An increasing number of shallow volcanic earthquakes has been observed in the Mayon Volcano since June 24, the Philippine Institute of Volcanology and Seismology (Phivolcs) said in an advisory Monday afternoon. An increasing number of weak and shallow volcanic earthquakes began on June 24 and steadily increased to 102 volcanic earthquakes during a 24-hour period between 25 and 26 June 2023, it said. Phivolcs said 100 volcanic earthquakes were also recorded between 5 a.m. to 3 p.m. Monday. Volcanic earthquakes are caused by movements or eruptions of magma from the volcano, compared to tectonic quakes which are caused by fault movements. Mayon Volcano has been under alert Level 3 (increased tendency towards hazardous eruption) due to the continuous increase in its rockfall events. Phivolcs said that since then, eruptive activity has been dominated by weak aseismic effusion of degassed lava from the summit crater. "This means that gas-less lava is slowly and quietly being poured out of the volcano's summit," Phivolcs officer in charge Teresito Bacolcol told the Philippine News Agency. Some of the analyzed earthquakes that could be located emanated from the summit lava dome, indicating origins from lava extrusion processes at the crater, the advisory read. Bacolcol explained that this means the more recent earthquakes were plotted or located on the crater where the dome is found. "This would suggest that the recent earthquakes were the results of lava being pushed out of the lava dome," he said. According to Phivolcs, the increased seismicity was accompanied by "a noticeable sharp jump in ground tilt on the southwest sector of the edifice that began on 25 June 2023." At present, the steady-rate lava effusion from the summit crater and sporadic generation of rockfall and pyroclastic density currents or PDCs still persist. Phivolcs, meanwhile, reiterated that areas inside the 6 km.-radius permanent danger zone must remain evacuated, and that communities within the seven and eight kilometer radius must always be prepared. Aviation authorities must advise pilots to avoid flying close to the volcano's summit as ash from eruptions can be hazardous to aircraft, Phivolcs said.
Source: Philippines News Agency