GARY HINCKS / SCIENCE PHOTO LIBRARY GARY HINCKS / SCIENCE PHOTO LIBRARY
Volcano distribution map. Locations of volcanoes are shown by red dots. The grey lines are the boundaries between the Earth's tectonic plates, and the map shows the correlation between the two. Volcanoes are regions where magma from deep in the Earth comes to the surface. This is most common at subduction zones, where one plate is forced beneath another as they collide. This process heats the plates by friction, melting the crust to magma, which then rises through the overlying crust to be released. They also occur where plates spread apart, as in the mid-Atlantic and Iceland. Sometimes there is a hotspot unassociated with a plate margin (for instance Hawaii).
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