Phivolcs’ monitoring system picked up 18 high-frequency and four low-frequency "short duration harmonic tremors" at the volcano in the past 24 hours.
Jaime Sincioco, officer-in-charge of the Phivolcs’ Volcano Monitoring and Eruption Prediction Division, said this indicated that magma was rising to the volcano’s summit.
"We advise the residents there to be ready, especially those in the southeast sector of the volcano," he told The STAR, referring to Legazpi City and the towns of Daraga and Sto. Domingo.
The Albay provincial disaster coordinating council (PDCC), meanwhile, has ordered 1,484 families or roughly 7,436 people living inside the six-kilometer permanent danger zone to prepare for evacuation after lava fragments were observed rolling off from the volcano’s summit Friday night.
Sincioco said the public should stay away from the six-kilometer permanent danger zone because this area is at high risk for volcanic flows.
The bright orange incandescent lava fragments, as they rolled from the summit crater, formed an apron of pyroclastic debris onto the middle slopes on the southeast flank of the volcano at the Bonga Gully, which pertains to the eroded portion of the volcano’s slope which could serve as channel for lava in case of an eruption.
Phivolcs had raised the five-step alert level for Mt. Mayon from 1 to 3 the other night after it emitted the lava fragments. This level means the volcano is in a stage of quiet and mild eruption.
The episode was recorded by small and imperceptible earthquakes associated with lava accumulation and falling volcanic debris, suggesting that magma is actively intruding into the cone and subsequently being pushed out as lava.
Steam emission was relatively higher than usual and sulfur dioxide emission rates increased slightly from 1,037 tons per day to 1,251 tons per day Friday.
"This is an old lava fragment from the volcano’s eruption in 2001," Phivolcs resident volcanologist Ed Laguerta said, referring to the detached lava fragments.
He added that the "slow lava trickle is continuing even though it is not perceptible during daytime." Lava or hot molten rock hardens once exposed to air, but Laguerta pointed out that "there is no lava flow yet."
"When it is already fresh lava flowing out of the crater, only then can we call it a lava flow that is usually characterized by continuous rolling of incandescent materials down the volcano’s slopes," he said.
Laguerta said the recent phreatic explosion ,which showered ash on residents of Barangay Bacolod in Malilipot town, uncorked the deposit on the crater from the volcano’s eruption five years ago.
During an emergency meeting, Albay Gov. Fernando Gonzales ordered the PDCC to closely watch the restive volcano and make complete preparations for rapid evacuation in case the volcano suddenly erupts.
Gonzales also told the different city and municipal disaster coordinating councils to prepare for evacuation.
There are about 7,436 residents in 10 barangays — Buhian, Magapo and Buang in Tabaco City; Calbayog in Malilipot, Miisi in Daraga, Anoling, Upper Quirangay, Upper Cabangan and Sua in Camalig and Barangay Baligang in Ligao City — who are still staying inside the danger zone.
Gonzales said the danger zone will be extended from six kilometers to eight kilometers should the situation worsen. This will result in the evacuation of 3,907 families or 21,666 people.
In a worst-case scenario, the danger zone will be extended to 10 kilometers and 13,870 families or 74,069 people will be evacuated.
Legazpi City Mayor Noel Rosal said the city has also called an emergency meeting to map out the evacuation of residents of Barangays Matanag, Mabinit, Boyuan and Boga which are located within eight kilometers from the volcano’s crater.
"I have already ordered the deployment of two trucks for the four barangays affected to pick up the evacuees in the designated areas so it will be easy to move them," Rosal said, adding that evacuation centers have already been identified and readied for the evacuees.
He added that there are 14 barangays which are affected by the volcano’s unrest.
"We are closely watching the volcano so we will be prepared to react, just in case it suddenly erupts, to achieve our goal of zero casualty," Cedric Daep, head of the provincial disaster management office, said.
Daep explained that the most important thing to do at this point is to ensure complete preparation for the evacuation procedure.
"We have successfully done this during the eruption in 2001," he said.
Authorities managed the needs of some 60,000 evacuees during the critical first three months. Although there was no casualty during Mayon’s eruption in 2001, damage to crops was placed at P284 million and P242,050 for livestock.
In a related development, Environment Secretary Angelo Reyes has directed regional directors and officials of the Mines and Geosciences Bureau to monitor disaster-prone areas and implement precautionary measures to safeguard lives and property and minimize possible damage caused by typhoons, floods and other natural calamities.
In an urgent directive, Reyes instructed Department of Environment and Natural Resources (DENR) officials to evaluate the structural stability of all critical mine facilities, specifically tailing ponds and waste dumps, for any possible damage or impending danger and report them to the proper authority for appropriate action.
Reyes issued the directive as he expressed concern that strong winds and floods could destroy mine facilities and cause mine spills that would contaminate the surrounding environment, especially coastlines and seas.
He said flash floods arising from forest denudation could also trigger landslides, posing a menace to towns and villages and other human habitat.
Reyes also ordered the DENR regional officers and bureau officials identify and determine the magnitude of the damage caused by geo-hazards such as landslides, floods in disaster-prone.
He also told them to immediately conduct geo-hazard mapping in the courts’ areas of jurisdiction to avert further damage to lives and property.
Reyes said DENR officials should stop all illegal quarry operations as they may adversely affect the geological stability of the ground during the rainy season.
The DENR has been conducting year-round surveillance and monitoring of the state of natural resources, including forests, seas and lands, as well as mine facilities, not just to protect the environment but also to protect the people against natural calamities.
"We must do everything not just to preserve our natural resources, but also to protect the life and health of our people, against environmental disasters and other calamities," Reyes said in his directive. — With Celso Amo, Cet Dematera and Perseus Echeminada