Plate tectonics is the theory that has been studied for over thirty years that states that the outside layer of Earth are actually large plates, approximately forty kilometers thick, that slide across the magma beneath the exterior of the planet. The theory of plate tectonics explains the enormous amount of volcanic and seismic activity surrounding certain areas of the world, stating that the sliding of these plates either away from each other, sliding past each other, or sliding into each other and causing one of the plates to slide beneath the other. When the plates slide away from each other, new ocean floor is formed. When the plates slide past each other, minor earthquakes will occur. When the plates slide toward each other and one plate subsides, volcanic activity will occur. The area around the subsiding plate is the subduction zone. The subduction zone is the seismically and volcanically active area nearby a tectonic plate that is submerging below another tectonic plate. The subduction zone supports the theory of plate tectonics by showing wherever two plates collide and one subsides, volcanoes are present. Also, the sedimentary rock found on the top and bottoms of plates is also present in the magma that is released in subduction zones in the Pacific Ocean. Any volcano formed around the edge of the Pacific Ocean tectonic plate is an example of a volcano formed in the subduction zone, like Mount Saint Helen.
Volcanoes that from in the middle of a plate are said to be a product of what is known to be a "hot spot". A hot spot is a region in the lithosphere that breaks and continually allows the release of magma onto the surface of the planet. Before the hot spot was considered the reason for volcanic eruptions, skeptics of the theory of plate .
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tectonics used the volcanic activity that took place in the middle of the plate as proof that the theory of plate tectonics was not true.
