Last week I travelled to Santorini — or, in Greek and on many maps, Thira.

Last light over the caldera Santorini is one of the southernmost islands of the Cyclades, nearer to Crete than to Athens. It’s shaped like a croissant, with the inner edge high and steep, tapering down to an outer edge which is low and beach-broken. The main town, Fira, trickles over the edge of the steep cliff face like cake icing. Two other islands (the larger, inhabited Thirasia and the tiny rock morsel Aspronisi) trace, by dint of facing Santorini, a rough circle. In the middle of the lagoon thus partly enclosed lie two more islands of singular and mottled appearance, Palea Kameni and Nea Kameni. The latter is the infant of the Mediterranean. It began to appear just 434 years ago.

Lagoon? Poor word. This is a caldera: a volcanic crater formed by the explosion and collapse of a cone. Santorini is a volcano. The only volcano in the world, indeed, with its caldera in the sea. It explodes with colossal force every 20,000 years or so. Its last eruption 3,621 years ago, which explains the equanimity with which modern-day tourists visit.

Santorini ash terroir You wouldn’t want to be around when the year 18386 draws near, though; Santorini’s explosions are prodigious. The eruption of 1614 BC was the biggest anywhere in the world in the last 10,000 years; much bigger than Krakatoa, for example. 150 billion tons of rock were hurled skyward; a two-year volcanic winter ensued. Tephra (ashes) rained down as far away as the Black Sea and the Nile Delta; rafts of pumice floated away from the island and, most destructively of all, a chain of tsunamis was unleashed in the Aegean and Mediterranean. It was this, some believe, which brought about the end of the Minoan civilisation on Crete.

Santorini before the Minoan eruption was not a unitary island. Instead it was almost circular, with a narrow sea entrance allowing the ingress of the sea. These waters formed a giant marine moat around the central core of the volcano. The result was something like the shipyards of ancient Carthage; a superb natural harbour, in other words, and the prosperity of the bronze-age island can be gauged by the luxuriousness of the murals (including graceful blue monkeys and a bending woman with bare, pendulous breasts) in some of the houses of the buried ‘town’ of Akrotiri, Santorini’s own Pompeii.

Santorini pyroclastic debris terroirSomething is missing in Akrotiri, though. No skeletons. No jewellery. The inhabitants got away. There had some warning. How much? Did they ride out the gigantic tsunamis or do their jewels and their bones lie at the bottom of the Aegean? Did they reach Crete, only to perish as the crops failed and civil order distintegrated after the catastrophe? Perhaps these are some of the questions pondered by those holidaymakers who lie on their sun-loungers like slabs of roasting steak, staring at the caldera; perhaps not.

Santorini was experiencing a heatwave last week, with daytime temperatures hovering around the 40C mark. This was causing considerable anxiety to the winegrowers, as the berries were beginning to show browning stress marks. The leaves, by contrast, were bearing up well, perhaps because May 2007 had brought unusual rain. Santorini’s vineyards are the most unusual I have ever seen, as I hope these photos show. Because of the island’s ferocious winds, the vines are not trellised (though Paris Sigalas is now experimenting successfully with trellis) but buried in scrapes in the stony volcanic soil. As time passes, those pruning the vines braid them into a circular basket shape, which affords still more wind protection (though it lowers productivity). The end result is a kind of leafy wicker basket from which grapes improbably sprout.

Santorini basket vineThe basket is the vine. When the vine eventually reaches the end of its life, the top of the plant is simply removed and the vine begins to grow again from zero. There is no phylloxera on Santorini. Result? The oldest vine roots in the world. Some are said to be 500 years old, though hard evidence is missing. Are these deep roots one reason for the astonishing minerality of the white Assyrtico wine from Santorini? Is it the volcanic soil itself? Is it the unique flavour profile of Assyrtico, with its scything acidity (and pH of 2.9) even at the end of a ferocious Aegean summer? Try them; only try them. The wines of Sigalas, Gaia and Hatzidakis can be recommended unreservedly.

Yiannis ArgyrosThere is something unsettling and eerie about a heatwave in Greece. Extremes of weather in Britain can always be assigned to a cause: low pressure (as we are currently experiencing, with attendant floods and rain: these islands have just endured the wettest June since 1914); fast moving fronts; the clash of warm air with cold. The heatwave in Greece seemed, on the ground, to come from nowhere. I asked those I met what was causing it, and got a series of different answers; no one seemed sure.

The sun sat in the sky, and grew bigger, and bigger, and bigger. The winds fell limp. The stones glowered. The caldera throbbed like a bright wound. What, one thinks, when struggling sweatily into a shirt at 11 at night to go out for dinner, if it just keeps getting hotter and hotter? When does the electricity fail? When do the ships fail to glide into view? When does the supply circuit stutter and stumble? When do you notice the first unclaimed corpse on the street?

The caldera seemed, in sum, to be an appropriate metaphor for global warming. Think of the surface serenity before the explosion; think of the prosperity of happy landforms, and a brimming sea, and easy trade routes (vases from Syria and Cyprus were found in the ruins). The cataclysmic pressures are largely invisible, just as the doubling of carbon dioxide in our atmosphere since the Industrial Revolution is invisible to us.

Then subtle changes are observed: rising sea temperatures; the bleeding of a little new rock. Suddenly there are dramatic warning signs: plumes of smoke; an intestinal thunder from far below; tremors; falling ash. Those alive in those interesting times hurry to act, but the tipping point has long been passed. Life changes utterly. The lucky ones die swiftly; it is the survivors who are cursed with the burden of a struggle for which none have prepared.