The seafloor

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The seafloor goes down four hundred miles after it goes into the trenches. On the way down, some of it melts, loses density, and-white-hot and turbulent-rises toward the surface of the earth, where it emerges as volcanoes, or stops below as stocks and batholiths, laccoliths and sills. Most of the volcanoes of the world are lined up behind the ocean trenches. Almost all earthquakes are movements of the boundaries of plates -shallow earthquakes at the trailing edges, where the plates are separating and new material is coming in, shallow earthquakes along the sides, where one plate is ruggedly sliding past another (the San Andreas Fault), and earthquakes of any depth down to four hundred miles below and flexplek huren rotterdam beyond the trenches where plates are consumed (Japan, i923; Chile, i960; Alaska, i964; Mexico, i985). A seismologist discovered that deep earthquakes under a trench had occurred on a plane that was inclined forty-five degrees into the earth. As ocean floors reach trenches and move on down into the depths to be consumed, the average angle is something like that. Take a knife and cut into an orange at forty-five degrees. To cut straight down would be to produce a straight incision in the orange. If the blade is tilted forty-five degrees, the incision becomes an arc on the surface of the orange. If the knife blade melts inside, little volcanoes will come up through the pores of the skin, and together they will form arcs, island arcs-Japan, New Zealand, the Philippines, the New Hebrides, the flexplek huren amsterdam Lesser Antilles, the Kurils, the Aleutians. Where a trench happens to run along the edge of a continent and subducting seafloor dives under the land, the marginal terrain will rise. The two plates, pressing, will create mountains, and volcanoes will appear as well. The Peru-Chile Trench is right up against the west coast of South America.

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