Introduction

Santorini is one of the few Greek destinations which attracted scholarly interest from very early on. The history of our planet, spanning hundreds of thousands of years, has left its indelible markings on its Caldera. And this unique geological book remains constantly open and readily accessible to anyone who wishes to study this aspect of history. On the other hand, the active volcano of Santorini, with its intermittent large or small eruptions, is a permanent attraction to both geologists as well as volcanologists.
It is not accidental, therefore, that there is a long-standing history of scientific research on the island and that scholarly interest has been preserved unabated to this day, its results never ceasing to constantly surprise us down to the present. Because the discovery in Santorini of one of the greatest geological events to have ever been witnessed by mankind over the past 10,000 years, namely the eruption of its volcano near the middle of the 2nd millennium B.C., is not a discovery to be passed over lightly…
This is an extract from the preface of Chr. G. Doumas, Professor Emeritusof Archaeology, Athens University, in Antonis N. Kontaratos’s book entitled “Thera: A march through time” (Heliotopos Publications).

According to Professor Antonis Kontaratos: “…behind the present serenity of the Cyclades lies a turbulent past. They have been repeatedly ravaged by man and destroyed by nature. Drought, war, pirate raids, earthquakes and volcanic eruptions are some of the calamities these islands have suffered during their several thousand year old history, driving the inhabitants to desert their blissful homes. Santorini is, without a doubt, the most exotic, the most spectacular, the most sensational, the most beautiful and the most tragic of the Aegean isles.
At the first crack of dawn the island resembles a menacing fortress with its sheer 300 meter cliffs hiding behind dark shadows amidst a sea which, according to Homer, resembles a deep red wine…Since the beginning of time Santorini has been tormented by geological upheavals: blasted from the sea, savagely torn apart and blown up again…”.
The island of Thera, although non-volcanic, did not always possess its present size. Prior to volcanic activity in the region, two large massifs still prominent today, of crystalline rocks such as schist, clay slate, limestone and marble, were all that the original island consisted of.
The first massif lay in the south-central and southeastern part of Thera, Mesa Vouno, extending northwest to Athinios by way of the prominent hills on which the monastery of the Prophet Elias and the village of Pyrgos now reside. The second massif, an extension of the first, runs from the northwest and terminates at Gavrilos. The most elevated region, by far, is the rocky mass of Prophet Elias at 565 meters. Next in size is Mesa Vouno at 369 meters. Mesa Vouno projects southeastward between the coastal plains of Kamari and Perissa to form a bold headland extending into the sea. Gavrilos (elevation 161 meters) also projects seaward towards Vlychada.
After the commencement of volcanic activity many hundreds of thousands of years ago, these extensive remnants were enlarged from time to time mainly towards the north, northwest and west by the spread of lava from various vents. By the first half of the second millennium B.C. the island had taken a round shape, part of the outline of which roughly corresponded to the present outer coastline of the Santorini isles –Thera, Therassia and Aspronisi.
To the northwest is the second largest island of the group, Therassia, which is about 6 kilometers long from north to south and 2 kilometers wide from east to west. It is wholly volcanic, composed of alternating sheets of lava and layers of tuff.
West of Thera and south of Therassia is the small, uninhabited island of Aspronisi (meaning white island). The name derives from the conspicuous and thick uppermost layer of white pumice adorning it which, from afar, resembles steep cliffs covered in snow.
Thera, Therassia and Aspronisi, the surviving land fragments of what was once a whole island, almost completely enclose an oval lagoon measuring about 11 kilometers from north to south and 7 kilometers from east to west. There are only three entrances to this lagoon. One opening is between Thera and Therassia in the northwest region. A second lies between Therassia and Aspronisi to the west and a third between Aspronisi and Thera in the southwest. The greatest depths of this lagoon are in the northern half, plunging more than 410 meters. However, considerable variations in its depth have been recorded at different times and at different places.
The sides of the island facing the lagoon form precipitous cliffs plunging almost vertically into the sea. These cliffs are generally as steep below the water as they are above. They reach a maximum height of 330 meters at Imerovigli. This stunning manifestation of nature, beautiful as it is, is the result of a brutal attack on the island, exposing its innards for all to see. Bare rock has been revealed and is under scrutiny for science to unearth the geological birth and history of this volcanic island long before it could ever be recorded by man.
The Caldera spans all three islands in a striking display of nature at its best. A spectrum of white, red and black shades are dispersed in panoramic dimensions only to reunite creating a dramatic, yet astonishing sight. Here and there on the rim of the Caldera, snowy white villages appear suspended precariously in mid-air. Spiraling paths descend from atop the cliffs to the water’s edge. Nowhere else on earth can one observe such perilous manmade dwellings among the harmony and almost magical array of nature’s hues.
It is no wonder that Santorini is formally considered the most beautiful island in the world.

