mount pinatubo philippines 1991 case study

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Remembering Mount Pinatubo 25 Years Ago

The world’s largest volcanic eruption to happen in the past 100 years was the June 15, 1991, eruption of Mount Pinatubo in the Philippines.

Bursts of gas-charged magma exploded into umbrella ash clouds, hot flows of gas and ash descended the volcano’s flanks and lahars swept down valleys. The collaborative work of scientists from the U.S. Geological Survey (USGS) , and the Philippine Institute of Volcanology and Seismology (PHIVOLCS) saved more than 5,000 lives and $250 million in property by forecasting Pinatubo's 1991 climactic eruption in time to evacuate local residents and the U.S. Clark Air Force Base that happened to be situated only 9 miles from the volcano.

U.S. and Filipino scientists worked with U.S. military commanders and Filipino public officials to put evacuation plans in place and carry them out 48 hours before the catastrophic eruption. As in 1991 at Pinatubo, today the USGS is supported by The US Agency for International Development’s (USAID) Office of U.S. Foreign Disaster Assistance to provide scientific assistance to countries around the world though VDAP, the Volcano Disaster Assistance Program . The program and its partners respond to volcanic unrest, build monitoring infrastructure, assess hazards and vulnerability, and improve understanding of eruptive processes and forecasting to prevent natural hazards, such as volcanic eruptions, from becoming human tragedies.

mount pinatubo philippines 1991 case study

Monitoring: 10 weeks before the eruption

At Pinatubo, the volcanic unrest began April 2, 1991, with a series of small steam explosions. In Manila, Dr. Raymundo Punongbayan, Director of PHIVOLCS, dispatched a team to investigate a fissure that opened on the north side of the volcano and was emitting steam and sulfur fumes. PHIVOLCS set up a seismograph and began monitoring earthquakes. Dr. Punongbayan also called his friend, Dr. Chris Newhall, at the USGS. The two scientists began working on how to get the USGS-USAID Volcano Disaster Assistance Program team to the Philippines to help monitor Pinatubo.

Three weeks later, Newhall, along with VDAP volcanologists Andy Lockhart, John Power, John Ewert, Rick Hoblitt and Dave Harlow, began unpacking 35 trunks of gear at temporary quarters on Clark Air Base. The seismic drum room was a maze of wires and cables; the daily drum roll of seismicity posted on the walls. Instrumentation was drawn principally from a permanent supply of specialized equipment kept ready for volcano crises under the auspices of the USGS Volcano Hazards Program and the joint USGS-USAID VDAP. They nicknamed the place PVO—the Pinatubo Volcano Observatory.

helicopter dropping off scientists and gear in open grassy field

With air assistance from the U.S. military, the PHIVOLCS-VDAP team installed seven telemetered seismic sites, two telemetered tiltmeters to measure ground deformation, and used a COSPEC (correlation spectrometry) instrument to measure sulfur dioxide gases that would presage arrival of new magma deep in the volcano’s plumbing. All efforts were focused on answering the questions — will Pinatubo erupt catastrophically, and when?

Volcanologists are first to admit that forecasting what a volcano will do next is a challenge. In late May, the number of seismic events under the volcano fluctuated from day-to-day. Trends in rate and character of seismicity, earthquake hypocenter locations, or other measured parameters were not conclusive in forecasting an eruption. A software program called RSAM (real-time seismic amplitude measurement), developed in 1985 to keep an eye on Mount St. Helens, helped scientists analyze seismic data to estimate the pent-up energy within Pinatubo that might indicate an imminent eruption.

There was no existing volcanic hazards map of the Pinatubo volcano, so one was quickly compiled by the PHIVOLCS-VDAP team to show areas most susceptible to ashflows, mudflows and ashfall. The map was based on the maximum known extent of each type of deposit from past eruptions and was intended to be a worst-case scenario. The map proved to forecast closely the areas that would be devastated on June 15.

Evacuation: 48 hours before the first ash eruption

The Clark Air Base sprawled over nearly 10,000 acres with its western end nestled in the lush, gently rolling foothills of the Zambales Mountains–only 9 miles (14 km) east of Mount Pinatubo. Military housing was located on the “Hill” closest to the volcano, with nearly 2,000 homes, elementary schools, a middle school, a new high school, a convenience store and restaurant. At the time, the population of Clark and nearby cities of Angeles, Sapangbato, Dau and Mabalacat numbered about 250,000. The PHIVOLCS-VDAP team developed an alert system and distributed it to civil defense and local officials as a simple means to communicate changing volcanic risk.

Senior base officials listened to daily briefings and put together plans to evacuate. Everyone agreed that if there were an evacuation, people must be moved to an area where they would be safe—not statistically safe, but perfectly safe. The location chosen was 25 miles (40 km) away at Naval Station Subic Bay and Naval Air Station Cubi Point.

Beginning June 6, a swarm of progressively shallower volcano-tectonic earthquakes accompanied by inflationary tilt (the “puffing up” of the volcano) on the upper east flank of the mountain, culminated in the extrusion of a small lava dome, and continuous low-level ash emission. Early June 10, in the face of a growing dome, increasing ash emission and worrisome seismicity, 15,000 nonessential personnel and dependents were evacuated by road from Clark to Subic Bay. By then, almost all aircraft had been removed from Clark and local residents had evacuated. The USGS and PHIVOLCS scientists did their own “bugout,” moving the monitoring observatory to an alternate command post located just inside the base perimeter near the Dau gate, an additional five miles (8 km) away from the volcano.

