Taal Volcano generated a “short-lived” and dark phreatomagmatic plume that reach up to one kilometer high on Thursday afternoon, July 1.
This led the Philippine Institute of Volcanology and Seismology (Phivolcs) to raise the alert status over the volcano to Alert Level 3 or “magmatic unrest” from Alert level 2 or “increased unrest.”
But what is a phreatomagmatic eruption and what causes this volcanic activity?
Phivolcs said that phreatomagmatic eruption occurs when new magma interacts with water.
“Ang magma at ang tubig na siyang nasa lawa ng main crater ay nagkaroon ng contact (The magma and the water that is in the lake of the main crater came into contact),” said Ma. Antonia V. Bornas, chief of Phivolcs’ Volcano Monitoring and Eruption Prediction Division.
“Kaya ang tubig ay bigla siyang nako-convert sa gas na in the form of water vapor. At yung conversion na ito ay sobrang bilis na ito ay nakakapaglikha ng shockwave o compression wave (So water is suddenly converted into gas in the form of water vapor. And this conversion is so fast that it can create a shockwave or compression wave),” she added.
This compression wave pulverizes the magma, Bornas said.
The Phivolcs official noted that a phreatomagmatic eruption is different from a phreatic eruption which is driven by the heat from magma interacting with water.
In a phreatic eruption, there is no interaction between magma and the water but only the heat from the magma which results to steam emissions.
“Ang phreatic ay steam-driven pero ang phreatomagmatic ay meron nang kasamang magma (The phreatic is steam-driven but the phreatomagmatic already involves magma),” Bornas explained.
Phivolcs said the phreatomagmatic eruption only lasted for around five minutes.
More dangerous
“Definitely mas delikado ang phreatomagmatic eruption dahil nandyan na yung interaction ng magma sa tubig (Phreatomagmatic eruption is definitely more dangerous because the interaction of magma with water is already there),” Bornas said.
“Kung ang magma ay dire-diretsyong nilalabas ay maaring tuloy-tuloy ‘yung phreatomagmatic eruption (If magma is released constantly, the phreatomagmatic eruption will continue),” she added.
Bornas said the volcanic hazards of a phreatomagmatic eruption include base surges or pyroclastic density currents and “volcanic tsunamis.” “Dahil kapag ang base surge ay pumasok na ng lawa, ito ay nakakapag-displace ng tubig (Because when the base surge enters the lake, it displaces water),” she said.
“At sa atin pong mga historical records ng mga dating pagputok, tuwing merong base surge ay nagkakaroon ng volcanic tsunami (And based on our historical records of previous eruptions, every time there is a base surge, there is a volcanic tsunami),” she added.
Bornas noted that the volcanic ash created by a phreatomagmatic eruption is muddy and fine, similar to ash fall experienced during the January 2020 eruption.
Since a phreatomagmatic eruption involves magma, she said that there is a possibility that minor fissuring will occur.