It’s Poppin’


Before taking any type of geology class, the only thought I had about volcanoes was how terrifyingly huge and explosive they were. I never would’ve thought that almost a year later, I’d be in Greece studying the eruption of the Santorini Volcano. Before getting to understand the development of Santorini, I had to first understand how a volcanic eruption occurs. 

Beneath the surface of the earth, a magma chamber is formed. A magma chamber is an enclosed space that holds magma and dissolved gases. There are three different types of magma: mafic, intermediate, and felsic. All magma starts out as mafic. Mafic magma has the greatest temperature and the lowest percentage of silica content. As the magma gets closer to the surface, the temperature decreases, but the silica content increases. If you put these two together, you get viscosity. Viscosity is how resistant the magma is to flow. For example, low viscosity is like oil, extremely runny. While high viscosity is like honey, very thick. In this case, mafic magma has low viscosity.(Figure 1)

Graph.jpgFigure 1, (Chart of Magma Types, the silica content, viscosity, temperature and volatiles.)

The longer the magma sits in the crust, the more volatiles (gases) are added making the magma more felsic. The magma becomes so felsic and highly viscous that it starts to stack creating a dome also known as what our professor calls the “cap.” The “cap” seals the magma chamber which increases the pressure inside. When the cap is removed or cracked, usually from earthquakes, the pressure is released and the gas leaves solution so rapidly the chamber produces a volcanic eruption, having the lava spread across landscapes.

In order to understand this concept, let’s look at this process in a different context. What really helped me was putting this concept into a geologic analogy. In order to see this work. Let’s use a soda bottle.magma chamber2.pngFigure 2, the comparison of a soda bottle and the process of an eruption.

Inside a soda bottle lies liquid soda mixed with carbon dioxide (CO2). The soda bottle is like the magma chamber (Figure 2) holding dissolved gases in an enclosed space. The magma is sealed by a cap just like the soda is closed with a cap.

If the soda bottle is shaken, the pressure increases because the cap is holding all of the liquid and gases inside. When removing the cap, the gases expand which explodes the liquid apart creating a messy, informational way of understanding a volcanic coke2Figure 3, the soda bottle being shaken and the pressure building up inside the magma chamber.

After the magma chamber empties, it starts to build up again. Again? I know. I was confused too. This is called periodicity. Periodicity is the eruptive frequency of a volcano. Periodicity of a volcano can depend on many things such as the composition of the magma or how the magma rises.

To understand periodicity, let’s look at the Santorini eruption. The islands of Santorini did not just form from one single event. The twelve eruptive phases and the four caldera collapses is what made the shape of Santorini. Each volcano eruption erupts at its own time and way. For a clearer understanding of the different layers refer to Jenna Chaffeur’s “Karavolades Stairs: A 600 step geologic wonderland.”

As I face the orange-yellow Santorini sky, overlooking the caldera, I now think about the gases building up under me. Beginning to understand how the earth is not just what I see. A magma chamber is like a shaken up soda bottle. As the magma sits in the magma chamber, it goes from mafic to felsic magma increasing the silica content and the addition of volatiles. The pressure creates a cap and once that cap gets slightly opened all the pressure is let out, the gases expand, leading up to a massive, scorching volcano. With the magma chamber empty, mafic magma begins to build again and it starts all back up. With all this information now embedded in my brain, I can never look at a volcano the same again. I will never just think of a volcano being terrifying and huge. I will think of how the volcano occurs, what really goes on underneath us and how it can affect the people, culture and the famous white and blue buildings this city is known for.




Friedrich, W, 2009, SANTORINI – Volcano – Natural History – Mythology;  Narayana Press, DanmarkThe Author and Aarhus University Press, 300 pages.


7 thoughts on “It’s Poppin’”

  1. Bri – thanks for incorporating all of my comments. The addition of the soda bottle pics and the diagram is informative. One critical fact check – magma becomes more felsic over time as it incorporates silica (not gases) and the increase in viscosity allows the magma to trap more gases. On your next blog post – have your note-taking partner take a good look at the explanations so that you can learn from one another. You should be proud of this post – i know you worked hard on it!

  2. Hi Briana,

    Your opening paragraph aptly explained what the rest of the post was going to be about. You write effectively for an audience that is not as informed as you are by defining unfamiliar terms and going into detail about concepts the average person would not know. An example of where you did this well is “After the magma chamber empties, it starts to build up again. Again? I know. I was confused too. This is called periodicity. Periodicity is the eruptive frequency of a volcano.” What is effective about this statement is that you introduce the term in the way it is meant to be used, then you define it for the people who would immediately wonder what it meant after reading it for the first time. Continue this pattern in future posts and it will work really well.

    This post had clear ideas and you represented yourself as an expert on the subject. There were a few instances in which you could expand on an idea or specify. One line, “For a clearer understanding of the different layers refer to Jenna Chaffeur’s “Karavolades Stairs: A 600 step geologic wonderland,” was a little difficult to process only because the reader does not have access to the same text, so we can’t get the same information from what this source might be. What you could do for this and future posts is quote or paraphrase from the text then–after writing out the ideas that add to your main points–you could cite the source and add that it could be useful for further reading.

    Something I noted in this post was that the final line seems a little out of place. For a post as strong as this, you want to end on a note of similar strength. A useful thing to keep in mind is not to introduce new ideas in the final paragraph. Though the city is not a new concept exactly, you didn’t go into too much detail about it in the rest of the post which is why it feels out of place as the final line. You could shorten the final line to only include the geography and volcano you discussed, or go back and write a bit more about it in the rest of the post. Either way, great work on this one!


  3. Hi Brianna,

    I’m sure one of the goals of the class is to show students how amazing volcanoes are, although I’m positive the labels huge and explosive can still apply!

    Great job explaining everything. You introduced new concepts and made sure to explain them. For example, as soon as you introduced magma, you instantly explained the different types and how they applied to volcanoes. Readers with extensive background in geology to readers who are just learning about this science can easily follow along with your post. Don’t forget to keep your audience in mind. Although this is a blog post–making it a little less formal than a research paper–you are explaining research-paper concepts on a platform that is readily available to anyone. All in all, I think you utilized the blog platform well.

    The diagrams also helped the reader understand the concepts you were talking about. Although, as a reader, I am left imagining the island’s volcano and landscape on my own. You could add photos of some of the locations around Santorini, which show what you are talking about (for example a picture of a volcanic “cap”).

    I enjoy the summary you provide in the end as it wraps things nicely for the reader. I’m looking forward to the next post!

  4. Hey, Bri!
    I really really enjoyed reading this post. It absolutely helped me understand the process going on under the earth. It’s crazy what nature is capable of.
    I think the soda bottle was a good analogy, especially for someone who might not understand what a volcanic dome is.
    The photos you used were extremely relevant to having your reader follow along with your analogy.
    Seriously, great job.
    So excited to read more from you!

  5. Hey Bri,

    Figure 1 = My favorite diagram from 112 ❤
    Anyways, great post. This is a very important lecture in 112 and you explain it well for your audience. This topic is basic to understanding everything about volcanoes and will be an important reference for future blog posts.
    This post could be strengthened by giving the reader time frames for the magma chamber evolution so the reader can comprehend the thousand year time bomb that is a volcano.
    So, what is Santorini Volcano’s periodicity? How can you determine the periodicity?


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