Distant view of erupting volcanic ash cloud rising over cars in parking lot in forground

On June 12 (Philippine Independence Day), the volcano’s first spectacular eruption sent an ash column 12 miles (19 km) into the air. Additional explosions occurred overnight and the morning of June 13. Seismic activity during this period became intense. The visual display of umbrella-shaped ash clouds convinced everyone that evacuations were the right thing to do.

Eruption: June 15, 1991

When even more highly gas-charged magma reached Pinatubo's surface June 15, the volcano exploded. The ash cloud rose 28 miles (40 km) into the air. Volcanic ash and pumice blanketed the countryside. Huge avalanches of searing hot ash, gas and pumice fragments, called pyroclastic flows, roared down the flanks of Pinatubo, filling once-deep valleys with fresh volcanic deposits as much as 660 feet (200 meters) thick. The eruption removed so much magma and rock from beneath the volcano that the summit collapsed to form a small caldera 1.6 miles (2.5 km) across.

If the huge volcanic eruption were not enough, Typhoon Yunya moved ashore at the same time with rain and high winds. The effect was to bring ashfall to not only those areas that expected it, but also many areas (including Manila and Subic Bay) that did not. Fine ash fell as far away as the Indian Ocean, and satellites tracked the ash cloud as it traveled several times around the globe. At least 17 commercial jets inadvertently flew through the drifting ash cloud, sustaining about $100 million in damage.

With the ashfall came darkness and the sounds of lahars rumbling down the rivers. Several smaller lahars washed through Clark, flowing across the base in enormously powerful sheets, slamming into buildings and scattering cars as if they were toys. Nearly every bridge within 18 miles (30 km) of Mount Pinatubo was destroyed. Several lowland towns were flooded or partially buried in mud.

The volcanologists at the Dau command post watched monitoring stations on Pinatubo fail, destroyed by the eruption. They watched telemetry go down but then come back up – a sign that a pyroclastic flow was headed down valley and temporarily interfering with the radio links. They moved to the back of a cinderblock structure to maybe provide a little more protection from hot gas and ash; there was nowhere else for them to go. Fortunately, the flow stopped before it reached the building.

Damaged jumbo jet airplane covered in volcanic ash, with collapsed rear end

Aftermath: Adapting and learning

The post-eruption landscape at Pinatubo was disorienting; familiar but at the same time, totally different. Acacia trees lay in gray heaps, trees and shrubs were covered in ash. Roofs collapsed from the tremendous stresses of wet ash and continuing earthquakes. No matter which way one turned, everything looked the same shade of gray.

aerial view of Clark Air Force base showing base covered in volcanic ash, and some buildings collapsed

Most of the deaths (more than 840 people) and injuries from the eruption were from the collapse of roofs under wet heavy ash. Many of these roof failures would not have occurred if there had been no typhoon. Rain continued to create hazards over the next several years, as the volcanic deposits were remobilized into secondary mudflows. Damage to bridges, irrigation-canal systems, roads, cropland and urban areas occurred in the wake of each significant rainfall. Many more people were affected for much longer by rain-induced lahars than by the eruption itself.

By the end of 1991, and into 1992, more than 23 USGS geologists, seismologists, hydrologists, and electronics and computer specialists had each spent between three and eight weeks at Pinatubo and helped PHIVOLCS advise community and national leaders and those at-risk and studying the volcano to better understand what causes giant eruptions and how to forecast them, whether in the U.S. or abroad.

Much weaker but still spectacular eruptions of ash occurred occasionally through early September 1991. From July to October 1992, a lava dome grew in the new caldera as fresh magma rose from deep beneath Pinatubo. For now, the volcano is quiet, and the U.S. transferred Clark Air Force Base to the Philippine government in November 1991. The base has been repurposed as a trade and commercial center with large airport.

What would be different if the situation occurred today? Consider that in 1991 there was no easy access to the internet, no connections to other data sets or scientists other than by telephone. The first popular web browser was a couple of years off, CD writers cost around $10,000, and scientific data and analysis were shared mainly by fax. The Pinatubo Volcano Observatory in 1991 was a self-contained unit; data from the monitoring network were radioed to it and the analysis was done by scientists on-site. Today, data received at PVO would be forwarded to colleagues in the U.S. and elsewhere for more sophisticated analysis with the results quickly transmitted back to PVO. Satellite data measuring ground temperatures, gas emissions, and inflation or deflation of the volcano would be sent to PVO where it would be integrated with other data sources to develop forecasts and inform hazard mitigation efforts. Tools and expertise would no longer be confined to what was physically at the observatory, but instead a global support group would be available to aid the response. Monitoring instruments have also improved greatly in performance while at the same time dropping in price and power consumption. There is no doubt that with the communication and monitoring tools available to us today, we would learn much more about the buildup to the eruptions and have more and better data to guide our decision-making.

For successful natural hazard mitigation, it all comes down to the right combination of monitoring data and scientific skill, and then just as important, scientists and public officials who are effective at communicating with each other and with the public who may be in harm's way. At Pinatubo, the quick deployment of monitoring instruments and preparation of a volcanic hazards map by the PHIVOLCS and VDAP team helped to better understand the precursors of volcanic activity and provided the basis for accurate warnings of impending eruptions. The willingness of base commanders, public officials and citizens to take the necessary precautions lessened the risk from this catastrophic eruption.

