Lake Superior

Lake Superior is a massive body of freshwater located in central North America.

It sits at the border of Canada and the United States. The Canadian province of Ontario lies to the north and east. In the United States, Minnesota is to the west. Michigan and Wisconsin are located to the south. Lake Superior is the largest freshwater lake on Earth by surface area. The Caspian Sea is larger in both area and volume, but it is a saline, or salty, body of water.

While Lake Michigan and Lake Huron have a larger combined surface area, they are usually viewed as two separate lakes.

The movement of water through the lake follows a specific path. More than 200 rivers feed the lake basin.

These include the Nipigon, St. Louis, and Pigeon rivers. The lake drains into Lake Huron through the St. Marys River. This outlet has a steep gradient with rapids. Ships use the Soo Locks to bypass these rapids and overcome the height difference. From Lake Huron, water flows through the lower Great Lakes. It travels through the St. Lawrence River to reach the Atlantic Ocean. Because of its massive size, the lake has a retention time of 191 years. This means it takes nearly two centuries for the water to cycle through.

The lake's physical characteristics are quite extreme. It has a surface area roughly the size of South Carolina or Austria. The maximum length is 350 miles, and the maximum breadth is 160 miles. The average depth is 483 feet, but it reaches a maximum depth of 1,333 feet.

On July 30, 1985, a scientist named J. Val Klump reached this deepest point. The lake holds 2,900 cubic miles of water. This volume could cover all of North and South America in 0.282 meters of water. The water temperature below the surface stays nearly constant at 39 degrees Fahrenheit. This causes the lake to be seasonally stratified, meaning it has layers. However, the water mixes thoroughly twice a year, a process called being dimictic.

History shows many different names for this water. The Ojibwe people call it Gitche Gumee, which means "great sea."

This name appears in the poem "The Song of Hiawatha." In the 17th century, French explorers arrived via the Ottawa River. They called it Lac Superior because it was the "upper lake" in elevation. After the British took control in the 1760s, they anglicized the name. They chose "Superior" because the lake was superior in magnitude to other lakes on the continent.

Geology has shaped the lake over billions of years. Most of the lake sits within the Midcontinent Rift, an extinct rift valley.

During the Precambrian era, magma rose to create granite rocks in the Canadian Shield. This process also deposited valuable metals like copper, iron, silver, and gold. Later, the continental crust split, creating one of the deepest rifts in the world. Magma also formed hard diabase sills between sedimentary rock layers.

About 10,000 years ago, the Wisconsin glaciation covered the region in ice. This ice was 2 miles thick. As the ice melted, it carved the current land contours. The retreating ice left behind deposits of gravel, sand, clay, and boulders.

Human activity and climate now affect the lake. The International Lake Superior Board of Control regulates water levels using the Compensating Works.

Water levels fluctuate, with highs often in October and lows in March or April. Recent studies show the lake may be warming faster than the surrounding land. Summer surface temperatures rose by about 0.3 degrees Celsius between 1979 and 2007. This warming might be linked to less winter ice cover. If ice cover decreases, more solar radiation can enter the water and warm it. This change could influence how much snow falls in nearby lake-effect snow belts.

Many people visit the lake for its scenery and islands. Isle Royale is the largest island in the lake.

Other notable islands include Madeline Island and Grand Island. Large cities like Duluth, Superior, and Thunder Bay sit along its shores. The Duluth-Superior area is the most inland port in the world. Travelers can also explore many protected areas, such as Pictured Rocks National Lakeshore and Isle Royale National Park.

These locations highlight the diverse geography of this massive freshwater system.