The Minoan eruption of Thera, also referred to as the Thera eruption or
Santorini eruption, was a major catastrophic volcanic eruption with a
Volcanic Explosivity Index of 6 or 7 and a dense-rock equivalent of 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, including the Minoan settlement at
Akrotiri, as well as devastating communities and agricultural areas on
nearby islands and on the coast of Crete due to a related earthquake and/or
tsunami. There are no clear ancient records of
the eruption, which seems to have inspired certain Greek myths, may have
caused turmoil in Egypt, and may be alluded to in a Chinese chronicle.
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 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. = Magnitude=
Research by a team of international scientists in 2006 revealed that the
Santorini event was much larger than the original estimate of 39 km3 of
Dense-Rock Equivalent, or total volume of material erupted from the volcano,
that was published in 1991. With an estimated DRE in excess of 60 km3, the
volume of ejecta was approximately 100 km3. If so, the eruption's Volcanic
Explosivity Index was 7. The volcano ejected up to four times as much as the
well-recorded eruption by Krakatoa in 1883. The Thera volcanic events and
subsequent ashfall probably sterilized the island, as occurred on Krakatoa.
Only the Mount Tambora volcanic eruption of 1815, Lake Taupo's Hatepe eruption
around 180 CE, and perhaps the Baekdu Mountain eruption around 970 CE released
more material into the atmosphere during historic times.
= Sequence= On Santorini, there is a 60 m 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. 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 7 m 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 flow and lava fountain activity and 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, lahars, debris flows,
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. During this period the area of the island was
smaller and the southern and eastern coastlines appeared regressed. During
the eruption period the landscape was covered by the pumice sediments. In some
places, the coastline vanished under thick tuff depositions, and 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 towards the lower ones. Volcanology
This Plinian eruption resulted in an estimated 30 to 35 km high ash 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 eruption also generated a 35 to 150
m high tsunami that devastated the north coast of Crete, 110 km away. The tsunami
affected coastal towns such as Amnisos, where building walls were knocked out of
alignment. On the island of Anafi, 27 km to the east, ash layers 3 m deep have
been found, as well as pumice layers on slopes 250 m 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.
Eruption dating The Minoan eruption is a key marker for
the Bronze Age chronology of the Eastern Mediterranean world. It provides a fixed
point for aligning the entire chronology of the second 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. Archaeologists have traditionally placed it at approximately
1500 BCE. Radiocarbon dates, including analysis of an olive branch buried
beneath a lava flow from the volcano which gave a date between 1627 BCE and
1600 BCE, suggest a date over a century earlier. Thus, the radiocarbon dates and
the archaeological dates are in substantial disagreement.
In 2012 one of the proponents of an archaeological date, Felix Höflmayer,
argued that archaeological evidence could be consistent with a date as early
as 1590 BCE, reducing the discrepancy to around fifty years.
Conversely, the radiocarbon dates have been argued to be inaccurate on
scientific grounds. This argument has been made in particular by Malcolm
Wiener. The primary problem is that 14C-deficient carbon, sourced from the
environment, might easily have affected the radiocarbon dates.
= Relative chronology= Archaeologists developed the Late Bronze
Age chronologies of eastern Mediterranean cultures by analyzing the
origin of artifacts found in each archaeological layer. If an 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 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 culture on Crete, LMIA is the baseline to establish
chronology elsewhere. The eruption also aligns with Late Cycladic I and Late
Helladic I cultures, but predates Peloponnesian LHI. Archeological digs on
Akrotiri have also yielded fragments of nine Syro-Palestinian Middle Bronze II
gypsum vessels. The Aegean prehistorians felt so
confident about their calculations that they rejected early radiocarbon dates in
the 1970s for LMI/LCI Thera, because radiocarbon suggested a date about a
century earlier than the "traditional" dates.
At Tell el Dab'a in Egypt, pumice found at this location has been dated to 1540
BCE, closer to the traditionally accepted date of Thera's eruption. This
matches the composition of the Thera eruption. This pumice has been
contentious since the 1990s, as it represents the most prominent supported
date that differs from the old chronology.
