Decade Volcano: Santorini


It’s hard NOT to get a world-class-travel-destination picture at Santorini, in Greece.

That island in the bay is Nea Kameni, the currently active center of a very famous caldera volcano that many of us have some misconceptions about.

Let’s start by taking the scenic route down to Nea Kameni from the caldera rim via a couple of videos.

After all, everyone wants to see a beautiful, sun-drenched citadel, perched atop colorful volcanic cliffs, where they applaud the sun setting into the Aegean Sea each evening.



Believe it or not, this town — called Oia — is actually a small village, with fewer than 2,000 inhabitants.

Those crowds? They’re just some of the estimated two million tourists who visit Santorini each year.

Now, about the volcano here that scientists considered worthy of Decade status:




It’s good to hear that another caldera-forming VEI 6 to 7 eruption is unlikely to happen any time soon.

So, in the face of smaller eruptions from Nea Kameni, how do the residents of Santorini keep up that picture-perfect look?

Well, they haven’t had to face this challenge yet.

People depended on farming and fishing to survive. (Image: Klearchos Kapoutsis via Wikimedia, CC BY-SA 2.0)

The human story

In 1950, when Nea Kameni last erupted (VEI 2), Santorini was an impoverished island.

Those now-famous “cave houses” are actually dug into the cliffs. They were made that way because there are no other building materials available.

And in 1956 many residents fled when two huge tectonic (Papadimitriou et al) earthquakes hit the region within 15 minutes of each other, destroying 500 homes on Santorini and causing a deadly tsunami.

Then tourism happened, and life improved dramatically.

Young, wealthy Boomers made Greek islands trendy — the more isolated and undeveloped, like Santorini, the better — and those preserved ruins at Akrotiri became an added attraction when excavations began there in 1969.

Here is how Michael Ermogenis, founder of Santorini’s Save Oia Campaign, describes the change in an online interview with Greece Is:


“The people here went from having nothing to, within two generations, holding the keys to Fort Knox.”


He’s not exaggerating.

Besides the scenery and lighting, there are local traditions. These men are escorting the bridegroom to the church. (Image: Klearchos Kapoutsis, CC BY 2.0)

Santorini got electricity in 1974. Cruise ships began arriving in the 1980s.

As the island’s fame spread, it also became an internationally renowned wedding and honeymoon destination.

And in the 21st century, as social media use became widespread, many people all over the world decided they had to take a selfie and other images at highly photogenic Santorini.

In the early 2000s, more than 850,00 people visited Santorini each year. (Chester et al.) By 2017, that number was up to two million annually, with an additional 620,000 day visitors — it works to about 108 tourists per hundred inhabitants per day! (Peeters et al.)

The residents of Santorini are now enjoying the good life for the first time in their history.

Nea Kameni, out in the bay, slept through this exciting human saga, only “dreaming” a little bit in 2011 and 2012.



Colors change as Nea Kammeni’s surface rises or falls.


But that “dream” brought a batch of magma large enough to build four Hoover Dams (an estimated 18.3 million cubic yards of molten rock, according to Nomikou et al., 2019) a little closer to the surface.

It’s still almost three miles underground, but the episode is a reminder that Santorini is still active, and its complex plumbing is slowly recharging. (Saltogianni et al.)

A world-changing big blast is probably thousands of years in the future, but someday soon, geologically speaking — perhaps in our lifetime — Nea Kameni will erupt again.

Fields of volcanoes in the Aegean

Back in the late 1980s/early 1990s, experts assessed hazards at Santorini and found good reasons to make it a Decade Volcano as well as a European Laboratory Volcano.

The disastrous effects of Santorini’s big eruption some 3,600 years ago had been known the 1930s, but (despite what you have heard on documentaries and in feature articles) scientists have never proved beyond a doubt that it caused the decline and fall of the Minoan culture centered on Crete, less than 100 miles away.

The residents of ancient Akrotiri enjoyed beautiful scenes, just like us. (Image: Jebulon via Wikimedia, public domain)

  • Records exist from that time, but they are written in a script, called Linear A, that has not yet been translated.
  • Precise dating could link the eruption to the Minoan collapse, but what Oppenheimer calls “smoking-gun” evidence of Santorini’s eruption that would give us the exact date has not been identified in ice-core records.
  • Geological evidence shows that a tsunami did hit northern Crete at the right time, but it didn’t penetrate far inland. Crete only got around 2 inches of ash from the eruption — bad, but not enough to cause long-term or severe problems. (Soldatus)

So this historic problem was worth looking into, too, with an eye on the chances for another “Minoan” blast in modern times and what such a catastrophe might do to our infrastructure, transportation, and social systems.

Santorini had become more accessible to volcanologists and their field research tools, thanks to tourism which was also increasing the number of people at risk from this volcano.

Thira, or Thera, are other names for Santorini. (Image: Ivanois via Wikimedia, CC BY-SA 4.0)

Those were all criteria for Decade Volcano status. In addition, there was also the puzzling eruption — outside the caldera! — at Kolumbo Reef, a few miles northeast of Santorini.

This VEI 4 blast in 1650 AD was powerful enough to be heard in the Dardanelles, hundreds of miles away, but was it connected to Santorini?

To make a long story a little shorter, much research was done at Santorini during the 1990s, and even more has been done since then.

Work is ongoing, but you’re not likely to see many scientists among the tourists.

