The Changing Face of the Thera Problem
J. V. Luce
A devastating volcanic eruption, the sudden decline of Minoan civilisation, and a possible source for the legend of Atlantis - these were the elements that first caught my attention a quarter of a century ago, and have held it ever since.
It was in 1967 that Professor Marinatos began to excavate a Bronze Age city buried under twenty feet of volcanic ash on the south coast of the Aegean island of Thera (Santorini). His discovery of well-built, well-furnished houses, with colourful frescoes still adorning their walls, became world news overnight, and focused historical and scientific attention on the question of how his finds were to be interpreted.
It so happened that in the spring of 1968 I was due to travel as a guest lecturer on a Swan Hellenic cruise. We were to visit Thera and Crete, and I had the task of giving a general lecture on Minoan civilisation. I naturally included some account of the new discoveries, and suggested, following leads in my reading, that they seemed to strengthen the possibility that Plato's picture of lost Atlantis embodied memories of Minoan Crete. I later found out that this hypothesis, then quite new to me, had first been put forward in 1909 by an ancient historian K.T.Frost, while on the staff of Queen's University, Belfast. Frost had not been able to give a convincing explanation for the sudden disappearance of Atlantis, but it now seemed plausible to relate this aspect of the story to the devastation caused by the great Bronze Age eruption on Thera. That Minoan Crete had indeed been wrecked by Theran vulcanism, had been first suggested by Marinatos in a celebrated article published in Antiquity in 1939. The editors of the journal had expressed the view that Marinatos's thesis required 'additional support from excavation on selected sites', and this now seemed to be forthcoming.
I have no record of how I presented all this to the cruise passengers, but Sir Mortimer Wheeler happened to be in the audience, liked what I said, and commissioned me on the spot to contribute a fuller account to his series New Aspects of Antiquity . Such was the genesis of my book, The End of Atlantis , which appeared in April 1969, the year of the first International Conference devoted to the issues raised by Theran vulcanism.
To date, there have been three such Conferences, and the published Acta (Athens 1971, 1978, 1990) provide full documentation on most aspects of the problem. They do not, however, deal with the Atlantis question, which is more properly a matter for literary criticism, and is, or should be, centred in the study of Plato's Timaeus and Critias . For the purposes of this article I shall leave Atlantis to one side, and concentrate on Thera and its volcano.
How to reconcile the findings of archaeology with evidence from other sciences, especially vulcanology? - that was, and still remains, the nub of the Thera problem. At the time of the first Thera Conference excavation had clearly documented a widespread 'destruction horizon' on Cretan sites datable to about the middle of the 15th century B.C. The date was deduced from the pottery found in the burned and flattened buildings, pottery which includes fine specimens of the style known as Late Minoan IB. Prosperous towns like Mochlos, Pseira, and Gournia were wrecked and abandoned. The palaces at Mallia, Phaestos, and Kato Zakro fell, and were never rebuilt. The era of the 'villas' - opulent mansions serving as district administrative centres - came to an abrupt end. The great palace at Knossos survived the disaster, but suffered damage, and was rebuilt and redecorated in a rather different style. When it too perished by fire, perhaps c. 1375 B.C., though this is disputed, it contained records written in Greek (the Linear B tablets), indicating a take-over by Mycenaean power in its final phase.
So far so good: the destructions at the end of L.M. IB could, it seemed, have been caused by Theran vulcanism. But if one turned to the Akrotiri site on Thera, one found that the pottery in its abandoned houses seemed to be at least a generation earlier in date, being painted in the Late Minoan IA style. This seemed, at first sight, to preclude the possibility that the Thera eruption could also have caused the devastation in Crete. However, the then current view of the eruption held that it occurred in two phases.
So it was possible to imagine the following sequence of events. In phase I, local tremors, poisonous fumes, and a considerable outpouring of ash and cinders, as at Pompeii, would have made Thera uninhabitable. The volcano then went dormant for 30 or 40 years. In Phase II the volcano suddenly burst its flanks like Mt. St. Helens in Oregon a decade ago. Immense quantities of ash were hurled into the stratosphere. When sea water entered the vent there were even more violent explosions that blasted away much of the cone. Eventually what was left of the mountain subsided into the magma chamber to form the central sea-filled caldera that is still such a striking feature of the island.
Cores taken from the sea-bed round Crete in 1964 had been found to contain considerable quantities of ash from the eruption, and it was known from Iceland and Indonesia that such ash fall-out could seriously disrupt agricultural production. If one asked for further evidence that an island volcano could be lethally destructive at a distance, the example of Krakatoa lay ready to hand. When Krakatoa exploded on August 26, 1883, it caused widespread destruction and loss of life on the coasts of Java and Sumatra. Blast waves cracked walls and broke windows up to 160 km. away. Tidal waves, reportedly up to 36 metres high, inundated the shores of the Sunda Strait, destroying nearly 300 towns and villages, and overnight more than 35,000 people lost their lives.