Learn more:

Pinatubo 1991 Case Study, Volcanic Ash Impact & Mitigation

The Cataclysmic 1991 Eruption of Mount Pinatubo, Philippines , USGS Fact Sheet 113-97

Benefits of Volcano Monitoring Far Outweigh Costs–The Case of Mount Pinatubo USGS Fact Sheet 115-97

FIRE and MUD: Eruptions and Lahars of Mount Pinatubo, Philippines , edited by Christopher G. Newhall and Raymundo S. Punongbayan, 1996

NOVA: In the Path of a Killer Volcano , TV program

The Ash Warriors , by C.R. Anderegg

The International Association of Volcanology and Chemistry of the Earth's Interior’s (IAVCEI) video for crisis education

USGS-USAID Volcano Disaster Assistance Program

The 1991 eruption of Mount Pinatubo

On 9 June 1991, Mount Pinatubo, a volcano in the Zambales Range, 80km (50 miles) north of Manila, capital of the Philippines, hit the headlines. It became one of the three largest eruptions in the world in the 20th Century. From the 9 June there were many eruptions (timeline of events). However, none matched that of 12 June. Ash turned day into night. The eruption caused the deaths of over 700 people. 200 000 buildings were destroyed.

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Science News by AGU

Pinatubo 25 Years Later: Eight Ways the Eruption Broke Ground

1. First Rapid Scientific Assessment of a Volcano’s History

Once Pinatubo started rumbling, PHIVOLCS set up three seismometers on its northwestern flank. After U.S. Geological Survey (USGS) scientists—part of the Survey’s Volcano Disaster Assistance Program (VDAP)—arrived on 23 April, they set up a seismic network of seven stations located between 1 and 19 kilometers away from the volcano. Throughout May, seismometers recorded at least 200 small earthquakes per day.

A helicopter-mounted spectrometer—a device originally developed to monitor emissions from smokestacks—tracked dramatic increases in sulfur dioxide emissions from vents. Gas escapes as magma rises within a volcano, so this sign of moving magma, along with increasing seismicity and deformation measured by tiltmeters, led scientists to believe that an eruption was imminent.

No baseline information about the volcano existed.

But scientists faced a huge problem: They had had only a few weeks to learn as much as possible about Mount Pinatubo’s eruptive history before it blew. Add to that another challenge: No baseline information about the volcano existed, except for one carbon date from a 1980s investigation of the area as a possible site for a nuclear power plant, said John Ewert, a geologist and member of the VDAP team deployed to the Philippines.

One of the first things the VDAP team did was consult the catalog of active volcanoes from the Smithsonian Institution’s Global Volcanism Program. Pinatubo wasn’t even it in it at the time, Ewert said.

Scientists install electronic tiltmeters prior to Pinatubo’s eruptions.

VDAP scientists wasted no time. They studied layers of ancient pyroclastic flows and lahars surrounding all sides of the volcano. They collected and dated samples of charcoal. They flew in helicopters around the volcano, mapping the extent of past flows and visiting outcrops.

From the air, the scientists saw that pyroclastic flows appeared “high up on ridges, or over ridges that would have blocked all but the largest flows,” Chris Newhall, a volcanologist who was a part of the VDAP team in the Philippines, told Eos . The observations confirmed how large the impending eruption could be.

From these studies the scientists figured out that the volcano had exploded in at least six eruptive periods over the past 5000 years, short bursts of activity followed by long, quiet periods . The most recent eruption occurred 500 years ago. What’s more, surrounding villages were built on old pyroclastic flows and lahars.

2. First Successfully Mobilized Widespread Evacuations

By early June the sulfur dioxide emissions dropped sharply to around 250 tons per day. Scientists suspected this meant that the viscous, rising magma had pinched shut cracks or had cooled and lost volatiles, either way preventing gas from escaping.

12 June 1991 eruption column from Mount Pinatubo.

Around the same time, earthquakes within Pinatubo increased in strength and duration. In early June the earthquake clusters moved from northwest of the volcano to just under its summit. On 7 June a lava dome started to surface, and on 10 June, sulfur dioxide emissions jumped to more than 13,000 tons per day . Over the next few days, explosions—some generating columns of ash and debris up to 24 kilometers high—shook the volcano.

These signs pointed to one thing: The volcano was about to blow . But how could scientists convince the nearly 1 million people living around the volcano that they may need to evacuate?

The stakes were high: Just 6 years earlier, Nevado del Ruiz in Colombia erupted and killed more than 23,000 people. A “breakdown of communications” among scientists and local authorities was partly to blame, Ewert said.

In just a few weeks, PHIVOLCS and VDAP scientists had to interpret all the data they gathered about the volcano’s eruptive history and mold it into a simple warning scheme. The scheme had to be effective and easily digestible—enough so that they could convince tens of thousands of people living around the volcano, who spoke several different dialects and even different languages , to evacuate.

“One of our biggest challenges when we got to the Philippines was to actually convince people [that Pinatubo] was in fact a volcano.”

Language wasn’t the only obstacle. “One of our biggest challenges when we got to the Philippines was to actually convince people [that Pinatubo] was in fact a volcano,” Ewert said. Many locals accused the scientists from both PHIVOLCS and USGS of lying for financial gain or political reasons.

