A Giant Volcano Lurks Beneath Santorini, Greece’s Most Touristy Island

Scientists are actively installing monitors along Kolumbo’s seafloor

Photos: Stav Dimitropoulos

OnOn a recent November morning, Giannis Bellonias was sipping tsipouro on the veranda of his cave house in Santorini, Greece. “Visibility is poor today. Hope Kolumbo won’t give scientists a hard time,” Bellonias said to his wife, looking out onto the Aegean sea. The alabaster paths leading down to Santorini’s famous sun-bleached, blue-shuttered cave houses, spread out below.

Kolumbo is a gigantic, active submarine volcano located roughly four miles to the northeast of Santorini and 550 yards underwater. When it last erupted in 1650 A.D., it formed a crater 1.5 miles wide, triggered a tsunami that smashed into the eastern and southern coast of Santorini, and killed over 50 people.

Bellonias, who has lived on and off the island for almost 60 years and owns a cultural center and library called the Bellonio Foundation, is keenly aware of the threat Kolumbo poses, and believes it is more dangerous than that of the two volcanoes that sit in the middle of the Santorini caldera, Palea Kameni (“Old Burnt,” inactive) and Nea Kameni (“New Burnt,” still active). Experts think he might be onto something. As Bellionas looked out onto the sea, scientists dropped new seismographs into Kolumbo’s crater in hopes of keeping a closer eye on the mysterious beast.

“I come from a generation of people who have made peace with the volcanic life.”

“Trust me, I’ve dived into the Kolumbo crater with a submersible and have seen the active hydrothermal field of the volcano with my bare eyes,” says Paraskevi Nomikou, a geologist-oceanographer at the National and Kapodistrian University of Athens who dove into the submarine volcano in October. “We need to monitor this active submarine volcano with the same urgency we grant to on-land volcanoes.”

Sulfur rises from the floor of Nea Kameni, an active volcano in the center of the Santorini caldera.

A Santorini native, Nomikou gives credence to local “folk wisdom”: Nea Kameni can cover the island in ash and destroy crops, but it’s Kolumbo that they should fear.

This month, the sudden eruption of New Zealand’s White Island volcano created a 3.7-kilometer-high column of ash and killed at least eight people, raising fresh concerns about the safety of volcano tourism. The 1.5 million tourists who wash up on Santorini’s shores each year may not realize it, but they, like the island’s roughly 15,000 permanent residents, dance with a constant volcanic threat.

In fact, the five islands that make up Santorini were formed over 2 million years of volcanic eruptions. The Late-Bronze Age eruption of 1627 B.C., which lasted for 27 years, sent up seven cubic miles of rhyodacite magma and collapsed 200-foot-thick landslides into the sea, creating tsunami waves nine meters high and forming Santorini’s early modern caldera. Eons later, volcanic activity outside the Minoan caldera created Kolumbo during the historic eruption of 1650 A.D. Palea Kameni and Nea Kameni formed over the course of six violent eruptions between 1570 and 1950 A.D. To many scientists, Nea Kameni is considered the most likely source of a future eruption, but Kolumbo’s silence weighs heavy.

“Santorini is not for the faint of heart.”

For 60 years, all seemed peaceful in Santorini. Then, between 2011 and 2012, GPS instruments on the island registered renewed activity. Data suggested a “rise of the island of Santorini and a parallel decline in sea levels, an unusual and gradually increasing tectonic activity inside the caldera, and a change in water temperatures,” says Christos Pikridas, a scientific council member at the Institute for the Study and Monitoring of the Santorini Volcano (ISMOSAV), a nonprofit organization formed under an E.U. research program in 1995. The observation alarmed locals and volcanologists alike. Nea Kameni has the potential to eject 3.5 million cubic meters of magma and blanket large areas of Europe with ash.

In 2012, the Greek government formed a two-year committee, the Special Scientific Committee for the Monitoring of Santorini Volcano, to monitor the new activity and predicted two potential outcomes: An extreme, “sub-plinian” eruption with a high discharge rate of magma lasting minutes to hours, or, more likely, the reactivation of the Kameni islands’ volcanic centers. They filed a report describing the two scenarios, their potential impact on the local population, and a mitigation plan to the Greek General Secretariat for Civil Protection in 2013. But today, there is still no emergency plan in case of a major eruption.

