Shaping the Landscape: A Topographical Change

When I think of topography, carved valleys, steep mountain slopes and flat plateaus come to my mind. It is the anatomy of the land and it can be used to enlighten anyone who may be inspired to further understand their surroundings. Lisa, my teacher calls this further comprehension of the land ‘spacial awareness’. I remember her saying, “You guys HAVE To HAVE TO understand where we travel on Santorini by map or you won’t learn anything!”. I am a land wanderer by nature so topography has been my hobby for a while. I like to study maps of where I have been and paste the stored memories of what I saw and experience into the contour lines of the canvas across my lap. What if I was a Minoan island goer from 1700 BC and Santorini was the land so familiar to me I called it home? Now what would my thoughts of my home be after the cataclysmic volcanic eruption of Santorini gave the land a major face-lift? 

In fact, the Minoan eruption drastically changed Santorini’s topography from its Bronze Age landscapes to its more recent slopes. Much of the island was completely ejected from the ground whereas other parts of the island received a significant extension of land. The layers of ash deposits increased the average elevation of Santorini by 60 meters in some parts. The volcanic ash has even gone to the extent of connecting masses of land together.

The Bronze Age or pre-eruption topography of the island was one solid horseshoe looking island ring with only one major passage into the islands giant bay (fig.1). When the volcano began to erupt, the vent, outlined in red, catapulted all the material from the north west into the sky. This explosion created a secondary water passage into the Santorini basin (fig.1).

 

The speculated sketch of the Pre-Minoan Eruption landscape of Santorini. The red dashed lines symbolize the land that the eruption exploded .
From the caldera rim, I can look across the from Fira, the town on Thira where we stay, and see the island of Therasia. This island was created when the north island connection was deleted from existence by the eruption. I can also see the very small island of Aspronisi to the south which was also isolated by the eruption. The explosion separated the main arcing island into two, three including Aspronisi, land masses that now make up the modern Santorini archipelagos (fig.2).

The Minoan eruption also layered the three islands with a varying thickness of ash and pumice called tephra. The great amount deposited impacted the topography of the islands. The thickest amount of ash has been recorded to be 60 meters[1]. However, the prevailing winds and elevation gradient had a defining role to play in the dispersive thickness of ash deposited island wide.

Topo
Figure 2: A modern day geological map of Santorini archipelago. The Dark green representing phases 1 through 3 of the eruption deposits and 4th phase represented by light green.
Phase one and two of the four main stages covered all of Thira with an average thickness of 15 meters from Oia in the north to Cape Akrotiri which is the southern tip of Thira island [1]. The phase one and two ash is found on Aspronisi and Therasia, however in much smaller quantities. Phase three covered all the land on Thira from Cape Plaka to just above Fira with an average thickness of 40 meters. Phase four was dispersed from just above Fira to Cape Mavropetra with a much less significant thickness. Also, south from Caldera beach to Vylchada, the thickness of phase four was deposited in immense amounts of 40 plus meters. Much of the ash, though it varies in thickness, matches the rolling topography of the pre Minoan surface.

Figure 3: The immense deposit of tephra reaches its greatest thickness at Cape Alonaki just south of Fira. I am standing at the base.
 The eruption deposited more than 180 feet of ash and pumice, however, there are some places where there is no ash or pumice even though it was well in range of the ash fall. Mt. Profitis Ilias is a good example of where there is no ash or pumice (fig.2). The mountain is 552 feet tall and is the highest point on Santorini. With its steep slopes, the ash and pumice that had fallen would have been eroded almost entirely away. However, there are still signs of volcanic deposits north of the mountain. The other reasons that might explain why there is an absence of volcanic deposits lies in the processes of the eruption phases 2, 3, and 4. The eruption pattern in these phases were not falling nor being lain down, but flowed across the land like that of a sporadically river. Mt. Profitis Ilias, being a high point, was out of reach to these flows and stayed untouched by the phases 2, 3 and 4. My friend Holly Buban explains these types of flows in her post Ballistic Blocks, Steam Explosions, and Turbulent Flows and I would suggest checking hers out if you wish to understand more.

