Dating the eruption of the Thera volcano

The eruption of the Thera volcano was an event that changed/re-shaped the Aegean and the entire Eastern Mediterranean. Specialists always wanted to know the exact time this disaster took place, as it would be a very helpful tool in dating archaeological sites of the same era with greater accuracy.

Dating the eruption of the Thera volcano is a long-standing debate. So far, the eruption has been archaeologically estimated as occurring sometime between 1570 and 1500 BC. Researchers using radiocarbon measurements estimated the date of the eruption to about 1600 BC. More recently, a new research using radiocarbon measurements from the annual rings of trees that lived at the time of the eruption dated the event to some place between 1600 and 1525.

Here we’re going to have a look at some relative publications.

Abstract The eruption of the volcano at Thera (Santorini) in the Aegean Sea undoubtedly had a profound influence on the civilizations of the surrounding region. The date of the eruption has been a subject of much controversy because it must be linked into the established and intricate archaeological phasings of both the prehistoric Aegean and the wider east Mediterranean. Radiocarbon dating of material from the volcanic destruction layer itself can provide some evidence for the date ofthe eruption, but because of the shape of the calibration curve for the relevant period, the value of such dates relies on there being no biases in the data sets. However, by dating the material from phases earlier and later than the eruption, some of the problems of the calibration data set can be circumvented and the chronology for the region can be resolved with more certainty.

In this paper, we draw together the evidence we have accumulated so far, including new data on the destruction layer itself and for the preceding cultural horizon at Thera, and from associated layers at Miletos in western Turkey. Using Bayesian models to synthesize the data and to identify outliers, we conclude from the most reliable 14C evidence (and using the INTCAL98 calibration data set) that the eruption of Thera occurred between 1663 and 1599 BC.

Introduction The question of the date of the eruption of Thera (or Santorini) is of great importance because it defines the relationship between different cultural developments in the east Mediterranean in the middle of the 2nd millennium BC (Manning 1999). Dating of the eruption has been determined by “traditional” archaeological techniques through the study of trade links, particularly to Egypt (see Bietak 2003 for a summary of this evidence; previously, Warren and Hankey 1989), linking it into the Egyptian historical chronology, which is thought to be secure for this time period because of the extensive documentary evidence (e.g. Kitchen 2000).

Radiocarbon dating since the mid-1970s has suggested a date for the eruption some 100–150 yr earlier than the traditional archaeological (“conventional”) chronology (e.g. Michael 1976; Betancourt1987; Manning 1988; Friedrich et al. 1990; Housley et al. 1990; Manning and Bronk Ramsey 2003).

In the 1980s, it was suggested that tree-ring and ice-core evidence also suggested similarly “early”dates in the mid- to later-17th century BC (LaMarche and Hirschboeck 1984; Hammer et al. 1987; Baillie and Munro 1988). But recent work has seriously questioned the case from ice-core evidence for a Thera eruption about 1645 BC (argued for by Hammer et al. 2003); there was a major volcanic eruption, just not it seems of Thera, given critical review of the currently available geochemical characterization data (Pearceet al. 2004a,b; Keenan 2003). Similarly, the case for a dendrochronologically-derived date has only ever been based on a hypothetical and suggestive proxy linkage. There is as yet no positive evidencefor a causal association.

Thus, attention turns ever more centrally and critically to the 14C evidence since at present this alone offers direct and independent science-based dating evidence for the great and archaeologically pivotal Thera eruption in the mid-2nd millennium BC. In this paper, we report on further 14C measurements which we have recently made on material from Thera and from a related Aegean site. These add important new elements to the 14C picture.

Conclusions The first conclusion we draw from the data presented here is a recurrent theme in publications on 14C dating: that where high-precision work is to be undertaken, high-quality samples of short-lived material and with very secure contexts are critical. In this case, we do have quite a few measurements which do not fit this category, and in the end, they do not add much to the analysis. We have 102 14C measurements to consider here and, of these, six are inconsistent with the others; all come from phases of sites but do not have the same certainty of context as the samples from secure architectural contexts, storage jars, etc. By looking at the calibrated 14C dates, it is clear that the chronology, particularly of the late LMIB period, must be earlier than the conventional archaeological chronology. We can also see from the secure short-lived material from Akrotiri and other related sites that the eruption of Thera is much more likely (by a factor of about 10) to be in the mid-later 17th century cal BC than a 100 yr (or more) later.

