Looking back: When Mount Pinatubo blew its top

Looking back: When Mount Pinatubo blew its top
Mount Pinatubo’s eruption on June 15, 1991, is considered the second largest volcanic eruption of the 20th century. It is also a case study on the importance of preparedness in reducing casualties from natural calamities.

MANILA, Philippines (UPDATED) – Leonor Pineda, a resident of San Fernando, Pampanga, could still remember the thrill she felt 27 years ago.

It was June 11, 1991 when she first saw minor emissions from Mount Pinatubo. While it was considered an active volcano, Pinatubo has been dormant for about 600 years already. It was the first time the 27-year-old mother of two has ever seen a volcano acting like that.

The emissions then were still small at the time, not enough to cause panic. From her office window, Pineda saw a convoy of American soldiers from Clark Air Base in Pampanga. They were evacuating their bases, just 16 kilometers away from the volcano, as Pinatubo continued showing signs of unrest.

Even on June 15, as some people stayed in their homes aware that a major eruption could happen anytime, Pineda and many like her still went to their respective offices.

At lunchtime, as the situation was getting worse, her boss asked everyone to go home. By the time she reached home at around 1:42 pm she remembered seeing a mushroom-like cloud over Mt Pinatubo.

Then darkness fell. She heard rocks fall on their roof. She felt the ground move from time to time.

Akala ko talaga katapusan na ng mundo,” she said. (I really thought it was the end of the world.)

Sister Emma and her early warnings

Mount Pinatubo did not fail to warn communities living near the slopes before its imminent eruption.

In March 1991, months before the volcano unleashed its full fury, a group of Aetas living in the upper slopes of Mount Pinatubo felt minor earthquakes (with magnitudes not greater than 4) around the volcano.  

Volcanologists called these swarms, according to Winchelle Sevilla, officer-in-charge of Volcano Monitoring and Eruption Prediction Division (VMEPD) of the Philippine Institute of Volcanology and Seismology (Phivolcs).

Soon after, the group, led by Sister Emma, a missionary based in that area, went to Raymundo Punongbayan, then director of Phivolcs, to report about their observation. Punongbayan immediately sent a quick response team to observe the volcano.

STEAM EXPLOSIONS. Steaming vents from different parts of Mount Pinatubo start to appear days before the cataclysmic eruption. Photo from Phivolcs

In April of that same year, Sister Emma returned to Phivolcs to report again about their new observation, this time, of steam explosions in some parts of Mount Pinatubo.

Seismic networks were then set up in the vicinity to locate the source of the swarms, according to Sevilla. Experts from the US Geological Survey (USGS) also came to help the agency.

By June 1991, the swarms became more frequent. And if in May, the swarms felt were scattered in different parts of the volcano, this time, they were concentrated in a single area. Phivolcs raised the alert status to 4 and a danger zone of 10 kilometers from the volcano was set.

“Parang nandoon na siya [swarms] halos sa ilalim ng bulkan kasi umaakyat na yung magma,” Sevilla said. (The swarms seemed to be coming from below the volcano itself because the magma was starting to rise.)

By June 7, a lava dome appeared at the summit of Mount Pinatubo, which meant that an eruption was about to happen. Two days after, Phivolcs raised its alert status to 5, and the danger zone was extended to 20 kilometers.

From June 12-14, a series of eruptions began.

‘Cataclysmic eruption’

THICK ASH. Eruption column from Mount Pinatubo on June 12, 1991. Photo from Phivolcs

On June 15, at 1:42 in the afternoon, the volcano ejected an eruption column 40 kilometers above its crater.

The volcano then started ejecting volcanic materials such as ashes, lava and rocks. Earthquakes and steam explosions were also felt. By 2:30, there was total darkness in nearby cities. Power was also cut.

“I could hear rocks on my roof. [Then there was] total darkness,” Leonor recalled.

Meanwhile, scientists from Phivolcs and USGS who were there at the vicinity of the volcano thought it was the end of their lives.

Tumatakbo sila (nasa sasakyan), away from the volcano kasi hinahabol na sila ng pyroclastic flow (PF). And this PF kasi, mainit ito masyado, tapos more than 60 kilometers per hour yung bulusok niya. Kailangan nilang makapunta sa safer ground that time,” Isabel Abigania, science research specialist from Phivolcs’ geology division recalled.

(They were running away from the volcano as pyroclastic flows continued to flow from the slopes. The PF was really hot and the speed was moving at more than 60 kilometers per hour. They had to be on safer ground at that time.)

The eruption went on for the next 9 hours.

During that time, Leonor and her family stayed home. By the time the eruption stopped, she went out, only to be shocked by what she saw. Luckily for them, they were not within the 12- to 16-kilometer zone that was affected by the pyroclastic flows.

Instead, they found themselves covered in ash. “Nabaon na kami sa buhangin – ‘yung ash (‘yung puti),” she added. (We were buried in white sand – white ashes.)

Affected by the 1990 Luzon earthquake?

There were reports that an earthquake caused Mount Pinatubo to erupt with that kind of magnitude.

On July 16, 1990, more than a year before the eruption, a magnitude 7.8-earthquake hit Northern and Central Luzon. Its epicenter was recorded in Nueva Ecija, and the shaking lasted for about a minute.

The earthquake caused several buildings in Baguio and nearby provinces to collapse, killing 2,412 people.

“May mga studies kasi na nagsasabi na ripe na talagang pumutok ang Pinatubo. Turns out, mas pinadali lang ng (1990 Luzon) earthquake. Mas pinaaga niya yung pagsabog,” Sevilla explained.

