An explosive eruption was reported from the volcano today, but it is still uncertain whether it was an actual volcanic eruption. The Volcanic Ash Advisory Center (VAAC) in Tokyo issued a warning about a possible, but very large ash plume that rose to flight level 440 (44,000 ft or 14,300 m alitude) and drifted west.
The Philippine Institute of Volcanology PHILVOLCS mentioned that seismic as well as infrasound signals were indeed registered, which indicate explosive activity. However, the signals were not typical for volcanic activity and it is currently being investigated what actually happened between 12.09 and 12.14 p.m. (local time) when the signals appeared.
Earlier, the volcano had only shown a mild increase of carbon dioxide emissions measured at 257 tons per day recently. An increase in seismicity had been observed in March and PHIVOLCS had raised the alert level to 1 (on a scale of 0-5). However, the volcano had been rather calm in the past weeks and no unusual activity had been mentioned.
If the reported explosions turn out to be volcanic in origin, they likely are phreatic (steam-driven) or phreatomagmatic (steam-magma interacting driven) in nature and illustrate once again that volcanoes might explode with little to no warning.