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Mount Pinatubo: Facts, Eruption & Effects

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.

We also recommend watching Earthquakes and Volcanoes: Evidence of Earth's Inner Layers and Rock Cycle: Igneous, Sedimentary, and Metamorphic rocks


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

Mount Pinatubo before erupting

Before the eruption, Mount Pinatubo was covered with tropical vegetation and was home to more than 30,000 people who lived in villages on its slopes. Thousands of other people 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, 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 the earthquakes increased and steam began erupting from the volcano, people recognized the seriousness of the situation. On June 7, 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-km diameter.

Eruption of Mount Pinatubo

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

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