The most famous caves these days are glacier caves. The difference between glacier caves and ice caves is that ice caves are bedrock caves that contain ice all year round, whereas glacier caves are formed within the ice of a glacier. When you come to Iceland you will really want to see a glacier cave, but for some reason or another everyone calls them ice caves.
Glaciers are constantly moving, or crawling, so glacier caves are therefore not permanent. Most of them are unstable and can collapse and can therefore be very dangerous to enter. Most glacier caves start forming by water running through or beneath the glacier or due to geothermal heat from volcanoes beneath the ice. They were measured to be 2.8 km long with a vertical range of 525 meters in the 1980’s!