A volcano famous for its glowing lava lake is hiding a surprisingly complex system of magma deep underground. Scientists at Penn State have uncovered evidence of two previously unrecognized magma sources beneath Nicaragua’s active Masaya volcano, raising new questions about how molten rock moves beneath the surface and offering a clearer picture of the geological forces driving one of the region’s most prominent natural landmarks.
The discovery is particularly important because approximately two million people live within 13 miles of the volcano, which is also a popular tourist destination. Understanding its underground activity could help scientists recognize warning signs of future eruptions and better protect nearby communities from potential hazards.
Using six years of satellite observations, researchers tracked subtle changes in rumblings and ground deformations around Masaya. They discovered that one part of the volcano initially sank before beginning to rise, possibly indicating that fresh magma was entering a deep reservoir. Meanwhile, the ground around its active Santiago crater and lava lake continued to sink, suggesting that a separate, shallower magma reservoir was behaving differently and independently from the deeper system.
The findings, published in the scientific journal Geophysical Research Letters, reveal that the volcano’s underground magma system may be considerably more complicated than previously understood by volcanologists.
"These observations help scientists better understand how magma moves beneath Masaya and may improve monitoring and eruption forecasting in the future," said lead author Lizzie Johnson, who earned her bachelor’s degree in geosciences from Penn State in May and has since embarked on her doctoral studies.
Why Masaya Volcano Is Closely Monitored
Located near Managua, Nicaragua’s capital, Masaya is a geologically complex volcano featuring multiple overlapping craters and calderas. Calderas are large, expansive depressions that generally form when the ground collapses after immense volumes of magma are removed from an underground chamber during eruptive episodes or subterranean shifts.
Although scientists have studied Masaya for years, the exact movement of magma through its underground reservoirs and narrow passageways remains poorly understood. These complex subterranean systems can change significantly over time, making it difficult to determine precisely what is happening deep beneath the active volcanic edifice.
"Having a thorough understanding of Masaya’s volcanic activity and its related hazards is critical as around two million people live near Masaya and the caldera is a national park and popular tourist destination," Johnson said. "Although Masaya last produced a major lava flow in 1772, its persistent degassing often produces dangerously high concentrations of sulfur dioxide volcanic gas."
Sulfur dioxide is a potentially harmful and pungent volcanic gas released as magma approaches or remains near the surface of the Earth. Even without a major, explosive eruption, elevated concentrations of this gas can create hazardous conditions for park visitors, local residents, and surrounding agricultural communities.
Young Cheol Kim, who completed his doctorate in geosciences at Penn State over the summer, explained that monitoring the volcano on a continuous basis is essential for distinguishing normal background activity from abrupt changes that might signal increasing volcanic hazards.
"Doing continuous monitoring allows us to understand the baseline activity and identify see if things are changing," he said, explaining that certain shifts in volcanic behavior could indicate a period of heightened activity or a possible future eruption. "And then if there is a need to warn people, we can do that in a timely manner."
Satellites Reveal Hidden Movements Beneath the Volcano
To investigate Masaya’s hidden underground activity, the researchers analyzed rigorous measurements collected by the European Space Agency’s Sentinel-1 satellite, which observes the volcano approximately once every 12 days as it passes overhead in orbit.
The research team utilized an advanced remote sensing technique called interferometric synthetic aperture radar, commonly known as InSAR, which can detect extremely small, millimeter-scale changes in the elevation of Earth’s surface over broad areas. By comparing satellite measurements taken at different points in time, scientists can precisely identify geographical regions where the ground is rising or sinking.
The technique combines two important technological capabilities. Synthetic aperture radar sends microwave signals toward Earth’s surface, allowing satellites to collect precise measurements even when thick clouds obscure the ground from optical view. Interferometry compares the returning radar signals to detect microscopic changes in distance between the satellite and the shifting surface below.
This capability is especially valuable in tropical regions, such as Central America, where frequent cloud cover and dense vegetation can make conventional satellite imagery and aerial photography far less reliable for geological studies.
