A remarkable “time capsule” from one of the greatest volcanic disasters in human history may provide compelling evidence of the cataclysmic event and perhaps even the very first physical remains from the tens of thousands of people who likely perished. Meanwhile, the first evidence of a medieval-era tsunami in the region provides rare data that can help us better understand the true destructive force of future tsunamis we will face.
In a paper published in late 2021 in the Proceedings of the National Academy of Sciences, an international team of researchers presented evidence of a destructive tsunami that followed the eruption of Thera (modern Santorini), a volcanic island in the Aegean Sea, some 3,600 years ago.
The “super-colossal” eruption of Thera, categorized as a 7 (out of 8) on the volcanic explosivity index, is estimated to have been one of the most destructive eruptions in human history, with some researchers likening it to the detonation of millions of Hiroshima-type atomic bombs. Many scholars believe the traumatic collective memory of the Bronze Age event, around 1600 B.C., could be seen in Plato’s allegory of the sunken city of Atlantis, composed more than a thousand years later, and the impact of the event may also be reflected in the biblical Ten Plagues. Akrotiri, a Minoan city buried in ash by Thera, is a popular tourist attraction often likened to Pompeii.
While there are no firsthand accounts of the eruption and subsequent tsunami, modern researchers have sought to define its scope as well as the impact it had on life in the Mediterranean at the time—most notably for the Minoans, a wealthy maritime power centered on the nearby island of Crete that went into decline around the same time, in the 15th century B.C.
Unearthing a tsunami
The Thera paper describes research at the archaeological site of Çesme-Bağlararası, located in the popular resort town of Çesme on Turkey’s Aegean coast and more than 100 miles north-northeast of Santorini.
Since 2009, archaeologist Vasıf Şahoğlu of Turkey’s Ankara University has directed excavations at what seemed to be a thriving coastal settlement occupied almost continuously from the mid third millennium to the 13th century B.C. But unlike the well-preserved buildings and roads from earlier phases of the site, Şahoğlu focused on an area where he quickly dug into chaos: collapsed walls, layers of ash, and jumbles of pottery, bone, and marine shells. He reached out to colleagues in various specialties who could help make sense of the mess, including Beverly Goodman-Tchernov, a professor of marine geosciences at Israel’s University of Haifa and National Geographic Explorer who has a particular focus on identifying tsunamis in the archaeological and geological records.
Signatures of past tsunamis may be difficult to identify—evidence such as collapsed buildings and fires may also be the result of earthquakes, floods, or storms. Even then, such evidence can fade quickly with time, particularly in more arid environments like the Aegean coast. While the impacts of the Thera eruption can be seen far away, in Greenland’s ice sheets and California’s bristlecone pines, only six physical sites with evidence for the Thera-driven tsunami that thundered through the Aegean have been identified so far, and none with the complexity provided by Çesme-Bağlararası.
“Tsunami are predominantly erosive events … not depositional events, thus the excitement when we find them!” says Floyd McCoy, a professor of geology and oceanography at the University of Hawaii, Windward College. McCoy, a National Geographic Explorer who has studied the Thera eruption and tsunami event but did not participate in the new project, calls the research “a real contribution not only to research on tsunami deposits but on their meaning and interpretation especially related to the [Bronze Age] eruption of Thera.”
Now researchers are creating increasingly sophisticated “checklists” to look for historical tsunami events, which also include physical and chemical signatures for marine life brought onto land with the inundating waves, and the particular patterning of sediment and rock deposits. At Çeşme-Bağlararası, for instance, mats of shellfish carried in from the ocean were found wedged against collapsed walls of buildings.
“It’s rare that I feel really confident in tsunami interpretation, especially in an arid environment, because you just don't have a lot of stuff to work with,” says Jessica Pilarczyk, an assistant professor of earth sciences and Canada research chair in natural hazards at Simon Fraser University, who did not participate in the Çesme-Bağlararası research. “But it seems in this case, there's some really great evidence that they were able to capture and process.”
Thera—a disaster with no victims?
One of the most puzzling aspects of the Thera eruption is the lack of victims: more than 35,000 people are estimated to have died in the tsunami spurred by the Krakatoa eruption, and similar numbers have been proposed for the Bronze Age Aegean.
Until now, however, only one individual has been identified as a possible victim of Thera: a man found buried under rubble on the Santorini during investigations in the late 19th century.
Theories about the lack of victims vary: smaller, earlier eruptions led people to flee the area before the cataclysmic eruption occurred; victims were incinerated by super-heated gases, or perished mainly in the sea, or were buried in mass graves that have yet to be identified.
“How does one of the worst natural disasters in history have no victims?” Şahoğlu asks.
Goodman-Tchernov suspects that, just as researchers may have been unable to recognize tsunami deposits in the past, they may have also already uncovered victims from the Thera disaster but failed to make the connection.
In Çesme-Bağlararası, however, the researchers say they have almost certainly found a victim of the event: the skeletal remains of a young, healthy man with signs of blunt force trauma, found prone in the rubble of the tsunami deposit.
Waves of terror
The researchers determined that four waves of tsunami landfalls hit Çesme-Bağlararası over the course of a few days or weeks. This is particularly fascinating to McCoy, who notes that there were four phases to the eruption of Thera; researchers have long wondered which eruption phase triggered what they thought was a single tsunami event.
As the waters receded between tsunami landfalls, it appears that surviving residents took the opportunity to dig into the chaos in search victims and of building materials. One such pit was found directly above the body of the young man; whoever dug it, however, stopped a few feet too soon to retrieve him.
This evidence of attempting to retrieve tsunami victims suggests concern about adequate burial after the disaster, possibly in mass graves to reduce disease in its aftermath.
Traditionally the eruption of Thera has been assigned to a time period known as Late Minoan IA, which is associated with Egypt’s 18th dynasty in the 1500s B.C. But radiocarbon dates of wood found in ash layers at Akrotiri date to the mid-late 1600s B.C.—a discrepancy of up to more than a century. This causes problems for researchers trying to correlate relative chronologies of the different cultures that lived around the Mediterranean at the time and how they interacted before and after the disaster.
According to the researchers, the eruption could not have occurred earlier than the earliest date they obtained from within the tsunami deposit at Çesme-Bağlararası—a grain of barley found near the remains of the young man, radiocarbon dated to 1612 B.C. Radiocarbon dates for other materials are currently in progress.
Evidence for a more recent tsunami that struck the eastern Mediterranean—some 2,300 years after the Thera event—appears in the the journal Geosciences. Goodman-Tchernov and her colleague C.J. Everhardt of the University of Haifa describe how an earthquake on the inland Dead Sea fault sparked destructive waves that damaged the ancient port of Caesarea Maritima on the coast of what is now Israel in 749 A.D.
Evidence comes from a harbor warehouse that was destroyed in the the event; the distinctive, chaotic signature of a tsunami was preserved by later building activity at the site.
Less than a few dozen coastal archaeological sites worldwide have reported tsunami deposits, making this study unique, Goodman-Tchernov says. "We really only have about a century of instrumental records on tsunamis, and maybe 20-30 years of refined satellite data, so in a lot of ways we effectively don't know everything that happens during a tsunami."
The geoscientist adds that the increasing loss of natural coastline buffers combined with more people living on coasts is making us only more vulnerable.
"A tsunami that happened 100 years ago is going to be much less dangerous than a tsunami that happens today."