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In the winter of 1811, the American frontier was shaken by a series of earthquakes so powerful they were felt across much of the continent.
The ground split open, forests were flattened, sand erupted from the earth, and the Mississippi River seemed to flow backwards.
Even more unsettling is the fact that the source of those earthquakes remains active today, and some say it could happen again.
Learn more about the New Madrid Earthquakes on this episode of Everything Everywhere Daily.
The New Madrid Seismic Zone, otherwise known as the NMSZ, is located in the midwest and southern US, covering territory in northeastern Arkansas, southeastern Missouri, western Kentucky and Tennessee, and southern Illinois.
The NMSZ is the most active seismic area east of the Rocky Mountains and could affect major cities such as St. Louis, Little Rock, and Memphis.
What makes the NMSZ unique is that it is an intraplate earthquake zone. This means earthquakes occur within the interior of a tectonic plate. These are relatively rare, since most earthquakes occur at tectonic plate boundaries, such as the Ring of Fire around the Pacific Ocean.
Tectonic plate boundaries experience considerably more stress as plates interact. Stress builds up against the plates until the energy is released as earthquakes.
By comparison, the interior plates are usually tectonically calm. These areas move significantly more slowly, so the interiors don’t experience the same stresses and therefore experience fewer earthquakes.
However, stress within tectonic plates can build up at weak points. These buildups can last for centuries, until they rupture at a level comparable to that of boundary earthquakes.
Intraplate rifts tend to occur in weak parts of the Earth’s crust that were once active tectonic zones. Because of their prior state, these areas are weaker than the surrounding rock, leading to eventual slippage.
The NMSZ appears to have formed roughly 600 million years ago, as shown by deformed ancient rocks. Scientists believe the North American continent almost broke apart around that time as part of a process known as continental rifting. This is happening today in East Africa, which I covered in a previous episode.
Continental rifting is a geological process in which tectonic forces pull continents apart. In the NMSZ zone, continental rifting failed. This created a rift in the middle of the United States, known as the Reelfoot Rift.
The faults here are difficult to see with the naked eye because rivers eroded the region’s surface and buried it under sediment. This causes the Reelfoot Rift’s faults and fractures to lie beneath the surface.
The New Madrid Zone is located in the northern part of the Mississippi Embayment. The Embayment is essentially a large trough, or long, shallow valley, filled with marine sedimentary rocks deposited 50 to 100,000,000 years ago and river sediment left behind less than 5 million years ago.
Ongoing tectonic activity in the east and west of the North American Plate can reactivate these rifts and faults. Pressure on these weakened points in the crust likely causes the region’s earthquakes.
There are hundreds of small earthquakes occurring in the zone each year. Most of these are not felt by humans and can only be detected by seismic instruments.
Although most earthquakes are small, catastrophic ones have occurred in the New Madrid Seismic Zone, the most notable of which occurred in 1811 and 1812 and are known as the New Madrid earthquakes.
The first earthquake occurred on December 16, 1811, around 2:15 AM, in what is now known as Blytheville, Arkansas. The earthquake was estimated at magnitude 7.5 on the Richter Scale.
Tremors were felt in the eastern United States over 900 miles away. President James Madison reportedly felt the ground shake in Washington, D.C.
After the initial earthquake, several large aftershocks followed, including one at dawn at 7:15 AM. This aftershock was estimated to be magnitude 6.8 to 7.
The earthquake itself caused only slight damage to man-made structures in Blytheville because the town had a small population. However, the area around present-day Memphis experienced very strong shaking, and villages farther north, such as Caruthersville, Missouri, suffered damage due to soil liquefaction.
Significant damage was observed over an area of 230,000 mi² (600,000 km²).
After the two initial earthquakes, another one hit on January 23, 1812, at 9:15 AM. This one was a magnitude 7.3 earthquake, with its epicenter in southern Missouri.
In the area of maximum damage, the ground experienced ejections, warping, fissures, landslides, and stream bank collapse.
Another earthquake hit on February 7, 1812. This magnitude 7.5 earthquake occurred near New Madrid, Missouri, which destroyed the entire town.
Faulting, uplift, subsidence, and enormous waves temporarily disrupted the Mississippi River. Contemporary observers reported the river flowing backward in places, although some of these observations may have involved upstream-moving waves rather than a sustained reversal of the river’s overall flow.
The aftermath of the earthquakes changed the region’s topography. The earthquake caused landslides, uplift, downward movement of the Earth’s crust, and the formation of fissures.
On top of the changing landscape, the shaking completely uprooted trees. The change in topography led to the expansion of lakes and the exposure of natural resources, such as sand and coal, from fissures. Swamps in the St. Francis River area also changed, with water levels rising by 8-9 feet.
Waves that formed on the Mississippi River washed boats ashore and destroyed sandbars, causing some islands to disappear.
