What actually pushed the magma out of the volcano? Where does the pressure come from? Also, some volcanoes explode and shoot lava high into the air, and some simply ooze lava slowly out of the top. What circumstances cause these differences?
In: Earth Science
The pressure comes from all the rock sitting over the magma…all that solid rock making up the volcano has weight that’s pushing down on the magma, pressurizing it. Normally it can’t go anywhere, like air in a balloon. But if you put a hole in it (the volcano) the pressurized magma comes out.
The size/shape of the hole, the thickness of the magma, and the pressure all influence how fast it can get out. Some magma has a lot of dissolved gas in it too, which causes it to expand as the pressure relieves. This is where foamy lava (pumice, etc.) comes from.
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