= Ice cores and tree rings= Greenland ice cores show evidence of a
large volcanic eruption in 1642 ± 5 BCE which was suggested as being associated
with Santorini. However, volcanic ash retrieved from an ice core does not
match the expected Santorini fingerprint. The late Holocene eruption
of the Mount Aniakchak, a volcano in Alaska, is now believed to be the source
of the minute shards of volcanic glass in the Greenland ice core.
Another method used to establish 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 of Scotch pines in Sweden. Bristlecone pine frost rings
also indicate a date of 1627 BCE, supporting the late 1600s BCE dating.
Procedural changes in how ice cores are interpreted would bring that data more
in line with the dendrochronological numbers.
= 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, 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 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 5 mm 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 devastated the Minoan coastal settlements. Another theory is
that much of the damage done to Minoan sites resulted from a large earthquake,
and the fires it caused, that preceded the Thera Eruption.
Significant Minoan remains have been found above the Late Minoan I era Thera
ash layer and tsunami level, and it is unclear whether these effects were
enough to trigger the downfall of the Minoan civilization. Some sites were
abandoned or settlement systems significantly interrupted in the
immediate aftermath of the eruption. As the Minoans were a sea power and
depended on ships for their livelihood, the Thera eruption likely caused
significant economic hardship to the Minoans. Whether these effects were
enough to trigger the downfall of the civilization is intensely debated. The
Mycenaean conquest of the Minoans occurred in Late Minoan II period. The
Mycenaeans were a military civilization. Using their functional navy and a
well-equipped army they were capable of an invasion. Mycenaean weaponry has been
found in burials on Crete. This demonstrates Mycenaean military
influence not many years after the eruption. Many archaeologists speculate
that the eruption caused a crisis in Minoan civilization, making them
vulnerable to conquest by the Mycenaeans.
= Chinese records= A volcanic winter from an eruption in
the late 17th century BCE has been claimed by some researchers to correlate
with entries in 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".
= Effect 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.
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. 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.
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's overcoming
the powers of chaos and darkness. = Greek traditions=
The Titanomachy The eruption of Thera and volcanic
fallout may have inspired the myths of the Titanomachy in Hesiod's Theogony.
The Titanomachy 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's 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.
= Book of Exodus= Geologist Barbara J. Sivertsen seeks to
establish a link between the eruption of Santorini and the Exodus of the
Israelites from Egypt in the Bible. See also
Timetable of major worldwide volcanic eruptions
References Further reading
Bietak, M. "Review—'A Test of Time' by S.W. Manning". Bibliotheca Orientalis
61: 199–222. Retrieved 2008-04-21. Callender, G. The Minoans and the
Mycenaeans: Aegean Society in the Bronze Age. Oxford University Press. ISBN
0-19-551028-3. Forsyth, PY. Thera in the Bronze Age.
Peter Lang Publishing. ISBN 0-8204-4889-3.
Friedrich, WL. Fire in the Sea, the Santorini Volcano: Natural History and
the Legend of Atlantis. Cambridge University Press. ISBN 0-521-65290-1.
Page, D. L.. The Santorini Volcano and the Destruction of Minoan Crete. The
Society for the Promotion of Hellenic Studies, London.
Warren PM. "The date of the Thera eruption". In Czerny E, Hein I, Hunger
H, Melman D, Schwab A. Timelines: Studies in Honour of Manfred Bietak.
Louvain-la-Neuve, Belgium: Peeters. pp. 2: 305–321. ISBN 90-429-1730-X.
External links Thera Foundation articles on
archaeology, chronology, geology, volcanology, etc.
Santorini Decade Volcano — Santorini's geology and volcanic history, the Minoan
eruption and the legend of Atlantis. The Thera Volcanic Eruption and the
Absolute Chronology of the Aegean Bronze Age - 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.
VolcanoWorld Information about the eruption with photographs
Thera 2006 Expedition – exploration of the submarine deposits and morphology of
Santorini volcano The eruption of Santorini in the Late
Bronze Age – Online doctoral thesis on the eruption, scientific analyses and
its environmental effects