Centuries of wave action, freezing, and thawing have sculpted shorelines throughout Apostle Islands National Lakeshore. Some of the Great Lakes' most spectacular scenery occurs where these forces interact with sandstone of the Devils Island Formation to create extensive sea caves. Nature has carved delicate arches, vaulted chambers, and honeycombed passageways into cliffs on the north shore of Devils Island, Swallow Point on Sand Island, and along the mainland near the Lakeshore's western boundary. People come to Apostle Islands National Lakeshore in summer and winter to visit the sea caves and witness Lake Superior's ever-changing handiwork.
Ancient Sands, Devils, Apostles, and Sea Caves
The story of the Apostle Islands Sea Caves is an ancient one. After the volcanism and subsidence of the failed Keweenaw Rift, high-energy, braided streams carried sand and gravel from granitic highlands in what is now southern Minnesota to the basin where the Apostle Islands eventually formed. Sediments filled the basin for hundreds of millions of years, long before fossils, and are described as three formations making the Bayfield Group. The Devils Formation, named after the island, is about 300' thick and accumulated in wide-spread sand flats covered with shallow ponds, some only a few inches deep, connected by shallow channels. Sand deposited in this environment was thinly-bedded, fine-grained, contains ripple marks, and is situated between the Orienta and overlaying Chequamegon Formations.
By February, an ice bridge might connect Sand Island to the mainland. The lake surface is usually a frozen white expanse. Lakeshore cliffs form a crimson red border to this arctic landscape. Pillars of ice extend to the cliff tops where waterfalls have hardened in place. Frozen lakewater encrusts the base of the cliffs. Inside the caves awaits a fairyland of needlelike icicles. The formations change from chamber to chamber and from day to day. In the right conditions, visitors can explore these ice caves.
Last updated: July 22, 2021