Radio emissions from volcanic lightning might provide a tool for quickly assessing the amount of ash in a volcanic plume occurring at night or in inclement weather, when neither satellites nor ground-based observers can see exactly what is happening, according to the new volcanic-lightning research, published in the journal Eos.
Other methods, such as seismometers or sound detectors, can't distinguish ash-producing eruptions from eruptions that pose no risk to air traffic, said report coauthor McNutt, a volcanologist at the University of Alaska, Fairbanks.
There are at least two types of volcanic lightning, the new radio-mapping study found. One occurs at the mouth of the volcano, and the other—as shown over Chile's Puyehue-Cordón Caulle volcano complex in 2011—electrifies the heights of the plume, possibly as rising water becomes a mix of droplets and ice-coated ash particles.
The water and frozen-ash particles, said McNutt—who's found volcanic plumes to be surprisingly water rich—rub against each other. As with shuffling shoes on carpet, the contact produces static charges. "That's what happens in ordinary thunderstorms" too, McNutt said.
With the right instruments, McNutt said, "you can see electrical activity right at the onset of the eruption," inside the crater.
These otherwise invisible lightning bolts (not pictured) are produced by the other mechanism for static-charge generation: the shattering of rocks thrust skyward in an eruption.
The in-crater bolts aren't huge, but they can strike thousands of times a second, creating a nearly continuous radio signal that would instantly mark the onset of the eruption, he said.
Photograph by Peter Vancoillie, Your Shot
Lightning branches out from behind a veil of ash clouds at Iceland's Eyjafjallajökull volcano in April 2010.
Every bolt travels a distinct direction, Martin Uman, a lightning expert at the University of Florida, told National Geographic News in 2012. A spark begins in an electrically charged spot and then travels either up, down, or sideways until it reaches an oppositely charged area.
Photograph by David Jon, NordicPhotos/Getty Images
A long-exposure picture of Chile's Puyehue-Cordón Caulle volcano complex in June 2011 turns individual bolts into a web of lightning. But to truly measure the amount of lightning in an ash plume requires the monitoring of radio emissions, according to the new study.
It doesn't take an explosive eruption to spark volcanic lightning. Here, hot lava from Hawaii's Kilauea volcano ambles into the cool sea in July 2008, producing towering lava fountains, steam—and electricity.
The first reported observation of lightning from a volcanic eruption came 2000 years earlier. During the destruction of Pompeii by Italy's Mount Vesuvius in A.D. 79, Roman historian Pliny the Younger described "frightening dark clouds, rent by lightning." He was fascinated, but was eventually persuaded to evacuate.
"There is lightning in the interior that you don't see in the pictures," McNutt said—bolts that are slowly coming to light, thanks to the researchers' potentially lifesaving new radio-emission readings.