The team persevered, gathering local leaders of cities, towns, and small villages to explain the dangers and answer questions. Part of this educational campaign involved showing gruesome video footage from the Nevado del Ruiz tragedy that depicted destructive ash flows, volcanic mudflows, ashfalls, landslides, lava flows, and more. Though the scientists were concerned about overstating the hazards, in the end they “judged then (and still judge) that strong images were needed to awaken the population,” reflected PHIVOLCS and USGS scientists in 1996.

Here scientists learned a powerful lesson in hazard mitigation. As Ewert explained, “Showing people what had happened in other places in the world was much more effective than a scientist standing up in a crowd trying to explain it with interpretive dance and hand gestures.”

By early June, officials called for the evacuation of 25,000 people living in the area, including American service people at Clark Air Base and the U.S. Naval Station at Subic Bay. “By June 14 the recommended evacuation radius was 30 kilometers, which would have applied to perhaps 400,000 people,” Newhall said. Never before had such a widespread evacuation attempt been made before a volcanic eruption.

By the time the volcano erupted on 15 June, scientists and public officials had convinced more than 65,000 people to evacuate. More than 350 died during the eruption, but USGS and PHIVOLCS estimate that evacuation efforts saved between 5000 and 20,000 lives .

Evacuation zones surrounding Mount Pinatubo, created by scientists before the 15 June 1991 eruption.

3. Importance of Effective Communication

In 1991, scientists had to look up information in books, make photocopies, and fax information to each other, Ewert said. This was a time before GPS and before data could be sent via satellite. Smartphones were science fiction.

Cars and people traverse a flooded river in June 1991 after lahars wiped out bridges.

In an era without a 24-hour news cycle, scientists at PHIVOLCS and USGS couldn’t supply the local populations with minute-to-minute updates, much less day-to-day, and rumors spread . One of these rumors claimed that a 3-mile-long fissure had formed after the eruption and that the nearby city of Olongapo would soon be hit by a giant lateral blast.

“Cellular telephones helped briefly, as long as their batteries lasted,” PHIVOLCS and USGS scientists reflected in 1996. “But it was not until June 16 that we could tell the country that a caldera had already formed and that the climax of the eruption had probably passed.”

Today’s advanced tools would have been helpful, but “in the end, for successful natural hazard mitigation, it all comes down to how effective scientists and public officials are at communicating with each other and the public,” Ewert told Eos.

4. New Understanding of Triggers for Eruptions Involving Multiple Types of Magma

After the blast, investigations of cooled lava revealed that the eruption involved a mix of different types of magma, a phenomenon that had been seen before but wasn’t fully understood. Scientists had been aware of mixed-magma eruptions, but they weren’t sure what triggered them, Ewert said.

Start of a small explosion on 1 August 1991.

Magma can be classified into types that distinguish how much silica they contain and how viscous they are, among other characteristics. Basaltic volcanoes, like those on Hawaii , have less viscous, “runny” magma pools. Silicic magma—made of dacite or rhyolite—is stickier and more viscous . It holds more gas that when depressurized, erupts more explosively.

Studies of lava deposits after Pinatubo exploded revealed something curious: minerals juxtaposed that would not normally coexist together had magma come from one source, Newhall explained. Thermal signatures—for example, crystals partially resorbing, chemical diffusion between crystals—suggested that magma was initially a mix of basalt and dacite prior to the eruption. But by the end of the eruption, magma was fully dacite.

Basalt magma is denser than dacite, so based on density alone, “the basalt should have been trapped beneath the dacite,” Newhall said. Instead, it rose into the dacite and mixed with it. But how?

First, when the fresh, water-rich, and considerably hotter basalt hit the cooler dacite reservoir, the basalt crystallized, Newhall explained. That squeezed the basalt’s water and other dissolved gases into the remaining melt. Rather than remaining confined, the volatiles escaped from the melt and “formed tiny bubbles that decreased the density of the overall basaltic magma,” Newhall said. “So it was buoyant and rose into and mixed with a small amount of the dacite. That added even more volatiles.”

The resulting slurry was still less dense than its surroundings, so it kept rising and was the first erupted. Eventually, the dacite itself heated enough to rise to the surface and erupt.

This magma mixing manifested as subtly rumbling quakes that at times lasted about a minute long, called deep long-period (DLP) earthquakes . Long-period earthquakes indicate that magma is intruding into surrounding rock , but scientists had more frequently observed these events at depths less than 10 kilometers. Before Pinatubo, DLP earthquakes had been rarely observed and were not fully understood.

Nowadays, DLP earthquakes are “something we look for if we have a volcano that’s waking up,” Ewert said. Such a signal gives scientists clues into movements within the volcano’s plumbing.

5. Discovery That More Gas Erupts Than Studies of Rocks Can Reveal

Until Pinatubo, scientists assumed that the amount of gas a volcanic eruption released—mainly water vapor, carbon dioxide, and sulfur dioxide—was governed by the volume of magma erupted and the saturation levels the gas could reach within the magma, depending on the magma’s temperature. Collecting this information involves studying crystals of cooled lava after an eruption, Ewert said.

Satellite image of Mount Pinatubo’s eruption cloud about 2 hours after the onset of the 15 June 1991 eruption. The yellow x marks the volcano. Credit: USGS

But what scientists found at Pinatubo by directly studying emissions was that “there was far more sulfur gas emitted in the atmosphere than could be accounted for” by studying crystals, Ewert said. This implied that emissions of water vapor and carbon dioxide—the gases that dominate emissions—were also more than scientists expected.

