For those who have been keeping an eye on any events at Taal in the Philippines, the current unrest won’t come as a surprise. Over the past few months the volcano has become progressively more restless and after the huge emission of SO2 on the 28th, there were several phreatomagmatic events on Thursday, July 1st. The alarm level has been elevated to 3 as of the same day, and forced evacuations of villages within the 7 km zone have begun.
On Twitter people tell they felt earthquakes that lasted a minute or more. At 3:16 PM a short phreatomagmatic eruption happened, and during the day there were 4 more small bursts (the total count for Thursday is 5). After that the volcano went back to a semi-sleeping state. But this might change any minute or in a few weeks.
After Taal erupted in January 2020, it was clear that this was not the end of the activity yet. We expected this eruption would lead to more frequent activity on Taal Island over the next years to decades. For the rest of 2020 the volcano stayed mostly quiet, while the world was focusing on battling a virus outbreak. But earlier this year things slowly changed and Taal woke up from her light sleep. There have been episodes with volcanic earthquakes and low-frequency events for many months now, a clear indication that magma is on the move beneath the Taal edifice. Steam-laden plumes grew increasingly higher, from a few meters to a kilometer or more in the past few weeks. Since 9:05 AM on 08 April 2021, the start of background tremor was added to the list, and this has persisted until now. There were steam and muddy emissions from fumarolic vents, and the amounts of emitted SO2 have gradually gone up.
On June 10, Taal released 9,911 tonnes of sulfur dioxide. That day it rained and people on Twitter mentioned that they saw their vegetable gardens, trees and grass turn brown before their eyes. On the 28th of June, the emissions averaged an insane 14,326 tonnes of sulfur dioxide (SO2), the highest daily amount ever measured on Taal. In the days after, resp. 8,982 tonnes/day on 29 June 2021 and 6,685 tonnes/day on June 30 were measured. Steam plumes went up to 2500 meter on these days.
But yesterday, suddenly a dark phreatomagmatic plume rose up that was a kilometre tall. Phivolcs warned of a magmatic intrusion at the main crater of Taal and that more of these events should be expected in the next hours and days. The plume went back to steamy after the phreatomagmatic events and reached 3000 m. Again, a huge amount of sulfur dioxide (SO2) was measured that averaged 13,287 tonnes/day, which created a heavy blanket of vog around Lake Taal. People around the lake were told to be ready to evacuate.
The 14,326 tonnes of sulfur dioxide of the 29th of June is an enormous amount, and cannot be understood differently than that there is a large amount of fresh magma rising up. It resulted in a thick layer of vog that stretched out over large parts of Luzon, including the metropole of Manilla. To give a comparison, Pinatubo emitted a SO2 cloud of over 13,000 tonnes on June 10, 1991, just 5 days prior to the climactic eruption that would shoot ash 34 km (21 miles) straight up into the sky – in spite of a raging typhoon that ravaged the islands at the same time. The action at Pinatubo had started on April 2 with a series of phreatic explosions. The first magmatic eruptions took place on June 3. Prior to the big boom, Pinatubo erupted several times.
Because in 1991 the Philippine government needed to convince the people living around the volcano to evacuate, the Philippine Institute of Volcanology and Seismology collaborated with USGS to create a plan to get everybody out in an orderly way. Thankfully it worked – and many thousands of lives were saved. The currently used five stages of volcanic alert that Phivolcs and the Philippine government use, were defined in the run-up to the Pinatubo eruption, and have been used ever since for all of the Philippine volcanoes. The Alert level for Taal was raised to level 3 on July 1, 2021, meaning that magmatic unrest had been detected at the main crater.
But comparing Pinatubo with Taal is, of course, comparing apples with durians. Taal is a different kind of volcano. Taal lays on top of a graben, has a large hydrothermal reservoir beneath its edifice and is completely surrounded by water. Therefore degassing happens on a much larger scale once magma is on the move and comes close to the surface in Taal, where it interacts with water. And once that happens, the white, steam driven plumes soon changed to dark columns, a clear sign that the style has changed to phreatomagmatic where ash becomes a component in play.
The first one of the series of phreatomagmatic eruptions that happened on July 1, was shared by Phivolcs. Besides a lot of steam and ash, there was a small pyroclastic flow.
Meanwhile, the first evacuations are underway. The Philippine Civil Defense and rescue organizations have started to evacuate Laurel and Agoncilo, villages on the west side of Lake Taal where about 15,000 people live. They are first in line for events like ash-fall, shock waves, earthquakes, a base surge and even tsunamis that can be generated by a violent eruption, a volcanic earthquake or even rock fall. Taal can throw out some serious boulders that are hot and can land well away from the main crater on the shores of the lake.
In 2020 these villages were also the first to be evacuated. More villages followed later as the danger zone was widened. The authorities did a very good job again. Eventually there were only 39 casualties, mainly people who refused to leave the area.
Places around Taal where not to be during an eruption
The best advise for any eruption, is usually, not be there! Unless it is of course Fagradalsfjall, which is pretty safe because it only erupts lava flows. Lava flows is about the only trick in the Volcanic Manual that Taal doesn’t do so well. Taal’s eruptive style is mainly ash and tephra. Any rare lava fountains would not directly endanger villages because they stay on the island. But Taal is quite well capable of all the other tricks in the book, as we know from the witness accounts of previous eruptions. So let’s have a look at some of them and why they are particularly dangerous for anyone living near Lake Taal. We are here looking at a worst case, i.e. the largest kind of eruption we have seen in historical time. This is what we know it can do – not necessarily what it will do.
