In 2010, the Eyjafjallajökull eruption in Iceland grounded planes and made a mess of European logistics, but also provided us with spellbindingly beautiful photographs of volcanic lightning. Now, volcanic lightning has been produced in a laboratory setting.
Lightning during the Eyjafjallajökull eruption. Image credit: AP Photo/ Jon Pall Vilhelmsson
While we can take photographs of lightning during volcanic eruptions, it's much harder to take detailed scientific observations. In the words of researchers at the Ludwig Maximilian University in Germany, the ability to make observations directly at the volcanic vent during an eruption is "severely impeded." Sneaking up close to the mouth of a volcano while it's erupting is dangerous, and equipment left behind to collect data is subject to an intense, dynamic environment that will probably destroy it. To get around this, Corrado Cimarelli and his team built a volcano in their laboratory.
Lightning in an ash column fired by a shock-tube. Image credit: C. Cimarelli/M.A. Ibargüengoitia.
Rapid decompression fires ash out of a shock tube, dropping from 10 MPa argon gas to 0.1 MPa atmospheric pressure. This ejects the ash through a narrow nozzle in a vertical column. They mounted high-speed cameras and a pair of antenna around the nozzle, and sat back to watch the show.
The experiment used real ash from real volcanoes, including Popocatépetl in Mexico, Eyjafjallajökull in Iceland, and Soufrière Hills in Montserrat, for their real-world analogues, then did a few more runs with spherical glass beads for the hyper-controlled scenarios.
The researchers released two videos of the experiment. The first uses 74.3 grams of real volcanic ash from the Popocatépetl volcano, sifted to make sure all particles are between 250 and 355 micrometers in diameter. The entire video covers 8 milliseconds in real time, shot at a 50,000 fps frame rate.
Video #2 is the same thing, but with lower humidity (53%, compared to 61% in Video #1), and covering 5 milliseconds of real-time shot at 25,000 fps frame rate at a higher exposure time.
Overall, the researchers concluded that volcanic lightning is really easy to make, matching up with how common it is to observe lightning during real eruptions. The more ash an column has, the more electrical discharges are observed. For the ash itself, size matters: fine ash clusters more, producing more lightning. That's cool because it means that if we get a better handle on how much lightning an eruption is producing (through high-speed cameras, and magnetotelluric, Doppler radar, or lightning mapping arrays), then we'll simultaneously be building a better picture of the fine ash distribution for the eruption. A better measurement of ash means better ash forecast models, in turn improving our ability to predict how any particular eruption will impact air travel.
...and maybe as a side-effect of all this science, we'll also get a steady supply of dramatic, beautiful volcanic lightning photographs.
Read the full open-access article in Geology: Experimental generation of volcanic lightning by C. Cimarelli et al. The International Space Station is running a new global experiment to track lightning.