For now, it is up to scientists to keep tabs on the region’s volcanic activity. Predicting Nea Kameni’s next eruption, says Pikridas, is “a dangerous game.” For 14 years, ISMOSAV monitored Nea Kameni 24/7 with a network of GPS, seismographs, and tide gauges. This October, the organization added four global navigation satellite systems (GNSS) around the volcano to increase its observational power, and next year, ISMOSAV plans to set up two more. Scientists know that any eruptions will be preceded by earthquakes six or seven months in advance, and Pikridas, who led the GNSS installation, hopes the new satellites will pick up these warning signs. “If the points where we have installed the antennae of the GNSSs move upward, this might reveal signs of volcanic unrest with an accuracy of a few millimeters.”

But nearby, the sleeping giant Kolumbo remains “a geological mystery,” says Nomikou.

The subterranean volcano is seven times more active than Nea Kameni and has its own magma chamber, separate from the one that feeds the on-land volcano. In fact, it’s considered by some to be the most active submarine volcano in Europe. But because it is underwater, Kolumbo is extremely hard to monitor. Scientists rely on earthquakes in the area to monitor it, says Nomikou.

In October, Nomikou spent 17 days on the research vessel Poseidon alongside scientists from the Helmholtz Center for Ocean Research Kiel and the Universities of Hamburg and Bologna investigated Kolumbo. They anchored five ocean-bottom seismographs around the volcano and one directly in its crater. It was an ambitious expedition — one that perhaps should have been done many years ago. “Greek authorities have not paid importance to the subject due to budget issues,” says Nomikou. “Of course, they know about the danger because we inform them right away after each and every one of our oceanographic expeditions.”

The team blasted the Poseidon’s air gun at the volcano seabed to penetrate it with sound waves, which were measured by 16 sonar detectors borne on thick, 300-meter-long cables as they rebounded. A detailed picture of the volcano’s structure and a complete representation of its seismic activity emerged. “We basically X-rayed Kolumbo,” says Nomikou. The microquakes caused by the air gun also confirmed that the ocean-bottom seismographs worked. “We recorded small earthquakes, which, of course, show again that the submarine volcano is active,” she says.

Nomikou believes Kolumbo should be the primary subject of scientific focus and innovation, especially as it has already “showed its teeth” by taking so many lives during the great eruption of 1650. The active volcano of Nea Kameni, meanwhile, has gone through several eruptive periods over the past 300 years, all without claiming any victims. “There’s nothing new on Nea and Palea Kameni. These volcanoes have been studied well by previous volcanologists,” Nomikou says.

The scant data on Kolumbo’s activity makes predicting its potentially explosive behavior difficult, but scientists know how to look for early warning signs. They are watching, for example, for earthquakes and discoloration of the seawater into shades of translucent green and white, caused by dissolved volcanic gases like sulfur dioxide, carbon dioxide, and hydrogen sulfide. Nomikou is particularly concerned that there is no permanent monitoring system on Kolumbo to watch for these signs, even though its grave risks to Santorini are clear.

The island has an evacuation plan, but only for earthquakes. The Municipality of Santorini provides online maps, listing places where locals can take refuge or stay for a few days in case one strikes. Pikridas agrees that the lack of emergency planning for an eruption poses a serious threat to the Santorini’s population — as well as the crowds of tourists who come to the island each year.

To a local like Bellonias, the endless stream of tourists scrambling up Santorini’s hills to get the perfect Instagram photo appear blissfully oblivious.“We could have an eruption any time now,” says Bellonias from the yard of his 17th-century home, which has outlasted several eruptions and earthquakes.

“I am actually situated right above the fault line,” Bellonias says with pride.

“I come from a generation of people who have made peace with the volcanic life,” he says. “Santorini is not for the faint of heart.”

Journalist (BBC and others). Columnist. Budding author.

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