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How Magma Behaves when It Gets Gassed Up

by Devin Reese -- Nov 14, 2017

Devin is the lead digital science writer for the Q?rius website. She writes and gathers media for the Smithsonian Science How? webcast series,...

The 2013 eruption of the Mount Etna in Italy sent materials skyward. Photo by gnuckx, public domain.
The 2013 eruption of the Mount Etna in Italy sent materials skyward. Photo by gnuckx, public domain.

Lava is the most famous hazard of volcanoes. It is featured in movies, and used to describe lamps, chocolate cakes, and mobile phone cases. But lava is only part of the volcano story. Lava is what we call magma when it flows out of a volcano, and magma is molten – or melted – rock. While you would not want to stand in lava, which can be as hot as 2,000°F, at a walking pace you could outrun the majority of lava flows. So, what’s so hazardous about a volcanic eruption?

Sometimes magma does not flow out of a volcano, but instead explodes. When that exploding mixture of hot gas, magma, and rock comes out, it is fast and unpredictable. In an explosive eruption, pieces of hardening magma and rock are spewed upward in a hot plume of gas. They range from the tiny particles that make up volcanic ash to chunks the size of cars. As the plume blows downwind, it drops materials like a hail storm, littering the landscape with volcanic rocks. A pyroclastic flow of hot gases carrying the heavier material may pick up speed as it sweeps down from the volcano. As the flow mixes with the surrounding air, lighter ash may get lofted up in a cloud and travel as far as thousands of miles. 

While the bigger chunks are an immediate hazard to people and wildlife around the volcano, the cloud of ash takes a long-term toll that can be devastating. The 1980 eruption of Mount St. Helens in Washington state produced a pyroclastic flow that scoured the landscape at speeds up to 600 miles per hour, and then lofted ash that settled on 11 states over the next few days. The 2010 eruption of Iceland’s Eyjafjallajökull volcano sparked electrical storms and an ash plume more than 5 miles high that spread over Europe and grounded airline travel for days. 

Lasers in simulator used by Ben Andrews to model volcanic eruptions. Photo by Ben Andrews, Smithsonian.Geologists who study volcanoes – volcanologists – are trying to better understand the behavior of these pyroclastic currents. Given the danger of capturing data directly from an explosive eruption, volcanologists such as Smithsonian’s Dr. Ben Andrews have found ways to capture data from a distance and simulate flows in laboratories. Ben’s Eruption Simulator uses laser beams and talcum powder to observe how erupted materials get distributed upward and outward in different scenarios.  

Learn more about Ben’s volcano research in the "Smithsonian Science How" webcast on Thursday, Dec. 14, 2017. During How Volcanic Eruptions Send Materials Up and Out (airs at 11 a.m. and 2 p.m. EST on the Q?rius website), Ben will take you on an explosive journey while answering your questions live. You can also get teaching resources to use with the webcast.