The Theran Eruption: Chronology and Controversy

I’m a bit late to the game here, but the Late Bronze Age eruption of Santorini (ancient Thera) has been in the news again lately, in relation (as so often) to the controversy surrounding when, exactly, that eruption happened. This post is intended a necessarily simplified primer to that debate, in an attempt to identify the few things we do know for certain as well as outline the reasons for uncertainty underpinning the issue as a whole. It will conclude with an assessment of how the new study changes our understanding of the situation.

Chronologies: Absolute and Relative

When an archaeologist is talking about chronology, there are in fact two separate issues they may be discussing. The first is perhaps what most people would immediately assume: the absolute dating of an event, which is to say when it happened in calendar terms. This is what radiocarbon dates offer (at least within a band of uncertainty). In some areas of classical archaeology, inscriptions, coins, and written records can narrow this down to a given year, month, or even day.  In the Bronze Age Aegean, though, we generally lack this sort of granular data (Linear B records narrow things down to year, and even in some cases to a month, but they are too specific — and of course late — to have any bearing here). As such, to arrive at an absolute date in the absence of modern scientific methods, we have to chart correlations and exchanges with a region where the evidence for dating is much more abundant: Egypt.

There, the detailed knowledge of regnal lengths, as well as their correlation with astronomical events, allow for a fair degree of certainty in dating individual pharaohs. When finds associated with their reigns are found outside of Egypt, or Aegean imports are found alongside such items in Egypt, we are then in a position to give at least an earliest possible date (terminus post quem) for that archaeological context or period. They don’t really help with a lower boundary (terminus ante quem), because fine, inscribed objects such as faience scarabs bearing royal cartouches often became heirlooms, and could finally be deposited decades or more after their manufacture.

Unfortunately, only relatively few such items have been found in the Aegean, and most are certainly later than the eruption; the same goes for items of Aegean manufacture (or at least style) in datable Egyptian contexts. It is around these very few “fixed” points that the traditional (or low) chronology is constructed.  The crux of the controversy is that these dates, as currently construed, clash violently with the ranges of dates allowed for the eruption yeilded by radiocarbon dating of biological remains from the destruction layer. More on all this later.

The other type of chronology is relative, and here we can speak with much greater confidence. At its simplest level, this is simply stating whether one event occurred before or after another. When dealing with a single site, this is established on the principles of stratigraphy: each successive period of habitation (or destruction, or abandonment) at a site is reflected in successive layer (stratum) of dirt, the most recent on the top, the oldest on the bottom. Here, for example, is a section of the mound at Hisarlik (Troy):

3868DB6B-CC81-4C7F-A26B-B62674C1B63E(Picture taken from livius.org.)

The various strata are easy to see, and represent the relative chronology of the site: Troy I antedated Troy II, and so on and so forth. Also visible is the “shaving” of the mound that occurred in Roman times for the construction of the temple to Minerva (visible on the left). This destroyed all the evidence for Troys VI and VII at the top of the mound, which correspond to the layers most commonly associated with the Late Bronze Age destruction some would link with the Trojan War, and vividly illustrates why our understanding of those florescent periods is so patchy. Of course, for those who aren’t careful, the notion that the oldest layer will be the deepest can be dangerous: Schliemann cut through a large part of the sixth and seventh cities looking for his “historical” Troy, which he identified with the impressive but much-too-early second city. Only once Wilhelm Dörpfeld took control of the excavations at the end of Schliemann’s life did the truth of the situation become clear.

Working across sites, relative chronology becomes slightly trickier, but is still based on the same broad principles. Here, the extensive pottery record of the Bronze Age Aegean takes centre stage: if pottery associated with the same style is found exclusively in strata at two different sites, then (generally) we can say that those two strata are contemporary. While not all strata offer a clear enough picture, and regional styles and variations have to be considered, this sort of evidence provides quite a firm basis for cross-site dating.

As mentioned, the controversy concerning the chronology of the eruption is linked to the absolute date. The relative date, however, is prefectly clear, and has been since Spyridon Marinatos began excavations at Akrotiri on Thera in 1967. While it’s a journalistic cliché to call archaeological sites “the Pompeii of…”, in this case it is perhaps a forgiveable label, for Akrotiri was buried by the eruption in much the same way Pompeii was. It therefore provides us with a remarkable picture of the city on the very day of its destruction.  Since it was such a heavily Minoanized settlement (though its exact political relation to the palatial centres of Crete is unclear), the style of pottery and frescoes uncovered there should enable us to correlate those with a specific period of Minoan history.

And indeed they do: the latest finds from the eruption layer on Thera are all Late Minoan (LM) IA. For those who wanted to posit a direct link between the eruption and the so-called Minoan Collapse, this presented a grave chronological complication: whatever the cause of that collapse, it most certainly occurred at the end of LM IB, some fifty years later (at least). For a time, regional variations were cited as a possible explanation; could not provincial Thera, only a colony or emulator of Cretan customs, not have lagged behind the artistic developments of the main palatial sites? No: the discovery of Theran ash in LM IA contexts on Crete put paid to that theory. New finds continue to cement this, such as the recent discovery of tsunami damage at Palaikastro in Eastern Crete at the same chronological horizon (for an account that isn’t behind a paywall, see here).

The evidence is therefore overwhelming that the eruption occurred in LM IA, not LM IB, and therefore will not admit of any interpretation that posits a direct link with the Minoan Collapse. Whatever the absolute date may be, this cannot and will not change. Of course, indirect links are quite possible; the classic exposition of this hypothesis is Jan Driessen’s and Colin MacDonald’s The Troubled Island (1997 – Aegaeum 17; you can read a review by Ilse Schoep here and Driessen’s follow-up here). While this interpretation is not universally accepted, I think on balance of probabilities that the eruption was simply too big and too close to Crete not to have a lasting impact, but the evidence does not exist (and probably never will) to confirm that interpretation. And, while we are here, it bears stating that we are not dealing with the origins of the Atlantis myth here, and anyone who tells you otherwise is lying.

