The Philippine Institute of Volcanology and Seismology – Department of Science and Technology (PHIVOLCS-DOST) commemorates the 1991 Pinatubo Eruption on its 25th year this June 15, 2016. The Pinatubo eruption is considered one of the largest eruptions of the 20th century.
On June 15, 1991, the Plinian eruption of Pinatubo Volcano produced a 40-kilometer ash column above its summit. A 12-16 kilometer zone of pyroclastic flows- the hazardous and dangerous high velocity mixture of hot gases, steam, fragmented rocks and ashes caused nearby cities to be enveloped in total darkness. The thick ash fall that accumulated and made heavier with rainwater from Typhoon Diding (Yunya- International Name) caused roofs of houses to collapse.
The ash fall affected not only Luzon Island, but also reached as far as the Indian Ocean. The eruption had also caused global temperatures to decrease by about 0.5°C temporarily from 1991 through 1993.
Smaller but still dangerous eruptions of ash occurred on the early part of September 1991. Due to the magnitude of the eruption, Pinatubo Volcano’s original summit was destroyed, creating a new crater almost 2-kilometers wide, which after sometime was filled with water thereby forming a lake months after the eruption. From July to September 1992, a lava dome was formed in the new crater as fresh magma was quietly effused out of Pinatubo Volcano. This dome has since been submerged with the continuous increase of the lake water level.
The hazardous effect of the 1991 Pinatubo eruption continued for more than 5 years wherein still hot and thick pyroclastic flow and ash deposits have been remobilized by monsoon and typhoon rains to form a rapidly flowing thick mixture of volcanic materials and water also known as lahars. Several major lahars buried numerous towns and villages including huge area of agricultural land that affected the livelihood of the communities.
Prior to the June 15, 1991 eruption, initial signs of restiveness of the Pinatubo Volcano started in April 1991 as reported to PHIVOLCS by residents living in the western flank (Zambales area). PHIVOLCS immediately installed a temporary seismic station in Poon Bato, Botolan, Zambales, and with the assistance of the USGS, a Pinatubo Volcano Observatory (PVO) was set up in Clark Air Base to study and monitor the activities of the volcano. A team of scientists from PHIVOLCS and USGS collaborated to produce hazard maps that were disseminated to local authorities, and Volcano Alert Signals was issued to the Office of the President, the national, regional, and provincial disaster coordinating councils, and the media to inform the public of the volcano’s activities and advise them on risks and safety measures. Proper coordination of these agencies and institutions, and right forecast of the 1991 Pinatubo eruption resulted to saving of at least 5,000 lives.
The eruption affected more than 249,000 families, displacing Aeta or Negrito tribes who lived on the volcanic slopes. The Office of Civil Defense (OCD) recorded 847 dead, 184 injured, and 23 missing persons. Properties, agricultural lands, water ways, and infrastructures were damaged. Ninoy Aquino International Airport in Metro Manila was also closed for four days.
Pinatubo Volcano is straddling the boundaries of Pampanga, Zambales, and Tarlac, and is part of the chain of volcanoes that lies in the central portion of the Zambales Mountain Range. According to radiometric age dating, Pinatubo Volcano’s last eruption prior to the 1991 eruption occurred about 400 years ago.
On the 25th year of the 1991 Pinatubo eruption, PHIVOLCS encourages everyone to look back and remember not only the tragedy, but also the lessons we learned. Awareness and preparedness would increase our chances against natural hazards and disasters. Through the continuous monitoring, and Information, Education, and Communication (IEC) campaign of PHIVOLCS, let us keep our communities safe from and resilient to volcanic eruptions, earthquakes, tsunamis and other related hazards.