At the end of the last glacial period, 10,000 years ago, the Great Lakes Basin was formed when retreating ice sheets carved basins in the land that filled with meltwater.
The Great Lakes are made up of Superior, Michigan, Huron, Erie, and Ontario. You can also think of it this way:
The Chicago River and the Calumet River (thanks to manmade alterations) connect to the Illinois River which then connects the Mississippi River to the Great Lakes Basin.
The St. Marys River (home of the Soo Locks) connect Lake Superior to Lake Huron.
The Straits of Mackinac (just five miles wide) connects Lake Michigan to Lake Huron.
The St. Clair River connects Lake Huron to Lake St. Clair (which might be considered a lesser Great Lake).
The Detroit River connects Lake St. Clair to Lake Erie.
The Niagara River, including Niagara Falls and the Niagara Escarpment, connects Lake Erie to Lake Ontario. (The Welland Canal bypasses the Niagara River and the Falls and also connects Lake Erie to Lake Ontario.)
The St. Lawrence River connects Lake Ontario to the Gulf of St. Lawrence, which connects to the Atlantic Ocean.
Sounds complex? Here's a map.
|Image courtesy of the Internet|
Lake Superior is the largest continental lake in the world. Together the five lakes form 21% of the world's surface freshwater and 54% of the world's liquid fresh water by volume. In other words, while aquifers in the south and west are running dry, the Great Lakes sit with more than half of all the non-ice water in the world right there.
I like to think of it this way: when the Zombie Apocalypse or the Great Drought or the Weirdness from Another Planet arrives and people are thirsty and just want to be around some nice fresh water, they will slowly make their way back to Michigan or Eastern and Northern Wisconsin or Northern Ohio or Northern Minnesota or Western New York (and a little bit of Illinois, Indiana, and Pennsylvania) because if you don't have water, you'll die. The Great Lakes will make that post-apocalyptic scenario a little less unpleasant. The infrastructure from days of glory are watiting to be revived. And Niagara Falls will certainly make the Weirdness from Another Planet say "Holy shit, will you look at that?"