Few volcanoes have such an ominous reputation as the Island volcano of Santorini. And it is in one way a justified reputation; after all it is one of the few volcanoes that have been the end of the civilization as we knew it when it happened.
Today’s island group of Santorini consists of a large caldera ring constructed of no less than six (6!) independent calderas constructed during massive caldera forming explosive eruptions. The largest island is to the east and is named Thera, than follows clockwise Aspronisi (small) and Therasia. Inside of this large caldera basin lays the two islands of Nea Kameni and the adjacent smaller Palea Kameni.
Against normal belief the islands are of a non volcanic origin. Instead they started as a mainly limestone based island as the sea bottom was pushed up by the same powers that made the Alps into the rather craggy mountain chain that much later gave name to the Alpinist tribe.
Later the Hellenic Trench Subduction Zone got active as the African Plate slammed into Europe and got pushed down under Europe. That little event started quite a bit of volcanic activity. Today Santorini, together with its neighbor Colombo Reef, share the distinction of being active Greek volcanoes with Kos, Methana, Milos, Nisyros and Yali.
Pre 1610BC caldera formations
The first mega cycle of caldera formations happened about 600 000 years ago. It was most likely the largest eruption at Santorini and is still responsible for the largest of the calderas. The next caldera formation came 360 000 years ago and had a different magmatic combination than the previous. It was highly siliceous and created highly evolved magmas through crystallization, this type of siliceous magmas are still the norm. 180 000 years ago it was then time for the southern caldera to form, then came the Skaros Caldera 70 000 years ago. After that came the Cape Riva Caldera about 21 000 years ago, the youngest caldera is of course the 3 600 year old Minoan Eruption Caldera.
Caldera formation process of Santorini
During a mega-cycle Santorini has series of cycles with smaller eruptions that build up a volcanic edifice. These eruptions are normally unimposing events ranging between VEI-2 and VEI-3 judging from historical records and excavations. But it is probably not impossible for a VEI-4s happening during a cycle. During the cycle the magma chamber evolves and becomes continuously larger with time. This gives more time for crystallization to happen to the cilicic magmas which gives more and more evolved magmas as the cycle continues. So any VEI-4 or larger would most likely come late in the cycle. The current cycle between caldera formations started in 187BC with an island forming event.
The different Caldera forming events have given differently coloured layers. The most recent is whitish.
1610BC Caldera formation
Few eruptions have such a reputation as the 1610BC Minoan Eruption. It has been given the blame of the biblical story of Noah, the sinking of Atlantis, the disappearance of the language of Linear-A, and of course the fall of civilization as that time knew it. It was not only the Minoan culture at Crete that started to dwindle, also the Hittite, Babylonian and Egyptian cultures showed a rather marked decline during the time after this. The only people that oddly enough seemed to benefited where the 12 tribes of pre-Israelites that formed Israel in the ensuing power vacuum. Jolly good that did for them, as soon as the Hittites, Babylonians and Egyptians got back on their feet they made short order of Israel. Sense moral is that no volcano may ever protect you from biblical revenge.
Technically the 1610BC event was a VEI-7. It is believed to have begun as a VEI-6 ultra-plinian eruption, with a massive effusive component that caused the by then very large magma chamber to subside enough for the ocean to fall into the half empty chamber. When we are talking about the magma chamber of 1610BC we should remember that it does not exist any longer. The size of that chamber was in the order of a 1 000 cubic kilometers or more judging from the erupted material, and the eruptive standard value of 5 to 10 percent of the magma being ejected. Today’s chamber is probably around 1 to 5 cubic kilometers.
As the water came into contact with the open magma chamber a violent Ultra-plinian VEI-7 event took place. It caused wide spread tsunamis and heavy weather affecting atmospheric conditions.
Santorinis normal eruptions
During the period from 187BC and up to 1950 Santorini have had 10 sub-aerial eruptions. And at least four separate island forming events. Two islands have later been subsumed by Nea Kameni. Neither of these eruptions has been spectacular in any sense of the word. In addition there has probably been sub-aquatic eruptions inside the caldera ring, but those has either not been written down, or was too deep to make a surface impact. The big exception is of course the Colombo Reef (6,5km NE of Thera) eruption of 1650AD which formed an ephemeral island.
Other than being small in scale, the eruptions are normally prolonged in time. Eruptions lasting between one and two years are not uncommon.
Signs of an upcoming eruption
Up until a couple of years ago Santorini was subsidizing, this together with cyclic swarms of earthquakes over at Colombo Reef lead researchers to believe that an eruption was up and coming at that location, and not at Santorini.
About a year ago a marked inflation started at Nea Kameni together with increase in CO2, SO2 and the Santorini marker gas of Radon. Together with an increase in seismic activity lead to the scientists starting to keep a bit of a closer watch on the volcano.
Lately we have seen quite a few more signs of an upcoming eruption. We have now had swarms of earthquakes inside the caldera at the right depth, microseismics that remind of popping giant popcorn in a spectral analysis, and of course harmonic tremoring lasting from hours to days.
We should though know that this has happened before in volcanoes of this type without anything happening. But let us say that the likelihood of an eruption happening has risen quite a lot.
What will an eruption look like?
Most likely an eruption now would be a dome forming event at Nea Kameni. The beginning will be explosive, and then trending to effusive as lavas are extruded. Most likely it will be a VEI-2 event, but a VEI-3 is not out of the question. The eruptive period is hard to predict, it could be anything from one month to four years. There is really no saying which. And historical records do not give much help; it is equally possible that the eruption will be short as long. Playing hard and fast with statistics here would only give silly results due to lack of substantiating occurrences.
One thing is for sure, there will be no end of civilization as we know it, this time around.
A special thanks to Summer who fixed the code in the last post, and told me how to not bungle it up again.
The earthquakes that some believe to be at Santorini are not really at Santorini, they are located 12 to 25 kilometres south to south west of Santorini. They are located at a faultline that is cause by the subduction of the African plate under the European plate. The same process that help sprout new members of the alpinist tribe.
It is quite possible that the tremoring noticed is also related to this, about that we will hav to wait and see.