The eruption of Thera

The story

An island shaped like a ring

Santorini, in the Cyclades, is one of the best-loved destinations in the Aegean Sea: white houses on top of very high cliffs, sunsets over the sea. Seen from above, though, it has a strange shape. The island is not a solid disc but a crescent, which opens onto a deep, circular bay. That bay is the caldera, an enormous crater formed when a volcano sank in on its own centre. In the middle of the bay is a small volcanic island, Nea Kameni.

Before the eruption we are talking about, the island looked different: it was almost a continuous ring of land, with only one gap between the islands of Thera and Aspronisi. Inside that ring was a sheltered sea, a natural harbour. Today we call the island Thera in archaeology books and Santorini in everyday speech.

A city frozen in time

In the southern part of the island stood Akrotiri, a village of fishermen and farmers that had begun as early as the fifth millennium BC and had grown over time thanks to trade and copper working. Before the catastrophe it had become a real small town, with streets, little squares and houses of several storeys. The town was Cycladic, but closely tied to Crete: its art has Minoan features, and inscriptions in Linear A have been found there.

In 1867 a French geologist carried out the first digs there. But the most important discovery began in 1967, with the Greek archaeologist Spyridon Marinatos. Beneath metres of pumice and ash there appeared streets and houses still standing, with buildings of several storeys, vases and pottery, plaster casts of wooden furniture that had disappeared, and above all frescoes whose colours are still vivid. Among the most beautiful are the “Spring Fresco” and the “Blue Monkeys”. After Marinatos died (1974), from 1975 the excavations were led by Christos Doumas.

The surprising thing is that in the whole excavated area no human body has been found, and only one gold object. In 1999 a gold figurine of an ibex came to light. For archaeologists this means that the inhabitants had time to leave, taking their valuables with them. This is also because it seems that, before the real eruption, there were tremors and warning signs for months.

The eruption

The eruption was among the biggest of the last ten thousand years. Volcanologists classify it as grade 7 on the VEI scale, which runs from 0 to 8. Recent estimates, based on data collected at sea, speak of an amount of material between 28 and 41 cubic kilometres of solid rock, and of a column of gas and ash about 30–35 kilometres high, reaching the stratosphere. In the final phase the centre of the volcano collapsed and the sea flooded into the enormous empty space: this created the caldera we see today.

The collapse and the explosions generated tsunamis, enormous waves, which struck the north of Crete. At Palaikastro geologists estimate waves of about nine metres; for other places the estimates are much higher and uncertain. On Crete ash fell and earthquakes shook the ground, and some villages were destroyed.

But when?

The date is one of the most debated problems in archaeology. On one side are the radiocarbon measurements, which say around 1627–1600 BC: an olive branch buried alive by the pumice was analysed. On the other, archaeologists who look at the pots and at links with Egypt suggest about 1550–1480 BC, a century later. In 2018 the team of Charlotte Pearson showed that the curve used to calibrate radiocarbon might have an error of a few decades; since then the two schools have drawn closer. In 2020 one study gave 1619–1596 or 1576–1545 BC; another, in 2023, gave a range between 1610 and 1510 BC. In practice today we say: between the late 17th and the 16th century BC, with the exact year still not fixed. This is why the event is dated to about 1600.

And the Minoans?

For a long time people believed that the eruption had destroyed Minoan civilisation. The excavations say otherwise: Crete recovered quickly, and the following period is considered the most splendid of its culture. Damaged sites were rebuilt and new palaces were built. Later on, however, that civilisation was swept away by other crises, which are discussed in the card on the Minoans.

A very famous idea holds that the eruption is the historical memory of Atlantis, the vanished island described by the philosopher Plato. The hypothesis was put forward by Marinatos himself, but today scholars do not consider it valid: Plato writes many centuries later and his account is a philosophical story.