Santorini follow up: why so many earthquakes?
In February this year, while we were preparing for our April–May trip to Cyprus, Crete and Santorini, we noticed many earthquakes popping off in Santorini. When looking at my QuakeWatch app, I saw that literally hundreds of earthquakes occurred each day—they were drowning out almost every other location on Earth!
At the time, no one seemed to know the cause of these earthquakes. Most were small—the average was 1.3 magnitude—but a few exceeded 5 magnitude. People evacuated Santorini and feared disruption to the upcoming tourist season.
We needed to pay a non-refundable payment to Cretan Adventures, the company that organized our self-guided excursion in Crete and Santorini (https://www.cretanadventures.gr/en/our-tours/self-guided-hiking-crete-santorini/). But we decided to risk it and—happily—by early March the earthquakes had largely ceased.
The danger of earthquakes in Santorini
With so many buildings clinging to the steep edge of Santorini’s caldera, residents and visitors can sense the risk when the ground starts shaking.
Fortunately, we did not experience any earthquakes and the trip was fabulous. My posts on April 23, 27 and May 4, 12 describe the island of Cyprus. Posts on May 18 and 24 describe the island of Crete, and posts on June 13 and 23 describe the island of Santorini.
So what was the cause of all those earthquakes?
Over 28,000 earthquakes shook Santorini and vicinity in just over a month. As luck would have it, scientists had recently started to monitor Santorini and Kolumbo, an underwater volcano just 7 km northwest of Santorini. The German- and Greek-led investigation had installed many geophysical instruments and was in full swing when the quakes began. Incredibly, the dense network of instruments enabled the geoscientists to discover an unknown connection between the Santorini and Kolumbo volcanoes and to identify the path of rising magma that caused the earthquake swarm.
a: The preparatory phase from June 2024 to January 2025. Magma from a mid-crustal magma reservoir moved upward into a shallow magma reservoir beneath Santorini, creating surface uplift and increased seismicity. Areas labeled with H=high velocity seismic waves in cooler crust. Areas labeled with L=low-velocity seismic waves in hot magma. The significance of these changes was only realized following the earthquake swarm and further analyses.
b: The volcano–tectonic crisis with diking and faulting. Starting on 27 January 2025, a dike intrusion was initiated from the mid-crustal magma reservoir and magma moved upward into the Anhydros block (white dashed line). Seismicity (colored dots) occurred at the tip and edges of the dike rupture, and shallow crustal normal faults were activated by changes in stress and fluid pressure (black lines). Deflation of the shallower mid-crustal melt reservoir led to subsidence, which was measured at Santorini and Kolumbo. VE=Vertical exaggeration. Figure from Nature article (see Resources below).
The National Geographic article (see Resources below) is a concise summary of the scientific findings. Although there was no evidence of connection between the shallow magma reservoirs of Santorini and Kolumbo (see “a” part of figure above), the geophysical instruments enabled scientists to image connections that are deep beneath the seafloor. Magma was injected upward as dike intrusions that caused faults to move and earthquakes to occur.
Fortunately, this time none of the magma made it to the seafloor and there was no volcanic eruption. The next time may be different, but at least the system is now much better understood because of the ongoing scientific study.
Resources
“This year thousands of mysterious earthquakes hit Santorini. Scientists finally know why”. 24 September 2025 article by Robin George Andrews in National Geographic that summarized conclusions of a research article in Nature: https://www.nationalgeographic.com/science/article/santorini-earthquake-swarm-volcano-magma.
“Volcanic crisis reveals coupled magma system at Santorini and Kolumbo”. 24 September 2025 research article in Nature (with 34 authors) that explains the results of their scientific investigation around Santorini: https://www.nature.com/articles/s41586-025-09525-7.
Super cool. Gotta love good science! Thanks for sharing!
At least other countries are still supporting their scientists. Thanks for reading!