What is Gravity's Role in Plate Tectonics?

February 14, 2024

Plate tectonics is an amazing geologic process. It is responsible for a lot of interesting stuff on Earth, such as earthquakes, volcanoes and mountain and ocean formations. Plate tectonics is driven by forces deep within the Earth's interior that are very complex and difficult to understand.

Plate movements are primarily driven by the movement of mantle convection. The mantle is a hot, viscous fluid that can slowly flow in response to steady forces applied over long periods of time. As the mantle convects, it drags overlying plates along with it. But a large portion of the plates do not have a subducting section, and this makes it unlikely that the mantle convection alone can drive the plates.

So what is gravity's role in plate tectonics? Scientists have two competing ideas for the answer. One idea is that, as magma rises from deep in the Earth, it cools and becomes denser. Then it will sink under less-dense plates. This is the ridge push model of plate tectonics.

The other idea is that the force of gravity is stronger than the ridge push. It is based on the fact that as cool, dense plates move away from mid-ocean ridges they become heavier and sink into the mantle. Then they will pull the rest of the plate with them at the subduction zone. This is the slab pull model of plate tectonics.

It is not clear which of these models is correct, but both can play a role in the overall motion of the plates. In any case, the tectonic plate system is constantly evolving and changing. Scientists are continuing to study it and learn more about the forces that drive it.

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