Geology, Local Travel

Volcanology Fieldwork in Bicol – Revisiting Eruptive Deposits of Mayon, Bulusan, and Irosin Caldera

It’s been a while since I last wrote about earth sciences. Here’s one blog post to teach your kids about volcanoes. I’ve chronicled my one week fieldwork around Mayon volcano and the Irosin Caldera. If you haven’t heard about Irosin Caldera, then you’ve probably heard only of Bulusan volcano being an active volcano. However, did you know that Bulusan volcano actually lies within a huge caldera? I will explain this one in a bit.

I’ve simplified some of the facts here for the young audience out there. I also did not included all our pictures because I don’t want any of the future volcanology students copying any part of this article. I’ve also included some of the fun stuff my fellow students and I did such as the food we ate during the field mapping activity. If you like this one, please feel free to share about it. It would be nice to have people appreciate mother nature and also consider being a scientist in the future as well. Science rocks! (pun intended)

Location 1: Mayon Volcano

Just like Mt. Fuji of Japan, Mayon volcano is a perfect cone-shaped active stratovolcano located in Albay, Bicol, a province in the southeastern part of Luzon island. From the city capital Manila, it’s only about 40-45-minutes plane ride or about 8-hours bus ride. Because our fieldwork to Mayon is part of our Volcanology class as graduate students, we took the school’s vehicle to get us there. The first stop after a long journey was to our accommodation in Sto. Domingo, Albay which is Mirisbiris Garden Resort. The resort is owned by a former US Geological Society scientist, Dr. Chris Newhall, who was our teacher in Volcanology in a one-week Volcanology 101 (blog post below). I will write about this resort in another post. If you like plants and the beach, this is one resort I’d recommend you stay in when you’re in Albay. More on Mirisbiris Nature Garden Resort in another post. πŸ™‚

PHIVOLCS Observatory at Lignon Hill Albay Bicol

We travelled for almost ten hours so understandably we were very exhausted by the time we arrived in the resort. I slept like a baby that night. The next day we prepared our gears for our first day of fieldwork. Our first stop was PHIVOLCS Observatory at LigΓ±on Hill. This is the central monitoring center of Mayon volcano and also where you can get official scientific information about the volcano for educational purposes. The objective of our visit was to learn about the equipment, method, and data processing being done when monitoring volcanic and earthquake activity around the volcano. It’s such a complicated process and I will not attempt to explain them here being not an expert. If you would like to know more, I do recommend you visit the Observatory when you have time. The scientists are very accommodating. You do need to secure permit from PHIVOLCS prior to your visit.

telescope at PHIVOLCS observatory
High power telescope to monitor the crater of Mayon Volcano just outside the data center of the observatory.

Mabinit Channel (Day 1)

After our educational visit of the observatory, we went back to our van that will bring us to Mabinit Channel – the site where erupted deposits from Mayon from different years of eruption are well-exposed. It took about half an hour land trip from PHIVOLCS Observatory to the newly constructed bridge over Mabinit Channel. From the bridge, we took the concrete stairs of the retaining wall/dike that protects the banks from erosion. The banks of Mabinit consist of layers of lahar deposits. Each layer you see in the photo below possibly represents each time that a lahar flow passed by the channel. Lahar is basically a flow process where water from heavy rains would bring down loose volcanic materials from the slopes of the volcano. The water will then dump these sediments along the banks and with time, these sediments will form the beds of deposits like in the picture. Take note that lahar flow can happen anytime during an active eruption and even years after the main event. We’ve seen that happen in Mt. Pinatubo.

On our second stop along the channel, we chanced upon a man-made ditch that exposed a layer of tephra fall deposit (photo below). Whenever we see rocks, it’s mandatory to take a photo along with a scale ruler like the one in the photo for two things: a. to mark the rock or sediment layer of interest and b. for grain size reference. In geology, it’s important to note sediment sizes. From this photo alone, you can already tell that the tephra grains (blocky grains that are reddish orange to brown in color) are more than 1 cm in size on average. The grains you see in the photo were the one that got thrown out of the volcano during a violent eruption and got deposited in this spot as projectiles.

tephra layer of Mayon

After taking note of our observations of the tephra fall deposit, we proceeded to trek upstream of the channel. Our objectives were to find more volcanic deposits from Mayon to describe and characterize them based on the theories we learned from our class. The weather was crazy because we experienced intermittent rains that alternate with the sun in full blast. It was humid that day. I forgot my umbrella in the resort and only had my poncho for when it rained and it became extremely warm when the sun was full blast again. It was all good though, crazy weather conditions is part of one’s experience as geologist in the field. Sometimes when I go out on a field day, I imagine I’m one of the hobbits off to bring the ring to Mordor.

Photo on the left is a volcanic bomb, one of the projectiles from Mayon that be common in Mabinit Channel. From what we saw, this one is one of the small ones. We saw bombs as big as 1 meter along the way.

