Bulusan volcano in Luzon, Philippines, erupted on February 22, 2016, sending a short column of steam and ash 500 m (1 640 feet) above the west-northwest fissure vent of the volcano summit. The explosion was registered as a high-frequency earthquake, followed by a low frequency one, 21 second long, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) reports.
Six volcanic earthquakes were recorded in the last 24 hours. The explosions of February 22 were accompanied by a rumbling sound heard at Puting Sapa, Juban, and Bolos, Irosin. No volcanic earthquakes were reported prior to the explosion. However, an increased seismic activity was observed between February 20 and 21. Volcanic ash traces were reported in Brgys, Puting Sapa, Sagkayon, and Caladgao in Juban and Brgy, Bolos in Irosin.
On February 23, moderate emission of 50 m-high (164 feet) white steam occurred at the west-northwest vent of the volcano, traveling southwestwards. Weak emission of steam was also observed from the southwest vent.
Video credit: Roman Jebulan
Before this event, an explosion was last registered at Bulusan volcano on July 17, 2015, at 13:10 local time, according to GVP. An explosion generated an ash plume that rose 200 m (656.2 feet) above the crater and drifted WNW. Ashfall was reported in areas to the N and NE in the Sorsogon Province, including Inlagadian (municipality of Casiguran), Tigkiw, Tugawe, Nazareno, Bugtong, and Rizal (municipality of Gubat), and Fabrica, San Isidro, Sta. Cruz, and San Ramon (municipality of Barcelona). The Alert Level remained at 1, indicating abnormal conditions and a 4-km (13 123.4 feet) radius Permanent Danger Zone (PDZ).
Alert Level 1 (abnormal) is currently in effect over Bulusan Volcano, according to PHIVOLCS, indicating that hydrothermal processes are underway beneath the volcano that could lead to steam-driven eruptions. An entry to the 4-km (13 123.4 feet) radius PDZ is strictly prohibited due to the possibility of sudden and hazardous steam-driven or phreatic eruptions. Residents of the valleys and river/stream channels, particularly at the southwest and northwest sector of the edifice should be aware of the sediment-laden streams and lahars in the event of heavy and prolonged rainfall.
Civil aviation authorities have been urged to advise pilots to avoid flying close to the volcano's summit as ash from any sudden phreatic eruption can be dangerous to the aircraft.
According to PHIVOLCS, precise leveling survey results from December 2-7, 2015, indicated slight inflationary changes of the volcano's edifice relative to September 2015, and consistent with ground deformation measurements from continuous GPS data since August 2015.
Luzon's southernmost volcano, Bulusan, was constructed along the rim of the 11-km-diameter (6.8 miles) (dacitic-to-rhyolitic Irosin caldera, which was formed about 36 000 years ago. Bulusan lies at the SE end of the Bicol volcanic arc occupying the peninsula of the same name that forms the elongated SE tip of Luzon. A broad, flat moat is located below the topographically prominent SW rim of Irosin caldera; the NE rim is buried by the andesitic Bulusan complex.
Bulusan is flanked by several other large intracaldera lava domes and cones, including the prominent Mount Jormajan lava dome on the SW flank and Sharp Peak to the NE. The summit of 1565-m-high (5 134.5 feet) (Bulusan volcano is unvegetated and contains a 300-m-wide (984.3 feet), 50-m-deep (164 feet) crater. Three small craters are located on the SE flank. Many moderate explosive eruptions have been recorded at Bulusan since the mid-19th century. (GVP)
Featured image: Footage of the phreatic explosion of Mt Bulusan in the province of Sorsogon, Philippines, February 22, 2016. Image credit: Roman Jebulan