The Grand Finale 

During my time here in Santorini I have done a lot of thinking. Thinking about life, volcanoes, and most of all trying to wrap my head around the earth that I am standing on. I have found a spot of my own here, it is off a beaten path, where no one goes and it has incredible view of the Kameni shield volcanoes. I have sat there for hours just trying to imagine the transitions and the magnificent power behind the construction of Santorini. There were many processes and five phases that have contributed to building this beautiful island, but the final phase, also known as phase four, and the phase I will be focusing on in this paper was catastrophic, the exit of this eruption was nothing short of grand.

Learning about all of the eruptions and phases, understanding strat columns and trying to sketch outcrops, in a setting as intriguing as Santorini. Has been a little overwhelming. What I have done for my self to help me remember the stages of phases, types of explosions, thier properties, and how they are presented now, is breaking them up. Phase zero, was small, and a warning for the Minoan people that inhabited the island for more information on Phase zero you can Rachel Niesen’s blog post. Phase one was pumice fall, this was a dry, and hot phase. Phase two has bedding in the out crops that we have seen at our sites, so that tells you that this was the phase of surges, for more information on this phase you can read Ballistic Blocks, Steam Explosions,and Turbulent Flows? by Holly Buban. Phase three was the first super plinian eruption that incorporated water and wet Pyroclastic flows. These are the first four phases that aren’t too hard to remember. These all built up to the truly epic phase four.

Before I go on about this phase of the eruption and the elements of it let me give you a quick over view of what kind of volcano this is and how it works. Fira is built on a caldera volcano. Caldera volcanoes  are very explosive, usually an explosion from this type of volcano is a catastrophic event. This is because the type of magma that is in the plume (the magma chamber underneath the earth) is a felsic magma, felsic magma contains more silica therefore making the magma more vesicular creating a huge mushroom cloud during the eruption. Another factor that makes calderas a highly explosive volcano is that water is often present around, and in the middle of the vent, water acts as a volatile (Fig. 1). Making the area of Santorini a prime area, for one day and one night of true misfortune for the minoans that were living here at this time (1).

Figure 1 Basic Caldera

Now that you roughly know what this caldera looks like, try and picture the first four phases: the first one small. You can imagine ash falling all around you, the next explosion a little bigger, now with large amounts of pumice falling and you almost become  buried. Then, all of the sudden, you are swept away in a wave of of ash and lithic matter coming from the volcano. Carrying you like a wave in an ocean, tumbling and tossing you violently until the next one comes, and then the next one. For a second it’s quite then you see an ash cloud fly up in to the sky you can’t see the top of it, and a pounding nose knocks you over and then you run because you can see a huge cloud of ash and debris falling from the sky and covering everything around you. (Fig. 2) This brings us to phase four.

Figure 2 Caldera Showing all Four Phases

There were two parts to the fourth phase of this eruption, one hot and dry, and one wet and cold. The first phase was hot and dry, this means that there was no water coming into the vent during the explosions. This is the factor that separates phase three and phase four. The hot and dry phase happened because during phase three there was a wall being built around the vent. We call this a tuff ring. A tuff ring is another explosive volcano, that formed from the fragments being blown out of the volcano. Once this was built the water from the sea was no longer rushing into the vent and allowed the volcano to break through the crust and is start emptying the magma plume (1) (Fig.3).

Figure 3 Tuff Ring

If you can imagine a pile of small rocks on top of a big rock and for whatever reason the big rock on the bottom cracks and splits open, all of the little rocks will start to collapse in to the open space that the split created. This is what happened in part two of phase four, the magma from the chamber below the volcano was being emptied, and so the vent of the volcano started to collapse, leading to the widening of the vent. This allowed the water to once again enter the vent, making the second part of phase four wet and cold. The collapse of the volcano didn’t stop it from erupting, so the explosions were still occurring (Fig4) (1).

