The Indiana Dunes National Park remind us the dangers of “Shelf Ice.”
Shelf ice forms when breaking waves and spray freeze in frigid air temperatures, creating irregularly patterned ice full of cracks, crevices, and holes. Shelf ice is an unstable formation that builds from the beach out to the lake, without freezing to the lake bottom. Due to the nature of its structure and fluctuating temperatures above and below freezing, shelf ice is unpredictable and unsafe to step on.
Shelf ice is not a continuous sheet. Thinned or weakened areas may be hidden, and the ice can collapse like a trapdoor leading to a plunge into icy waters. Entering the water, your body goes into shock, and the nature of the ice makes it difficult to remove yourself. Hypothermia begins in a matter of minutes. Wave action and fragile ice obstructs rescue potential.