Yesterday the US Geological Survey posted this reminder to their Facebook page:
The New Madrid Earthquake is well known though mostly as the answer to trivia questions. The presence of a major and active fault line in the middle of the continent is not unusual. But as it sits in the middle of the United States, it is perhaps one of the most studied such faults. What most interests me, having lived in that area and having a strong interest in the history, is how the earthquake affected the land in ways still visible today. Specific to the Civil War, it is that changed landscape we must consider when studying several campaigns. Most notably the Battle of Island No. 10.
The USGS website (linked in the post above) provides more details about the earthquake. An important point to understand is the earthquake was not simply one incident on one date. Yes, the most violent of the quakes was on February 7, 1812 measuring 7.5 in magnitude. But that was just one among over 200 recorded between December 16, 1811 and March 15, 1812, “… ten of these were greater than about 6.0; about one hundred were between M5.0 and 5.9; and eighty-nine were in the magnitude 4 range.” The quakes caused major damage across parts of the central Mississippi Valley. Shaking was observed as far away as Washington and other cities on the Atlantic Coast. In short, this was a “big one.” But at the time, the location was among the westernmost settlements in the United States. So it was not as bad as it could have been – one recorded death in the sparsely populated region.
In terms of physical affects, the web article summarizes:
The earthquakes caused the ground to rise and fall – bending the trees until their branches intertwined and opening deep cracks in the ground. Deep seated landslides occurred along the steeper bluffs and hillslides; large areas of land were uplifted permanently; and still larger areas sank and were covered with water that erupted through fissures or craterlets. Huge waves on the Mississippi River overwhelmed many boats and washed others high onto the shore. High banks caved and collapsed into the river; sand bars and points of islands gave way; whole islands disappeared. Surface fault rupturing from these earthquakes has not been detected and was not reported, however. The region most seriously affected was characterized by raised or sunken lands, fissures, sinks, sand blows, and large landslides that covered an area of 78,000 – 129,000 square kilometers, extending from Cairo, Illinois, to Memphis, Tennessee, and from Crowley’s Ridge in northeastern Arkansas to Chickasaw Bluffs, Tennessee. Only one life was lost in falling buildings at New Madrid, but chimneys were toppled and log cabins were thrown down as far distant as Cincinnati, Ohio, St. Louis, Missouri, and in many places in Kentucky, Missouri, and Tennessee.
And I would point out that many of those affects are still visible today. Driving through the area, one will often see discolored patches of sandy soil marking the location of a fissure or sand-blow. However, one very notable remnant of this quake was large subsidence in Tennessee:
A notable area of subsidence that formed during the February 7, 1812, earthquake is Reelfoot Lake in Tennessee, just east of Tiptonville dome on the downdropped side of the Reelfoot scarp. Subsidence there ranged from 1.5 to 6 meters, although larger amounts were reported.
If you refer to the map embedded with the post above, Reelfoot Lake is just to the upper right of the bold Reelfoot Fault line, on the Tennessee side of the Mississippi River. Where the river crosses the fault line is the area where Island No. 10 was located. I’ve written some on Island No. 10 in the past. Specifically how the topography has changed between 1862 and today, thanks in some part to work aimed at keeping the river in check.
But reflecting back to the earthquakes of 1811-12, there is another geographic and geologic component to consider. Reelfoot Lake and the expansion of similar low areas on the Missouri side created a natural barrier. One of my favorite contemporary illustrations to use when discussing the topography around Island No.10, New Madrid, and Reelfoot Lake is this one:
Yes, horribly stylized with exaggerated features. But the point is served, between Crowley’s Ridge and the Tennessee River lay a vast area of swamps and lowlands, interrupted at intervals with high ground such as the Chickasaw Bluffs. These swamps inhibited transit on land, making the river a vital transportation and communication artery.
When studying terrain as it relates to military campaigns, normally we are drawn to mountains were passes become key terrain features that might be easily defended. But in this case the “passes” are in fact waterways. And therefore we see a natural barrier that might be defended – not with fortifications cited on lofty purchases – but by batteries carefully placed on narrow strips of dry land to contest the passage of ships. The Federals could not by-pass Island No.10 and its associated batteries due to the expanse of swamp. Eventually, the key to unlocking this barrier lay in cutting a passage through the swamps. And that effected, Reelfoot Lake turned from a feature anchoring the Confederate right flank, into a roadblock preventing retreat. You see, those areas of subsidence caused by the New Madrid Earthquake figured prominently in the course of a major campaign.
And those were formed 205 years ago as the earth around New Madrid, Missouri shook.