How Where The Great Lakes Formed

how where the great lakes formed

Drain the Great Lakes -- Post 1

Last night I watched a companion show to the one I watched a couple of weeks ago about draining the oceans. This show aired on the National Geographic Channel was Drain the Great Lakes.

The program featured all five of the Great Lakes and some interesting things that scientists have found on the bottom of the lake beds. I admit that I am biased, but the show started and ended with Lake Superior -- which I love.

There is more than I include in one post, so I'll summarize what the show presented in a series of blog updates.

The Late, Great Lakes: An Environmental History (Great Lakes Books)
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William Ashworth
In the first segment of the show, they drained the water out of Lake Superior.
Northwest of Grand Marais, there are a series of parallel canyons.  I remember back in the 1970s when Jacques Cousteau researched Lake Superior, that he was the first to find these mysterious canyons.   Here is what one would look like, according to this documentary.
Of course the Great Lakes were geologically formed by the glaciers.  Some scientists think that there may have actually been a series of seven glaciers to scour the northern part of the Americas.
I just love the next two shots.  The documentary shows what the Chicago sky line would look like in scale to the glaciers that the show says were a mile high.  I have read accounts that the glaciers may have been up to three miles high.
The Dynamic Great Lakes
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Barbara Spring

What they figured out is that when the glaciers were last retreating north, as they passed through what is now the Lake Superior region, they stalled enough to allow large glacial runoff rivers to form perpendicular to the direction of retreat.  The channels we now find in Lake Superior are the river beds left over from these glacial rivers.
The next story the documentary covered is about the Straits of Mackinaw.  Today there is the Mackinaw Bridge that connects the two Michigan peninsulas.  It is interesting that for reference, the show left the bridge in all of their graphics.
Apparently around 6,000 years ago a significant drought lowered the level of all the Great Lakes a significant amount. At that time, the five lakes for the most part were not connected.
  But first, let's drain the water from under the bridge.

Near the Bruce Peninsula in Canada, which separates Lake Huron from the Georgian Bay, scientists found evidence of just how low the level of the Great Lakes was 6,000 years ago.  In fact they have found underwater escarpments in the area that during that period were huge waterfalls, some even larger than Niagara Falls today.
Also during that time of low lake levels, they think there was only a small channel connecting Lake Huron to Lake Michigan that still exists today.

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