At first glance, Santorini is a picturesque pastel paradise. White Cycladic buildings, churches with domes as brilliantly blue as the sea they overlook, even the thick pumice cliffs give the island its blissful ambiance. It has been a week since arriving on this angelic island, and we have swam in the ocean almost every day. This, being from Arizona, has been a much needed godsend, but the view was not at all what I was expecting. Unlike the pearly cities, the beaches we have visited are bejeweled with black porous pebbles.In our geology class, we have learned that the entire island was molded by multiple volcanic eruptions. The most recent Minoan eruption of around 1613 BC  blanketed the entire archipelago with white pumice stones (rock #1). So, why were these beaches the exact opposite of the surrounding environment? With a little guidance from our fabulous professor, I came to the embarrassingly simple conclusion. Density!
To the untrained eye, like my own, the 20 meter thick layer of Minoan ash and pumice is a spectacular white barricade. Take a closer look to the figure below, and you will see a clear band of large dark rocks sandwiched between the pumice (rock #2). This was caused by different stages of the historic eruption, and is a much heavier, denser rock type. These are andesite, a mafic to intermediate rock, meaning it was formed during the early stages of lava and have a lower silica content than pumice .
Before a large eruption occurs, a rigid dome forms above the volcanic vent. This essentially puts a cap on the volcano and traps magma in until the pressure builds enough to blow it off. These black rocks are fragments of the dome that were ejected during the eruption and thrown several kilometers away.
Aside from being great at rubbing calluses off of your feet, pumice is a light, vesicular volcanic rock that floats in water. This light material, along with ash, eventually washed away, leaving the dense andesite behind. Notice how the cliff on this beach below does not contain either pumice or andesite. This limestone was here long before the Minoan eruption and has watched the pumice come and go to form the beach.
The longer a rock is exposed at the surface of the earth, the rounder and smoother it becomes due to weathering. These rocks, over the course of centuries, have been rubbing, crashing, fracturing against each other to create beautifully smooth pebbles which line the captivating shores (rock #3).
Volcanic deposits, stratigraphy, and the life cycle of rocks may not at first seem alluring to those who are not geologists. I for one, as a civil engineer, never expected to travel across the planet to ponder how pebbles formed and how they got there. But as I sit on Kamari Beach “researching” this topic while sunbathing, I can’t help but to forebode over the idea of leaving this geologic paradise.
 Friedrich, W, 2009, Santorini: Aarhus, Denmark, Aarhus University Press, 312.
 Strickler, M, 1997, Mafic vs Felsic, University of Oregon, http://www.jersey.uoregon.edu