The Clashing of Giants

I grew up in Anchorage, Alaska and have experienced my fair share of earthquakes. I remember when I was ten years old and I woke up to my bed moving back and forth. I thought my brother was playing a prank on me, but I quickly understood that this was not due to human hands. I was scared of course, but I was also curious about why the ground was moving so violently. 

It wouldn’t be until years later that I found out it’s because of plate tectonics. Our planet is made up of giant plates floating like sheets of ice on water that are about 100 km thick and are in constant motion (1). This first 100 km or so is called the lithosphere which is a rigid solid, and then below that is the more plastic solid asthenosphere. When two plates converge, the denser one will essentially sink into the earth like a rock sinking into liquid soap which creates a deep trench or, in other words, a subduction zone. These subduction zones create powerful earthquakes much like the one I experienced as a child in Alaska.

image

 

Figure 1: This shows the movement of the Eurasian, African, Aegean, and Anatolian Plates. It also shows the movement of the north Anatolian Fault (NAF). The red lines in the middle are the normal faults that the magma followed to create the Southern Aegean Active Volcanic Arc (SAAVA).

People experience similar earthquakes in the Aegean Sea because of the convergence of the African Plate and the Eurasian Plate, and this clashing of giants has created the Southern Aegean Active Volcanic Arc (SAAVA) (1). The story of the volcanic arc gets a little bit more complex though when you add in subduction rollback, the Aegean Microplate, the Anatolian Microplate, the north Anatolian Fault (NAF). Let’s start with picturing subduction rollback like a suction cup effect. The African Plate, when it descends into the earth, is dragging the Aegean Microplate with it like a suction cup against a piece of glass.

image

 

Figure 2: A cross section of the regional tectonics of the Aegean Sea showing the subduction of the African Plate and the pulling effect it has on the Aegean Microplate. The two pieces of land sticking up are metamorphic rock.

This pulling motion, from the sinking of the African Plate, is causing thinning of the crust on the northern side of the subduction zone where it meets the Aegean Microplate. Thus normal faults (extension) are creating a path of least resistance for magma to follow. If you look at Figure 2 they’re also uplifting metamorphic rock from deep within the earth. Metamorphic rock has been specially deformed from high levels of pressure and heat that become more intense as you delve deeper into our planet.

These normal faults though are getting younger the farther east you go because of the NAF. It goes the same for the volcanoes, meaning they’re becoming younger and are more active than the ones to the west. The southwest movement of the NAF is causing the Anatolian Microplate to move in a counter clockwise rotation which is creating an arc of normal faults, the volcanic arc!

The Southern Aegean Active Volcanic Arc (SAAVA) though makes for some of the most fascinating geology in the world, and yet there is still so much we don’t know about it. The clashing of the African and Eurasian giants 170 km below the surface is groundbreaking (1). To venture out on a boat through the Aegean and see all of this history first hand makes me wish I could see it all for the first time again and again. It is exciting how our planet lives and breathes every day.

Citations

[1] Friedrich, Walter, 2009, Santorini: Denmark, Aarhus University Press, 312 pages

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8 thoughts on “The Clashing of Giants”

  1. Aaron – first off, you are brave for tackling such a difficult topic. I didnt realize this during our edit session but the EAF on your map is in the wrong position! It does not pass through Turkey but to the east of Jerusalem. The suction cup analogy works SO much better. There are some important steps missing in explaining the normal faulting and magmatism. Maybe we can sit over a frappe and discuss. 🙂

    1. It definitely wasn’t easy, but it was fun! I’ll just take out the EAF completely since I didn’t really go into any detail on how it plays into the story. I’d love to get a frappe and talk about those steps too. 🙂

  2. Hello Aaron,

    Fascinating post. At first glance there is much geology jargon but you do well in describing these formations and processes so that an outside reader can follow along with the natural wonder of volcanic formation. Your introduction is solid in that it subtly introduces yourself and your topic. However, I would suggest more concise writing. This is more of a nitpicky point as your post is typically on topic and to the point, but some language in your first paragraph can be cut. For instance saying, “My soccer trophies fell off the shelf along with some rocks I had collected the other day,” is oddly specific and potentially detracts from a reading. Instead you can say that items fell from your shelves or simply cut the whole sentence as it is already clear what you are writing about.

    Your use of visuals greatly assisted my reading and overall, I believe you’ve done a nice job in depicting such complicated processes into a streamlined blog post. Your writing begins and ends on solid paragraphs stating your purpose for writing and your writing’s main ideas.

    Happy Writing,

    Jose Martinez

    1. Thank you so much for the help Jose! I decided to just take out the sentence completely, and I think it sounds a lot better. Your comments are insightful, thoughtful, and very much appreciated. Thank you again and have a wonderful day.

  3. Hi Aaron!

    I loved your blog! I liked that you included your experience in Alaska.
    As someone who had a pretty hard time understanding the concept of plate extension and compression, it was really helpful that you defined the terms.

    I also agree with Lisa that the suction cup analogy was really useful, it really put a picture in my mind as to how the subduction rollback process occurred.

    Can’t wait for your next blog, Aaron!

    1. Hey Jenna!

      I’m so happy that you liked my blog and that it helped you understand plate tectonics a little better! That means a lot because I thought your blog was written superbly.

      Thank you so much for the feedback and I can’t wait to read your next blog too!

  4. Hey Aaron,

    I like the giant link ☺
    Such a difficult concept to tackle and you did well. This is a good, quick-and-dirty explanation to a concept that took a whole lecture to understand. Two comments to strengthen your figures:
    1- Your first figure is essential to the big picture, but a legend defining the subduction symbol, volcanoes and normal faults, and the strike slip fault would be beneficial to your readers.
    2- Your second figure has two concepts that could be better portrayed if split. If you did a ‘Before’ and ‘After’ of the slab rollback this would show your reader what a normal subduction zone looks like and what changes during slab rollback (i.e. the normal faulting and angle of the subducting slab).
    You made a hidden point when saying Alaska experiences the same earthquakes as the SAAVA since Alaska is also on a subduction zone. So what are the similarities and differences between the SAAVA and the Aleutian Islands? Is the subduction zone near Alaska also experiencing slab rollback?

    Well done.

    Alex

    1. Hi Alex,

      I just wanted to say thank you so much for the feedback! This was a very intimidating blog to write because the tectonics of the SAAVA are so complex, and there’s still a lot that I didn’t touch on. Your comments are greatly appreciated, and I will try to incorporate those into my future blogs.

      Kindly,
      Aaron

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