The plates consist of an outer layer of the Earth, the lithosphere, which is cool enough to behave as a more or less rigid shell. Occasionally the hot as the no sphere of the Earth finds a weak place in the lithosphere to rise buoyantly as a plume, or hot spot. The satellite image below shows the volcanic islands of the Galapagos hot spot. In cross section, the Earth releases its internal heat by convecting, or boiling much like a pot of pudding on the stove. Hot as the no spheric mantle rises to the surface and spreads laterally, transporting oceans and continents as on a slow conveyor belt. The speed of this motion is a few centimeters per year, about as fast as your fingernails grow. The new lithosphere, created at the ocean spreading centers, cools as it ages and eventually becomes dense enough to sink back into the mantle. The sub ducted crust releases water to form volcanic island chains above, and after a few hundred million years will be heated and recycled back to the spreading centers. The map below of Earth's solid surface shows many of the features caused by plate tectonics. The oceanic ridges are the as the no spheric spreading centers, creating new oceanic crust. Sub duction zones appear as deep oceanic trenches. Most of the continental mountain belts occur where plates are pressing against one another. The white squares locate examples given here of the different tectonic and earthquake environments.
Jan 8th, 2015
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