"Cloud penetration is important for volcanoes because many of them, like Masaya, are in tropical areas where there is often cloud cover," Kim explained. "And when we look at all the different satellite images across multiple years, we can see how the distance between the satellite and the ground changes, where it is uplifting or subsiding."
By examining these subtle movements over long periods, researchers can investigate dynamic geological processes happening far below the surface without needing to directly observe the molten magma itself.
Two Magma Reservoirs Behaving in Different Ways
The detailed satellite measurements revealed an intriguing and unexpected pattern between 2018 and 2024. During the first part of the multi-year study, the ground within Masaya’s broader caldera gradually subsided, meaning it moved downward relative to its surroundings. Later in the timeline, the exact same general area began to rise, or undergo uplift.
Scientists believe this behavioral transition could reflect shifting volumes in the amount of magma stored underground. When magma drains away from a deep reservoir, the overlying ground can lose internal support and sink. Conversely, when additional magma enters and increases fluid pressure within a reservoir, the surface above may rise.
The most surprising finding of the study was that the immediate area surrounding the active Santiago crater did not follow this same pattern. Instead, it continued to subside continuously throughout the entire six-year study period, even as the broader caldera surrounding it began rising.
"When it’s subsiding, that means that there’s probably magma draining away from the volcano, but once the ground starts uplifting again, that can mean that there’s potentially new magma moving in," Johnson said. "At the same time, the area directly around the active Santiago crater deflated over the entire study period independently of the transition to inflation of the main reservoir. This indicates that the plumbing system is more complex and could be due to decreasing magma in a second, shallower reservoir."
Together, these observations strongly suggest that Masaya may possess at least two distinct parts of its subterranean magma storage system undergoing different, simultaneous changes. A deeper source could be actively supplying additional magma to the main reservoir at depth, while a separate, shallower reservoir situated near the active Santiago crater may be simultaneously losing magma or deflating.
This dual-system dynamic helps explain why different geographical sections of the exact same volcano moved in opposite directions during the study period.
What the Discovery Means for Future Eruptions
Understanding these complex underground movements is important because shifts in surface ground elevation can provide critical clues about where magma is accumulating, where it is migrating through crustal pathways, and how it might eventually reach the surface in future eruptive phases.
The researchers emphasized that their satellite observations did not reveal any immediate or imminent danger to the communities surrounding Masaya. However, identifying the volcano’s normal baseline behavior and gaining a deeper understanding of its intricate magma supply system could make it much easier to recognize unusual anomalies and warning signs in the future.
Continued satellite observations, combined with more detailed computer models of underground fluid dynamics, could also help scientists better understand the complex connections between deep magma reservoirs and persistent volcanic activity observed at the surface.
"Further long-term geodetic and modeling studies will provide a more thorough understanding and allow for effective hazard monitoring and mitigation at Masaya and other lava-lake hosting basaltic volcanoes," Johnson said.
The findings may therefore hold broad implications extending well beyond Nicaragua, particularly for other active volcanoes around the globe that contain persistent lava lakes and similarly complex underground plumbing systems.
From Undergraduate Research to Volcano Science
Johnson first became involved in the detailed geological project after attending an academic presentation by Christelle Wauthier, a Penn State professor of geosciences and computational sciences hub director at the university’s Institute for Computational and Data Sciences.
She completed the demanding research as part of her undergraduate thesis for Schreyer Honors College, working alongside graduate researchers, including Kim, to analyze complex satellite measurements and develop her scientific expertise.
"I appreciated learning how a research group works," said Johnson, who has recently started a doctoral program in Earth sciences at the University of Hawaii at Manoa, where she will continue studying active volcanoes by using seismic waves to image deep below the surface of Kilauea volcano. "I had never had any experience with research, so it was great to be able to join in the group meetings and get to hear about everybody’s work. And learning coding was also useful as I continue with my Ph.D."
The research received financial support from the U.S. National Science Foundation through specific awards, along with essential high-performance computational resources provided by Penn State’s Institute for Computational and Data Sciences. The authors remain solely responsible for the scientific findings and conclusions presented in the study.
