Santorini: Encyclopedia II - Santorini - Ancient volcanic eruption

Santorini - Ancient volcanic eruption

The devastating volcanic eruption of Thira has become the most famous single event in the Aegean before the fall of Troy. The eruption would have caused a significant climate upset for the eastern Mediterranean region. It was one of the biggest volcanic eruptions on Earth in the last few thousand years.

Santorini - Physical effects of the eruption

The violent eruption was centred on a small island just north of the existing island of Nea Kameni in the centre of the caldera. The caldera itself was formed several hundred thousand years ago by collapse of the centre of a circular island caused by the emptying of the magma chamber during an eruption. It has been filled several times by ignimbrite since then and the process repeated, most recently 21,000 years ago. The northern part of the caldera was refilled by the volcano and then collapsed again during the Minoan eruption. Before the Minoan eruption, the caldera formed a nearly continuous ring with the only entrance between the tiny island of Aspronisi and Thera. The eruption destroyed the sections of the ring between Aspronisi and Therasia, and between Therasia and Thera, creating two new channels.

On Santorini, there is a deposit of white tephra thrown from the eruption; it is up to 60 metres thick overlying the soil marking the ground level before the eruption. The layer is divided into three fairly distinct bands indicating different phases of the eruption.

A series of warning earthquakes must have been alarming enough and early enough before the eruption for all the residents to pack up and move out, as not a single body has been found at the Akrotiri site. (The single body found on Therasia has now been identified as a much earlier funerary burial). The thinness of the first ash layer and the likelihood of this layer being eroded by winter rains indicate that the volcano may have given warning at most months in advance and not years as previously believed ^[1]. It remains to be seen if further excavations will show bodies of people huddled along the coast, too late to get off in a boat to escape the volcano's fury, akin to the finds at Herculaneum, which was buried by the much smaller eruption of Mount Vesuvius in 79 AD.

In a classic Plinian eruption marked by columns of smoke and ash extending high into the stratosphere, the Minoan eruption created a plume 30-35 km in height, and magma coming into contact with the shallow marine embayment would have caused a violent phreatic eruption. The eruption also generated a 35 to 150 m high tsunami (estimates vary) that devastated the north coast of Crete, 110 km (70 mi) away. The impact of the tsunami pummelled coastal towns such as Amnisos, where building walls have been knocked out of alignment. The tsunami would also certainly have eliminated every timber of the Minoan fleet along Crete's northern shore. On the island of Anaphi, 27 km to the east, ash layers 10 feet deep have been found, as well as pumice layers on slopes 250 meters above sea level. Elsewhere in the Mediterranean there are pumice deposits that could be caused by the Thera eruption [2]. Ash layers in cores drilled from the seabed and from lakes in Turkey, though, show that the heaviest ashfall was towards the east and northeast of Santorini. (Ash found in Crete is now known to have been from a precursory phase of the eruption, some weeks or months before the main eruptive phases, and would have had little impact ^[3].)

The volume of ejecta is estimated to have been much more than four times what was blown into the stratosphere by Krakatau in 1883, a well-recorded event. Every vestige of life is likely to have been eliminated or smothered in the ashfall, leaving an island that had essentially been sterilized, as was Krakatau.

Santorini - Dating the volcanic eruption

The Minoan eruption provides a fixed point for aligning the entire chronology of the 2nd millennium in the Aegean, because evidence of the eruption occurs throughout the region; however, its exact date is unknown. Current opinion based on radiocarbon dating indicates that the eruption occurred between about 1650 and 1600 BC. These dates, however, conflict with the usual date from archaeology, which is between about 1500 BC and 1450 BC.

Some scholars believe the radiocarbon dates to be completely wrong. Some suggest re-scaling archaeological chronologies with the radiocarbon dates. Others look for a compromise between the archaeological and radiocarbon dates for best fits of both sets of data. Re-scaling archaeological chronologies is controversial, because revising the Aegean Bronze Age chronology could require, by association, revising the well-established conventional Egyptian chronology. The debate about the date continues.

It has long been hoped that information from Greenland ice cores would determine the date exactly. A large eruption, identified in ice cores and dated to 1644 +/- 20 BC years was suspected to be Santorini. Volcanic ash was retrieved from an ice core, and this was shown not to be from Santorini[4]; so the 1644 BC date is incorrect.

Tree ring data shows that a large event interfering with normal tree growth occurred in 1629-1628 BC, which may be the same event as the 1644 BC signal in the Greenland ice cores. However, no firm evidence links these two events and, while unlikely but plausible, the two signals could be separate events. At the present time no hard evidence linking or refuting the 1628 BC tree-ring date with Thera has been found.

While a VEI-4 or greater eruption can leave signals in tree rings and ice cores, the absence of such a signal does not mean the absence of an eruption. It is still hoped that Santorini ash might be found in another layer of the ice core, which would fix the date of the eruption.

Santorini - Size of the eruption

Until 2003, the Minoan eruption of Thera was classified with Krakatau, given a VEI-6. Recent studies of ashfall have suggested upgrading the intensity of the eruption to a VEI-7, although this is not agreed by all researchers. A VEI-7 eruption would rival the 1815 eruption of Tambora. The 1815 eruption was of such a large volume and kicked so much sulfur dioxide into the air that it caused 1816's Year Without a Summer. The impact of this colossal eruption on human civilizations at the time are not yet fully understood and still open to speculation.

Santorini - Chinese records

Some scientists correlate a volcanic winter from the Minoan eruption with Chinese records documenting the collapse of the Xia dynasty in China. Per the Bamboo Annals, the collapse of the dynasty and the rise of the Shang dynasty (independently approximated to 1618 BC) was accompanied by "'yellow fog, a dim sun, then three suns, frost in July, famine, and the withering of all five cereals".

Santorini - Egyptian records

Oddly, there seem to be no surviving Egyptian records of the eruption. Santorini ash deposits were at one time claimed to have been found in the Nile delta, but this is now known to be a misidentification ^[5]. Suggestions have also been made that the eruption of Thera and volcanic fallout inspired myths of the Titanomachy in Hesiod's Theogony and calamities of the Admonitions of Ipuwer of the Middle Kingdom of Egypt.

Santorini - Association with Atlantis

Starting with Spyridon Marinatos' 1939 landmark paper, this cataclysm at Santorini and its possibility to have caused the fall of the Minoan Civilization centered on Crete is sometimes regarded as a likely source or inspiration for Plato's story of Atlantis. Detractors of the theory say that Santorini and Crete combined would not be the size of Plato's Atlantis, and the date of the Minoan collapse does not match Plato's dates for the fall of Atlantis. Scholars such as James Luce and A. G. Galanopoulos argue that the error in date and size could be caused by a mistranscription of the Ancient Egyptian or Mycenaean Linear B symbol for "hundred" as "thousand" (the former is unlikely because there would be little confusion in the visual appearance of hieroglyphic symbols of Egyptian numeric values). These significantly smaller values would make Atlantis the size of Crete's Messara Plain and the fall of the Atlantis c. 1450 BC.

Adapted from the Wikipedia article "Ancient volcanic eruption", under the G.N U Free Docmentation License. Please also see http://en.wikipedia.org/wiki