Before Pinatubo, scientists thought that gas that couldn’t be dissolved into the magma escaped through vents to the surface. But a whopping 17 megatons of sulfur dioxide was released by the explosion, as measured by satellite spectrometer. This implied that large amounts of gas could accumulate as bubbles and remain in the magma chamber, Newhall explained

Because this excess gas makes an eruption more explosive, it might even be that such free gas is required for a Pinatubo-like eruption, Newhall said. If volatiles are already in excess, they can expand immediately once the pressure drops, without any delay from diffusing through melt.

Knowing that magmas can hold excess gas can help with forecasting efforts, Newhall explained. For example, if a volcano has been plugged since its previous eruption yet has been continuously recharged with fresh magma and gas from depth, scientists can examine the time between its eruptions to gauge whether the volcano has accumulated enough excess gas to make it particularly explosive.

6. Illumination of Details About Atmospheric Circulation

The total amount of sulfur dioxide released before and during the eruption caused the most profound effect on the stratosphere since Krakatau in 1883. The sulfuric aerosols that formed from the sulfur dioxide circled the Earth within 3 weeks and remained in the atmosphere for 3 years , reflecting enough sunlight to cool the entire planet by half a degree Celsius during that time.

Satellite measurements of aerosol missions from Mount Pinatubo on 16 June 1991.

However, during the following winter, Europe experienced surprisingly warm temperatures. This winter warming hadn’t been observed after past volcanic eruptions, like Mexico’s El Chichón in 1982. What could be going on?

Using atmospheric circulation models and computer simulations to study how Pinatubo’s sulfur aerosol cloud traveled around the globe, scientists found that sulfuric aerosols reflect sunlight outward while absorbing heat from below, leading to cooling of the troposphere while heating the lower stratosphere, explained Alan Robock , an atmospheric scientist at Rutgers University in New Brunswick, N.J.

This temperature gradient strengthened the Arctic Oscillation , a wind pattern circling the Arctic. In its strong phase, the Arctic Oscillation pulls warm air from the ocean, heating northern Europe and shifting northward the global jet stream —the “river” of wind that flows around the globe.

The shifted jet stream allowed warm winds to flow over the Northern Hemisphere during the winter, Robock said. Because the jet stream flows like a wave, while Europe was receiving warm air from the south, the Middle East received colder air from the north, bringing to Jerusalem the worst snowstorm in 40 years .

“At the time of the Pinatubo eruption, nobody knew about winter warming,” Robock said. Armed with advances in modeling, plus the highly monitored atmospheric effects from Pinatubo’s eruption, atmospheric scientists are better prepared to forecast the global effects of the next big eruption, Robock added.

7. A Bolstered Case That Humans Cause Global Warming

The eruption helped scientists definitively declare that human emissions of greenhouse gases are to blame for at least the past 60–70 years of warming.

Scientists tracked sulfur aerosols sourced from Pinatubo’s eruption as they traveled around the world. For 2 years following the blast, surface temperatures cooled , as forecasted by climate models that included Pinatubo’s injections into the atmosphere. Temperatures rose again once the cooling aerosols fell out of the atmosphere.

Pinatubo, in a sense, served as a natural climate experiment to test and calibrate models.

Pinatubo, in a sense, served as a natural climate experiment to test and calibrate models. Scientists plugged observed volcanic emissions into climate change models with and without anthropogenic emissions of greenhouse gases. In the simulations that included only volcanic eruptions, scientists didn’t see the past 60–70 years of consistent warming, Robock explained.

This observation helped climate scientists sharpen their models further, confirming that humans—and the unprecedented amounts of greenhouse gases they pump into the atmosphere every year—are to blame for the warming climate. The Intergovernmental Panel on Climate Change was able to use these newly sharpened models to further support the attribution of climate change to human activities.

8. More Weight to Arguments Against Geoengineering

Some scientists have suggested hacking into our own atmosphere to counteract the effects of climate change, but Pinatubo’s eruption raised great concerns over whether such direct manipulation could be controlled. Known as “ geoengineering ,” one of these methods would involve injecting sulfur dioxide particles into the atmosphere just like a volcanic eruption would.

Robock and other scientists agree that this kind of injection would have negative consequences. One consequence is the destruction of the atmosphere’s ozone layer, which prevents dangerous ultraviolet rays from hitting Earth.

To halt global warming, humans would have to inject 100 million tons of sulfur dioxide into the atmosphere every year—that amounts to about five Pinatubo eruptions per year.

Clouds of sulfuric acid particles—created when sulfur dioxide newly injected into the stratosphere meets water—provide surfaces on which ozone-destroying chemical reactions take place. In the 2 years after the eruption, atmospheric ozone destruction sped up, and the ozone hole over the Southern Hemisphere increased to an “ unprecedented size .”

Robock said that to halt global warming, humans would have to inject 100 million tons of sulfur dioxide into the atmosphere every year—that amounts to about five Pinatubo eruptions per year. Scientists generally agree that the consequences of geoengineering are too risky to attempt. It would be safer and more practical to reduce carbon dioxide emissions and “keep fossil fuels in the ground,” Robock said.

A view of Mount Pinatubo’s caldera, now filled with a lake, in 2013.

