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Flooding the Santorini Caldera

Flooding the Santorini Caldera

The flooded caldera of Santorini volcano holds many secrets, buried beneath the ash and pumice of its last great eruption. In the Late Bronze Age, about 3600 years ago, an explosive eruption several times larger that of Krakatoa, 1883, wreaked devastation across this thriving island.

View, looking North, of the northern part of the Santorini caldera. The island of Thersia (left) is separated from the island of Thera (right) by a channel, that is now thought to have formed at the end of the Late Bronze Age eruption.

View, looking North, of the northern part of the Santorini caldera. The island of Therasia (left) is separated from the island of Thera (right) by a channel, that is now thought to have formed at the end of the Late Bronze Age eruption.

A great trading port, Akrotiri, was buried under metres of pumice; preserving for future generations a snapshot of Late Cycladic urban life.

Akrotiri ruins

Bronze Age street scene – Akrotiri, Santorini. Precursory earthquakes damaged the town. But there was time for the residents to clear up rubble (foreground), and rescue furniture (those are casts of bed frames in the street), before the town was buried in pumice.

Once the eruption was over and the dust had, literally, settled the geography of Santorini would have looked much like it is today: a group of three islands, forming a ring around a caldera occupied by the sea. The central ‘Kameni’ islands would not have begun to emerge for another thousand years, or more.

But when did the sea flood the caldera, and what were the consequences? It has long been suspected that the Santorini eruption triggered tsunamis, implicated in Late Bronze Age destruction along exposed coastlines around the Aegean. Observations of the Krakatoa eruption in August 1883 include harrowing accounts of the great sea waves that swept across low-lying areas of Java, Sumatra as this eruption reached a climax. These tsunami were triggered either by the convulsions of the sea-floor, as the island of Rakata collapsed into the newly-forming caldera; or, as now seems more likely, by the displacements of colossal volumes of water as the pyroclastic currents raced into the sea.

Krakatoa - before and after images.

Krakatoa – before and after: notice how much of the island of Rakata (labelled Krakatau) has disappeared in the eruption; and the large shoals of pumice that formed new islands north-west of Krakatau (Proceedings of the Royal Geographical Society).

But could tsunami have been triggered by the Santorini eruption; and how? Until now it has been thought that collapse of the caldera could have triggered a tsunami; but only if the caldera was already flooded by the sea. A growing body of geological and archaeological evidence suggests that the crater of Santorini volcano was not open to the sea, as it is today, at least at the beginning of the Late Bronze Age eruption. Large blocks of stromatolites, an algal concretion, and chicken-wire gypsum that were caught up in the eruption debris point to the presence of a muddy lake in the northern part of Santorini. Before the eruption, this would probably have been an area of hot, bubbling mud-pools, fed by volcanic heat and fluids from depth. Among the wall-paintings from Akrotiri is one, the flotilla fresco, that shows a city on a hill, with a river running by. Are these features that might have been found inside the caldera of the volcano?

Metre-wide block of stromatolite, thrown out during the LBA eruption

Metre-wide block of stromatolite, thrown out during the LBA eruption, now in the entrance to the Heliotopos hotel.

In a new paper in Nature Communications, we present some new evidence that may help to resolve some of these questions. High-resolution mapping of the seafloor shows the presence of a remarkable scour at the northern end of the deep channel that separates the islands of Therasia and Thera, below the town of Oia. This feature can be seen on older sea-floor maps; but not in such detail. Using sound-waves to look at the structures that this channel cuts through shows that the channel didn’t form until most of the material thrown out in the eruption had already been deposited. The shape of the scour will be familiar to anyone who has built dams of sand on a wet beach, and then let it fail. This shape shows that the channel formed quickly, and that the sea broke through and poured down a great waterfall into the caldera, but only after the eruption was over. Any tsunami waves that formed during the eruption must have been triggered by the entry of the pyroclastic currents into the sea.

Image of the northern 'breach' in the Santorini caldera, and the scour and channel that cut through it.

Image of the northern ‘breach’ in the Santorini caldera, and the scour and channel that cut through it. From Nomikou et al., 2016.

This new evidence, along with new ‘cosmic ray exposure’ age measurements showing that the cliffs of the northern part of Santorini are ancient and formed before the Late Bronze Age, may strengthen arguments that the pre-eruption interior of Santorini island was not filled with seawater as it is today. It doesn’t, however, have any direct connection to the events that led to the collapse of the major Late Cycladic culture on Crete, the Minoan, a few decades later. Disruption caused by the loss of a major trading hub and short-term damage caused by fallout of ash across the islands of the eastern Aegean might well have contributed to the eventual decline and fall of Minoan culture; but the later destruction of the Cretan palaces must have another cause. Earthquake, anyone?

