Contextual Framing

Historical introduction: Minoan Crete and Santorini among volcanoes of the world

Introduction

Mt. Tambora on Sumbawa Island in Indonesia exploded in April 1815 and caused 60,000 to 100,000 deaths on Sumbawa and neighbouring islands alone (Oppenheimer 2003; 2011). It is the most disastrous volcanic eruption in recent history. The voluminous sulphur emissions from this eruption degraded the Earth’s climate and 1816 is famously known as the ‘Year without a Summer’ because of severe climate abnormalities that caused average global temperatures to drop (Self et al. 1984). This resulted in poor harvests and food shortages across the Northern Hemisphere and was probably responsible for an outbreak of diseases and major social upheavals in Europe (D’Arcy Wood 2014). The 1815 eruption also produced voluminous tephra, a fragmental material deposited by falling through the air. The tephra-affected area was probably over 500.000 km² and destroyed or inflicted severe damages to forests, agriculture, livestock and buildings across the whole region (Self et al. 1984; Oppenheimer 2011; Kandlbauer & Sparks 2014). Moreover, a giant raft of volcanic rock, light enough to float on the surface of water, clogged the nearby sea for two to three years after the eruption.

The eruption of Mt. Tambora provides some clues about the various potential local, regional and global impacts of ancient, catastrophic volcanic events on environment and society. One such eruption was that of Santorini volcano (also called the Thera eruption, the Minoan eruption or the Late Bronze Age eruption) in the Aegean Sea, which shook the Mediterranean world approximately 3,600 years ago. This eruption occurred when the Minoan civilisation on Crete and on the Aegean Islands was at its height. Tephra from Santorini has been found as far away as the Black Sea indicating a minimum fallout area exceeding two million square kilometres. Tephra fall entirely covered the Minoan settlement of Akrotiri on Santorini (Doumas 1983), but also affected communities and agricultural areas on nearby islands and the coast of Crete, probably in combination with seismic shocks and tsunamis. A generation or so after the event, the palaces and major towns on Crete and the other islands were suddenly destroyed and Minoan society collapsed (Driessen & Macdonald 1997; Driessen 2019). Eventually, the Mycenaean civilisation of Mainland Greece took advantage and expanded geographically, politically and economically.

While many studies highlight that a volcanic eruption can effectively affect the trajectory of human society (e.g. Sheets and Grayson 1979; Sheets 2004; Grattan & Torrence 2007; Sheets 2008; Oppenheimer et al. 2018; Torrence 2019), the causal sequence, if any, between the Santorini event and the breakdown of Minoan society is not yet resolved. In particular, several scholars point out that not much tephra fell on the island of Crete, the centre of Minoan civilisation, and that a volcanic tsunami would not have been strong enough to cause large destructions (Perianez & Abril 2014). Perhaps even more puzzling, there is a time lapse of several decades between the eruption and the downfall of Minoan society. However, recent disaster studies stress that evaluating the response of a society impacted by a natural hazard should go beyond solely physical hazard assessment and event-focused reactions (e.g. Oliver-Smith and Hoffman 2002; Wisner et al. 2004). In other words, disasters are inherently multidimensional and they unfold over time, often even over considerable periods of time (Oliver-Smith 2002). As such, it is essential to appraise the social and cultural determinants of their nature and extent.

Arguably, the Santorini case epitomises the difficulty to unravel the response, and its underlying mechanisms, of a human society subjected to a catastrophic natural event such as a large volcanic eruption. It provides one of the most intriguing examples where the complex relationships and interactions between volcanic hazards and socio-cultural traits may have shaped the level and duration of social disruption. Shedding light on this problem necessitates the recognition of culture, including the interplay of belief and knowledge systems of various kinds, as a critical component mediating the volcanic disaster and exacerbating or mitigating its impact (e.g. Lavigne et al. 2008; Bachri et al. 2015; Torrence 2018).

