How Glacier Caves Form
Glacier caves form within glacier ice rather than rock. They are fundamentally different from rock caves: they form quickly, change seasonally, and rarely survive more than a few decades unchanged. The bright blue colour of glacier ice is the most photographed feature.
Moulins
The simplest glacier caves are moulins — vertical shafts where surface meltwater plunges into the glacier. Moulins are formed by warm summer water exploiting cracks in the ice; the falling water enlarges the conduit, sometimes to chamber proportions.
Subglacial rivers
Beneath the glacier, meltwater accumulates and flows under pressure toward the snout. These subglacial rivers can carve sizable horizontal cave passages. The famous Briksdalsbreen caves in Norway and Vatnajokull caves in Iceland are subglacial- river caves.
Why the ice is blue
Glacier ice is dense and contains little dissolved gas. Light penetrating into the ice has the red wavelengths absorbed preferentially; what reaches your eye is the longer-pathlength blue. Newer surface ice with more air bubbles appears whiter.
Geothermal interactions
Iceland's glacier caves are heated from below by volcanic activity. The Katla and Grimsvotn glaciers maintain subglacial chambers warmed by geothermal heat. Sometimes these are stable multi-year features.
Safety
Glacier caves are dynamic and dangerous. Roof collapses are frequent; meltwater rivers can flood passages without warning; ice falls from above. Visit only with experienced guides who have inspected the cave that day. Many caves only open November-March when conditions are most stable.
Photography
Long exposures at low ISO capture the blue ice colour. Wide aperture for blue-light absorption depth. Take care of equipment in the cold — batteries die quickly, lenses fog when warmer than ambient.
Best destinations
Vatnajokull (Iceland), Briksdalsbreen (Norway), Mendenhall (Alaska), Athabasca (Canada). Iceland is the most accessible.
Explore on the map
See glacier caves on the interactive map.