Mount Bulusan in Sorsogon had a phreatic eruption on Sunday morning, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) said.
PHIVOLCS raised the alert status of Bulusan Volcano from 0 (normal) to Alert Level 1 (low-level unrest).
“Alert Level 1 status is now raised over Bulusan Volcano, which means that it is currently in an abnormal condition,” PHIVOLCS said.
PHIVOLCS Director and Science Undersecretary Renato Solidum Jr. said the phreatic eruption occurred at 10:37 a.m. and it lasted for 16 minutes.
“Kanina, nagkaroon ng phreatic eruption ang Bulusan Volcano... 'Yung pagsabog ay sanhi ng pagpapakulo ng tubig sa ilalim ng crater. Tumagal ito ng 16 minutes at patuloy natin itong sinusubaybayan,” Solidum said in an interview on Super Radyo dzBB.
(Bulusan Volcano had a phreatic eruption this morning... The eruption was caused by the boiling of water underneath the crater. It lasted for 16 minutes, and we are still monitoring it.)
PHIVOLCS later said in a bulletin issued at 11:40 a.m. that the eruption lasted for approximately 17 minutes. A steam-rich grey plume reaching up to one-kilometer high was observed from the municipality of Juban, before it drifted west, it added.
“Hindi naman kataasan ang taas ng pagsabog. May mga maitim o dark gray na eruption cloud na nakikita na umuusli sa crater nito na hindi naman kataasan. Posible itong mangyari sa Bulusan (Volcano) na madalas magkaroon ng phreatic eruption,” he added.
(The height of the plumes from the explosion was not high. There are dark or dark gray eruption clouds that could be seen being emitted from the crater, and these plumes are not that tall. This can possibly happen in Bulusan Volcano which often has phreatic eruptions.)
“With the ongoing activity ng Bulusan, magtataas tayo ng Alert Level 1 [we will raise it to Alert Level 1],” he said, adding that they have noticed that the number of volcanic earthquakes in the volcano has increased to 77 overnight.
According to PHIVOLCS, a phreatic eruption refers to a steam-driven explosion that occurs when water beneath the ground or on the surface is directly heated by hot rocks or new volcanic deposits (e.g. pyroclastic density currents, lava) or indirectly by magma or magmatic gas.
PHIVOLCS said ashfall was reported in Juban and Casiguran.
Four barangays in Irosin also had ashfall, the municipal disaster risk reduction and management office (MDRRMO) said.
Irosin, Sorsogon MDRRMO officer Fritzie Michelena said in an interview on Super Radyo dzBB that nearly 800 families were slightly affected by the ashfall in barangays Cogon, Bolos, Gulang-Gulang, and Tinampo.
While the local government is already preparing for possible evacuation of the residents, Michelena said that there is no need yet to transfer them to evacuation centers upon initial assessment.
In its 8 p.m. update, PHIVOLCS retained Alert Level 1 over the volcano, registering 27 weak volcanic earthquakes until 4 p.m.
'Avoid 4-km radius of PDZ'
Solidum said residents must avoid the four-kilometer radius of the permanent danger zone.
PHIVOLCS also said pilots should avoid flying close to the summit of Bulusan Volcano "as ash from any sudden phreatic eruption can be hazardous to aircraft."
"Furthermore, people living within valleys and along river/stream channels especially on the southeast, southwest and northwest sector of the edifice should be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall should phreatic eruption occur," it added.
Under Alert Level 1, the following may be observed in Bulusan Volcano, PHIVOLCS said in an explainer on its website:
- slight increase in volcanic earthquake and steam/gas activity;
- sporadic explosions from existing or new vents;
- notable increase in the temperature of hot springs; and
- slight inflation or swelling of the edifice.
This means "hydrothermal, magmatic or tectonic disturbances. The source of activity is shallow, near crater or in the vicinity of Irosin Caldera. Entry into the PDZ must be prohibited," it added.
In October 2016, Bulusan Volcano spewed ash for about 20 minutes covering four nearby barangays. —KG/BM, GMA News