figure 4: Taken from the saddle just south of Mt. Profitis Ilias, the image shows the Pre-Minoan surface sloping down right towards the beautiful city of Kameni. In the background, one can see the airport constructed on the ash and pumice deposits that added on to Thira.
The ash added a great amount of land to the east of Thira as can be seen in light green (fig.2). The ash here was in enough quantities to connect the small island called Monolithos to the main island of Thira. The ash and pumice driven extension was deposited very flatten East Thira and because of the plateau it created, an airport was able to be built for people like me who would rather fly 45 minutes to Athens than take a ferry 8 hours to he same destination (fig.4).

The Minoan Eruption completely altered the topography of Santorini in just 24 hours. The explosion and collapse of the caldera opened the inner bay of Santorini that was once completely shielded by its horseshoe geography and added another 60 meters of elevation across the landscape. The eruption flows extended much of the land to the east allowing Thera to reach out and grab the small neighboring island of Monolithos to be joined in an archipelago geological matrimony. I’m forever bewildered that such a process has the capacity to shape a landscape in just a blink of an eye.

Citations

[1] Druitt,T, Francaviglia,V, 1991, Caldera Formation on Santorini and physiography of the island in the Bronze Age, Bulletin of Volcanology, V54, N6, p484-493

[2] Friedrich, W. L., 2009, Santorini – volcano, natural history, mythology: Denmark, Narayana Press, pg 90-96

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4 thoughts on “Shaping the Landscape: A Topographical Change”

  1. Hi Ray,
    First, your images are great for this kind of blog! The initial image is creative and rouses jealousy as I sit here in a café, in Flagstaff, AZ, wishing that I too could be standing on a shoreline off any body of water! It it rains today, I just may take my umbrella and go stand by one of our rain barrels.

    All of your images are appealing for their simplicity and visual experience of what happened because of the Minoan eruption. I especially like the first map (is it from a text or your own?) because the colored lines provide an image that I can hold onto as I continue reading your description. Your selfie in front of the deposit of Tephra was a good choice because it helps me imagine what a lot of ejected materials just may look like.

    In addition to images, your choice of adjectival phrases are very helpful for one on the mountain in a desert. The only question that I have has to do with American education. I know that 60 meters are 197 feet (rounded up), but it may help your readers if you provide both the metric and whatever we call what we U.S. Americans use (It’s not Imperial, is it? Professor Skinner will know). I know that I find it useful to see conversions side-by-side. It helps me remember a few trivial measurements.

    Also, I see that you sometimes leave out words, and have a few typos. While it’s a not a big deal, it can become one later. Now is a good time to have an outside reader look for missing words, typos, and so on. Such writing hiccups means that your writer’s voice is quite strong. My guess is that even if you read over your post 3x, you’ll fill in the missing word in your head because you know it’s supposed to be there even if it is not. Outside readers are golden.

    I really liked your post. I learned a lot and now I’m looking forward to learning how the maps help you enjoy Santorini!

  2. Ray – I agree with Nancy. Your choice of adjectives and writing style clearly indicates that you are a strong writer and have a solid knowledge of how the island has changed geographically and topographically over time. Great post. I particularly LOVE your first map. Well done.

  3. Hi Ray,
    Wow, what a great blog. I was especially drawn in by your introductory paragraph, which provides contextual information, shows us that you are on location, and also introduces the concept of how historical periods are important when we are trying to interpret a geological event (the eruption means something else to a Minoan traveler than it means to a student in 2015).

    When I read through your blog, I am wondering whether you can make this connection to history a bit more obvious. Bring in your Minoan Island Traveler from 1700 BC and show us how you imagine her reaction. What would she have thought about? Would it be an act of the Gods? Would it be purely destruction? What would the ashes be for her? I know that this will all be supposition, but with the scientific detail (very nicely done) that you included, it might be super fun to read.

    I enjoyed learning from your blog. Nice work!

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