Cochise College Student Papers in Geology
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Roger Weller, geology instructor
wellerr@cochise.edu
Santorini
by Latina Williams
Physical Geology
Spring 2007
The Eruption of Santorini
A Trip to Néa Kaméni in the center of the caldera. Courtesy: unknown source
Santorini is located in the Cyclades Island chain about 125 miles to the
southeast of Greece in the Aegean Sea. It is also home to one of the most
devastating volcanic eruptions in the last several thousand years. The
incredible eruption, which has also been known as The Minoan Eruption of Thera,
occurred during the Bronze Age. Radiocarbon dating on some samples has given us
a date range of 1630-1600 B.C., which has been corroborated by other samples
dated at 1654-1611 B.C. This eruption has become the single greatest event in
the Aegean Sea since the fall of Troy, and many historians and archeologists
believe this eruption is responsible for the loss of the Minoan civilization.
With an estimated dense-rock equivalent up to 61 cubic kilometers, this eruption
was by far the largest to happen on the planet in the last few thousand years.
The eruption was centered on the small island just north of the currently existing island of Nea Kameni, which is the center of the caldera. The caldera was formed several hundred thousand years ago by the collapse of the center of a circular island when the magma chamber emptied during an eruption. The northern part of the caldera was refilled by the volcano, but then collapsed again during the Minoan eruption. Prior to the eruption, the caldera formed a nearly continuous ring with the only entrance between the tiny island of Aspronisi and Thera. The Minoan eruption destroyed the sections of the ring between Aspronisi and Therasia, and between Therasia and Thera, creating two new channels.
The white layer at the top is Tephra left over from the Minoan Eruption. Photo
Courtesy: Robert Decker
The Minoan Eruption is considered a classic example of a Plinian type eruption.
This type of eruption is marked by columns of smoke and ash extending high into
the stratosphere. Another key characteristic of these types of eruptions are
large amounts of pumice thrown from the volcano and very powerful continuous gas
blast eruptions. The Minoan Eruption created a plume that reached 30-35 km in
height, as well as magma that came into contact with the shallow ocean waters
below. This contact between the magma and the ground water below the water table
caused another violent eruption known as a pheratic eruption. A tsunami was
generated from the eruption as well. It reached heights between 35 to 150m, and
devastated the north coast of Crete, 110 km away. Amnisos, one of the coastal
towns impacted by the tsunami, had walls knocked out of alignment, and the
Minoan fleet along Crete’s northern shore would have been destroyed as well. The
volume of materials ejected during the eruption is estimated to have been up to
four times more than what was thrown into the stratosphere when Krakatau erupted
in 1883. Recent archealogical research conducted by an international team of
scientists in 2006 indicates that the Santorini event was even more massive than
previously believed. As stated earlier, 61 cubic km of magma and rock were
expelled into the Earth’s atmosphere, compared to earlier estimates of 39 cubic
km as reported in 1991.
An exposed area of about 150 feet (50m) of
Minoan Tephra, which consists of pumice,
pyroclastic surge, and pyroclastic flow deposits. Photo Courtesy: Robert Decker
On Santorini,
there is a 60 m thick deposit of white tephra. Tephra is air-fall material
produced by the eruption regardless of composition or fragment size. Tephra
tends to be rhyolitic in composition as they are associated with explosive
volcanoes which have a high silica magma content. Santorini’s ash layer is
divided into three distinct bands indicating the different phases of the
eruption. Ash layers 10 feet deep have been found on the island of Anaphi, 27 km
to the east. Also found on Anaphi, have been slopes covered in pumice that
reaches 250 m above sea level, which have also been located elsewhere in the
Mediterranean. However, ash layers discovered in the seabed and lakes in Turkey
have shown that the heaviest ash fall was toward the east and the northeast of
Santorini. In Crete, ash found there is now known to have been from a precursory
phase of the eruption, which likely occurred weeks or months before the main
eruption, and had little or no impact. One area that was misidentified as to
having ash deposits from the Minoan Eruption was the Nile Delta.
Akrotiri Excavation Site. Photo Courtesy:
Robert Decker
Akrotiri was a Minoan
city on the south part of Thera. The city, which had a population of 30,000, was
covered in 3 to 6 feet (1 to 2 m) of ash. Since the city has been excavated, it
appears that the its citizens were successfully evacuated. No bodies have been
found at the site like those found at Pompeii. Also, it appears some movable
objects were taken from the city. This could indicate that the volcano gave some
kind of warning before the major eruption occurred. The thinness of the first
ash layer and the likelihood of this layer being washed away by winter rains
shows at most there was a warning months in advance instead of years, as
previously thought.
The impact of the Santorini eruption on human civilizations at the time are not
well understood, and still open to great speculation. Being able to date the
eruption would provide a fixed point in aligning the entire chronology of the 2nd
millennium BC in the Aegean because evidence of the eruption occurs throughout
the region. However, being able to pinpoint an exact date has been difficult.
Based on radiocarbon dating, the current opinion is the eruption occurred
between 1630 and 1600 BC. However, these dates conflict with the given date by
archaeology, which is around 1550 BC.
The Minoan eruption has also been linked to the legend of the lost city of Atlantis. Starting in 1939 with Spyridon Marinatos’s paper, the eruption is believed to have not only possibly caused the fall of the Minoan civilization, but also been the source or inspiration for Plato’s story of Atlantis. Detractors of the theory say that Santorini and Crete combined would not be the size of Plato's Atlantis, and the date of the Minoan collapse does not match Plato's dates for the fall of Atlantis. Scholars such as James W. Mavor and A. G. Galanopoulos argue that the error in date and size could be caused by a mistranscription of the Ancient Egyptian or Mycenaean Linear B symbol for "hundred" as "thousand". There would be little confusion in the visual appearance of hieroglyphic symbols of Egyptian numeric values; but if the Atlantis story does derive from Egypt, it has at some point been translated into Greek, which Galanopoulos suggests is the point of confusion.
Works Cited:
http://www.mystae.com/restricted/streams/thera/thera.html
http://www.decadevolcano.net/santorini/santorini.htm
http://www.mlahanas.de/Greece/Cities/Santorini.html
http://volcano.und.edu/vwdocs/volc_images/europe_west_asia/santorini.html
http://www.nat.au.dk/default.asp?id=11296&la=UK
http://www.therafoundation.org/