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 Some volcanoes explode with the force of an atomic bomb. Others spill rivers of gently flowing lava. Why? The force of a volcano’s eruption and the type of lava it oozes depend upon the amount of gas and silica that make up the volcano’s magma (molten rock):
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Silica is a chemical compound found in magma. More silica makes the magma more viscous (thick and gooey), so it’s stiffer and flows more slowly, like molasses or tar. Magma with less silica is runnier and flows more easily.
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Dissolved gases expand and form bubbles within the magma as it rises. Just like when you open a soda bottle, these bubbles escape when the volcano erupts and the pressurized magma is released. The more bubbles under pressure, the more explosive the reaction. |
The proportion of silica to gases in the magma determines the force and type of a volcano.
Stratovolcanoes
The most explosive eruptions come from stratovolcanoes and the high-silica, high-gas content of their magma. When these powerhouses blow, they can spew an awesome column of gases and ash into the air. This mass collapses into a pyroclastic flow: a speeding cloud of heat, gas, and ash that destroys everything in its path.
Stratovolcanoes form over many thousands of years, with layers of pyroclastic material and cooled lava flows building up to form a steep cone, often with multiple vents.
Continue to More Types of Volcanoes. >>
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