1991 eruption of Mount Pinatubo
The 1991 eruption of Mount Pinatubo in the Philippines' Luzon Volcanic Arc was the second-largest volcanic eruption of the 20th century, behind only the 1912 eruption of Novarupta in Alaska. Eruptive activity began on April 2 as a series of phreatic explosions from a fissure that opened on the north side of Mount Pinatubo. Seismographs were set up and began monitoring the volcano for earthquakes. In late May, the number of seismic events under the volcano fluctuated from day-to-day. Beginning June 6, a swarm of progressively shallower earthquakes accompanied by inflationary tilt on the upper east flank of the mountain, culminated in the extrusion of a small lava dome.
Eruption column on June 12, 1991
Pinatubo as viewed from the north in late April 1991. Grayish-tan ash and several craters from the April 2 phreatic explosions are visible at the left.
View to the west from Clark Air Base of the major eruption of Pinatubo on June 15, 1991. The June 15–16 climactic phase lasted more than fifteen hours, sent tephra about 35 km (22 mi) into the atmosphere, generated voluminous pyroclastic flows, and left a caldera in the former summit region. Later dubbed Black Saturday, the day of darkness stretched for 36 hours.
The eruption cloud a few minutes after the start of the climactic eruption
Novarupta is a volcano that was formed in 1912, located on the Alaska Peninsula on a slope of Trident Volcano in Katmai National Park and Preserve, about 290 miles (470 km) southwest of Anchorage. Formed during the largest volcanic eruption of the 20th century, Novarupta released 30 times the volume of magma of the 1980 eruption of Mount St. Helens.
Novarupta's lava dome in July 1987
Colorful ash in the Valley of Ten Thousand Smokes