(PNA file photo)

MANILA – A small-volume lahar flow has been observed in Mount Bulusan, the Philippine Institute of Volcanology and Seismology (Phivolcs) reported early Monday.

In an advisory at 1 a.m., Phivolcs said lahar flow began around 7:04 p.m. Sunday. This lasted 54 minutes during a period of thunderstorms over Sorsogon province.

"Ocular investigation by the Bulusan Volcano Observatory confirmed thin channel-confined lahar deposits along Calang Creek in Barangay Cogon, Irosin, the major channel draining the southwestern slopes of Bulusan," Phivolcs said.

On Monday, Phivolcs said that for the past 24 hours, seven volcanic earthquakes caused by movements or eruptions of magma from the volcano, were recorded.

Moderate plume emission reached 150 meters tall; while sulfur dioxide flux was 559 tons on June 26.

Alert Level 1 (low-level unrest) remains hoisted over Mount Bulusan.

Those living within valleys and along river/stream channels, especially on the southeast, southwest and northwest slopes of the volcano edifice, should be vigilant against sediment-laden stream flows and lahars during heavy and prolonged rainfall.

Phivolcs also reminded local government units and the public that entry into the 4-kilometer radius permanent danger zone must be strictly prohibited, and that vigilance in the 2-kilometer extended danger zone on the southeast sector must be exercised due to the increased possibilities of sudden and hazardous phreatic eruptions.

Aviation authorities are, likewise, urged to advise pilots to avoid flying close to the volcano’s summit as ash from any sudden phreatic eruption can be hazardous to aircraft. (PNA)