PHIVOLCS- The lowering of Mayon Volcano’s status from Alert Level 3 (decreased tendency towards hazardous eruption) to Alert Level 2 ((moderate level of unrest).SUMMARY | Mayon’s volcano monitoring network and active observation of day-to-day conditions have recorded a general decline in unrest, as indicated by the following monitored parameters:
1. Volcanic Earthquake Activity: For the past two weeks, seismic activity has waned from a peak of eighty-two (82) to less than ten (10) rockfall events attributed to the collapse of unstable lava flow deposits on the Miisi, Bonga and Basud drainage systems. Low frequency earthquakes associated with magma degassing and short ash plumes were last recorded on 15 March 2018, although lava flow effusion from the crater could be detected until 18 March 2018. The overall decline in seismicity indicates that there is currently no active transport of eruptible magma to the shallow levels of the edifice.
2. Ground Deformation: Since 20 February 2018, medium-term deflation of Mayon’s edifice has been recorded by electronic tilt and Precise Leveling (PL) surveys despite short-term episodes of inflation of its lower and middle slopes. The downtrend in ground deformation follows a period of continuous inflation that began in October-November 2017 and implies that magma recharge from deep to shallower levels of the edifice has decreased. Based on medium-term PL data, nonetheless, the volcano is still inflated relative to January 2010 baselines, most likely due to the presence of remnant magma beneath the edifice.
3. Volcanic Degassing: Magmatic sulfur dioxide or SO2 flux measured for the past two weeks has fluctuated within the range of 500-2000 tonnes/day, which is lower than 700-4500 tonnes/day for the period of eruption from 13 January 2018 to 8 March 2018. The current concentrations of SO2 reflect the diminishing volumes of gas exsolved from unreplenished magma beneath the edifice as well as from cooling lava deposits on the summit and volcanic slopes.
4. Visual Parameters: Since the last observation of lava effusion on 18 March 2018, no new lava has been detected on Mayon’s summit crater. Crater glow, which is incandescence associated with superheated gas emission at the summit vent, has diminished from intense to faint. Gravity-driven lava flow has begun to stabilize, producing less rockfall and infrequent pyroclastic density currents, the last of which occurred on 27 March 2018. The decline in observable surface parameters is consistent with the cessation of magma supply to the shallow levels of the volcanic edifice.