A base surge is somewhat similar to a pyroclastic flow, but has less rock fragments and more super heated gas in it. Base flows are typically generated by the interaction of hot magma and water that gets super heated and expands dramatically in size when transformed into gas. This creates a shock wave. Because that shock wave travels over water and has very little resistance, it moves incredibly fast and has enough momentum to rise up over the edges of the lake and even the crater walls, except perhaps Tagaytay Ridge in the north which is the high ridge on which Tagaytay City is located. Base surges are considered the most dangerous possible volcanic side-effects of a Taal eruption: they are simply too hot and too fast to escape.
Volcanic Tsunami and Flooding
Volcanic tsunamis on Lake Taal can be generated in several ways. A volcanic earthquake may set it off, large ejecta that fall in the lake, when a chip of the crater wall that surrounds the lake breaks off, and of course if a violent eruption starts. Again, the villages close to the lake are most in danger, and the area to the south west that lays lower and has a sedimental character and may flood. On the image above you see that even an opening to the sea may be created. This is where the former Taa-lan River was located, broad enough for sailing ships to enter Lake Taal. During the 1754 eruption it was blocked by eruptive materials. A new small river river would form later, Pansit River, which still exists. After 1754 the water level in Lake Taal became higher and the lake went from a salt water basin to freshwater. A strong enough tsunami might open up a broader channel once more.
In 1754, Father Buencuchillo wrote down his eye-witness account. It was re-published in 1912 in The National Geographic Magazine, Vol. XXIII, Nº 4: “At 7 in the evening of November 28 occurred a new paroxysm, during which the volcano vomited forth such masses of fire and ejecta that in my opinion all the material ejected during so many months, if taken together, would not equal the quantity which issued at the time. The columns of fire and smoke ascended higher than ever before, increasing every moment in volume and setting fire to the whole island, there being not the smallest portion of the latter ‘ which was not covered by the smoke and the glowing rocks and ashes. All this was accompanied by terrific lightning and thunder above and violent shocks of earthquakes underneath. The cloud of ejecta, carried on by the wind, extended itself toward west and south, with the result that we saw already some stones fall close to our shore. I therefore shouted to all those who were still in the town to take to flight, and we all ran off in a hurry; otherwise we would have been engulfed on the spot, as the waves of the angry lake began already to flood the houses nearest to the beach.”
Ejecta and Huge Boulders
Again, the villages closest to the volcano, like Agoncilo and Laurel are in the front seat for another threat: falling stones and ‘huge boulders’. Most of these will fall on the island and into the lake, but it cannot be ruled out that large chunks of rock will fall on villages close to the lake. Again, it is best to be further inland when a large volcanic explosion takes place.
Taal eruptions usually come with a large earthquakes. Other dangers for low lying areas around the lake are subsidence and a complete reshaping of the coast line. In 1749, a lower lying area, known as Tierra Destruída, sank into the lake after 2 huge volcanic quakes happened. “During these terrible convulsions of the earth fissures opened in the ground amid horrifying roars, said fissures extending from the northern and north-eastern beach of the lake as far as the neighborhood of the town of Calamba. Here, as well as elsewhere, the whole shore of Lake Bombon has been disturbed” [NG, Vol. XXIII, Nº 4, 1912].
And that brings us to another danger: fissures. During the 2020 eruption we saw pictures of fissures appearing in the villages outside the lake. No need to say that these can destroy houses, roads, and break gas and electricity lines. They also happened in earlier eruptions.
Other dangers are ash fall, lahars, and of course the noxious gases that are emitted by erupting volcanoes. Sulphur dioxide can burn your lungs, eyes and skin, and when it mixes with rain in the atmosphere, it becomes sulphurous acid, H2SO3, also known as acid rain, which kills plants and is not drinkable.
As before, we can only advise anyone near Taal to follow the advice of Phivolc and to evacuate when told to do so.The Philippine authorities have done great jobs with the evacuation of Pinatubo and Taal in 2020. Phivolcs does a great job monitoring the events and although we cannot see what the measurements of Taal show, we can trust them to take the right decisions when it comes to evacuations. If Taal were to erupt, it is best to follow their and Lurking’s advice: do not be there!
The National Geographic Magazine, Vol. XXIII Nº4, 1912
Rappler has a live blog with the latest Taal updates: https://www.rappler.com/nation/updates-taal-volcano-unrest-eruption-2021
Some live videos of Taal:
Volcanoverse (various volcanoes in one): https://www.youtube.com/watch?v=YeoRx59dZkc
Marlon Abuyo TV (Phillipine, Marlon does drone overflies too): https://youtu.be/bVQINH0qtcU
Meditation & Relaxation (livestreams from Tagaytay; check for the latest): https://www.youtube.com/channel/UCiHhbYyc3OygMA5n6f_b7-Q
Kaetami (Livestream from Lipa): https://youtu.be/zPX54q2nIRE
MADAM RUTSA: https://youtu.be/SN5GDUc64vQ
GMA News (Philippino news station that has a great playlist with all the latest news; they also have livestreams on Taal set up during the day): https://youtu.be/H_W7JlzmRq0
CCTV Solutions: https://fb.watch/6vyZ4bxchV/