The things that I witness and record from working on the volcanic island of Santorini never cease to take my breath away. My curiosity took control of me one day while I was conducting field work. While working on stratigraphic columns at such places as Cape Plaka and Vlychada, small discolored rocks kept appearing in the preserved Minoan eruption deposits. The rocks easily grabbed the attention of my eye for the colors that the rock held on its surface were nothing less than mesmerizing.
The red is that of the surface of Mars that is coated with iron-rich rock. The yellow is dusted over the surface as if someone sprinkled little flakes of the sun all over it. The orange can only be compared to that of a setting sun, a sun that sets over the horizon of an endless sea glistening over the waves. Finally the purple, it is as if flames of scorching temperature kissed the surface and stained the rock in misshaped ways.
Questions raced through my mind. Questions of where could this rock have come from? What caused the rock to have such bewildering colors? Are the rocks volcanic or did they arise from some other source? I yearned to know more about this tantalizing creation and the secrets it holds.
All these colors are found on a select few rocks here in Santorini. These rocks are lithic fragments that have been hydrothermally altered. Lithic fragments are pieces of the vent of a volcano that break free from the vent and end up in volcanic material such as pumice and ash. What I am interested in is the lithic fragments that have been hydrothermally altered. Hydrothermal alteration means that the rocks have been affected by gasses and water at a high temperature. This causes alteration of the rocks. The high temperature even crystallizes some of the minerals in the gas and those crystals end up on the rock.
There are two volcanic processes to hydrothermal alteration. The first process is magmatic. In this case, magma is decompressing and the gasses are making their way to the surface. As the gasses make their way to the surface they “stick” to the rocks and stain them due to the minerals in the gas. The second process is hydrothermal activity. This is where water is penetrating the ground and gets heated by the magma. Once hot, the water then returns to the surface. Again like the gasses in the magma, the hot water affects the rocks on the way up.
Presently, hydrothermal alteration is happening on the center island of Santorini, this being Nea Kameni. Fumaroles are currently being released from vents at the summit of Nea Kameni. These fumaroles are composed of mostly CO2, H2O, S, H2, and CH4. The rocks surrounding the vents are undergoing hydrothermal alteration as the minerals in the gases are getting deposited on the rocks. Fumaroles are also being released around Nea Kameni which creates hot springs. The hot springs are iron rich, as well as other chemicals, which stains the rocks a red color (1).
The Nea Kameni fumaroles are a result of magmatic degassing. Therefore, what is escaping from the vents at the summit are a result of the gases from deep in the magma chamber rising to the surface.
The evidence at Nea Kameni is an ongoing hydrothermal alteration event, but when looking at the Minoan eruption rocks with the same type of coloring and crystals can be found. Most of the discolored rocks are found in the first layer of the eruption which is called Phase 1. This is where the volcano had its first part of the eruption in which large amounts of pumice fall were deposited. The question is how did hydrothermally altered rocks end up in this volcanic deposit?
Water and fumaroles had to be involved before the first stage of the eruption began. Prior to the eruption, there was a preKameni dome which rested above the volcanic vent. This is where rocks would have been vulnerable to magmatic or hydrothermal alteration. It is possible that a lake or lagoon rested either partially on or surrounded the dome. This would have allowed water to penetrate the rocks around the vent and when heated by the magma it turned to steam. The steam would have then mixed with the minerals that came out of the gas and precipitated onto the surrounding vent rocks.
When the Minoan eruption began, these rocks would have been broken off the vent walls and shot through the air with other volcanic material. This is how these hydrothermally altered lithic fragments ended up in the Phase 1 layer of the Minoan deposit.
With almost 4,000 years of separation between the hydrothermal alteration that occurs at Nea Kameni and that at the time the Minoan eruption began, the processes are most similar. This is can be assumed because of the Principle of Uniformitarianism. This principle dictates that the geologic processes and rules that we view today can be applied to interpret those processes that may have occurred in the past. Therefore the process that can be viewed at Nea Kameni is giving the world a glimpse at what could have been going on almost 4,000 years ago.
If I had to choose one thing that truly captivated me during this study abroad program it would have to be hydrothermal alteration. From the moment I extracted the discolored rock from its 4,000 year old resting place, I knew that this is something that I had to share with others. The colors alone pull you deeper into the rocks grasp, and the history and process that altered the rock is the cherry on top. Until now, I did know the what beautiful artistry could come from such a dangerous volcanic process.
(1) Tassi, F., O. Vaselli, C, B. Papazachos, L. Giannini, G. Chiodini, G. E. Vougioukalakis, E. Karagianni, D. Vamvakaris, and D. Panagiotopoulos. Geochemical and Isotopic Changes in the Fumarolic and Submerges Gas Discharges during the 2011-2012 Unrest at Santorini Caldera (Greece). N.p.: n.p., n.d. Print.