The Ultimate Collapse

I started out my day sweating more than I would like, staring up at a large wall of rocks. It was weird because I never thought I would be doing that, let alone in Santorini. The sun was sweltering hot, sweat was dripping from every part of my body, and I could feel the stinging of my burning skin. Against my instinct I turned my body away from the beautiful crystal blue water crashing against the rocks under my feet. I sat uncomfortably with my feet and legs falling asleep on the hot rocks. We were learning about part of phase 4 of the Minoan eruption at Cape Mavropetra.

There were 5 phases of the Minoan eruption, each differing by how the volcano was erupting. When looking up at the deposits from the Minoan eruption (around 1613 BC), there are distinct layers that you see; each of these is a phase of the eruption [1].

As I sat there staring up at the massive wall of rocks in front of me, I tried to make sense of what I saw. Lisa was having us draw outcrop sketches which meant we sat there staring up at the wall, studying it, to try and understand how everything got there. Above phase 3 was the part of phase 4 we were studying for the day (image 1). Looking up, there were thinner bands of pumice and ash that were a light tan color. At the bottom of the layer there were huge lithic fragments.

Overall this bed of phase 4 was  full of lithic fragments.  These were not the same lithic fragments that we had been seeing for the past two weeks. These lithic fragments are from every volcano (shield, cinder cone, composite cone, tuff ring, and dome) that had built up this island and even the basement rock that was here before the volcanoes. Not only are the lithic fragments every type of rock, there are also an incredible amount of them, unlike anything we had seen anywhere on the island (seen in the image below). They were red, grey, and many shades of black, scattered chaotically throughout, but also in bands of their own along the wall. 

image1
Image 1: Lisa showing the class where phase 4 cold was deposited.

You might be wondering how all of these lithic fragments got there just like I was. These lithic fragments were carried by a mix of pyroclastic flows and surges. These pyroclastic flows deposited the heavier rocks before the lighter rocks which is why this part of phase 4 has so many lithic fragments.

The lithic fragments in the deposit are the same ones that make up the beach. The only difference is that the rocks on the beach have been rounded from years of water rushing over them from the ocean.

image3
Image 2: This shows the lithic fragments in the cliff. The same lithic fragments make up the beach.

This part of phase 4 was a phreatomagmatic eruption. Phreatomagmatic eruptions are eruptions where water pours into the vent where it mixes with the magma and instantly turns to steam which causes shallow explosions and eruptions. It is like pouring water into a hot pan and watching it immediately turn to steam. The water also cools the temperature of the eruption to around 200-300 degrees celsius causing the pyroclastic flow to be wetter. In the case of this phase of the Minoan eruption, the vent was emptying, meaning it was releasing all of its stored up magma. When most of the stored magma had been ejected from the magma chamber, the dense rocks around the vent caused a collapse and then  water poured into the vent. Instead of causing shallow eruptions, the seawater rushed in and caused the pyroclastic flows and surges. 

The explosions and collapse would have blown the vent out along with the remainder of the magma in the chamber. Since the vent area had rock from all of the volcanoes making up the island, cinder cones, shield, composite cones, domes, and others, those rock fragments became part of the flows and surges.

While sitting in class that night after having stared at the massive wall of rock, and analyzing and imagining what the eruption could have looked like, Lisa told us something that would forever change my view of the island. She told us that with evidence from ash and pumice that was deposited in Crete and western Turkey, and deposits from the tsunami (a result of the caldera collapse), the whole Minoan eruption probably went down in around 24 hours. That left me speechless in class, and even now, two days later, I am having trouble grasping the fact that this beautiful island was changed so drastically in that short amount of time.

