How did the Great Lakes get so deep? The Great Lakes are deep due to the heavy glaciers slowly moving north over time. The weight of these glaciers caused the now Great Lakes to become deeper as they moved.
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The story of the Great Lakes began over 1 billion years ago, when the ancient supercontinent Laurentia began splitting in half. Over the course of about 10 million years, the Midcontinent Rift System opened a massive fissure on its way to becoming a new ocean basin.
While there have been past “sightings,” most have turned out to be pranks or misidentifications. The reality is that the largest of the Great Lakes (Lake Superior and Michigan) are extremely deep lakes that are too cold for sharks.
Geology of Lake InferiorLake Inferior is an underground lake that is located beneath Lake Superior. It is believed to be formed by a process known as karstification, which is the dissolution of limestone and dolomite rock. This process creates sinkholes, caves, and underground rivers and lakes.
About a billion years ago, a fracture in the earth running from what is now Oklahoma to Lake Superior generated volcanic activity that almost split North America. Over a period of 20 million years, lava intermittently flowed from the fracture.
Since there was no channel linking Lake Huron to prehistoric Lake Erie, researchers believe Erie was in inland sea, with its water level controlled by the balance between the inflow from rivers draining into it, as well as precipitation and evaporation.
At 1,943 feet (592 meters), Crater Lake is the deepest lake in the United States and one of the deepest in the world. The depths were first explored thoroughly in 1886 by a party from the U.S. Geological Survey.
There are some odd geological finds at the bottom, including a 2007 archeological find that was described as Stonehenge-like, although it was actually more in a V-shape. One of the stones is said to have a mastodon image on it (although it's not fully clear if it was man-made or just a natural formation).
Dreyer is the only person who has swum the width of Lake Michigan between Wisconsin and Michigan, having swum from Two Rivers, Wisconsin, to Ludington, Michigan, in 1998. In the 2023 swim, he was attempting to beat his own record by swimming 25 miles further in the route from Milwaukee to Grand Haven.
Threats & ConservationThe source of toxic pollutants includes decades of industrial waste, raw sewage overflows, runoff from cities, and mining operations. Excess nutrients that throw the ecosystem out of balance enter the lakes from agricultural runoff and untreated sewage.
Lake Superior is the world's largest freshwater lake by area (31,700 mi2 /82,100 km2). It is also the coldest and deepest of the Great Lakes, with a maximum depth of 406 meters (1,332 feet).
Lake Erie is the shallowest, warmest, and most productive of the Great Lakes. Three distinct basins provide a variety of offshore habitats. The Detroit River, Maumee River, and smaller tributaries drain into the western basin, which averages 24 feet deep and contains extremely nutrient-rich water.
During the 1960s, Lake Erie was declared a “dead lake” due to eutrophication and pollution. The children's book, The Lorax, written by Dr. Seuss, actually included the following line referring to fish: “They will walk on their fins and get woefully weary in search of some water that isn't so smeary.
Currents in Lake Erie can be dangerous! Any current flowing faster than 2 mph is considered dangerous. Dangerous currents can exceed 5 mph — faster than an Olympic swimmer can swim. Currents can pull swimmers away from shore.
Lake Superior's beaches are open and safe for swimming over 90% of the time, and the water is extremely clear, with an average underwater visibility of 8.3 m (27 ft).
Lake sturgeon are the largest fish in Lake Superior. They are among the oldest fish in the lake too. Did you know that a lake sturgeon can live to be older than 100 years? This species of fish has also been around for a long time—about 150 million years.
Lake Michigan wrecks: the oldest and the mostestLake Michigan contains more shipwrecks than any of the other Great Lakes, as well as the oldest recorded one: the French ship Griffon, the first European vessel to sail the Lakes.