Why the Mississippi surged upstream
A river’s current is usually steady, but the water is not locked to the ground beneath it. During a powerful earthquake, the riverbed and banks can jerk suddenly while the water, because of its inertia, keeps moving in its previous direction for a moment. The mismatch sets up waves and powerful back-and-forth sloshing.
In the New Madrid region, intense shaking also disturbed the river corridor. The resulting waves could push water upstream in particular stretches, briefly overwhelming the local downstream current. This is similar to what happens when a bathtub is jolted: water piles up at one end, then rushes the other way. At river scale, however, the motion is shaped by the channel and the force of the current, so the reversal is uneven and short-lived.
A local reversal, not a river turned around
“Flowed backward” describes what the water did in a limited part of the Mississippi, not a reversal of the whole river. The river’s overall course and drainage did not change; rather, earthquake-driven surges temporarily sent water against the current in affected reaches.
That distinction makes the episode easier to picture: the Mississippi did not become an upstream-flowing river. For a brief time, the shaking made parts of it behave like a moving body of water being violently stirred—its ordinary current still there, but momentarily overtaken by a surge.