Absolute Chronology: The Two Camps

Before radiocarbon entered the picture, the limited evidence for interconnections with Egypt had been used to establish an apparently consistent chronology for the Aegean Bronze Age. By this interpretation, Thera erupted in c. 1500 B.C., during the reign of Hatshepsut in Egypt, and a short LM IB period followed, ending in c. 1450, early in the reign of Amenhotep II. The arguments put forth to support this dating are immensely complex, and to assess them fully requires a comprehensive grasp of Egyptian, Aegean, and Cypriot pottery styles.  While the data can be marshalled to create an image that is internally consistent, it should be stressed that there is no smoking gun, and indeed very few pieces of evidence that are truly unambiguous.

That said, we should not have much cause to doubt this interpretation if not for the radiocarbon data. This, quite explosively, pointed to a date around 1630 B.C. for the eruption, and was entirely incompatible with the traditional date of 1500 B.C. This, it should be re-iterated, had no bearing on the relative date: the eruption still must have occurred in LM IA. The consequence, therefore, is that LM IA must have been much earlier than we thought, and LM IB much longer.

This is the origin of the controversy. Various attempts have been made to cast aspersions on the specific tests used — the key evidence was, at first, an olive branch which (it was argued) may have been long dead at the time of the eruption, and (it is universally agreed) is not the ideal sort of wood for radiocarbon dating, since its annual growth rings are small and inconsistent. It was further argued that the eruption may have “tainted” it because of the quantities of carbon dioxide released. However, the early date was maintained by each successive test, and we now possess more floral and faunal remains associated with the eruption, including some from Crete, all of which support the early date when tested.

Because of this consistency, the archaeological evidence has come under increasing scrutiny, with successive articles, chapters, and monographs revealing the gaps of our knowledge and the paucity of unambiguous evidence. The same vase can support the low or high chronology, depending on whether we assume the coffin closest to the door is the earliest or latest in an Egyptian tomb — there seems to be no conclusive evidence. Broadly speaking, those who support the high chronology can read the evidence in such a way that it just about works if you squint, while those who support the low maintain that our understanding of radiocarbon is insufficient at this stage. This may seem old-fashioned, but it should be remembered that, in the early days of radiocarbon dating, when it clashed with the traditional Egyptian chronology, it was the latter that won out.

With that said, the possibility has emerged in recent years of a “compromise high” chronology, which would place the eruption in the early 16th century B.C.  This emerged from the realization that some evidence once through to corroborate the radiocarbon date, derived from tree rings and ice cores, did not quite hold up, and the fact the confidence intervals from various tests consistently allowed it. It also allows an understanding of the archaeological evidence influenced by knowledge of the radiocarbon dates (such as the “requirement” for a longer LM IB period than previously thought) to fit the picture in a more satisfactory manner. But the facts of the matter are not democratic, and a solution which makes the most people somewhat happy is not obviously true.

New Developments: Refining the Radiocarbon Data

Earlier this month, a new study was published in the journal Science Advances which refines the radiocarbon curve for the second millennium B.C. — you can read it here. As a consequence, the radiocarbon date ranges for the Theran eruption are moved away from the late seventeenth century B.C. and into the 16th. This is an important development, and seems to be the sort of “evolving understanding” that defenders of the low chronology insisted would come. Various media sites have in fact framed it in this manner. But this is not entirely the case. Here is a graph from the paper, illustrating the old date ranges (in pink) against the new ones (in blue):

2D0098AC-161A-4C5A-BB5F-67B3EA4B8BF5

While we have clearly moved towards the sixteenth century, the higher probabilities remain earlier rather than later. As the authors of the study put it: “We do note, however, that our data indicate that a date for the Thera eruption more recent than c.1510 BCE is highly unlikely, which remains at odds with certain archaeological arguments, and credible intervals do not exclude an eruption in the late 17th century BCE.” A table further illustrates that the new calibration brings the mean dates (variously derived) down by somewhere around 30 years in every case:

5316F31E-2CCF-4F87-8E0B-A47505A09CB7

While almost every range is now much larger, and so admit of lower chronologies, the data still seem on aggregate to support the high chronology more than the traditionally low; indeed, the compromise high seems to come out quite well.

Two things, I think, bear noting in conclusion. The first is that this study does not support the low chronology to the exclusion of the old. The second is that it is far from the last word on the matter. Only the evidence from Thera has been re-calibrated; while I expect the effect should be similar on data from elsewhere, I do not know that this will be the case. There are also other records, such as the growth of stalactites and bristlecone pines that might help narrow down the range of possible dates. While we are undoubtedly moving closer to a full understanding of events, we are very definitely not there yet.

4 thoughts on “The Theran Eruption: Chronology and Controversy

    1. I only referred to that evidence obliquely, and should perhaps have brought it in. While there was a brief period where everyone was quite sure that gave us a fairly exact date, further research showed that it’s not at all clear those records point to Thera and not other eruptions.

      Like

  1. Nicely written summary of a complex topic, which, as you say, will keep evolving. One minor quibble – in your first sentence you refer to the eruption of “San Torini”. I assume this is a typo – I’ve never seen that name used in any context before.

    Like

    1. Aha, yes! Not a typo so much as a bona fide error, though a kind editor might chalk it up as an orthographic variant.

      Like

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

%d bloggers like this: