Dormant volcanoes may be more dangerous than previously thought

For decades, scientists believed that magma chambers beneath volcanoes were transient, forming before an eruption and then dissipating as the volcano quieted. However, new research suggests that large magma bodies persist beneath volcanoes for much longer than previously thought. These findings could reshape how scientists monitor volcanic hazards.

Recent advances in seismic imaging provide a clearer picture of magma systems in the Earth's crust. Traditional methods suggested that magma chambers were long-lasting pools of molten rock that cooled over time. However, mineral diffusion studies indicate that magma migrates through the crust much more rapidly, sometimes over months or years.

These findings challenge conventional models of volcanic systems, revealing that magma reservoirs are more dynamic and widespread than once believed.

A key challenge in studying volcanic magma systems is the difficulty of obtaining detailed subsurface images. Geophysical methods, such as seismic and magnetotelluric imaging, offer insights into the structure and composition of magma reservoirs. However, most studies focus on individual volcanoes, making it difficult to identify general trends across an entire volcanic arc.

The Cascade Range, stretching from California to British Columbia, presents an ideal setting for investigating magma systems. This volcanic arc includes some of the most hazardous volcanoes in the United States, with millions of people living in proximity.

Despite this, only a handful of Cascade volcanoes have been studied in detail using geophysical imaging. These studies have revealed signs of partial melt beneath certain volcanoes, but results have been inconsistent.

A recent study led by researchers at Cornell University used seismic imaging to examine magma chambers beneath six Cascade volcanoes. The team analyzed seismic waves passing through the Earth's crust, focusing on P-to-S wave scattering, which occurs when waves interact with molten rock. These signals allowed researchers to construct detailed subsurface images beneath the volcano summits.

Surprisingly, the study published in the journal Nature Geoscience found that large magma bodies exist beneath all six volcanoes, regardless of their eruption history. This discovery challenges the idea that magma chambers drain completely after an eruption.

Instead, it suggests that magma reservoirs persist throughout a volcano’s lifetime, refilling gradually as heat from the Earth’s mantle melts the surrounding rock.

"Regardless of eruption frequency, we see large magma bodies beneath many volcanoes," said Guanning Pang, the study’s lead author. "It appears that these magma bodies exist beneath volcanoes over their whole lifetime, not just during an active state."

This finding has significant implications for volcanic monitoring. Scientists previously assumed that detecting a large magma body beneath a volcano meant an increased risk of eruption. The new study suggests that such magma bodies are a normal feature of volcanic systems rather than a sign of imminent activity.

“We used to think that if we found a large amount of magma, that meant increased likelihood of eruption,” Pang explained. “But now we are shifting perception that this is the baseline situation.”

Understanding the distribution of magma within the Earth's crust is critical for predicting volcanic eruptions. The U.S. Geological Survey (USGS) has been expanding its volcano monitoring network as part of the National Volcano Early Warning System. By improving seismic and geophysical observations, researchers hope to detect warning signs of eruptions earlier and more accurately.

“If we had a better general understanding of where magma was, we could do a much better job of targeting and optimizing monitoring,” said Geoffrey Abers, a co-author of the study. He noted that many volcanoes remain sparsely monitored, making it difficult to assess potential hazards.

The study’s findings suggest that eruptions do not completely empty a magma chamber. Instead, they release some pressure while magma continues accumulating over time. This gradual process complicates efforts to predict eruptions based solely on the presence of subsurface magma.

The research also highlights the need for more comprehensive studies across different volcanic arcs. While the Cascade Range provides valuable insights, similar studies in other regions, such as Alaska, could reveal whether persistent magma reservoirs are a global phenomenon. Plans are already in place to expand seismic monitoring efforts to additional volcanic regions.

Seismologists are now working to refine models of magma transport through the crust. Using 3D numerical simulations, researchers can better understand how wavefront healing affects seismic signals, which can help improve the accuracy of subsurface imaging. This technique allows scientists to correct for distortions in seismic data and more precisely estimate the volume and location of magma bodies.

Another challenge is distinguishing between molten and semi-solid magma. Seismic waves travel differently through these materials, making it difficult to determine how much of a magma body is eruptible. More sophisticated imaging methods, combined with data from multiple geophysical techniques, could help resolve this uncertainty.

The findings from the Cascade study underscore the importance of sustained monitoring. As technology improves, scientists will be able to track long-term changes in magma systems more effectively. Expanding monitoring networks and integrating data from multiple sources will provide a clearer picture of how magma moves through the crust and how it contributes to volcanic activity.

As researchers continue to study volcanic systems, one thing is clear: magma reservoirs are more persistent and complex than previously thought. Understanding these systems will be crucial for improving volcanic hazard assessments and protecting communities at risk.

Note: Materials provided above by The Brighter Side of News. Content may be edited for style and length.

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