Thera volcanic eruption

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Thera, November 21, 2000, from NASA satellite

Thera, also called Santorini, is a small archipelago in the Aegean Sea about 240 kilometers (150 miles) southeast of Athens. The islands in the archipelago form the circular ring of a caldera formed from volcanic eruptions. One of these eruptions, in the middle of the 2nd millennium BC, was of such magnitude that everything on the islands was buried in about 200 feet of tephra (solid volcanic debris). It is thought that the effects of the eruption were worldwide. The present article deals with attempts to date this cataclysmic event.

When did Thera explode? Background to the problem

Attempts to date the Thera eruption have relied on three lines of evidence: (1) radiocarbon dating, (2) archaeological artifacts, chiefly pottery, and (3) evidence of its effect in other locales besides the archipelago itself. Most archaeologists are of the opinion that the latter two of these categories are in agreement with their chronology for the various civilizations that interacted in the middle of the second millennium BC. The radiocarbon evidence, however, has been interpreted as requiring that the Thera event be dated about 150 years earlier than the other two lines of evidence would seem to permit. The controversy is ongoing, and an agreement between the various parties to the dispute is not likely anytime soon. A series of three scholarly monographs has been largely devoted to this ongoing controversy, entitled The Synchronisation of Civilisations in the Eastern Mediterranean in the Second Millennium BC. These large volumes will be abbreviated as SCIEM in what follows. The most recent is Volume 3 (SCIEM 3),[1] published in 2007. The controversy is also being played out in the pages of the journal Radiocarbon, which, as the name suggests, is devoted to various aspects of the measurement and dating of samples based on their ratio of radioactive (C14) to non-radioactive (C12) carbon.

Radiocarbon dates for Thera

After digging through the vast mantle of tephra, archaeologists found the remains of the Theran town Aktorini. There were no bodies in the remains of the village, indicating there were warning signs that were heeded by the residents before the full eruption. They left behind some storage jars with seeds. Short-lived vegetation such as seeds, when available, are always preferable for radiocarbon dating to larger vegetation specimens such as building lumber, because the dating of lumber reflects the time the tree was growing, which may have been decades before it was cut down and another unspecified length of time while it was in use in the building. These seed specimens were analyzed in a 2004 Radiocarbon article.[2] The results of this analysis placed the eruption of Thera between 1663 and 1599 BC at a 95% confidence level. Other results obtained from an olive branch with leaves still on it were in agreement: 1627 to 1600 BC with a 95% confidence level.[3]

Pottery dating of the Thera event

The fleeing residents left behind not only the jars containing grain, but also various other ceramic artifacts that archaeologists routinely use in assigning a date to the various strata in their excavations. The general pottery style found at Thera was the type called Late Minoan IA (LMIA), with distinctive spirals and floral motifs. This type of pottery was traded widely across the Mediterranean and in the Near Eastern countries. There were no examples of a successor style called Late Minoan IB (LMIB), which had motifs of octopi, dolphins, and other sea creatures. Therefore, archaeologists were confident in dating the Theran pottery to some time around 1500 BC, the transition point between LMIA and LMIB. Further, one style of pottery found at Thera is found in Egypt but not in any context earlier than the 16th century BC, i.e. over 100 years later than the 1660-1600 bracket for the Thera eruption calculated by radiocarbon analysis.[4] Archaeologists therefore date the Thera eruption at roughly 1500 BC or slightly later. The eminent Egyptologist Manfred Bietak maintains that the radiocarbon dates differ from what can be accepted archaeologically by 120 to 150 years.[5] Other archaeologists agree. ""There are no current grounds for thinking that the Egyptian historical chronology could be out by more than a few years," says archaeologist Peter Warren of the University of Bristol, U.K. "This chronology has been constructed by hundreds of expert Egyptologists over many decades.""[6]

Residue from the eruption at other locales

Originally it was thought that some ash deposited in the Greenland ice pack that could be dated by ice-layer analysis supported the 1660-1600 date for the Theran eruption, but later chemical analysis showed that the ash came from some other volcano, so that this argument is now abandoned by Sturt Manning and the physicists.[7]

Another type of residue from a volcano is pumice. Pumice is a rock with myriads of glass-walled tiny bubbles that make it less dense than water, so that after a volcanic eruption it would have floated across the Mediterranean to many different shores. It was valued in antiquity as a scouring agent, a use which continues today in "Lava" soap.

