How The Great Lakes Were Formed

Have you ever looked at a map of North America and wondered how the Great Lakes were formed? The answer to that question lies in a period of Earth's geological history known as the "ice age." The term "ice age" refers to a period of the Earth's geological history when much of the Northern Hemisphere was covered by ice. The climate during this time period was much different from what it is today, with temperatures on the continents as much as 15 degrees C(27degrees F) colder.

The most recent Ice Age, known as Pleistocene Epoch, occurred between 1.6 million and 10,000 years ago. At least four times during the Pleistocene Epoch, large masses of ice, known as "glaciers", advanced and retreated over the surface of what is now North America. The last glacier, called the "Laurentide" began to form around 100,000 years ago. At its peak, around 18,000 years ago, the Laurentide covered almost all of Canada and extended into the United States, as far south as Chicago, Illinois, this massive glacier was almost 4 km thick. As the glaciers advanced, giant sheets of ice flowed across the land, leveling mountains and carving out massive valleys, which is a process known as "glacial erosion".

Around 14.000 years ago, the Laurentide began retreating and melting due to warmer temperatures. The geological changes caused by this resulted in the formation of the Great Lakes. When the glaciers began receding, their leading edges left behind ridges, glacial deposits, and other land formations. Evidence of this can be seen today in the topography of Canadian Shield, the Niagara Escarpment, the Oak Ridges Moraine and the Bruce Peninsula. When the glaciers melted, the resulting water, called "meltwater", filled huge holes left by the glaciers.

During this time, the lakes were much larger than they are now, and they had different river outlets. But as the ice retreated the St. Lawrence River Valley revealed itself as the outlet to the Atlantic Ocean and the lake levels eventually dropped to current levels.

Without the immense weight of the glaciers, the land began to rebound. Even today, virtually all of the land in the Great Lakes basin continues to rise at a rate of about 7.5 cm every 100 years. Today, rebounding of earth's crust, erosion, and changes in climate continue to alter the shapes and sizes of the Great Lakes. As one of the youngest natural features on the North American continent, the lakes remain a dymatic, evolving system. Our Great Lakes are in danger of being tapped into for fresh water by other states and even other countries.

I live on the shores of Lake Michigan, this is such a beautiful lake, it is so big we can't see across it. My teacher in grade school taught us how to remember the great lakes, they spell "HOMES", ===Lakes Huron, Ontario, Michigan, Eries and Superior, isn't that cool.