Pinatubo’s Legacy

In 1996, USGS and PHILVOLCS scientists wrote this sobering reminder of how, if factors had been different, disaster may not have been averted at Mount Pinatubo: “In hindsight, we should have been less concerned about overstating the hazard and more concerned about speeding preparations for evacuations. Pinatubo almost overtook us.”

Mount Pinatubo, for now, stands relatively quiet, some 300 meters shorter than it was before it exploded 25 years ago. What might the next 25 years bring to Pinatubo? Time will tell.

—JoAnna Wendel, Staff Writer; and Mohi Kumar, Scientific Content Editor, Eos.org

Wendel, J.,Kumar, M. (2016), Pinatubo 25 years later: Eight ways the eruption broke ground, Eos, 97 , https://doi.org/10.1029/2016EO053889 . Published on 09 June 2016.

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Remembering Mt. Pinatubo

A conversation with nasa disasters program associate manager, john murray.

The second-largest volcanic eruption of the 20th century occurred at Mount Pinatubo in the Philippines on June 15, 1991. By far the largest eruption in the past 100 years to affect a densely populated area, Pinatubo produced high-speed avalanches of pyroclastic flows and a cloud of volcanic ash hundreds of miles across. Meanwhile, Typhoon Yunya brought cascading hazards such as flooding and fast-moving lahars when it arrived within 75 km of the volcano during the eruption’s peak activity.

The effects of Mt. Pinatubo’s eruption combined with Typhoon Yunya were devastating. The disaster impacted approximately two million people directly, primarily by widespread ashfall and damaged crops. Reports estimated $700 million in damage , including $100 million of damages to aircraft flying at the time of the eruption, with the rest a combination of agriculture, forestry and land.

Still, because the eruption was forecast by scientists from the Philippine Institute of Volcanology and Seismology (PHIVOLCS) and the U.S. Geological Survey (USGS), civil and military leaders were able to undertake massive evacuations and measures to protect property before the eruption. Seventeen ships evacuated tens of thousands of U.S. Department of Defense civilian personnel and their dependents from Clark Air Base and U.S. Naval Base Subic Bay during "Operation Fiery Vigil." Those actions saved up to 5,000 lives and $250 million in property.

NASA Disasters associate program manager John Murray was there. At the time, he served on the Navy's newest aircraft carrier, the USS Abraham Lincoln, which evacuated 4,400 people from the island in two days. Murray currently serves as an associate program manager for the Disasters program area of NASA's Earth Science Applied Sciences Program and the program's lead response and risk reduction coordinator at NASA's Langley Research Center. We caught up with him recently and asked if he would share some of his recollections of that momentous event 30 years ago and its implications that carry forward to today.

Q: Thank you for sharing your experience with us, John. What brought you to Mt. Pinatubo during the eruption?

A: At the time, I was Meteorology and Oceanography Officer for the USS Abraham Lincoln aircraft carrier battlegroup and a crew member on the Lincoln. Our weather office advised the ship, the embarked airwing and the admiral’s staff on weather and oceanographic matters. In addition, we put together forecasts for the battle group and conducted pilot weather briefings for aircraft sorties from the Lincoln, which normally cycled every 90 minutes or so, 24/7. We had deployed from Alameda, California and were en route across the western Pacific to the Persian Gulf when we were told to divert and evacuate all the military dependents that were stranded from the eruption of Mt. Pinatubo. The eruption was ongoing as we were steaming in. We had hoped to approach directly from the north to save time, but since Typhoon Yunya was threatening, we went into Subic Bay from the south through the San Bernardino Straits to avoid the storm.

Image: Tropical Storm Yunya arrives about 5 miles away from land in this image taken by the NOAA-12 satellite on June 14, 1991. The eruption column from Mt. Pinatubo (in dark grey) can be seen through the storm's clouds. Credits: NOAA

Q: Did the weather briefings include things like ash clouds from volcanoes?

A: After Pinatubo erupted, definitely. When we went into the Philippines, we were very concerned about the potential for damage from volcanic ash, so we had an exclusion zone where we didn't fly. Our aircraft engines operated at about 1500 degrees (Fahrenheit), but volcanic glass melts at about 1200 degrees and can very quickly foul them and cause the engine to lose thrust or fail. It's also very abrasive and will score an aircraft windscreen, and in fairly short order, will turn it opaque. It's definitely a threat, so several days before we arrived, we took most of the aircraft into the hangers below deck. We wrapped the engines of the ones remaining on deck in tarps so no volcanic aerosols could contaminate them.

Q: Months before the “big” eruption, what signs told researchers that an eruption was imminent?

A: I wasn’t part of the group that monitored the pre-eruptive activity, so I wasn’t aware of any degassing or whether the size of the lava dome had begun to typically expand before the eruption. These days we use synthetic aperture radar from space to monitor the deformation of the Earth’s surface, so you can see the rate of expansion. We use instruments like the Ozone Monitoring Instrument (OMI) on the NASA Aura satellite and the Ozone Mapping and Profiler Suite (OMPS) on the NASA/NOAA Suomi NPP and NOAA JPSS satellites to detect sulfur dioxide emissions before and after a major eruption. Thermal infrared observations from the latter two satellites also can show us where heat anomalies from magma in the lava dome are occurring. Back then, you had to rely mainly on seismic instrumentation and optical observations. Seismic instrumentation is important; it’s still the primary source of information to monitor volcanic activity. But I’m grateful for the increased insight that we have with Earth-observing satellites compared to 30 years ago.

