That geologic fire – intense volcanic activity – created the critical beginning for Lake Superior, though not for the other Great Lakes basins, formed where the ice sheets found soft, shaly sedimentary rocks laid down in shallow seas about 500 million to 350 million years ago. read more
Lake Superior empties into Lake Huron via the St. Marys River and the Soo Locks. Lake Superior is the largest freshwater lake in the world in area (if Lakes Michigan and Huron are taken separately; see Lake Michigan–Huron), and the third largest in volume, behind Lake Baikal in Siberia and Lake Tanganyika in East Africa. read more
Lake Superior's basin was formed over one billion years ago by tectonic forces. Lava escaped around the edges of a large caldera or plateau, causing it to collapse and form a basin that solidified over time. read more