The 1991 eruption of Pinatubo began on April 2 with a small phreatic eruption on the north flank. The eruptions occurred from a 1.5-km-long, E-W-trending fissure and produced several new explosion craters. Steam rises from a vent at the SW end of the fissure. Steam and minor ash were emitted after April 2, and increased prior to birth of a small lava dome at a NW-flank vent on June 7. Ash emission increased prior to the first large vertical explosion on June 12. During the climactic eruption on June 15 eruptive vents migrated to the summit.
Photo by Chris Newhall,1991 (U.S. Geological Survey).