The New Madrid Earthquake in Missouri, USA
The Mississippi River and the Earthquake of 1811
At 2 a.m. on the night of December 16, 1811, a continuous roar of thunder echoed through the darkness and the hellish stench of sulfur permeated the air. Log cabins and houses broke apart. The residents of New Madrid, Missouri raced screaming from their homes out into the darkness.
No place was safe from the earthquake tremors. Horses shrieked and stampeded through the streets trampling over anything or anyone who might be in their way. Trees cracked, snapped and fell to the ground. Roosting birds flew out of their tree-top havens in the dark, and then attracted to light, the night-blinded birds crashed into the lanterns carried by the townspeople. Many thought that the end of the world was at hand.
The town of New Madrid suddenly dropped 15 feet in elevation. The normally gentle Mississippi River turned deadly as it receded from its banks and water bulged up in the center of the riverbed. Any boats anchored nearby found themselves resting momentarily on the sandy river bottom. Observers reported that the swell of water rose to fifteen or twenty feet before it suddenly collapsed and flooded the banks. Most of the boats tore loose from their moorings as the river began a violent retrograde flow. The next day these broken boats lay grounded on the river banks as much as a quarter of a mile upstream.
Other Impacted Areas
In the Missouri boot-heel, the land itself was destroyed by fissures in the earth which ripped open and spewed out pungent gases, sand and rancid water. The soil in that area was unsuitable for farming for many years after the event.
A new lake formed on the opposite side of the Mississippi River where the land surface subsided as much as 18 feet in elevation, and the river flooded an area one hundred miles in length by one to six miles in width. Today it is known as Reelfoot Lake.
Seismic Energy
The New Madrid earthquake event resulted from the largest burst of seismic energy east of the Rocky Mountains in the history of the United States. It was several times larger than the San Francisco earthquake of 1906. In comparison, the California Loma Prieta earthquake in October, 1989 scored a Richter Scale magnitude in the range of 6.9.
Between 1811 and 1812, four cataclysmic earthquakes occurred during a three-month period from December of 1811 through February of 1812. Although the Richter Scale was not yet in use at that time, present-day seismologists estimate the most violent earthquakes showed magnitudes ranging from 7 to 8 on the Richter Scale.
Aftershocks
Over 200 aftershocks accompanied these quakes and eighteen of those tremors rang church bells in Boston and as far south as Charleston, South Carolina. At times newspapers recorded the aftershocks as far north as Montreal.
Earthquake Risk in the United StatesPresently the highest earthquake risk in the United States outside the West Coast is along the New Madrid Fault Zone. This fault system extends 120 miles southward from the Charleston, Missouri and Cairo, Illinois area through New Madrid, Missouri. It then follows Interstate 55 to Blytheville and ends at Marked Tree, Arkansas. This fault system crosses five state lines and cuts across the Mississippi River in three places and the Ohio River twice.
Fault Zones
Earthquakes generally occur in areas where two tectonic plates either collide or rub against each other. The San Andreas fault in California is located where the Pacific plate moves northward as it grinds against the North American plate. In South America, the Pacific plate is diving under the South American plate resulting in the formation of the Andes Mountains.
The New Madrid Fault Zone is located in the middle of the North American tectonic plate and neither explanation can account for the earthquakes in that area. Another theory proposes that the North American plate is thinner and weaker near to its center forming a rift zone. As the Pacific plate rubs against the west side of the North American plate in California, a buckling effect near the center of the North American plate may account for the New Madrid earthquakes.
The New Madrid fault system is still active today and averages over 200 events per year at a magnitude of 1.0 or greater on the Richter Scale. Several tremors large enough to be felt (2.5-3.0 magnitude) occur annually. On average, every eighteen months the fault releases a shock of magnitude 4.0 or greater which is capable of local minor damage. An earthquake in the 6.0 magnitude range occurs about once every eighty years. The last one of this magnitude occurred in 1895. The area is now overdue for such a quake.
Future Earthquake PredictionsA catastrophic earthquake in the magnitude range of 7.5 or greater may occur every 200-300 years. The last one happened in 1812. At the time, the area was sparsely populated and most of the structures were no higher than two stories. Today such an event would be felt throughout half the United States and serious damage would be expected in at least 20 surrounding states.
Earthquake probabilities for active faults increase with time as stresses within the earth slowly build up year by year until the rock reaches its physical limits of stress and strain. Then a sudden rupture is inevitable. Occasionally the two plates may hang up on each other, and when they suddenly break loose, seismic energy is released in the form of an earthquake shock. Researchers now predict that a 6.0 or greater magnitude earthquake has a 90% chance of occurring by the year 2040.
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