If we combine this information in a Bayesian model and take only those models that are internally consistent, we can see that 4 different analyses all give dates for the eruption of Thera in the range of about 1663–1599 BC. This is consistent with suggestions from the mid-1970s onwards of a mid- to late-17th century BC date for the Thera eruption. We emphasize that this dating is direct on the context of interest; it is not a proxy (as current tree-ring evidence) nor subject to debate over the provenance of the tephra-derived glass shards/acidity spike in Greenland ice cores (e.g. Zielinski and Germani 1998a, 1998b; Manning 1998, 1999: 288–307; Hammer et al. 2003;Keenan 2003; Pearce et al. 2004a, b).

We conclude that if the 14C evidence is considered in isolation, one would deduce that the eruption of Thera took place sometime between 1663 and 1599 BC with 95% confidence. However, there is other archaeological evidence and specific interpretations of this, which clearly need to be taken into account (see Bietak 2003). Ultimately, one’s conclusions will depend on how much weight is given to the alternative evidence and especially its interpretation. If, for example, after considering the archaeological evidence, it is concluded that a mid-16th century BC date for the eruption of Thera is 10 times as likely as a 17th century BC date, then this will lead to a different final conclusion. Others, meanwhile, have argued that the archaeological evidence is potentially consonant with a 17th century BC date for Thera (Kemp and Merrillees 1980; Betancourt 1987, 1998; Manning 1988, 1999). Perhaps most interesting of all is that new evidence is now beginning to suggest that the historical-numerical chronology of Egypt in this period may not be as secure as had been supposed (see Kutschera et al.). Such evidence might open the way for the reconciliation of archaeological linkages with Egypt to the 14C evidence.

(Source: “Dating the volcanic eruption at Thera”, by Christopher Bronk Ramsey, Sturt W Manning, Mariagrazia Galimberti, 2004)

Abstract The volcanic mega event of the Minoan Santorini eruption constitutes a time anchor in the 2nd millen-nium BCE that is inherently independent of archaeology and political history. It was a geological event. Yet the dimension of time in geology is not different than in archaeology or human history. Why then does archaeological dating usually place the Minoan Santorini eruption in the 18th Dynasty around 1500 BCE, whilst radiocarbon dating of the volcanic event at Akrotiri (Thera) yielded a calibrated age of 1646–1603 cal BCE, a difference of more than a century? The crux of the problem lies apparently in the correlation between archaeological strata and political history. We present radiocarbon dates of Ashkelon Phases 10 and 11 in comparison to Tell el-Dabca and the Santorini eruption, based only on 14C dating. Tell el-Dabca Phase D/2 is slightly older than the volcanic event. But Phase D/1 or Phase C/2-3 could have witnessed the eruption. Ashkelon Phase 11 has similar radiocarbon dates as Tell el-Dabca Phases E/2, E/1 and D/3, all being significantly older than the Minoan eruption. It seems that the duration of Ashkelon Phase 10 includes the temporal occurrence of the Minoan Santorini eruption within the Second Intermediate Period.

Introduction The Minoan Santorini eruption, classified as “super-colossal” with a volcanic explosivity index (VEI) of 7, may have been the largest known volcanic eruption in the world during the Holocene (Johnston et al. 2014). It certainly was the largest eruption in the eastern Mediterranean region during this time period. The date for the latter eruption is controversial. Studies about cultural archaeological associations with Egypt are usually understood to suggest a link between the Minoan Eruption and the 18th Dynasty around 1500 BCE (Doumas 1983; Bietak 2003, 2013, 2015, 2016; MacGillivray 2009; Warren 2009; Wiener 2009). However, radio-carbon dates of organic materials related stratigraphically to the time of the eruption favor a calibrated age range in the second half of the 17th century BCE (Bronk Ramsey et al. 2004; Friedrich et al. 2006; Friedrich and Heinemeier 2009; Manning 2014; Manning et al. 2006, 2014; Bruins et al. 2008, 2009; Bruins 2010; Bruins and van der Plicht 2014).

The significance of the controversy is well expressed by Warren (2009:181): “Why is it important to fix the date of the Minoan eruption of Santorini? Essentially the answer is that in order to write the history of international relations of the later Middle and the Late Bronze Age in the eastern Mediterranean we need to establish whether, at the time of the Minoan eruption of Santorini, the Egypt which was linked to the Aegean, Cyprus and the Levantine region was that of late Dyn. XIII or earlier Second Intermediate Period on the one hand or that of the early New Kingdom (early Dyn. XVIII) on the other.”

