Recipes for Eruption

by AMNH on

Research posts

Basalt rock tends to form lavas that flow from volcanoes, rather than exploding violently.

Early in their course work, some of the Earth science students in the Museum’s Master of Arts in Teaching program get an explosive object lesson in the petrology lab of geologist James Webster. They recreate a volcano.

 “They are very excited to be able to do that,” says Dr. Webster, curator in the Department of Earth and Planetary Sciences, who notes that visitors can try their hands at erupting a virtual volcano in the special exhibition Nature’s Fury

The way Webster’s experiment works is this: The students take a small chip of igneous rock, like pumice or basalt, and tuck the sample, along with water, inside a tiny gold cylinder, which in turn is put into 200-pound steel reaction vessel. (Why gold? Because it won’t interfere with chemical reactions inside the vessel, but will allow pressure to affect the sample.) The cylinder then is subjected to extreme pressure and high heat—nearly 2,000° Fahrenheit—which causes the water and its constituent gases to “dissolve” into the molten rock sample. Finally, when the pressure is dropped, the gases come back out of the melt, they expand, and voila! A tiny volcano is born.

The experiment is a vivid example of painstaking efforts being employed by Earth scientists to unlock the variables that make some volcanoes the destructive powerhouses they are.

St Helens
Even eruptions that take place over the course of days, like the 1980 eruption of Mount St. Helens, can be violent and destructive.

By changing the kinds and amounts of added materials—water, sulfur, chlorine, carbon dioxide—and varying the heat and pressure, Webster and his colleagues calculate the effects of different combinations of gas, rock, heat, and pressure and their potential to create a major eruption. The type of rock is a factor too. Basalt’s low-gas, low-silica, and low-viscosity makeup results in eruptions of slow-moving lava, while pumice, with its high levels of gas and silica and higher viscosity, creates a more explosive outcome.

“Ultimately we are trying to generate enough data to create models,” says Webster. “There are so many combinations, there’s no way to replicate all of nature. But models can tell us how certain materials under certain conditions will likely behave.”

Design and erupt your own volcano in an interactive feature of Nature’s Fury: The Science of Natural Disasters