Missouri Shakes

The Overlook

By Tom Clavin

“The Overlook” appears every Wednesday at tomclavin.substack.com. An overlook is usually a place from which one can see in many if not all directions, including where one has been and where one is going. If you enjoy the column, please "like" it and let me know what you think by commenting (check out previous ones while you're at it). All support is appreciated. Don't forget to hit the ‘Subscribe’ button – it’s free!

          This coming Saturday is the 212^th anniversary of what some scientists consider the most powerful earthquake event in the continental U.S. No, not the famous one in San Francisco – it’s the one in Missouri. And it could happen again, with much more devastating consequences.

          The quake that struck on December 16, 1811, was the first in a series of powerful earth-shakers which extended into February of the following year. The initial quake of “moment magnitude” 7.2 – 8.2 was followed by a 7.4 aftershock on the same day. Two additional earthquakes of similar magnitude followed in January and February 1812. They remain the most powerful earthquakes to hit the contiguous United States east of the Rocky Mountains (that we know of). The earthquakes, as well as the seismic zone of their occurrence, were named for the Mississippi River town of New Madrid, then part of the Louisiana Territory.

          The epicenters of the earthquakes were in an area that at the time was at the distant western edge of the sparsely populated American frontier. Yet the region’s earthquakes were felt strongly throughout much of the central and eastern United States, across an area of roughly 50,000 square miles and moderately across nearly 3 million square miles. The San Francisco earthquake in 1906, by comparison, was felt moderately over roughly 6200 square miles. The New Madrid earthquakes were interpreted variously by Indigenous tribes – for Tecumseh’s alliance of tribes, they meant that he and his brother the Prophet must be supported in their efforts against white intruders.

          The epicenter of the December 16 quakes was in what is now northeast Arkansas. They caused only slight damage to man-made structures, mainly because there were so few of them. The impact of the January 23rd (1812) was general ground warping, some landslides, and the caving of stream banks. The epicenter of the February 7 quake was New Madrid and the town was destroyed. In St. Louis, many houses were severely damaged and chimneys were toppled.

          Overall, the quakes caused extensive changes to the region's topography. Subsidence, uplift, fissures, landslides, and riverbank collapses were common. Trees were uprooted by the intense shaking; others were drowned when subsided land was flooded. Reelfoot Lake was formed in Tennessee by subsidence ranging from two to eight feet in some places. Lake St. Francis, in eastern Arkansas, was expanded by subsidence, with sand and coal being ejected from fissures in the adjacent swamps as water levels rose by as much as 10 feet. Waves from the Mississippi River caused boats to wash ashore; riverbanks rose, sand bars were destroyed, and some islands completely disappeared. Sand blows also occurred in Missouri, Tennessee, and Arkansas, destroying farmland.

The underlying cause of the earthquakes is not well understood, but modern faulting seems to be related to an ancient geologic feature buried under the Mississippi River alluvial plain, now known as the Reelfoot Rift. The New Madrid Seismic Zone is made up of reactivated faults that formed when what is now North America began to split or rift apart about 750 million years ago.

In recent decades, minor earthquakes have continued. The epicenters of over 4000 earthquakes can be identified from seismic measurements taken since 1974. They originate from the seismic activity of the Reelfoot Rift. New forecasts estimate a 7 to 10 percent chance, in the next 50 years, of a repeat of a major earthquake like those that occurred in 1811–1812, which possibly had magnitudes up to 8.0. A 25 to 40 percent chance exists in a 50-year time span of a magnitude 6.0 or greater earthquake.

Obviously, the resulting damage would be exponentially more severe than over two centuries ago. In a report filed in November 2008, the U.S. Federal Emergency Management Agency warned that a serious earthquake in the New Madrid Seismic Zone could result in "the highest economic losses due to a natural disaster in the United States,” further predicting "widespread and catastrophic" damage across Alabama, Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri, and particularly Tennessee, where a 7.7 magnitude quake or greater would cause damage to tens of thousands of structures affecting water distribution, transportation systems, and other vital infrastructure. Ongoing research should help identify which areas are most in danger.

And you thought all we had to worry about was climate change!

Tom Clavin is the bestselling author/co-author of 25 books, including The Last Hill (with Bob Drury) and The Last Outlaws, which was published last month by St. Martin’s Press. Both would make enjoyable holiday gifts! Please go to your local bookstore or to Bookshop.org, Amazon.com, BN.com, or tomclavin.com to purchase a copy.