VOL. 21 November ISSUE YEAR 2020

Off the Beaten Track

in Vol. 21 - November Issue - Year 2020
On the Verge of Dissolution
from ©Encylopaedia Britannica. Inc.

from ©Encylopaedia Britannica. Inc.

In December 1811, William Pierce was floating in a flat-bottomed boat down the Mississippi River, about 200 km south of where it is joined by the Ohio River. There was something about the unusually thick and heavy air that made him uneasy. Suddenly, the earth opened up before Pierce and his traveling companions. In a letter written days later to the New York Evening Post, he described the “volcanic discharge of combustible matter” skyward. “The earth and river, torn with furious convulsions, opened in huge trenches. Through a thousand vents, sulphurous streams gushed from its very bowels, leaving vast and almost unfathomable caverns. The bed of the river was excessively agitated, whilst the water assumed a turbid and boiling appearance. Everywhere Nature itself seem tottering on the verge of dissolution,” wrote Pierce.
Although minor and imperceptible earthquakes occur the world over, the most powerful and violent earthquakes are normally associated with certain areas such as the Pacific Rim or the Mediterranean Sea. For this reason, the three extremely violent earthquakes and thousands of powerful aftershocks that shook the Mississippi River valley from December 1811 to February 1812 continue to baffle scientists. This sequence is usually referred to as the New Madrid earthquakes, after the name of the largest settlement in the area in present-day Missouri.
The first earthquake struck on December 16, 1811 at 2:15 a.m. with an estimated magnitude of 8.1 on the Richter scale. Thunderous roars similar to cannon fire awoke residents, while houses swayed and brick chimneys collapsed. A terrible stench of sulphur greeted the terrified people as they rushed about aimlessly in the darkness outside. It was bitterly cold. One settler wrote “the night (was) made loud with the cries of fowls and animals, the cracking of the trees, and the surging torrent of the Mississippi.” The mighty Mississippi was indeed rolling in high violent waves. Riverbanks collapsed, flooding thousands of acres of woodlands. Entire forests were swept into the water. Numerous boats capsized, drowning crews and passengers.
The dazed and frightened survivors were still trying to overcome their shock when a powerful 7.4 Richter aftershock hit six hours later. This time the ground movement was more undulatory. A young boy saw the ground “rolling in waves” and many people observed the river rise up “like a great loaf of bread to the height of many feet.” Some parts of the Mississippi rose so high that the river ran backwards. Thousands of fissures appeared in the fields and geysers spewed water and mud high into the air. This aftershock did much more damage compared to the earlier quake. Over the next two days, there were another five aftershocks ranging between 5.5 and 7.0 Richter.
A second earthquake (7.8 Richter) struck at 9:00 a.m. on January 23, 1812 in what is now Missouri, with numerous reports of widespread fissuring, ground warping, severe landslides and riverbanks collapsing.
Just when they thought that they had been through enough in their lifetime, residents were jolted out of their beds at 3:45 a.m. on February 7, 1812 by a third quake, the most powerful and most damaging in the sequence (8.8 Richter). The town of New Madrid was destroyed and many houses in St. Louis were severely damaged. Thirty boats went over two waterfalls that appeared briefly, with a total loss of crew. After breaking its banks, the Mississippi formed Reelfoot Lake in Tennessee and Big Lake in Arkansas.
Thousands of aftershocks occurred over the following decades, with almost 2,000 of them strong enough to be felt in Louisville, Kentucky, about 300 km away.
Underground rock formations east of the Mississippi have few faults to interrupt the propagation of seismic waves. Ground vibrations generated by earthquakes can easily travel thousands of miles. The New Madrid earthquakes caused strong ground shaking in Canada and on the Gulf Coast. Numerous eyewitness accounts reported church bells ringing as far away as Boston, Massachusetts and chimneys collapsing in Cincinnati, Ohio. Dolley Madison, wife of the 4th U.S. President James Madison, was reportedly thrown out of her bed in the White House.
It has been calculated that residents within an area of 600,000 km2 experienced damage and very strong ground shaking, and people within an area of 2,500,000 km2 experienced shaking strong enough to frighten them. The USGS reports that “the area of strong shaking associated with these shocks is two to three times as large as that of the 1964 Alaska earthquake and 10 times as large as that of the 1906 San Francisco earthquake.”

By Giovanni Gregorat, Contributing Editor MFN