Caves can form within glaciers as a result of water running through or under a glacier. They are often called ice caves, but the term more accurately describes caves in bedrock that contain ice throughout the year. Water usually forms on the glacier’s surface through melting, before flowing down a moulin (vertical to nearly vertical shafts within glaciers or ice sheets) to the base of the glacier. Glacier caves can also form as a result of geothermal heat from hotsprings or volcanic vents beneath glaciers, such as the Kverkfjöll glacier cave in Vatnajökull glacier in Iceland, or where glaciers meet a body of water, with wave action.
Glacier caves can collapse or disappear because of glacier retreat. For example, the Paradise Ice Caves on Mount Rainier in Washington had 8.23 miles of passages in 1978. However, it collapsed in the 1990s, and the section of the glacier that contained the caves retreated between 2004 and 2006. Prior to collapse, caves can be used to access the interior of glaciers for research purposes, with the study of glacier caves sometimes known as glaciospeleology. Others also serve as popular tourist attractions due to their beauty.
Sandy Glacier Caves, Mount Hood, Oregon, CA – Photograph via Josh Hydeman pic.twitter.com/hWEPMllbqS
— Life on Earth (@planetepics) January 31, 2016
Read about a time when Putin visited a glacier cave here.