Here’s what you’ll learn when you read this story:

• From December 1811 to February 1812, the central U.S. was rocked by a series of earthquakes, the last of which was the largest in modern history.
• The earthquakes were so powerful that they consumed islands along the Mississippi River, created entirely new lakes, and even temporarily reversed the river’s flow due to a “fluvial tsunami.”
• The New Madrid earthquakes, as there known, are a particularly powerful example of “intraplate earthquakes”—seismic activity that occurs far from typical rumbling hotspots, such as plate boundaries and subduction zones.

Before the dawn of seismology and our modern understanding of plate tectonics, earthquakes were often viewed divine acts of punishment, and the catastrophic New Madrid earthquakes of 1811-1812 seemed to lend credibility to that admittedly unscientific belief.

According to local reports, the first tremors in the area began early on the morning of December 16^th, 1811.

“We were visited by a violent shock of an earthquake, accompanied by a very awful noise resembling loud but distant thunder, but more hoarse and vibrating,” Eliza Bryan, a longtime resident of New Madrid, Missouri, wrote about these first tremors in a letter to Methodist evangelist Lorenzo Dow years later. “The screams of the affrighted inhabitants running to and fro, not knowing where to go or what to do—the cries of the fowls and beasts of every species, the cracking of trees falling, and the roaring of the Mississippi—the current of which was retrograde for a few minutes, owing as is supposed, to an irruption in its bed—formed a scene truly horrible.”

This initial eruption, according to a calculation by seismologist Otto Nuttli in 1973, would’ve measured approximately 7.2 on the body-wave magnitude scale (neither it nor the Richter scale would be invented until more than a century after the New Madrid quakes). Although small earthquakes were almost a daily occurrence in the region at this time, and remained so until 1814, major quakes were much rarer. And that’s a big part of what made this particular string of events so shocking to residents—subsequent major quakes on January 23, 1812, and February 7, 1812, would’ve measured approximately 7.1 and 7.4 respectively on the same scale. In later work (1983), Nuttli estimated surface-wave magnitudes as high as 8.5, 8.4, and 8.8 for the three main shocks—figures that, if accurate, would make the February 7 earthquake the strongest ever recorded in the continental U.S.

Despite being sparsely populated—the closest city, 150 miles north of New Madrid, was St. Louis, which only had a population of some 5,700 people at the time—the earthquakes still caused significant damage. Extensive landslides impacted 125 miles of bluffs on the east side of the Mississippi, tree-lined river banks collapsed into the river, and the small town of New Madrid was severely damaged. The earthquakes destroyed so log cabins so frequently that many people decided to switch to living in tents while the quakes continued to rumble in the region.

The largest earthquakes even impacted faraway regions of the nation—chimneys toppled in St. Louis, bells rang in Boston, and it was reported the wife of President James Madison, Dolly, was awakened by the first quake as she slept in Washington, D.C., some 900 miles away.

During the last earthquake, boatmen on the Mississippi River reported that the river actually began to run backwards in parts, likely due to what’s called a “fluvial tsunami.” The earthquakes caused tectonic uplifts that effectively dammed the river in spots and temporarily reversed its flow. Reports say it took days for the river to eventually wind around these newly formed obstructions. The earthquakes also consumed entire islands and formed new lakes as water rushed into new depressions. By the time the series of earthquakes came to an end, the course of the Mississippi River—already known for its meandering ways—had changed drastically. Luckily, due to the sparse population of the region at the time, deaths remained low for earthquakes of this magnitude. An estimated 1,000 people died, though that number could be higher, since data is incomplete for certain populations, including Native Americans and enslaved people.

Centered primarily in Missouri—but stretching into the nearby states of Arkansas, Illinois, Kentucky, and Tennessee—the New Madrid fault was never your typical seismic hotspot. Most of the earthquakes in the United States are what's known as “interplate” quakes, meaning they occur along areas where two plate boundaries meet. These types of faults include the San Andreas Fault, the Cascadia Subduction Zone, and the Queen Charlotte Fault in Alaska. Missouri, however, is famously located in the center of the North American plate. As a result, the New Madrid fault creates what are known as “intraplate” earthquakes, which are rumbles occurring far from typical plate boundaries. And from December 1811 until February 1812, the region learned just how powerful and devastating those kinds of earthquakes can be.

In a more modern, densely populated context, intraplate earthquakes can be incredibly deadly, as the regions where they occur simply aren’t prepared for them. The 2001 Gujarat earthquake in India and Pakistan was also an intraplate earthquake, and it claimed the lives of more than 20,000 people. Given that the population’s much larger now than in the early 19^th century, if a New Madrid earthquake event happened again today, it would be far costlier in lives lost. And experts place the likelihood of such an event happening within the next 50 years at around 7 to 10 percent. Though the New Madrid fault formed some 750 million years ago during the Neoproterozoic Era, it can still be activated by stress traveling across the North American plate, whether from the continuous retreat of the Laurentide Ice Sheet, the downcutting of the Mississippi River, or alternations of mantle flow.

Real wrath-of-the-gods type stuff.