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Thera eruption
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The Minoan eruption of Thera, also referred to as the Thera eruption or Santorini eruption, was a major catastrophic volcanic eruption (Volcanic Explosivity Index (VEI) = 6 or 7, Dense-rock equivalent (DRE) = 60 km3) which is estimated to have occurred in the mid second millennium BCE.
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The Minoan eruption of Thera, also referred to as the Thera eruption or Santorini eruption, was a major catastrophic volcanic eruption (Volcanic Explosivity Index (VEI) = 6 or 7, Dense-rock equivalent (DRE) = 60 km3) which is estimated to have occurred in the mid second millennium BCE. The eruption was one of the largest volcanic events on Earth in recorded history. The eruption devastated the island of Thera (also called Santorini), including the Minoan settlement at Akrotiri as well as communities and agricultural areas on nearby islands and on the coast of Crete. The eruption may have contributed to the collapse of the Minoan culture. It has also sometimes been claimed to have caused climatic changes, but this is not known.
The eruption seems to have inspired certain Greek myths. It also possibly caused turmoil in Egypt and influenced the biblical Exodus stories. Additionally, it has been speculated that the Minoan eruption and the destruction of the city at Akrotiri provided the basis for or otherwise inspired Plato's story of Atlantis.
Eruption
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. Another famous volcano known to repeat a similar process is Krakatoa in Indonesia.
Immediately prior to the Minoan eruption, the walls of the caldera formed a nearly continuous ring of islands with the only entrance lying 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.
On Santorini, there is a thick layer of white tephra that overlies the soil clearly delineating the ground level prior to the eruption. This layer has three distinct bands that indicate the different phases of the eruption. Since no bodies have been found at the Akrotiri site, Floyd W. McCoy, Professor of Geology and Oceanography, University of Hawaii, notes that the local population had advance warning of the impending eruption, leaving the island prior to its destruction. However, 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 only a few months warning.
Recent research by a team of international scientists in 2006 revealed that the Santorini event was much larger than the original estimate of of Dense-Rock Equivalent (DRE), or total volume of material erupted from the volcano, that was published in 1991. With an estimated DRE in excess of , the volume of ejecta was approximately , placing the Volcanic Explosivity Index of the Thera eruption at 6 or 7. This was up to four times what was thrown into the stratosphere by Krakatoa in 1883, a well-recorded event. The Thera volcanic events and subsequent ashfall probably sterilized the island, as occurred on Krakatoa. Only the Mount Tambora volcanic eruption of 1815 released more material into the atmosphere during historic times.
Physical consequences
Volcanology
This Plinian eruption resulted in an estimated to high plume which extended into the stratosphere. In addition, the magma underlying the volcano came into contact with the shallow marine embayment, resulting in a violent steam eruption.
The event also generated a to high tsunami that devastated the north coast of Crete, away. The tsunami had an impact on 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 there are pumice deposits which could have been caused by the Thera eruption. Ash layers in cores drilled from the seabed and from lakes in Turkey, however, 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 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.
Date
The Minoan eruption provides a fixed point for aligning the entire chronology of the 2nd millennium BCE in the Aegean, because evidence of the eruption is found throughout the region. Despite this evidence, the exact date of the eruption has been difficult to determine. Current estimates based on radiocarbon dating indicate that the eruption occurred between 1627 BCE and 1600 BCE. However, this range of dates conflicts with the previous estimate, based on archaeological studies utilizing conventional Egyptian chronology, of about a century later.
Archaeologists developed the Late Bronze Age chronologies of eastern Mediterranean cultures by analyzing the origin of artifacts (for example, items from Crete, mainland Greece, Cyprus or Canaan) found in each archaeological layer. If the artifact's origin can be accurately dated, then it gives a reference date for the layer in which it is found. If the Thera eruption could be associated with a given layer of Cretan (or other) culture, chronologists could use the date of that layer to date the eruption itself. Since Thera's culture at the time of destruction was similar to the Late Minoan IA (LMIA) culture on Crete, LMIA is the baseline to establish chronology elsewhere. The eruption also aligns with Late Cycladic I (LCI) and Late Helladic I (LHI) cultures, but predates Peloponnesian LHI. Archeological digs on Akrotiri have also yielded fragments of nine Syro-Palestinian Middle Bronze II (MBII) gypsum vessels.
