“When snow and ice melts on the surface of a glacier, it flows from the top of the glacier to the bed. This flowing water cuts through the ice and forms a channel, much like a river cuts through rock. In winter, there is no active melting, so there is no running water. Snow falls and closes the top of the channel. What’s left is a narrow, tall ice cave. Over the course of the winter, some water is able to move through the channel and form intricate icicles and crystals. There are a few other ways that caves within glaciers can form, but it all comes back to flowing water.”

From the blog “On Thin Ice”, the blog of a University Centre in Svalbard (!) student. http://kiyainsvalbard.blogspot.com/2010/02/glacio-speleology.html