Sudden eruption of Bulusan volcano, Philippines

A sudden, steam-driven explosion was generated by the Bulusan volcano, the Philippines at 03:35 UTC on June 10, 2016.

According to PHIVOLCS, the eruption lasted for approximately 5 minutes, based on the seismic record, and produced a 2 km (6 561 feet) grayish ash plume above the volcano's summit that drifted towards the northwest. This is about 3 500 m (11 480 feet) above sea level.

Bulusan’s seismic monitoring recorded one hundred thirteen (113) volcanic earthquakes during the 24 UTC hours of June 9. Weak emission of white steam plumes rose up to 100 meters and drifted towards southwest yesterday. Precise leveling survey results from April 27 to May 5, 2016, indicated slight deflationary changes of the edifice relative to February 2016, the agency reported. However, the ground deformation measurements from continuous GPS data as of June 2, 2016, indicated slight inflation of the edifice since May 2016.

Alert Level 1 (abnormal) remains in effect over Bulusan Volcano. This indicates that hydrothermal processes are underway beneath the volcano that may lead to more steam-driven eruptions.

Bulusan volcano erupting on June 10, 2016 – 02:40 UTC. Credit: PHIVOLCS

The local government units and the public are reminded that entry to the 4-kilometer radius Permanent Danger Zone (PDZ) is strictly prohibited due to the possibility of sudden and hazardous steam-driven or phreatic eruptions.

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.

Furthermore, people living within valleys and along river/stream channels especially on the 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.

A similar explosion occurred at Bulusan on February 22, 2016. A steam-and-ash plume rose 500 m (1 640 feet) above the WNW fissure vent at the time. The event was accompanied by a high-frequency earthquake followed by low-frequency earthquakes that lasted 4 minutes and 21 seconds. Rumbling sounds were heard in Puting Sapa, Juban, and Bolos, Irosin, and minor amounts of ash fell in barangays Puting Sapa, Sagkayon, and Caladgao in Juban, and barangay Bolos in Irosin.

Bulusan erupting on February 22, 2016. Video credit: Roman Jebulan

Geological summary

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: Bulusan volcano erupting on June 10, 2016 – 02:40 UTC. Credit: PHIVOLCS