MANILA, Philippines – In response to criticism from a vice mayor, an official from the Philippine Institute of Volcanology and Seismology (Phivolcs) said they are "doing their best" to provide information on the restive Taal Volcano.
Taal remains under Alert Level 4 as of Tuesday, January 21, which means a hazardous eruption remains possible "within hours to days." High-risk areas surrounding the volcano, including Talisay, were evacuated. (READ: Año orders stop to 'visiting hours' to Taal Volcano danger zone)
"We can understand that he (Natanauan) is under so much stress.... We would like to respect 'yung feelings ni vice mayor (the vice mayor's feelings), but at the same time, we are firm in our science that we are doing our best," said Maria Antonia Bornas, chief of the Phivolcs Volcano Monitoring and Eruption Prediction Division, in a press briefing on Tuesday morning.
There are at least 38,906 families or 148,514 persons in evacuation centers, according to the National Disaster Risk Reduction and Management Council. (WATCH: Taal Volcano eruption hits small vendors hard)
"We understand their plight, so we are working doubly hard so we can give them the best information. We will be the first one to say if it's safe to go back because we have them (evacuees) in mind all the time," Bornas said.
Fluctuating gas, rising magma
In its 8 am bulletin on Tuesday, Phivolcs said "weak steam emission" persisted from Taal's main crater in the past 24 hours. This "generated ash plumes 500 to 600 meters tall and dispersed ash southwest of the main crater."
The sulfur dioxide (SO2) emission, meanwhile, was measured at an average of 344 tons per day, which is relatively low compared to over 4,000 tons in previous measurements. SO2 is a major gas component of magma.
Bornas explained that SO2 levels have been fluctuating, so far.
"The fluctuation actually reflects [the] interaction between [the] groundwater and the magma.... This could be one of the reasons, but definitely it means that magma is at the shallow level of the volcano," she said.
As for volcanic earthquakes, Bornas said the numbers are going down, but "the eruptible magma...is already in place."
"The trend of the seismicity is lowering...but the type of earthquake signifies that there is magma intrusion," she explained.
"We have ground deformation signifying that the volcano is still inflated and is still inflating," she added, referring to another indication that magma is rising.
Phivolcs is using two networks to monitor volcanic earthquakes – the Philippine Seismic Network which covers the whole country, and the Taal Volcano Network, which includes small earthquakes undetected by the former.
The Philippine Seismic Network has plotted 718 volcanic earthquakes since 1 pm of January 12. Of these, 176 were magnitudes 1.2 to 4.1 and were felt at Intensities I to V.
From 5 am on Monday, January 20, until 5 am on Tuesday – or a 24-hour period – there were 5 volcanic earthquakes plotted at magnitudes 1.6 to 2.5, with no felt event.
The Taal Volcano Network, meanwhile, recorded 448 volcanic earthquakes, including 17 low-frequency earthquakes, in the past 24 hours.
"Such intense seismic activity likely signifies continuous magmatic intrusion beneath the Taal edifice, which may lead to further eruptive activity," Phivolcs said in its bulletin.
Asked when Alert Level 4 could be lowered to Alert Level 3, Bornas said the typical observation period would be two weeks. During that period, there should be an "overall trend" that all parameters – not just some – have gone down.
"Every day, ine-evaluate po natin 'yung mga monitoring data.... As long as may considerable na probability talaga [of a hazardous eruption], hindi namin puwede ibaba," Bornas said.
(Every day, we evaluate our monitoring data. As long as there's considerable probability [of a hazardous eruption], we can't lower the alert level.)
"We record earthquakes still, nakaka-record pa tayo ng mataas na SO2, the volcano is inflated...so meron pang tumutulak na magma sa taas.... May seeming paghina ng activity, but it doesn't mean that the danger is over," she added.
(We record earthquakes still, we still record high levels of SO2, the volcano is inflated, so magma continues to rise. There's seeming weakening of activity, but it doesn't mean that the danger is over.)
If a hazardous eruption occurs, Alert Level 5 – the highest – would be raised. This may or may not happen. (READ: TIMELINE: Taal Volcano eruptions since 1572)
Phivolcs stressed that there must be "total evacuation" of Taal Volcano Island as well as high-risk areas within a 14-kilometer radius from the main crater and "along the Pansipit River Valley where fissuring has been observed." (WATCH: Fishermen risk lives for catch around restive Taal Volcano)
Fissures or cracks had appeared in parts of Batangas province, particularly in the towns of Lemery, Agoncillo, Talisay, and San Nicolas, which are all high-risk areas. (READ: Duterte wants P30-B supplemental budget for Taal Volcano eruption)