On February 7, 1812, the most violent of a series of earthquakes near Missouri caused a so-called fluvial tsunami in the Mississippi River, actually making the river run backward for several hours. The series of tremors, which took place between December 1811 and March 1812, were the most powerful in the history of the United States.

The unusual seismic activity began at about 2 a.m. on December 16, 1811, when a strong tremor rocked the New Madrid region. The city of New Madrid, located near the Mississippi River in present-day Missouri, had about 1,000 residents at the time, mostly farmers, hunters and fur trappers. At 7:15 a.m., an even more powerful quake erupted, now estimated to have had a magnitude of 8.6. This tremor literally knocked people off their feet and many people experienced nausea from the extensive rolling of the earth. Given that the area was sparsely populated and there weren’t many multi-story structures, the death toll was relatively low. However, the quake did cause landslides that destroyed several communities, including Little Prairie, Missouri.

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Source: history.com