The Cataclysmic 1991 Eruption of Mount Pinatubo, Philippines, Fact Sheet 113-97 U.S. Geological Survey Fact Sheet 113-97 The Cataclysmic 1991 Eruption of Mount Pinatubo, Philippines The second-largest volcanic eruption of this century, and by far the largest eruption to affect a densely populated area, occurred at Mount Pinatubo in the Philippines on June 15, 1991. The eruption produced high-speed avalanches of hot ash and gas, giant mudflows, and a cloud of volcanic ash hundreds of miles across. The impacts of the eruption continue to this day. A huge cloud of volcanic ash and gas rises above Mount Pinatubo, Philippines, on June 12, 1991. Three days later, the volcano exploded in the second-largest volcanic eruption on Earth in this century. Timely forecasts of this eruption by scientists from the Philippine Institute of Volcanology and Seismology and the U.S. Geological Survey enabled people living near the volcano to evacuate to safer distances, saving at least 5,000 lives.

Precursors to the 1991 Eruptions On July 16, 1990, a magnitude 7.8 earthquake (comparable in size to the great 1906 San Francisco, California, earthquake) struck about 60 miles (100 kilometers) northeast of Mount Pinatubo on the island of Luzon in the Philippines, shaking and squeezing the Earth's crust beneath the volcano. At Mount Pinatubo, this major earthquake caused a landslide, some local earthquakes, and a short-lived increase in steam emissions from a preexisting geothermal area, but otherwise the volcano seemed to be continuing its 500-year-old slumber undisturbed. In March and April 1991, however, molten rock (magma) rising toward the surface from more than 20 miles (32 kilometers) beneath Pinatubo triggered small earthquakes and caused powerful steam explosions that blasted three craters on the north flank of the volcano. Thousands of small earthquakes occurred beneath Pinatubo through April, May, and early June, and many thousand tons of noxious sulfur dioxide gas were also emitted by the volcano.

Following Mount Pinatubo's cataclysmic June 15, 1991, eruption, thousands of roofs collapsed under the weight of ash made wet by heavy rains (see example in photo above). Ash deposits from the eruption have also been remobilized by monsoon and typhoon rains to form giant mudflows of volcanic materials (lahars), which have caused more destruction than the eruption itself (photo at right shows village buried by lahars). (Photo above courtesy of Peter Baxter, University of Cambridge. The Eruptions From June 7 to 12, the first magma reached the surface of Mount Pinatubo. Because it had lost most of the gas contained in it on the way to the surface (like a bottle of soda pop gone flat), the magma oozed out to form a lava dome but did not cause an explosive eruption. However, on June 12 (Philippine Independence Day), millions of cubic yards of gas-charged magma reached the surface and exploded in the reawakening volcano's first spectacular eruption.

When even more highly gas charged magma reached Pinatubo's surface on June 15, the volcano exploded in a cataclysmic eruption that ejected more than 1 cubic mile (5 cubic kilometers) of material. The ash cloud from this climactic eruption rose 22 miles (35 kilometers) into the air. At lower altitudes, the ash was blown in all directions by the intense cyclonic winds of a coincidentally occurring typhoon, and winds at higher altitudes blew the ash southwestward. A blanket of volcanic ash (sand- and silt-size grains of volcanic minerals and glass) and larger pumice lapilli (frothy pebbles) blanketed the countryside. Fine ash fell as far away as the Indian Ocean, and satellites tracked the ash cloud several times around the globe. Huge avalanches of searing hot ash, gas, and pumice fragments (pyroclastic flows) roared down the flanks of Mount 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 below the volcano that the summit collapsed to form a large volcanic depression (caldera) 1.6 miles (2.5 kilometers) across. Much weaker but still spectacular eruptions of ash occurred occassionally through early September 1991. From July to October 1992, a lava dome was built in the new caldera as fresh magma rose from deep beneath Pinatubo. Continuing Hazards Even after more than 5 years, hazardous effects from the June 15,1991, climactic eruption of Mount Pinatubo continue. The thick, valley-filling pyroclastic-flow deposits from the eruption insulated themselves and have kept much of their heat. These deposits still had temperatures as high as 900&#176F (500&#176C) in 1996 and may retain heat for decades. When water from streams or underground seepage comes in contact with these hot deposits, they explode and spread fine ash downwind.