Selected references 

Heiken G, McCoy F, 1984, Caldera development during the Minoan eruption, Thira, Cyclades, Greece. Journal of Geophysical Research 89, 8441–8462

Manning SW et al., 2006, Chronology for the Aegean Late Bronze Age 1700-1400 B.C.,  Science 312, 565-569

Nomikou P et al., 2016, Post-eruptive flooding of Santorini caldera and implications for tsunami generation, Nature Communications 7: 13332, 8 November [open access]

Novikova T et al., 2011, Modelling of tsunami generated by the giant Late Bronze Age eruption of Thera, South Aegean Sea, Greece. Geophys J Int 186, 665-680.

Paris R, 2015, Source mechanisms of volcanic tsunamis, Phil Trans Roy Soc London A 373: 20140380

Pichler H, Schiering W, 1977, The Thera eruption and Late Minoan-IB destructions on Crete, Nature 267, 819 – 822

Acknowledgements

Thanks to NERC for funding for my work on Santorini; the organisers of NEMO 2016 and Heliotopos Conferences for a recent visit to Santorini; to Christos Doumas, Lefteris Zorzos, Clairy Palyvou and Maya Efstathiou for introductions to Akrotiri and the Late Bronze Age, and Floyd McCoy for discussions.

Into the Inferno: an anth(rop)ology of volcanoes

Into the Inferno: an anth(rop)ology of volcanoes

What do volcanoes mean to you? This is perhaps not a question to ask a volcanologist (cue: a paean to their current flame); but what do they mean to the publics? Fire and brimstone? Death and destruction? Of humans pitted against mountains? Or is it something else? Perhaps the answer is obvious, but it is certainly something we need to think about when preparing for an audience: what will they expect to find? and how can I surprise them?

It is a question that the volcanologist Clive Oppenheimer has pondered for some time. Five years ago his book ‘Eruptions that Shook the World‘ caught the attention of film director, Werner Herzog. They had already met earlier (on the Antarctic volcano, Erebus, of course); and have now released the fruits of their collaboration on Netflix.

Running at 1 hr 44 minutes, Into the Inferno is part anthology, part anthropology, and part conversation between volcanologist and film-maker. Taking in breathtaking footage of some of the volcanoes ‘du jour’, Herzog and Oppenheimer explore their own, rather different, attractions to volcanoes – as objects; as cultural symbols; as places incidental to the life and living that goes on around them.

Clive Oppenheimer introducing 'Into the Inferno' at the Cambridge Film Festival

Clive Oppenheimer introducing ‘Into the Inferno’ at the end of the 36th Cambridge Film Festival

For Herzog, volcanoes are not the main attraction. Sitting on the rim of Erebus, the world’s most southerly volcano, it is almost as if he couldn’t care less about the fuming crater below. It’s the people, and their stories that he wants to capture.  So it is that the film takes us from the roiling chasm of the crater of Mt Yasur on Tanna, to the verdant slopes of Ambrym: devastated in a hurricane just the year before, but with the scars hidden by the new tropical growth. Here, Chief Mael Moses explains how the volcano is a part of the neighbourhood, but not a part of their lives. Later, he relates a story of how, glimpsing into the crater, he explains how the swirling fires looked like the tumbling waters of the sea; and of what this implies for the future.

Exploring the origins of the film takes Werner Herzog and crew back to Erebus; while the origins of Clive Oppenheimer’s relationships with volcanoes takes him to Toba, Sinabung and Merapi: into an observatory bunker room, stocked with a month’s supplies of food, and a Church in the shape of a chicken; or is it a dove? The search for human origins and volcanoes takes us to the Danakil desert of Afar, Ethiopia; where Tim White has just found the skeleton of another early human. Entombed in the ashes a hundred thousand years ago, and exhumed as the visitors arrive. The origin tale takes us to the Codex Regius and Iceland, where we hear the stories of eruptions of Heimay, Eyjafjallajokull and the great Laki fires of 1783. En route, newsreel of past eruptions are spliced with some footage from the peerless volcano filmmakers, Maurice and Katia Krafft. Katia sampling, as surging rolls of lava surf in a channel, and a moment of Chaplin-esqe fun as a foil-coated Maurice toddles towards a wall of fire. Footage of the hot rock avalanche and surging pyroclastic cloud that brought their lives, and the lives of 41 others, to an abrupt end in Japan in 1991 creates a pause for reflection.

To conclude his curious tales of people around volcanoes, Herzog takes us to the mysterious and closed world of DPRK (North Korea). This is a country under international sanction, with rhetoric that is throwback to the last century. Its northern border is anchored by the ‘long white mountain’, the volcano known as Paektu-san in Korea, and Changbaishan in China. This volcano looms large in the national psyche, with links to the nation’s origins, and those of the present regime; and where the Paektu-san song is almost a national anthem.

Volcanoes as icons: Mt Paektu, on the DPRK (North Korea) - Chinese border

Volcanoes as icons: Mt Paektu, on the DPRK (North Korea) – Chinese border

This is a delightful film that shows off volcanoes and their context in a quirky and entertaining way. In a cinema setting, the mesmerising footage and soundscape pull you right in to the crater. But ‘Into the Inferno’ is about much more than fire and brimstone; it gives voices to the people who live, work on or are drawn to volcanoes, revealing in their own words what it is, or is not, that volcanoes symbolise for them, and their kin.

 

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