One of the most important sites in Egypt in relation to the above controversy is Tell el-Dabca, excavated during many years by Bietak (1975, 2003, 2013, 2015, 2016). Seaborn epumice of the Minoan Santorini eruption has been found in phase C/2 in the Palace District ‘Ezbet Helmi (Bietak 2003; Bichler et al. 2003; Bietak and Höflmayer 2007). Radiocarbon dates on charcoal were not useful (Bruins 2007), but short-lived material (seeds) from Tell el-Dabca gave important results, showing an offset of about 120 years between archaeo-historical ages and 14C dating (Kutschera et al. 2012). Concerning this enigma, Bruins (2010:1490) expressed a key question: “What is erroneous here—the14C dates …or the associations between the Tell el-Dabca archaeological phases and dynastic history?” The rather comprehensive 14C dating investigations of Egyptian dynasties by Bronk Ramsey et al. (2010) and Dee (2013a, 2013b) do not show a systematic offset of 120 years between dynastic history and 14C dating. In fact, the 14C results grosso modo corroborate historical chronological compilations of ancient Egypt.

Therefore, the problem seems to be the association between archaeological phases and political history. Indeed, alternative historical-archaeological associations or interpretations concerning Tell el-Dabca have recently been developed by Höflmayer (2017), also in relation to new radiocarbon dates of other Middle Bronze Age sites in the Levant (Höflmayer et al. 2016a, 2016b).

A key archaeological site in southern Israel is Tel Ashkelon, where important excavations were conducted by Stager and his team since 1985 in the framework of the Leon Levy expedition (Stager et al. 2008). The Middle Bronze Age stratigraphic phases of Tell el-Dabca and Ashkelon have been related to each other on the basis of ceramic studies (Bietak et al. 2008). This stratigraphic linkage between the two sites enables evaluation whether the radiocarbon dating offset found for Tell el-Dabca (Bietak and Höflmayer 2007; Kutschera et al. 2012) is also present at Tel Ashkelon? Entailed in the above question is the chrono-stratigraphic position at both sites of the Minoan Santorini eruption, according to14C dating only (Bruins and van der Plicht 2003), which is the main focus in this preliminary study. The 14C dates presented and evaluated in this article include Ashkelon Phases 10 and 11, as well as the related Phases D/1 to E/2 of Tell el-Dabca. In addition, Phases C/2 and C/3 of Tell el-Dabca are also considered in this study, because these immediately predate Phase D/1 in the stratigraphic archaeological sequence, while pumice from the Minoan Santorini eruption was found in Phase C/2 (Bietak 2003; Bichleret al. 2003). Using radiocarbon dating as the principal chronological tool is a legitimate methodological approach, carried out in countless archaeological and geological studies all over the world.

Discussion and Conclusions Since radiocarbon dating is not at odds with the investigated parts of Egyptian Dynastic history (Bronk Ramsey et al. 2010; Dee 2013a, 2013b), the crux of the problem, in our opinion, may be in the correlation between archaeological strata and political history during parts of the 2nd millennium BCE. Indeed, cultural change does not necessarily follow historical change in a coeval manner, as pointed out by Marée (2010) with respect to the Second Intermediate Period. The latter period is missing in the investigation by Bronk Ramsey et al. (2010), for obvious reasons. Ryholt (1997:1) succinctly summed up the problematic nature of this historical period in ancient Egypt: “The Second Intermediate Period, covering the time span between the Twelfth and the Eighteenth Dynasties (c. 1800-1550 B.C.) …is an epoch on which research is still in its pioneer stages. It is not entirely clear how many kingdoms existed during the period, and those that are known are poorly defined insofar as both their territorial and chronological extent remains uncertain. ”Indeed, King Khyan for example, linked with the archaeological stratigraphy of Tell el-Dabca (Bietak 2003,2013, 2015), has been placed in various historical chronological positions within the Second Intermediate Period (Ward 1984; Ryholt 1997; Moeller and Morouard 2011). A new study by Höflmayer gives additional chronological options concerning Khyan that may have considerable effect on archaeo-historical dating. Radiocarbon dating places the Minoan Santorini eruption in the Second Intermediate Period (Bruins 2010).

