A small cylindrical hole on the surface of a glacier, formed by patches of cryoconite that absorb more short-wave radiation than the surrounding ice, melting downwards at a faster rate and adding to submetre-scale spatial variability in ablation

Glossary of glacier mass balance and related terms. Working Group on Mass-balance Terminology and Methods of the International Association of Cryospheric Sciences (IACS)

Cryoconite holes occasionally appear on the surface of glaciers and ice sheets. They are formed when cryoconite - fine, windblown dust - gathers in patches on the ice. The sun then heats up the dust, and this melts the ice. A hole forms, filled with melt water, with the dust visible at the bottom. Bubbles are often visible on the inside edge of the ice, beneath the melt water. These come from air that was trapped inside the ice when it was first formed. Hundreds or even thousands of years ago, as the snow fell, air pockets formed inside the snow pack. Gradually the snow was compressed as more layers built up on top, turning into ice and trapping the air in tiny pockets within the ice. This means the bubbles contain air that is often thousands of years old, from the time when the snow fell that formed the ice

https://www.alamy.com/stock-photo-cryoconite-hole-a-small-melt-hole-in-a-glacier-filled-with-water-92441421.html

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