After more than one hour of trekking, we finally saw the lava flow of Mayon from its eruption in 2006 (photo below). Notice how in just few years it’s already overgrown with vegetation. Soils that form over volcanic rocks are rich in nutrients such as magnesium, iron, calcium, and sodium. The sharp peaks you see in these lava flows are solid lava flow rocks – often the hardest part of the flow deposit.

2006 lava flow deposit of Mayon
2006 lava flow deposit of Mayon
Mayon’s 2006 eruption produced this lava flow that is now overgrown with vegetation.
cauliflower bomb Mayon
The pyroclastic flow of Mayon contains these bombs that look like cauliflowers that’s why they are called cauliflower bombs. The one above is almost one meter long. Imagine one falling down on you! Projectiles such as this cauliflower bomb is one reason why you should go near an actively erupting volcano.

Mayon Volcano is considered a stratovolcano because it alternately produce lava flows and pyroclastic flows. The main difference between the two is that lava flows are the ones you often see in videos of Hawaii volcanoes where hot molten lavas cascade down the slopes of a volcano. They can be fast or slow when they flow down the slopes. If the flows are slow enough, you can run away from a lava flow to safety. This is not to say that you can go near a lava flow! It’s not safe to go near a molten lava flow because it’s hot, the temperature can go as high as 700 to 800 degrees Celsius or more than 1200 Fahrenheit.

A pyroclastic flow happens during a particularly violent eruption of a volcano. This happens when there’s too much gas in the magma. During a violent eruption, large eruption column shoots out of a volcano and this column contains bombs, tephra, molten rocks (magma), gas, and ash. The column then eventually collapse and flows down the slope as pyroclastic flow due to gravity. Watch the video I have included below made by a professional videographer who took close shots of the 2006 eruption of Mount Etna. The photo on the left is a pyroclastic flow deposit near the 2006 lava flow deposit.

Close shots of small pyroclastic flow and lava flows from the eruption of Mount Etna, Italy, in 2006. The brown smoke at the end of the video is pyroclastic flow after the column has collapsed.
Mabinit Channel as viewed from the newly constructed bridge (Bonga bridge). Although Mayon was already hidden in the clouds, I liked how the sky had pinkish orange hue the whole landscape. I would like to paint this one someday.

A trip in Bicol will never be complete without dropping by the famous ice cream of Colonial Grill. We braved the traffic of Legaspi just to get our hands on these icy treats! Colonial Grill’s famous ice cream flavor is “sili” ice cream – chilies made into ice cream. I honestly am not a fan of spicy ice cream but their three other flavors get a big thumb up from me – tinotong na bigas (burnt rice), ube (purple yam), and gabi (taro). All three ice cream scoops are for only Php 99 (about 1.8 USD).

Colonial Grill ice cream

Basud Channel (Day 2)

Basud Channel lies northeast of Mabinit Channel. Just like Mabinit, we were able to observed pyroclastic flow deposits from different eruption periods of Mayon. Below are some of the photos with captions.

The pyroclastic flow deposits along Basud Channel are layered which indicate different violent eruptive events of Mayon volcano. The photo on the left shows charred wood – possibly a part of a tree that got hit by the hot pyroclastic flow during one eruption. Geologists often take samples of these for radiometric carbon dating.

Basud Channel pyroclastic deposit from Mayon and the whole class all huddled together
My classmates and prof, all huddled together under our umbrellas to stop for bit because of rain while discussing the pyroclastic deposits in front of us.
Mayon Volcano in full view.

At the end of our trek, we unknowingly already encroached the 50-kilometer permanent danger zone of the volcano. Since it was already late in the afternoon anyway, we decided to stop for a bit to take a photo of Mayon as she displayed her majestic self before hurriedly trekking back to our van that brought us back to the base camp (Mirisbiris Resort).

Irosin Caldera, Sorsogon Province (Day 3-5)

On the third day, we bid goodbye to Mayon and Mirisbiris Nature Garden Resort and went on our way towards Sorsogon to map out Irosin Caldera deposits. We had our first stop to have lunch at the famous eatery in Sorsogon, AJ Eatery.

badoy a local Bicolano seafood dish
AJ Eatery

The eatery, AJ Eatery, is famous for their affordable but yummy Bicol dishes. I have dined here several times before along with colleagues at the previous company I worked in. The photo on the left is my favorite dish from this eatery, locally called badoy. It’s a type of soup made of bivalve shellfish that are sautΓ©ed with onion, garlic, and ginger, then added with water. The ginger and onion flavors plus the natural flavor of the shellfish always get a thumbs up from me! Try this when you’re in Bicol.

AJ Eatery Sorsogon

So many tourists and travelers come here to eat and rest along the bay walk across this eatery which has the nice view of Sorsogon Bay.

Irosin view deck
View deck at Irosin along the highway where one can have a fantastic view of Irosin Caldera and the active volcano within it which is the Bulusan volcano.