Historical background

Since at least 2000 BCE, the island of Crete (Fig. 1) was home to an elaborate palatial culture that focussed on a series of complex monumental structures that have been called ‘palaces’ and which were essentially public court-centred buildings with ceremonial, religious, economic and probably also political-administrative functions. Primarily meant to enhance social cohesion of the surrounding urban settlements and regions through a series of ritual practices, these so-called ‘palaces’ epitomise what is known since Arthur Evans’ excavations at Knossos as the Minoan civilisation. Built immediately after 2000 BCE, the first generation of these palace buildings was violently destroyed, either by human action and/or earthquake in the 18^th c. BCE. Even though ignored for a long time in archaeological literature, knowledge on the following Middle Minoan III period, roughly between 1675 and 1600 BCE, significantly advanced thanks to a series of recent studies (cf. Macdonald & Knappett 2014). While showing an increased pace of development at Knossos, they also illustrate at least a temporary decline in older palatial centres such as Malia and Phaistos while Knossos-inspired constructions are constructed elsewhere (Galatas, Kommos, Sissi, Palaikastro). These features, combined with other indications within the material culture (Wiener 2016), may provide some support for the claim of an increasing Knossian supremacy during this period. This would evidently have been accompanied by an agricultural overspecialisation and an intensification in the complexity of hierarchical and administrative structure, rendering the system potentially unstable and hence vulnerable (Hamilakis 1996; Haggis 2002). All palatial buildings, including those at Malia and Phaistos, seem again to have been damaged late in the 17^th c. BCE, in early Late Minoan IA in ceramic terms (henceforth LM IA) (Fig.1). Aegean archaeologists traditionally suggest that this destruction was caused by a massive earthquake, which is also attested on the island of Thera or Santorini, an island that like many other Aegean islands, had a material culture quite close to that of Minoan Crete. As on Crete, at the site of Akrotiri on Santorini, this so-called Seismic Destruction, acted as a catalyst of social, economic, religious and political change. On both islands, it provoked a new, more generalised, building boom and immediately preceded yet another phase of prolific artistic production, overseas trading and ritual elaboration (Doumas 1983; Palyvou 2005). This phase on Crete is known as that of the ‘New Palaces’ and the period is known as the Second or New Palace period, which is mainly, in ceramic terms, of Late Minoan I style.

Late Minoan I represents both the acme of Minoan civilisation and the prologue to its ruin 150 years later. Somewhere during this long period, Santorini volcano erupted. The precise absolute date of this event remains a matter of considerable discussion since traditional dating methods, primarily based on synchronisms with Pharaonic Egypt, indicate a date that is up to 100 years later than the date(s) suggested by dendrochronology, ice cores, speleothems and C-14 (Hoflmayer 2012; Wiener 2009; 2015). Partly because magmatic CO² that biases C14 dating (Holdaway et al. 2018), certain adjustments of scientific dating seem now to close the temporal gap and a date around the middle of the 16^th c. BCE (ca. 1550-1540 BCE) now appears as more likely (Friedrich et al. 2006; Heinemeier & Friedrich 2009; Cherubini et al. 2013; Cherubini et al. 2014; Ehrlich et al. 2018; Pearson et al. 2018). It is not unlikely that some palatial centres on Crete, such as those at Kommos, Galatas, Zominthos and Sissi, were destroyed or abandoned at or around the moment that the volcano erupted, in Late Minoan IA.

During Late Minoan IB (henceforth LM IB), between 1520 and 1450 BCE, fire destroyed most Cretan settlements and palaces and afterwards site numbers dwindle. Only Knossos shows during Late Minoan II, between 1450 and 1400 BCE, signs of renaissance and prosperity, but now with a Mycenaean veneer, especially materialised by the adoption of a new language, Greek, for its administration in Linear B, and entirely new burial customs. The Late Minoan IB destructions can really be considered as the collapse of the Minoan poly-palatial system and most of the conspicuous material correlates that characterised the acme of Minoan society disappear together with these ‘palaces’.

The question is: what caused the downfall of this culture?

