Phivolcs warns of deadly Bulusan phreatic eruptions

THE Philippine Institute of Volcanology and Seismology (Phivolcs) has seen increased possibility for sudden and potentially deadly phreatic eruptions of Mount Bulusan in Sorsogon.

Phivolcs volcanologist Paul Alanis said some changes in Bulusan's sulfur dioxide (SO2) emission lately have given rise to the possible eruptions.

“At times, we even monitor increases in the number of Bulusan's volcanic earthquakes,” he added.

Alanis again cautioned against entering Bulusan's 4- kilometer permanent danger zone ( PDZ) and 2- kilometer extended danger zone ( EDZ), noting that phreatic eruptions can occur anytime without warning.

According to experts, phreatic eruptions are steam- driven blasts that occur when water beneath the ground or on the surface transforms into steam after coming into contact with hot volcanic materials.

Phivolcs volcanologist Winchelle Sevilla earlier said there is still no means of giving advanced warnings about looming phreatic eruptions. Research on the matter is still in progress, he added. In its bulletin released on Friday, Phivolcs said hydrothermal processes in progress beneath Bulusan volcano may lead to steam- driven or phreatic eruptions.

It reminded the public to refrain from entering Bulusan's PDZ owing to the high possibility of “sudden and hazardous” phreatic eruptions in the volcano.

Last October 18, Phivolcs declared on Bulusan's southern slope an EDZ stretching two kilometers downslope of the PDZ as an extra precaution against possible phreatic eruptions when alert levels 1 and 2 are prevailing in the volcano.

Alert level 1 is prevailing in Bulusan as the volcano is manifesting low- level volcanic unrest, it also noted.

Alanis said such alert level indicates that magmatic eruption is not yet imminent there.

He, however, added that phreatic eruptions are still possible even if alert level 1 or even zero is prevailing.

The deadly May 2013 phreatic eruptions of Mayon Volcano occurred while under alert level zero.