Breakdown: Why the Mississippi River once flowed backwards
MEMPHIS, Tenn. (WMC) - When people think of earthquakes in the United States, they tend to think of the west coast. But earthquakes also happen in the eastern and central U.S.
Until 2014, when the dramatic increase in earthquake rates gave Oklahoma the number one ranking in the conterminous U.S., the most seismically active area east of the Rocky Mountains was in the Mississippi Valley area known as the New Madrid seismic zone.
Since 1974, seismometers (instruments that measure ground shaking) have recorded thousands of small to moderate earthquakes that encompasses the New Madrid fault in northeastern Arkansas, southwestern Kentucky, southeastern Missouri, and northwestern Tennessee.
The faults that produce earthquakes are not easy to see at the surface in the New Madrid region because they are eroded by river processes and deeply buried by river sediment.
A series of three large earthquakes occurred new New Madrid, Missouri between December 1811 and February 1812.
There were thousands of aftershocks, of which 1,874 were large enough to be felt in Louisville, Kentucky, about 190 miles away.
Magnitude estimates for each of the three events associated with the 1811–12 earthquake sequence vary widely, largely because they rely on historical accounts and analyses of the present-day landscape rather than data provided by modern seismic instrumentation.
The magnitude of the December 16, 1811, event ranged from 6.7 to 8.1, whereas the ranges for the earthquakes of January 23 and February 7, 1812, were 6.8–7.8 and 7.0–8.8, respectively.
More-precise figures have been presented by the United States Geological Survey (USGS) Earthquake Hazards Program: magnitude 7.7 for the December earthquake and magnitudes 7.5 and 7.7 for the January and February earthquakes, respectively.
Scholars do agree, however, that the New Madrid earthquakes were the strongest such events recorded in North America east of the Rocky Mountains.
So strong, in fact, the Mississippi River switch courses and flowed in reverse after one of the earthquakes. According to http://www.new-madrid.mo.us:
After the February 7 earthquake, boatmen reported that the Mississippi actually ran backwards for several hours. The force of the land upheaval 15 miles south of New Madrid, drowned the inhabitants of an Indian village; turned the river against itself to flow backwards; devastated thousands of acres of virgin forest; and created two temporary waterfalls in the Mississippi. Boatmen on flatboats actually survived this experience and lived to tell the tale.
How did this happen?
It happened when a thrust fault created a sudden dam several feet high near the bottom of the river loop near New Madrid.
This animation from Incorporated Research Institutions for Seismology (IRIS) shows how a river can be forced backwards, albeit only long enough to find a new route.
Several written accounts from the New Madrid earthquake of 1811 and 1812 describe the horror as great waters washed up on previously dry land.
According to the USGS, this particular earthquake occurred on a fault that actually crossed the river three times. The uplift along this fault formed a scarp or cliff that caused both a dam and waterfalls at different locations. The damming of the river would have temporarily backed the river up, which may account for the descriptions of the river boat pilots.
The University of Memphis center for Earthquake Research and Information has obtained eyewitness accounts of these powerful earthquakes that give a glimpse at what was seen and experienced by people as the quakes occurred.
You can also learn more interesting earthquake facts here.
Many areas of the globe are prone to earthquakes (see links below) You could be anywhere when an earthquake strikes: at home, at work, at school or even on vacation. Are you prepared to survive and to recover quickly?
On October 21 International Shakeout Day is observed with the mission to educate the public about the importance of taking immediate action in case of an earthquake. This day, which falls on the third Thursday in October, remains our best opportunity to learn (and practice) how to protect ourselves and put our loved ones out of harm’s way.
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