In the Shadow of the Caldera, On the Brink of Subduction

As all great adventures do, ours began with a quest: to study the geology of Santorini. But before our studies could begin, we had to reach our destination. After three long flights, only a ferry ride stood between us and the island that would become our classroom, our playground, and our home for three weeks.

We left the port of Pireas near Athens around 7:30AM and settled in for our eight hour journey, which we knew would be made longer by our anticipation. The route we took made three stops at Paros, Naxos, and Ios between mainland Greece and Santorini. The ports we stopped at were marked by the signature Mediterranean architecture I had seen in the many pictures I had looked at while researching the trip. I was even able to pick out a few ancient ruins among the mass of white homes with blue doors and trim.

On the ferry to Santorini
On the ferry to Santorini

As we cruised by the islands, I began to wonder what they revealed about the geology of the region. How were they formed? How were they related to the caldera at Santorini? Luckily my questions were answered on our first day of class, the following day.

It all comes down to plate tectonics, a theory that was proposed by Alfred Wegener in 1915 (1). Santorini and the islands that we passed on our way from Athens all lay on the plate boundary between the Eurasian and African plates. The African plate is subducting beneath the Eurasian plate at a rate of about 5cm/year (1). As the subducting plate moves into the asthenosphere, the asthenosphere melts, and the resulting magma rises to the surface forming volcanoes. The series of volcanoes formed by this phenomena is known as a volcanic arc. The arc that Santorini is a part of is called the South Aegean Volcanic Arc.

Map of Subduction Zone

Now, you’re probably thinking what I was thinking when I learned this: the islands we passed on the ferry ride must be the other volcanoes in the arc, right? Wrong. The islands we passed are actually metamorphic islands, thrust up out of the Aegean along normal fault lines. But how? Here’s where things get interesting. As the African plate subducts, it is pulled back under itself. This movement creates a tensional force that causes the brittle lithosphere of the Eurasian plate to crack, forming the normal fault lines that built the metamorphic islands.

As much as I hate to think about leaving Santorini, I am looking forward to the ferry ride back to Athens; I’ll be seeing the islands through new eyes. There is something incredibly rewarding about being in the setting you are learning about. The more I learn and the more we are in the field, it becomes clearer to me that you cannot fully understand what you are learning about until you are there. You can learn about subduction zones and volcanic arcs for years, but it will never fully make sense until you stand in the shadow of the caldera, walk in the white washed pumice, and wash the tan ash from your hands and face.

Sources:

(1) Friedrich W. L., 2009, Santorini: Volcano, Natural History, and Mythology, Denmark: Aarhus University Press, 312 p.

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5 thoughts on “In the Shadow of the Caldera, On the Brink of Subduction”

  1. Awesome post. I couldn’t agree more about things becoming very real when you’re standing there in the field. Seeing is believing.

  2. I too really enjoy your conclusion. It really gives me a sense of who you are and transports me to remembering my own experiences. Also, I am impressed with your map making skills!

    1. You did such an awesome job explaining the formation of Santorini and the rest of the volcanic arc! You made a really complex process incredibly simple and easy to understand

  3. Hi Allaire,

    Your blog entry provides a very nice combination of experiential writing at the beginning and writing about geology. It moves your entry from a class paper to a blog post that draws in readers because now we are not just learning about geology, but we find out about how you situate your own experiences traveling to the region within the field of geology. Nicely done.

    Isn’t it amazing that already in 1915 we were introduced to plate tectonics? I would be really interested in learning more about what the theories were before Wegener proposed his concept of plate tectonics. A brief history on this would be great.

    Your entry shows that you had fun writing, and that you are really interested in this topic. It’ll be great to see more of your entries.

    1. I’ll have to look into some of the running theories before plate tectonics were introduced. I too would be interested in learning more about the going theories of the day before 1915. Thanks so much for he question!

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