Since the initial discovery of antiquities on Santorini and the subsequent geological explorations of the island by Ferdinand Fouqué in 1866, the eruption has been linked to the mythological destruction of Atlantis (Fouqué 1870; Figuier 1872, Nicaise 1885) and already in 1909, K.T. Frost suggested that the Atlantis myth could reflect the demise of Minoan Crete, the civilisation discovered by Sir Arthur Evans from 1900 onwards. Other myths as that of the Flood of Deukalion or Talos have likewise been connected to this event, as have been the Seven Plagues of Egypt (Ellis 1999; Zellinga de Boer & Sanders 2002). The archaeological evidence, however, paints a less dramatic picture. Following the recognition of LM IB fire destructions in the archaeological record, potential culprits were looked for. Because these destructions were absent from Knossos but very visible elsewhere, Arthur Evans blamed them on 'the tyrannous lust of domination on the part of the lords of Knossos' (Evans 1922: 348; 1928: 308). In 1939, John Pendlebury (1939) considered the fire destructions to be 'a deliberate sacking on the part of the enemies of the most powerful cities of Crete'. Only in the late 1950s were LM IB fire destruction deposits also found at Knossos showing that the site had not escaped the problems that the other settlements had faced (Hood 1962). By then, Michael Ventris had deciphered the Knossian Linear B tablets, proving that, by Late Minoan II, immediately after the fire destructions, the administration at Knossos was run by Mycenaean Mainlanders. From then onwards, the latter were considered as the agents of the LM IB destructions, progressively expanding their domination over the island and the Aegean (Hood 1986). Other scholars, however, blamed a series of devastating earthquakes as responsible for the LM IB destructions (Pichler & Schiering 1980; Warren 1991; cf. Jusseret & Sintubin 2017).

That the Santorini eruption was responsible for damage on Crete was, however, already recognised by Arthur Evans in 1922, who blamed some of the earlier, LM IA destructions at Knossos on the eruption (Jusseret 2014). This line of thought was categorically picked up by Spyridon Marinatos in 1939, who, having excavated the coastal villa of Amnissos on Crete, assumed it was devastated by the eruption and its accompanying tidal waves (Marinatos 1939; already Schoo 1937, however). Marinatos explicitly linked the LM IB fire destructions of Cretan sites with the eruption, believed to have been one of the largest in the history of mankind. He was followed in this by several archaeologists (e.g. Platon 1972) while others saw the eruption as causing a climate change, responsible for the Minoans’ downfall (Tsonis et al. 2010). The opening of the excavations at Akrotiri on Santorini from 1967 onwards by the same Marinatos, however, clearly confirmed that the eruption happened when Late Minoan IA ceramic styles, characterised by vegetal and floral decoration, were in use, while, at the moment of the LM IB fire destructions on Crete, a marine ceramic style was popular (Doumas 1983). The discovery of Theran ash in clear LM IA contexts in different sites on Crete (Fig. 1) and Rhodes from the late 1980s onwards, settled the chronological difference between the moment of the eruption and that of the fire destructions on Crete (e.g. Molloy et al. 2014; Driessen 2019).

Using all available evidence as well as theoretical principles of emerging disaster studies, Driessen & Macdonald (1997) recognised a pattern of modifications in the Cretan archaeological record after the eruption. By the time of the LM IB destructions, for example, many sites saw their internal circulation pattern changed with accesses to houses made more difficult, houses being subdivided, and enclosure walls being constructed. Agricultural and artisanal production was seen as receiving more attention while religious and artistic changes were noted. They also stressed certain features of the LM IB destructions: hence, in some settlements, only the palatial buildings burnt down in LM IB while the settlement was simply abandoned and elsewhere too, sites were abandoned and left empty. Some of the fires that brought down palatial buildings appeared to have been carefully prepared and in certain sites, the malicious destruction of some fine pieces of art took place. Moreover, many LM IB destruction contexts include hoards of bronze vessels or precious items, hidden beneath floors or vases, showing advance warning of disaster. All these features were considered as reflecting a crisis before the LM IB destructions, caused by humans. Since more detailed pottery studies had shown that the LM IB destructions were not a one-time event but on ongoing and long-term process, an internal crisis of Minoan society was suggested, triggered off by the Santorini eruption and its collateral damage. Their hypothesis was contested by some (Christakis 2014; Warren 2001) while incorporated in more general schemes of breakdown processes by others (Knappett et al. 2011). Using computational network analysis, Knappett and colleagues suggest that the Minoan collapse at the end of LM IB was one result of an incremental increase in exchange costs required to maintain commercial ties following the disappearance of Santorini as a key node in the network, with the remaining sites concentrating their exchange/trade efforts into a smaller number of stronger links at the expense of weaker ones.

Forensic volcanology?

