The Minoan eruption was a catastrophic volcanic eruption that devastated the Aegean island of Thera (also called Santorini) 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 (VEI) of 7, it resulted in the ejection of approximately 28–41 km3 (6.7–9.8 mi3) of dense-rock equivalent (DRE), 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 (similar to 1816, the Year Without a Summer, after the 1815 eruption of Mount Tambora).
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 13–86 km3 (3.1–20.6 mi3) 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 28–41 km3 (6.7–9.8 mi3) DRE.
The study revealed that the initial Plinian eruption was the most voluminous phase, ejecting 14–21 km3 (3.4–5.0 mi3) magma and accounting for half of total erupted materials. This was followed by 3–4 km3 (0.72–0.96 mi3) DRE co-ignimbrite fall, 5–9 km3 (1.2–2.2 mi3) DRE pyroclastic flows and 5–7 km3 (1.2–1.7 mi3) 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 60 m (200 ft) 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 (BO1/Minoan A) of the eruption deposited up to 7 m (23 ft) 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 (BO2/Minoan B) and third (BO3/Minoan C) 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 (BO4/Minoan D) 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 30 to 35 km (19 to 22 mi) 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 35 to 150 m (115 to 492 ft) high tsunamis that devastated the northern coastline of Crete, 110 km (68 mi) away. The tsunami affected coastal towns such as Amnisos, where building walls were knocked out of alignment. On the island of Anafi, 27 km (17 mi) to the east, ash layers 3 m (10 ft) deep have been found, as well as pumice layers on slopes 250 m (820 ft) 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 (LM-IA) in the Crete chronology, late/end Late Helladic I (LH-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 workshops 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 (IntCal04) or 1569–1548 BC (IntCal20). 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 workshops 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:
In 2018, a team led by tree ring scientists 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, a study examining the bomb peak further questioned the validity of wiggle-matching of the olive branch, arguing that growth cessation could cause the radiocarbon dates of the outermost brand layer to differ by up to a few decades and potentially allowing the olive branch to 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 the 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 the 16th century BC, offering a way to at least mitigate the long-standing age disagreement. However, the exact year of eruption has yet to be settled. The table below summarizes the dating results: