Volatile condition of Mt. Bulusan baffles Phivolcs

October 12, 2011 9:57 pm 

By Danny O. Calleja

SORSOGON CITY, Oct. 12 -– Volcanology experts are studying deeper the condition of Mt. Bulusan as local watchdogs are baffled by its unusual attitude that has become extremely unpredictable.

Crispulo Diolata, resident volcanologist of the Philippine Institute of Volcanology and Seismology (Phivolcs) based at the Mt. Bulusan Observatory in Barangay Cabid-an here, said the Department of Science and Technology (DOST) is fielding a team of experts to conduct more in-depth studies to determine “what really this active volcano wants to prove”.

For the meantime, Diolata said they are maintaining alert level number one over the volcano based on the steaming activities being exhibited by at least two of its seven craters located at its northwestern shoulder fronting this city and the municipalities of Casiguran, Juban and Magallanes. Low and high frequency volcanic tremors are also being constantly monitored.

The alert level means that the volcano remains restive and may erupt anytime although major explosions are not likely to take place given the “non-explosive” character of Mt. Bulusan based on its past eruptions, the first one in 1885, he said.

Nonetheless, Diolata said, under alert level one, human activities are being forbidden within the four-kilometer permanent danger zone (PDZ) as sudden intense activities dangerous to life may occur.

Mt. Bulusan, which has an elevation of 5,135 feet above sea level, last erupted in May 13 this year. Residents near its foot described the eruption as thunderous rumbling sounds accompanied by a massive discharge of volcanic ash that reached as high as five kilometers.

Heavily affected by the ash fall were 12 barangays in the municipalities of Irosin, Juban and Casiguran, all located within the northwest quadrant of the volcano where 10 high frequency volcanic quakes were also felt before the explosion, Phivolcs records show.

Diolata said it was a phreatic type of eruption, the 12th of the same type since the volcano was declared abnormal following observations of severe volcanic activities over five years ago.

The Phivolcs declared alert level one on March 19, 2006 after it recorded increased seismic unrest that was followed by an explosion in June 8 of the same year. This prompted volcanologists to raise alert level two which means the volcano has erupted although major eruptions of vulcanian or any other explosive types were ruled out to be imminent.

Another eruption took place on April 8, 2007 and on the morning of July 31, a loud explosion described by local residents as bomb-like rocked the volcano. Six months later, on October 4, two episodes of ash explosions followed and after that, series of ash emissions accompanied by mild explosions were recorded until November that year.

After months of less significant activities, the volcano suddenly erupted last February and sent a plume of ash two kilometers high. Volcanologists said that eruption was triggered by the reaction of hot magma with water brought about by a heavy downpour. A lull again occurred until May 13.

Most of the 12 eruptions that took place within the span of more than five years came in near surprise as signs could hardly be monitored or would appear very close to the major activities giving the Phivolcs very limited time to issue warnings. Each eruption occurred after lulls in significant activities lasting within an average of four months.

Diolata said the present condition of Mt. Bulusan is considered the longest running period of abnormality in its recorded history or that of any other active volcanoes in the country and this is the matter that makes it very unpredictable this time.

Bulusan is generally known for its sudden steam-driven or phreatic explosions and considered as the fourth most active volcano in the Philippines after Mayon, Taal, and Kanlaon.

Mt. Mayon in Albay, its neighbor separated by only about 70 kilometers does not have the same attitude as well as Taal or Kanlaon and even Mt. Pinatubo as all of these, when calm really rest and when restive, really act up intensely, he explained.

The experts coming to conduct the in-depth study would perhaps find out how Mt. Bulusan gathers pressure to suddenly stage short-duration eruptions within the average of only four months lull or why it cannot arrive at a normal condition within the span of more than five years unlike its past that took it decades to regain restiveness following eruptions, Diolata said. (PNA)

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