Minoan eruption

The Minoan eruption was a catastrophic volcanic eruption that devastated the Aegean island of Thera circa 1600 BC. It destroyed the Minoan settlement at Akrotiri, as well as communities and agricultural areas on nearby islands and the coast of Crete with subsequent earthquakes and tsunamis. With a Volcanic Explosivity Index of 7, it resulted in the ejection of approximately of dense-rock equivalent, the eruption was one of the largest volcanic events in human history. Because tephra from the Minoan eruption serves as a marker horizon in nearly all archaeological sites in the Eastern Mediterranean, its precise date is of high importance and has been fiercely debated among archaeologists and volcanologists for decades, without coming to a definite conclusion.
Although there are no clear ancient records of the eruption, its plume and volcanic lightning may have been described in the Egyptian Tempest Stele, though recent studies have disputed this based on the carbon dating of early 18th Dynasty artefacts. The Chinese Bamboo Annals reported unusual yellow skies and summer frost at the beginning of the Shang dynasty, which may have been a consequence of volcanic winter.

Eruption

Background

Geological evidence shows the Thera volcano erupted numerous times over several hundred thousand years before the Minoan eruption. In a repeating process, the volcano would violently erupt, then eventually collapse into a roughly circular seawater-filled caldera, with numerous small islands forming the circle. The caldera would slowly refill with magma, building a new volcano, which erupted and then collapsed in an ongoing cyclical process.
Immediately before the Minoan eruption, the walls of the caldera formed a nearly continuous ring of islands, with the only entrance between Thera and the tiny island of Aspronisi. This cataclysmic eruption was centered on a small island just north of the existing island of Nea Kameni in the centre of the then-existing caldera. The northern part of the caldera was refilled by the volcanic ash and lava, then collapsed again.

Magnitude

The magnitude of the eruption, particularly the submarine pyroclastic flows, has been difficult to estimate because the majority of the erupted products were deposited in the sea. Together, these challenges result in considerable uncertainty regarding the volume of the Minoan eruption, with estimates ranging between DRE.
According to the latest analysis of marine sediments and seismic data gathered during ocean research expeditions from 2015 to 2019, the estimated volume of the material expelled during the volcanic eruption ranges from DRE.
The study revealed that the initial Plinian eruption was the most voluminous phase, ejecting magma and accounting for half of total erupted materials. This was followed by DRE co-ignimbrite fall, DRE pyroclastic flows and DRE intra-caldera deposits.
This eruption is comparable with the 1815 eruption of Mount Tambora, the 1257 Samalas eruption, Lake Taupo's Hatepe eruption around AD 230, and the 946 eruption of Paektu Mountain, which are among the largest eruptions in the last two thousand years.

Sequence

On Santorini, there is a thick layer of white tephra that overlies the soil clearly delineating the ground level before the eruption. This layer has three distinct bands that indicate the different phases of the eruption. Studies have identified four major eruption phases, and one minor precursory tephra fall. The thinness of the first ash layer, along with the lack of noticeable erosion of that layer by winter rains before the next layer was deposited, indicate that the volcano gave the local population a few months' warning. Since no human remains have been found at the Akrotiri site, this preliminary volcanic activity probably caused the island's population to flee. It is also suggested that several months before the eruption, Santorini experienced one or more earthquakes, which damaged the local settlements.
Intense magmatic activity of the first major phase of the eruption deposited up to of pumice and ash, with a minor lithic component, southeast and east. Archaeological evidence indicated burial of man-made structures with limited damage. The second and third eruption phases involved pyroclastic surges and lava fountaining, as well as the possible generation of tsunamis. Man-made structures not buried during Minoan A were completely destroyed. The third phase was also characterized by the initiation of caldera collapse. The fourth, and last, major phase was marked by varied activity: lithic-rich base surge deposits, lava flows, lahar floods, and co-ignimbrite ash-fall deposits. This phase was characterized by the completion of caldera collapse, which produced megatsunamis.

