The secret of the volcanic tsunami in the Aegean Sea solved after 400 years

The 1650 eruption of the underwater volcano Kolumbo in the Aegean Sea triggered a devastating tsunami described by historical eyewitnesses. Now, a group of researchers led by Dr. Jens Karstens from the GEOMAR Helmholtz Centre for Ocean Research has examined Kolumbo's underwater crater with modern imaging technologies and reconstructed these historical events.

IT OCCURRED AT THE END OF THE SUMMER MONTHS OF THE 17TH CENTURY

Scientists have discovered that this natural disaster, described by eyewitnesses, can only be explained by a landslide that occurred following an explosive eruption. The findings were published yesterday in the journal Nature Communications.

According to Popular Science Turkey, the eruption was visible from the Greek island of Santorini for several weeks. In the late summer months of 1650, people reported that the color of the water changed and the water began to boil. About 7 km northeast of Santorini, an underwater volcano rose from the sea and began to spew glowing rocks.

Meanwhile, flames and lightning were seen, and the sky darkened with clouds of smoke. Then, the waters suddenly receded, and a few seconds later, they rose toward the shore, creating waves that reached 20 meters. Following a giant explosion sound that was heard even from the Aegean coasts, pumice stones and ash rained down on the surrounding islands. Some people lost their lives due to a spreading cloud of toxic gas.

Dr. Jens Karstens, a marine geophysicist at the GEOMAR Helmholtz Centre for Ocean Research, says, “We know these details of the historical Kolumbo eruption from reports of that time, which were compiled and published by a French volcanologist in the 19th century.” So how did these devastating events occur? To find the answer, Karstens traveled to the Aegean Sea in 2019 with his German and Greek colleagues to study this volcanic crater with special technologies. “We tried to understand how the tsunami emerged and why the volcano erupted so violently at that time,” he says.

The research team, which set sail with the now-decommissioned research vessel POSEIDON, used 3D seismic methods to create a three-dimensional image of the crater, which is currently 18 meters below the water surface. Co-author of the paper, Dr. Gareth Crutchley, says: “This gave us the opportunity to look inside the volcano.” While the 3D imaging method suggests that this crater, which turned out to be 2.5 kilometers in diameter and 500 meters deep, was indeed a massive explosion, the seismic profiles created also showed that a serious deformation occurred on the side of the volcanic peak. “This part of the volcano definitely slid,” says Crutchley.

The researchers then, with a detective-like approach, compared various mechanisms that could have led to the tsunami with the accounts of historical eyewitnesses. As a result, they concluded that the tsunami could only be explained by a landslide that occurred following the volcanic eruption. The scientists' findings were published yesterday in the journal Nature Communications.

Combining 3D seismics with computer-run simulations, the researchers were able to show how high these waves could have been if they had been formed only by the explosion. “According to this, six-meter waves would be expected in a certain place,” says Karstens. “But from the eyewitness accounts, we know they were 20 meters there.” Furthermore, it was said that the sea first receded at another point. However, in the computer simulation, a wave crest reaches the shore first. For this reason, the explosion alone cannot explain the tsunami event. But when a landslide is included in the simulations, the data matches the historical observations.