Mount Bulusan ejected a ash plume on May 1, 2015 at around 9:46 PM, lasting for 3.5 minutes. The incident is classified as a minor explosion event by PHIVOLCS leading to the raising of Alert Level 1 (abnormal activity) for the surrounding area. A second ash explosion lasting for five minutes also occurred on the same day. PHIVOLCS determined the cause of the eruptions to be hydrothermal activity beneath the volcano. People were advised not to enter the Permanent Danger Zone. Further advisories were given to low-flying aircraft against the dangers of sudden phreatic eruptions, and to local residents near rivers and streams in case of lahar flows. There were also concerns that rains from Typhoon Noul could trigger lahars and mudslides near the mountain. However, after Noul recurved to the north, the threat did not materialize and the evacuees were permitted to return to their homes.