This is a notice for the lowering of the alert status of Mayon from Alert Level 3 to Alert Level 2.
Since the last recorded seismic swarm on 29 November 2014, a general decline in the overall activity of Mayon Volcano has been observed, as indicated by the following monitored parameters:
Volcanic Earthquake Activity: For nearly the past three weeks, seismic activity has declined to an average 2-3 mostly volcano-tectonic earthquakes daily that are attributed to rock fracturing beneath the northern flank of the edifice. There have been even lesser low frequency earthquakes associated with magma or volcanic gas movement recorded, while few minor rockfall events detected were more likely enhanced by intense rainfall over the volcano summit rather than by lava extrusion at the crater. Such overall low-level seismicity indicates that there is currently no active transport of eruptible magma to the shallow levels of the volcano.
Ground Deformation: Since June 2014, Mayon’s edifice has been inflating or swelling due to very slow intrusion of subsurface magma beneath the northern flank of the edifice, based on Precise Leveling (PL) surveys and continuous electronic tilt measurements. Distinct short-term increases in edifice inflation in October 2014 notably preceded episodes of short lava flow from the summit crater on 12 and 19 October. However, short-term increase in edifice inflation recorded by PL surveys in the last week of November 2014 was not succeeded by lava extrusion. Although the volume of yet unerupted magma accumulated beneath the volcano since June 2014 is in the order of 107 m3 based on ground deformation data, intrusion to shallow levels has not occurred in nearly three weeks, based on stationary tilt data for the corresponding period.
Gas Emission: Sulfur Dioxide emission or SO2 flux from Mayon crater has declined since 2 October to below 500 tonnes/day, which is the baseline value during quiescence. SO2 flux levels have decreased from a high of 2,360 t/d on 6 September, with the latest flux measured on 9 December at 259 t/d. The low levels of SO2 flux indicate that shallow magma degassing has declined, due to either the progressive loss of volcanic gas from shallow magma, or the generally low volcanic gas content of magma intruded at deeper levels beneath the edifice, or both.
Visual Observation of the Summit: Since the last observation of lava flow on 19 October, no new lava material has been observed at Mayon’s summit crater. Crater glow, which is incandescence associated with superheated gas emission at the summit vent, has not been observed since 28 November. The decline in observable parameters at the summit is consistent with the cessation of magma supply to the shallow levels of the volcanic edifice.
In view of the above, PHIVOLCS-DOST is now lowering the alert status of Mayon from Alert Level 3 to Alert Level 2. This means that the likelihood of hazardous eruption within days to weeks has lessened. However, the lowering of the alert status should not be interpreted that the volcano’s unrest has ceased, considering that deeper beneath it eruptible magma has already accumulated. If there is a resurgence of volcanic unrest based on any one or combination of the above monitoring parameters, the alert status may step up to Alert Level 3 again. On the other hand, if there is a noticeable return to baseline levels of ground deformation and sustained low levels of other parameters, then the Alert Level may further step down. The public is still reminded to avoid entry into the 6-km Permanent Danger Zone or PDZ due to perennial hazards of rockfalls, avalanche, ash puffs and sudden steam-driven or phreatic eruptions at the summit area. Furthermore, people living in valleys and active river channels are cautioned to remain vigilant against sediment-laden streamflows and lahars in the event of prolonged and heavy rainfall. PHIVOLCS-DOST is closely monitoring Mayon Volcano’s activity and any new development will be immediately posted to all concerned.