In addition to the pottery evidence, the contexts of waterborne pumice from the Theran eruption found in Egypt and the Near East have ben considered as evidence relating to the date of the eruption. At Tell el-Dabca, Theran pumice in large quantities was found at five locations, three of which the excavator believes were workshops active during the reign of Thuthmosis III and not abandoned until late in his reign or the following reign of Amenophis II, in any event after c. 1450 B.C. . . . Pumice from the Theran eruption has also been found in Eighteenth Dynasty, likely post-1525 B.C. contexts at Tell elcAjjul and Tell Nami in Canaan.[8]

The "excavator" at Tell el-Dabca mentioned in this quote was Manfred Bietak. Bietak takes the "low chronology" for Egypt's Dynasty that places the reign of Tuthmosis III from 1479 to 1425 BC. (The "high chronology" of 1504 to 1450 BC is still held by some historians.) On p. 15 of SCIEM 3, Bietak has a chart that locates the Thera pumice in the palace district at Tell el-Dabca to about 1450 or 1455 BC.

This latest statement from Egyptologists, therefore, maintains that the 1663 to 1599 (median 1631) BC date for the eruption of Thera is about (1631 – 1450) = 180 years too early, in contrast somewhat with the earlier statements by Bietak[9] that radiocarbon dates were too high by 120 to 150 years. This represents a movement away from, rather than toward, a compromise solution. The latest version of SCIEM (Vol. 3) carries on the debate, with no resolution in sight. Articles in SCIEM 3 by archaeologists Manfred Bietak, Felix Hoffmayer, and Kenneth Kitchen maintain that it is not possible to move Egyptian and related histories 100 or more years back in time, while Sturt Manning and the physicists insist that this must be done if archaeologists are to be consistent with the findings of "science." For those who are not familiar with the issues, the bias would be in favor of the physicists, since in the current culture physicists are higher on the totem pole than archaeologists. For those who are more acquainted with the actual facts of the case, however, there remains adequate reason for questioning the various assumptions that the physicists rely on to arrive at their results.

Possible explanations of the conflict

It has been proposed by various observers that the Thera event itself may be responsible for the discrepancy between radiocarbon dates and archaeological dates in the middle of the second millennium BC. It is already recognized that a change in the earth's magnetic field will affect the number of cosmic rays reaching the upper atmosphere, and hence the number of C14 isotopes being formed, and this explanation is used as part of the explanation of why the C12/C14 ratio does not follow a straight line over the centuries, as compared to figures derived from dendrochronology. But a cataclysmic event can also distort the ratio of these two isotopes. Nuclear and thermonuclear tests in the late 1950s and early 1960s that were carried out mostly (entirely, for the thermonuclear events) in the South Pacific affected the C12/C14 ratio in both southern and northern hemispheres. If the Thera event gorged up old carbon material from inside the earth, then the distribution of the old carbon in the atmosphere would make any plant material that took it up to appear older than it actually was when measured in mass spectrometers some 3500 years later.

This explanation, however, does not seem possible because of the olive branch that was buried in Thera's eruption. Growth rings in the branch represented 70 years of growth for the tree. Samples from various rings were subjected to radiocarbon analysis. The result was that the earliest rings returned values that measured about 70 years earlier than the latest rings and the leaves. This implies that if something had disturbed the atmospheric C12/C14 ratio for the mid-second millennium BC, the disturbance was in effect at least 70 years before the Thera eruption.

Another explanation for the apparently too-early C14 readings is that the calibration curves are distorted because these curves are based largely on reconstructions of the dendrochronology for this time, and it is conjectured that the dendrochronological data are in error. Dendrochronological adjustments continue to be a matter of controversy, partly because of the failure to publish a thorough sequence of tree-ring data back as far as the second millennium BC.

