A volcanic eruption ten times larger than that of Mount St. Helens in 1980 – 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 giant cloud of volcanic ash hundreds of miles across. The two largest U.S. military bases in the Philippines – Clark Air Base and Subic Bay Naval Station – were heavily damaged. Although Pinatubo’s eruption threatened the lives of a million people, a more serious disaster was averted by timely, accurate warnings.
Complicating the eruption was the arrival of Typhoon Yunya, which created a lethal mix of ash and rain. The surrounding areas were severely damaged by pyroclastic flows, ash deposits, and lahars (huge mudslides) caused by rainwaters which altered river systems and destroyed infrastructures, rice paddies, and sugar cane fields; those buried by the lahars will be out of use for years to come. The effects of the eruption were also felt worldwide. The volcano injected large amounts of aerosol into the stratosphere – more than any eruption since that of Krakatoa in 1883 – and ozone depletion temporarily increased substantially. Satellites tracked the ash cloud several times around the globe, and global temperatures dropped by about 0.5 °C (0.900 °F).
Ironically, before the eruption of 1991, Pinatubo’s volcanic history was mostly unknown because the mountain was heavily eroded, inconspicuous, and obscured from view since it was covered by dense forest. Pinatubo wasn’t the largest volcanic eruption of the 20th century, either – that distinction goes to the eruption of Novarupta on the Aleutian Range of the Alaskan Peninsula from June 6 – June 8, 1912.
The Cataclysmic 1991 Eruption of Mount Pinatubo, Philippines – U.S. Geological Survey Fact Sheet 113-97
Mt. Pinatubo vs. Mt. St. Helens – A research paper comparing the eruption of Mt. St. Helens with Mt. Pinatubo.
Mount Saint Helens – Homeschool Library post on the Mount Saint Helens eruption.