The phreatic eruption of Taal has me walking down the memory lane the past days. I remember my Volcanology training in June 2012 when my colleagues and I had the privilege to get mentored by former USGS Geologist and Volcanologist, Chris Newhall. This is going to be a short blog with the intention to share the photos of the workshop which I remember enjoying tremendously. I still have my notes from that workshop.
Chris Newhall, along side then director of PHIVOLCS, Rey Punongbayan, played a major role in monitoring the seismic activities and gas levels of Mt. Pinatubo before its eruption in 1991. He also devised the Volcanic Explosivity Index (VEI) which is a relative measures of explosivity of a volcanic eruption. During the workshop, Chris, taught me and my fellow geologists the different types of volcanoes; the rocks associated with different types of eruptions; the VEI; methods used for monitoring volcanic activities; and so much more. We also had a fieldwork at the foot slopes of Mayon where we walked for kilometers to map out and classify different types of volcanic rock deposits. The fieldwork ended at the foot of a well-preserved lava flow – a product of the volcano’s 2009 eruption. Below are the series of photos of our workshop:
Sometimes the volcanic eruption can be so explosive, it breaks apart its crater rock and pieces get thrown out along with magma and steam. Imagine a coke bottle exploding and the dark cola liquid shoots up along with the shards of the glass bottle – eruptions can be like that. Exploded volcanic materials can also contain pieces of the rocks underneath the volcano. This is why clasts like in the photo above are also studied by Volcanologists in order to understand the type of rocks underneath the volcano which relates to the chemistry of the magma.
Volcanologists also study the eruptive history of a volcano by characterizing the rocks surrounding it. Photo above shows brown fine-grained layer (bottom) which is possibly the old soil layer or the old ground. We usually call it “paleosol” or “fossil soil”. The grayish layer over this brown paleosol layer is a pyroclastic flow which formed when the eruptive column (or mushroom) of Mayon collapsed and flowed horizontally along its flanks covering the ground on its path. The reason why I took this photo was that this outcrop is a textbook example of pyroclastic materials getting deposited over the “old ground” level due to an eruption event. Volcanic eruptions play a significant role in changing the landscape. There won’t be islands on the Philippines were it not for volcanic eruptions millions of yeas ago – formed when layers of erupted volcanic materials got deposited on top of one another eventually becoming mountains and ridges, with valleys in between.