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Philippines: Mt. Pinatubo Volcano - Jun 1991

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The second-largest volcanic eruption of the 20th century, and by far the largest eruption to affect a densely populated area, occurred at Mount Pinatubo in the Philippines on June 15, 1991. Prior to the eruption, 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. (USGS, 28 Feb 2005) The consequences of these eruptions were aggravated by a tropical storm and four earth tremors (the first one of magnitude 3 on Richter scale) affecting the Northern Philippines around the volcano area on 15 June. (UN DHA, 16 Jun 1991)

Volcanic activity recommenced in July 1992. On 4 August 1992, Mount Pinatubo erupted again, violently showering mud and hot pebbles on to Angeles City (200 km from Manila) and 4 towns in Pampanga and Tarlac. (UN DHA, 20 Aug 1992) The largest cause of death and injury was the collapse of roofs due to the weight of wet ash from the eruption and typhoon. In total, 42,000 homes were destroyed by the wet ash and 847 people were killed with many more being injured. About 1.2 million people lost their homes, 150km2 of reforestation projects and 800km2 of farmland were destroyed, and 800,000 livestock were killed. In 2005, resettlement camps were still housing some of the indigenous people who originally lived on the slopes of Mt. Pinatubo. There has been significant, permanent change to the region surrounding Mt. Pinatubo as thousands of people were permanently displaced, many agriculture fields indefinitely disabled, and the citizens that have returned home still face threats of small, residual lahars from the 1991 eruption. (ESRI, 20 Aug 1992) 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°F (0.5°C). (USGS, 28 Feb 2005)