Saturday, November 7, 2009

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.


Shelby said...

I love reading about places people are from.. take care!


A most enjoyable post Margaret, having been to the US a few times and saw some wonderful sights
your history of the lakes brought back many lovely memories.


Tea said...

Great post, Margaret! The Great Lakes...I think they're named appropriately as they are wonderful lakes.

Patty said...

Interesting article and a very creative teacher. Hope you have a great week ahead.

Judy said...

This is such an interesting post and I love the "Homes" thingy. It will help me to remember, too. I always have trouble naming them.

Anonymous said...

There are so many things that bother me about Earth and what people are doing to it. I am glad that I won't be here to see it all happen. But water will be more important than gasoline and those who have it will need armies to protect it. The Great Lakes will be drained so people in California can sprinkle their desert golf courses. It is enough to make me sick.

Commercial fishing is destroying the world's tuna supply and without the largest fish as predators in the oceans, the rest of the ocean will go crazy.

My father grew up in nearby Preble county and a part of the glacier stopped there and melted out tons of stones and boulders. He said they spent lots of time just picking up and hauling stones and used them to build fences. I wish I had lived then just to see what it was like.

Gramma Ann said...

Very interesting and informative post today. I also learned to remember the Great Lakes the same way you were taught. But, I learned it later in life while reading something or other, that explained the easy way to remember the names of them was to remember HOMES and you will never forget them again. And believe it or not it works!

Becky and Gary said...

That IS cool Margaret, and thank you for the interesting lesson. We live 25 miles from the shores of Lake Erie, the shallowest of the Great Lakes. There are 100's of old ship wrecks off the southern shore of Lake Erie near Erie, Penna

A New Beginning said...

Another interesting post :) Thanks Margaret and have a great week ahead!!!!

Doug Cloud said...

"My teacher in grade school taught us how to remember the great lakes, they spell 'HOMES' - Lakes Huron, Ontario, Michigan, Erie, and Superior."

I never realized that before. That is cool. I always think of Lake Michigan as an inland ocean. When I look out over it I imagine what's on the other side and wonder at the size of it all. When I first saw Lake Superior I was in awe of it's dark and mysterious splendor.

'The Great lakes are a national treasure, but at the rate people are destroying them they';ll soon be a national garbage dump.

OldOldLady Of The Hills said...

A great reminder of something I once knew, but had completely forgotten...Thanks for this, my dear, And I love the HOMES reference for remembering the Lakes is GREAT!

Merle said...

Dear Margaret ~~ What a great way to remember the
great lakes. The history was interesting, thank you. I am glad you liked my flowers and the jokes.
The poor guy Ole thought he was going to be shot.
My foot also changed direction, it is strange.
Take great care, my friend and have a wonderful
week. Love, Merle.

Midlife Mom said...

That is such a super way to remember the names of the lakes! I never could have remembered them without that!!! Great post!

Linda said...

Yes, that's a very cool tip! :)

Thanks for the informative post. Hope you have a blessed week,


Lynn@ The Vintage Nest said... cool is that Margaret? Love that and will teach my grand-daughter that. She lives almost on one of the great lakes. :) Have a super great day.

Kay said...

Hi again, Margaret. Thank you so much for your visit. I haven't seen this blog before. This is a lot of fun. You've got such interesting information. We used to live right next to Lake Michigan in Illinois. I kept calling it ocean when I first moved there.

caspersmom said...

Hope you and yours has a very Happy Thanksgiving.

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