WHAT WERE THE CAUSES, IMPACTS, RESPONSES AND MANAGEMENT TECHNIQUES? Mount Pinatubo, Philippines, Asia June 12th-15th, 1991

What, where and when? Mount Pinatubo is a Strato (or composite cone) volcano, located in north-west Philippines, Asia. It is north-west of the capital, Manila. A series of events led to the several volcanic eruptions between June 7 th and June 15 th, So what were these events?

What caused the eruptions? Mount Pinatubo was dormant for 500 years. On July 16, 1990 a magnitude 7.8 earthquake (roughly the size of the 1906 San Francisco earthquake) struck about 60 miles (100 kms.) northeast of Mount Pinatubo on the island of Luzon in the Philippines. This caused the shaking and squeezing of the Earth's crust beneath the volcano. “At Mount Pinatubo, scientists recorded a landslide, some local earthquakes, and a short-lived increase in steam emissions from a pre- existing geothermal area, but otherwise the volcano seemed to be undisturbed.” ( In March and April 1991, magma started rising towards the surface from more than 20 miles (32 kms.) beneath Pinatubo, triggering more small earthquakes and causing powerful steam explosions that blasted three craters on the north side of the volcano. Thousands of small earthquakes occurred beneath Pinatubo throughout April, May, and early June 1991, and many thousand tons of noxious sulphur dioxide gas were also emitted by the volcano.

The eruptions On June 7th 1991, the first magma reached the surface of Mount Pinatubo but because it had lost most of the gas contained in it on the way to the surface, the magma merely oozed out to form a lava dome. However, on June 12th, large amounts of gas-charged magma reached the surface and exploded in the volcano's first eruption. When even more highly gas charged magma reached Pinatubo's surface on June 15th, the volcano exploded in a massive eruption that ejected more than 5 cu. Kms of volcanic material The June 15 th eruption is recognised as the largest volcanic eruption in 80 years, the second-largest volcanic eruption of this century. It is by far the largest eruption to affect a densely populated area.

What were the primary impacts? The ash cloud from this huge eruption rose 22 miles (35 kms.) 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 south- westward. Fine ash fell as far away as the Indian Ocean, and satellites tracked the ash cloud several times around the globe. Huge Pyroclastic flows (avalanches of red hot ash, gas, and pumice fragments) roared down the sides of Mount Pinatubo, filling the deep valleys with fresh volcanic deposits as much as 660 ft (200 m) thick.

What were the secondary impacts? Social:  300 people killed.  About 75,000 people were evacuated.  About 20,000 indigenous Aeta highlanders, who had lived on the slopes of the volcano, were completely displaced, and as late as 2005 most still waited in resettlement camps for the day when they could return home.  The eruptions have dramatically changed the face of central Luzon, home to about 3 million people.

What were the secondary impacts? Economic:  Although much equipment was successfully protected, buildings on two U.S. military bases in the Philippines--Clark Air Base and Subic Bay Naval Station--were heavily damaged by ash.  A number of jets flying far to the west of the Philippines encountered ash and sustained about $100 million in damage.  Ash fall also inundated the two largest U.S. military bases in the Philippines. On Clark Air Force Base, which was home to more than 15,000 American servicemen and dependents, many buildings collapsed under the weight of rain-saturated ash. Facilities at the U.S. Naval Station at Subic Bay, 25 miles from Pinatubo, were also severely damaged.  The drifting ash cloud from the June 15, 1991, eruption of Mount Pinatubo damaged more than 20 passenger jetliners (including those of American air carriers), most of which were flying more than 600 miles from the volcano.

What were the secondary impacts? Environmental:  A blanket of volcanic ash and larger pumice lapilli (frothy pebbles) blanketed the countryside.  The eruption removed so much magma and rock from below the volcano that the summit collapsed to form a large volcanic caldera (depression) 1.6 miles (2.5 kms.) across.  Nearly 20 million tons of sulphur dioxide were injected into the stratosphere and the spread of this gas cloud around the world caused global temperatures to drop temporarily ( ) by about 0.5°C.  “Much weaker but still spectacular eruptions of ash occurred occasionally through early September From July to October 1992, a lava dome was built in the new caldera as fresh magma rose from deep beneath Pinatubo.” (

That are continuous hazards? Even after more than 5 years, hazardous effects from the June 15,1991 eruption continued.  The thick pyroclastic-flow deposits from the eruption insulated themselves and have kept much of their heat.  These deposits still had temperatures as high as 900°F (500°C) in 1996 and may retain heat for decades.  When water from streams or underground seepage comes in contact with these hot deposits, they explode, spreading fine ash downwind.  Since the eruption, ash deposits have also been remobilized by monsoon and typhoon rains to form giant mudflows of volcanic materials (lahars).

What were the responses from volcanologists and seismologists? 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 an alert for evacuation. This saved at least 75,000 lives and at least $250 million in property through evacuation up to a radius of 30km. Commercial aircraft were warned about the hazard of the ash cloud from the June 15 eruption, and most avoided it. This saved hundreds of millions of dollars in military aircraft and hardware.

Immediate/ short-term responses 200,000 people relocated to safer areas Manila airport closed. Temporary shelters set up by the government for those who had been displaced. Evacuation camps built for refugees. Red Cross, Action Aid and Oxfam provided food and blankets in evacuation camps. 23 USGS (U.S. Geological Survey) helped advise the community and government officials for 8 weeks.

Long-term responses and hazard management President Ramos created the Mount Pinatubo commission to raise 10 billion Philippine Peso. Long and short term aid organized especially from the Red Cross and the United States, with Norway and UK sending millions in aid. Overseas Philippino workers provided clothes for victims. New houses have been built on stilts so that any future lahars will not burry them. Volcano continued to be monitored and new technology was used such as lahar detectors

Was the management successful? Due to the careful monitoring of the volcano once strange activity began to occur, the eruptions were predicted, saving thousands of lives. However, some people argue that the relatively low-impact eruption was due to the timing of the events that occurred:  (the aftermath) Additionally: About 20,000 Aeta highlanders, who had lived on the slopes of the volcano, were completely displaced, and as late as 2005 most still waited in resettlement camps for the day when they could return home. About 200,000 other people who evacuated from the lowlands surrounding Pinatubo before and during the eruptions have returned home but face continuing threats from lahars (mudflows) that have already buried numerous towns, villages and fields.