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Mount Pinatubo 

Mount Pinatubo is an active stratovolcano located on the island of Luzon, at the intersection of the borders of the Philippine provinces of Zambales, Tarlac, and Pampanga. It is located in the Tri-Cabusilan Mountain range separating the west coast of Luzon from the central plains, and is 42 km (26 mi) west of the dormant and more prominent Mount Arayat, occasionally mistaken for Pinatubo. Ancestral Pinatubo was a stratovolcano made of andesite and dacite. Before 1991, the mountain was inconspicuous and heavily eroded. It was covered in dense forest which supported a population of several thousand indigenous people, the Aeta, who had fled to the mountains from the lowlands during the protracted Spanish conquest of the Philippines which first commenced in 1565.

Aerial view west across Pinatubo caldera showing fumaroles and crater lake.

The volcano's ultra-Plinian eruption in June 1991 produced the second largest terrestrial eruption of the 20th century (after the 1912 eruption of Novarupta) and the largest eruption in living memory. The colossal 1991 eruption had a Volcanic Explosivity Index(VEI) of 6, and came some 450–500 years after the volcano's last known eruptive activity (estimated as VEI 5, the level of the 1980 eruption of Mount St. Helens), and some 1000 years after previous VEI 6 eruptive activity. Successful predictions of the onset of the climactic eruption led to the evacuation of tens of thousands of people from the surrounding areas, saving many lives, but surrounding areas were severely damaged bypyroclastic flows, ash deposits, and later by lahars caused by rainwater remobilizing earlier volcanic deposits: thousands of houses and other buildings were destroyed.

June 12, 1991 eruption from Mount Pinatubo taken from the east side of Clark Air Base.

Pinatubo is part of a chain of volcanoes which lie along the western edge of the island ofLuzon. They are subduction volcanos, formed by the Philippine Mobile Belt sliding over the Eurasian Plate along the Manila Trench to the west. Mount Pinatubo and the other volcanoes of the West Luzon volcanic arc arise due to magma occlusion from this subduction plate boundary.

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.

In June 1991, the second largest volcanic eruption of the twentieth century* took place on the island of Luzon in thePhilippines, 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 Mount Pinatubo eruption, 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.

Aftermath

The Aeta people were the hardest hit by the eruption. The total destruction of many villages by pyroclasts and lahar deposits meant that many Aeta were unable to return to their former way of life. After the areas surrounding the volcano were declared safe to return to, those whose villages had not been destroyed moved back, but most people moved instead to government-organized resettlement areas. Conditions on these were poor, with each family receiving only small plots of land, which were not ideal for growing crops. Many Aeta found casual labor working for lowland farmers, and overall Aeta society became much more fragmented, and reliant on and integrated with lowland culture.

Cultural History

The word 'pinatubo' means 'to have made grow' in Tagalog and Sambal, which may suggest a knowledge of its previous eruption in about AD 1500, although there is no oral tradition among local people of earlier large eruptions. Pinatubo might instead mean a fertile place where crops can be made to grow. An indigenous group of people, the Aetas (also spelled as Ayta), had lived on the slopes of the volcano and in surrounding areas for several centuries, having fled the lowlands to escape persecution by the Spanish. They were a hunter-gatherer people who were extremely successful in surviving in the dense jungles of the area. These people also grew some staple crops such as wheat, barley, and rice.

Before the catastrophic eruption of 1991, Pinatubo was an inconspicuous volcano, unknown to most people in the surrounding areas. Its summit was 1,745 m (5,725 ft) above sea level, but only about 600 m above nearby plains, and about 200 m higher than surrounding peaks, which largely obscured it from view. Philippine President Ramon Magsaysay, a native of Zambales, named his C-47 presidential plane "Mt. Pinatubo". The plane crashed in 1957, killing the President and 24 others onboard.