There is a newly devoloped theory which explains some of the geological anomalies of the Ozark region. These anomalies are:

• The isolation of the Ozark (Oachita) Mountains
• The powerful New Madrid earthquakes of 1811-1812
• The existence of diamond deposit sites in Arkansas

The theory asserts that the Oachita Mountains were originally just the tail end of the Appalachian Mountain chain. A geologic event resulted in the destruction of the mountains connecting the Appalachians and the Oachita Mountains. The mountains did not just disappear; there appeared in their place a depression, called the Mississippi Embayment, an extention of the Gulf of Mexico into the interior of the North America. This allowed the rainfall of the Midwest to drain into the Gulf of Mexico thus forming the Mississippi-Missouri-Ohio Rivers system.

According to the theory the continuous chain of mountains isolated what is now the Midwest of the United States from the Gulf. The North American plate is slowly moving west thus enlarging the Atlantic Ocean. There is now in mid-ocean a hot spot where molten rock, magma, reaches the surface. It is where the Bermuda Islands are now. At one time the North American plate was over that hot spot. When the region that is now the Mississippi Valley between the Appalachians and the Oachita Mountainswas over the hot spot it caused the land about it to rise, perhaps as much as a mile or two in elevation. This elevated land was eroded, in the course of time, to the level of the surrounding land. But in the course of time as well the region passed beyond the hot spot. The land then cooled and shrunk back to its original position but then a mile or two of rock and soil were gone so there was a deep depression or canyon where the mountains had been. The waters of the Mid-West could then drain into the depression. In time the depression filled in and it became just the lower part of the Mississippi River Valley.

According to the theory when the region was over the hot spot there were volcanoes in the area. Diamonds form in the cooling pipes of volcanoes so this is where the diamonds of Arkansas came from. Also the period over the hot spot created earthquake faults. The New Madrid earthquakes were apparently due to land slides into the canyon depression. At another period the region around Charleston, South Carolina was over the hot spot. This accounts for the active earthquake zone around Charleston that produced severe earthquakes in the 19th century. However not all regions which passed over the hot spot have experienced volcanoes and earthquakes. This is because, according to theory, the hot spot experiences cycles of activity. The hot spot was in a particularly active phase when the region between the Oachita and Appalachian Mountains was over it. Since supposedly the hotspot was also active when the Charleston area was over it one should look a distance west of New Madrid equal to the distance from Charleston to New Madrid and find some evidence of similar geological phenomena. A linear extrapolation of the trajectory from Charleston to New Madrid would put that point where Colorado, Kansas and Nebraska come together. There is not anything of notable geological signficance at that location but a several hundred miles to the southwest in New Mexico there is evidence of considerable ancient volcanic activity. Since a hotspot cycle would not be precise and the path of North American plate may not have been linear the volcanic activity in west central New Mexico could be supporting evidence for the theory. The New Mexican volcanic activity is probably datable so it would be worth pursuing.

And, of course, several hundred miles farther west of the place where Colorado, Kansas and Nebraska come together is the Yellowstone area, an area of extraordinary geological structure.

Source:
Roy G. Van Arsdale and Randel T. Cox, "The Curious Origin of the Mississippi", The Scientific American, January 2007, pp. 77-84.