Did you know that the wide plain in the photo above, around Bulusan volcano, is a caldera known as Irosin Caldera? If you’ve seen photos of Taal or Mount Pinatubo, you’d see the one main thing that’s missing in Irosin Caldera. I’ll give you a moment to think about it. In the meantime, look down below for another shot of Irosin Caldera:

Have you guessed which feature is missing in Irosin Caldera? It’s WATER! Both Taal and Pinatubo have caldera lakes, Irosin Caldera has no water. It is possible that a long time ago Irosin Caldera had water or that it used to be a caldera lake. I believe this is the case based on the deposits we saw around it. However, very little studies have been done in the area that would explain why the lake dried up to what is is now. Something must have happened a long time ago that breached the lake. One thing is for sure though. The vast rice fields in the caldera owes its existence to Irosin Caldera. The volcanic materials underneath these rice fields contributed to the nutrients of the soil. We may as well call Irosin Caldera literally the rice bowl in Bicol because of its partial bowl-shaped topography owing to its geologic history.

ignimbrite deposit Sorsogon
Volcanic fragment with crystals and pumice

The first volcanic deposit from Irosin Caldera that we saw along the way is this deposit of ignimbrite along the highway in Casiguran. From the highway this deposit would look cream to white with patches of orange due to soil formation process (weathering). There would be plenty of this type of deposit along the highway as we went around the caldera for three days.

Matnog Ignimbrite

The photo above is an old volcanic deposit produced during the formation of Irosin Caldera. Photo on the left is a volcanic glass fragment with crystals and pumice fragments. In order to identify the crystals in volcanic fragments, geologists use hand lens such as my black one in the photo which has minimum of 10x magnification. You won’t catch a geologist at work without one, that’s for sure!

In the photo above is another deposit from the formation of Irosin Caldera. The yellow notebook is one of my Rite-in-the-Rain notebooks – yes, it’s waterproof and one can write on it even when there’s a heavy downpour.

Do you see the different colors of the deposits above? The colors define the different layers of deposits. The oldest one in this outcrop is the orange one at the base. πŸ™‚

The new road constructions happening around Sorsogon Province was so advantageous for us – it exposed so many of Irosin Caldera deposits. The more deposits exposed, the more observation points geologists can have on the field. According to my professor, we saw more rock outcrops during our fieldwork because of new road networks compared to the last time she offered this volcanology course which was about two years ago. I guessed luck was on our side! πŸ™‚

The outcrop was not pink. The sunset color of the sky somehow got reflected on the white surface of this outcrop which gave it pinkish hue. Beautiful, isn’t it?

Photo below was taken of the first outcrop we visited on our second day in Sorsogon. This one is in Juban, Sorsogon. The abundant pumice fragments observed in this deposit and the presence of tephra fall layer near the top of this outcrop indicate one thing – the eruption that resulted in the formation of Irosin Caldera was a violent one.

Irosin Caldera volcanics exposed along the highway in Juban, Sorsogon.
Close-up photo of the deposit in Juban. The white fragment just below my yellow notebook is a pumice fragment. We usually put ordinary objects on an outcrop like this notebook (or my hand lens) prior to taking photos for size scale. So from this photo, it can be obvious that the pumice fragment is a few centimeters long. The black grains in this outcrop are volcanic glass fragments – molten magma that froze in the atmosphere during an eruption. A collapsed eruption column may have formed this deposit.
My favorite outcrop during the fieldwork.

The photo above is an spectacular outcrop of an epiclastic deposit. This outcrop indicates that some of the volcanic deposits were transported by water (e.g. river) from the vicinity of the caldera towards this site. Notice also how the erosion pattern resulted to pinnacle structures in this deposit? Pinnacle-shaped erosion formed because of the presence of less erosive grains that protect the deposit underneath. πŸ™‚ If you can’t imagine what I just said, take a look at the photo below. The pumice grains and rock fragments in the layers sort of protected the sandy deposit underneath them, avoiding erosion, and thus, forming pinnacles. Awesomesauce!

Tiny pinnacles form underneath less erodible materials such as rocks and pumice in epiclastic deposits. πŸ™‚

Speaking of erosion, one of the things that’s unique in volcanic materials that were violently exploded by a volcano such as the one in the photo above is the deep rills that form on it during erosion by rain water. From the different way rocks are eroded (look at the upper layer) then we know at first glance that there are at least two layers of deposits on the outcrop above. The color difference also indicates the same. Geologic work requires detailed observation of rocks. πŸ™‚

Lava flow deposit possibly from an older eruption of Bulusan?

Remember the molten lava in the video of Mt. Etna? When the molten lava freezes into solid rock it can look like the one in the photo above. For scale, look at my classmate in the photo and you can already tell that this lava flow was sooo thick!

There is still much to learn about Irosin Caldera and the several events that led to its formation which resulted to the birth of the active Bulusan Volcano. If you read this far, I hope you are inspired to consider geology as future career. The country needs more geologists especially ones who will pursue volcanology so our volcanoes can be understood. Understanding each volcano’s eruption events and their characteristics can help with predicting future volcanic eruption events. πŸ™‚



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