Volcanic explosive eruptions are characterised by multiple hazards that can unfold at different times and in different places. They violently unleash tephra (a fragmented rock) and toxic gases into the atmosphere, often together with searing avalanches known as pyroclastic density currents. On volcanic islands and coastal volcanoes, the brutal entry into the sea of materials released by an eruption may initiate a tsunami. Other hazards, including lava flows, debris avalanches and debris flows can also occur. Because volcanoes are often located in densely populated areas, their eruptions can be particularly disruptive to society; they put lives and assets directly at risk. The destructive force of an explosive eruption materialises most strongly locally. However, for high magnitude events, disturbances can also be felt far away from the volcano. A large volcanic blast has the potential to blanket tens to hundreds of thousands of square kilometres with several centimetres of fine-grained tephra. To illustrate this, the rock material expelled by an eruption with a size comparable to that of the largest volcanic event of the last century (Katmai in 1912 in Alaska) is sufficient to bury the entire UK under 11 centimetres of tephra (Oppenheimer 2011). Even a few millimetres of tephra deposition can initiate a wide range of impacts on both the natural and built environments, with ripple effect in human society. Further, if the eruption injects a massive amount of sulphur gas into the atmosphere, cooling of the climate may ensue and the impact becomes global (Oppenheimer 2011 and references therein). Few places in the world would be immune if a volcano somewhere were to explode in a manner similar to some of the catastrophic eruptions that occurred in prehistoric and historic times.

In the span of human life, eruptions can change a landscape from forest to desert, degrade the global climate (the 1815 eruption of Tambora in Indonesia and more recently, the 1991 eruption of Mt. Pinatubo in the Philippines), induce great floods, and even bury entire cities (the Late Bronze Age eruption of Santorini which destroyed Akrotiri, the AD 79 eruption of Vesuvius which ruined Herculaneum and Pompeii, the 1902 eruption of Mt. Pelée in Martinique which devastated St. Pierre). Through the environmental havoc they create, they can deviate the cultural trajectory of society, its structure and functioning. Although such change is most likely to happen near the volcano where (almost) complete obliteration occurs, as on the island of Sumbawa, there is abundant archaeological and anthropological evidence that cultures that are more distal can also be impacted profoundly by a large volcanic eruption. Sheets (1979) and Dull et al. (2001) provides a fascinating description of the intersections between the voluminous eruption of Illopango in El Salvador, possibly in the first half of the sixth century, and society. Popocatépetl volcano in México is another example where an eruption precipitated social disturbances. The archaeologists Plunket and Urunuela (2006) believe that this eruption probably served as a catalyst to accelerate deep social transformation that was already on its way. In Ecuador, the ca. 2900 BCE and ca. 1200 CE eruptions of Cuicocha and Quilotoa, respectively, have been linked to modifications in agricultural practices in the Andes (Mothes 1998). In Melanesia, the work led by Torrence (e.g. 2009; Torrence 2016) highlights the complex relationships between the Papuans and volcanic disturbances of varying magnitude and frequencies. Around 13,000 years ago, Laacher See volcano in present-day Germany erupted and spread tephra across an estimated 225,000-km² area. This event triggered significant demographic fluctuations, which in turn resulted in a number of material culture transformations (Riede 2007; 2008).

Undoubtedly, volcanoes and their eruptions are crucibles of changes. However, it often proves difficult to establish firmly how these unfold and to disentangle causation from correlation. This is partly due to poor, or lack of, distal records of eruption-induced environmental disturbances, the trigger that may ultimately alter the trajectory of a society. Besides, the social response to these more or less severe perturbations in the physical environment can take various forms, which are inherently difficult to apprehend as they are shaped by the vulnerability and resilience of the affected population. Vulnerability and resilience are themselves complex traits; they are shaped by socio-cultural variables and evolve with time. Further, the effect of an eruption on a cultural group’s worldview may be long lasting, or may have acted as catalysts for social change not apparent until many years after the volcanic event (Torrence 2019). The long and still on-going debate surrounding the role played by the Late Bronze Age eruption of Santorini in the downfall of Minoan culture is an emblematic illustration of these difficulties (Driessen 2019). On the one hand, we currently lack substantial evidence of the environmental impacts of the eruption in the region and, on the other hand, we have only limited knowledge of the vulnerability and resilience of the Minoan culture that was affected. Overall, various interpretations of how past volcanic eruptions affected human society have emerged but, often, these have not been put to the test.

