- Mt. Pinatubo started its eruption on June 7, 1991, spewed a 20-kilometer high ash column on June 12, and rumbled a climactic eruption on June 15, 1991.
- 200,000 families were affected by the eruption
- It was the second largest volcanic eruption of the 20th century.
- The volcanic ash reached many areas not in the hazard map because of typhoon "Diding" (international name “Yunya")
It started with earthquake swarms in April 1991, led to an initial explosion on June 7, 1991, spewed an ash column reaching 20 kilometers high on June 12, and finally — at the early morning of June 15, 1991 —a cataclysmic or climactic eruption occurred, rumbling on till the early morning of June 16, 1991, changing the mountain terrain, the rivers flowing through it, and burying structures along the path of its lahar.
(ALBERTO GARCIA / FILE PHOTO / MANILA BULLETIN)
That was the Mt. Pinatubo eruption 30 years ago today, which was recorded as the second-largest volcanic eruption of the 20th century.
The United States Geological Survey (USGS) reported that Mt. Pinatubo "ejected more than one cubic mile (5 cubic kilometers) of material" during its cataclysmic eruption.
"The ash cloud from this climactic eruption rose 22 miles (35 kilometers) into the air," it added.
200,000 families affected families
Mt. Pinatubo's eruption produced pyroclastic flows, lahars, and clouds of volcanic ash that affected more than 200,000 families and the indigenous Aeta people in Central Luzon, the Philippine Institute of Volcanology and Seismology (Phivolcs) said.
Typhon Diding
Volcanic hazards were aggravated by the passing of typhoon "Diding" (international name "Yunya") as the volcanic ash released by Mt. Pinatubo reached areas, not in the hazard map for ashfall.
Traces of ash reached Metro Manila and some Southeast Asian countries, such as Cambodia.
Lahar
The typhoon also triggered lahar, or flows of mud and debris, into the major river channels, affecting the communities downstream.
In a video clip shared by Phivolcs on Saturday, June 12, 2021, former USGS volcanologist Dr. Christopher G. Newhall explained that when they were assessing the geology of Mt. Pinatubo in April-May 1991, volcanologists saw that Mt. Pinatubo "had the potential for really big explosive eruptions."
"At that time, we didn't know whether it would erupt. In fact, we were far away from that. All we knew was that if it did erupt it could be bad," said Newhall, who was part of the joint Phivolcs-USGS Pinatubo Volcano Monitoring Team based at Clark Airbase in Pampanga.
Phivolcs was then headed by the late Dr. Raymundo Punongbayan.
Monitoring the volcano
When earthquake swarms were being reported, Newhall said that "immediately we knew we had to get monitoring started around the volcano."
"At that time, Phivolcs had a tripartite network out on the west side of the volcano...the Botolan side. Those were three seismographs connected by radio or cable...and the locations they were getting from that network all appeared to be out northwest of the volcano, which was quite strange and sa totoo duda ako diyan (in fact, I was doubtful about it) at first. I was doubting the location. It is possible there was bias in the tripartite network," Newhall said.
"But as soon as we put up our stations around the volcano and had the signals telemetered to the central observatory at Clark, we could see that tama man yung mga hypocenters (the hypocenters were right) that Phivolcs has determined. They were indeed about 5 kilometers northwest of the volcano," he added.
Pinatubo Volcano Observatory
The sudden phreatic explosions from the Mt. Pinatubo summit on April 2, 1991, that heralded its Plinian eruption in June compelled Phivolcs to set up a temporary monitoring station on Sitio Yamut, Botolan, Zambales on April 5, 1991.
In May 1991, Phivolcs said the Yamut station was transferred to Burgos then to Poonbato within Botolan.
The temporary station was responsible for issuing daily updates and hazard warnings on the volcano’s growing unrest.
To accommodate the increasing updates on the volcano's activity, Phivolcs, together with the USGS, deemed it necessary to establish the Pinatubo Volcano Observatory (PVO) inside the Clark Airbase in Pampanga.
Phivolcs said the "very first state-of-the-art seismic telemetry and ground deformation networks in the country" were set up on Pinatubo, linked to computers in PVO for rapid location of escalating earthquake activity.
However, much of the original monitoring network was destroyed by the 1991 eruption, and post-1991 networks that included acoustic flow monitoring of lahar channels were subsequently damaged or lost in the volcano’s harsh and changing terrain in the next 10 years.
In 2010, Phivolcs constructed the PVO-Magalang Station inside the Pampanga Agricultural State University campus, and slowly re-established its monitoring network on the volcano.
The original PVO inside Clark Airbase was finally relinquished to the Philippine Air Force Command in 2018, and all its functions were transferred to the Magalang Station, Phivolcs further noted.
At present, the agency said that the PVO operates solar-powered autonomous stations operating the latest state-of-the-art systems in volcano monitoring, which include broadband and short-period seismic, physico-chemical, IP camera, and digital WiFi or VSat systems.
All monitoring data are acquired by PVO and transmitted to the Phivolcs main office in Quezon City in real-time via internet or satellite communications.
Mt. Pinatubo today
On January 20, 2021, Phivolcs raised the status of Pinatubo Volcano from Alert Level 0 to Alert Level 1.
This means that there is low-level unrest that may be related to tectonic processes beneath the volcano.
No imminent eruption, however, is foreseen by Phivolcs amid the observance of persistent seismic activity.
(SOURCES: Philippine Institute of Volcanology and Seismology, Manila Bulletin archives)