Bulusan volcano produces steam and ash explosion, Philippines


Bulusan volcano produced a steam and ash explosion at 00:09 UTC today (08:09 local time) which lasted for 5 minutes based on seismic records,​ Philippine Institute of Volcanology and Seismology (PHIVOLCS) reports. The last eruptive phase of this volcano started on November 6, 2010 and lasted until May 13, 2011.

Today's event was not observed visually due to thick rain clouds covering the summit. At around 02:30 UTC, when the crater became visible, strong to moderate, dirty white steaming was observed which reached 200 m high and drifted west-northwest coming from the northwest vent of the volcano.

Only 5 volcanic earthquakes were detected during the past week by the Bulusan seismic network. After the steam and ash explosion, the network has recorded approximately 40 volcanic earthquakes.

Ed Laguerta, resident volcanologist of PHIVOLCS in the Bicol region, said the ash drifted toward the villages of Puting Sapa and Sangayon in Juban town, and in the villages of Cogon, Gulang-Gulang, and Tinampo in Irosin town.

“This is just a minor explosion, which coincided with Labor Day celebration. We’re closely monitoring the activity if it will escalate in the coming days,” Laguerta added.

Alert Level 0 status currently prevails over Bulusan volcano. However, 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 ejecta from any sudden phreatic eruption can be hazardous to aircraft.

Furthermore, people living within valleys and along river/stream channels should be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall. 

PHIVOLCS is closely monitoring volcano’s activity and any new development will be relayed to all concerned.

The last time this volcano appeared in GVP's weekly volcanic report was during the week of July 9 – 15, 2014:

On July 13, PHIVLOCS reported that several days of elevated seismicity at Bulusan continued. During the previous 24 hours, 13 volcanic earthquakes were recorded by the local network. GPS and leveling surveys determined that the volcano was slightly inflated. 

Alert Level 0 and the 4-km restricted zone, the Permanent Danger Zone (PDZ), were maintained due to the possibility of sudden and hazardous steam-driven or phreatic eruptions.

Events that marked the start of its last eruptive phase 

On November 6, 2010, ​PHIVOLCS reported an explosion-type earthquake at Bulusan coincident with a steam-and-ash plume that rose 600 m above the crater at 00:11 UTC (08:11 local time). Trace amounts of ashfall were reported in multiple areas 6 – 10 km NW.

The Alert Level was raised from 0 to 1 (out of 5), and PHIVOLCS reminded the public not to enter the permanent danger zone, defined as a 4-km radius around the volcano. White steam plumes were observed rising 200 m above the crater before 06:00 UTC, when cloud cover prevented observations. 

On November 7, 2010, PHIVOLCS noted that seismic activity had increased during the previous 24 hours. A phreatic explosion on November 8 was produced a brownish-to-light-gray plume that rose 700 m above the crater.

Several neighborhoods to the NW, W, and WSW reported ashfall. Steam rose from the crater after the explosion. On November 9 two consecutive ash explosions, accompanied by rumbling sounds, produced ash plumes that rose as high as 1 km above the crater and drifted SW. Ashfall up to 2 mm thick was reported in areas to the SW and WNW.

On April 24, 2012, PHIVOLCS reported that the Alert Level for Bulusan was lowered to 0 following a decline in activity after a phreatic eruption on May 13, 2011. The frequency of earthquakes decreased to baseline levels of 0 – 2 per day, measurements indicated deflation since late November 2011, and steaming activity from the crater and known thermal vents had been frequently weak compared to more moderate steam emissions during periods of unrest.

Entry into the permanent danger zone, defined by a 4-km radius around the volcano, remained prohibited.

Geologic summary

Luzon's southernmost volcano, Bulusan, was constructed along the rim of the 11-km-diameter 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 Bulusan volcano is unvegetated and contains a 300-m-wide, 50-m-deep 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 eruption on May 1, 2015. Credit: EPA

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