On the 15th June of 1991, the second largest volcanic eruption of the twentieth century took place on the island of Luzon in the Philippines, 90 km northwest of the capital city Manila. It was also, by far, the largest eruption to affect a densely populated area. Mount Pinatubo, a stratovolcano, is part of a chain of volcanoes along the Luzon arc on the west coast (refer map). The arc of volcanoes is due to the subduction of the Manila trench to the west. The mountain has a very huge eruptive history. It was known to be thermally active and had been explored as possible geothermal energy resource by the Philippine National Oil Company. Mount Pinatubo is among the highest peaks in west-central Luzon. Its lower flanks were made, mostly, of pyroclastic deposits from voluminous, explosive prehistoric eruptions. Although the 1991 eruption was one of the largest and most violent of the 20th century, it was weaker than the previous Pinatubo eruptions.
During the eruption, approximately 350 people were killed by the 35 km ash column, the hot blast and, most importantly, from the collapsing roofs. But the casualties and death toll could have been greater. The Philippines Institute of Volcanology and Seismology (PHIVOLCS) and the USGS were able to inform the locals of the disaster ahead and were able to carry out the most successful volcanic hazards mitigation in the history, thus able to save lives of thousands of people and an estimated billion dollars worth of properties.
The Events Leading to the Eruption
The events of the 1991 eruption began back in July 1990, when a magnitude 7.8 earthquake struck a region 100 km northeast of Pinatubo. This shook the earth's crust beneath the volcano and caused a landslide, some local earthquakes and some small steam emissions too. The following year, sometime in March, villagers of Patal Pinto felt some earthquakes around the volcano. On the 2nd of April the villagers witnessed small explosions