A beautiful "Kverkfjöll" glacier cave in the Vatnajökull glacier in Iceland, measured in the 1980s at 2 .8 kilometers long with a vertical range of 525 meters.
A glacier cave is a cave developed within the ice of a glacier. Glacier caves are usually known as ice caves, however this term is properly used to explain bedrock caves which contain year-round ice. The majority of glacier caves are involved with water flowing through or under the glacier. This water often starts on the glacier’s surface by means of melting, getting into the ice at a moulin and exiting at the glacier’s snout at base level. Heat transfer from the water might cause enough melting to generate an air-filled cavity, typically assisted by solifluction. Air flow can then support expansion from melting in summer season and sublimation in winter. Certain glacier caves are developed by geothermal heat from volcanic vents or hot springs beneath the ice.