Since the climactic 1991 eruption, ash deposits have also been remobilized by monsoon and typhoon rains to form giant mudflows of volcanic materials (lahars). The June 15, 1991, explosive eruption of Mount Pinatubo, Philippines, was the second largest volcanic eruption of this century and by far the largest eruption to affect a densely populated area. The eruption produced high-speed avalanches of hot ash and gas (pyroclastic flows), giant mudflows (lahars), and a cloud of volcanic ash hundreds of miles across. (U.S. bases have reverted to Philippine control since 1991.) Impacts of the Eruptions Fortunately, scientists from the Philippine Institute of Volcanology and Seismology and the U.S. Geological Survey had forecast Pinatubo's 1991 climactic eruption, resulting in the saving of at least 5,000 lives and at least $250 million in property. Commercial aircraft were warned about the hazard of the ash cloud from the June 15 eruption, and most avoided it, but a number of jets flying far to the west of the Philippines encountered ash and sustained about $100 million in damage.

Although much equipment was successfully protected, structures on the two largest U.S. military bases in the Philippines--Clark Air Base and Subic Bay Naval Station--were heavily damaged by ash from the volcano's climactic eruption. Nearly 20 million tons of sulfur dioxide were injected into the stratosphere in Pinatubo's 1991 eruptions, and dispersal of this gas cloud around the world caused global temperatures to drop temporarily (1991 through 1993) by about 1&#176F (0.5&#176C). The eruptions have dramatically changed the face of central Luzon, home to about 3 million people. About 20,000 indigenous Aeta highlanders, who had lived on the slopes of the volcano, were completely displaced, and most still wait in resettlement camps for the day when they can return home. About 200,000 people who evacuated from the lowlands surrounding Pinatubo before and during the eruptions have returned home but face continuing threats from lahars that have already buried numerous towns and villages.

Rice paddies and sugar-cane fields that have not been buried by lahars have recovered; those buried by lahars will be out of use for years to come. 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 For more information or paper copies of this fact sheet contact: U.S. Geological Survey Mount Pinatubo | volcano, Philippines | Britannica.com Mount Pinatubo Mount Elbrus Mount Pinatubo, volcano , western Luzon , Philippines , that erupted in 1991 (for the first time in 600 years) and caused widespread devastation. Mount Pinatubo is located about 55 miles (90 km) northwest of Manila and rose to a height of about 4,800 feet (1,460 m) prior to its eruption. After two months of emissions and small explosions, a series of major explosions began on June 12.

These explosions reached a peak on June 14–16, producing a column of ash and smoke more than 19 miles (30 km) high, with rock debris falling the same distance from the volcano. The resulting heavy ashfalls left about 100,000 people homeless, forced thousands more to flee the area, and caused 300 deaths. The ashfalls forced the evacuation and eventual closing of U.S.-leased Clark Air Force Base, 10 miles (16 km) east of the volcano. Mount Pinatubo, Philippines. Wildfire2383 The ash and smoke cloud ejected by Mount Pinatubo in 1991 contained about twice as much matter as that thrown up by the El Chichón volcano (1982), making Pinatubo perhaps the largest eruption of the 20th century. Pinatubo erupted again in late August 1992, killing more than 72 people. Gas and ash rising from Mount Pinatubo, central Luzon, Philippines, just prior to eruption in June … David H.