Geomorphology

Although the fracturing process is not yet known, the altitudinal statistical analysis indicates that the caldera had formed just before the eruption. The area of the island was smaller, and the southern and eastern coastlines appeared regressed. During the eruption, the landscape was covered by the pumice sediments. In some places, the coastline vanished under thick tuff depositions. In others, recent coastlines were extended towards the sea. After the eruption, the geomorphology of the island was characterized by an intense erosional phase during which the pumice was progressively removed from the higher altitudes to the lower ones.

Volcanology

The eruption was of the Plinian type, involving rhyodacite, and it resulted in an estimated high eruption column which reached the stratosphere. In addition, the magma underlying the volcano came into contact with the shallow marine embayment, resulting in violent phreatomagmatic blasts.
The eruption also generated high tsunamis that devastated the northern coastline of Crete, away. The tsunami affected coastal towns such as Amnisos, where building walls were knocked out of alignment. On the island of Anafi, to the east, ash layers deep have been found, as well as pumice layers on slopes above sea level.
Elsewhere in the Mediterranean are pumice deposits that could have been sent by the Thera eruption. Ash layers in cores drilled from the seabed and from lakes in Turkey show that the heaviest ashfall was towards the east and northeast of Santorini. The ash found on Crete is now known to have been from a precursory phase of the eruption, some weeks or months before the main eruptive phases, and it would have had little impact on the island. Santorini ash deposits were at one time claimed to have been found in the Nile Delta, but this is now known to be a misidentification.

Eruption dating

The Minoan eruption is an important marker horizon for the Bronze Age chronology of the Eastern Mediterranean realm. It provides a fixed point for aligning the entire chronology of the second millennium BC in the Aegean, as evidence of the eruption is found throughout the region. Yet, archaeological dating based on typological sequencing and the Egyptian chronology is significantly younger than the radiocarbon age of the Minoan eruption, by roughly a century. This age discrepancy has resulted in a fierce debate about whether there is an upheaval in the archaeological synchronization between the Aegean and Egypt.

Archaeology

Archaeologists developed the Late Bronze Age chronologies of eastern Mediterranean cultures by analyzing design styles of artifacts found in each archaeological layer. If the type of artifacts can be accurately assigned, then the layer's position in a chronological order can be determined. This is known as sequence dating or seriation. In Aegean chronology, however, the frequent exchange of objects and styles enables relative chronology to be compared with the absolute chronology of Egypt, so absolute dates could be determined in the Aegean.
Since the Minoan eruption has been conclusively placed in late/end Late Minoan IA in the Crete chronology, late/end Late Helladic I in the mainland chronology, the contention concerns which Egyptian period was contemporaneous with LM-IA and LM-IB. Decades of intensive archaeological work and seriation on Crete in the last century had confidently correlated the late LM-IA with Dynasty XVIII in Egypt and the end of LM-IA at the start of Thutmose III. Stone vessels discovered in the Shaft Graves in LH-I are also of the New Kingdom type. Multiple archaeological sites of Theran pumice workshop used by the local inhabitants are only found in the New Kingdom strata. A milk bowl on Santorini used before the volcanic eruption has a New Kingdom pottery style. An Egyptian inscription on the Ahmose Tempest Stele recorded an extraordinary cataclysm resembling the Minoan eruption. Taken together, the archaeological evidence points to an eruption date after the accession of Ahmose I. The year of accession based on the conventional Egyptian chronology and radiocarbon-based chronology is either 1550 BC and 1570–1544 BC or 1569–1548 BC. The archaeological evidence argues for a Theran eruption date between circa 1550 and 1480 BC.
Proponents of an earlier date argue that Aegean-Egyptian pottery correlation allows considerable flexibility. Several other archaeological interpretations of LM-IA and LM-IB pottery differ from the "traditional" and could be consistent with a much earlier beginning time for LM-IA and LM-IB. Pottery synchronisms were also assessed to be less secure before the LM-IIIAI/Amenhotep III period. Pumice in workshop and the inscription on the Tempest Stele have been argued to only reflect the lower bound of the eruption age. The date of the production of pottery with the Santorini milk bowl style in other regions has not been determined and could pre-date the Minoan eruption. The chronology of stone vessel styles during this critical period is lacking.

