Scientists have uncovered how a huge underground magma surge shook Portugal’s São Jorge Island with thousands of earthquakes.
In March 2022, São Jorge Island in Portugal’s Azores experienced thousands of earthquakes caused by a huge underground surge of magma (molten rock), according to a new study led by researchers at UCL (University College London). The magma traveled upward from more than 20 kilometers below Earth’s surface before stopping just 1.6 kilometers beneath the island, narrowly avoiding an eruption.
Researchers found that the magma rose rapidly over only a few days. The amount of molten rock involved was enormous, enough to fill about 32,000 Olympic-sized swimming pools. Surprisingly, much of the magma’s movement produced little seismic activity, with most of the earthquakes occurring only after the magma stopped rising.
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 Map a Hidden Magma Surge
The study, published in Nature Communications, brought together researchers from several countries to reconstruct the magma’s underground path in remarkable detail. The team used seismometers placed both on land and across the Atlantic seafloor to identify exactly where earthquakes were happening. They also relied on satellite observations and GPS measurements to track how the island’s surface shifted during the event.
Data from satellites showed the ground above the volcano rose by about 6 centimeters, confirming that magma had entered the shallow crust beneath São Jorge Island. However, the magma never reached the surface, creating what scientists describe as a “failed eruption.”
Researchers say these underground magma intrusions play an important role in shaping and expanding volcanic islands over time. The new earthquake maps produced during the study provide one of the clearest views yet of how this process works beneath the surface.
Fault Zone Helped Guide the Magma
Scientists determined that the magma moved upward through one of the island’s major geological fault systems called the Pico do Carvão Fault Zone. Previous studies of ancient earthquake traces had already shown that this fault system was capable of generating powerful earthquakes in the past.
Instead of producing one large earthquake, however, the rising magma triggered thousands of smaller quakes clustered along the fault zone.
The research team concluded that the fault likely acted as a pathway that directed 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 an eruption from occurring.
Lead author Dr. Pablo J. González of 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 Insights Into Volcano Forecasting
The findings suggest that large magma intrusions can develop quickly and with little warning. Researchers also found that major fault systems can strongly influence whether magma erupts at the surface or becomes trapped underground. Scientists say the results could improve future volcanic hazard forecasting.
Dr. Ricardo Ramalho, a co-author from Cardiff University, 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 localization of seismic events and ground deformation.”
Professor Ana Ferreira, a co-author from UCL Earth Sciences, said: “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.”
Reference: “Fault-mediated magma propagation and triggered seismicity revealed by the 2022 São Jorge Azores unrest” by Stephen P. Hicks, Pablo J. Gonzalez, Anthony Lomax, Ana M. G. Ferreira, Ricardo S. Ramalho, Neil C. Mitchell, Graça Silveira, Nuno Afonso Dias, João Fontiela, Rui Fernandes, Susana Custódio, Maria Tsekhmistrenko, Virgilio Mendes, Adriano Pimentel, Rita Silva, Gonçalo Prates, William Sturgeon, Augustin Marignier, Fernando Carrilho, Rui Marques, Miguel Miranda and Arturo M. Garcia, 23 April 2026, Nature Communications.
DOI: 10.1038/s41467-026-71668-6
The research 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 field assistance was provided by the Portuguese Navy (Marinha Portuguesa), while geophysical equipment came from NERC’s Geophysical Equipment Facility (GEF).
Institutions involved in the project 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).
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