How Lake Superior Formed

“Those who have never seen Superior get an inadequate idea by hearing it spoken of as a lake. Superior is a sea. It breeds storms and rain and fog like a sea. It is cold, masterful, and dreaded.” Rev. George Grant, 1872

Despite this dire view by the late Reverend, there is no denying the beauty of the largest in the Great Lake chain, Lake Superior. A favorite vacation destination for water lovers each summer, this awe inspiring lake offers 31,280 square miles of water surface, roughly the size of South Carolina, the largest surface area of fresh water anywhere. It spans the borders of Minnesota, Wisconsin, and Michigan in the United States, but sits primarily in Ontario, Canada.

This wonder of nature is surprisingly a baby by geological standards at just 10,000 years of age, making it one of the planet’s newest natural wonders, though its northern shore dates to Earth’s beginnings. Perhaps reflective of the opening quote and Lake Superior’s current fitful moods, the ancient history of the area’s formation is tumulus. Some 2.7 billion years ago magma flowed over the land forming the granite of the Canadian Shield. Through multiple eras of the rock sinking into the earth’s mantle, eventually the land rose and cooled leaving large deposits of silver, iron, copper, gold and other minerals, many of which are mined today. Some of Earth’s oldest rocks, 2.7 billion years old, can be found on the Ontario shore.

The area in which the lake sits became an active rift zone one billion years ago which nearly tore the North American continent in two. This became one of the deepest rifts in the world and the chaotic period continued for 20 million years. An arc-shaped scar was left behind that stretches from Kansas to Minnesota down to Michigan where the land ripped apart. Luckily the area settled down, but the Keweenawan Rift left its mark and thanks to the gouging affects the glaciers of the last Great Ice Age are famous for, the massive lake’s basin was born beneath 1.25 miles of ice. As the last ice age melted, water flooded the depression and left behind a lake even more massive than today’s Lake Superior. At 600 feet above current lake level, Glacial Lake Duluth eventually gave way to today’s lake as the ice cap receded. St. Mary’s River formed releasing part of the lake volume.

Today, peering over the tranquil glassy surface of Lake Superior can make one forget the erratic forces that forged it. Offering its bounty of minerals, wildlife, and natural shipping routes, the lake will remain a shared treasure of Canada and the United States.