Bulusan sustains drop in seismic activity

LEGAZPI CITY, Philippines — Despite showing a sustained drop in seismic activity in the past week, Bulusan Volcano’s condition remains abnormal as its other parameters continue to be high, the Philippine Institute of Volcanology and Seismology (Phivolcs) reported yesterday.

Winchille Sevilla, science research specialist at Phivolcs, said the sudden drop in volcanic earthquakes means that degassing activities inside the volcano are not strong enough to cause movements in the volcanic faults.

But Sevilla said the low tremors do not necessarily mean that the volcano is returning to its normal condition.

“We can only tell that Bulusan is going back to normal if the drop in its volcanic tremors is accompanied by a decrease in the sulfur dioxide and plume emissions,” Sevilla told The STAR yesterday.

Six volcanic quakes, 128 tons of sulfur dioxide and a plume emission of 500 meters above the main crater were recorded yesterday, Phivolcs said.

On Sunday, Bulusan generated four volcanic quakes, 919 tons of sulfur dioxide and a half-kilometer-high plume emission.

While the seismic events came in single digits in the last three days, Bulusan’s sulfur dioxide and plume emissions remain high, Sevilla said.

“The figures in the abnormal signs tell us that hydrothermal activities are ongoing inside the volcano and can lead to a phreatic eruption any time,” he added.

Phivolcs said more weeks of observation are needed before it could conclude an upward or downward trend in the overall condition of the volcano.

“We have to closely watch the still fluctuating abnormal behavior of Bulusan before we can tell where it is leading us,” Sevilla said.

He said the activities being detected daily over Bulusan remain within the parameters of Alert Level 1 or abnormal condition.

Phivolcs warned the public against entering the permanent and extended danger zones around the volcano due to the possibility of sudden hazardous phreatic eruptions.

Alert Level 1 was hoisted over Bulusan following a phreatic eruption on June 15.