Editing Glacier (section)

== Formation ==
[[File:153 - Glacier Perito Moreno - Grotte glaciaire - Janvier 2010.jpg|left|thumb|A [[glacier cave]] located on the [[Perito Moreno Glacier]] in Argentina]]
Glaciers form where the [[Glacier ice accumulation|accumulation]] of snow and ice exceeds [[ablation]]. A glacier usually originates from a [[cirque]] landform (alternatively known as a corrie or as a {{Lang|cy|cwm|italic=no}}) – a typically armchair-shaped geological feature (such as a depression between mountains enclosed by [[arête]]s) – which collects and compresses through gravity the snow that falls into it. This snow accumulates and refreezes, turning into [[névé]] (granular snow). Further crushing of the individual snowflakes and expelling the air from the snow turns it into [[firn]] and eventually "glacial ice". This glacial ice will fill the cirque until it "overflows" through a geological weakness or vacancy from the edge of the cirque called the "lip" or threshold. When the mass of snow and ice reaches sufficient thickness, it begins to move by a combination of surface slope, gravity, and pressure.<ref name=nps/><ref name=dkp/><ref name=nv>{{cite web | url=http://people.hofstra.edu/j_b_bennington/33notes/glaciers.html | title=Geol 33 Environmental Geomorphology | publisher=Hofstra University | access-date=25 January 2025 | archive-url=https://web.archive.org/web/20160303204533/http://people.hofstra.edu/j_b_bennington/33notes/glaciers.html | archive-date=2016-03-03 | url-status=dead }}</ref><ref name=vdb>{{cite journal |last1=van den Broeke |first1=Michiel |title=Depth and Density of the Antarctic Firn Layer |journal=Arctic, Antarctic, and Alpine Research |date=1 May 2008 |volume=40 |issue=2 |pages=432–438 |doi=10.1657/1523-0430(07-021)[BROEKE]2.0.CO;2 |s2cid=198156588 |url=https://www.tandfonline.com/doi/full/10.1657/1523-0430%2807-021%29%5BBROEKE%5D2.0.CO%3B2 |issn=1523-0430}}</ref> On steeper slopes, this can occur with as little as {{Convert|15|m|ft|abbr=on}} of snow-ice.

In temperate glaciers, snow repeatedly freezes and thaws, changing into granular ice or [[névé]]. Under the pressure of the layers of ice and snow above it, this granular snow fuses into denser firn. Over a period of years, layers of firn undergo further compaction and become glacial ice.<ref name=nv/><ref name=vdb/>{{sfn|Huggett|2011|loc=Glacial and Glaciofluvial Landscapes|pp=260–262}} Glacier ice is slightly more dense than ice formed from frozen water because glacier ice contains fewer trapped air bubbles.

Glacial ice has a distinctive blue tint because it absorbs some red light due to an [[overtone]] of the infrared [[Infrared spectroscopy|OH stretching]] mode of the water molecule. (Liquid water appears blue for the same reason. The blue of glacier ice is sometimes misattributed to [[Rayleigh scattering]] of bubbles in the ice.)<ref>{{cite web|url=http://webexhibits.org/causesofcolor/5C.html |title=What causes the blue color that sometimes appears in snow and ice? |publisher=Webexhibits.org |access-date=2013-01-04}}</ref>