Estimates of the volume of material displaced by the Thera eruption indicated an intensity five or six times as great as that of Krakatoa, so it was reasonable to posit a sudden and total disaster for population centres on or near the north coast of Crete. One could also envisage the destruction of the ships on which Minoan power depended, and the longer term disruption of agriculture by a heavy overlay of ash.
This convincing scenario soon encountered a major snag. The vulcanologists attending the Conference argued that their predecessors had misinterpreted the data of the ash layers. They insisted that the whole eruption was a single-phase rather than a double-phase event. They allowed that there might have been some preliminary tremors and rumblings as at Krakatoa, sufficiently frightening perhaps to cause an evacuation of Thera, but this, they said, would have occurred months rather than years in advance of the main paroxysmal outburst.
How were the archaeologists to react? Some at once gave up the idea of the volcanic destruction of Crete, arguing that the main eruption occurred at the end of L.M. IA c. 1500 B.C., totally devastating Thera but causing only minor damage further afield. The destruction in Crete, c. 1450 B.C., was caused, they said, by an invading army looting the palaces, burning the towns, and slaughtering the inhabitants. This instant solution was, however, open to various objections. It played down the intensity of the eruption, which went against the scientific evidence. Nor did it explain how an enemy force, presumably coming from Mycenae, could have landed and inflicted such rapid and total devastation on a large and populous island whose sea power remained unimpaired. In particular, it could not account for the fact that the depositories of the palace at Kato Zakro remained unlooted.
Others, myself included, tried to find alternative ways of handling the concept of a single-phase eruption, while still maintaining the devastation of Crete by natural causes. One possibility was to try to narrow the time gap that apparently existed between the destruction horizons on Thera and Crete. This meant disputing the traditional allocation of up to 50 years for the evolution of the L.M. IB style, and arguing that the brilliant 'marine style' vases found on Cretan sites, but not on Thera, were just a local 'ripple' on the broad stream of an L.M. IA style that continued down to c. 1450 B.C. However, an intensive re-examination and comparison of the pottery assemblages from Thera and Crete has confirmed the existence of a stylistic evolution for which decades rather than months must be allowed. The older view that town life on Thera ended c. 1500 B.C., towards or at the end of the L.M. IA pottery period, has stood its ground.
Another possibility was to date the eruption c. 1450 B.C., and to suppose that the Akrotiri site lay derelict and largely uninhabited, apart from occasional squatters, for a generation or so, until it was finally buried deep in the fall-out from the main eruption.
In the absence of coins or other firmly datable artefacts pottery sequences yield relative rather than absolute datings. To solve the chronological problem, should one not look to techniques other than the inevitably somewhat subjective assessment of sherds? The Thera eruption was a sharp-edged event at the centre of the problem. If it was really one of the largest eruptions of the past 5,000 years, it must have affected the environment in ways that could be detected and assessed by the methods of disciplines other than archaeology. Such were the considerations that dominated research in the run-up to the third Thera Conference. The upshot was some progress, but more perplexity.
The progress resulted from closer study of the ash fall-out. The ash from an explosive eruption consists of fine particles of volcanic glass, and each eruption generates particles with a different and distinctive refractive index. The particles are very durable, persisting unchanged on the sea-bed or in the soil for thousands of years. At the time of the first Thera Conference Theran ash had not yet been identified on any site in Crete. But in the 1970s the picture changed dramatically thanks to pioneering surveys by Dr and Mrs Vitaliano from Indiana University. By microscopic examination they identified particles of the ash on scores of sites from Heraklion to Kato Zakro, though its exact stratification remained uncertain.
Furthermore, at the second Thera Conference, the German geologist Dr Keller created a major sensation by announcing his find of layers of ash, still visible to the naked eye, near the town of Cos. These layers were not in an archaeological context, but Professor Doumas, assisted by Professor Renfrew and the writer, was soon to find similar layers at the Minoan site of Trianda on Rhodes. These deposits of Theran ash, some up to a metre thick, lie over 200 km. from the volcano - impressive testimony to the force of the eruption. Very recently similar deposits have been discovered in lake-bed sediment near Sardis in western Turkey, 320 km. from source.
Naturally enough, excavators on Minoan sites are now very alive to the possibility of discovering Theran ash in well stratified contexts, and this has been achieved in the re-examination of the island sites of Pseira and Mochlos just off the north coast of Crete. Here there can be no doubt that the ash has turned up in sealed floor deposits that are to be dated to L.M. IA rather than L.M. IB.
So the eruption was to be dated to c. 1500 rather than c. 1450. Archaeologists would have been happy enough to accept the finding, but enter the perplexity! The third Thera Conference turned into a battleground between archaeology and the newer disciplines of dendrochronology and radio-carbon (C14) dating. Findings from these fields were thrown into the ring, and their supporters argued strongly that the eruption was to be dated more than a hundred years earlier to 1628/7 B.C.
The precision of this date rests on the pattern of tree rings established by dendrochronologists, a pattern that reflects the annual growth of trees, with the varying width of the rings related to annual climatic variations. The pattern has been found to be remarkably consistent over the whole of the northern hemisphere, and it has proved possible to extend it back in time for up to 7,000 years, thanks to specimens from the extremely long-lived bristle-cone pines of the high sierras in California. A straightforward year count yields dates back along the sequence.
