Some volcanoes have a unique way of releasing their energy: they blow rings of vapor that drift near their craters. While these rings have been occasionally observed at volcanoes like Etna and Eyjafjallajökull, researchers have recently uncovered new insights into how bursting gas bubbles create these phenomena. Simona Scollo, a volcanologist at the National Institute of Geophysics and Volcanology in Italy, states that most volcano research focuses on the strong eruptions that threaten human lives, but "we want to understand how our volcanoes work," not just when they create disasters. She and her team investigated the rings, typically associated with relatively mild volcanic activity, and published their findings in the journal Scientific Reports. According to the researchers, there are similarities between how volcanoes produce these halos and how dolphins blow bubble rings or how smokers exhale smoke rings. While they are commonly called smoke rings, they are made mostly of water vapor. The researchers discovered that x exiting a volcano’s opening slows down when they encounter a surface, causing the gas to loop over on itself. However, it’s not precisely clear what is happening within a volcano that leads to a vapor ring. Even volcanoes known for such puffery don’t make rings all the time. Dr. Scollo’s team scoured the internet and research footage for vapor rings caught on camera. The rings they found were 30 to 650 feet in diameter and lasted up to 10 minutes.
The researchers modeled the possible motion of gas and bubbles within the barrel of a volcano. For vapor rings to form, "small gas bubbles had to merge and float up through the magma to create pressurized gas pockets. They could push out some gas fast enough to make a vapor ring when such pockets explode." However, the volcano’s opening also needed to be circular or slightly squashed. Volcanoes with irregular or more elliptical openings didn’t typically form rings. When they did, these apertures warped the doughnut shape or caused the ring to wobble, the team reported. Combining photo and video observations with the model allowed the team to find the physical conditions needed to make the rings. “Once we understand that then we can understand something about the volcano itself,” said David Fee, a volcanologist at the University of Alaska Fairbanks who was not part of the work. As an example, ring emissions may say something about a volcano’s magma. Volcanoes that release hoops of vapor have a liquid rock that is more likely to flow.
When a volcano becomes dangerous like Mount St. Helens did in Washington and continuously gushes gas and spews a lot of solid material, it isn’t going to blow rings, said Boris Behncke, who is Dr. Scollo’s colleague at the Institute of Geophysics and Volcanology but was not part of this work. Dr. Behncke has witnessed hundreds of vapor rings, including many at Etna during a rather prolific period. In 2000, Mount Etna blew thousands of vapor rings from one of its four craters over a few months. “That was a most spectacular coincidence and there’s never been anything like this — neither at Etna nor any other volcano,” Dr. Behncke said. “Sometimes you would see five or six of them rise into the sky one after the other,” he said. Dr. Scollo and her team hope to further investigate these intriguing vapor rings using high-speed cameras and instruments that can pick up the sounds of gas explosions. By catching the rings as they form and studying their physical conditions, the researchers aim to gain a better understanding of the mechanisms at work within volcanoes. Dr. Behncke noted that vapor rings are not as rare as one might think, occurring at volcanoes more frequently than people realize. With further research, these ephemeral rings of vapor could provide valuable insights into the behavior of volcanoes and the properties of their magma, shedding light on these enigmatic and powerful geological phenomena.
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