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.
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.
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.
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).
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.
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.
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!”
1. Kwak, C H. “Santorini Map and Guide.” Tripsavvy, 14 July 2017. Accessed 8 July 2018.
2. Druitt. The Geological Society. 1999, p. 25.