Why do Tectonic plates move?
Tectonic plates comprise of crust and upper mantle rock. The upper mantle rock is less dense than the denser mantle. The increase and decrease of convection currents in the mantle result in slow progressive movement in the plates. The heat origin during the convection currents was obtained from the creative process of Earth, pressure in gravity, and radioactive decay in the metals. The distribution of convection currents in the Earth was found to be responsible for the movement of plates.
The surface of the earth constitutes seven large plates and several small moving plates. These plates which had thickness of 50 miles could move few inches in a year on an average. The plate movements are of three types. They are convergent, divergent and transform fault. The plates move towards each other in the case of convergent type and form deep ocean trenches. They move away from one another in the divergent type as in the case of Mid-Atlantic ridge. In the boundaries called as transform fault, the pacific plate bearing Los Angeles is moving on the North American plate where San Francisco is lying.
The rapid movement of tectonic plates was studied to be due to the forces that are initiated from the radioactive earth and solid iron core. The movement happens on the top of hot, soft and malleable rock known as athenosphere. As this layer has high temperatures and more pressures, it flows under the surface of the earth allowing the plates to move very slowly.
The flowing nature of athenosphere is achieved by it due to convection currents. The mantle rocks lying close to the radioactive core gets heated up, rises high and become less dense. The cooler rocks remain down while the hot rocks move up. Due to the convection currents these rocks keep moving every year inch by inch. This movement of mantle rocks will form an area called convection cells in the circular format in the mantle. The movement of these convection cells might act as the stimulant for the movement of tectonic plates in the athenosphere.