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Mount Pinatubo Case Study (Effects (Economic (The eruption cost 700…

  • The formation of Mount Pinatubo begins with the formation of the chain of volcanoes, the Luzon Volcanic arc. A chain of volcanoes most likely means that a destructive plate boundary must have occurred there, which in fact is what actually happened. The denser oceanic philippine plate subducted under the less dense continental Eurasian plate. The more the philippine plate subducted, the hotter it got and the plate began to melt. This magma goes up through the cracks because of the pressure. The magma creates a row of volcanoes along the fault line
  • an earthquake with a 7.3 on the richter scale happened around 100 kilometers from the volcano, which moved the crust beneath Mt Pinatubo.
  • The eruptions damaged central Luzon, home to about 3 million people. 20,000 indigenous Aeta highlanders, who had lived on the slopes of the volcano, were displaced. About 200,000 people who evacuated from the area around Pinatubo before and during the eruptions have returned home but face the threat of lahars that have buried so many towns and villages. Those who didn't return home had to migrate to Manila
  • the authorities of the Philippine government moved over 60,000 people away from their homes.
  • 75,000 people evacuated. The US air force helped
  • Alert systems were put into place to warn of eruption.
  • The government created multiple shelters for disease control and long term aid
  • More than 400 people died during the eruption, 300 of them died of falling roofs whilst another 100 from mudflow. Disease that broke out in evacuation camps and the continuing mud flows in the area caused more deaths, bringing the total death toll up to 847 people.
  • Many of the school there had were destroyed and thus education was halted
  • The eruption cost 700 million US dollars
  • 650,000 people lost there jobs
  • 1.2 million homes distroyed
  • Heavy rainfall caused multiple buildings to collapse
  • Lots of infrastructure was destroyed
  • The airport had to shut down
  • The Farmland was destroyed by the ash and this made the farmlands useless, and many lost there jobs because of it
  • The volcano was so strong that it created a huge crater now known as lake Pinatubo as it filled up with water.
  • Fast flowing volcanic mudflows (lahars) caused a lot of erosion effecting many things like rivers bridges ect.
  • Volcanic ash is blown in all directions over very long distances, destroying fields and buildings.
  • The sulfur dioxide also caused acid rain which killed ecosystems and damaged buildings.
  • 20 million tons of sulfur dioxide were injected into the atmosphere in Pinatubo's eruption, and the release of the gas cloud around the world caused global temperatures to drop by 0.5°C
  • 15th June 1991
  • South East Asia, Philippines, the island of Luzon. It is in the middle of the Eurasian and Philippine plate it is part of the chain of volcanoes known as the Luzon volcanic arc.
  • On April 2nd the volcano showed signs of volcanic activity, which slowly became stronger. Sulfur dioxide started to be released by the volcano. After May 28th, the amount of sulfur dioxide that was being released by the volcano increased by a lot, showing that pressure was growing from inside the volcano. On June 15th, the eruption began
  • It generated an ash column that was over five km high
  • The eruption produced high-speed avalanches of hot ash and gas, mudflows, and a cloud of volcanic ash.
  • Mt Pinatubo is created by the Eurasian plate subducting underneath the Philippine Sea Plate. The two plates are responsible for the volcano's formation

Pinatubo 1991

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  • Emergency Management

Mt. Pinatubo is a stratovolcano in the Philippines. June 15, 1991, it erupted, resulting in the second-largest eruption of the 20 th century. The ash plume height reaching more than 40 km (28 mi) high and ejecting more than 10 km 3 of magma , classifying it as plinian /ultra plinian eruption style and VEI 6 in eruption size.

A complicating factor in the dispersal of ash was at the same time as the eruption, Typhoon Yunna channeled the ash from the usual dispersal out to the ocean toward the island of Luzon. This combination gave rise to wet ash, increasing loading on structures with a large proportion of the 847 death toll due to roof collapse.

1991 Mt. Pinatubo eruption caused widespread impacts across societal, economic and environmental areas. Pyroclastic flows, lahars as well as the ashfall hazard all resulted in damage and casualties. The eruption cost $700 million in damage, $100 million of which was damage to 16 aircraft flying at the time of the eruption and $250 million in property with the rest a combination of agriculture, forestry and land.

The Cataclysmic 1991 Eruption of Mount Pinatubo, Philippines

Chris Newhall, James W. Hendley II, and Peter H. Stauffer

Graphics by Susan Mayfield and Sara Boore

Banner design by Bobbie Myers

Web design and layout by Carolyn Donlin

COOPERATING ORGANIZATIONS Armed Forces of the Philippines National Disaster Coordinating Council, Philippines Philippine Institute of Volcanology and Seismology U.S. Agency for International Development United States Air Force United States Navy

Related Fact Sheets

What Are Volcano Hazards? (USGS Fact Sheet 002-97)

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

Lahars of Mount Pinatubo, Philippines (USGS Fact Sheet 114-97)

See a list of other volcano-related fact sheets published by the U.S. Geological Survey

PDF version of this fact sheet (284 KB)


Learn more about volcanoes and the hazards they pose at the USGS Volcano Hazards Program website

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  • 1. slidesharCase Study: Mount Pinatubo - 1991 Where did it happen?Mount Pinatubo is a stratovolcano found in the north east Philippines. It formed where the Eurasian plate is being subducted beneath the Philippine plate. It last erupted in 1993. What happened? 15th March 1991 earthquakes felt by villagers on the north western side of the volcano. Earthquakes of increasing intensity for the next 2 weeks. 2nd April 1991 phreatic eruptions along a 1.5km fissure on the summit. Small eruptions of volcanic ash over the next few weeks. 3rd May first eruption of magma. 7th June Large explosion generated an ash column 7km high. 12th June more violent eruptions with small earthquakes producing ash columns 24km high. 15th June ash was ejected 34km into the atmosphere. Pyroclastic flows travelled up to 16km and the ash mixed with rain from typhoon Yunya creating lahars. The eruption lasted for 3 hours. Primary effects Secondary effects E n v i r o n m e n t a l Ash cloud covered 125000km2 bringing darkness to central Luzon. Volcanic ash smothered 80000 hectares of land. 150km2 of reforestation projects destroyed. Lahars caused severe erosion to rivers. Global cooling caused by the ash. Temperatures dropped by 0.5°C. Lahars continued to affect the area for 6 years. Acid rain due to the 22million tonnes of SO2 erupted. E c o n o m i c 800km2 agricultural land destroyed and 800000livestock and poultry killed costing 1.5 billion pesos. Full economic recovery cost £10 billion. S o c i a l 847 people killed by collapsing roofs Ash and pumice destroyed 42000 homes 1.2 million people lost their homes 100 people killed by lahars 500 people died from diseases such as measles in refugee camps Many indigenous Aeta people had to move into government organised resettlement areas because their homes were destroyed. This caused the Aeta society to become fragmented.
  • 2. Immediate responses Long term responses Manila airport closed 200000 people relocated Red Cross, Action Aid and Oxfam provided food and blankets in evacuation camps 23 USGS personnel helped advise the community and government officials for 8 weeks President Ramos created the Mount Pinatubo Commission to raise 10 billion Filipino pesos in aid. New houses have been built on stilts so future lahars will not bury them. Norway and UK government sent millions in aid Overseas Filipino Workers provided clothing for victims 5 billion pesos spent on used to build dykes for lahars (later washed away by the lahars) How was the hazard managed? The hazard was managed. There were lahar detecters in place and hazard maps. The volcano was being monitored by scientists and evidence suggested that there was going to be an eruption soon.
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Internet Geography

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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Remembering Mt. 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.

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.

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.

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.

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.

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

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