Giant “stealth” magma surge triggered thousands of earthquakes beneath Atlantic island

Researchers found that much of the magma's rise happened quietly, with relatively little seismic activity during its ascent. Most of the earthquakes struck only after the magma stopped moving upward. The enormous intrusion unfolded within just a few days and involved enough magma to fill roughly 32,000 Olympic-sized swimming pools.

Lead author Dr. Stephen Hicks of UCL Earth Sciences said: "This was a stealthy intrusion. Magma moved quickly through the crust, but much of its journey was silent, making it difficult to forecast whether an eruption would occur."

Scientists Reconstruct the Hidden Magma Movement

The research, published in Nature Communications, involved an international team that combined several methods to track the magma's underground path. Scientists used seismometers placed both on land and on the Atlantic seafloor to pinpoint earthquake activity. They also analyzed satellite and GPS measurements to monitor how the island's surface shifted during the event.

Satellite data revealed that the ground above the volcano rose by about 6 centimeters, confirming that magma had entered the shallow crust beneath the island. However, the magma never broke through to the surface, creating what scientists call a "failed eruption."

These underground intrusions are important because they help build and reshape volcanic islands over time. Researchers say the highly detailed earthquake maps produced during the study provide new insight into how those geological changes happen.

Fault Zone May Have Prevented an Eruption

The magma traveled upward through one of São Jorge Island's major fault systems known as the Pico do Carvão Fault Zone. Earlier geological studies had shown that this fault has produced powerful earthquakes in the past. During the 2022 unrest, however, the rising magma triggered thousands of smaller earthquakes clustered along the fault rather than one major quake.

The researchers concluded that the fault zone likely acted as a pathway that guided the magma upward. At the same time, it may also have allowed gases and fluids to escape sideways, reducing pressure within the magma and preventing it from erupting.

Lead author Dr. Pablo J. González from the Spanish National Research Council (IPNA-CSIC) in Tenerife said: "The fault acted like both a highway and a leak. It helped magma rise, but may also have prevented an eruption."

New Clues for Volcano Forecasting

The findings suggest that large magma intrusions can happen rapidly and with limited warning signs. The study also highlights how major geological faults can strongly influence whether magma erupts or becomes trapped underground. Researchers say these insights could improve future volcanic hazard forecasting.

Dr. Ricardo Ramalho of Cardiff University, a co-author of the study, said: "This study supported local authorities in assessing a potential volcanic threat, highlighting the value of combining onshore and offshore geophysical data for accurate detection and localisation of seismic events and ground deformation."

Professor Ana Ferreira of UCL Earth Sciences added: "Securing urgent NERC funding to access equipment from its Geophysical Equipment Facility (GEF), alongside additional support from Portugal, was a tremendous collective effort and a clear example of transnational cooperation between academic and civil institutions in Portugal, the UK, and Spain."

The project received funding from the Natural Environment Research Council (NERC; UK), the European Research Council (ERC), Fundação para a Ciência e a Tecnologia (FCT; Portugal), Agencia Estatal de Investigación (Spain), and the Regional Government of the Azores. Offshore deployment support was provided by the Portuguese Navy (Marinha Portuguesa), while geophysical equipment came from NERC's Geophysical Equipment Facility (GEF).

Institutions involved in the research included UCL, Spanish National Research Council (IPNA-CSIC), Cardiff University, University of Manchester, Universidade de Lisboa (Portugal), Instituto Politécnico de Lisboa (Portugal), University of Évora (Portugal), University of Beira Interior (Portugal), Centro de Informação e Vigilância Sismovulcânica dos Açores (CIVISA; Portugal), Research Institute for Volcanology and Risk Assessment (IVAR), University of the Azores (UAc), University of Algarve (Portugal), Instituto Português do Mar e da Atmosfera (IPMA; Portugal), AIR Centre (Portugal), and C4G (Portugal).