Tectonics the Ups and Downs

Tectonics

The Ups and Downs of Plate Tectonics

Traditionally, we think of plate tectonics as occurring laterally along the Earth's surface as the crust's plates are pushed back and forth along the top of the mantle. In fact, recent research and computer modeling has illustrated that there are more forces at work within the mantle that have a significant impact on the orientation and characteristics of features on the surface of the planet.

One of the persistent problems in geology has revolved around the African superswell, a plateau in South Africa that is 1,000 miles wide and more than a mile high (Gurnis 40). Unfortunately, classical tectonic theory was unable to account for how the superswell had risen so high above sea level. Other similar issues have cropped up over the decades, including Cretaceous sea levels around Denver, Colorado in North America.

New computer models have demonstrated a solution to this problem. It has long been known that the mantle is semi-liquid in nature and that the crust floats upon the surface of this liquid. However, what is becoming clearer is the extent to which the mantle behaves like a liquid. As the mantle heats and cools unevenly, areas of differing density slowly move through the mantle. As they do, these areas of density variance have effects on surface features on the crust. For instance, there is a denser mass in the mantle shaped like a mushroom thousands of miles across and rising 900 miles from the Earth's core. The gentle rise of this mass has had the immediate effect of producing the African superswell, proof that motion in the mantle can have vertical as well as horizontal effects on the crust (Gurnis 40).