At one time, it was believed that data from Greenland ice cores could be useful in ascertaining the exact date of the eruption. A large eruption, identified in ice cores and dated to 1644 BCE (+/- 20 years) was suspected to be Santorini. However, volcanic ash retrieved from an ice core demonstrated that this was not from Santorini, leading to the conclusion that the eruption may have occurred on another date. The late Holocene eruption of the Mount Aniakchak, a volcano in Alaska, is proposed as the most likely source of the minute shards of volcanic glass in the Greenland ice core.
Another method used to established the date of eruption is tree-ring dating. Tree-ring data has shown that a large event interfering with normal tree growth in North America occurred during 1629-1628 BCE. Evidence of a climatic event around 1628 BCE has been found in studies of growth depression of European oaks in Ireland and in Sweden.
In 2006 two research papers were published arguing that new radiocarbon analysis dated the eruption between 1627 BCE and 1600 BCE. Samples of wood, bone, and seed collected from various locations in the Aegean, including Santorini, Crete, Rhodes and Turkey, were analyzed at three separate labs in Oxford, Vienna, Austria, and Heidelberg, Germany in order to minimise the chance of a radiocarbon dating error. Results of the analysis indicated a broad dating for the Thera event between 1660 to 1613 BCE. Also that year the radiocarbon-indicated date of the eruption of Thera was narrowed to between 1627 and 1600 BCE, with a 95% probability of accuracy, after researchers analyzed material from an olive tree that was found buried beneath a lava flow from the volcano. Because the tree grew on the island, the results may have been affected by volcanic outgassing, which would have skewed the accuracy of the radiometric studies.
Although radiocarbon indicates a 1600 BCE eruption dating, archeologists believe that the date is contradicted by findings in Egyptian and Theran excavations. For example, some archeologists have found buried Egyptian and Cypriot pottery on Thera that is dated to a later period than the radiometric dates for the eruption. Since the Egyptian historical chronology has been established by numerous archaeological studies, the exact date of the eruption remains controversial. If radiocarbon dating is accurate, there would be significant chronological realignment of several Eastern Mediterranean cultures.
Climatic effects
Hydrogeologist Philip LaMoreaux asserted in 1995 that the eruption caused significant climatic changes in the eastern Mediterranean region, Aegean Sea and much of the Northern Hemisphere, but this was forcefully rebutted by volcanologist David Pyle a year later.
Around the time of the radiocarbon-indicated date of the eruption, there is evidence for a significant climatic event in the Northern Hemisphere. The evidence includes failure of crops in China (see below), as well as evidence from tree rings, cited above: bristlecone pines of California; bog oaks of Ireland, England, and Germany; and other trees in Sweden. The tree rings precisely date the event to 1628 BCE.
Historical impact
Minoan civilization
The Minoan eruption devastated the nearby Minoan settlement at Akrotiri on Santorini, which was entombed in a layer of pumice.
It is believed that the eruption also severely affected the Minoan population on Crete, although the extent of the impact is debated. Early theories proposed that ashfall from Thera on the eastern half of Crete choked off plant life, causing starvation of the local population. However, after more thorough field examinations, this theory has lost credibility, as it has been determined that no more than of ash fell anywhere on Crete. Other theories have been proposed based on archeological evidence found on Crete indicating that a tsunami, likely associated with the eruption, impacted the coastal areas of Crete and may have severely devastated the Minoan coastal settlements. A more recent theory is that much of the damage done to Minoan sites resulted from a large earthquake that preceded the Thera Eruption.
Significant Minoan remains have been found above the Late Minoan I era Thera ash layer, implying that the Thera eruption did not cause the immediate downfall of the Minoans. As the Minoans were a sea power and depended on their naval and merchant ships for their livelihood, the Thera eruption likely caused significant economic hardship to the Minoans -- and probable loss of empire in the long run.
Whether these effects were enough to trigger the downfall of the Minoan civilization is under intense debate. The Mycenaean conquest of the Minoans occurred in Late Minoan II period, not many years after the eruption, and many archaeologists speculate that the eruption induced a crisis in Minoan civilization, which allowed the Mycenaeans to conquer them easily.
