Warning signs: we see them every day, from hazard signs on the roads, to symptoms in sickness. Some warning signs are only found in certain areas, for example mass wasting signs are usually only next to steep slopes. When getting sick, most people will experience symptoms before a full blown fever. It just so happened that the day we learned about warning signs, I was beginning to have warning signs of a cold myself (talk about one with the classroom). The warning sign that caught my eye though, was a thin layer of ash in between non-Minoan ash and Minoan pumice when our class visited Caldera Beach.
Known as Phase 0, Santorini had a small (less than one km high) sub-plinian eruption consisting of ash before the main eruption of the volcanic vent. Phase 0 was produced by a subaerial, phreatomagmatic explosion. For any non-geologist, a phreatomagmatic explosion is an explosion produced by steam. This steam is formed when water is flash heated by magma, lava or hot rocks. Even though the explosion was subaerial, there is evidence the eruption was wet due to the low percentage of vesicles, along with the presence of angular clasts and smaller ash pieces (Friedrich). This thin layer of ash can only be seen on certain sections of the island because of the prevailing wind moving south during the beginning of the eruption (Fig. 1). Phase 0, therefore, encompasses sites such as Akroteri, Caldera Beach, and Vlychada Beach. The thickness of the ash also varies depending on location; The ruins of Akroteri held roughly eight cm of brown ash in its walls (Fig. 2). Caldera Beach had a thin, less than five cm layer in between non-Minoan ash and phase one pumice fall. Lastly, on the far southeast boundary of Phase 0, we saw Vlychada with only three cm of ash. As we saw in the field, Phase 0 thins around the edges of the deposit as well as farther away from the erupting vent.
Though each volcano is unique in their own way, many volcanoes that produce plinian eruptions will have a throat clearing period or a Phase 0. Mt. Vesuvius in Italy, known for the destruction of Pompeii, erupted a thin layer of ash, roughly seven hours before the main eruption in 79AD (Cioni et al 2000). A more recent example includes Mt. Pinutubo of the Philippines which erupted in 1991. Along with many other precursors, there was a small, ash filled steam eruption before the main eruption (Pappas). Though every volcano is unique, both eruptions demonstrate that precursors are common for volcanoes (For more on warning signs of eruptions, see Defcon 0 by Katie Crowley).
Now, you may be asking at this point, why was Phase 0 special if other volcanoes can also produce phreatomagmatic explosions? Well, Phase 0, along with a few other warning signs, pushed the Minoan people to leave Akroteri. It warned them to pack up their belongings and rid themselves of the dangers on the island (pretty amazing right?). Evidence of their departure included: bed frames being stacked and pushed against walls, pots being placed all in one room and lack of footprints in the ruins of Akroteri (Fig.3). It wasn’t Phase 0 that was unique, it was how the people of Akroteri interpreted the ash fall and saved themselves that made phase 0 special.
At this point you’re probably thinking, what do warning signs have to do with us, why is it important to the modern generation? I was born and raised in the Pacific Northwest of the United States. Many people, including Oregonians, are unaware of th massive earthquake and tsunami that will soon hit our shores. Off the coast of Oregon is a subduction zone where the Juan de Fuca plate is merging under the North American plate (Fig. 4). Eventually, the two plates will snap back within the next 50 years, producing a potential 8.0 and above magnitude earthquake (Goldfinger). Not only could this earthquake create a 40 foot high tsunami, destroying the coastline I grew up around , but it could result in volcanic activity along the Cascades. These three aspects combined could cause millions of thousands of dollars in damage in the Portland City area and along the coast. If that’s not scary, I don’t know what is. Therefore, I look for warning signs everyday so that when the earthquake does occur, I am prepared (hopefully I’ll be in a park and not at the beach). My livelihood, among with many others, is threatened by the well overdue earthquake and tsunami haunting the Pacific Northwest.
For me, when I learned about Phase 0, I was in utter shock. Not only at the fact that the Minoan people had vanished but at the fact that today, volcanologists use highly technical equipment to determine when a volcano will erupt whereas the people of Akroteri based their decision on the thin, barely visible, layer of ash. Phase 0 was not only important for the survival of the Minoans but it is also essential to archeologist who study the lifestyle of the Minoans. The thin layer of ash, that most tourists overlook, demonstrates the advance and intelligent culture of the Minoans. Understanding the geological aspect of where you live is extremely important. Even if you don’t live next to a plate boundary or volcanoes, warning signs in geology are vital to survival, the people of Akroteri knew that, do you?
Cioni, R., L Gurioli, A Sbrana, and G Vougioukalakis . “Precursors to the Plinian Eruptions of Thera (Late Bronze Age) and Vesuvius (AD 79): Date from Archaeological Areas .” (2000): 722. Print.
Friedrich, Walter L. Santorini . Denmark : Aarhus University Press, 2009. Print.
Goldfinger, Chris . “Odds are 1-in-3 that a huge quake will hit Northwest in next 50 years.” Oregon State University , 24 June 2010. Web. 12 June 2015. <http://oregonstate.edu/ua/ ncs/archives/2010/may/odds-huge-quake-Northwest-next-50-years>.
Pappas , Stephanie. “Pinatubo: Why the Biggest Volcanic Eruption Wasn’t the Deadliest.” LiveScience. 15 June 2011. Web. 12 June 2015. <http://www.livescience.com/14603- pinatubo-eruption-20-anniversary.html>