Why Did São Jorge Island Shake 30,000 Times Without Erupting?

The Short Answer

In 2022, magma surged upward from more than twelve miles beneath São Jorge Island in the Azores, triggering over 30,000 earthquakes in two months — then retreated without ever breaking the surface, in one of the most extraordinary volcanic intrusion events ever recorded in real time.

What Happened Beneath São Jorge in 2022?

In March 2022, seismic monitoring networks began detecting unusual activity below São Jorge, a narrow volcanic island in the Azores archipelago roughly thirty-three miles long and five miles wide. Magma was on the move, rising from a depth of more than twelve miles — far deeper than most volcanic intrusions scientists have previously been able to track with modern instruments. Over the following two months, the island registered more than 30,000 earthquakes, most of them small but collectively enough to rattle nerves and shake foundations across a community of around 8,000 residents who had no high ground to retreat to and no precedent in living memory for what they were experiencing.

Satellites equipped with InSAR technology — interferometric synthetic aperture radar — detected the ground along the northeastern coast bulging upward by several inches. The magma was physically deforming the island from below, forcing the crust to flex under its pressure.

Why Didn’t the Volcano Erupt?

This is the question that has captured the attention of volcanologists worldwide. The last time São Jorge actually erupted was in 1808, more than two centuries before this crisis began. In 2022, despite all the indicators pointing toward a potential eruption — deep seismicity, ground deformation, sustained magma ascent — the system simply reversed course. The magma stalled, the earthquakes tapered off, and the island went quiet.

Scientists describe this as a failed eruption or, more precisely, a magmatic intrusion: a pulse of molten rock that entered the upper crust but never found a pathway to the surface. The reasons an intrusion stalls rather than erupts are complex and not fully understood, but factors likely include the viscosity and volatile content of the magma, the structural resistance of the surrounding rock, and whether existing fracture systems can channel material upward with enough force to breach the surface.

Why Scientists Call This Event Unprecedented

What made the 2022 São Jorge event exceptional was not merely that the magma retreated — failed intrusions are not unheard of — but that the entire sequence was captured in extraordinary detail using modern geodetic and seismic instruments. Volcanologists had never before recorded a deep intrusion event of this scale progressing in real time from initiation to arrest, providing a complete dataset of how magma behaves when it rises and stops.

Researchers are now analyzing that data to identify signatures that might distinguish intrusions destined to erupt from those that will quietly dissipate. The practical implications are significant: better forecasting models could help civil authorities issue more precise warnings and make better evacuation decisions during future unrest events anywhere in the world.

What This Means for Volcanic Hazard Science

The Azores sit atop the boundary between the North American, Eurasian, and African tectonic plates, making the region geologically dynamic and historically prone to eruptions. The 2021 eruption of Cumbre Vieja on La Palma in the Canary Islands — another Atlantic island chain — was still fresh in public memory when São Jorge began shaking, heightening anxiety among residents and emergency planners alike.

The 2022 event adds an important new data point to the global record of volcanic behavior, reinforcing that volcanic unrest does not always culminate in eruption and that the processes governing the final ascent of magma remain one of earth science’s most consequential open questions. For the people of São Jorge, the silence that followed was a relief. For scientists, it was an invitation to keep digging.