Sitting on the beach in the sweltering sun, drenched in more sweat than I care to admit, looking up at a wall of rock deposited there by pyroclastic flows and surges, was a helpful step in understanding just what happened during the Minoan eruption. I also learned that all of the lithic fragments, and rocks on the beach that came from the deposit, were from all of the volcanoes that helped build up the island. I solidified that knowledge while sitting in the breakfast room and finally learning that this massive caldera collapse happened in just around 24 hours. It amazes me that something that took thousands of years to build up was destroyed in such a short amount of time. As I sat with my classmates that night reflecting on what we just learned, I marveled in the wonder of this beautiful island and how the chaos turned into beauty.

  1. Druitt, T, 2014, New insights into the initiation and venting of the Bronze-Age eruption of Santorini (Greece), from component analysis: Bull Volcanol, vol.  , 1-21.
  2. To learn more about pyroclastic flows and surges, refer to Jessica Aerts’s blog “The Forces that Drive Rock” !
  3. If you want to learn more about the first part of phase 4 of the Minoan eruption, go read Jenna Chaffeur’s blog “To The Moon, Pyroclastic Flows, and Beyond!”!
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3 thoughts on “The Ultimate Collapse”

  1. Hi Erin,

    I have to admit I really enjoy the way you began your post. It makes me thankful to be inside with AC, although it also makes me want to get up and book a ticket to Greece!

    Something I had a hard time understanding was lithic fragmentation. From the reading I gather it has to do with the different rocks coming from the different volcanoes. However, because it’s a term used throughout the post, a concrete definition could help your readers with little to no geology knowledge better understand the terms and how they apply later in the post. You also mentioned the variety of volcanoes that make up the island. Before this post, I was under the assumption that the island was only made up of one volcano. Don’t assume your readers instantly know everything you do, by adding background information you can be sure everyone is on the same page.

    I really enjoyed the use of voice throughout the post. You utilized the blogging platform well—not too serious but not too light hearted either. The use of photos does help the reader picture what you’re talking about in their heads; however, maybe one or two more pictures could be beneficial. Pictures help the reader rest their eyes from the chunks of text and helps keep their interest. I also kind of wish there was a diagram of the entire island showing where the caldera was. This could help show those of us who aren’t on the island the drastic difference before and after the eruption.

    Can’t wait to read more about your adventures!

  2. Hi Erin,

    This is definitely an interesting topic, and I was interested by your personal reaction in your conclusion to the knowledge that the drastic Minoan Eruption only lasted 24 hours. After reading about the geological processes involved in the eruption, this was a major revelation that also surprised me. For me, your conclusion was the strongest part of your post because it clued me in about the significance of your topic to the overall makeup of Santorini.

    For the most part, your personal narrative was consistent throughout your post, and I liked how you took your audience through your own processing of this complex topic. Despite your narrative, I still felt a bit excluded as an outside reader. Much of your discussion about geological concepts was not introduced or thoroughly explained so that people outside of your class could easily follow along. For your last post, make sure that you do not simply describe what is happening and then jump into geological information. You have to slow it down for outside readers by guiding us along and providing transitions between your ideas so that we understand the connection. It also helps when you explicitly discuss geological concepts by explaining jargon and showing readers the significance of this information in relation to your topic. I am unfamiliar with the phases of the Minoan Eruption, so when I first started reading your post I was a bit lost as to what Phase 4 meant and why it was significant. As I continued reading I think I understood a bit more, but it seems like I am left on my own to figure it out. For outside audiences especially, being as explicit as possible early on is usually the best way to make sure your audience knows what you’re talking about and why.

    Overall, please make sure to focus on presenting your ideas and research to an outside audience that is unfamiliar with geological concepts and the significance in relation to Santorini. It’s better to be overly explicit when discussing ideas and correlations than leave readers on their own to assume things. You obviously have done thorough research, now you just have to present it so your audience can follow along.

    Marisa

  3. Kalimera Erin – Aside from the insightful comments from the interns, I would just add that any figures you use should have clear annotations on them. The first picture is annotated, but the reader is left to themselves to figure out what about the second picture is important. Don’t forget to provide detailed (and concise) captions as well.

    I really enjoyed your tone throughout this post. Keep that up! Lisa

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