The New Madrid Earthquakes of 1811 and 1812

The first of the 1811 and 1812 New Madrid earthquakes occurred on the sixteenth of December 1811. Its magnitude was 7.2. The second quake hit the same area on the fifth of February 1812. Its magnitude was 7.4. In between there were numerous aftershocks. Both earthquakes were centered on a part of the Mississippi embayment close to where the states of Missouri, Arkansas, Kentucky, and Tennessee meet. The ensuing destruction was similar and widespread for both events; buildings collapsed, trees toppled, and the Mississippi River changed course. What could be called mini-tsunamis appeared on the river as fissures opened and closed below the surface. The shock waves rang church bells in Washington, D.C., and they were felt from Indiana to Massachusetts. Fortunately, there were few people living in the area at the time so, in spite of the great intensity of the earthquakes, the loss of life was very small.

On the basis of the size of the area damaged and the extent to which awareness of the events was felt across the continent, the New Madrid earthquakes can be considered the most powerful to have hit the UnitedStates since Europeans first settled here. An area of more than 200,000 square miles showed evidence of significant damage by these earthquakes and one million square miles experienced shaking that was strong enough to alarm the general population. This last-mentioned area can be compared with the effects of more recent events. It was more than twice the size of the area affected by the 1964 Alaska earthquake and ten times larger than that of the San Francisco earthquake of 1906. The complex physiographic changes that occurred on the Mississippi River within the earthquake areas were extensive. An uplift of land thirty miles long and fifteen miles wide raised the river’s valley by as much as thirty feet.

The first effects of the earthquakes on those who lived in and around New Madrid were the sounds of timbers groaning, creaking, and cracking, of furniture being thrown around, and of chimneys crashing down. People got out of their homes as quickly as they could in order to avoid the falling debris. The log cabin was the most common type of building in the area, a structure that is well able to withstand earthquakes, yet one that did not stand up in this instance because of the extensive ground movements. Earth waves similar to those experienced in water kept moving across the surface, bending trees and opening up deep cracks in the ground. Landslides, one after another, swept down from the steeper bluffs and hillsides and, simultaneously, large areas of land were uplifted. Water emerged from below through the cracks. On the river huge waves overwhelmed a number of boats. Others were thrown on to land high above the level of the water and the returning waves took back with them trees and other debris, rather like the actions of a tsunami. Whole islands in the river disappeared.