Q: What did you see as you approached the Philippines?

A: We had to rely mostly on optical imagery to give us an idea of what was going on with respect to the eruption and its coincidence with the typhoon. For the eruption itself, we were receiving messages based on analysis done back in the states by the U.S. Geological Survey and their sources. Compared to today, the technology we had in the weather office was limited to teletype equipment and a Unix machine onboard the ship that received and processed (data from) NOAA Polar-orbiting satellites and ran a rudimentary plume model that wasn't designed to forecast volcanic ash movement. Approaching the island of Luzon, we observed the path where the typhoon intersected with the volcano with great concern. The eye (of typhoons and hurricanes) isn't always reflected at the same location on the ground as it is aloft; it's canted. From what I recall, as we were looking at the imagery, it looked like the volcano was erupting directly through the eye. This was the only information we had. The Navy had a meteorology office near Subic Bay that I'd visited in the past, but it had been effectively shut down because of all the ash fall.

Q: What did you see when you arrived?

A: As we pulled up pierside, it was an eerie experience. The ash had been accumulating over several days, so they had swept most of the roofs and taken road construction equipment and plowed the roads, much like you would plow the roads for snow. I'm from upstate New York, and when I was a kid, I'd look out my bedroom window and see snowbanks all the way down the street. It wasn't a nice bright white snowbank, but it looked much a typical winter scene after a real heavy snowfall. The volcanic ash was dull gray with some brown, and some of the roofs still had significant ash accumulation on top of them.

Ash covers the Subic Bay naval station following the eruption of Mount Pinatubo in 1991. Credits: U.S. Navy/SGT PAUL BISHOP

Q: What were the cascading dangers that Typhoon Yunya brought?

A: Yunya created a real humanitarian disaster. Much of the area around there became totally uninhabitable, so many local inhabitants who could evacuate had gone to other parts of the island. The rainfall was so heavy, however, that the night before we arrived, a large group of people who remained had sheltered in a gymnasium for protection from the hurricane. Once saturated, several feet of ash on the roof became like heavy concrete, and the roof collapsed. There were a significant number of fatalities from that. In addition, there were many structural failures off base due to the weight of the ash on buildings. The combined effect of the water and the ash was devastating.

Q: Tell us more about the evacuation.

A: The evacuation was all of the military families from the Subic Bay Naval Station, Cubi Point Air Station, and Clark Air Force Base. Some of the military was redeployed to other areas, but the civilian dependents who couldn't get out on their own, had to be evacuated by us. We embarked many of these families on board the aircraft carrier and made two trips from Subic Bay south to the island of Cebu, where the Air Force was flying large transport aircraft out from an old airstrip left over from World War II.

We were taking thousands of people. Interestingly, people come with a lot of stuff, including pets! Down in the hangar bay, there are tie-down spots in the deck every 10 feet or so to secure aircraft. Many now had a dog carrier, cat carrier, or birdcage attached. The U.S. government is very supportive of military families and their dependents, so their pets were also taken on board. People had to go down periodically to comfort, feed, and clean up after them. In addition to a very unhappy Doberman giving birth to a litter of puppies under some yellow gear (aircraft tows), at least one other unusual situation also stuck with me. There were some local people who had been potentially stranded, and it appeared that a few hastily arranged marriages may have occurred. I recall a distraught young lady searching for her husband, and she didn't know his last name! There was no alternative but to get on the intercom like they do when a child wanders off in a department store to ask for a young newlywed named “Ricky” to please report to the quarterdeck because his wife was frantically searching for him.

U.S. military dependents board the nuclear-powered aircraft carrier USS Abraham Lincoln (CVN-72) on June 17, 1991, as they prepare to depart in the aftermath of Mount Pinatubo's eruption. Credits: U.S. Navy/Patrick Muscott

Q: Even with the success of the evacuations, there were still fatalities. The eruption disproportionately impacted the native Aeta, a small aboriginal tribe that numbered about 60,000 before the eruption. What can we do to protect the most vulnerable populations from events such as this?

A: In the more developed world, you can improve infrastructure, right? You don't always have those options in a lot of developing countries. So, the best you can do, I think, is to provide as much assistance is as you can both technically and on a humanitarian basis. The USGS has a Volcano Disaster Assistance Program (VDAP), which is one of our primary collaborators through the Disasters Program. They provide warnings and assessments in the event of a potential eruption or after one has occurred. In the US., the National Institute of Standards and Technology (NIST) has a group that works on building codes. They work closely with the insurance industry. There are parallels in the international community with the reinsurance industry working with different technical and engineering groups to provide consulting to improve infrastructure resilience and resistance to the impacts of things like volcanic eruptions–but more often for earthquakes, hurricanes and floods.

On the humanitarian side, NASA collaborates with a lot of different humanitarian organizations ranging from the Red Cross, FEMA (the Federal Emergency Management Agency, NOAA (the National Oceanic and Atmospheric Administration) the National Weather Service (NWS), National Guard units, the U.N. (United Nations), CEPREDENAC (the Coordination Center for Disaster Prevention in Central America and the Dominican Republic) and many, many other local, state, federal and international institutions to protect communities across the globe throughout the disasters cycle. Just this month, I’d note NASA’s role and support in the establishment of the newest volcano research supersite in Nicaragua , which will increase the region’s access to Earth observation data.

