MANILA (UPDATED) — Mayon volcano in Albay could unleash a "more vigorous" type of eruption, a volcanologist warned on Wednesday, as the number of evacuees topped 15,000.

"There is a possibility that it will turn violent or what we call a more vigorous type of eruption," said Paul Alanis, resident volcanologist of the Mayon Volcano Observatory.

• Mayon Volcano to stay on Alert Level 3 amid recent ‘effusive eruption’

In the last 24 hours, Alanis said Phivolcs recorded 309 rockfall events and 7 volcanic earthquakes at Mayon, which continued to ooze lava "very quietly."

The Albay volcano also emitted 149 tons of sulfur dioxide, which is "quite lower than the average of 500 tons per day."

Eruptions are energized by gas pressure mixed with magma or underground molten rocks, Alanis noted.

"Currently, the sulfur dioxide is quite low, which could mean 2 possibilities. One is that there's really not much gas in the magma, which is the reason why we have a very quiet type of eruption occurring. The second scenario, possibility is that the volcano is blocked right now and that pressure is building up," he told ANC's "Headstart."

"We have to check if the energy of the earthquake is high enough to signify an impending eruption. At the moment, the energy of the earthquake, not just the number, is quite low."

A de-escalation could take longer compared to an escalation because volcanologists need "to make sure that the parameters are really downgrading," Alanis noted.

"What we want to avoid when we de-escalate is what they call 'lull before the storm scenario,' where the volcano is just gearing for a bigger eruption, for example," he said.

• Albay local gov’t braces for Mayon Volcano alert level shift

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PROLONGED UNREST

State volcanologists have said that the Mayon Volcano could continue rumbling for months.

• Phivolcs: Mayon unrest may take months as thousands stay in evacuation centers

A total of 4,286 families or 15,241 people have so far been evacuated from the volcano's 6-kilometer danger zone, Eugene Escobar, research chief of the Albay Public Safety and Emergency Management Office.

"Base po doon sa mga nakaraang pag-evacuate sa Bulkang Mayon gano’n po talaga ‘yung average natin, 3 months po ‘yung pinaka-minimum at umabot po ng almost 5 months to 6 months ‘yung pinakamahaba," he told ABS-CBNs TeleRadyo.

(Based on the previous evacuations due to Mayon volcano, that's our average, 3 months is the minimum and the longest is almost 5 months to 6 months.)

Escobar said the national government and other organizations would help fund the needs of the evacuees in the next months.

The National Grid Corporation of the Philippines (NGCP), for its part, said there is no need to preemptively shut down any of its facilities in the province.

The agency's spokesperson, Atty. Cynthia Alabanza, said power supply also remains stable in the area as none of their transmission lines are located in danger zones.

"Iyong preemptive shutdown, hanggang maaari iniwasan na gawin ng NGCP," she said.

(As much as possible, we want to prevent preemptive shutdowns.)

Phivolcs Director Teresito Bacolcol earlier said that the Mayon Volcano is "following the template of the 2014 eruption, which was a quiet eruption, effusive eruption."

"Based on our previous experiences, this activity may persist for a few months," he added.

Five years ago, Mayon displaced tens of thousands of people after spewing millions of tons of ash, rocks, and lava.

• Mayon Volcano now in initial stages of eruption, but not yet hazardous: Phivolcs

Mayon lies in a region also hit by many of the roughly 20 typhoons or tropical storms to strike the Philippines each year.

The frequent weather disasters often kill people, ravage farms, and help to keep millions poor.

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— With a report from Agence France-Presse