In 1811 and 1812, the city of New Madrid and its surrounding areas were caught in a series of three large earthquakes ranked as some of the most powerful in the U.S. since its settlement by Europeans. (Earthquake info from the USGS).
These earthquakes shook over 2.5 million square kilometers (1.6 million square miles). It created massive waves in the Mississippi River that covered boats, tossed others ashore, and destroyed whole islands. The ground rose and fell, bending trees until their branches intertwined and opening deep cracks in the terrain.
The most affected areas were characterized by large areas of land that were uplifted permanently, larger areas that sank and were filled with water that burst through fissures or craters, and massive landslides that covered an area of 78,000-129,000 square kilometers.
Interesting, isn’t it? But what makes it so special? Big earthquakes happen all the time.
Earthquakes usually occur along tectonic plate boundaries, where the plates are sliding beneath, scraping past, or pulling away from each other. They can also happen near volcanoes, where increasing pressure in the magma chamber causes the earth to shake.
New Madrid, Missouri is miles away from any plate boundary or volcano. The most interesting thing near it is the Mississippi River (geologically, anyway). Basically, there shouldn’t have been an earthquake there, let alone three.
So, why did they happen?
Let’s take a dive into earth’s history. I hope that everyone is familiar with the theory of plate tectonics. A long, long time ago, the North American Plate began to tear apart. This is called ‘rifting.’ We don’t know why it did this, but it did, and it began to tear the North American continent apart.
Then, along comes another plate and shoves the North American plate back together. The rifting stops, but it left a deep wound in the continent that never fully healed.
So, in the middle of the continent is North America’s fractured backbone. In 1811 and 1812, it shifted a bit, causing the massive earthquakes.
To understand the concept better, a similar thing happened in Africa. This you should recognize – you see it every time you look at a globe. In that part of the world, the rifting wasn’t interrupted.
The rift continued into eastern Africa (have you ever heard of the Great Rift Valley?) and continues to pull to this day. In a couple million years, there’ll be a new peninsula.
Here are the directions the continent is pulling:
Be grateful the rifting was stopped in North America, or it would be the Mississippi Sea instead of a river.