Volcanoes are exposed all over the islands of Santorini. Do these volcanoes act the same way or do they all behave differently? What makes them different from each other? What styles of eruption do these volcanoes have? Read more to discover how each volcano is its own piping hot mess!
The first volcanic rocks to appear above sea level in this region formed 645 +/- 92 Ka (Ka = thousands of years ago). These rocks compose the southern portion of the island, the Akrotiri Peninsula, as shown on the map and rose from the depths of the sea as circular, mound shaped domes. Volcanic domes are different from what we usually think of when we think of volcanoes. Instead of being chaotic with a large, earth-shaking explosion, the domes have an effusive eruption style. This means the lava oozes slowly out of the ground. The lava is rich in silica, attributing to its viscous quality that enables the domes to build upwards in a steeper manner. These domes are non-explosive and monogenetic, meaning they only erupt once. The domes build up slowly and, once they complete their formation, more and more domes pop up! While we don’t have many domes present in Northern Arizona, this event reminded me of the volcanic dome that formed on Mt. St. Helens after it’s eruption in 1980.
Not all of the volcanoes on the Akrotiri Peninsula are domes. Cape Mavrochidi, or Red Beach, is a cinder cone that formed 522 +/- 104 Ka. Cinders are small pieces of basalt, a mafic lava low in silica, that fly into the air after an eruption. The eruption style for cinder cones is called Strombolian and is similar to cooking popcorn. Water comes into contact with magma and expands into gas. Then….POP! POP! POP! Cinders are shooting out of the volcano just like popcorn at a movie theater! Although, its not butter and seasoning that give these cinders their red color. It’s oxidation! These cinders accumulate and build a cone-shaped volcano with a hole in the center. However, they can’t become too steep due to their shallow angle of repose, which is the angle at which unconsolidated material is stable. I was happy we were able to visit Red Beach since it reminded me of all of the cinder cones back home in Northern Arizona.
The next volcano that we were able to visit was Peresteria, a composite cone that formed 530-430 Ka. Located in the northern part of the island, this composite cone was formed from a strike-slip fault known as the Kolumbo line. This fault controls where the magma goes and is even responsible for creating Nea Kameni, Palea Kameni, and the Christiani Islands that are southwest of Santorini. Peresteria was originally much larger, but was blown up by all four of Santorini’s caldera forming eruptions. I compared this volcano to the composite cone near Northern Arizona University (NAU), the San Francisco Peaks, in order to help me visualize and understand how it formed. Composite cones have an intermediate composition, about 60% silica content, and a Plinian eruption style. This eruption style is explosive, gas-rich, and occurs in volcanoes with more silica. You definitely don’t want to pick a fight with these guys!
This next volcano is Megala Vouno, a shield volcano that erupted 76 Ka right next to Peresteria. The layers of Megalo Vouno look like pancakes stacked on top of each other that pile up next to Peresteria and the upper layers of Megalo Vouno flowed over the top of Peresteria like syrup. However, instead of a sugary breakfast, these layers were made of lava! Shield volcanoes are composed of the same basalt that creates cinders, but with a less poppin’ eruption. The eruption style of shield volcanoes is effusive, rather than Strombolian. Back in my home town in central Arizona, we have a shield volcano near our town center. It was interesting to see the different layers of the shield volcano exposed here on Santorini and makes me curious to see what the layers of the volcano at home look like.
The only volcanically active parts of Santorini are in the middle of the Santorini islands. These two islands, Palea Kameni on the left and Nea Kameni on the right, are resurgent domes with an effusive eruption style. Resurgent domes rebuild themselves after caldera forming eruptions. Volcanism here started in 197 BC with Palea Kameni, which was later faulted and exposed. Nea Kameni is the more recently active dome that started erupting in 1570 AD. The last eruption occurred in 1950 on Nea Kameni.
All of these volcanoes constitute the caldera complex of Santorini. Calderas have a Plinian eruption style, like composite cones only much more dangerous. Caldera eruptions devastate landscapes and have transformed the islands of Santorini into it’s present day crescent shape.
Boy, all of this writing sure has made me hungry! If you’re curious about how calderas form and the hazards these geologic features pose on the island, check out some of my colleagues’ blogs! Keep a lookout for my next blog and I’ll see you all then!