all of Antarctica’s glaciers melted, sea level...

What is a Benchmark Glacier?

“ Benchmark Glacier ” refers to four North American glaciers that have been selected for long-term glacier monitoring that investigates climate, glacier geometry, glacier mass balance, glacier motion, and stream runoff. They are Gulkana Glacier and Wolverine Glacier in Alaska, South Cascade Glacier in Washington, and Sperry Glacier in Montana.

How do we know glaciers are shrinking?

In addition to qualitative methods like Repeat Photography , USGS scientists collect quantitative measurements of glacier area and mass balance to track how some glaciers are retreating ( Glacier Monitoring Studies ). For example, ablation stakes show the seasonal gain and loss of snow, snow-pit analyses measure density of snow, and precision GPS...

Is there a size criterion for a glacier?

While there is no global standard for what size a body of ice must be to be considered a glacier, USGS scientists in Glacier National Park use the commonly accepted guideline of 0.1 square kilometers (about 25 acres) as the minimum size of a glacier. Below this size, ice is generally stagnant and does not have enough mass to move.
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Image: Denali Fault: Canwell Glacier
November 9, 2002

Denali Fault: Canwell Glacier

Peter Haeussler prepares to measure the offset of a crevasse on the Canwell Glacier.

Image: Matanuska Glacier

Matanuska Glacier

Matanuska Glacier, Alaska