Chinese records
Some scientists correlate a volcanic winter from the Minoan eruption with Chinese records documenting the collapse of the Xia dynasty in China. According to the Bamboo Annals, the collapse of the dynasty and the rise of the Shang dynasty, approximately dated to 1618 BCE, were accompanied by "'yellow fog, a dim sun, then three suns, frost in July, famine, and the withering of all five cereals".
Impact on Egyptian history
There are no surviving Egyptian records of the eruption, and the absence of such records is sometimes attributed to the general disorder in Egypt around the Second Intermediate Period. However, there are connections between the Thera eruption and the calamities of the Admonitions of Ipuwer, a text from Lower Egypt during the Middle Kingdom or Second Intermediate Period.
Heavy rainstorms which devastated much of Egypt, and were described on the Tempest Stele of Ahmose I, have been attributed to short term climatic changes caused by the Theran eruption. This theory is not supported by current archaeological evidence which show no pumice layers at Avaris or elsewhere in Lower Egypt during the reigns of Ahmose I and Thutmosis III.
While it has been argued that the damage from this storm may have been caused by an earthquake following the Thera Eruption, it has also been suggested that it was caused during a war with the Hyksos, and the storm reference is merely a metaphor for chaos, upon which the Pharaoh was attempting to impose order.
There is a consensus that Egypt, being far away from areas of significant seismic activity, would not be significantly affected by an earthquake in the Aegean. Furthermore, other documents, such as Hatshepsut's Speos Artemidos, depict similar storms, but are clearly speaking figuratively, not literally. Research indicates that this particular stele is just another reference to the Pharaoh overcoming the powers of chaos and darkness.
Greek traditions
The eruption of Thera and volcanic fallout may well have inspired the myths of the Titanomachy in Hesiod's Theogony. The background of the Titanomachy may derive from the Kumarbi cycle, a Bronze Age Hurrian epic from the Lake Van region.
However, the Titanomachy itself could have picked up elements of western Anatolian folk memory as the tale spread westward. Hesiod's lines have been compared with volcanic activity, citing Zeus' thunderbolts as volcanic lightning, the boiling earth and sea as a breach of the magma chamber, immense flame and heat as evidence of phreatic explosions, among many other descriptions.
Atlantis
There is some archaeological, seismological, and vulcanological evidence that the myth of Atlantis, described by Plato, is based upon the Santorini eruption.
Biblical traditions
Researchers have hypothesized that some of the ten plagues resulted from the eruption of Thera; however, the presumed dates of the events of Exodus, approximately 1450 BCE, are almost 150 years after the radiometric date of the eruption.
According to the Bible, Egypt was beset by such misfortunes as the transforming of their water supply to blood, the infestations of frogs, gnats, and flies, darkness, and violent hail. These effects are compatible with the catastrophic eruption of a volcano in different ways. While the "blood" in the water could have been red tide which is poisonous to human beings, the frogs may have been displaced by the eruption, and their eventual death would have given rise to large numbers of scavenging insects. The darkness could have been the resulting volcanic winter, and the hail the large chunks of ejecta that spewed from the volcano. The tsunami that resulted from the Thera eruption could have been the basis for the parting of the sea, when the sea receded from the shore immediately prior to the arrival of the tsunami. Shallow areas of the sea would have allowed the Israelites, under Moses, safe passage across the Red Sea, while the ensuing tsunami devastated the Egyptian army. Exodus mentions that the Israelites were guided by a "pillar of cloud" during the day and a "pillar of fire" at night, and Colin Humphreys, Professor of Material Science at Cambridge University, has argued that a volcanic eruption perfectly fits "the description “pillar of cloud by day and pillar of fire by night”.
Further reading
External links
- on archaeology, chronology, geology, volcanology, etc.
- — Santorini's geology and volcanic history, the Minoan eruption and the legend of Atlantis.
- - A WWW companion site to: Sturt W. Manning, A Test of Time: the volcano of Thera and the chronology and history of the Aegean and east Mediterranean in the mid second millennium BC.
- with photographs
- – exploration of the submarine deposits and morphology of Santorini volcano
- – Online doctoral thesis on the eruption, scientific analyses and its environmental effects (by David A. Sewell, 2001)
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