A week after Mount Bulusan increased seismic activity, the volcano erupted at 4:36 a.m. on Monday morning. The explosion lasted until 5 a.m., the Philippine Institute of Volcanology and Seismology (Phivolcs) said. Phivolcs director Teresito Bacolcol described the event as a phreatic eruption and said the volcanic plume reached a height of 4,500 meters above the crater before drifting west to southwest. Dong Mendoza, spokesman of the Sorsogon provincial government, told The Manila Times that the eruption affected residents in the towns of Juban and Irosin, and ashfall incidents were reported in the villages of Cogon and Bolos in Irosin and Puting Sapa, Guruyan, Buraburan, and Tulatula Sur in Juban. Mendoza said that they are currently conducting a ground survey to assess the impact of the eruption to the communities in Juban and Irosin. Mount Bulusan in Sorsogon has a summit elevation of 1,565 meters (5,135 feet), It is a stratovolcano located on the Irosin caldera, covering the northeast rim of a caldera formed approximately 40,000 years ago. Following the phreatic explosion of Bulusan Volcano, the Phivolcs raised the alert level from 0 to 1. "This serves as a notice for raising the alert status of Bulusan Volcano from Alert Level 0 (Normal) to Alert Level 1 (Low-level Unrest)," Phivolcs said. Local government units and the public are reminded that entry into the 4-kilometer radius Permanent Danger Zone (PDZ) must be strictly prohibited and that vigilance in the 2-kilometer Extended Danger Zone (EDZ) on the southeast sector must be exercised due to the possible impacts of volcanic hazards such as PDCs, ballistic projectiles, rockfall, avalanches and ashfall on these danger areas. Communities that experience ashfall must take all necessary precautions and use protective masks or wet cloth to prevent ash inhalation. The civil aviation authorities must also advise pilots to avoid flying close to the volcano's summit as ash from any sudden phreatic eruption can be hazardous to aircraft. Phivolcs also warned the people living within valleys and along river/stream channels especially on the southeast, southwest and northwest sector of the edifice should be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall should phreatic eruption occur.