Question

What conditions make for a violent volcanic eruption?

Answer 1

Relatively thick magma containing significantly high levels of gas cause violent volcanic eruptions.

Thick magma (viscous magma) doesn't flow easily. What makes a magma viscous is high silica content. Rhyolitic (silica-rich and high gas content) magma has a high viscosity and a lot of dissolved gas. If pressures beneath the surface push this magma upward and it gets trapped, the pressure builds to very high levels. Eventually, the pressure gets so high, the gas in the magma can't be contained and a violent volcanic eruption results. Rock, ash, gas, and lava explode out of the volcano in a tremendous explosion.

Answer 2

A notable example is the 1980 eruption of Mount St. Helens. Such eruptions result when sufficient gas has dissolved under pressure within a viscous magma such that expelled lava violently froths into volcanic ash when press