BICOL ICONS | A tricycle loaded with abaca fiber traverses the national highway in Ligao City, Albay, amid a scenic backdrop provided by Mt. Mayon. The volcano, with its perfect cone visible during cloudless days, and abaca are among the most recognizable landmarks and products of the Bicol region. (File photo by MICHAEL B. JAUCIAN / Inquirer Southern Luzon)
LEGAZPI CITY, Albay, Philippines — The Philippine Institute of Volcanology and Seismology (Phivolcs) has lowered the alert status of Mayon Volcano from level 2 (increasing unrest) to level 1 (abnormal) Tuesday due to a “steady decline” in its activity since that start of the year.
According to Phivolcs, alert level 1 means that the volcano has a low level of unrest and the likelihood of an eruption has decreased. Mayon had its alert level lowered from 3 (increased tendency toward hazardous eruption) to 2 on Dec. 8, 2023.
But state volcanologists said this situation did not mean that the unrest had completely stopped.
The public, Phivolcs said, is still not permitted to enter the 6-kilometer permanent danger zone around the volcano.
Among the monitoring parameters cited by Phivolcs in lowering the alert status include volcanic earthquake activities, which declined to an average of two to three daily; lower sulfur dioxide gas emissions averaging at 1,148 tons per day; and weak to moderate degassing plumes observed on the summit crater.
While the long-term ground deformation data still showed that the edifice of the volcano was still inflated, the short-term data indicated deflation of the northern middle slopes, according to Phivolcs.
Gravity observation
“Ground deformation and microgravity anomalies are interpreted to be caused by crystallization of the resting magma beneath the volcano,” the Phivolcs bulletin said.
“The gravity is not constant throughout the world. On volcanoes, that force is especially affected once there is magma. It will either weaken or strengthen,” Paul Karson Alanis, resident volcanologist at Phivolcs’ Mayon Volcano Observatory in Albay, told Inquirer in a phone interview Wednesday.
According to Alanis, this can only happen when magma hardens and becomes heavier, and in turn, able to pull matter above the surface, making gravity stronger.
“We saw during gravity observations that it was strengthening [in] other areas of Mayon Volcano, particularly in the middle,” Phivolcs said.
READ: Phivolcs: Mayon Volcano alert level down from 2 to 1
“In the event of a renewed increase in any one or combination of the above monitoring parameters, the alert status may step up once again to alert level 2,” it added.
More time
The alert level may further be lowered when monitoring parameters improve.
“On the other hand, if there is a noticeable return to baseline levels of ground deformation and sustained low levels of other monitoring parameters, then the alert status may further step down,” Phivolcs said.
However, Alanis told the Inquirer that lowering the volcano’s alert level to zero (quiet or no alert) would take more time.
“If the lowering from [alert level] 3 to 2 would take two weeks of relatively improving parameters, and the 2 to 1 would take about a month of relatively lowering trend, the 1 to 0 [shift] would be a lot longer,” Alanis told Inquirer. “In general, it may take up to three months or more.” —WITH A REPORT FROM RUSSEL P. LORETO