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Volcanoes don’t always play by the rules. Most of the time, scientists can predict an eruption using early signs like ground swelling or a series of small earthquakes. These warnings happen when underground chambers fill with magma and gas, causing pressure to build.
But not all volcanoes are as transparent. Some remain eerily quiet, showing no signs before erupting. These are known as “stealthy” volcanoes.
One such volcano is Veniaminof, a glacier-covered peak in Alaska’s Aleutian Arc. Researchers from the University of Illinois have taken a closer look at its behavior. They’ve developed a model that helps explain why Veniaminof – and volcanoes like it – can erupt without any obvious warning.
“Despite major advances in monitoring, some volcanoes erupt with little or no detectable precursors, significantly increasing the risk to nearby populations,” said Dr. Yuyu Li, lead author of the study.
“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.
“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.”
A sleeping giant in Alaska
Veniaminof isn’t just any volcano. Since 1993, it has erupted 13 times, but only twice did it show enough warning signs for scientists to catch it in advance. One eruption in 2021 wasn’t detected until three days after it began.
“Veniaminof is a case study in how a volcano can appear quiet while still being primed to erupt,” said Li. “It is one of the most active volcanoes in Alaska.”
Li confirmed that, in recent decades, this volcano has produced several VEI 3 eruptions. These are moderately sized explosive events that can send ash up to nine miles high, disrupt air traffic, and pose regional hazards to nearby communities and infrastructure, often without any clear warning signs.
To better understand this behavior, the scientists focused on the time leading up to Veniaminof’s 2018 eruption, which was another stealthy one.
The team gathered data from three summer seasons before the eruption and built computer models to simulate different volcanic conditions.
These models tested various scenarios. They changed the size and shape of the underground magma chamber, the depth at which it sat, and how quickly magma flowed into it.
The goal was to match the models with what actually happened in order to understand which conditions cause eruptions in stealthy volcanoes.
What the numbers revealed
The simulations uncovered some patterns. A high flow of magma into a large chamber often causes the ground to swell, which is a visible warning.
If magma rushes into a small chamber, it can trigger an eruption with clear signs like earthquakes or deformation. But when the flow of magma is slow and the chamber is relatively small, an eruption can sneak by with little to no warning.
In Veniaminof’s case, the data suggested that it has a small magma chamber and a slow magma flow. These factors work together to hide typical signs of an impending eruption.
The signs of stealthy volcanoes
The model also explored how the shape and depth of the magma chamber affect what warnings we might see. Large, flat chambers might lead to quiet earthquakes. Long, narrow chambers might produce only subtle ground changes.
However, stealthy eruptions only happen when everything lines up just right – from magma flow to chamber dimensions.
Next, the researchers added one more factor: temperature. They found that when magma sticks around long enough, it warms the rock that surrounds the chamber. That heat changes everything.
Warm rock is less likely to crack or shift as magma fills the chamber. That means fewer earthquakes and less ground movement – both key signs that scientists look for. In warm rock, an eruption can be all but silent.
Monitoring stealthy volcanoes
“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,” said Li.
“Machine learning has also shown promise in detecting subtle changes in volcanic behavior, especially in earthquake signal picking.”
At Veniaminof, installing more tiltmeters and strainmeters could help fill the gaps in current monitoring. Improved satellite coverage could also catch eruptions sooner.
Most importantly, scientists now know what kinds of volcanoes are more likely to erupt without warning. They’re the ones with small, warm magma reservoirs and slow-moving magma.
“Combining these models with real-time observations represents a promising direction for improving volcano forecasting,” said Li.
“In the future, this approach can enable improved monitoring for these stealthy systems, ultimately leading to more effective responses to protect nearby communities.”
The full study was published in the journal Frontiers in Earth Science.
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