Volcanic quakes, sulfur dioxide emissions remain a week after Taal's initial eruption

Alert Level 4 is still raised over the restive Taal Volcano as indicators still suggest that a possible hazardous eruption may occur within hours to days, according to PHIVOLCS on Monday morning.

Since 5 a.m. on Sunday to 6 a.m. on Monday, 23 volcanic earthquakes were plotted through the Philippine Seismic Network, with registered magnitudes ranging from 1.2 to 3.8, PHIVOLCS said.

This brings to 714 the total number of volcanic earthquakes recorded since Taal Volcano's initial eruption on January 12.

On the other hand, the Taal Volcano Network — which detects even small earthquakes — recorded a total of 673 volcanic earthquakes in the past 24 hours. PHIVOLCS said 12 of these were low-frequency ones.

According to the United States Geological Survey, low-frequency earthquakes are "caused by cracks resonating as magma and gases move toward the surface."

"They are often seen prior to volcanic eruptions, but their occurrence is also part of the normal background seismicity at some volcanoes and their occurrence does not necessarily indicate that an eruption is imminent," the USGS said.

PHIVOLCS Director Renato Solidum said the occurrence of volcanic earthquakes serves as the volcanologists' main parameter in determining the appropriate Alert Levels for active volcanoes.

He previously stressed that Taal Volcano's activity can only be deemed slowing down when "earthquakes have diminished and the trend is continuing."

Meanwhile, the latest measurement of Taal Vocano's sulfur dioxide emission remains at  4,353 tons/day — same as indicated on PHIVOLCS' bulletin at 6 p.m. on Sunday.

Sulfur dioxide emission indicates the upward movement of magma to the surface, according to PHIVOLCS.

In the past 24 hours, the activity in the main crater was characterized by "steady steam emission and infrequent weak explosions."

White to dirty white ash plumes, 500 to 1,000 meters tall, were generated and ashes were dispersed to areas southwest of the main crater.

Citing PAGASA's wind forecast, PHIVOLCS said that volcanic ashes will be drifted to the south and southwest of the main crater if the eruption plume remains to be lower than three kilometers.

Parts of Cavite province will be affected by ash if the eruption plume rises between three to five kilometers.

Meanwhile, in case of a major eruption and the ash column exceeds five kilometers, ashfall may be experienced over Metro Manila, Laguna, and some parts of Rizal and northern Quezon.

PHIVOLCS said that the Taal Volcano Island, the areas within the 14-kilometer radius from the main crater, and areas along the Pansipit River Valley must be evacuated due to hazards such as base surge and volcanic tsunami.

Other communities around the volcano must also prepare against the effects of heavy and prolonged ashfall.

The airspace around Taal Volcano remains unsafe to aircraft due to airborne ash and ballistic fragments from the eruption column. —KBK, GMA News