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The second-largest volcanic eruption of last century, and by far the largest eruption to affect a densely populated area, occurred at Mount Pinatubo in the Philippines on June 15, 1991. The eruption produced high-speed avalanches of hot ash and gas, giant mudflows, and a cloud of volcanic ash at an altitude of more than 20 000 meters. Ash deposits from the eruption have also been remobilized by monsoon and typhoon rains to form giant mudflows of volcanic materials (lahars), which have caused more destruction than the eruption itself. Thousands of roofs collapsed under the weight of 10-30 cm ash made wet by heavy rains. With a total of less than 1000 deaths, evacuation in the days before the eruption certainly saved tens of thousands of lives.
The eruptions have dramatically changed the face of central Luzon, home to about 3 million people. About 20 000 indigenous Aeta highlanders, who had lived on the slopes of the volcano, were completely displaced. About 200 000 people who evacuated from the lowlands surrounding Pinatubo before and during the eruptions have returned home but faced continuing threats from lahars that have already buried numerous towns and villages.
Life had disappeared in a 14 kilometers radius around the volcano. Rice paddies and sugar-cane fields that had not been buried by lahars have since recovered ; those buried by lahars have been out of use for years.
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 0,5°C. Quantities of metals brought to the surface were estimated at 1 000 tonnes of cadmium, 10 000 tonnes of arsenic, 100 000 tonnes of lead, 600 000 tonnes of copper, and 800 000 tonnes of zinc.