Volcanic Ashfall

When volcanoes erupt, molten rock called magma is ejected into the air where it cools and becomes volcanic ash—bits of jagged rock and glass sometimes no bigger than a few micrometers in diameter. But this ash isn’t like the ash leftover in a charcoal grill or a campfire; it’s hard, and depending on where and how it falls, it can be deadly.

According to Dr. Kim Genareau, a professor in the Department of Geological Sciences, airplane pilots can’t see fine ash on radar, so they can fly through an ash cloud without knowing it.

“And when the ash gets into the engine, it can melt and cause the engine to shut down,” she said.

The models used to predict where and how ash will fall are determined in part by the size and shape of ash, and Genareau recently hypothesized that lightning changes both.

To learn more about the relationship between volcanic ash and lightning, a phenomenon that has only recently been studied in detail, the National Science Foundation awarded Genareau more than $600,000 through three grants, including a CAREER award.

Typically, ash particles are jagged and have unusual shapes, but in an article published last year in Geology, Genareau discusses a few microscopic sphere-shaped ash particles that showed up in samples she took from the 2010 eruption of Iceland’s Eyjafjallajökull volcano.

She hypothesized that these spheres were created when lightning struck the ash cloud and instantaneously melted the glass portions of the ash. Then, as the liquefied glass fell through the air, she theorized that it morphed into the sphere-like shapes.

In order to test that hypothesis, Genareau will use a portion of her grant money to artificially strike volcanic ash with lightning to see if she can recreate the spheres.

“We will put the samples in a PVC pipe, connect it to a wire, and launch that wire into a thunderstorm,” Genareau said.

When the lightning travels back down the wire and strikes the samples, Genareau expects to see changes in the ash shape.

Genareau’s research is still so new that she doesn’t know whether it will allow pilots to anticipate changes in ash travel—as very little of the ash may be affected—but her research will allow future scholars to trace volcanic lightning in the geologic record for the first time.  They will be able to look at ash samples from unobserved volcanic eruptions and know that lightning occurred.

In addition to her research, the grant also funds an outreach component, allowing Genareau to develop a local grade-school curricula on natural hazards, such as flooding and tornados.

She also hopes to involve local high school students in her research by having them help run the triggered lightning experiments.

“Even if they don’t go on to study volcanoes or rocks, these students will have experience using analytical instruments,” she said, “which will help them in any field.”