MANILA – The Taal Volcano is still erupting but its activity has gone weaker than in previous days, according to the country's chief seismologist on Wednesday.
But how long the eruptions would last depends on the speed of the rise of magma.
Phivolcs executive director Renato Solidum said Wednesday they still record a lot of earthquakes at the Taal volcano and its general area, and many of these temblors have been felt.
"These can be interpreted as magma intruding from beneath the volcano causing fissures to move, causing earthquakes and also lifting off the ground. Hence, if these magma would continue to rise there can still be further activity related to the current situation," Solidum said on ANC's Headstart.
Solidum cannot exactly tell how long Taal's eruptions will be as he said the volcano has exhibited various styles of eruptions in the past, lasting from a few days to several months.
In 1911, Solidum said the eruption lasted for only 3 to 4 days. In 1965, it lasted for a month and in 1754, the eruption continued on for around 7 months.
"These would be dependent on the ascent of the magma, how fast it would move up or whether the magma would stop moving. As we try to analyze this we rely on 2 things: the earthquakes and deformation on the ground," he explained.
He said volcanoes have different styles and speeds of eruption and precursors. Taal’s behavior, he said, could go from having precursors and not erupting to having precursors and then erupting within several days to several weeks.
“When any volcano would erupt, it has to show signs of the activities escalating. However, that volcano did not accelerate its activity and in fact even half a day or a day before there were no significant earthquake events or even maybe 12 or 6 hours before, if you look at seismic record, there was no record,” he said.
The volcano’s activity accelerated in a span of around 6 hours, prompting Phivolcs to immediately raise its alert level.
In comparison, Mount Pinatubo, which erupted in 1991, recorded activity that signaled its destructive eruption on June 15 of that year.
There were quakes that March, phreatic eruptions a month later, steam emissions in May, and then a small ash emission prior to its major eruption.
“You can see clearly the big difference in the timing and sequence of the events versus what happened last Sunday,” he said.
Solidum said Phivolcs, the local government, and disaster management teams have been preparing for the possibility of Taal's hazardous eruption.
"The explosive eruption scenario, and this is the scenario we have been preparing for together with the Batangas Provincial Risk Reduction [and] Management Office, is still possible simply because of the fact that we still have a lot of earthquakes and ground deformation within the area," he said.
Sunday's activity initially started as a phreatic eruption. When the crater was depressurized, he said magma suddenly rose and produced more eruptions turning it into a phreatomagmatic eruption.
"The highest eruption column that we saw was around 10 to 15 kilometers last Sunday, late afternoon and evening, and for many volcanoes that would really be considered hazardous," he said.
Lava fountaining was observed by early Monday morning, resulting in a magmatic eruption.
While it was hazardous, Phivolcs said they have not yet seen pyroclastic density currents or the flow of rocks and ash down the slope of the volcano or even horizontally-moving out of the crater towards the lake.
"That is what we call a hazardous volcanic eruption when Taal would exhibit not only tall eruption columns, but horizontally-moving clouds more than 60 kilometers per hour that even reach the mainland and cross above the water," he said.
Thousands of residents were evacuated after the volcano spewed ash and destroyed homes, plants, and animals on Sunday.
"If the volcano would rapidly increase in activity then there will be additional evacuation and that has happened. Unfortunately the volcano changed its condition very rapidly," he said.