Minoan Caldera: An essay on the Santorini Volcano

Introduction

The Mediterranean region has always been known as a “hot spot” for volcanic and tectonic activity. Italy and Greece, especially, have centuries of detailed histories of eruptions and earthquakes. Most of the truly dramatic events occurred thousands of years ago. The effects of the devastating natural events can still be seen today. One such example is the Minoan Caldera, more commonly referred to as the Santorini Volcano located on the island of Santorini in Greece (36.4200° N, 25.4317° E).

At the present, Santorini is a very popular tourist destination among the Greek islands. It is frequented by tourists wanting to experience Greek culture as well as the breathtaking beauty of the island chain’s landscapes. These beautiful landscapes were created through violent volcanic activity. The most famous volcanic activity to occur also happens to be one of the largest known volcanic eruptions in the past few millennia. It was this eruption that caused this shield volcano to collapse forming the caldera we see today. Santorini lies in an area where a northward subduction of the African plate with the European plate is occurring. This subduction is what causes the area to be so geologically unstable

Minoan Eruption

There have been several types of eruptions on Santorini. According to Dr Vic Camp, “The geologic record over the past one million years indicates that less explosive Strombolian and Vulcanian eruptions have occurred at Santorini about once every 5000 years, and that Plinian-type events have occurred about once every 20,000 years.” The largest such known eruption was a Plinian-type that occurred sometime in the Bronze Age.

Although there is still some debate as to when the eruption that gave shape to the Santorini we know today occurred, most scientists agree it happened around 1630 B.C. Through study and analysis it has been determined that the eruption occurred in four phases. The eruption was a Plinian eruption of enormous magnitude, with an estimated Volcanic Explosivity Index of 6.9. Only seven other eruptions in the past four millennia have equaled or surpassed the Minoan eruption (Camp). Below is an outline of the four phases as described by the ThinkQuest article, “The Minoan Eruption of Santorini”:

The first phase, lasting about eight hours, was marked by two Plinian columns, rising perhaps 36km, which distributed hot, coarse ‘rose’ rhyodacitic pumice that reaches 6m in thickness.

 

The second phase gradually became more hydrovolcanic as magma erupted violently within the flooded ‘Lower Pumice’ caldera. Ash and pumice exploded vertically and surged sideways and knocked down walls in Akrotiri. This second phase probably lasted about a day.

 

The third phase was also hydrovolcanic and was responsible for more than half the materials expelled by the Minoan eruption, forming massive chaotic layers of white rhyodacitic pumice, lapilli and ash, replete with blocks of old lava and bread-crust bombs. These beds reach up to 55m in thickness and are well displayed in the pumice quarry south of Phira. It was then that the Minoan caldera began to founder as lahars and ashflows surged down all the outer slopes of Santorini. This phase may also have lasted a day.

 

The final phase, which may have lasted only several hours, saw the expulsion of ochre-coloured pumice and ashflows, and the creation of the Minoan caldera. Its collapse began in the west and progressed eastwards … until a caldera some 8km wide and 9km long had foundered in the northern part of the island and joined the ‘Lower Pumice’ caldera where the Kameni Islands were later to erupt from the fractures created. Its confining rim still has steep walls, which, in places, rise 700m from its flooded base lying 380m below sea level. About 36km3 of pumice was ejected during these four days.

As you can see, the eruption that took place on Santorini was quite massive. So large and powerful, in fact, that research has shown that it generated tsunamis. Sedimentary deposits as far away from Santorini as Israel have been tested and linked to tsunamis caused by the Minoan eruption (Goodman-Tchernov, et al).

Effect on Inhabitants

 

As stated in the introduction, the eruption was strong enough to cause the collapse of the edifice of the volcano, creating a caldera; the land sank into the ocean. The island was home to an outpost Minoan civilization (thus the name, Minoan Caldera) which was very advanced for the Bronze Age. The eruption either destroyed or buried towns on the island. Some areas on Crete also show damage from a tsunami that was created due to the collapsing of the volcano, as well as pyroclastic flows pouring into the Aegean Sea.  As stated on the website, PhotoVolcanica, “It is … unlikely that the caldera formed without any tsunamigenesis, since it covers an area of about 65 square km and is approximately 1.6 km deep … Viewing the thickness of Phase 4 deposits on the outer coasts of the islands, it is clear that massive pyroclastic flows must have entered the sea at these locations. There is little doubt that such voluminous pyroclastic flows will lead to the generation of tsunamis.” Through excavation on Santorini, it seems as though the inhabitants were able to flee the island before the major eruption as they were most likely warned by the increase in seismic activity. Inhabitants of the towns that were hit by the ensuing tsunami in Crete, however, were not as fortunate.