Figure 4 Caldera Collapse

This is where it starts to become complicated. Not only was all this happening at the vent of the volcano but volcanic weather was being created in the clouds above, and pyroclastic flows falling and then flowing throughout the land scape followed by tornadoes, creating scour channels. There was earth quakes and tsunamis. It is chaotic, but this is the grand finale of the Minoan eruption (1)! The finale, as epic as it sounds can be hard to imagine, it’s hard to incorporate all the elements that make this eruption so unique.

Thankfully throughout this class we have been working on piecing parts of the eruption together with outcrops, and cross sections, and sketching stratographic columns (Fig 5-6), making it easier to imagine what actually happened. In the field we can see the scour channels, we can see where the lithic fragments are more present, and based on that we see we can infer how powerful the eruption was at that time, or what happened to allow the lithic matter to settle the way it did. Giving us an open window to look into the past and see the eruption happening step by step, layer by layer, bed by bed.

Figure 5 Stratograpgic Column From Part One of Phase Four

 

Figure 6 Outcrop Sketch of Part Two of Phase Four

Going back to the beginning I am sitting on this wall that I have found, this all running through my mind. Thinking about the earth that we are living on, and how much power it holds. How that in less then 24 hours it can change a piece of land completely; how it buries ancient cities; how it can create five phases of one eruption that changed the world; how it can break its surface; collapse and then start to build again; all of this in less than one full day. It humbles me to know that I am living on a planet that holds so much magnificent power. Phase four was only one of five explosions that occurred during the Minoan eruption, but phase four captured this power, with is chaos, and phenomenons.

Refrences:

[1] Druitt T. H., 2014, New insights into the initiation and venting of the Bronze-Age eruption of Santorini (Greece), from component analysis, v. 794, p. 1-21, doi: 10.1007/s00445-014-0794-x

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5 thoughts on “The Grand Finale ”

  1. I really like your field sketches and your description of what a tuff ring is. It’s very cool that you can see evidence of a feature like that in the stratigraphic record, even though it was completely blown away during part two of Phase 4!

    Careful when you say, “felsic magma contains more silica therefore making the magma more vesicular creating a huge mushroom cloud during the eruption”, as this is not exactly right. Higher silica makes the magma more viscous, which traps the gases within and leads to a more violent eruption when the magma finally comes to the surface and releases the gas.

    I am equally humbled by the awesome power our planet holds, and how quickly it can be released. Nice topic for this post!

  2. Gracie,

    Good post. I really liked the sketches you made on notes plus! I did a couple of edits and drawings on the same app and I understand how frustrating it can be to make the pics right. Maybe fix a few sentences to help flow? I’m right next store and would be down to give 20 min of my time if you want help.

  3. Gracie – you did a great job of explaining the changes and power of phase 4 of the Minoan eruption while including your own unique voice and impressions. Excellent use of figures to show the evolution of this process over time. And your field sketches are really well done. I’m very proud of the work you have done here and am looking forward to your next post.

    paragraph 2 – I believe you meant for the first 2 sentences to be combined.
    paragraph 3, last line – Capitalize Minoans

  4. Gracie,
    Your topic was very interesting. It truly is amazing how powerful these geological phenomena can be. I really liked the transition you made in your introduction from your personal thoughts to introducing your topic. It flowed very well and gave me an idea of where your post was going. I also really appreciated that you let your reader into your head by sharing with us your thoughts about this topic. It made your post personal and let your reader follow along with your own thought process. While it was great that you mentioned outside sources and other students’ posts, it would have been nice to get a quote or a brief summary in addition to the referral. A reader may not have the time to read, or even be interested in reading, another post or article. By giving a snippet of information, you can intrigue them and help explain your own point better.
    My major suggestion for the future is to make sure to revise. There were a few grammatical errors that can be fixed in the future with revision. It’s often a good idea to step away from a piece after you write it and then come back to it with fresh eyes. Or even get an outside reader such as Ray who was kind enough to offer his eyes. This will help you catch any smaller mistakes that you may not have been focused on at first.
    Overall, very nice post with great information, but make sure to revise!

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