At 12:43 PM yesterday, a dense, five-kilometer tall eruption column was generated by a short-lived phreatomagmatic eruption at Mayon Volcano that lasted eight (8) minutes based on the seismic record. The event generated pyroclastic density currents or PDCs on gullies and barrancos heading the Miisi, Bonga, Buyuan, Basud, San Andres, Buang, Anoling and other minor rivers within four (4) kilometers of the summit vent, well within the Permanent Danger Zone (PDZ). Volcanic ash was blown west and fell on the Municipalities of Guinobatan, Camalig, Oas, Polangui and Iriga City. This was followed by a minor degassing event at 5:51 PM that generated a short, 500 meter-high ash plume. Between 9:37 PM and 5:25 AM the following morning, five (5) episodes of intense but sporadic lava fountaining from the summit crater lasting three (3) to thirty (30) minutes occurred. The lava fountains reached 500 meters to 700 meters high and generated ash plumes that reached 2.5 kilometers to 3 kilometers above the crater. The events fed lava flows on the Miisi and Bonga Gullies, sprayed near-vent lava spatter and fed incandescent rockfall on the summit area.
A total of two (2) explosion-type earthquakes corresponding to the vertical column eruptions, fifteen (18) tremor events, some corresponding to lava fountaining episodes, thirty five (35) rockfall events and (2) pyroclastic density currents or PDCs from lava collapse were recorded by Mayon's seismic monitoring network. Rockfall events were generated by the collapsing lava front and margins of the advancing lava flow on the Miisi Gully and by shedding from the summit dome onto the Bonga Gully. Currently, the Miisi and Buyuan lava flows have advanced to three (3) kilometers and 200 meters, respectively, from the summit crater. Sulfur dioxide gas emission was measured at an average of 992 tonnes/day on 22 January 2018 prior to the phreatomagmatic event. Electronic tilt and continuous GPS measurements indicate a sustained swelling or inflation of the edifice since November and October 2017, consistent with pressurization by magmatic intrusion.
PHIVOLCS has raised the alert level to Alert Level 4 yesterday in effect over Mayon Volcano. The public is strongly advised to be vigilant and desist from entering the eight (8) kilometer-radius danger zone, and to be additionally vigilant against pyroclastic density currents, lahars and sediment-laden streamflows along channels draining the edifice. Civil aviation authorities must also advise pilots to avoid flying close to the volcano’s summit as ash from any sudden eruption can be hazardous to aircraft. DOST-PHIVOLCS maintains close monitoring of Mayon Volcano and any new development will be communicated to all concerned stakeholders.
