Why do volcanic eruptions vary in intensity?

Volcanic eruptions vary in intensity depending on the composition of the magma, gas content, and pressure. Magma high in silica is more viscous, trapping gases and causing explosive eruptions, like those of Mount St. Helens. Low-silica magma flows more easily, resulting in less violent eruptions, such as those in Hawaii. The type of volcano and tectonic setting also influence the eruption’s intensity.