There is a silence as I enter the climate controlled dome to see the ancient city of Akrotiri. This is partially due to being told “Shhhhhh” by our professor Lisa, but it’s also because everyone’s jaw dropped while staring at these ruins. The only thing that could be heard was the pitter patter of feet from children and even they weren’t saying anything. It was like entering a 3600 year old church frozen in time by ash and pumice with even the colors of the frescoes being preserved.
Akrotiri laid hidden for thousands of years until 1967 when Professor Spyridos Marinatos began systematic excavations of the site. He quickly discovered this was an advanced civilization with siphoning toilets and multistory buildings that were quite extensive. There is also pottery and many pieces of slate found in the city that are foreign to Santorini indicating trade with cities from across the sea.
Figure 1: The Porters Lodge where casts of food were found in the pithoi (storage jars)
How did the buildings, pottery, and colors get preserved so well? The key to this puzzle box is phase 1 of the Minoan eruption which has 5 phases or stages overall. Phase 1 is interpreted to be Pumice Fall which blankets the landscape like a sheet of snow. This requires a very large Plinian eruption that is by definition at least 11 km (7 miles) high. Plinian refers to a very powerful volcanic eruption which is measured by the amount of material ejected from the vent and how high it goes into the air. Now, take a second to imagine this giant mushroom cloud of pumice looming over a volcano. Do you have a good picture in your head? Good, Let us continue!
Figure 2: Layers of Pumice Fall (Phase 1) and Pyroclastic Surges (Phase 2) found in Akrotiri
The first clasts of pumice that rained down from the sky were very small due to magma fragmentation. This refers to how efficiently or quickly the gas is expanding. The more efficiently the gas expands the more fragmented the pieces. It makes sense that the gas would expand very quickly at first making smaller pieces, and then expand less quickly as time went on creating bigger pieces. I imagine this like when you put mentos into a 2 liter container of soda causing it to explode magnificently at first, but then it uses up its fuel and dies down.
This process caused a layering of smaller pieces of pumice on the bottom and bigger pieces on top called reverse grading. Akrotiri was covered by this pumice shower very quickly protecting the frescoes, buildings, and pottery from the pyroclastic surges in phase 2 of the eruption (see Jessica’s blog The Forces that Drive Rock for more on pyroclastic surges). The pottery was protected so well that delicate handles and spouts remained intact (See figure 3).
Figure 3: An intact piece of pottery from the museum in Santorini
The objects that survived this destructive force though were covered by ash and somewhat protected by the rest of the explosion. I say somewhat protected because there are giant blocks of basalt from the vent of the volcano scattered throughout the city. As I walked around the ruins of the ancient city I pictured a scene of Armageddon with giant flaming bombs of rock falling from the sky crushing whatever lies in their path.
Figure 4: Blocks of basalt from the vent of the volcano
I like to think optimistically that they made it off the island before the eruption because there have been no bodies found at Akrotiri. The Pumice Fall would preserve their bodies the same way it preserved the pottery, frescoes, and the rest of the city. There has only been about 10,000 square meters excavated, and they estimate that that is only 3% of the city so there is still so much to discover. As the excavation continues, I remain with high hopes that there was a happy ending to their story.
Figure 5: The fourth day of excavation on June 9th 2016 after no activity for 42 years