Harlow/U.S.Geological Survey Lahars of Mount Pinatubo, Philippines, Fact Sheet 114-97 U.S. Geological Survey Fact Sheet 114-97 Online Version 1.1 Lahars of Mount Pinatubo, Philippines On June 15, 1991, Mount Pinatubo in the Philippines exploded in the second largest volcanic eruption on Earth this century. This eruption deposited more than 1 cubic mile (5 cubic kilometers) of volcanic ash and rock fragments on the volcano's slopes. Within hours, heavy rains began to wash this material down into the surrounding lowlands in giant, fast-moving mudflows called lahars. In the next four rainy seasons, lahars carried about half of the deposits off the volcano, causing even more destruction in the lowlands than the eruption itself. Background Before April 1991, when steam explosions blasted out three small craters on the north flank of Mount Pinatubo on the island of Luzon in the Philippines, the volcano had been dormant for 500 years, allowing lush tropical vegetation to cover its slopes.

Eventually, the population of the region grew to nearly 1,000,000 people, as towns, cities, and hundreds of villages, as well as the largest U.S. military base in the Philippines (Clark Air Base), were built on the broad gentle slopes surrounding the volcano. When Pinatubo reawakened in April 1991, scientists from the Philippine Institute of Volcanology and Seismology (PHIVOLCS) intensified their monitoring of the volcano; they were soon joined by scientists from the U.S. Geological Survey (USGS) and other organizations. While evaluating the threat from the volcano, these scientists discovered that the gentle slopes surrounding Pinatubo had largely been created by countless giant mudflows of volcanic debris (lahars) from the powerful ancient eruptions that built the volcano. They also concluded that lahars would again rush down Pinatubo's slopes in its next major eruption, threatening the communities that were built while it slumbered.

In August 1991, 2 months after Mount Pinatubo, Philippines, exploded in a cataclysmic volcanic eruption, this house (see roof) along the Sacobia-Bamban River 15 miles from the volcano was buried by a fast-moving mudflow of volcanic ash and debris (lahar) caused by heavy rains. Inset photo shows the house before it was buried. (Photos by Raymundo S. Punongbayan, Philippine Institute of Volcanology and Seismology.) Nature and Causes of Lahars Explosive eruptions can deposit huge amounts ash and other volcanic debris on a volcano's slopes. Lahars form when water from intense rainfall, melting snow and ice, or the sudden failure of a natural dam, mixes with this loose volcanic material, creating mudflows that can be particularly dangerous and destructive. Although lahars contain at least 40% (by weight) volcanic ash and rock fragmentsmaking them dense and viscous like wet concretethey actually flow faster than clear-water streams.

These mudflows can rush down the flanks of a volcano at speeds as great as 40 miles (65 kilometers) per hour and can travel more than 50 miles (80 kilometers). Lahars that contain the most debris (as much as 90%) move the fastest and are the most destructive. The village of Lourdes, built on lowlands 15 miles northeast of Mount Pinatubo, was inundated by giant, fast-moving mudflows of volcanic debris (lahars) in the months following the volcano's cataclysmic June 1991 eruption. Since that eruption, lahars have destroyed the homes of more than 100,000 people in the area surrounding Pinatubo. Conditions that Create Lahars at Pinatubo Annual rainfall at Mount Pinatubo ranges from 80 inches (2,000 millimeters) on the volcano's northeast flank to more than 160 inches (4,000 millimeters) on its summit and southwest flank. Nearly all of this rain falls during the time of the southwest monsoon (June to September) and the overlapping typhoon season (June to October).

Rainfall during typhoons can be as intense as 2 inches (50 millimeters) per hour. Since the volcano's cataclysmic June 1991 eruption, the maximum rainfall at Pinatubo in one 24-hour period was more than 30 inches (780 millimeters)as much rain as many parts of the United States receive in a whole year! Ash and other deposits from Mount Pinatubo's 1991 eruption destroyed or buried much of the lush vegetation that had covered the volcano. When rainfall on Pinatubo exceeded about 0.5 inches (12 millimeters) in 30 minutes, rapid runoff down the still bare slopes quickly grew into torrents that became lahars by eroding these deposits. Fortunately, vegetation is beginning to grow on the 1991 deposits, and new stream channels are becoming established, reducing the runoff and erosion that create lahars. Lahars at Pinatubo Since 1991 The volume of Pinatubo's lahars staggers the mind.

