São Jorge Island’s ‘Stealthy’ Magma Intrusion: A Failed Eruption Revealed

Thousands of earthquakes struck São Jorge Island in March 2022. The culprit? A massive sheet of magma that rose rapidly from deep beneath the Earth’s crust before stalling just short of an eruption.

Key Findings

In March 2022, a swarm of thousands of earthquakes occurred on São Jorge Island in the Azores, Portugal.
The earthquakes were linked to a sheet of magma rising from a depth of more than 20 kilometers to approximately 1.6 kilometers beneath the island.
The volume of magma was estimated to be enough to fill 32,000 Olympic-sized swimming pools.
Satellite observations recorded a surface uplift of 6 centimeters, confirming the magma’s entry into the shallow crust.
The magma ascent happened over a few days with little seismic activity; the majority of the earthquakes occurred after the movement stopped.
The intrusion stalled before reaching the surface, an event classified as a “failed eruption.”

Magma Movement and Fault System

The magma is understood to have risen through the Pico do Carvão Fault Zone. While this fault system has produced large earthquakes in the past, the 2022 unrest produced many small earthquakes clustered along this specific fault.

The research team concluded that the fault guided the magma upward and may have allowed gases and fluids to escape sideways, potentially lowering pressure and halting the ascent.

Research Methods

The study utilized a combination of seismometers placed on land and on the Atlantic seafloor, along with satellite data and GPS, to map magma movement and ground deformation.

Statements from Researchers

Lead author Dr. Stephen Hicks (UCL Earth Sciences) described the event as a “stealthy intrusion,” noting that the magma moved quickly through the crust but much of its journey was seismically quiet.
Lead author Dr. Pablo J. González (Spanish National Research Council, IPNA-CSIC) stated the fault “acted like both a highway and a leak,” facilitating the magma’s rise but potentially preventing an eruption.
Co-author Dr. Ricardo Ramalho (Cardiff University) noted that the study supported local authorities in assessing the potential volcanic threat.
Co-author Professor Ana Ferreira (UCL Earth Sciences) highlighted the transnational cooperation required to secure urgent NERC funding and deploy equipment.

Institutions and Funding

The research was a collaboration involving numerous institutions, including UCL, the Spanish National Research Council (IPNA-CSIC), Cardiff University, the University of Manchester, the Universidade de Lisboa, the Instituto Politécnico de Lisboa, the University of Évora, the University of Beira Interior, CIVISA (Azores), IVAR, the University of the Azores, the University of Algarve, IPMA, the AIR Centre, and C4G.

Funding was provided by:

Natural Environment Research Council (NERC, UK)
European Research Council (ERC)
Fundação para a Ciência e a Tecnologia (FCT, Portugal)
Agencia Estatal de Investigación (Spain)
Regional Government of the Azores

Field assistance was provided by the Portuguese Navy, and equipment was supplied by NERC's Geophysical Equipment Facility.

The study was published in Nature Communications.