Everything Everywhere Daily: History, Science, Geography & More - The New Madrid Earthquakes

Starting point is 00:00:00 In the winter of 1811, the American frontier was shaken by a series of earthquakes so powerful that 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. Comprehensive. Witty.

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Starting point is 00:01:25 You can't get people to understand the humaning that happens in this damn show. Keep doing what you're doing because it's awesome. You might not think it, but you are far more important than you realize. Thank you. At the nexus of all things, there is a diner. Look for Midnight Burger on your favorite podcasting app, or just go to we open at 6.com. The New Madrid Seismic Zone, otherwise known as the NMSZ, is located in the Midwest and Southern

Starting point is 00:01:55 United States, covering territory in northeastern Arkansas, southeastern Missouri, western Kentucky, and Tennessee, and southern Illinois. The zone 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 New Madrid Seismic Zone unique is that it is an intramed. plate 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. Stresses build up against the plates until the energy is released as

Starting point is 00:02:42 earthquakes. By comparison, the interior of plates are usually tectonautics. These areas move significantly more slowly, so the interiors don't experience the same stresses, and therefore experience fewer earthquakes. However, stresses within tectonic plates can sometimes 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,

Starting point is 00:03:23 leading to eventual slippage. The New Madrid seismic zone appears to have formed roughly 600 million years ago, as shown by deformed ancient rocks. Scientists believe that the North American continent 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've covered in a previous episode. Continental Rifting is a geological process in which tectonic forces pull continents apart. In the New Madrid seismic zone, continental rifting failed. This created a rift in the middle of the United States, known as the Real Foot Rift. The faults here are difficult to see with the naked eye because rivers eroded the region's

Starting point is 00:04:07 surface and buried it under the sediment. This causes the Real Foot 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 rock deposited 50 to 100 million 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 caused the region's earthquakes. There are hundreds of small earthquakes occurring in

Starting point is 00:04:48 the zone every year. Most of these are so small that they're 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 16th, 1811, around 2.15 a.m. in what is now known as Blytheville, Arkansas. The earthquake was estimated to be at a magnitude 7.5 on the Richter scale. Tremors were felt in the eastern United States over 900 miles away, and President James Madison reportedly felt the ground shake in Washington, D.C. After the initial earthquake, several large

Starting point is 00:05:36 aftershocks followed, including one at dawn at 7.15 a.m. This aftershock was estimated to be of a 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 further north, such as Carruthersville, Missouri, suffered damage due to soil liquefification. In the end, significant damage was observed over an area of 230,000 square miles or 600,000 square kilometers. After the two initial earthquakes, another one hit on January 23, 1812, and 9.15 a.m. This one was a magnitude 7.3 earthquake with its epicenter in southern Missouri. In the area of maximum damage, the ground experienced ejections,

Starting point is 00:06:31 warping, fissures, landslides, and stream bank collapses. Yet another earthquake hit on February 7, 1812. This magnitude 7.5 earthquake occurred near New Madrid, Missouri, which destroyed the entire town. Faulting, uplifting, subsidence, and enormous waves temporarily disrupted the flow of the Mississippi River. Contemporary observers reported the river flowing backwards in places, although some of these observations may have involved upstream moving waves rather than a sustained reversal of the river's flow. The aftermath of the earthquakes changed the region's topography. The earthquakes caused landslides, uplift, downward movement to the earth's crust, and the formation of fissures. On top of the changing

Starting point is 00:07:17 landscape, the shaking completely uprooted many 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 and the St. Francis River area also changed with water levels rising by 8 to 9 feet. Waves that formed on the Mississippi River washed boath ashore and destroyed sandbars, causing some islands in the river to completely 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.

Starting point is 00:07:57 This happens during the shift. 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 towards the surface. And 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 as much as 10 to 20

Starting point is 00:08:43 feet into the air. The sand blows made a large portion of the area completely unusable for agriculture for years. Farmers in the Missouri River Valley still find sand from the eruption when plowing 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 was poor. Even homes that survived, likely still suffered damage as intense shaking caused chimneys to collapse and structures to crack. Only a small number of deaths can be documented directly, including one person killed by a collapsing building at New Madrid,

Starting point is 00:09:33 while an unknown number of people may have drowned when boats capsized or riverbanks collapsed. So, because the region was sparsely populated and because 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 disaster relief 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. That earthquake was recorded on November 9, 1968 near Dale, Illinois.

Starting point is 00:10:28 It was felt in 23 other states and caused some property damage. In 2008, the United States Federal Emergency Management Agency, or FEMA, 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.

Starting point is 00:11:07 If a magnitude 7.6 earthquake hit the New Madrid seismic zone, the bedrock in that part of the United States would shake over an area 20 times larger than the area affected by a similar-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.

Starting point is 00:11:55 So 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 New Madrid seismic zone, including studies of past earthquake activity and monitoring ground motion during earthquakes. However, scientists are still uncertain whether the earthquake will occur at all. Little land movement is apparent on the New Madrid fault system, which confuses scientists. The fault moves by no more than 0.2 millimeters per year. This slip rate contrast with that of other faults, such as the San Andreas fault in California, which averages 37 millimeters of movement per year.

Starting point is 00:12:45 This has led some scientists to believe that the New Madrid system could be shutting down, and that tectonic stress may be building up somewhere else. This is gaining some acceptance among researchers, but it has not been accepted by the National Earthquake Predictive Evaluation Council. Despite these beliefs, the U.S. Geological Survey and the scientific consensus remains that a major earthquake within the New Madrid seismic zone is still possible. Their main concern is that small earthquakes still happen and have not been decreasing over time. These observations differ from what we would expect were small earthquakes to diminish over time if the system were dying out.

Starting point is 00:13:29 Combined with the archaeological record over the past 4,500 years, this provides further evidence that another large earthquake is possible. The United States Geological Survey issued a paper in 2009 stating that there is a 7 to 10,000, 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.

Starting point is 00:14:25 The events of 1811 and 1812 are more than just a historical curiosity. There are a reminder that some of the greatest natural disasters can lie far from where we would normally expect to find them. The executive producer of Everything Everywhere Daily is Charles Daniel. The associate producers are Austin Otkin and Cameron Kiefer. Research and writing for this episode was provided by Olivia Ash. My big thanks go to everyone who supports the show over on Patreon. Your support helps make this podcast possible. And I also want to remind everyone about the community groups on Facebook and Discord.

Starting point is 00:15:02 This is where everything happens that's outside of the show. As always, if you leave a review on any major podcast app, or in the above community groups, you two can have it run on the show.

Everything Everywhere Daily: History, Science, Geography & More - The New Madrid Earthquakes

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