Increased possibility for sudden, deadly eruptions at Mt. Bulusan


Scientists monitoring Mount Bulusan, Philippines warn there is an increased possibility for sudden and potentially deadly phreatic eruption at the volcano.

Volcanologist Paul Alanis of the state-run PHIVOLCS, said the changes in Bulusan's sulfur dioxide (SO2) emission level and the inflation of its edifice are among the developments that raise such a possibility.

“At times, we even monitor increases in the number of Bulusan’s volcanic earthquakes,” Alanis said for the Manila Times. “Phreatic eruptions can also occur anywhere in that volcano,” he said.

Winchelle Sevilla, another PHIVOLCS volcanologist, said earlier there is still no means of giving advanced warnings about looming phreatic eruptions, steam-driven blasts that occur when water beneath the ground or on the surface transforms into steam after coming into contact with hot volcanic materials. Research into the matter is still in progress, Sevilla noted.

Between 00:00 UTC on December 5 and 6, seismic monitoring network detected 3 volcanic earthquakes under the volcano, but steaming activity could not be observed due to thick clouds covering the summit.

SO2 emission was measured at an average of 232 tons/day on November 28, 2016. Precise leveling data obtained on October 17 – 23, 2016 indicated inflationary changes of the edifice relative to August 2016. Inflation was also recorded by continuous GPS measurements as of December 2, 2016, indicating pressurization beneath the volcano edifice.

The public is reminded that Alert Level 1 (abnormal) remains in effect over Bulusan Volcano, entry into the 4-kilometer radius Permanent Danger Zone (PDZ) is strictly prohibited and that vigilance in the Extended Danger Zone must be exercised due to the increased possibilities of sudden and hazardous 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 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.

A sudden phreatic eruption at the volcano on May 7, 2013 killed 5 people who were within the danger zone.

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 1 565-m-high (5 134.5  feet) Bulusan volcano is unvegetated and contains a 300-m-wide (984.2 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: Mount Bulusan, Philippines. Credit: Chris Newhall (U.S. Geological Survey).

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