Geology

Geological studies have revealed that the first volcanic activity in the broader area of Santorini can be dated to 2.5 million years ago and that it gave rise to the Christiana complex. In the area closely bordering the island of Santorini, the volcano became active about 1 million years ago while, within the last 400 thousand years, it has seen at least 12 violent eruptions. They take place at 20 thousand year intervals, as a rough estimate, and cause giant collapse craters (calderas). In between these violent eruptions that decimate the island, there are intervals characterized by milder outbursts, which vary in duration.
These calm interludes are marked by an array of eruptions of lower intensity, which slowly build up the island’s land mass anew. Santorini’s volcanic activity is modulated by a tectonic rift, which begins at Christiana, traverses Santorini and culminates in the island of Amorgos. This rift remains active to this day and was responsible for the deadly earthquake of 1956.
It thus follows that Santorini’s course of volcanic activity follows a pattern of a cyclical series of eruptions. Over the span of many millennia, the volcano is intermittently activated without exhibiting violent eruptions. Nevertheless, the lava which accumulates in the meantime gradually expands and elevates the volcanic cones. However, the higher the cones rise, the longer the course that needs to be covered by the magma before reaching the surface, thus making it all the harder for it to escape and giving rise to the phenomenon of its more generalized premature freezing within the cones. This way, the Theran magma gradually freezes and solidifies within the cones before reaching the earth’s crust, thus blocking the craters.
Following the congestion of the craters, there follows a long period of relative calm, during which large quantities of magma are trapped underground, causing the increasing pressure being exerted on the surface to steadily mount. It periodically finds an outlet for its release by furrowing small explosion vents which, however, do not suffice in order to fully release the pent up energy.
However, as soon as the intensity of the pressure exercised on the subterranean cones exceeds the force binding the overlying cones to one another, which have mounted rows upon rows of lava layers, then the magma finds an outlet for its release through the surface, escaping with ferocious intensity, in an explosive outburst that utterly razes and explodes everything in its path.
The cones are crushed and destroyed and immense quantities of volcanic material are thrust at immense force to great heights and over extensive distances. The remnants of the volcano collapse into the subterranean chambers which, now emptied of magma, can no longer support the weight of the overlying layers. In the place of the cones which have been razed, exploded and collapsed there remains a giant circular collapse crater (Caldera), which is surrounded by tall and steep cliffs and is swiftly infiltrated by the advancing sea, by means of the creation of a vast tidal wave (tsunami).
Steam at an extremely high temperature also escapes together with the magma. It bursts forth through the surface and is instantaneously converted to aqueous vapor.
The two latest violent eruptions on Santorini occurred roughly 21 and 3.6 thousand years ago, respectively. Indeed, the latest one took place during the Minoan Period and has been dated specifically to the second half of the 17th century B.C., based on various methodologies (such as the carbon dating method, as well as by analysis of tree barks and volcanic ash on fossils found in ice). Moreover, this eruption led to the disappearance of a great civilization that had flourished on the island and whose origins dated all the way back to the beginning of recorded history, to the prehistoric era.
However, the Caldera found on Santorini today was not formed during the latest violent eruption, which took place in the Minoan era. It was formed gradually, as the result of a series of collapses spanning a succession of historical periods marked by volcanic activity, which cumulatively led to the geomorphology of the island as we see it today.

12 circles of volcanic activity

Volcanologists and geologists have detected 12 cycles of volcanic activity in the last 200.000 years.

