In the restless geology of the Azores, where the earth is never entirely still, a new international study has shed light on one of the most unsettling episodes in recent memory. The 2022 seismic crisis on the island of São Jorge Island—which rattled communities and prompted widespread concern—was not triggered by a traditional volcanic event, but by a rapid and largely silent ascent of magma from deep within the Earth.

Published last week in the scientific journal Nature Communications, the research reveals that a column of magma surged upward from the mantle to just 1.6 kilometers below the surface before being halted by a critical geological structure: the Pico do Carvão fault. What might have become a volcanic eruption instead ended as what scientists now describe as a “failed eruption”—a phenomenon as complex as it is revealing.

Led by researchers Stephen Hicks and Pablo J. González, the study draws on a combination of satellite radar imaging (InSAR), high-precision GPS, and an array of seismometers placed both on land and along the ocean floor. Together, these tools reconstructed a remarkable sequence: a vertical “dike” of magma, roughly six kilometers long, rising from a depth of 26 kilometers in the upper mantle to near-surface levels in just a matter of days.

What makes this event particularly striking is how much of this ascent occurred in silence. For a significant portion of its journey, the magma moved without triggering detectable earthquakes. Only when it reached the upper crust and began interacting with local tectonic structures did the ground begin to shake—ultimately producing more than 18,000 seismic events.

At the center of this geological drama lies the Pico do Carvão fault, the most active fault line on the island and one capable of generating earthquakes of magnitude 7. According to the study, the fault played a dual role. It initially facilitated the vertical rise of magma, acting as a pathway through the crust. But it also served as a release valve: allowing magmatic fluids to escape laterally, reducing internal pressure and increasing the viscosity of the magma. In effect, it stopped the eruption before it could break through the surface.

This interaction had further consequences. The stress regime in the region temporarily shifted, causing a 90-degree rotation in tectonic forces and reversing the fault’s usual motion—from right-lateral to left-lateral movement during the crisis. The seismic swarm itself was concentrated along one flank of the intrusion, tracing the hidden pathways of fluid migration beneath the island.

The findings underscore the complexity of the Azores, located at a rare triple junction of tectonic plates. They also highlight the importance of new monitoring technologies, particularly ocean-bottom seismometers, which allowed scientists to map earthquake activity with unprecedented precision. These instruments revealed narrow “filaments” of seismicity—signatures of fluids moving through rock at speeds of up to 800 meters per hour.

Yet the study carries a sobering message. The rapid and largely undetectable rise of magma poses a significant challenge for volcanic forecasting. In São Jorge, warning signs at the surface appeared almost simultaneously with the magma’s arrival in the shallow crust, leaving little margin for early detection.

Although the 2022 crisis did not culminate in an eruption, the underlying system remains active. The fault that halted the magma is still under stress, and the island’s volcanic plumbing system remains in motion beneath the surface.

In the Azores, the absence of eruption does not mean the absence of risk. It means, rather, that the story continues—quietly, invisibly, and with a force that science is only beginning to fully understand.

Translated and adapted from a story in Diário Insular – José Lourenço, director.