English: Dacite pumice (air-fall tephra) from the late Holocene of the Philippines. (3.5 cm across at its widest)

Located near the western margin of Luzon Island in the northern Philippines, Mt. Pinatubo is one of several subduction zone stratovolcanoes in the Luzon Volcanic Arc. Published information indicates that Pinatubo is >35,000 years old and is composed principally of dacitic and andesitic rocks.

Mt. Pinatubo had a large explosive ash eruption in 1991 that was the largest anywhere on Earth since 1912. Pinatubo's eruption is also famous for having been successfully predicted by American volcanologists. The prediction and subsequent evacuation saved thousands of lives.

The mid-June 1991 eruptions from Pinatubo blanketed ash, pumiceous lapilli, and pumice over the surrounding countryside, including two American military bases (Clark and Subic Bay). The sample shown above is dacite pumice from the 15 June 1991 eruption - it was collected at the U.S. Subic Bay Naval Base, ~20 miles south of Mt. Pinatubo.

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For additional geologic information on the 1991 Pinatubo eruption, see:

Newhall & Punongbayan (1996) - Fire and Mud, Eruptions and Lahars of Mount Pinatubo, Philippines. Quezon City & Seattle & London. Philippine Institute of Volcanology and Seismology & University of Washington Press. 1126 pp.