In the first few years following the cataclysmic 1991 eruption, they have deposited more than 0.7 cubic miles (3 cubic kilometers; equivalent to 300 million dump-truck loads) of debris on the lowlands surrounding the volcano, burying hundreds of square miles of land. During heavy rains, lahars at Pinatubo can transport and deposit tens of millions of cubic yards of mud in a single day. When the largest and fastest lahars reach the lowlands surrounding Pinatubo, they have speeds of more than 20 miles (32 kilometers) per hour, are as much as 30 feet (10 meters) thick and 300 feet (100 meters) wide, and can transport more than 35,000 cubic feet (1,000 cubic meters) of debris and mud per second. Within minutes, such powerful lahars can erode many feet into the banks or floor of a channel. They can carry large boulders, cars, or even bridges and can destroy or bury almost anything in their paths.

When lahars reach low-lying areas, they spread out, slow down, and deposit their vast loads of debris over many square miles. One particularly dangerous type of lahar has occurred at Mount Pinatubo as a result of the damming of stream channels and tributary valleys by the 1991 ash deposits or by subsequent lahars, creating temporary lakes. After a few weeks or months, the lakes overtop and quickly erode through their dams, releasing large volumes of water that generate major lahars. Because these large and powerful mudflows can occur without warning, even when there is no rain, they are among the most dangerous of Pinatubo's lahars. One lake on the Pasig-Potrero River, on the volcano's east flank, has formed and broken out three times (1991, 1992, and 1994), creating giant lahars that have killed dozens of people. Mitigation Efforts and Continuing Hazards When Pinatubo erupted in 1991, stream channels were small and were quickly filled by lahars deposits.

Civil engineers raced to trap the sediment behind small dams and to confine it between levees, but most of these measures were too small to contain the lahars. Near the base of the volcano, lahars eroded whole city blocks, and in the lowlands they inundated and buried entire towns. Since the 1991 eruption, lahars from Pinatubo have destroyed the homes of more than 100,000 people. With most old stream channels filled, lahars can now spread widely on the gentle slopes and lowlands surrounding Mount Pinatubo, threatening successors to the early dams and levees. Fortunately, by 1995, the volume of material carried by Pinatubo's lahars had already decreased to less than a quarter of that carried in 1991, and new towns had been built on high ground for many of those displaced or threatened by lahars. Nonetheless, 100,000 people remain at risk from the volcano's lahars.

Within hours of Mount Pinatubo's explosive June 15, 1991, eruption, heavy rains began to wash the ash and debris deposited by this explosion down into the surrounding lowlands in giant, fast-moving mudflows called lahars. By 1993, lahars had already caused more devastation in the lowlands than the eruption itself. Fortunately, a system to monitor and warn of lahars was rapidly established in the days following the eruption by the Philippine Institute of Volcanology and Seismology, U.S. Geological Survey, and other organizations. This system has saved hundreds of lives by enabling warnings to be sounded for most but not all major lahars at Pinatubo. U.S. bases have reverted to Philippine control since 1991. Subic Bay and Cubi Point are naval stations. 1, O'Donnell River; 2, Sacobia-Bamban River; 3, Pampanga River; 4, Pasig-Potrero River; 5, Marella River. Lahar Warnings Once the potential for lahars at Mount Pinatubo was recognized, scientists quickly prepared a preliminary hazard map.

Since mid-June 1991, when violent eruptions triggered the volcano's first lahars in 500 years, a system to monitor and warn of lahars has been in operation. Radio-telemetered rain gauges provide data on rainfall in lahar source regions, acoustic flow monitors on stream banks detect ground vibration as lahars pass, and manned watchpoints further confirm that lahars are rushing down Pinatubo's slopes. This system has enabled warnings to be sounded for most but not all major lahars at Pinatubo, saving hundreds of lives. Chris Newhall, Peter H. Stauffer, and James W. Hendley II Graphics by Susan Mayfield and Sara Boore Banner design by Bobbie Myers Web design and layout by Carolyn Donlin For more information or paper copies of this fact sheet contact: U.S. Geological Survey 5400 Mac Arthur Blvd., Vancouver, WA 98661 Tel: (360) 993-8900, Fax: (360) 993-8980 Also, visit the Cascade Volcano Observatory on the Web.

