MANILA, Philippines – A week after a phreatic eruption triggered the declaration of Alert Level 1 for Bulusan Volcano in Sorsogon, a similar eruption occurred early Sunday, June 12.

The Philippine Institute of Volcanology and Seismology (Phivolcs) said in an advisory at 4:20 am that a phreatic or steam-driven eruption was detected at 3:37 am on Sunday, lasting around 18 minutes.

Phivolcs later explained in a separate update at 4:30 pm that the eruption “was recorded as an explosion-type earthquake by seismic and infrasound instruments, but could not be visually observed in the dark of night.”

“The explosion was felt at Intensity III by residents of Barangay Añog, Juban, and at Intensity II in Barangay Inlagadian, Casiguran, all within 5 kilometers of the Bulusan summit,” the agency said.

“Rumbling sounds accompanying the eruption were also reported by witnesses in Sitio Bagong Barrio, Barangay Santa Lourdes, Barcelona; Barangay Inlagadian and Barangay San Juan, Casiguran; Barangay Bentuco, Gubat; and Barangays Añog, Calateo, and Puting Sapa, Juban. A brief incandescence at the base of the eruption plume was also reported in Barangay Inlagadian, Casiguran.”

“Multiple active vents” were then observed spewing ash and steam for several hours after the phreatic eruption.

“In the morning, six vents – the major crater called Blackbird, three explosion pits on the summit, and the lateral vents on the northwest and north sides of the summit – were actively degassing short plumes which entrained ash until at least [9 am]. The plumes dispersed into a long veil of ash extending several kilometers to the northwest,” Phivolcs said.

The Sorsogon Provincial Information Office (PIO) said ash from Sunday’s eruption spread to more areas.

“Sa kasalukuyan, halos lahat ng barangay ng Juban ang apektado, at ilang mga barangay ng Irosin, Casiguran, at Magallanes. Pinapayuhan ang mga motorista na mag-ingat o kung maaari ay iwasan muna ang pagbiyahe o pagdaan sa mga apektadong lugar,” the Sorsogon PIO said in a Facebook post.

(At the moment, nearly all barangays in Juban are affected, and some barangays in Irosin, Casiguran, and Magallanes. Motorists are advised to take precautions or if possible, avoid traveling to or passing through the affected areas.)

More than 11,000 individuals or over 2,800 families evacuated in Juban on Sunday, said the Office of Civil Defense.

Phivolcs added on Sunday afternoon that ash also drifted to Sorsogon City, the municipality of Pilar, and even to Daraga, Albay, 50 kilometers northwest of Bulusan Volcano.

The Civil Aviation Authority of the Philippines ordered the cancellation of all domestic flights at the Bicol International Airport in Daraga on Sunday.

Sorsogon Governor Francis “Chiz” Escudero also instructed local personnel to clean up Maharlika Highway on Sunday morning, a task which the governor said was completed 12 hours after the eruption. Visibility along the highway had been poor due to the ashfall.

Phivolcs reminded the public that exposure to ashfall can cause irritation and breathing problems, with the elderly, children, pregnant women, and those with respiratory illnesses most at risk.

“Affected populations are advised to protect their mouths and noses using N95-grade face masks or wet cloth or towel,” the agency said.

Last Thursday, June 9, Phivolcs had warned that another phreatic eruption may be imminent, after an increase in the number of volcanic earthquakes was observed at Bulusan.

In a separate summary released at 8 am on Sunday, Phivolcs said it observed 136 volcanic earthquakes at Bulusan from 5 am on Saturday, June 11, to 5 am on Sunday, or over a 24-hour period.

The volcano was placed under Alert Level 1 on June 5 following the first phreatic eruption that day. The first eruption also left parts of Sorsogon covered in ash, and forced families to flee their homes.

“Alert Level 1 status remains in effect over Bulusan as all other monitoring parameters as of this time indicate that current unrest is driven by the volcano’s restive hydrothermal system,” Phivolcs said on Sunday.

The agency maintained that entry into the 4-kilometer-radius permanent danger zone around the volcano must be strictly prohibited. – with a report from Rhaydz Barcia/Rappler.com