A minor phreatic eruption occurred in Taal Volcano last Thursday night, as it remains under Alert Level 1.

The Philippine Institute of Volcanology and Seismology reported that the eruption lasted for four minutes, from 9:18 p.m. to 9:22 p.m., producing a 1.5-kilometer-tall volcanic plume.

Phivolcs Director Teresito Bacolcol said in a radio interview that phreatic eruptions can occur unmonitored as long as “the ingredients” are there, which can suddenly trigger steam-driven explosions without warning.

“Phreatic eruptions can occur without warning, like what happened last night. As long as the ingredients are there — such as water and hot volcanic materials — it can happen anytime without warning,” Bacolcol said.

There were also no reports of ashfall in nearby barangays and towns, suggesting that the released ash settled within the volcano island.

The last recorded phreatic eruption of the Batangas-based volcano happened on 16 February, which generated a 2.1-kilometer-tall moderate volcanic plume emission.

Despite the latest volcanic activity, Bacolcol said that the occurrences of phreatic eruptions are becoming normal in Taal Volcano.

“This is not unusual for Taal Volcano, but what we are seeing is the occurrences of these events are becoming fewer and fewer,” the Phivolcs director added, noting that last year, phreatic eruptions were occurring on a monthly basis.

Based on the latest 24-hour monitoring by the state seismologists, Taal Volcano emitted 3,057 tonnes of sulfur dioxide on Thursday, slightly higher than the 2,719 tonnes emitted on Wednesday, 28 May.

There is also long-term deflation observed in the volcano and short-term inflation on the southeastern flank of the volcano island.