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“The Mississippi River follows what is known as the Mississippi Embayment,” David tells me. “This is a syncline, or a trough-shaped fold in the earth, that stretches from Illinois south to the Gulf of Mexico and beyond. The Jackson Volcano is on the east side of this syncline and the Monroe Uplift, another Cretaceous volcano, is on the west side. They’re kind of symmetrical. Further north is the Murfreesboro, Arkansas Volcano. And then, there’s a buried volcano at the mouth of the Mississippi River called the Door Point Volcano. So there’s a ring of volcanoes around what’s now this slumped syncline. And the New Madrid Fault is part of that over-all feature.”

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