Minnesota quakes are the result of the bedrock shifting back up after sitting under a ice sheet until just 10,000 or so years ago. which is a strange thought in itself.
I was reading a history of the Great Lakes area. It said that at one point during the process (~7K years ago) the weight of the retreating ice sheet depressed the land so far that what is now Lake Michigan drained northward (like pressing down on one edge of a bowl full of water), leaving thousands of square miles of what is now lakebed exposed.
Mind-boggling.
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