MT. BULUSAN in Sorsogon province was rocked with 166 volcanic earthquakes on Wednesday, signifying a rising level of volcanic activity for the past three days (May 10-12).
The Philippine Institute of Volcanology and Seismology (Phivolcs) raised the volcano's status to Alert Level 1 (Abnormal) on Tuesday.
Paul Alanis, Phivolcs resident volcanologist here, said in a phone interview that the series of volcanic quakes were due to hydrothermal pressure that has been building up in the volcano’s vent.
He explained that hydrothermal activity is caused by water mixing with hot rocks, producing gas pressure and rock movements in the volcano’s vent.
Phivolcs seismic instruments have recorded a series of quakes totaling 290 since Monday and bulging of the edifice at the upper slopes near the crater.
Alanis described the volcano’s abnormality as “localized,” since the quakes generated were not related to magma but hydrothermal pressure detected near the crater.
Other parameters being observed include the sustained inflation of the upper slopes, indicating that shallow hydrothermal pressures are occurring beneath the edifice.
These volcanic precursors such as quakes and bulging at the slopes could lead to “phreatic or steam-driven” eruptions, which the volcano exhibited during past eruptions, Alanis said.
Historically, Mt. Bulusan has had phreatic eruptions under Alert Level 1.
Phivolcs records indicate that Bulusan's last eruption was in 2017. In July 2020, volcanologists raised the volcano’s alert status to Level 1 but in October last year, scientists returned the status to “normal".
Under Alert Level 1, residents near the volcano are strongly advised to always be on alert and keep out of the designated four-kilometer Permanent Danger Zone (PDZ), and the two-kilometer extended danger zone (EDZ) due to the possibility of sudden and hazardous phreatic eruptions. (By Mar Serrano)
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