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Mount Pinatubo Eruption
The Volcanic Eruption of 1991 that Cooled the Planet
by Matt T. Rosenberg
March 9, 2001
In June 1991, the second largest volcanic eruption of the twentieth century* took place on the island of Luzon in the Philippines, a mere 90 kilometers (55 miles) northwest of the capital city Manila. Up to 800 people were killed and 100,000 became homeless following the eruptions, which climaxed with nine hours of eruption on June 15, 1991. On June 15, millions of tons of sulfur dioxide were discharged into the atmosphere, resulting in a decrease in the temperature worldwide over the next few years.
Mount Pinatubo is part of a chain of composite volcanoes along the Luzon arc on the west coast of the island (area map). The arc of volcanoes is due to the subduction of the Manila trench to the west. The volcano experienced major eruptions approximately 500, 3000, and 5500 years ago.
The events of the 1991 eruption began back in July 1990, when a magnitude 7.8 earthquake occurred 100 kilometers (62 miles) northeast of the Pinatubo region, determined to be a result of the reawakening of Mount Pinatubo. In mid-March 1991, villagers around Mount Pinatubo began feeling earthquakes and vulcanologists began to study the mountain. (Approximately 30,000 people lived on the flanks of the volcano prior to the disaster.) On April 2, small explosions from vents dusted local villages with ash. The first evacuations of 5,000 people were ordered later that month.
Earthquakes and explosions continued. On June 5, a Level 3 alert was issued for two weeks due to the possibility of a major eruption. The extrusion of a lava dome on June 7 led to the issuance of a Level 5 alert on June 9, indicating an eruption in progress. An evacuation area 20 kilometers (12.4 miles) away from the volcano was established and 25,000 people were evacuated.
The following day (June 10), Clark Air Base, a U.S. military installation near the volcano, was evacuated. The 18,000 personnel and their families were transported to Subic Bay Naval Station and most were returned to the United States. On June 12, the danger radius was extended to 30 kilometers (18.6 miles) from the volcano resulting in the total evacuation of 58,000 people.
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