One of the most powerful quakes to hit North America occurred in the Midwest in the early 1800s. The earthquake was so powerful, that it caused the Mississippi river to flow backwards and caused exotic ‘Sand Blows‘. Sand blows are essentially sand volcanoes which spew dirt and sand up from the ground. The violent tremors caused the land underneath the sand layers to shift and bulge, which caused the pockets of sand to pop out of the ground, like a zit.
All this chaos happened during the New Madrid earthquakes of Dec. 1811 & Feb. 1812. We don’t know exactly how strong the earthquakes were because unfortunately, there were no seismographs back then. However, by gauging the extent of land changes, researchers can extrapolate that there were at least three, closely related quakes that were a magnitude of 8 or more on the Richter seismograph scale.
Going The Distance
The New Madrid earthquakes were so powerful, that they were felt over nearly 1 million square miles. Not only did the quake reverse the flow of the Mississippi, but it damaged the sidewalks in Washington D.Cand reportedly rang church bells in Boston.
That’s an incredibly powerful quake, especially for the Midwest where strong earthquakes are virtually non-existent. It was more powerful than the deadly San Francisco quake of 1906. While it was one of the strongest North America has seen, it wasn’t the most powerful. That title lies with the Alaskan earthquake of 1964, which was 8.4 on the Richter scale. It was the second most powerful earthquake every recorded on a seismograph. The Alaska earthquake also caused a tsunami which resulted in deaths on a few small islands in the Pacific, and caused damage to the shores of Japan and Hawaii.
The Mississippi river flowed backwards temporarily due the quake shifting around the land. Once the land was settled and the quakes had ceased, the river begun to flow normally again. The river hasn’t flowed backwards since.
A Bleak Future?
Today, New Madrid has tens of thousands of citizens in the region and is a well developed city. In 1811, New Madrid only consisted of roughly 400 log cabins. Regarding speculation of the the New Madrid earthquakes happening today, a USGS spokesman said, “Should a category-8 quake occur there today, those cities would be mostly destroyed and thousands of people killed“.
Regarding future quakes, the USGS gives this warning: “The probability of a magnitude 6 to 7 earthquake occurring in the New Madrid seismic zone within the next 50 years is higher than 90 percent.”