Monday, September 23, 2019

Phivolcs forecasts more phreatic eruptions in Mt. Kanlaon

MANILA – The Philippine Institute of Volcanology and Seismology (Phivolcs) is expecting more onslaught of dangerous phreatic eruptions in Negros Oriental province's restive Mt. Kanlaon.

"The earthquakes in Mt. Kanlaon and this volcano's continuing tremor indicate such eruptions are still possible there in forthcoming days," said Phivolcs volcanologist Paul Alanis.

He reminded the public to steer clear of Mt. Kanlaon's four-kilometer permanent danger zone (PDZ), warning phreatic eruptions cause ash fall and can even trigger there deadly flows of pyroclastic materials as hot as 600°C to 800°C and moving down "very fast like storm surges."

Phreatic eruptions also occur without warning, Alanis said.

"There's no precursor for such eruptions so these are difficult to predict," he added.

According to experts, phreatic eruptions are steam-driven explosions that occur when water beneath the ground or on the surface is heated by magma, lava, hot rocks or new volcanic deposits.

Alanis noted such eruptions are among Mt. Kanlaon's usual manifestations when this volcano is in a state of unrest.

"Mt. Kanlaon has been registering phreatic eruptions since November last year," he said.

Data from Phivolcs also show occurrence of such eruptions there in 1985, 1992 and 1993.

In its 8 a.m. bulletin released on Thursday (March 31), Phivolcs reported recording in the past 24 hours a total of four volcanic earthquakes in Mt. Kanlaon.
"Those earthquakes were of short duration only," said Alanis.

Phivolcs also reported recording a long-duration volcanic tremor that commenced on Wednesday (March 30) at 1:30 a.m.

"There's been constant shaking in Mt. Kanlaon since then -- this tremor still persisted as of 8 a.m. Thursday," Alanis said.

The shaking indicates gas is rising inside the volcano's vent, he noted.

He said Mt. Kanlaon spewed volcanic materials during its minor eruption on March 29 this year, clearing the volcano's vent so gas inside is able to rise.

"Shaking there commenced shortly after such minor eruption," he said.

Phivolcs hasn't yet monitored rising magma inside Mt. Kanlaon, however, Alanis clarified.

"We're not yet expecting a magma-spewing eruption there," he said.

Phivolcs said Mt. Kanlaon is still under alert level 1, being in a "low" level of volcanic unrest.

Aside from discouraging entry in the volcano's PDZ, Phivolcs cautioned about flying near the summit there.

"Airborne ash from sudden eruption can be hazardous to aircraft," Phivolcs said.

Phivolcs reported monitoring in Mt. Kanlaon, during the past 24 hours, a 700-meter high steam and ash plume that drifted south-southwestwards.

"In consequence, traces of light ash intermittently fell on Barangay Sag-ang in La Castellana, Barangay Ara-al and Barangay Yubo in La Carlota City and Barangay Ilijan in Bago City, Negros Occidental," Phivolcs said.

Data as of March 14 this year indicated slight inflation of Mt. Kanlaon's edifice since December 2015, Phivolcs added. (PNA)

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