Phivolcs hoists Alert Level 1 in restive Mt. Pinatubo; no imminent eruption seen
CLARK FREEPORT—THE Philippine Institute of Volcanology and Seismology (Phivolcs) said in its 7 a.m. bulletin on Thursday that Alert Level 1 has been raised in areas around Mt. Pinatubo.
Phivolcs said Alert Level 1 means there is low-level unrest in Pinatubo but no imminent eruption is foreseen despite the observance of persistent seismic activity.
Phivolcs said a total of 1,722 imperceptible earthquakes beneath the Pinatubo edifice were detected since January 2020.
Situated 87 kilometers northwest of Manila, Mt. Pinatubo is located at the boundaries of Zambales, Tarlac and Pampanga provinces.
It was thought to be a dormant volcano until its eruption in June 1991, one of the worst volcanic eruption in the country’s history. The eruption sent tens of thousands living in communities around it to flee for safety as volcanic ashes spit out by the volcano
rained over Central Luzon, covering many areas in the main island with ashfall.
Years after its eruption, debris from Mt. Pinatubo continues to flow in the event of rain in the form of lahar, burying houses and other abandoned structures as rivers and streams overflow. Vast tracts of agricultural lands were also buried under volcanic ash and for years were rendered unproductive.
“The earthquakes ranged between ML0.5 and ML2.8 in magnitude; all earthquakes recorded are associated with rock-fracturing processes,” Phivolcs said.
Carbon dioxide, temperatures and acidity showed slight increases or remained unchanged, it said.
It added: “Given the persistence of seismic activity, Department of Science and Technology-phivolcs is raising 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 and that no imminent eruption is foreseen.”
Phivolcs also advised that entry into the Pinatubo crater area “must be conducted with extreme caution and should be avoided if possible.”
Communities and concerned local government units surrounding Mt. Pinatubo were told to be prepared for both earthquake and volcanic hazards and to revisit their disaster preparedness plans.
Phivolcs likewise discouraged visits to the crater lake. The Philippine Air Force secures the entry to the volcano via Barangay Sta. Juliana in Capas, Tarlac.
Aeta communities closest to the volcano are in Barangay Inararo in Porac, Pampanga; Sitio Tarukan in Barangay Sta. Juliana, Capas, Tarlac; and several villages in San Marcelino, Zambales.
Last January 27, 2021, Phivolcs notified the public and concerned authorities of recent earthquake activity in the Pinatubo Volcano. Since January 20, 2021, the Pinatubo Volcano Network (PVN) and the
Philippine Seismic Network (PSN) have detected a total of 826 imperceptible earthquakes east-northeast of Pinatubo Volcano in the vicinities of the City of Mabalacat, Pampanga.
The strongest of these earthquakes occurred on January 25, 2021 at depths of 15 to 28 kilometers and ranged between ML1.0 and ML2.5 in magnitudes.
Based on the general distribution of located events, these earthquakes were generated along a segment of the Sacobia Lineament, a fault that was last active during the post-eruption period of 1991.
This development serves to remind us once again that several faults occur around the volcano and that these can generate earthquake activity that can be sometimes imperceptible and harmless but that can also sometimes be damaging.
On April 22, 2019, a M6.1 earthquake on the southern foot slopes of Pinatubo Volcano shook the Central Luzon region and caused fatalities and substantial damages to buildings, roads and other structures.
It can be recalled that after nine weeks of unrest, Mt. Pinatubo erupted on June 15, 1991, accompanied by Typhoon Yunya that dispersed ash to surrounding countries.