Basement Rocks at the Ceiling: The Story of Mesa Vouno

I’m standing at the bottom of a 369 meter tall mountain, ready to walk up a 30% gradient trail (That’s approximately 1,210 feet for all you non-metric people). The trailhead (Figure A) looks inviting yet slightly menacing. The sun is beating down on me and its a long walk up. Mesa Vouno rises up like a god amongst kings in this island paradise. How did a (nonvolcanic) mountain end up as a part of this caldera island?

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Figure A: The trailhead at Mesa Vouno

After a few minutes of hiking, I came up to the first exposure of the rock. This rock was not of volcanic origin, unlike the rest of the island. This was undeniably limestone (Figure B), a sedimentary rock deposited in a shallow sea setting. It appeared to be slightly baked in appearance. How did it end up as part of the highest points in Santorini?

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Figure B: This limestone was slightly metamorphosed. Generally a greyish color. This outcrop had bands of white in it.

The answer lies within the complex tectonics of the Aegean Sea. The Aegean Sea is situated near a convergent plate boundary, meaning two plates are crashing into another. As this happens, one plate moves under the other. Under normal circumstances, this would simply create a volcanic island arc, but only 3 islands in the Cyclades (Greek islands) are volcanic. Unlike other convergent boundaries, this subducting plate is rolling back, meaning the plate is curling back under itself. In figure C below, two arrows point in a southwestern direction to denote the plate motion. The plate rollback mentioned before in turn causes the area closest to the rollback (near the bigger plate direction arrow) to move faster than the area farther away (the smaller plate direction arrow). As a result of these different movement speeds, the Aegean Sea is experiencing an episode of extension, leading to normal faulting. Figure C helps to visualize this. Other major faults around the area such as the North Anatolian Fault and the Dead Sea fault (not pictured on figure C) are forcing the entire Aegean Sea to rotate, adding more extension in places not accounted for by the plate rollback. As I go up the trail farther, the rocks record this extension and uplift in their morphology.

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Figure C: Map of the Aegean Sea Tectonics. (Piper and Perissoratis, 2003, 1). Santorini is shown here in a zone of crustal extension.

As previously stated, the Aegean Sea is and has been undergoing extension and normal faulting. Mesa Vouno and Profitias Ilias are parts of those faults; the footwall blocks. Faults work by a force of extension or compression (extension in this case) and force one block upwards (See figure D). This is how these basement rocks are found at the ceiling of the island.

Figure D: The extension denoted by the large arrows on the top pull the blocks apart, forcing the footwall block up and the hanging wall down. Mesa Vouno and Profitas Ilias are footwall blocks. http://hrsbstaff.ednet.ns.ca/mcallip/Geog10/chapter_4.htm (3)

Going up further, the limestone changed into a contact with a different rock type. This rock, called metapelite, is heavily metamorphosed and contained pieces of the lower limestone within (figure E). This metamorphism is seen in macro scale in figure F. As the limestone and metapelite moved up, metamorphism (heat and pressurization of rock realign crystal structure) warps and changes them. The Alpine orogeny (mountain building event that formed the Alps) can also be accredited for the metamorphism of this rock. The approximate age of these basement rocks at the ceiling is 50-23 M.a., in the Eocene.

 

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Figure E: Metapelite with limestone contained within. Notice the baked, platy surface: a characteristic of metamorphosed rock

 

This phenomena of fault blocks rising above the surface of the sea is the reason why the Cyclades exist. If there was no volcanic activity here in Santorini, this mountain Mesa Vouno, its counterpart Profitas Ilias to the north of it, and some other rocks in the vicinity of the two would be the only land here. That is a considerable size difference, as seen in figure F below. The red circled area roughly represents what Santorini would be like without volcanism.

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Figure F. Red circled with lines through represent the basement rocks of Santorini.

As I reach the top of the trailhead, the view behind is beautiful (figure G). The hike in blazing, sweating weather immediately pays off. The town of Perissa lies below. It took millions of years to build these mountains and it does not disappoint. At the very top there is a snack bar and a road with cars that leads to the real reason a trail exists up this way: Ancient Thira.

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Figure G: The saddle between Mt. Profitas Ilias and Mesa Vouno: the end of the hiking trail

At the top of Mesa Vouno exists the first settlement of the island after the last caldera eruption. The very trail I hiked up was most likely used by those who settled Ancient Thira: the Spartans. This ancient city still continues to stand in a ruinous state after thousands of years. The ruins are mainly composed of limestone, but also contain some rocks that are not found anywhere around the basement rocks; they are volcanic in nature (figure H).

 

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Figure H: The dark rusty-red rocks are not in-situ to this place. They must have been carried all the way up Mesa Vouno by the Spartans

Throughout Ancient Thira, there are carvings and inscriptions that are carved straight onto the limestone (figures I and J). The level of skill and time it must have taken to complete them is significant, considering how long ago they were carved (~3rd Century AD) (Friedrich, 2).

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Figure I: A carving of an eagle, the symbol of Zeus. This entire limestone carving also included a dolphin and a lion, and was a dedication to various Greek gods.
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Figure J: An inscription in the side of a limestone pillar. The distinctive “tearpants” weathering surface characteristic of limestone is seen here (the holes in the limestone surface).

The very end of the trail to Ancient Thira was a beautiful view. It overlooked all of the southeast part of Thira (the island). This city a thousand feet above the ground was the perfect strategic place to build a city for the ancient Spartans (figure K). Without the tectonics of the Aegean sea, this beautiful place and view would have never existed. This great mound of limestone and metapelite was deposited and took millions of years to get where it is today. The immense power of the Earth to lift rocks through faulting creates unique and beautiful islands all throughout the Aegean Sea. This is Santorini’s own basement at the ceiling: Mesa Vouno.

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Figure K: The very end of my traverse. The town of Perissa is below this spectacular view in Ancient Thira.

References:

  1. “Quarternary neotectonics of the South Agean Arc” D.J.W. Piper and C. Perissoratis. 14 April 2003.
  2. “Santorini”, Walter L. Friedrich. The Author and Aarhus University Press. 2009.
  3. “Chapter 4: Continents Adrift”. http://hrsbstaff.ednet.ns.ca/mcallip/Geog10/chapter_4.htm
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3 thoughts on “Basement Rocks at the Ceiling: The Story of Mesa Vouno”

  1. Hey I enjoyed learning about the movement and creation of non volcanic mountain formation while reading your entry. Good job using questions to engage the reader in your story and you explained your figures quite clearly. However there was one typo in your last caption. If you change ‘are’ to ‘is’ then it will be perfect. What you did well in this entry was the clear explanations and understandable background information you gave while explaining your photos. Keep doing that and you will not have any problems.

  2. You did a good job of incorporating our edits and I think the blog is more substantial as a result. Figure F doesn’t appear for me (not sure why…check on this…maybe it didn’t fully upload?). One of the most powerful things about that hike is reaching the top and realizing how much effort it must have taken the Spartans to build atop this steep, ominous rock protruding out of the sea. How did they get all their materials up that slope?!

  3. Really nice combination of the geology and the cultural setting it established. It’s crazy to think that Greek triremes were parked on some of those beaches. Fig. F not showing.

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