In 1984 two Californian scientists, Lamarche and Hirschboek, published evidence indicating that the pines had suffered severe frost damage in 1627 B.C., and suggested a possible cause in a global lowering of temperature following the massive emission of ash from the Thera eruption. The suggestion was taken up by Dr Baillie in Belfast, who looked at his records for Irish (bog) oaks, and found a 'narrowest ring event' starting in 1628 B.C. Bailie has argued strongly that there is a causal relationship with Thera, and that the eruption provides a unique solution for the frost damage.
Some Minoan experts, Philip Betancourt for instance, are prepared to accept the alternative 'high' dating for the eruption. Their willingness to do so is influenced by another line of evidence, that of radio-carbon (C14) dating. I have so far shrunk from deploying this subject because of its extreme complexity. At the time of the third Conference it did seem that on balance C14 dates derived from organic materials from the Akrotiri site favoured the higher dating. But there are many complicating factors, and the case is still being argued by the experts. There appear to be problems about sample contamination, and re-runs of tests on the same material sometimes produce different results. There are also fundamental problems about the recalibration curve and margins of error. It is possible that the C14 method may never be sufficiently precise to settle the issue. Archaeologists, like Peter Warren, who stick to the lower dating, can quote a modicum of dates that favour their side, and for the time being suspension of judgement seems the safest course.
That leaves dendrochronologists to be dealt with. It must be emphasised that their data is 'proxy' evidence only. They have a significant 'event' in their records, but nothing to prove a direct connection with Thera. They use the 'argument from silence', saying that if the eruption were as large as claimed it must have caused frost damage on a global scale, but they cannot find any trace of such damage around 1500 B.C. However, one can point to the fact that some very large ash eruptions in the A.D. era, whose dates are known, have not left any mark on the tree-ring record. This may be due to a low sulphur content in their ejecta, and experts have said that this was true of Thera. There is also the very real possibility that there were other major eruptions in the second half of the 17th century B.C. capable of accounting for the 1628/27 cluster. Candidates mentioned include Mt. St. Helens, Vesuvius (Avellino), and Aniachak (Alaska).
It is a sobering thought that after several decades of concentrated effort the earth sciences have still not produced an agreed date for the Bronze Age Thera eruption. Colin Renfrew has predicted that by the next Thera Conference the 'high' dating will have prevailed. But I would be prepared to bet against it! One must start from the pottery which indicates that Akrotiri was abandoned when the evolution of the L.M. IA style was already well advanced. As a result of prolonged archaeological investigation on a multitude of sites from Greece to Egypt there is a broad consensus that this evolution is to be dated to the 16th century B.C. The L.M. IA period (about 75 years) is followed by L.M. IB (about 50 years) and L.M. II (also about 50 years), which brings one down to the start of L.M. III at about 1400 B.C. At this point synchronisms between Aegean sites and Egypt become so firm that one can use the absolute chronology of Pharaohs like Tutankhamen to date Mycenaean styles to within a decade or so. Such accuracy is not yet possible for earlier periods, but I think there are strong grounds for supposing that the lines of the received system are not seriously skewed. If so, the lower dating for the eruption must hold its ground. The protagonists of the higher dating have to bring the L.M. IA period up by a hundred years or so into the Middle Bronze Age. This in itself runs counter to much good evidence, and also, to my mind, entails an unacceptable stretching of the subsequent L.M. IB and L.M. II periods.
There has recently been such concentration on the eruption date that the broader and ultimately more important historical problem of the decline of Minoan power has been somewhat neglected. One can no longer suppose that the paroxysmal eruption was the direct cause of the destruction and abandonment of so many sites in East Crete c. 1450 B.C. But any attempt to play down the destructive force of the eruption has been more than counteracted by the new evidence on the extent of the ash fall-out. I still believe that the eruption, which I would date closer to 1470 than 1500, was a severe body blow to Minoan power and prosperity, and that it greatly undermined their morale. The sudden extinction of their naval base on Thera, and devastation extending past their shores to Rhodes and Cos, would indicate that they had lost the favour of the great Mother Goddess of earth and mountain.
Sir Arthur Evans believed that the destruction horizon of 1450 B.C. was caused by that perennial scourge of Crete, a tectonic earthquake. That still seems to me the best explanation for such a simultaneous and pervasive disaster. The former reaction of the Minoans to earthquakes had been to rebuild on a more ample scale, but now the old resilience had been totally sapped. The survivors moved to the west of the island, or were dispersed overseas, and the power centre at Knossos fell an easy prey to a Mycenaean dynastic take-over. As I wrote in 1969, 'Minoan Crete was battered to her knees by the brute forces of nature and never rose again'. And I still think that a dim memory of these extraordinary happenings was preserved in Egypt, and that Plato picked it up there in a garbled form and worked it into the texture of his Atlantis legend.