Volcano Volume Eruption for a Science Project

Types

The composition of the magma or molten rock determines its viscosity -- i.e., how sticky or runny it is. Stickier types of magma tend to trap gases while runnier types allow them to escape. Volcanoes featuring the first type of magma tend to build up pressure then rupture violently, scattering huge clouds of superheated dust, ash, and debris. Eruptions from the second group, by contrast, feature eruptions where molten rock flows outwards to create a gently sloping mound called a shield volcano.

The total volume of material ejected during the eruption is one way to gauge its violence. Small eruptions with low total volumes are more frequent, but big eruptions with larger total volumes are much more dramatic. According to San Diego State University, eruptions with volumes ranging from 0.001 to 0.01 cubic kilometers occur every few months on average. The biggest eruptions expel 100 to 1000 cubic kilometers and only take place every 10,000 years or even more infrequently. The volume of Lake Erie is just 484 cubic km by comparison.

There are many intermediates that lie somewhere in between these extremes. Etna-scale eruptions, for example, eject from 0.01 to 0.1 cubic km and take place every five years or so; larger Mount St. Helens-scale eruptions expel from 0.1 to 1.0 cubic kilometers and take place on average every 10 years. The biggest of all are eruptions on the scale of the last Yellowstone Caldera blast. Eruptions this size take place every 100,000 years or so and expel 1000 cubic km or more from beneath the ground.

If you're working on a science project, you'll want to take this variability into account. Explain in your paper or presentation that the eruption of a volcano depends on the type and the plate tectonics involved. It might be a good idea to present a range of possible volumes in a table, together with the frequency of eruptions in each range. Also point out that the gases trapped in sticky magma expand rapidly when they reach the surface and encounter atmospheric pressure. This rapid expansion is a crucial ingredient in violent eruptions.