Practical considerations

Although it would seem easy to maintain that the radiocarbon results are derived from "hard science," and thus should take precedence over all the protests of the archaeologists, it remains a matter of practical observation that virtually no one has been able to apply this principle to the history of the ancient Near East. To illustrate this, it is only necessary to examine the dates given to Egypt's New Kingdom (Dynasties 18 through 20) in any current reference work, either book-bound or in one of the on-line encyclopedias. Here there is no question: the approximately 150 year adjustment required by the physicists is usually not even mentioned; the conventional archaeological dates hold complete sway. Although it might be tempting to try to move Tuthmosis III 150 years earlier, so that his dates coincided with the Theran eruption (as demonstrated above), to move this one pharaoh that amount of time would require moving both his predecessor and successor by the same amount of time. The ripple effect would go on throughout Egyptian history. No one has been able to make such a move and at the same time construct a coherent history of Egypt and its surrounding nations, including the disruptions this would cause in the later links between Egypt and Assyria. So the failure of any encyclopedia to include the adjustment required by the physicists is itself a testimony in favor of the Egyptologists' position and against the proposition that Egyptian chronology must be moved back in time, for the New Kingdom, by some 150 years.

There is a consequence to this that follows logically and which will be fought desperately by those who realize where this logic is leading. It means that other radiocarbon dating from the middle of the second millennium BC must, if the archaeologists are right, also be brought down by the approximately 150 years that the Thera event must be brought down. This includes the date of Jericho City IV, the city that has every other mark of being in the right place at the right time to correspond to the Jericho of Joshua chapter 6. Currently, the strongest (indeed, almost the only) argument against City IV being the city taken by Joshua is that grain from the full storage jars there has been radiocarbon dated to 1550 BC, in agreement with the dating for the site given by Kathleen Kenyon. But if the Egyptologists are right (and that they are right is conceded implicitly by all encyclopedias, including those that are hostile to the Biblical account), then this date must be reduced by about 150 years to around 1400 BC, the time that Garstang and Bryant Wood maintain is mandated by the Biblical evidence. Although there is some room for adjustment to this 150-year figure (see the discussion of Bietak's varying from 120 to 180 years given above), it is certain that even the smaller of these adjustments (120 years) would mean that Kenyon's date is no longer viable. The radiocarbon evidence, so triumphantly proclaimed by those who maintained that there was no Jericho in Joshua's day, and hence the Bible's account was fiction, would be turned around to become another evidence, in addition to all the stratigraphic and ceramic evidence gathered by the archaeologists, that Jericho really did fall just as, and when, the Scripture said it did. It will be expected that this conclusion, a necessary consequence if the Thera event needs to be moved later, will provide a good reason for those with an anti-Biblical, anti-supernatural bias to join the ranks of the physicists against the archaeologists, calling for an updating of the dates of Egypt's New Kingdom (and the preceding and following epochs necessarily also), even though the Egyptologists on their own web sites say that this is not possible.

Another interesting consequence if the archaeologists are right is that the Thera eruption, in Bietak's latest writing on this matter, is to be dated to about 1450 BC, based on his extensive excavations at Tell el-Dabca. If this is the case, it reopens the possibility, explored by various writers in the past, that the Thera event was responsible for some (but not all) of the plagues that struck the Egyptians before the Exodus. In a sense, however, this is secondary to the consequence that the required down-dating of radiocarbon dates for the 15th and 16th centuries BC means that Kenyon's date for the destruction of Jericho City IV could no longer be maintained.

For those who are not willing to follow this logical conclusion, it would be reasonable to put in abeyance all judgments on the radiocarbon question for the 2nd millennium BC, relying instead on the archaeological (including ceramic) arguments until the conflict between the physicists and the archaeologists is resolved one way or another. This would mean that reliance must be placed on the other determinatives of the chronology of the time, whether for Egypt or Canaan. These other arguments definitely support the conventional chronology of Egypt and the surrounding countries. They also support a date for the fall of Jericho City IV in the latter half of the 15th century BC, once the main prop for Kenyon's date, the radiocarbon argument, is put in abeyance or (as seems more likely) is negated altogether.


  1. The Synchronisation of Civilisations in the Eastern Mediterranean in the Second Millennium BC, eds. Manfred Bietak and Enrst Czerny (Vienna: Österreichische Akademie der Wissenschaften, 2007.
  2. "Dating the Volcanic Eruption at Thera," by Christopher Ramsey, Sturt Manning, and Marigrazia Galimberti, Radiocarbon 46 (2004), pp. 325-344), available here
  3. Science 312, April 28, 2006, p. 508.
  4. Ibid., p. 509.
  5. Ibid., p. 509.
  6. Ibid., p. 509.
  7. SCIEM 3, p. 28.
  8. Malcom H. Wiener, "Times Change: The Current State of the Debate in Old World Chronology," in SCIEM 3, p. 40.
  9. Science 28 April 2006, p. 509.