A major problem caused by the earthquake was sand blows. A sand blow is essentially a sand volcano. These occur when a water-saturated sand surface is pressurized and forced upward.
This happens during the shaking of an earthquake, or when extreme pressure, like that caused by a flood, compacts water-saturated soil layers. This process is known as soil liquefaction.
As pressure builds, the weight of the upper soil squeezes water out of the pore spaces between each sand particle. If this liquid is trapped in a dense layer, high-pressure water and gas can burst through weak spots in the soil, pushing liquefied sand toward the surface.
From there, the liquefied sand shoots up like a geyser and deposits around the vent.
During the New Madrid earthquake, thousands of sand blows formed within a 4,000-square-mile radius. Witnesses reported seeing geysers of sand blasting 10 to 20 feet into the air.
The sand blows made a large portion of the area completely unusable for agriculture for years. Farmers in the Mississippi River Valley still find sand from the eruptions when plowing their fields today.
Other earthquake damage included flooding. As large areas of land sank along the Mississippi and Ohio River valleys, River water poured into the area, completely submerging forests and fields.
The number of fatalities from these earthquakes is unknown. At the time, the region was sparsely populated, and communication and record-keeping were poor. Even homes that survived likely still suffered damage, as intense shaking caused chimneys to collapse and structures to crack.
Only a small number can be documented directly, including one person killed by a collapsing building at New Madrid, while an unknown number of people may have drowned when boats capsized or riverbanks collapsed.
Because the region was sparsely populated and most inhabitants lived in surprisingly resilient log cabins, historians and seismologists generally believe the overall death toll was low relative to the enormous scale of the earthquakes.
In 1814, the Missouri territorial governor, William Clark, requested federal relief for the residents of New Madrid County.
Congress passed the New Madrid Relief Act of 1815 which was the first example of a disaster relief act in United States history.
The New Madrid seismic zone has not calmed down over the years. While there haven’t been any major earthquakes, there have been earthquakes as large as magnitude 5.4 in the 20th century.
This earthquake was recorded on November 9, 1968, near Dale, Illinois. It was felt in 23 other states and caused some property damage.
In 2008, the US Federal Emergency Management Agency reported that another large earthquake could happen again in the area. They reported that if a major earthquake occurred, the United States would face the largest economic loss in its history from a natural disaster.
If an earthquake hit that area, it would cause catastrophic damage across multiple states, including Arkansas, Alabama, Indiana, Illinois, Kentucky, Mississippi, Kansas, Texas, Oklahoma, Missouri, and Tennessee.
If a magnitude 7.6 earthquake hit the NMSZ, the bedrock in that part of the United States would shake over an area 20 times larger than the area affected by a similarly sized earthquake in California.
According to a FEMA-supported study, a major scenario involving a New Madrid earthquake could result in nearly 86,000 dead and injured, leave around 7.2 million people displaced within three days, and inflict approximately $300 billion in direct economic losses.
On top of the general natural dangers of earthquakes, like landslides and flooding, another risk in the region is that many buildings were not designed to withstand an earthquake of this magnitude. If one were to occur, the structural damage would be catastrophic.
To put it bluntly, this part of the country is simply not prepared for a large earthquake.
Nonetheless, fear of a potential earthquake and its impact has led to intensive research into the NMSZ, including studies of past earthquake activity and monitoring ground motion during earthquakes.
However, scientists are still uncertain whether the earthquakes will recur. Little land movement is apparent on the New Madrid Fault system, which confuses scientists.
The faults move by no more than 0.2 millimeters (0.08 inches) per year. This slip rate contrasts with that of other faults, such as the San Andreas Fault in California, which averages 37 mm (1.5 inches) of movement per year.
This has led some scientists to believe the New Madrid system could be shutting down and that tectonic stress may be building up elsewhere. This is gaining some acceptance among researchers but has not been accepted by the National Earthquake Predictive Evaluation Council.
Despite these beliefs, the USGS and the scientific consensus remains that a major earthquake in the NMSZ is possible. The main concern is that small earthquakes still happen in the region and are not decreasing over time.
This differs from what we would expect, where small earthquakes would diminish over time if the system were dying out. Combined with the archaeological record over the past 4,500 years, this provides further evidence of another large earthquake.
The USGS issued a paper in 2009 stating that there is a 7-10% chance of an earthquake comparable to the 1811 and 1812 earthquakes occurring in the next 50 years and a 25 to 40% chance of a magnitude 6.1 earthquake.
The New Madrid earthquakes were extraordinary not simply because of their size, but because of where they happened. Far from the edges of a tectonic plate, they transformed the landscape, disrupted the Mississippi River, and shook a vast portion of North America.
More than two centuries later, the region remains seismically active, and scientists still study it to understand why such powerful earthquakes can occur in the middle of a continent.
The events of 1811 and 1812 are more than a historical curiosity. They are a reminder that some of the greatest natural hazards can lie far from where we normally expect to find them.