Radiocarbon age

A major cause of inaccuracy in raw radiocarbon dates is fluctuation in the level of atmospheric radiocarbon. Hence, raw dates are adjusted with calibration curves which are periodically updated by international researchers. Derived calibrated calendar date ranges are highly dependent on how accurately the calibration curve represents radiocarbon levels for the time period. As of 2022, the most updated calibration curve is IntCal20. Early radiocarbon dates in the 1970s with calibration were already showing massive age disagreement and were initially discarded as unreliable by the archaeological community. In the following decades, the range of possible eruption dates narrowed significantly with improved calibration, analytical precision, statistical methods, and sample treatment. Radiocarbon dating has built a strong case for an eruption date in the late 17th century BC. The table below summarizes the history and results of radiocarbon dating of volcanic destruction layer with pre-2018 calibration curves:

Source	Calibrated date	Calibration used	Sample context and statistical method
Hammer et al., 1987	1675–1525 BC	Pearson and Stuiver, 1986	Weighted average of 13 samples from volcanic destruction layer at Akrotiri
Ramsey et al., 2004	1663–1599 BC	INTCAL98	Bayesian model of sequence of samples from before, during and after eruption
Manning et al., 2006	1683–1611 BC	IntCal04	Bayesian model of sequence of samples from before, during and after eruption
Friedrich et al., 2006	1627–1600 BC	IntCal04	Wiggle-matching of olive tree buried alive in pumice layer
Manning et al., 2010	1660–1611 BC	IntCal09	Bayesian model of sequence of samples from before, during and after eruption
Höflmayer et al., 2012	1660–1602 BC 1630–1600 BC	IntCal09	Tau boundary function on 28 samples from VDL Wiggle-matching of olive tree buried alive in VDL
Pearson et al., 2018	1664–1614 BC 1646–1606 BC 1626–1605 BC	IntCal13	Weighted average of 28 samples from VDL Tau boundary function on the 28 samples from VDL Wiggle-matching of olive tree buried alive in pumice layer

In 2018, a team led by tree ring scientist reported a possible offset of a few decades in the previous IntCal calibration curves during the period 1660–1540 BC. The resulting new calibration curve allowed previous raw radiocarbon dates to be calibrated to encompass a substantial part of the 16th century BC, making it possible for radiocarbon dates to be compatible with archaeological evidence. The measured offset was then confirmed by other laboratories across the world and incorporated into the most updated calibration curve IntCal20. In the same year, study of bomb peak further questioned the validity of wiggle-matching of the olive branch because the radiocarbon dates of the outermost branch layer could differ by up to a few decades caused by growth cessation, then the olive branch could also pre-date Thera by decades.
In 2020, speculation of regional offset specific to Mediterranean context in all calibration curves was reported based on measurements made on juniper wood at Gordion. If the regional offset is genuine, then calibration based on the regional dataset, Hd GOR, would place the eruption date back to 17th century BC. Others have argued that these site-specific offsets are already incorporated into the IntCal20 prediction interval since it is constructed from a much wider range of locations and any locational variation is of similar magnitude to the inter-laboratory variation.
While the refined calibration curve IntCal20 does not rule out a 17th-century BC eruption date, it does shift the probable range of the eruption date to include the majority of 16th century BC, offering a way to at least mitigate the long-standing age disagreement. However, the exact year of eruption has not been settled. The table below summarizes the dating results:

Source	Calibrated date	Calibration used	Sample context and statistical method
Manning et al., 2020	1663–1612 BC	Hd GOR	Bayesian model of sequence of samples from before, during and after eruption
Manning et al., 2020	1619–1596 BC 1576–1545 BC	IntCal20	Bayesian model of sequence of samples from before, during and after eruption
Şahoğlu et al., 2022	1612–1573 BC 1565–1501 BC	IntCal20	The youngest sample near victims from Theran tsunami layer at Çeşme
Ehrlich et al., 2021	1624–1528 BC	IntCal20	Eight scenarios of olive wood growth to account for possible growth cessation
Manning, 2022	1609–1560 BC	IntCal20	Bayesian model of sequence of samples from before, during and after eruption but more comprehensive to include samples from VDL, tsunami and distal fallout from across southern Aegean region
Pearson et al., 2023	1610–1510 BC 1602–1502 BC	IntCal20	Therasia olive shrub