What is the purpose for magma?

Answer 1

Magma is a product of earth processes. To say it has a purpose may be a subjective statement.

**The first question this raises is: what exactly is this "material from the inside"? On our planet, it's magma, fluid molten rock. This material is partially liquid, partially solid and partially gaseous.

magma production around plate boundaries. This interplatevolcanic activity is caused by unusually hot mantle material forming in the lower mantle and pushing up into the upper mantle. The mantle material, which forms a plume shape that is from 500 to 1000 km wide, wells up to create a hot spot under a particular point on the earth. Because of the unusual heat of this mantle material, it melts, forming magma just under the earth's crust. The hot spot itself is stationary; but as a continental plate moves over the spot, the magma will create a string of volcanoes, which die out once they move past the hot spot. The Hawaii volcanoes were created by such a hot spot, which appears to be at least 70 million years old.

So what happens to the magma formed by these processes? We saw that the magma produced at ocean ridges just hardens to form new crust material, and so doesn't produce spewing land volcanoes. There are a few continental ridge areas, where the magma does spew out onto land; but most land volcanoes are produced by subduction zone volcanism and hot spot volcanism.

When the solid rock changes form to a more liquid rock material, it becomes less dense than the surrounding solid rock. Because of this difference in density, the magma pushes upward with great force (for the same reason the helium in a balloon pushes up through the denser surrounding air and oil pushes upward through denser surrounding water). As it pushes up, its intense heat melts some more rock, adding to the magma mixture.

The magma keeps moving through the crust unless its upward pressure is exceeded by the downward pressure of the surrounding solid rock. At this point, the magma collects in magma chambers below the surface of the earth. If the magma pressure rises to a high enough level,or a crack opens up in the crust, the molten rock will spew out at the earths surface.