The River Before The Chaos

At first, I don’t see it. I look up and down the massive outcrop of pumice, ash, and lithic fragments that were launched from the volcanic vent during the Minoan eruption over the years and I still don’t see it. It wasn’t until my partner, Ray, pointed it out that I finally notice it: an odd, cluster of rocks that don’t match the rest. Lisa, our instructor, wanted us to try to figure it out before she told us the story behind the rocks. She left my partner and I to think about it while we started our stratigraphic section.

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Left Picture: Whole outcrop. Right Picture: Zoomed in picture of unknown rock.

As we went to work, my mind kept wandering back to the cluster. I’m a very curious person. I like seeing how things work, how they get there, and what was involved in the process. This is the reason why I love geology. Every single rock has a story that connects to a different story, which is then traced to another and another. It’s in an infinite and intricate web of knowledge. So here was this cluster of rocks, and I had no idea how they got there. As much as I wanted to know, I focused on my stratigraphic column instead. After about an hour of working, Lisa came back to check on us. While I had no idea what it could’ve been, Ray thought that it was some kind of erosion. Lisa then excitedly took us into a river channel that had the same exact cluster of rocks. Little by little, the story started to come together. She explained that what we were looking at was river scouring. River scouring occurs when a river runs through a channel and starts to erode the surface. The faster the water runs, the more erosion occurs. Also, with more turbulent water, the bigger the rocks will be. The erosion cuts into the pre-existing rock and starts to deposit the rocks from the river. These rocks stick into the pre-existing rock and form a clast. With this in mind, this means that the water level was up approximately 13 meters up. We know this because when doing a stratigraphic section, we measure every bed or anomaly.

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Left Picture: River deposit. Right Picture: Holly and Katie standing in the river bed.

You might be asking yourself, what’s so special about a river deposit?? This river deposit is between two different beds, which can only mean one thing: something happened between Phase 2, which is pyroclastic surges, and Phase 4, which are hot pyroclastic flows (read Micah’s and Gracie’s blog for information.) These river scours are found in many places, such as Vylchada Beach and Cape Mavropetra. The rivers most likely formed as a result of thunderstorms created during the volcanic eruption. Thunderstorms sometimes occur during volcanic eruptions. What happens is after an eruption, hot ash rises and collides with the surrounding, cold air. The air expands and then cools, which causes water to condense and fall down as acidic rain. If the scour did occur from a rainstorm, it would have happened during the eruptions, since there is no break between Phase 2 and 4 (Read Holly’s blog for more information on Phase 2.) It was incredible seeing a river scour from modern times and one from thousands of years ago within walking distance from each other. It was such an “aha” moment when I actually opened my eyes and saw river scours throughout the whole river bed. Whether it was rainstorm or not, we know that water passed through the ash. It’s exciting because it gives us another piece of the puzzle. We have so many clues right in front of us. It’s just simply a matter of putting them together that helps us imagine the Minoan Eruption in all it’s glory.

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4 thoughts on “The River Before The Chaos”

  1. Marcella,

    Great post! I remember when Lisa to told us that she wanted us to do that specific stat outcrop and when she pointed that little unconformity out like she anted us to figure it out… Haha then she just left us when we still had no idea what the heck it was! Just tell us!”. It was a defiant ‘aha’ moment for me to.

  2. Marcella – I always get super excited when my students have “aha” moments in the field and your writing shows that. I am very happy with the way you explained this very simple, yet important process that shows breaks in time in deposition of rocks. Rocks have all of these hidden stories if you take the time to figure them out!

    At the end of paragraph 4 you say “With this in mind…the water level was 10-15 meters higher.” Couldn’t you say, based on your stratigraphic section exactly how high it used to be? I also think this paragraph could benefit from one sentence explaining why that is.

    There is an error in paragraph 5. The scour channel is eroding Phase 2 surges, not phase 3. Remember that phase 3 is not present at Vlychada. Later you explain this, so I think that was a just a mistake? Check the sentence and correct please.

    Overall, I am super proud of your effort. Keep it up this week!

  3. Nice post! I liked the way you set up the beginning I think many people who study geology, like we are now can say they share the feelings you were having. You made me feel excited for you once you saw the channel. Great job, I enjoyed reading your post 🙂

  4. Marcella,
    I thought it was great how you created a narrative in your post. You included your reader in your journey before you learned about the river scouring and it was like we went along with you and we also learned from Lisa what really happened there. Your narrative helped the piece flow and made it easy and fun to read. I also thought that the images you used were perfect because they were personal and fun, but they also showed your audience what you and your partner were seeing.
    Even though I am unfamiliar with this topic, you explained things in a way that I could easily understand. I’m sure that most people in your field already know what certain terms mean, such as river scouring, but I really appreciate that you took the time to explain these details. As an outside reader I make assumptions about what you are discussing, but when you explain these things it helps me understand not only your post, but your excitement as well! I was happy to see that you conveyed your excitement, thought processes, and passion about geology with us as well because I felt like I got to know you better and that made me even more interested in your topic. When you really care about what you’re talking about your passion shines through and I think that is what happened with this post. It was fun for me to read and your post was put together very well overall.

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