Q: In your role at NASA today, you are at the cutting-edge of volcano research technology. If the folks dealing with Mt. Pinatubo’s eruption in 1991 could have access to today's monitoring equipment back then, what–in your personal opinion–do you think they would wish for most?

A: I really think that the remote sensing capabilities we have from space are the big game-changer these days. Ground-based monitoring hasn’t changed all that much, although the technology is better. Obviously, communication is faster. We had extremely low-capacity communications lines compared to today. The big changes between now and then are instantaneous broadband communications via the internet and satellite remote sensing, primarily via radar sensors. We also didn't have the benefit of sophisticated plume trajectory models like NASA's Disasters Team uses today, such as NOAA's HYSPLIT model and the Langley Trajectory Model (LaTM).

When I was looking at Pinatubo imagery (in 1991), the area was tropical, and there was a lot of convection. It was tough to distinguish between the regular and ash clouds with the naked eye, so we had to be extra conservative. We couldn't take the risk if we couldn't tell the difference between ash, water and ice clouds. So, we had thousands of square kilometers of warning area in which ash was only a fraction of that area. Fast forward to 2007, work with the University of Wisconsin supported by NASA's Applied Sciences Program helped to improve our ability to differentiate between ash and ice clouds. So, now people can go in and look at multi-channel spectroscopy and very easily differentiate between the ash and the water clouds. The International Civil Aviation Organization (ICAO), an agency of the United Nations , has also set up a worldwide network of Volcanic Ash Advisory Centers, or VAACS, since the time of the Pinatubo eruption. I'm pleased to say that type of information (differentiating between ash and ice clouds) has been incorporated into the warnings that the VAACs provide.

Q: What other resources does NASA provide now to help people understand and make informed decisions about volcanos with increased confidence?

A: When you look at NASA, you must realize that we are a research agency. We don't have the same responsibilities as those who actually have to provide a forecast or have a statutory responsibility like NOAA for weather, or the USGS for geological information and hydrological information. What we really offer is information that fills critical gaps in technology and in science knowledge. Much of what we have is experimental in nature. Clearly, we have high confidence in many of the things that we produce because we understand the underlying science behind it. We're able to add value and insights based on cutting-edge technologies that may be under development and not yet part of the normal warning process. Our website and the Disasters Mapping Portal are good places to see how people use NASA products to inform disaster risk reduction and response.

Q: Considering the next 30 years, what do you anticipate will be the next major innovation in volcanology research?

A: The launch of more Synthetic Aperture Radar satellites, such as the upcoming NASA/ISRO SAR ( NISAR ) mission scheduled to launch in January 2023, will be a game-changer. I could see hints of this advance in our NASA Disasters Program's recent use of the Japanese Space Agency's ALOS-2 satellite in monitoring the lava dome expansion of LaSoufrière volcano on the Caribbean Island of St. Vincent. We did this for several months before its eruption this past April. Increasing the frequency and number of observations like this may also aid the development of prediction models, which currently are only used for research purposes because they do not yet accurately predict the time or magnitude of an eruption. I'm also excited about the increasing involvement of the commercial sector in space, which will hopefully make observations such as these and others more ubiquitous in the future.

Q: What else comes to mind when reflecting on the significance of the Mt. Pinatubo eruption?

A: Everyone always thinks about the proximate spatial and temporal impacts of major eruptions, but in the long term, understanding the impact of volcanoes on climate change is another important aspect. Average global temperatures are normally cooler after significant eruptions because less solar radiation reaches the lower atmosphere in their aftermath. Sulfate aerosols a from the eruption plume ejected into the stratosphere and stayed there for more than five years. NASA’s Langley Research Center, where I’m based, played a key role in monitoring that using data from SAGE II . Mt. Pinatubo had a significant impact on ozone loss in the stratosphere and is the only major eruption we have on record showing the climate impacts of volcanoes. (Editor’s note: Because of the sunlight-absorbing effect of the aerosols in the stratosphere, scientists measured a drop in the average global temperature of about 1 degree F [0.6 degrees C] over the 15 months following the eruption.)

Ashfall from Mount Pinatubo's 1991 eruption covers vehicles near Clark Air Base in a snowlike blanket of tephra deposit on June 16, 1991. Credits: USGS/R.P. Hoblitt

Q: What final thoughts would you like to share with us?

A: Major eruptions generate public awareness of various societal vulnerabilities and other impacts, even climate change. They are often what motivates policymakers to engage the science community to redouble its efforts to close critical knowledge gaps to help understand, mitigate or prevent impacts of future events. However, it is essential not to wait for an imminent eruption to put focus on volcano research. It is always important to continue to strive to improve our science capabilities to observe, forecast, assess, respond, recover and reduce the risk for disasters.

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Looking back: When Mount Pinatubo blew its top

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This is AI generated summarization, which may have errors. For context, always refer to the full article.

Looking back: When Mount Pinatubo blew its top

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

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.

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

Remembering the 1990 Luzon Earthquake

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:

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.

MAP: Active volcanoes in the Philippines

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.edu , www.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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A Level; volcano case study - Mount Pinatubo, Philippines 1991

Subject: Geography

Age range: 16+

Resource type: Lesson (complete)

Last updated

3 March 2020

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This lesson includes a range of maps, photos and facts which tell the story of the andesitic eruption in 1991. Pupils can take notes to build up their case study of the eruption.

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A Level; volcanoes

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Remembering Mt. Pinatubo 25 Years Ago