It’s Monday, November 30th, 2015, 11:30 am. Today is the day I will be learning about a topic I have anticipated since the beginning of Geologic Disasters. I will be learning all about rivers and flooding! Sitting in class I hear moans and groans about this. A lesson that seems so tedious and dull to my classmates was actually fascinating and thrilling to myself. I was finally going to learn about a topic I could personally connect with.
Rivers and floods are nothing new to me. Northern Arizona is filled with hidden dry washes that wind all throughout the towering Ponderosa forest. Every summer where I grew up, I experience flash floods, now I have learned that floods occurred during the Santorini cataclysmic eruption!
In the middle of a chaotic volcanic eruption, not only was there falling ash and pumice, but there was also heavy amounts of rain pouring down in, resulting in flash floods. The flash floods occurred due to volcanic weather. Volcanic weather is the result of rising hot ash drawing in heat and then lifts surrounding air. The air expands, cools, then causes water to condense and fall down as rain! (Figure 1) Interestingly, volcanic eruptions can create their own weather system! In the midst of an eruption, lightening, rain, and flooding occurs because of volcanic weather.
Evidence of volcanic weather must be found in order to assume that flooding occurred. A remote beach located on the northern tip of Santorini called Cape Mavropetra provided the necessary details needed to make the assumption that volcanic weathering did occur during the eruption. This evidence is a phenomenon called scour channels! Scour channels are a stream erosional feature (Figure 2). It proves that there had to be large amounts of flooding at the same time as the eruption. It took me quite a while to soak in this feature, an erosional feature that was nothing but foreign to me.
Scour channels also provide more evidence of volcanic weathering. It is clearly evident that there is a dipping motion occurring in the rock. There is well preservation of the cut bank and point bar in the scour channel (Figure 3). The cut bank is the outside of the river, it is also where erosion occurs. As opposed to the cut bank, the point bar is the inside of river. The inside of the point bar is where deposition occurs, such as sand and sediment (Figure 4).
Volcanic weather is like nothing I have ever heard of. It can have a very short duration of a few hours or a large duration of up to a week. The duration of volcanic weather during the cataclysmic eruption of Santorini is estimated to have lasted from a few hours to a day! Just within a day, volcanic weather created a large flood and channel, approximately 15 meters in width!
Today, it’s Sunday, June 12th, 5:50 pm. The presence of a scour channel at cape Mavropetra provided two pieces of evidence that volcanic weather did occur. The scour channel first identifies a clear outline of a river, it also contains remarkable preservation of the cut bank and point bar. It was very hard for me to accept that volcanic weather created floods while a colossal eruption was occurring at the same time! I knew that the eruption created layers and layers of pumice and ash; however, I never gave much thought to think of the possibility of flooding.