Thera and Its Volcanic History
Thera has a long and active Volcanic history. The last eruptions occurring in 1707, 1769 and 1926.
It is a crescent shaped island, the most southerly of the group known as the Cyclades. There was once circular in shape, but through the shifting of the earth's surface its shape has become greatly changed. Its arc is now completed by the two islands Therasia and Aspronisis and several small islets Palaeus Nice and Milkia Kaimini. Only Mount Elia is composed of other than volcanic rock - being marble and metamorphic rocks. It was at one time part of the continent which, in the beginning of the tertiary period was the bridge between Greece and Africa.
Both Thera and Therasia possess lofty coasts exhibiting horizontal beds of lava. Thera's hills face west across the bay towards Therasia, rising perpendicular to a height of about 400 meters.
The evolvement of the Mediterranean coasts, as we know them today, occurred during the pliocene-tertiary period between 12 and 1 million years ago. This change was not completed without shifts and deep dislocations occurring in the earth's crust and forming the Greek and Aegean volcanos. The mightiest of these rifts lay may have been towards what is the centre of the bay separating Thera and Therasia. MT Elna is now the sole relic of another continent which was an early claimant to the Atlantis myth. At the same time that the volcanic peak raised itself from the waters the island of Thera appeared - where now its bay is situated two mighty peaks rose, mount Elia and the volcanic cone.
The quaternary period had seen fresh eruption add to the size of the island and during the inactive periods man became an inhabitant. Not long after a catastrophy came to the island and destroyed this settlement which was probably a colony of the Minoan Empire at the greatest point in its civilization.
We know that at the time of its destruction the Minoan 'floral style' of pottery decoration was beginning to gain favour among the population. The finds are few and the style local but a more advanced and well developed style of this decoration was found on the main island of Crete. The date could have been around 1525-1520 BC.
The centre of Thera lay upon a subterranean cleft into which the greater mass of the island suddenly sank leaving a bay now surrounded by the islands of Thera, Therasia and Asponsi. The vacuum formed by the falling central mass, which took part of the northern coast with it, sucked the sea into the yawning chasm with fantastic force, tearing away the thin rampart that remained on the western side.
After this violent eruption which brought the Minoan empire to a close on Crete, the present crater, a crater that is the largest of its kind, entered into one of those periods of calm that at common to all volcanos.
From the size of the crater (83 sq. kilometers in extent and 60 meters deep) the eruption must have been great in extent and can perhaps be best compared to the 1883 AD eruption of Krakatoa in the pacific. This volcano has a crater only 22.8 kilometer in extent.
Volcanos are divided into classes and both Krakatoa and Santorini (Thera) are placed in the same class. It is from the evidence of eruptions in the same class of volcano that we must go to reconstruct that eruption of Thera that brought the end of the minoan Empire to its final closing years.
In the Krakatoa eruption the vent of Perauoten became active during the month of May 1883. During the following weeks many new vents were formed and in their turn became active. By the last week in August the climax had finally been reached. On the morning of August 26th the atmosphere was punctuated by formidable detonations at the rate of one every 10 minutes. These were so loud that they were easily heard 100 miles away. In the city of Batavia the shocks caused windows to shatter and walls to crack. By this time volcanic clouds had formed and reached a height of 17 miles. The incessant falls of rain, so common during events of this type, caused a transformation of cloud into mud which descended over the city. The area was plunged into blackness relieved only by the visit flashes of lightning that turned the area from darkness into earry light.
On the following morning , August 27th, 4 stupendous explosions were heard, the greatest was audible 3,000 miles away in Australia and a vast cloud of incandescent pumice and ash rose 15 miles into the sky, glowing and lighting the whole area for miles in all directions.
We are aware that the eruption of Thera was 4 times as great as that of Krakatoa. Only 9 sq. miles of the Krakatoa complex blew up and sank into the ocean during the 1883 eruption compared to 33 sq. miles of land destroyed during the 1500 BC eruption of Thera.
As Thera is only some 60 miles to the north-west of Crete it seems highly improbable that an eruption of this magnitude would not have had some effect on the island. The distance is far less than between Krakatoa and her neighbouring islands that were destroyed and damaged in the 1883 eruption.
An eruption of any extent would have been heralded by earth tremors and volcanic clouds, as well as volcanic storms over the effected area. These would have been in evidence for some time prior to the actual eruption.
Thera suffered a volcanic convulsion in 1848 AD, minor in comparison to what the island experienced in previous eras. The records show that this explosion of activity lasted for a period of three months, during which time it caused a great shoal, and an earthquake that destroyed many homes on the island. The sulphur and hydrogen fumes that issued from the sea caused the death of many animals and of members of the island population.
This was a relatively minor disturbance and yet the damage that it caused was extensive and effected life over a wide area.
In the Krakatoa disaster the greatest damage was caused by a series of tidal waves, colossal in size, reaching to a height of fifty feet. They hit the shores of Java and Sumatra with indescribable force. The towns of Telveg, Tjazingin and Betoeng, in Sumatra, were utterly and completely destroyed. Everything from railway lines to houses and even rock boulders were washed away. A Steamer - the Marun - was washed several miles inland from the sea onto dry ground. The floods caused lamps to overturn and fires raged in Tjazingin as a result. The death role rose into the 36,000s as a result of this catastrophe.
As tidal waves are generally associated with an eruption of the Krakatoa- Thera type of volcano it seems more than certain that a wave of some magnitude also swept along the coats of not only Crete but other island in the area, causing a certain amount of damage during BC eruptions of Thera.
The tidal waves in the Kralkatoa area not only had a further distance to travel before hitting land but the depth of the sea around Krakatoa is much shallower than in the Thera region. Between Thera and Crete the sea bed reached 300 meters at one point. It is a well know fact that waves of this type increase in velocity and height as the depth of the sea increases. Therefore it is conceivable that this early eruption of Thera would have been accompanied by waves that could easily have reached the coast of Crete within half an hour, overwhelming the northern coastal regions within a matter of a few minutes after they were first sighted.
This could then explain the destruction of the coastal sites of Crete during the final phase of the Minoan Empire at an early date than appears to be recorded for those place sites which were more inland.