In March 2022, thousands of earthquakes occurred on the island of São Jorge in the Azores, Portugal, after giant magma (molten rock) rose from deep underground, according to a new study led by researchers at UCL (University College London). The magma traveled from more than 20 kilometers below the surface and stopped just 1.6 kilometers below the island, narrowly avoiding an eruption.
The researchers found that much of the magma’s rise occurred quietly, with relatively little seismic activity during the rise. Most of the earthquakes occurred after the magma stopped rising. This massive incursion spread over just a few days, engulfing enough magma to fill approximately 32,000 Olympic-sized swimming pools.
Lead author Dr Stephen Hicks from UCL Earth Sciences said: “This was a stealthy intrusion. Magma moved rapidly through the Earth’s crust, but much of that movement was silent, so it was difficult to predict whether an eruption would occur.”
Scientists reconstruct hidden magma motion
This research nature communicationsinvolved an international team that combined several methods to trace the underground path of magma. Scientists used seismometers located both on land and under the Atlantic Ocean to pinpoint seismic activity. They also analyzed satellite and GPS measurements to monitor how the island’s surface changed during the event.
Satellite data confirms that the ground above the volcano has risen by about 6 centimeters, allowing magma to enter the shallow crust beneath the island. But the magma never made it to the surface, causing what scientists call a “failed eruption.”
These underground incursions are important because they help build and reshape volcanic islands over time. Researchers say the highly detailed seismic maps created during the study provide new insights into how geological changes occur.
Fault zone may have prevented eruption
The magma migrated upward through one of São Jorge Island’s major fault systems, known as the Pico do Calvin fault zone. Previous geological studies have shown that this fault has caused powerful earthquakes in the past. But in the 2022 uprising, rising magma caused thousands of smaller earthquakes clustered along the fault, rather than one large quake.
The researchers concluded that the fault zone likely acted as a pathway for magma to flow upward. At the same time, gases and fluids may have escaped sideways, lowering the pressure within the magma and preventing it from erupting.
“This fault acted both like a highway and a leak. It helped the magma rise, but it may also have prevented an eruption,” said lead author Dr. Pablo J. González of the Spanish National Research Council (IPNA-CSIC) in Tenerife.
New clues for volcano prediction
The results of this study suggest that large-scale magma intrusions can occur rapidly and with limited warning signs. The study also highlights that major geological faults can have a major impact on whether magma erupts or becomes trapped underground. Researchers say these insights could improve predictions of future volcanic hazards.
Co-author of the study, Dr Ricardo Ramalho from Cardiff University, said: “This study supports local authorities in assessing potential volcanic threats and highlights the value of combining onshore and offshore geophysical data for accurate detection and localization of seismic events and ground movements.”
Ana Ferreira, Professor of Geosciences at UCL, added: “Securing NERC’s emergency funding to access the Geophysical Equipment Facility (GEF) instruments, alongside additional support from Portugal, was a huge joint effort and a clear example of cross-border collaboration between academic and private institutions in Portugal, the UK and Spain.”
This project was funded by the Natural Environment Research Council (NERC; UK), the European Research Council (ERC), Fundação para a Ciência ea Tecnologia (FCT, Portugal), Agencia Estatal de Investigación (Spain), and the Regional Government of the Azores Islands. Maritime deployment support was provided by the Portuguese Navy, and geophysical equipment was provided by NERC’s Geophysical Equipment Facility (GEF).
Institutions involved in the research included UCL, Spanish National Research Council (IPNA-CSIC), Cardiff University, University of Manchester, University of Lisbon (Portugal), Polytechnic University of Lisboa (Portugal), University of Évora (Portugal), University of Beira Interior (Portugal), Azores Earthquake and Volcano Information and Monitoring Center (CIVISA, Portugal), Azores Earthquake and Volcano Information and Monitoring Center (CIVISA, Portugal), Volcanology and Risk Assessment (IVAR), University of the Azores. (UAc), University of the Algarve (Portugal), Portuguese Institute of Marine and Atmospheric Research (IPMA; Portugal), AIR Center (Portugal), and C4G (Portugal).
