Plate Tectonics
How landforms are formed and why volcanism exists can best be explained by the use of plate tectonics. Plate tectonics theorize that segments of the Earth's lithosphere called tectonic plates, move about, giving rise to earthquakes and volcanic activity. For example, the North American and Eurasian plates are separating along the Mid-Atlantic ridge about two centimeters a year. (Zeilinga de Boer and Sanders, 109).
Plate tectonics was firmly established by 1968. Three seismologists published papers showing how successful the plate tectonics theory explains the distribution of earthquakes. (Tarbuck and Lutgens, 497). This plate tectonics model also accounts for earthquakes along subduction zones while showing which are shallow, intermediate, or deep-focus. Deep focus earthquakes occur only in association with convergent plate boundaries and subduction zones. (Tarbuck and Lutgens, 507).
The plate tectonics theory describes plate motion and the effects of this motion.The unequal distribution of heat within the Earth is the cause of plate movement. Plates move as coherent units relative to all other plates along boundaries. For example, there are three distinct boundaries depicted by the type of movement they exhibit according to Tarbuck and Lutgens. In divergent boundaries, plates move apart resulting in upwelling of material from the mantle to create new seafloor. In convergent boundaries, plates move together in the subduction of oceanic lithosphere into the mantle. In transform fault boundaries, plates grind past each other without the production or destruction of lithosphere (Tarbuck and Lutgens, 483).
Most divergent boundaries are located along the crests of oceanic ridges, a few exceptions being the Red Sea, the site of a young divergent boundary. Here the Arabian Peninsula separated from Africa, embarking on a northeast movement. The Gulf of California, which separates the Baja Peninsula from the rest of Mexico, was created by seafloor spreading. Convergent boundaries zones usually produce strong earthquakes when the spreading axis is located near a young, warm and buoyant lithosphere. The Peru-Chile trench is an example of this type of a subduction zone. Convergent zones can form between two oceans, an ocean and a continent, or two continents. I will use several videos and CDs from the Bibliography to convey the role plate tectonics play in volcanic formation and volcanism.
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