"The formations in the [sea] caves are really like what you see in limestone caves, where it takes hundreds to thousands of years to form. Here, it happens in days to weeks. It's a very dynamic system. Last year we were within a half-hour of opening [access to the caves across a frozen portion of Lake Superior] when we checked the wave camera. The ice on Lake Superior had broken up overnight. It was gone by the end of the day."
Bob Krumenaker, superintendent, Apostle Islands National Lakeshore, Wisconsin
Ice line: 1-715-779-3397, ext. 3