Learning about Volcanoes

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I'm reading a book written by the professor of the online courses I've been taking about earth sciences. He is a very good teacher and very detailed. So, in my last reading I learned that the driving force behind volcanic eruptions is not the magma, but the gas dissolved in it. Gases such as CO2, SO2, etc. are in solution with melted magma when it is very hot and under pressure. As it comes toward the surface it cools a bit, and each gas has its own area of temperature where it turns into bubbles instead of continuing to be dissolved. Just like your carbonated soft drink forms visible bubbles when you open the can, when pressure decreases over magma (from a landslide taking away some of the top, or magma coming up a conduit nearer the surface) the gas comes out of solution and forms bubbles. When enough bubbles form, it pushes out the magma in an explosive or effusive eruption. Isn't that interesting? CO2 turns into bubbles at a higher temperature and pressure than SO2 does, so if CO2 is detected at a volcano, magma is coming up from depth, but SO2 means it is already near the surface. What would you like to learn about volcanoes? I'll see if I can tell you!