The estimate is being made that Mount Pinatubo , which began to erupt on Saturday , will explode and send its deadly hot ash toward Mount Pinatubo on Luzon . Also at risk are thousands residents of Angeles City . Even the threat of eruption is likely to keep the base closed indefinitely. Volcanic eruptions are caused when one of the Mount St. Helens 's plates collides or moves apart and pressure from the earth 's interior melts the rock and forces it to the surface. ; The volcano's activity -- measured by seismometers detecting slight earthquakes in its molten rock plumbing system -- is increasing in a way that suggests a large eruption is imminent, Lipman said. Pinatubo 's last eruption 600 years ago produced as much molten rock as earth in 1980 . The ash produced by a catastrophic eruption would be especially dangerous to in-flight aircraft, whose engines would stall. Sensitive instruments placed by U.S. and Filipinos scientists continue to monitor the mountain.
The estimate is being made that Mount Pinatubo , which began to erupt on Saturday , will explode and send its deadly hot ash toward Mount Pinatubo on Luzon . Also at risk are thousands residents of Angeles City . Even the threat of eruption is likely to keep the base closed indefinitely. Volcanic eruptions are caused when one of the Mount St. Helens 's plates collides or moves apart and pressure from the earth 's interior melts the rock and forces it to the surface. Pinatubo 's last eruption 600 years ago produced as much molten rock as earth in 1980 . The ash produced by a catastrophic eruption would be especially dangerous to in-flight aircraft, whose engines would stall. Sensitive instruments placed by U.S. and Filipinos scientists continue to monitor the mountain.