Global Volcanism Program | Image GVP-01922
A thick stack of pre-1991 pyroclastic flow and lahar deposits outside Clark Air Base is testimony to the long history of explosive eruptions at Pinatubo. Six major eruptive periods took place in the past 35,000 years, each separated by long periods of quiescence. Most of the previous eruptive periods produced explosions that were even larger than the 1991 eruption. The last major eruption prior to 1991 occurred about 500 years ago.
Photo by Chris Newhall (U.S. Geological Survey).