The Santorini caldera is a hole in the sea 11km across, and the villages everyone photographs are perched on its inner rim. That is the whole island in one sentence. Once you know what happened here the view stops being pretty and becomes genuinely unsettling.
The eruption
Around 1600 BC the volcano threw out somewhere between 40 and 60 cubic kilometres of rock and ash, one of the largest eruptions of the last 10,000 years, and the centre of the island collapsed into the emptied magma chamber. The sea poured in. What had been a roughly circular island became a crescent, a smaller crescent called Thirasia, and a lot of water.
The ash layer buried a Bronze Age town at Akrotiri so completely that it survived intact, which is why we know what a Cycladic town looked like in 1600 BC and almost nothing about most others.
Reading the cliff
Stand at Imerovigli and look at the rock face below you. The stripes are readable: dark red and black bands are older lava flows, the thick pale layer at the top is the pumice and ash from the Minoan eruption itself. That white band is between 20 and 60 metres thick depending where you stand, and everything above it is only 3,600 years old.
The cliff drops around 300 metres to the water, and the water then goes down nearly 400 more. Cruise ships anchor in a flooded volcano.
The two black islands in the middle
Nea Kameni and Palea Kameni are the new cone, still growing. Nea Kameni first appeared above the water in 1707 and last erupted in 1950. The walk to the crater takes about 30 minutes over loose black scree with no shade whatsoever, and the ground near the top is warm to the touch.
Bring water and do not wear pale shoes. The hot springs off Palea Kameni, where the boats stop, are lukewarm rather than hot and the iron in the water stains swimwear permanently.
Is it still active
Yes, and it is monitored constantly. There was a period of unrest in 2011 and 2012 when the caldera floor inflated measurably, then it settled. The Greek volcanological network keeps instruments across the island. None of this is a reason not to visit; it is a reason the geology is interesting rather than decorative.
Where to see it properly
- Skaros Rock at Imerovigli. A short scramble onto the old fortified promontory, and the only place you see the cliff from outside it.
- The Fira to Oia path, 10km along the rim, three to four hours, best started at 7am.
- Thirasia, the far side, reachable by boat and almost empty. It shows you what Oia looked like before tourism.
- The sea itself. The cliff only makes sense from below.
A note on what this page is
It is a geology and travel piece. This agency works in Athens and Mykonos and has no presence on Santorini, arranges nothing here, and is not represented on the island by anyone. That was not always clear on this page and it is now.
If the Athens end of your trip matters, see Athens.
