Mount Pinatubo: Facts, Eruption & Effects

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  • 0:00 Facts
  • 0:46 Eruption
  • 2:24 Effects
  • 3:29 Lesson Summary
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Lesson Transcript
Instructor: Jeff Fennell

Jeff has a master's in engineering and has taught Earth science both domestically and internationally.

Mount Pinatubo in the Philippines is an active volcano that erupted in 1991. The eruption was one of the largest on record during the 20th century. This lesson will cover the facts about Mount Pinatubo and its eruption.


Mount Pinatubo is an active stratovolcano located on the island of Luzon in the Philippines. Pinatubo is located in the central portion of the Zambales mountain range. The volcano lies 55 miles northwest of Manila. With an elevation of 1,486 meters, Pinatubo is composed of andesite and dacite.

Before the eruption, Mount Pinatubo was covered with vegetation and was home to more than 30,000 people, who lived in villages on its slopes. Thousands of others lived in the valleys surrounding the volcano, including U.S. military personnel stationed at Clark Air Base and Subic Bay Naval Station. Before 1991, there had been no record of volcanic activity.


An eruption of steam blew from the top of Mount Pinatubo on April 2, 1991. After receiving the report of activity, coupled with a series of earthquakes in the preceding weeks, seismologists began observations of Pinatubo's seismic activity. This was the first time that monitoring had occurred at Pinatubo. Since there was no background information on seismic activity in the area, it was difficult to determine if the occurrence was normal or not.

As the frequency of earthquakes increased and steam continued erupting from the volcano, people recognized the seriousness of the situation. On June 7, when magma oozed out to form a lava dome, local authorities declared the highest alert and ordered evacuations for a 20-kilometer radius around the volcano.

By June 10, about 25,000 people had evacuated from the villages around the volcano, and over 14,000 families evacuated the nearby U.S. military base in Clark. On the afternoon of June 15, 1991, Pinatubo's most intense eruption began. Pyroclastic flow deposits filled valleys, and a huge plume of volcanic ash and gasses escaped into the atmosphere. In the aftermath, Mount Pinatubo had formed a crater of 2.5-kilometer diameter.

In order to prevent more casualties, the evacuation radius was increased to 40 kilometers. However, the volcanic ash and rain from Typhoon Yunya, which hit at the same time, formed heavy muds that rained down on densely populated areas. About 200 people died from collapsed roofs.


The eruption of Mount Pinatubo caused significant damage to the economy and infrastructure of surrounding cities. The volcano's eruption also had significant global environmental effects. Mount Pinatubo ejected roughly ten billion tons of magma onto the surrounding landscape and millions of tons of sulfur dioxide gas into the atmosphere, spreading an ash cloud over much of the earth.

Average temperatures worldwide decreased by almost one degree Fahrenheit for several years after the eruption. The sulfur dioxide, which mixed with water and oxygen in the atmosphere to create sulfuric acid, also contributed to a rapid destruction of ozone. The ozone layer hole over Antarctica reached its largest size the year following the eruption.

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