In 2021, Alaska’s Veniaminof volcano began erupting explosively, sending ash 15 kilometers into the air—but scientists didn’t detect the eruption until three days after it started. This event, like many at Veniaminof, lacked the typical warning signs of ground deformation or earthquakes.
Now, a study published in Frontiers in Earth Science explains why some volcanoes erupt “stealthily” and offers a roadmap to improve eruption forecasting.
“Some of these volcanoes are located near major air routes or close to communities: examples include Popocatépetl and Colima in Mexico, Merapi in Indonesia, Galeras in Colombia, and Stromboli in Italy,” explained Dr. Yuyu Li, a volcanologist at the University of Illinois and lead author of the study, in a press statement. “Our work helps explain how this happens, by identifying the key internal conditions — such as low magma supply and warm host rock — that make eruptions stealthy.”
The research team focused on Veniaminof’s 2018 eruption, which produced ambiguous signals despite careful monitoring. By analyzing three years of pre-eruption data, they built a model simulating how magma dynamics underground translate—or fail to translate—into detectable surface changes.
The team found that the way magma moves into a volcano’s underground chamber plays a key role in whether or not an eruption will give warning signs. When a large amount of magma flows quickly into a chamber, it usually causes the ground above to swell or shake, which are the typical signs that an eruption might be coming. If this fast flow enters a large chamber, an eruption might not happen, but if it does, the warning signs will be clear. Similarly, if a high flow enters a small chamber, an eruption is likely, and there will still be obvious warnings. However, “stealthy” eruptions are most likely when a small amount of magma slowly enters a small chamber. This situation matches what scientists have observed at Veniaminof volcano, which has a small magma chamber and slow magma flow.
The shape and size of the magma chamber also affect the warning signs. For example, larger, flatter chambers might cause only minimal earthquakes, while smaller, more elongated chambers might not make the ground swell much. Stealthy eruptions only happen when all the right conditions—magma flow, chamber size, shape, and depth—come together. Temperature is another important factor. If the rock around the chamber stays warm because magma is always present, it becomes less likely to crack or shift in ways that would alert scientists. This makes stealthy eruptions even more likely, as the usual warning signs like earthquakes or ground deformation are less likely to occur. In summary, stealthy eruptions are most likely when there is a small, warm magma chamber with slow magma flow, making them much harder to predict.
“To mitigate the impact of these potential surprise eruptions, we need to integrate high-precision instruments like borehole tiltmeters and strainmeters and fiber optic sensing, as well as newer approaches such as infrasound and gas emission monitoring,” suggested Li. “Machine learning has also shown promise in detecting subtle changes in volcanic behavior, especially in earthquake signal picking.”
Veniaminof’s stealthy behavior isn’t unique. The study highlights similar risks at Colombia’s Galeras and Italy’s Stromboli, where eruptions can threaten millions. Traditional monitoring—tracking earthquakes and ground swelling—often fails here.
The study’s model isn’t just explanatory—it’s predictive. By combining real-time data with physical models, scientists could forecast stealthy eruptions hours or days earlier. While challenges remain, such as deploying costly sensors to remote volcanoes, the payoff is clear: improved early warnings could save lives and reduce economic disruptions from ash-clouded airspace.
“In the future, this approach can enable improved monitoring for these stealthy systems, ultimately leading to more effective responses to protect nearby communities,” Li stated.
As climate change increases glacial melt on ice-clad volcanoes, which can alter magma dynamics, such advances are urgently needed.
MJ Banias covers space, security, and technology with The Debrief. You can email him at mj@thedebrief.org or follow him on Twitter @mjbanias.