 (There were studies saying that Mount Pinatubo was ripe for an explosion. Turns out, the 1990 Luzon earthquake made the impending eruption happen earlier than expected.)

 ‘20th century’s second largest volcanic eruption’

The 1991 Mount Pinatubo eruption was the second largest volcanic eruption of the 20th century, next to Novarupta in Alaska which erupted in 1912, according to Sevilla.

“Usually sa volume ng materials na inilabas ang tinitingnan nila dito. So in terms of materials na nilabas, yung Pinatubo yung pangalawa doon. Pero, in terms of yung sulfur dioxide yung nilabas, pinakamadami yung Pinatubo,” Sevilla said.

(Usually, the volume of the materials ejected is what they look at. In terms of materials ejected, Pinatubo ranks second. But in terms of sulfur dioxide ejected, Pinatubo ranks first.)

Pinatubo’s eruption, according to USGS, had caused global temperatures to decrease temporarily.

The ash fall, which affected provinces in Luzon, including Metro Manila, also reached some countries in Southeast Asia – as far as India, Sevilla added.

Because of the magnitude of the eruption, Mount Pinatubo’s original crater was destroyed, creating a new one with a lake, just like that of Taal volcano, months after the eruption.

Typhoon Yunya and lahar flows

As if the eruption itself was not damaging enough, Typhoon Diding (Yunya) passed through Luzon on the same day, causing roofs of houses to collapse as the rainwater mixed with the ashes ejected by Mount Pinatubo.

The typhoon also mobilized fresh volcano deposits, burying nearby communities with large rocks and thick, hot lahars. These communities stood on 500 to 600-year-old deposits from the volcano, according to Abigania, making the lahar flows worse.

BURIED. A school buried by lahar flows. Photo from Phivolcs

Major lahar flows continued to affect nearby cities for the next 6 years. Even today, minor lahar flows still affect some provinces during the Habagat (southwest monsoon) season, Abigania said.

Early evacuation

Despite the extent of the destruction, the number of casualties from the Mount Pinatubo eruption was relatively low, according to Sevilla.

Given an increasing number of people living in areas near volcanoes, the death toll from volcanic eruptions in the 20th century could potentially reach thousands. Pinatubo, despite being one of the largest, had less.

Here is a list of some of the most devastating eruptions of the 20th century:

Year Volcano No. of Casualties
1985 Nevado del Ruiz (Colombia*) 23, 000
1982 El Chichon (Mexico) 2, 000
1980 Mount  St. Helens (United States) 57
1963 Agung (Indonesia) 1, 184
1951 Lamington (Papua New Guinea) 2, 942
1951 Hibok-Hibok (Philippines) 500

According to Phivolcs data, the 1991 eruption had affected about 1.25 million inhabitants. 717 people lost their lives – 281 of whom died indirectly from the eruption, 83 from lahars, and 353 from exposure to diseases at evacuation centers.

While a number of people died, reports say that about 5,000 lives were saved from the eruption.

“The people living in the lowlands around Mount Pinatubo were alerted to the impending eruption by the forecasts, and many fled to towns at safer distances from the volcano or took shelter in buildings with strong roofs,” according to the USGS report.

As early as April of that year, 2,000 people were already being evacuated, according to Phivolcs data.

“Sa volcano, ang magagawa mo lang diyan ay lumayo ka as far as possible. Hayaan mo lang siyang pumutok pero ang gagawin mo i-evacuate mo lahat ng mga nakatira doon as much as possible,” Sevilla said.

(With a volcano, what you can do is to just move away from it as far as possible. Just let it erupt but you should evacuate everyone as much as possible.)

Close coordination between government agencies and communities near the volcano also helped minimize the number of casualties.

“It really helped that the communities reported what they have observed. They knew their surroundings better, so the information coming from them were really important,” Abigania said. The inputs of experts have certain limits, unless, they too, will give their inputs, Abigania explained.

It would take centuries for Mount Pinatubo to erupt with that same amount of force again. But the Phivolcs reminds the public, especially those living near volcanoes to not become complacent.

Phreatic or sudden steam-driven eruptions can happen anytime, according to Phivolcs director Renato Solidum. This is why a number of active volcanoes already have designated a Permanent Danger Zone (PDZ), where human settlement is prohibited. (READ: When mountaineers climb active volcanoes)

So far, there are 5 active volcanoes in the Philippines with PDZs: Mayon (6 km), Taal (whole island), Kanlaon and Bulusan (4 km) and Hibok-Hibok (3 km). These volcanoes frequently erupt, according to Solidum.

“As long as the right ingredients are there – heavy and continuous rainfall plus old volcanic deposits – lahar flow is possible. That holds for any other active volcanoes that we have,” Abigania added. – Rappler.com

Sources: Philippine Institute of Volcanology and Seismology, U.S. Geological Services, The New Wider World by Alison Rae, Neil Anthony Punnet, www.volcano.oregonstate.eduwww.volcanolive.com, various news websites

The Philippine Institute of Volcanology and Seismology (Phivolcs) is a partner of Rappler in Project Agos, a collaborative platform that combines top-down government action with bottom-up civic engagement to help communities learn about climate change adaptation and disaster risk reduction. Project Agos harnesses technology and social media to ensure critical information flows to those who need it before, during, and after a disaster.

Project Agos is supported by the Australian Government.

Editor’s Note: In a previous version of this story we said Nevado del Ruiz was located in Mexico. It is located in Colombia, instead. We have corrected the error.

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