Hot gas, ash, and rock raced down the Mi-isi Gully in Albay on Monday, Feb. 9, as Mayon Volcano produced the largest pyroclastic density currents (PDCs) of its 2026 eruption.

In an update early Tuesday, Feb. 10, the Philippine Institute of Volcanology and Seismology (Phivolcs) explained that the PDCs were triggered by lava-fed collapses at the summit crater, which disintegrated deposits of oxidized and degassed lava and generated brownish ash clouds.

A series of at least 12 major PDCs swept down Mayon’s slopes between 10:35 a.m. and 11:37 a.m. on Feb. 9, with the largest occurring at 10:59 a.m. and lasting seven minutes.

Phivolcs said the 10:59 AM flow and the subsequent events traveled as far as four kilometers down the Mi-isi Gully, marking the farthest runouts recorded so far in the 2026 eruption.

“Based on total seismic energy release, the Feb. 9, 2026 major PDC activity represents only a brief intensification of unrest at Mayon, which has progressed in near-steady conditions since the onset of eruption,” Phivolcs said.

PDCs, locally called “uson,” are fast-moving avalanches of hot gas, ash, and fragmented rock that can travel at hundreds of kilometers per hour.

Unlike slower lava flows, they sweep down slopes suddenly and unpredictably, carrying enough heat and force to destroy everything in their path.

Phivolcs explained that even a mostly effusive, or non-explosive, eruption like Mayon’s can suddenly produce these dangerous flows if lava collapses from the summit.

The Feb. 9 PDCs also produced prominent ash clouds more than two kilometers tall, drifting southwest with winds of roughly 40 kilometers per hour.

Several barangays were blanketed in ash, including Sua, Cabangan, Tumpa, Quirangay, Sumlang, Ligban, Libod, Bariw, Salugan, Anoling, and Gapo in Camalig, and Travesia, Sinungtan, Maninila, Quitago, Ilawod, Inamnan Pequeño, Lower Binogsacan, Doña Mercedes, Malipo, Poblacion, Quibongbongan, Tandarora, San Rafael, and Masarawag in Guinobatan.

Since the eruption began on Jan. 6, Phivolcs said Mayon has produced 1,690 PDCs, 9,941 rockfalls, and 1,346 volcanic earthquakes.

Lava flows have advanced between 1.3 and 3.8 kilometers down the Mi-isi, Bonga, and Basud Gullies, while ground measurements show the eastern and northeastern flanks are still swelling from magma intrusion.

Mayon Volcano remains under Alert Level 3, signaling continuing magmatic unrest.

Phivolcs reminded the public that effusive eruption continues to feed new lava flows, PDCs, and rockfalls on the southern and eastern slopes.

Residents were advised to refrain from entering the six-kilometer permanent danger zone.

“Residents within the eight-kilometer radius, particularly on the southern and eastern slopes of Mayon, must also be prepared for evacuation in case monitoring parameters suddenly escalate and the volcano status is stepped up to Alert Level 4,” Phivolcs added.