SORSOGON CITY, June 20 (PNA) -- The Philippine Institute of Volcanology and Seismology (Phivolcs) is closely monitoring the restive Mt. Bulusan, which has recently exploded twice in a span of one week.
Mt. Bulusan erupted at about 1:03 p.m. Sunday.
Last week, the volcano exploded at 11:35 a.m., emitting ash column of about 6,562 feet or 2,000 kilometers high.
Ed Laguerta, Phivolcs resident volcanologist in Bicol, said Mt. Bulusan's Sunday explosion was steam-driven, spewing 300-meter ash column above the crater.
The event lasted for seven minutes.
“The explosion is a bit weak, not so energetic and lacked pressure. The steam-driven explosion was just 300 meters above the crater,” he said.
The Phivolcs official said the recent explosion is also phreatic or steam-driven in nature.
Last week, the explosion lasted for about five minutes, based on the seismic record, which a high-column ash that drifted towards the northwest portion of the volcano.
Mt. Bulusan, some 70 kilometers southeast of Mayon volcano and approximately 250 km southeast of Manila, suddenly ejected a grayish cauliflower-shaped steam ash after a week.
Bulusan's last magmatic eruption took place more than 40 years ago.
The volcano is one of the active volcanoes in the country with an elevation of 1,547 meters above the sea level and is said to have been formed almost 40,000 years ago.
The mountain has four hot springs and four craters, just like a caldera, which was formed due to eruptions.
One of these craters is Crater No. 1, which is called Blackbird Lake and is 20 meters in diameter and 15 meters deep.
The oval Crater No. 2 is 60 meters by 30 meters and 15 meters deep; crater No. 3 is about 90 meters in diameter and 20 meters deep, while Crater No. 4, which is near the northeastern rim, opened during the 1981 eruption.
There is also a 100-meter fissure, measuring 5 to 8 meters wide, below Crater No. 4.
Aside from the four calderas formed due to eruption, the volcano has several hot springs surrounding it -- San Benon Springs, Mapaso Springs, San Vicente Springs and Masacrot Springs.
Its adjacent volcanic edifices are Mt. Homahan, Mt. Binitacan, Mt. Batuan, Mt. Calungalan, Mt. Calaunan, Mt. Tabon-Tabon, Mt. Juban and Mt. Jormajan.
The volcano has erupted 15 times.
The last major eruption of Mt. Bulusan took place in the 17th century.
Bulusan volcano is classified as stratavolcano (composite volcano) and one of the most active volcanoes in the country with a base diameter of 15 kilometers.
The volcano’s seismic monitoring network did not record any volcanic earthquake during the past 24-hour observation period when the explosion took place.
Steaming activity could not be observed due to rain clouds covering the summit.
Precise leveling survey results from April 27 to May 5, 2016 indicated slight deflationary changes of the edifice relative to the February eruption.
However, the ground deformation measurements from continuous GPS data as of June 2 indicated a slight inflation of the edifice since May.
Alert Level 1 remains in effect over Mt. Bulusan, indicating that hydrothermal processes are underway beneath the volcano that may lead to more steam-driven eruptions.
The local government units near he volcano and the public are reminded that entry into the four-kilometer radius Permanent Danger Zone 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, the Phivolcs advised.
Similarly, residents living along river channels -- especially on the southwest and northwest sector of the edifice, should be vigilant against sediment-laden stream flows and lahar in the event of heavy and prolonged rainfall.(PNA) JMC/FGS/RBB/CBD