Volcanoes are Like People and Taal Eruptions Follow This Pattern

Volcanoes are like people, while they are hard to predict, their behaviors follow a certain pattern, much like Taal, which jolted the country last Thursday, with a water-meets-magma eruption 18 months after its last major eruption, according to a geologist.

Taal is known to take a long slumber (taking a couple of years, or even decades in length) before waking up in a strong eruption that will then be followed by succeeding eruptions year after year, its intensity receding each time, said Mahar Lagmay, who heads the UP Resilience Institute.

The phreatomagmatic eruption on July 1 was nowhere near as devastating as the one on Jan. 12, 2020, one that cloaked large swaths of Luzon with volcanic ash and halted air travel before the pandemic.

Taal erupted twice with Volcanic Intensity Index or VEI 4, the fifth highest in an eight-step scale -- in 1911 and 1965, that's nearly half a century apart. After 1965, VEI 1 and 2 eruptions were recorded in 1967, 1968, 1969 and 1970, Lagmay said.

Seen a pattern yet?

After 1970, Taal Volcano went into another slumber, erupting again in 1976, then followed by two eruptions (1976 and 1977). Taal did not erupt again until January 2020. 

"So kung titignan ko yung ganitong historical eruptions ng Taal, yung malakas yung kapag nagpahinga siya tapos pumutok ulit. Yung malakas ay yung nauna.. Tapos 'pag pumutok ulit, mas mahina kesa dun sa nauna," he said, noting this is the behavior one can expect, if history were the basis. 

Lagmay said this also means Taal's recent behaviors are "normal", 

"Nangyari na ito dati, at normal para sa Taal yan na nagigising ulit tapos kada taon ay pumuputok hanggang siguro ay mawalan na talaga ng laman na magma ng ilalim ng bulkan," he said.

What is a phreatomagmatic eruption?

Phivolcs on Thursday placed Taal Volcano under Alert Level 3, indicating magmatic unrest that is one notch higher from Level 2 (increasing unrest), after it belched a kilometer-high plume, an explosion dubbed as phreatomagmatic.

This type of eruption results from the interaction between water (phreato) from the lake and the extremely hot semi-liquid rock inside the volcano called magma (magmatic), said professor Mahar Lagmay, executive director of the University of the Philippines Resilience Institute.

"Ibig sabihin non, yung tubig doon sa lawa, doon sa isla ay nagcontact o tumama, nagdikit 'dun sa magma. At dahil mainit yung magma at mas malamig yung tubig ay nagkaroon ng explosive eruption," he said.

At Taal Volcano's main crater on Thursday, the first phreatomagmatic eruption occurred at 3:16 p.m. It lasted for five minutes, generating the one-kilometer-high dark plume. 

Four short phreatomagmatic explosions followed, lasting up to two minutes each. It resulted to short jetted plumes which rose 200 meters above the main crater lake.

Phreatic, Phreatomagmatic, Magmatic—What's the Difference?

Taal Volcano erupted in January of 2020, triggerring the largest displacement by a geophysical hazard in the entire world for that year. The eruption was phreatic, which refers to how water beneath the ground or on the surface is heated by volcanic activity, causing it to boil and lead to an eruption.

"Habang hindi pa nakakaangat nang mabuti yung magma at hindi pa nagdidikit dun sa tubig, naiinitan na yung tubig sa lawa. Yung ang phreatic eruption, ibig sabihin tubig lang," Lagmay said.

When the eruption is caused by magma mixing with water from the lake or any type of water, then it's phreatomagmatic, he said.

Once it's purely magma coming out of the volcano--referred to by then as "lava"--the eruption is magmatic.