At first, I don’t see it. I look up and down the massive outcrop of pumice, ash, and lithic fragments that were launched from the volcanic vent during the Minoan eruption over the years and I still don’t see it. It wasn’t until my partner, Ray, pointed it out that I finally notice it: an odd, cluster of rocks that don’t match the rest. Lisa, our instructor, wanted us to try to figure it out before she told us the story behind the rocks. She left my partner and I to think about it while we started our stratigraphic section.
As we went to work, my mind kept wandering back to the cluster. I’m a very curious person. I like seeing how things work, how they get there, and what was involved in the process. This is the reason why I love geology. Every single rock has a story that connects to a different story, which is then traced to another and another. It’s in an infinite and intricate web of knowledge. So here was this cluster of rocks, and I had no idea how they got there. As much as I wanted to know, I focused on my stratigraphic column instead. After about an hour of working, Lisa came back to check on us. While I had no idea what it could’ve been, Ray thought that it was some kind of erosion. Lisa then excitedly took us into a river channel that had the same exact cluster of rocks. Little by little, the story started to come together. She explained that what we were looking at was river scouring. River scouring occurs when a river runs through a channel and starts to erode the surface. The faster the water runs, the more erosion occurs. Also, with more turbulent water, the bigger the rocks will be. The erosion cuts into the pre-existing rock and starts to deposit the rocks from the river. These rocks stick into the pre-existing rock and form a clast. With this in mind, this means that the water level was up approximately 13 meters up. We know this because when doing a stratigraphic section, we measure every bed or anomaly.
You might be asking yourself, what’s so special about a river deposit?? This river deposit is between two different beds, which can only mean one thing: something happened between Phase 2, which is pyroclastic surges, and Phase 4, which are hot pyroclastic flows (read Micah’s and Gracie’s blog for information.) These river scours are found in many places, such as Vylchada Beach and Cape Mavropetra. The rivers most likely formed as a result of thunderstorms created during the volcanic eruption. Thunderstorms sometimes occur during volcanic eruptions. What happens is after an eruption, hot ash rises and collides with the surrounding, cold air. The air expands and then cools, which causes water to condense and fall down as acidic rain. If the scour did occur from a rainstorm, it would have happened during the eruptions, since there is no break between Phase 2 and 4 (Read Holly’s blog for more information on Phase 2.) It was incredible seeing a river scour from modern times and one from thousands of years ago within walking distance from each other. It was such an “aha” moment when I actually opened my eyes and saw river scours throughout the whole river bed. Whether it was rainstorm or not, we know that water passed through the ash. It’s exciting because it gives us another piece of the puzzle. We have so many clues right in front of us. It’s just simply a matter of putting them together that helps us imagine the Minoan Eruption in all it’s glory.