While they’re well aware of Santorini’s risks, volcanologists know that the big caldera is almost totally free of earthquakes at the moment and that Nea Kameni’s hot springs are relatively cool, which would not be the case if they were sitting over an active magma body.

No, Kolumbo is where you’ll find the boffins now. It’s the site of most volcanic seismicity; its hydrothermal springs are intense; and it is not a reef — it is a submarine volcanic field.

Videos like this are just as beautiful to nerds as the more traditional ones are to visitors on Santorini (the island is appears in the background here):



There are more than 19 volcanic cones down there.

Kolumbo, source of the 1650 AD eruption, is the largest submarine cone in this fiery field. Bathymetry studies show it to be about two miles wide at the base and roughly a thousand feet high, with an almost 6,000-foot-wide central crater.

They called it a reef because part of the crater rim is only 60 feet below the waves (during the 1650 eruption, a small island formed here, but wave action quickly eroded those pyroclastic deposits away).

Kolumbo’s restlessness suggests that the next eruption might happen here, not at Nea Kameni. (Nomikou et al., 2014)

That could still be bad news for Santorini.

In 1650, Kolumbo’s ashfall and gases, along with an eruption-related tsunami, killed 120 people there (Brown et al.) and more than a thousand head of livestock.

Only a few miles separate Santorini and Kolumbo. Is there a connection?

Yes, there is, but it’s not what you might think.

In brief, there are forces operating here that are even more powerful than those behind Santorini’s caldera-forming explosions.

To look at the geological powerhouse in this part of the world, you could sail far south of Santorini and eventually reach Africa. Or you could wait at Santorini, and let Africa come to you.

Plate tectonics is moving the African continent northward into a collision with Eurasia. Among other results, this has broken the seafloor underlying the Aegean Sea into a faulted “microplate.”


Continental collisions are messy. (Image: Mike Norton via Wikimedia, CC BY-SA 3.0)


One of those Aegean fault zones runs from the Christiana Islands (extinct volcanic structures of uncertain age) northeast, through Santorini and Kolumbo volcanoes, to nearby Amorgos (which is an island, not a volcano).

The volcanic centers formed wherever magma found a conduit up to the surface.

That probably first happened at what is now Santorini around two million years ago. Kolumbo’s history is less well understood, but it may have begun erupting “only” 70,000 years ago. (Nomikou et al., 2019; Soldatus)

Kolumbo Volcano might be connected directly to the mantle. Santorini’s magma apparently pauses for a while in crustal reservoirs before it erupts. (Nomikou et al., 2019)

Even though the two volcanoes have different plumbing, they belong to the same group. There may even be others, hidden beneath the wine-dark sea, that have not yet announced their presence with an eruption.

With better knowledge of this complex region since the Decade Volcano programs of the 1990s, volcanologists have new names for it, typically either the “Santorini Volcanic Complex” (Dominey-Howes and Minos-Minopoulos) or the “Christiana-Santorini-Kolumbo Volcanic Field” (Nomikou et al., 2019).

But the public will always know it as “Santorini,” until an eruption happens at Kolumbo or some other vent.

Location:

36.404° N, 25.396° E, in Cyclades Prefecture, Greece. The GVP Volcano Number is 212040.

Nearby Population:

Per the Global Volcanism Program, and not counting tourists:

  • Within 5 km (3 miles): 5,176
  • Within 10 km (6 miles): 12,266
  • Within 30 km (19 miles): 12,336
  • Within 100 km (62 miles): 67,468

Current Status:

Normal, no warnings at Nea Kameni or Kolumbo.

Eruptions:

  • Eruption styles: Alternating explosive eruptions and relatively quiet lava effusion that forms domes and thick flows. (Parks et al.)
  • Biggest recorded event: The VEI 4 eruption in 1650 AD at Kolumbo Volcano. There might be eyewitness accounts of Santorini’s VEI 7 “Minoan” eruption in the 1600s BC, but ancient writing in that language, called Linear A, hasn’t been translated yet.
  • Most recent eruption: Between 1925 and 1950, Santorini had four effusive eruptions in the Kameni islands, which are the visible part of a roughly 5 km3 lava dome complex. Nea Kameni still shows fumarole and outgassing activity. In 2011-2012, the number of earthquakes here increased for a while and the land rose as much as 5 inches in some places before things quieted down again.
    Kolumbo’s last known eruption was in 1650.
  • Past history: See the Global Volcanism Program for details. Basically, what looks to us like a single drowned volcanic crater is the product of four caldera-forming eruptions at Santorini, the first one happening about 180,000 years ago, then again at roughly 70,000, 21,000, and 3,600 years ago. That last one was the famous “Minoan” blast. In between catastrophic blow-outs — we seem to have few millennia before the next one, if Santorini stays true to form — there are occasional, much quieter lava flows.

Monitoring:

The Aristotle University of Thessaloniki and the Institute for the Monitoring of Santorini Volcano (ISMOSAV) operate a seismic monitoring network, as well as observing geochemical, geophysical, and deformation changes at Santorini. (Newman et al.; Soldatus)

I don’t know what regular monitoring is done at Kolumbo or elsewhere in this volcanic complex.


Featured image: Navin75, CC BY-SA 2.0.


Sources:

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Brown, S.K.; Jenkins, S.F.; Sparks, R.S.J.; Odbert, H.; and Auker, M. R. 2017. Volcanic fatalities database: analysis of volcanic threat with distance and victim classification. Journal of Applied Volcanology, 6: 15.

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