While being an essential component for appraising the significance of a past volcanic eruption as an agent of environmental and social changes, the destructive potential of the event as inferred from various measurements must be matched with impacts on the atmosphere, environment, climate and society. Knowledge of the magnitude, sulphur loading of the atmosphere and location of an explosive volcanic event of the past helps to infer the potential it had to degrade the global climate. When the eruption is strong enough, the sulphuric acid particles that derive from the sulphurous gases injected into the mid atmosphere may eventually be trapped in glaciers and ice sheets, leaving a readable chemical fingerprint. These data can sometimes be cross-checked with tree-ring anomalies, the latter being able to reveal temporary climate changes. For some of the very large volcanic events, historical accounts suggest a connection between climate alteration and crop failure, food shortage and even famine thousands of kilometres from the eruptive centre (Oppenheimer 2011).

There is temptation to use the magnitude of an explosive eruption to speculate on the distal environmental impacts from tephra (e.g. Riede 2018; Sevink et al. 2019). However, this metrics is too coarse and certainly captures neither the multiple nature of the tephra hazard nor the complex interconnections of their impacts on the environment (Ayris & Delmelle, 2012). In order to improve our understanding of the range of inter-relationships between a large volcanic eruption and distal societies, one needs to assess the types of physical and chemical volcanic hazards, and their likely intensity, which can exist at several tens or hundreds kilometres away from the volcano. Typically, this requires careful field observations in order to identify tephra layers preserved in soil profiles or in archaeological excavations. Modelling of tephra dispersion and deposition may complement the task, although in most cases insufficient data are available for parameterizing correctly the volcanic conditions at the source (Bonnadona et al. 2015; Biass et al. 2019). While often regarded as the primary driver of environmental impact, the thickness of a tephra deposit at some distance from the volcanic source is only one aspect of the hazard intensity; grain size, surface composition, hardness and even colour are the other tephra properties that may strongly dictate impacts on vegetation, soil and water (Ayris & Delmelle 2012; Arnalds 2013; Craig et al. 2016). For example, our recent work in Ecuador demonstrates that a few millimetres of fine tephra can be far more damaging to crops than a thicker but coarser deposit (Guevara 2015). The presence of salts on the tephra surface also considerably increases the potential for injury to plants (Ayris & Delmelle 2012). When fluoride is associated to the tephra, its deposition on soil and in water bodies may represent a serious health hazard to both animals and humans (e.g. Thorarinsson 1979; Cronin et al. 2000; Cronin et al. 2003; Weinsten & Davison 2004).

Recognizing that the impact of a volcanic eruption on society is the result of the complex interactions and intersections between people, environment, volcanoes and volcanic activity implies not only to describe the volcanic hazards but also the conditions of the natural and cultural environments in which they occur. This is to say that the exposure, vulnerability and resilience of the natural and human assets vary greatly from one place to another (Blong 1984; Aspinall & Blong 2015). Thus, obtaining information on the climate, ecosystem type, agricultural system, social, political and belief systems and eruption timing is essential to attribute impacts to volcanic hazards. However, discipline-bound forensic observations cannot encapsulate this complex realm of interactions. This is true for contemporaneous eruptions but even more so when dealing with past events. For example, the traces of previous agricultural practices may not be apparent in a modern environment, or the tephra deposit laid down distally by an eruption may have been thick enough for causing damage to agriculture but too thin for being preserved as a visible layer in soil profiles. Nevertheless, the impacts from past volcanic eruptions are recorded in diverse ways in archaeological assemblages that can be recovered through various methods (see below). Moreover, memories and records of eruptions in oral or inscribed forms offer a mine of information that can be decrypted and interpreted in terms of the nature of the volcanic hazard and its potential link to the identified environmental effect (Cashman and Cronin 2008; Fast 2008). Thus, it is only through the combination of volcanological environmental, archaeological and anthropological studies that we will able to unravel fully the changes brought about in the environment and society by a catastrophic volcanic event see also Riede 2018). Arguably, little effort has been made to adopt this approach and there is ample room for considerable progress. The reconstruction of the Long Island volcano eruption that occurred in Papua New Guinea some 300 years ago (Blong 1982) probably represents the most comprehensive attempt to confront observations from volcanology and anthropology.