Cape Plaka: A Trail Through History

The day was June 06, 2018. My day began atop a landscape overlooking the Aegean Sea. The heat was blistering and the air was humid, but I will not forget what I saw this day. To the front of me is the Aegean Sea, but positioned to my right is the explosive history of Santorini. I examined the wall, taking in each gradational layer piled one on top of the other. It is unlike any view I have seen: the top most layer is colored a bright white, but the layer directly below it is a dark black, varying from brown to red, and in some areas back to white. To the human eye it is easy to see that the rock side isn’t one color, but rather, varying colors. Every layer here has a story, and color is a good indication of it. The different layers shown here were once part of something bigger; the different phases of the eruptions on the island. Today I will write about the four major explosive products that I observed throughout the hike.

Figure 1: This is the view I had from the Cape Plaka lookout. Presented here are the major explosive products that Santorini produced over the years, beginning as far back as 1.2 million years ago and ending around the 1613 BC. The top most layer as described above, is a bright white, and called the Minoan Tuff. The black layer beneath it is the Cape Riva Tuff.

Figure 2: This is the map of Santorini. Cape Plaka is located at the starred area of the map. This is where we began our hike. Note that Cape Plaka isn’t an actual volcano or vent, rather, it’s a deposit of the caldera explosions demonstrating the pyroclastic flows.

I began my hike down Cape Plaka around 11 in the morning. Surrounding me is the Minoan Tuff, also known as the explosive product that buried the Minoan civilization back in 1613 BC. The Minoan Tuff is composed of a thick layer of volcanic ash and pumice ( 80 – 120m) and it’s spread throughout most of the island. This layer is the result of the fourth caldera eruption of the island, also known as the Little Bronze Age eruption. It’s the last volcanic layer deposited on the island before civilization rebuilt itself. Due to wind, vent location, and the erratic nature of pyroclastic flows, this layer varies in thickness throughout the island.

Figure 3: As explained above, the white pumice layer is the result of the fourth caldera eruption, therefore making it the youngest volcanic deposit on the island. The temperature in this area is hotter than other areas because the rock it is composed of (pumice) is fast heating. Due to its felsic and rhyodacitic chemical composition, the pumice absorbs and retains heat easily. If a rock is light in color, like the figure above, it’s felsic, meaning the eruption must have been more explosive.

Beneath the layer of Minoan Tuff is the Cape Riva Tuff. This layer is darker in color due to it being less felsic in composition as seen in (figure 4) below. Rock color is an indication of explosivity, so even though this layer wasn’t as explosive as the eruption that deposited the Minoan Tuff, it still was explosive. The Cape Riva Tuff is was made from the third caldera eruption of the island. It was deposited on the island 21,000 years ago (21 Ka) and it’s the layer the Minoans would have walked on prior to the Minoan eruption! This is difficult for me to imagine considering the thick layer of pumice that covers it.

Figure 4: The black layer above is the Cape Riva Tuff. You can see the start of another eruptive layer directly below it.

As I continue my hike, I couldn’t help but notice another gradual change in the layering of the rock. So far, most of the hike down is composed of white colored rock and darker grey rocks. In this area, the rock changed from black to red. We stopped in this area and I came to learn that this layer is the result of the second caldera eruption, also called the Upper Scoria. Scoria is a rock that is typically red. The areas that appear more brown or red are oxidized, meaning that they’ve been altered high concentrations of water. The more red a rock is, the longer oxidation occurred. The Upper Scoria portion of Cape Plaka is 76,000 years old (76 Ka).

Figure 5: This is a picture I took of the Upper Scoria. As mentioned above, you can see that the rock has variants of brown and red, due to the oxidation process it underwent.

At the end of our venture, we came across the Lower Pumice and the basement rock. The Lower Pumice was deposited around 200-180 thousand years ago, and it’s the first volcanic material deposited on the island from the first caldera eruption. The basement rock is the rock that was here before volcanism occurred on the island. Prior to Santorini’s volcanic history, Santorini was made up of a small portion of limestone. This limestone is the primary material of the island, dating as far back as 50 to 30 million years ago (50 Ma)! The part of the island that is composed of the basement rock is considered the safest part of the island because it’s the most stable.

Figure 6: Here we see the basement rock (limestone) at the very bottom of the Cape Plaka cliff. It extends up towards the cliff and continues outward towards the Aegean Sea. A good indication of a volcanic rock’s age is the vegetation growth on top of it. The more vegetation there is, the older the volcanic rock layer could be.

It was mentioned during our hike that the information I provided above is not the only volcanic deposits on the island. What I mentioned above is a simplified version of the complex eruptive history of the island. Figure 7 below provides a more in depth look back into the eruptive phases of the island.

Figure 7: This schematic log shows the products of the 12 major pyroclastic eruptions of Santorini. (Druitt, 1999. Fig. 3.17, p. 23)

As our hike to the bottom came to an end, I came to appreciate the island for what it truly is. As I hiked down through Cape Plaka, not only did I begin to realize how complex the geologic history of the island is, but I also came to understand how deeply entrenched volcanism is in the topography of Santorini. When we began our hike back up, a few tourist stopped me along the way and asked, “Was it worth it?” I looked down at my sweat drenched body that had become slightly sunburnt from the blistering heat, and I told them “Yes, it was definitely worth it!”

References:

1. Kwak, C H. “Santorini Map and Guide.” Tripsavvy, 14 July 2017. Accessed 8 July 2018.

2. Druitt. The Geological Society. 1999, p. 25.

5 thoughts on “Cape Plaka: A Trail Through History”

Your introduction was amazing. As a reader I felt compelled to read more about what you had to say! Good job!

brittnleo says:

June 10, 2018 at 9:08 am

Thanks! I tried to make it intriguing, but I noticed that I lost the “narrative” part of the blog as I continued typing.

Reply

Brittany,

I was captured by the descriptors in your introduction and the diary style of your writing. These disappeared as you continued, until the last sentence in your post where I felt I heard you speaking and could picture exactly what you were feeling. In your next blog post, I challenge you to keep your voice and experience throughout the post. I think it was important that you included a map of the location in your post, as well as figure 7. For your figure 7, I thought it would have been helpful if you had circled the layers you described while walking down through the stratigraphy to help readers better understand the sections you were explaining. Good job overall.

brittnleo says:

June 10, 2018 at 9:02 am

Thank you for the feedback! Yes, I noticed that as I was typing, I gradually began to to lose my voice. I wasn’t sure how I could keep it in the diary format because the majority of the information I provided was more scientific in terms of writing. I’ll definitely work on bettering that! As for figure 7, I had initially tried to do as you suggested by circling the layers I described above. However, I had issues with notes plus, so it didn’t work out as planned. I’ll try to familiarize myself with it more.

Reply

Volcanic activity began here around 1.2 my ago (not 50 Ma – that was basement (non-volcanic) material). Please correct that in the caption of your first photo.

Your pictures would greatly benefit from annotations. While saying in the caption things like “the bright white layer” is good, drawing on the photo and labeling it is even better. Keep this in mind for your third post.

You refer to the thickness of the Minoan Tuff as “diameter”. That is not correct – please fix it.

The Cape Riva Tuff is certainly a product from a caldera-forming eruption (as you stated), but in the sentence before that you say that material was not very explosive. Please correct this conflict. Cape Riva is not as felsic as the Minoan Tuff, but it is not mafic. Please correct.

In the caption on the last picture note that vegetation cover is only good to use for volcanic rocks (lava flows). That rule doesn’t really apply to other rock types. Please correct that.

Good work Brittany, this really came together!