What is the typical source of pressure buildup inside a volcano?
centrifugal force of Earth rotation
boiling of rainwater
degassing of magma
The whole process begins when hot magma is lifted by convection to the magma chamber. As the pressure in the chamber is lower than deep in Earth's crust, the gas starts to release. Since degassed magma has lower density, it may then sink and be replaced with new one. This process may build up huge pressure of gases, eventually causing explosion.
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+5 Very interesting! globalquiz.org