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 Remembering Mount Pinatubo 25 Years Ago: Mitigating a Crisis Remembering Mount Pinatubo 25 Years Ago: Mitigating a Crisis Remembering Mount Pinatubo 25 Years Ago Release Date: June 13, 2016 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. Seismographs at Mount Pinatubo Monitoring Observatory site at Clark Air Base, Philippines. Public domain 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. U.S.

Air Force helicopter dropping off USGS and PHIVOLCS scientists and gear to be installed on the flanks of Mount Pinatubo.Public domain 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. USGS volcano seismologist David Harlow conducts analysis of Mount Pinatubo seismicity. Public domain USGS scientists set up instrumentation to monitor Mount Pinatubo. Public domain USGS and PHIVOLCS scientists loading volcano monitoring gear into an Air Force helicopter. Public domain 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. The June 12 eruption of Mount Pinatubo, three days before the much larger eruption on June 15, 1991. Public domain 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. World Airways DC10 airplane sitting on its tail because of the weight of wet volcanic ash. Public domain NASA's TOMS satellite image showing how Pinatubo's ash had circled the globe by June 30, 1991. Public domain. The eruption of Mount Pinatubo sent lahars and pyroclastic flows down the mountain, wiping out bridges and other infrastructure downstream.Public domain 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. Damage from volcanic ash fall at Clark Air Force Base from the June 15, 1991 eruption of Mount Pinatubo. Public domain Damage to Clark Air Force Base airplane hangers collapsed under the weight of wet volcanic ash from the eruption of Mount Pinatubo in 1991. Public domain 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: Mt Pinatubo Volcano, Philippines | John Seach Mt Pinatubo Volcano | John Seach Luzon, Philippines summit elevation 1486 m stratovolcano The Mt Pinatubo eruption of 1991 was the second largest eruption of the 20th century. Mount Pinatubo Volcano had been dormant for 400 years. Before 1991 Pinatubo was an inconspicuous volcano which was known to be active in the past 1000 years and was the site of a failed geothermal development.

The area was the home of the Aetas people, who considered the mountain the home of Apo Namalyari, the Great Protector and Provider. Before 1991 Pinatubo had a height of 1745 m, and was only 200 m higher than nearby mountains which obscured it from view. The surrounding mountains are remains of an older Mt Pinatubo. Geology of Mt Pinatubo Pinatubo is flanked on the west by the Zambales Ophiolite Complex, which is an easterly-dipping section of Eocene ocean crust which was uplifted during the late Oligocene. The Tarlac Formation consists of marine, nonmarine and volcaniclastic sediments in the north, east and southeast of Pinatubo which was formed in the late Miocene and Pliocene. Ancestral Pinatubo was an andesite and dacite stratovolcano whose centre was in the same location of the current volcano. The old volcano is exposed in the walls of an old 3.5 x 4.5 km wide caldera.

Ancestral satellite vents include the domes of Mount Negron, Mount Cuadrado, Mataba, Bituin plug, and Tapungho plug. Eruptions of Mount Pinatubo The largest eruption at Mt Pinatubo volcano occurred 35,000 years ago, and produced pyroclastic flow deposits up to 100 m thick on all sides of the volcano. The Sacobia eruption period 17,000 years ago produced two debris flow deposits which are visible on the north bank of the Sacobia River. Pasbul eruptive period occurred 9,000 years ago and is visible as pyroclastic flow and tephra deposits exposed along the road between Sitio Pasbul, Camias, Porac, and Gumain River. Crow Valley eruptions 6,000-5,000 years ago produced pyroclastic flow deposits on both sides of upper Crow valley. Maraunot eruptions occurred from about 3,900 to 2,300 years ago.