(Source: “The Minoan Santorini Eruption and its 14C Position in Archaeological Strata: Preliminary Comparison Between Ashkelon and Tell El-Dabca”, by Hendrik J Bruins1, Johannes van der Plicht, 2017)

Abstract The mid-second millennium BCE eruption of Thera (Santorini) offers a critically important marker horizon to synchronize archaeological chronologies of the Aegean, Egypt, and the Near East and to anchor paleo-environmental records from ice cores, speleothems, and lake sediments. Precise and accurate dating for the event has been the subject of many decades of research. Using calendar-dated tree rings, we created an annual resolution radiocarbon time series 1700–1500 BCE to validate, improve, or more clearly define the limitations for radiocarbon calibration of materials from key eruption contexts. Results show an offset from the international radiocarbon calibration curve, which indicates a shift in the calibrated age range for Thera toward the 16th century BCE. This finding sheds new light on the long-running debate focused on a discrepancy between radiocarbon (late 17th–early 16th century BCE) and archaeological (mid 16th–early 15th century BCE) dating evidence for Thera.

Introduction The Minoan eruption of Thera (Santorini) in the second millennium BCE was one of the largest volcanic eruptions in the past 4000 years. The event has been intensively studied from archaeological andpaleoenvironmental perspectives because it provides a geological marker that, if precisely dated, could synchronize Bronze Age histories of the Aegean, Egypt, and the Near East and anchor a wide range of contemporary environmental data. Dating has, however, proved problematic because of observed discrepancies between timelines derived from archaeological evidence and those based on radiocarbondating.

Debate over a date for the Thera eruption Measurements of radiocarbon (14C) from legumes and grains buried directly beneath the eruption deposits, and an olive branch buried within them, cluster in the range c.1650–1600calBCE relative to the internationally agreed radiocarbon calibration curve, IntCal13, which converts radiocarbon determinations from samples of unknown age into calendar age estimates. This places the eruption in thesecond half of the 17th century BCE. The reliability of this radiocarbon-based date range has been debated because it places the event earlier in time than certain archaeological synchronizations between sites in the Aegean, Egypt, and Levant would suggest possible. Evidence indicates that the eruption occurred after the start of the New Kingdom in Egypt, which, according to proponents of conventional, archaeologically based chronology, is considered to be sometime after c.1550 to 1500 BCE, although arguments have been presented to move the start of this range as early as c.1570BCE. An extensive integrated radiocarbon and archaeological study of dynastic Egypt, covering 1700 years and incorporating 211 radiocarbon dates, can be used to support both the conventional and earlier proposed date ranges by indicating a start date for the New Kingdom of between 1570 and 1544BCE. The problem remains, however, that direct radiocarbon evidence for the Thera eruption currently places this event multiple decades earlier than the earliest possible start of the New Kingdom. Arguments in support of the most recently proposed late 17th century calibrated calendar range for Thera have focused on the consistency with which a large number of radiocarbon determinations from different laboratories, on different sample types, from secure archaeological contexts immediately predating the eruption, calibrate to the same point in time. While this logic confirms the synchronicity of the network of archaeological contexts, and the inter-laboratory agreement on an approximate temporal window during which the eruption occurred, the derived calibrated calendar date ranges are highly dependent on how accurately IntCal13 represents radiocarbon levels for the time period. Many of the existing radiocarbon determinations have been recalibrated multiple times, with calibrations to older iterations of IntCal returning probability distributions ranging into the 16th century because of a slight shift in the position of a well-described radiocarbon plateau in the calibration curve. Given the sensitivity of these critical data to the shape of the calibration curve, any improvement or insight regarding calibration in this period would clearly be widely beneficial.

Exploring annually resolved 14C Understanding of past timelines for human and environmental inter-action has been transformed by the development of an internationally agreed radiocarbon calibration curve based on the best available
14C measurements produced from samples with independently estimated or known calendar ages. For the past 12,000 or so years, measurements are largely derived from consecutive, sometimes over-lapping, decadal and semidecadal blocks of known-age tree rings. These determinations are then drawn together to form a single calibration curve against which new measurements on a range of carbon-based materials can be compared. The accuracy and precision to which one can date a new determination depend critically upon three factors: the volume and faithfulness of the calibration database in representing the level of atmospheric 14C; the statistical methodology; and, crucially for precision, the shape of the curve itself, where many plateaus and inversions limit the potential precision achievable. Previous investigations as to whether calibration accuracy and precision could be improved by the use of radiocarbon determinations for single years (versus multiyear blocks) focused on the question of improving calibrated ranges for materials representing a single, short season of annual growth. With typical year-to-year variations of c.8 to 16 14C years (1 or 2‰) reported, a sampling resolution of less than c.10 or so years appeared to offer little advantage, given that errors on individual determinations are also typically within that range or greater. However,the discovery that variations of up to 96 14C years (12‰) can simultaneously occur between single years in tree ring series in both hemispheres, and the use and potential of these marker events to synchronize multiple chronologies, has initiated re-newed investigation of annual 14C. As increasing numbers of annual resolution radiocarbon determinations become available for inclusion in IntCal, the utility of these data and the consequences of other subdecadal variability that may be hidden in the current multiyear resolution record must be explored. We selected the period 1700–1500 BCE for a systematic investigation of the potential contribution of annual 14C to improve or better define the limitations for radiocarbon dating during the period most closely associated with the eruption of Thera.