The eruption was so catastrophic that it may have inspired the story of Atlantis, told and written by Plato. In Timaeus, Plato quotes Critias’ account of the legend, as told to Solon by one of the Egyptian priests:

 

 “Now in this island of Atlantis there was a great and wonderful empire which had rule over the whole island and several others, and over parts of the continent . . . But, there occurred violent earthquakes and floods, and in a single day and night of misfortune. . . the island of Atlantis . . .disappeared in the depths of the sea.”

Present Day

Today, the Santorini Volcano has an elevation of about 1204ft. Although no major volcanic events have occurred in the past few years, the volcano is still active. The last eruption occurred on January 10, 1950. This eruption is described in the article, “The Volcano Erupts: 20th Century Seismic Activity” on the Santorini.com website, “… an explosion blew the acid rock plug to the southern foot of the Niki dome, opening a vent for the new magma which began to pour out. This was punctuated by intense
As recently as 2012, the island of Santorini was in the news for a new development concerning volcanic activity. An expedition discovered that, between January 2011 and April 2012, the chamber of molten rock beneath Santorini’s volcano expanded 10-20 million cubic meters making the surface of the island rise 8-14 centimetres. Another way to look at this is that the new amount of molten rock underneath Santorini during this time is the equivalent of about 10-20 years of growth for the volcano (University of Bristol). Although this is no indication that another Minoan type eruption will occur, it serves to show us that the Santorini volcano is still active and poses risks for the surrounding area and its inhabitants (Santorini alone is home to about 14,000 people). A large underwater eruption could cause minor tsunamis that will have a drastic impact on the surrounding areas with negative impacts on shipping, tourism, and the general lives of the surrounding population. Most likely, however, an eruption within the next few years will be very similar to the 1950’s explosion, creating new volcanic rocks and domes. Volcanoes, however, can be very unpredictable and caution should always be used. explosive activity which spewed tephra 1000 meters into the air, and dropped lava fragments within a range of 850 meters all around. The phreatic explosions and lava flow continued until February 2nd, creating the youngest volcanic rocks in Greece and was named the ‘Liatsikas Dome’ after the Greek geologist…”. This was the last eruption to have occurred, however it is not the last volcanic activity the island has experienced.

Bibliography

               Camp, Vic, Dr. “How Volcanoes Work – Santorini Eruption.” How Volcanoes Work – Santorini Eruption. NASA, n.d. Web.17 June 2013. <http://www.geology.sdsu.edu/how_volcanoes_work/santorini.html&gt;.

“The Minoan Eruption of Santorini.” ThinkQuest. Oracle Foundation, n.d. Web. 17 June 2013.http://library.thinkquest.org/C0112681/Eng/Normal/Volcanoes_World/Accounts/Santorini.htm

Goodman-Tchernov, Beverly N., Hendrik W. Dey, Eduard G. Reindhardt, Floyd McCoy, and Yossi Mart. “Tsunami Waves Generated by the Santorini Eruption Reached Eastern Mediterranean Shores.” Tsunami Waves Generated by the Santorini Eruption Reached Eastern Mediterranean Shores. Geological Society of America, 27 May 2009. Web. 17 June 2013. http://geology.gsapubs.org/content/37/10/943.abstract

“Santorini (Thera) Volcano.” Santorini (Thera) Volcano. PhotoVolcanica, n.d. Web. 17 June 2013. http://www.photovolcanica.com/VolcanoInfo/Santorini/Santorini.html

“The Volcano Erupts: 20th Century Seismic Activity.” Santorini Volcano 20th Century Eruptions Santorini History Volcanic Islands Santorini Island Greece. Santorini.com, n.d. Web. 17 June 2013. http://www.santorini.com/santorinivolcano/volcaniceruptions.htm

University of Bristol. “Giant ‘balloon of magma’ inflates under Santorini’s volcano.” ScienceDaily, 9 Sep. 2012. Web. 17 Jun 2013.

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