100.000 years ago, the south part of Caldera had been created by a large eruption.
The 1600 B.C. eruption, when Stroggili was fragmented, had created the north part.
In 197 B.C., Stravonas described the eruption by which an island called Iera had emerged, which in turn had been gradually corroded (it is the reef now called Bangos).
In 46-47 A.D. the volcano’s eruption had created Palaia Kameni.
In the summer of 726 A.D., the volcanic ash had been ejected a long distance and the eruption’s magma is found in the NE part of Palaia Kameni until the present day.
In 1570 A.D. the volcano had again been activated. Its activity lasted three years and the emersion of great quantities of magma had created the Mikri Kameni.
In 1707 and for the next 4 years, successive eruptions and phenomenons were the reasons of Nea Kameni’s emersion. Its present form though had been taken after newer cycles of volcanic activity during 1866-1870, 1925-1928, 1939-1941,1950.

The creation of Nea Kameni

Reading the following text, one begins to understand the true nature of Santorini and its people. An island, Nea Kameni, was born before their eyes, and the unprecedented phenomenon was almost unbearable to witness. Still, all these years, the people were there, across the volcano, drawing near on their boats to see it up close. The 1707 eruption, which created the islet of Nea Kameni, was witnessed and described by father Tarillon, a Jesuit traveller who had settled in Thera, in a report to his superiors. On May 23, 1707, he saw a new island rising from the sea between Mikri and Megali Kameni.

The narration

“On May 18, two small tremors were felt on the island; however, no one paid any attention. That morning, seeing the peaks of the island over the waves, sailors thought these were the remains of some ship wrecked the previous night. So, they took their boats and went to pick up whatever was left of the “ship”. Instead, they were almost wrecked on the rocks! Full of fear, they went quickly back to the island to talk about the strange phenomenon they had just witnessed.
Panic spread throughout Santorini, as people agonized over impending explosions or foundering. But three days went by and nothing happened. Then, some of the more courageous ones decided to approach and see what was going on. They circled the volcano with their boats, inspecting it carefully. Then, seeing no apparent danger, they drew even closer and stepped on the brand-new land. As they trod around curiously, they realized they were on a white rocky mass that broke off like bread. Indeed, the color, texture, even the taste was so similar that some said it was barley bread. But the real prize was the innumerable oysters stuck on the rocks – a rarity in Santorini. So they all started gathering as many as they could… Suddenly, they felt the rocks shuddering under their feet. Terrified, they jumped quickly onto their boats and left the tiny island. That vibration was simply a small movement of the island as it was growing; in a few days, it was six meters high and twelve meters long.
The island, however, did not grow evenly: many times, it went down and got smaller in one place, while swelling and spreading in another. One day, a huge rock emerged in the middle of the islet, about 15-metres high. I watched it carefully for four days. Then, suddenly, it sank back again and disappeared into the sea. Other rocks, though, kept sinking and rising again and again for several days, and then, finally, came out of the water and stayed there. As Mikri Kameni tossed and turned, a deep crack appeared on its peak for the very first time. Meanwhile, the bay waters kept changing colors: from bright green, to red to yellowish. A heavy smell rose from the sea depths.
On July 16, smoke arose for the first time from the new island, but not from any visible source: it spewed out of a string of black rocks that had emerged at a place where, until then, the sea was bottomless. These rocks formed two separate islets: One was called Aspronisi (White Island) and the other Mavronisi (Black Island), because of their color. Soon, however, they came together, and the black rocks formed the center of the island. And the thick whitish smoke kept rising.
In the night of the 19th to the 20th of July, big flames leaped out of the smoke’s heart. People in Skaros were terrified. The houses were built just half a league away, and the castle balanced on sheer cliffs rising from the sea. They expected to be blown sky-high at any moment. So, they decided to gather their belongings and leave the castle.
However, the fire was still small, hardly visible during the day as it came out of a single spot on Mavronisi. Aspronisi seemed quiet: no smoke or flames. But the other one kept growing. Huge rocks appeared as days went by… Within a month, there were four black islands. Then, suddenly, they came together in one big lump… At night, a pillar of fire rose towards the sky, and the sea frothed all around, reddish in some spots, yellow in others. The cloud of smoke spread, wrapping itself around Santorini. People gasped and choked; in order to mask the terrible stench, they burned incense and lit fires on the streets. Fortunately, this only lasted a couple of days; then, a strong southeastern wind blew the smoke away. But the smoke had already passed over the vines, burning the grapes that had started to ripen; all things brass and silver were now blackened and dull.
On July 31, the sea started boiling in two circular areas, nine and eighteen meters off the black island. There, the water was as hot as frying oil. It kept boiling for a month; day and night, dead fish were washed ashore.
On August 1, there was a deep, hollow boom, as if many cannons fired at once. And soon, two flames leapt out of the underwater furnace, rose vertically, and then died down.
On August 17, blazing fountains shot from the island, and the waters around it seethed and smoked. Fire poured from more than 60 mouths. The sea was still covered with that reddish froth. Each night, after the usual deep roars, fiery tongues leaped up from the sea depths, and millions of lights shot up to the sky, then fell back down on the glowing island like a rain of stars. In this fiery game, a strange sight came to shock people. As flames flickered in the air, a blazing tongue suddenly seemed to separate itself, long and still, lingering for a while over Skaros castle. And while the hearts of Santorini’s people pounded in their chests as they witnessed this bad sign, the tongue of fire leapt up and disappeared into the clouds.
On August 26, 1707, French traveller Aubry de la Motraye arrived on the island. He went to Skaros; nobody there. Only two men remained in the village; one was a priest. Volcanic fumes had eroded all metals, mainly silverware, which had turned pitch-black. Smoke surrounded the island, and the air was suffocating.
On September 2, there was an earthquake, accompanied by a terrible explosion. Huge incandescent rocks were hurled from the volcanic crater. Breathing was hard and sleep almost impossible from the endless booming.
On September 9, the two islets came together into one solid mass. Of the 60 craters, only four continued to spew out fire. Smoke and flames came out of the mouths with growls and whistles, like animals howling.
After September 12, the underwater turmoil seemed to quiet down a bit. The clouds of smoke turned into whirlwinds, and an endless rain of ash fell on the island.
On September 18, the explosions seem to get stronger. Enormous rocks were flung from the craters, hitting each other in the air with a terrible bang, then crashed back down on Santorini and the sea. Many times Mikri Kameni was completely covered in these molten boulders, glowing at night.
On September 21, Mikri Kameni was ablaze. Suddenly, three bolts of lightning illuminated the horizon from end to end. Then, the new island shook all over, shivered and quaked. One of the craters sank, and massive stones were thrown three miles away. Four days of calm followed, and then the wrath broke out again: nonstop explosions were so loud that two people screaming side by side could not possibly hear each other at all; folks ran to the churches; the Skaros rock seesawed, and all house doors opened from the rumble.
The explosions never ceased until February 1708.
On February 10, the volcano finally erupted. Entire mountains sprung up from the crater, the island trembled, infernal growls made hearts stop, the sea boiled. Every couple of minutes there was an explosion. For the first time, flames were visible during the day.
This hell lingered until the 23rd of May. The new island kept spreading and rising. The big crater widened with the lava. Then the turmoil subsided…”.

