Mount Pinatubo

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Mount Pinatubo
Pinatubo ash plume 910612.jpg
Ash plume of Pinatubo during 1991 eruption

Elevation 1,486 metres (4,875 feet)
Location Zambales, Luzon, Philippines
Tarlac, Luzon, Philippines
Pampanga, Luzon, Philippines
Range Zambales Mountains
Coordinates 15°7.8′N, 120°21.0′E
Type Stratovolcano
Age of rock 1.1 million years
Last eruption 1993 [1]

Mount Pinatubo is a volcano known for producing the second largest terrestrial eruption of the twentieth century. Pinatubo lies at the intersection of the borders of Zambales, Tarlac and Pampanga and was covered with lush forest growth prior to the eruption. It had also supported several thousand Aeta. The volcano's eruption in June 1991 caused the destruction of billions of pesos' worth in economic and property damage and the loss of 847 lives. Aside from the massive damage to the Philippine economy, the eruption also had world-spanning ramifications.


1991 eruption

A magnitude 7.8 earthquake in July 1990 which struck 100 kilometers northeast of Pinatubo is said to be the catalyst of the volcano's awakening. Tremors shook the surrounding area in mid-March 1991. Vulcanologists began their investigations. Small explosions from vents dusted the nearby villages with ash on 2 April. At the onset of the ashfall, 5,000 people were evacuated from the area. After continued tremors and minor explosions, a Level 3 alert was issued on 5 June. On 9 June, a Level 5 alert for an eruption in progress was issued due to the extrusion of a lava dome two days prior. 25,000 people were evacuated from a 20 kilometer radius around the volcano. On 10 June, Clark Air Base was evacuated and 18,000 personnel and their families were relocated to Subic Bay Naval Station. Most were sent back to the United States. On 12 June, the danger radius was extended to 30 kilometers from the volcano, leading to the evacuation of a total of 58,000 people. Mount Pinatubo erupted on 15 June, 1:42pm local time. The eruption lasted nine hours, causing numerous earthquakes and collapsing Mount Pinatubo's summit. The collapse, which reduced the peak from 1745 meters to 1485 meters, formed a caldera 2.5 kilometers in diameter. The eruption happened while tropical storm Yunya was passing 75 kilometers northeast of the volcano, causing large amounts of rainfall. The volcanic ash mixed with the water vapor in the storm and caused a rainfall of tephra that fell across almost the entire island of Luzon. The ash deposits reached 33 centimeters at its thickest, approximately 10.5 kilometers southwest of the volcano while 10 centimeters of ash covered an area of 2000 square kilometers. Most casualties were caused by roofs collapsing under the weight of the ash. Mount Pinatubo also ejected 15 to 30 million tons of sulfur dioxide gas which, mixed with water and oxygen in the atmosphere, becomes sulfuric acid, an agent of ozone depletion. The eruption plume reached an altitude of 34 kilometers, the largest disturbance of the stratosphere since the eruption of Krakau in 1883. The aerosol cloud spread around the earth in two weeks and covered the planet within a year. This caused the ozone hole over Antarctica to reach an unprecedented size during 1992 and 1993. The cloud reduced global temperatures by 0.4 to 0.5 degrees Celsius and is believed to have influenced events such as the flooding along the Mississippi river in 1993 and the drought in the Sahel region of Africa.


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