The decreased activity at the volcano has been continuing for some time since mid-November.
The number of earthquakes related to magma squeezing through rocks and degassing have reduced from a monthly mean of 11 events per day to nearly 0 event/day in early December.
A recorded frequency of glowing avalanches and block-and-ash flows, generated by collapsing parts of viscous lava flow fronts and partial summit lava dome collapses, also significantly decreased from monthly means of 87-122 events/day and 2-5 events/day in October/November, respectively, to 0 event/day in early December. This indicates the lowered magma supply rate within the volcano’s main feeder pipe into the summit crater and lava dome.
The diminished magma supply rate in the conduit related to the shortening of the upper incandescent lava overflow in late November. As seen in the attached timelapse of the entire effusive eruption episode of the volcano so far, the length of three lava flow arms on the southeastern Bonga, southern Mi-isi and eastern Basud flank remains unchanged (3.4 km, 2.8 km and 1.1 km from the summit) since July-August 2023. Lava flows are cooling, i.e. undergo a process of crystallization. Therefore, the total volume of erupted deposits has remained at approximately 49 million m3 since then. The thermal anomaly is currently confined on the summit vent only as seen in the latest acquired satellite image on 5 December.
The short-term electronic tilt and GPS monitoring continue to detect the northwest upper flank inflated. However, the long-term ground deformation in general suggests the ongoing uplifting of the edifice since 2020.
Sulfur dioxide (SO2) emission values have varied between October and November between 1,100 and 1,400 tonnes/day, but in early December, have weakened down to 1,095 tonnes per day. The flux of SO2 emissions lowered to 859 tonnes/day yesterday.
Due to generally reduced activity at the volcano, the PHIVOLCS lowered the local alert level for the volcano from Level 3 (tendency towards a hazardous eruption) to Level 2 (moderate level of unrest).
In order to mitigate the risk, people are forbidden to enter an area of 6 km distance from the summit crater due to impacts of rockfalls, pyroclastic falls and/or phreatic eruptions.
Source: Philippine Institute of Volcanology and Seismology volcano activity update 8 December 2023
