Santorini Caldera from the Water: Volcanic Geology for Yachts

Most visitors meet Santorini from the top of its cliffs, looking down into a bay of impossibly blue water. Seen from a boat, the picture flips. The cliffs become the walls of a drowned volcano, the small dark islands in the middle become young lava, and the deep water under the hull tells the story of an eruption that reshaped the eastern Mediterranean. This guide explains that geology in plain terms and what it means if you plan to explore the caldera by private yacht.

What the caldera actually is

According to a 2024 report from Columbia University’s Lamont-Doherty Earth Observatory, Santorini is the remains of the ancient island of Thera. Today it is “just a fragment of its former self”, a rugged semicircle partly surrounding the sea-filled crater that used to be the island’s centre. The island attracts around 2 million tourists each year, yet most of them experience only the rim.

The caldera is the hollow left behind when the volcano emptied and collapsed, and the sea flooded in. That is why the inner cliffs are so steep and why the water inside is so deep. From the water, the layered colours of the cliffs are cross sections of past eruptions stacked on top of each other.

The Minoan eruption and the eruptions before it

Around 1600 BC, one of the biggest volcanic explosions in human history blasted away much of Thera, burying communities and farmland under hot ash and sending out tsunamis and earthquakes. The Columbia report notes that some archaeologists link the disaster to the decline of the Minoan civilisation on nearby Crete, while others think it may have inspired the legend of Atlantis.

It was not a one-off. Previous research cited in the same report shows that the Minoan eruption was the last of about a dozen such blowups in the area over the past 360,000 years. Scientists drilling aboard the research vessel JOIDES Resolution in 2022-23 also found evidence of a far older underwater eruption, some 520,000 years ago, which they estimate was about 30 times bigger than the Minoan event. It left a layer of pumice up to 150 metres thick as far as 70 kilometres away on the seabed.

When you sail across the caldera, you are moving over this buried history. The calm surface hides a landscape built by repeated, enormous explosions.

Nea Kameni and Palea Kameni: the young islands

In the middle of the flooded caldera sit two dark, barren islets. Nea Kameni (“new burnt”) and Palea Kameni (“old burnt”) have formed over roughly the last two thousand years through repeated eruptions of dacite lava and ash. The Roman historian Cassius Dio recorded a new islet appearing near Thera in 47 CE, which may refer to Palea Kameni.

Nea Kameni is nearly round, about 2 kilometres across, with an area of 3.4 square kilometres and a highest point of 114 metres. Major eruptions in the last 300 years took place in 1707-1712, 1866-1870, 1925-1928 and 1939-1941, and the most recent small eruption in 1950 involved lava dome extrusion. The island is monitored closely by the Institute for the Study and Monitoring of the Santorini Volcano and is a protected scientific site. Visitors can climb a gravel path to the rim of its crater, about 130 metres high, and walk a full circuit, passing vents including an active sulphur vent locals call Jorgo.

Is the volcano still active?

The Columbia report describes the area as generally calm since the Minoan eruption, with the last activity at Santorini itself being minor rumbling and lava flows on the small islands inside the crater in 1950. It also mentions subterranean rumbling around Santorini in 2010-11 and studies in 2020 and 2022 showing magma collecting near the island, which is one reason scientists keep a close watch. For visitors, the practical message is simple: the Kameni islands are a living geological site, and walking among steaming vents is part of the experience.

What the geology means for anchoring

The same collapse that created the spectacular cliffs also creates a challenge for boats. Because the caldera floor drops away so steeply, the water stays very deep almost to the shore. As Angel Yachting explains on its page about yacht charter in Santorini, overnight anchoring inside the caldera is difficult because holding is poor, so yachts generally lie at Vlychada on the south coast and come into the caldera for the day.

That shapes a typical caldera day. The operator describes a route taking in Red Beach and White Beach on the southern shore, the hot springs at Palea Kameni where the water turns a rust brown, a landing on Nea Kameni to walk to the crater, and then across to Thirassia, the surviving piece of the old island rim, for lunch.

Timing your visit

Because Nea Kameni is visited daily by dozens of tourist boats through the summer, timing matters. The charter page suggests the Palea Kameni springs are best in the morning before the boats arrive, and lists May, June and September as the best months. Santorini is also a long passage from Athens, listed at about 126.9 nautical miles and roughly 4.9 hours from Flisvos, so planning the day around an early start makes sense.

Seen from the water, Santorini stops being a postcard and becomes a readable landscape: the rim as a broken volcano, the Kameni islands as its newest chapter, and the deep blue between them as the scar of the eruption that made it famous.

Sources

• news.climate.columbia.edu, A Volcanic Explosion 520,000 Years Ago Dwarfed One That Devastated the Minoan Civilization – State of the Planet. https://news.climate.columbia.edu/2024/01/16/a-volcanic-explosion-500000-years-ago-dwarfed-one-that-devastated-the-minoan-civilization/
• Wikipedia, Nea Kameni – Wikipedia. https://en.wikipedia.org/wiki/Nea_Kameni

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