The previous eruptions before 1991 (Baug Eruptions) occurred in 1450 ± 50 years and produced pyroclastic flow deposits in all valleys of Pinatubo except Gumain and Porac rivers. 2009 Earthquake On 31st October 2009 a magnitude 5.0 earthquake hit 37 km WSW of the summit of Mt Pinatubo volcano. The earthquake focus was at a depth of 79 km. 2009 Mudflows Heavy monsoon rains caused by typhoon Kiko triggered mudflows which 12 people and flooded the town of Botolan in August 2009. There were some volcanic materials mixed with water, but the flows were not a lahar. During 2001 the crater lake on Mount Pinatubo reached dangerous levels, and the crater lake changed colour in January 2004. 1991 eruption On 16th July 1990 a magnitude 7.8 earthquake hit 100 km northeast of Mt Pinatubo. 3rd August 1990 Loud rumbling heard, a landslide near the summit, and steaming ground.

First volcanic activity in 400 years. August 1990 Rumbling and earth tremors. 2nd April 1991 Steam and ash exploded from a 1.5 km long fissure high on the northern slopes of Pinatubo. Smell of sulphur and ash fell 10 km away. 3rd April 1991 200 small earthquakes registered at the volcano. 23rd April 1991 US Geological Survey arrived with monitoring equipment. 26th April 1991 Monitoring station set up at Clark Air Base 25 km to the east of the volcano. 13th May 1991 30-180 earthquakes per day were being recorded. Volcano releasing sulphur dioxide indicating molten magma was rising beneath the volcano. Alert level 2 issued. 23rd May 1991 A tenfold increase in sulphur dioxide emissions in previous 2 weeks. 1st June 1991 Earthquakes became centered 5 km below the volcano. 5th June 1991 Sulphur dioxide emissions almost stopped as the vents became blocked.

Earthquakes continued and the mountain started to bulge as magma moved towards the surface. 7th June 1991 1500 earthquakes under Pinatubo. An ash eruption sent a cloud to 8 km high. Alert level 4 issued stating an eruption could happen within 24 hours. Danger zone extended to a 20 km radius. Lava reached the surface and formed a small dome 1 km northwest of the main crater. 9th June 1991 Sulphur dioxide began escaping again from the volcano. The first nuee ardentes rolled down the volcano. A large eruption of ash. People evacuated from a 20 km radius. 10th June 1991 Evacuations begun at Clark Air Base. (14,400 people) 12th June 1991 Ash eruptions to 20 km above the volcano on Philippine Independence Day. 13th June 1991 Ash eruption to 25 km high followed by 28 hours without an explosion. Earthquakes continued. 14th June 1991 Violent explosion at 1:09 pm.

Eruption column to 21 km in 15 minutes. Nuee ardentes devastated the main valleys radiating from Mt Pinatubo. 15th June 1991. The Main Eruption Typhoon Yunya passes 100 km northeast of Pinatubo. Mudflows raged down the mountain at 30 km/hr. At 3:39 pm the main eruption began. In 9 hours 90 percent of the total material for the eruption was expelled from the volcano. Cauliflower columns of ash, gas and steam rose 34 km high and traveled 400 km. At 4:30 pm the summit of Pinatubo began to sink. The evacuation area was increased to 40 km radius. The eruption stopped at 10:340 pm. Effects of the Eruption A huge caldera was formed 2.5 km across. 260 m was lost off the summit of the volcano. The ash entered the stratosphere and covered the whole earth within 12 months. Global temperatures were reduced by 0.5 degree C the year after the eruption.

Forests buried under 50-200 m deep ash and pumice. During the last five months of 1991 200 mudflows raced down the valleys of Pinatubo. Damage amounted to $450 million dollars. 8,000 houses were destroyed and 75,000 houses damaged. 2 million people were affected by the eruption. The biggest volcanic disaster of the 20th century was avoided due to good planning and monitoring. Mt Pinatubo Volcano Eruptions 1992, 1991, 1450 ± 50 years, 1050 BC ± 500, 3550 BC?, 7030 BC ± 300, 7460 BC ± 150, 15,000 BC, 33,000 BC.

Question: The volcano Mt Pinatubo is in which country?
Answer: The Philippines