On the Aeolian island of Vulcano, off the coast of Sicily, a buzzing drone pauses in front of a laser beam on the crater's edge as researchers test whether the devices can measure gases to predict eruptions. The last eruption of the island's Grand Crater occurred in the late 19th century, but the volcano continues to show intense degassing activity, to the awe of visitors allowed to walk around the rim.
Laser-Based Gas Measurement
German researcher Marius Schaab, from the Technical University of Munich (TUM), stands next to a gas sensor mounted on a tripod, waiting for a drone his colleague has just launched to draw closer. The sensor works by sending a laser beam through volcanic gas emissions and onto a reflector on the drone, measuring the intensity of the transmitted light. The drone can move around and switch angles to take full measurements.
Using a laser allows the sensor to avoid the corrosive gas plume, which would require any sensor inside it to be constantly recalibrated. "Our drone flies behind the plume and also our ground unit is not in the plume," Schaab told AFP. Based on signals sent back to the sensor, an algorithm calculates a map of gas concentration in the 10 or 15 minutes it takes for the drone to follow a predefined path at a distance of up to 60 meters (nearly 200 feet).
Advancements in Volcanic Monitoring
Although drones have been used in monitoring volcanoes for about 15 years, scientists are now developing gas measurement tools that are increasingly accurate and risk-free. Further around the crater, another team of German scientists from the University of Mainz uses sensors carried on a drone to measure concentrations of chemical substances in the air.
"One reason for measuring gases and particles is to better understand the impact of volcanic eruptions and volcanic emissions on the atmosphere," said Tjarda Roberts, a researcher at the National Center for Scientific Research (CNRS) in Paris, who collaborates with the Mainz team. "Another reason is to anticipate volcanic eruptions, because the gas composition can change before an eruption occurs," she added. The greater the pressure exerted by lava rising from inside the Earth toward the surface, the larger the amount of gas released.
It is the first time the TUM team has tested its drone system—which can work at altitudes up to 3,000 meters—on a volcano.
Flexibility and Safety
A checklist in hand, Jonas Krajewski, a student at the Johannes Gutenberg University Mainz, checks that "Tina"—the name given to the drone—is ready to fly safely. The drone, weighing 2.5 kilograms (5.5 pounds), lifts into the air and heads toward the rising gases. Following a predefined flight path lasting up to 40 minutes, the drone flies into the heart of the fumaroles, where temperatures range between 100 and 140 degrees Celsius.
"Tina" is equipped with sensors measuring gases, particles, and halogens like chlorine and bromine. "We have a very constant output of gas... so we can have very reliable sensor data," said Krajewski. For Roberts, one of the biggest advantages of the drone is its great flexibility and ability to move around more diluted parts of the plume and quickly switch direction if the plume suddenly changes angles.
With the drone, researchers no longer need to carefully enter the area of gas emissions, a dangerous activity requiring masks and other protection. "Here we don't have a major risk of an imminent eruption but there are volcanoes where you can't reach the summit on foot," Roberts said. But with a drone, "you can take measurements... without putting yourself in danger."
Skimming over rocks speckled with yellow sulfur crystals deposited by the fumaroles, "Tina" soon reappears on the horizon. In the coming days, a new challenge awaits the drone—Mount Etna, the 3,000-meter-high active volcano in eastern Sicily, where a new eruption has just occurred.
