When I walked about 40 yards under the ice I came to the remnant of the river that had carved the tunnel I had been walking through. Large blocks of ice lay scattered about like discarded childs toys. On this Alaskan Photo Safari I spent about 2 hours under the ice telling myself nervously that in "ten minutes and I'm out of here". Because of the arch shape of the ice I calculated it was structurally strong, but then again it was only a guess. Months later I came back and the tunnel and all the surrounded ice had melted and disappeared.