Glacier

To describe glaciers, they “are defined as ice masses that move under their own weight, and currently cover ~ 10% of the land surface of the Earth” [1]. The National Geographic Society [2] also states that glaciers are ‘often called “rivers of ice,”' and that glaciers fall into two groups: alpine glaciers and ice sheets. When it comes to glacier formation, “for a glacier to form, snowfall is the first step in the formation of glacier ice,” and “as snow builds up, snowflakes are packed into grains, and the weight of the overlying snow causes the grains below to become coarser and larger (dense grains known as firn), followed by melted snow quickly refreezing, forming ice” [3]. Ultimately, as the Alaska Satellite Facility (ASF)[3] notes, “how the snow changes and how much time it takes to develop into glacier ice depends on the temperature.”

Of the two major glaciers, alpine glaciers are those that are “pulled by gravity and move slowly down a valley" and some of these alpine glaciers, "called hanging glaciers, don't flow the entire length of a mountain." On the other hand, ice sheets “spread out from the center,” with “the great mass of ice in a glacier behaving plastically, or like a liquid. It flows, oozes, and slides over uneven surfaces until it covers everything in its path” [2].

A formation of snow officially becomes a glacier “when the weight of the ice and snow (thickening snowfield) becomes great enough, and the formation begins to move (flow down-slope),” and the appearance of “signs of flow in a perennial snow patch” will occur [3]. The immense glacial weight leads to “so much pressure that the firn and snow melt without any increase in temperature. The meltwater makes the bottom of the heavy glacier slicker and more able to spread across the landscape” [2].

For this glacial formation, temperatures are expected to be “at or close to 0°C [32°F] for temperate glaciers, while the upper part of the ice sheet may be as cold as -40 to -60°C [-40 to -76°F]” [4].

A physical feature that stands out about glaciers are crevasses that may be seen along the surface. These are caused by tension “building within the brittle, upper part of the ice,” leading to “the top of the glacier fracturing,” which develops from “the different speeds at which the glacier moves." A similar feature are moulins, which “are deep, nearly-vertical pipeline in the glacier formed by meltwater on top of the glacier falling through a crack in the ice, and are often much deeper than crevasses” [2].

Lastly, in the case of “where a glacier meets the coast, it becomes a tidewater glacier” with “its leading edge floating in the water, forming cliffs of ice,” with “chunks of ice at the edge of the tidewater glacier breaking away into the water—a process called calving,” which produces icebergs [2].

References

[1] ScienceDirect. (2020, October 1). Properties of Glacial Ice and Glacier Classification. Retrieved (2021, July 21), from https://www.sciencedirect.com/science/article/pii/B9780128182345000146?via%3Dihub

[2] National Geographic Society. (2011, January 21). Glacier. Retrieved (2021, July 21), from https://www.nationalgeographic.org/encyclopedia/glacier/

[3] Alaska Satellite Facility (ASF). (2019, December 4). Glacier Power - How do Glaciers Form?. Retrieved (2021, July 21), from https://asf.alaska.edu/information/glacier-power/glacier-power-how-do-glaciers-form/

[4] Climate Policy Watcher. (2021, April 1). Temperature Distribution in Glaciers and Ice Sheets. Retrieved (2021, July 21), from https://www.climate-policy-watcher.org/environmental-change/temperature-distribution-in-glaciers-and-ice-sheets.html