The Philippine Institute of Volcanology and Seismology raised Alert Level 1 over Mount Bulusan due to increased seismic activity, a day before a magnitude 5.4 tremor shook parts of the Ilocos and Cagayan.
From May 4 to 5, Phivolcs recorded a total of 16 volcanic earthquakes, according to the agency’s Bulusan Volcano Bulletin on Sunday.
It also noted the active volcano’s tilt data from April 29 to May 5 which indicated a slight inflation in the upper slopes.
The agency also observed increase in water temperature of nearby hot springs.
Phivolcs said that raising Alert Level 1 or abnormal status “indicates that hydrothermal processes may be underway beneath the volcano that may lead to steam-driven eruption.”
Phivolcs said the quake in Ilocos Norte and Cagayan was tectonic in origin with a depth of 15 kilometers.
Intensity V was felt in Pasuquin, Bacarra and Laoag City, and in Tuguegarao City, Cagayan.
Meanwhile, Intensity IV was felt in Paoay, Ilocos Norte.
Intensity III was recorded in Sinait and Santa, Ilocos Sur, and in Sudipen, La Union, and Intensity II was reported in Baguio City.
With increased volcanic activity, the agency reminded residents and local government units near the volcano to avoid entry into the 4-kilometer Permanent Danger Zone around the volcano.