Discussion The resultant shift in the posterior distributions for calibrated ages of pre-Thera eruption contexts in previously published scenarios illustrates how radiocarbon evidence for the dating of Thera can now be argued to be compatible with multiple lines of evidence for dating of the New Kingdom (18th dynasty) in Egypt. The revised calibrated ranges provide the flexibility for the long debated dating discrepancy to be resolved where the earlier proposed start of c.1570/1560 BCE is accepted, but also, extended credible intervals beyond 1550BCE offer a period of overlap with conventional, archaeologically based chronology. 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.

The recalibrated results provide a new focus to search the proxy records for markers that can be directly linked to Thera, in particular, the ice core records, where volcanic acidity and tephra can be used to more closely define specific eruptions. There is some indication that dating for the ice core record during this period may need adjustment. New radiocarbon determinations for the Aniakchak II eruption (3270 ± 40 14C years B.P. for a peat layer just below the tephra) suggest that the geochemically anchored ice layer for this event (c.1641 BCE) should become more recent, in which case new acidity levels in the ice could become viable candidates for Thera in the 16th century BCE. In particular, this should be explored using the well-established correlation between volcanic acidity layers in the ice and anomalous growth in upper treeline bristlecone pine. While our data place previous tree ring marker dates suggested for Thera (1626-1628 BCE) outside the 95% probability range, the bristlecone pine chronology has a ring width minimum at 1597 BCE and a frost-damaged ring at 1560 BCE, indicating major volcanic events around these years. The 1597 BCE date is earlier than indicated by the posterior mean of our revised dating of the olive branch and Akrotiri assemblage but within the 95% credible interval and could be argued to correlate with a chemical response recorded in a speleothem at Sofular Cave in Turkey, which is independently dated using 230Th dating and layer counting. However, given the complexity of the cave environment and errors associated with the dating method used, it also seems quite possible that this chemical signature could also extend to a connection with an eruption at 1560 BCE (and beyond), with sulfur elevated between c.1620 and 1530 ± 25 BCE. The 1560 BCE date, which represents the first proxy marker for a volcanic event in the bristlecone pine record beyond the posterior mean values derived for this study, is particularly noteworthy, as it would fit with the earlier proposed start for the New Kingdom in Egypt, the revised reign of Ahmose, and the description of an unusual and catastrophic storm from the Ahmose “Tempest Stela”. Equally, other bristlecone growth anomalies at 1546 and 1544 BCE also warrant further investigation, given the 95% credible intervals for the new radiocarbon ranges and compatibility with conventional, archaeologically derived dates for the start of the New Kingdom.

This study demonstrates the advantages of annual 14C time series to beneficially augment the coarser-resolution measurements of IntCal13. We show that this can be particularly important in transition periods around 14C plateaus, where small changes in the curve can have a large effect on calibrated ages. Here, annual measurements are able to provide finer detail than measurements on multiyear blocks. The results indicate that the Thera eruption occurred during a plateau in 14C production, making current radiocarbon ranges less precise and limiting the potential of radiocarbon dating to provide an exact date for the event. Results do, however, provide a strong basis for new investigation of the utility of solar cycles, and patterns of more rapid 14C production identified c.1580–1520 BCE in improving this situation. They also provide a basis for a renewed focus on proxy records for the 16th century BCE, starting with the precise bristlecone calendar dates of 1597, 1560, 1546, and 1544 BCE. Future work will also address any potential impact of the suggested alteration to the calibration curve for other established models overlapping with the time period; however, the annual time series for this period should also be extended and replicated at other laboratories using different regional tree ring chronologies to more fully explore the implications for accuracy and precision made possible via an annually based calibration resource. Work is also needed to explore the degree of interlaboratory variation in annual 14C data and to fully understand the combination of factors leading to the difference between IntCal13 and the annual time series. No definitive calibrated radiocarbon range for the Thera eruption is currently possible, but the altered position of the 14C plateau indicates that improved calibration has much to offer chronological synchronization of human and environmental timelines in this period.

(Source: “Annual radiocarbon record indicates 16th century BCE date for the Thera eruption”, by Charlotte L. Pearson et al.)

We let our reader decide about the above.

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