Visiting the new island

On July 15, 1708, Tarillon decided to take a closer look at the new island. Along with some locals, he boarded a well-caulked boat. The bright company approached a spot where the sea was not boiling, but only smoked. The missionary leaned over the side and put his arm into the water; it wasn’t hot. The new island was 60-metre tall at its peak and more than 300-metre long, with a perimeter of about five miles. They drew closer, with the intention of disembarking, but 200 meters offshore the water was scalding. A new explosion forced them to return to Santorini.
Explosions, tremors, sea boiling, and underwater flames kept on for many years before the volcano finally settled…
A letter from Santorini (September 1712) to the author of this chronicle, who was in Paris by then, provides new evidence: “I circled the island many times from afar, since the waters are boiling a quarter of a league offshore. While we row, someone must keep their hand in the water, since there is always the danger the hull tar melts suddenly -as has happened before- and we’ll sink”.

More eye witnesses

The 1707 eruption was described by two more eye witnesses: Jesuit missionary Goree and local resident Ioannis Delendas. These direct testimonies are complemented by the chronicle of French traveller Aubry de la Motraye, who visited Santorini twice, in August 1707 and in 1710. On his second trip, the volcano was still active. Flames, though not big ones, leapt out of the crater and some lava flowed down the sides.
“Fishermen told me that, braving the heat coming out of the volcano, they set foot on the islet and picked up pieces of sulphur so thin, so well-crafted by nature that human hands could have never made”.