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Roger Weller, geology instructor

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.


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