In March of 2022, an unexpected seismic crisis struck Portugal's São Jorge Island in the Azores province, plunging residents into confusion and fear. A recent international study published in the journal Nature Communications has revealed that the seismic activity was caused by a rapid intrusion of magma at a depth of approximately 26 kilometers beneath the Earth's surface. This resulted in magma rising to a depth of 1.6 kilometers below the island's surface, as noted in a study led by University College London.
Failed Eruption Identified
The researchers employed a combination of seismometers, including both surface-based and seabed instruments, satellite data, and GPS data to identify what they termed a 'failed eruption'. They believe this event provides another example for volcanologists on how large geologic faults can serve both as pathways for magma travel and as pressure-release valves during signs of active volcanism. Portugal's São Jorge Island narrowly escaped what could have been a 'stealthy' eruption.
Magma Movement and Prediction Challenges
The movement of magma was slow until it reached the surface, making it extremely difficult for volcanologists to predict whether a full eruption would occur. The intrusion was large enough to fill 32,000 Olympic-sized swimming pools with magma. According to Dr. Stephen Hicks of UCL, the lead author of the study, the magma moved quickly through the Earth's crust with largely aseismic, or silent, ascent, demonstrating that predicting volcanic hazards can be extremely challenging.
Role of Fault Systems in Volcanic Activity
The magma traveled along the Pico do Carvão Fault Zone, the island's primary fault system. This fault zone functions as a dual-purpose structure, acting not only as a highway for moving magma toward the surface but also as a 'leak' that allows gases and fluids to move laterally away from the magma. This process relieves pore fluid pressure in the magma and prevents its movement toward the surface, thereby averting a volcanic eruption. This finding highlights the complexity of tectonic environments and their direct influence on whether volcanic unrest results in an eruption or remains buried beneath the Earth.
Importance of Advanced Monitoring
The study published in Nature Communications underscores the critical need for an integrated approach using onshore seismometers combined with offshore seafloor sensors to monitor large-scale geological changes occurring below the Earth's surface. By utilizing these data types along with satellite radar imaging (InSAR) and high-precision GPS data, researchers reconstructed the underground movements of magma with unparalleled accuracy. Such findings provide a greater understanding of how large magma intrusions can occur in short periods with little to no surface indicators. Experts now believe that applying these monitoring techniques to other geologically complex areas will be key to enhancing the accuracy of forecasting future volcanic hazards and improving how local emergency management agencies respond.
