Icicles and hoar frost form on the ceiling of an ice cave by Lake Superior, the world's largest freshwater lake, at the Apostle Islands National Lakeshore near Cornucopia, Wisconsin February 14, 2014. According to the National Oceanic and Atmospheric Administration (NOAA) Great Lakes Environmental Research Laboratory, about 94% of Lake Superior is covered with ice, enabling thousands of people to visit the islands on foot for the first time since 2009. The Great Lakes, which contain one fifth of the world's surface fresh water, are 88% covered with ice. Picture taken February 14, 2014. [Photo/Agencies]