What exactly causes huge plates to move and collide with such a colossal force? How do they not create extremely wide trenches in places where they move apart? Why isn’t the place where they move apart just molten magma? What is the force propelling magma and ash upwards during an eruption? I searched on the Internet, but I want a deeper explanation, which I couldn’t find. TIA!
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Magma moves mostly due to convection. When an upward moving magma stream reaches the Earth’s mantle/crust it spreads out, draging techtonic plates with it. Where plates separate, volcanic eruptions occur. Magma from these eruptions eventually cools and seals the gap for a while.
These processes happen so slowly as to make the fast majority of volcanos seem dormant.
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