Day 4 IN PHOTOS: Large Cracks After 466 Quakes; Faster Mass Evacuation Pushed Over ‘Base Surge’
A base surge is a horizontal movement of clouds of ash, rocks and gases at very high speed that can cross water and reach the mainland of Batangas, and kill people as well as destroy properties.
A total of 466 volcanic quakes were recorded since 1 p.m. on Sunday as Taal Volcano exploded, according to the Philippine Institute of Volcanology and Seismology (Phivolcs).
Of these, 156 were felt with intensities ranging from 1 to 5.
Between 5 a.m. on Tuesday and 5 a.m. yesterday, 159 temblors were detected, 28 of which were felt with intensities ranging from 1 to 3.
The occurrence of volcanic earthquakes and the type of tremors are the parameters used by Phivolcs in raising or lowering the alert levels over active volcanoes in the Philippines.
Phivolcs advised authorities yesterday to speed up the mass evacuation of people from the danger zone around Taal Volcano, which continued to convulse and spew lava, causing more hazardous ground cracks in several towns in Batangas.
New fissures or cracks were observed in Barangays Mataas na Bayan in Lemery and Bilibinwang in Agoncillo town yesterday.
On Tuesday, cracks were documented in Sinisian, Mahabang Dahilig, Dayapan, Palanas, Sangalang, Poblacion and Mataas na Bayan in Lemery; Pansipit and Bilibinwang in Agoncillo; Poblacion 1, Poblacion 2, Poblacion 3, Poblacion 5 in Talisay and Poblacion in San Nicolas. A fissure transected the road connecting Agoncillo to Laurel, Batangas.
The road connecting Agoncillo to Laurel, Batangas also had a crack, according to Phivolcs.
Phivolcs also said threats from pyroclastic density currents – fast-moving current of hot gas and volcanic rocks – as well as volcanic tsunami and a base surge still loom in areas within the 14-kilometer radius from the main crater of Taal Volcano, the second most active volcano in the country and a popular tourist attraction set in the center of a picturesque lake.
Science and Technology Undersecretary and Phivolcs director Renato Solidum Jr. said despite the seemingly calmer activity yesterday, the 311-meter-high volcano remains dangerous.
“The volcano cannot sustain strong eruptions. It needs to have a supply of magma. If the rise of magma is slow, it will only create a small eruption. If the ascent of magma is fast, that’s when you can see stronger eruptions,” Solidum said in a press briefing.
A base surge is a horizontal movement at very high speed of clouds of ash, rocks and gases that can cross water and even reach the mainland, Solidum explained. It could instantly kill people and destroy property along lakeshore communities near the volcano island, should a hazardous eruption occur.
Base surges have been recorded in previous eruptions of Taal Volcano.
“In 1965, Taal deposits crossed the town of Agoncillo. In 1911, a base surge affected the entire island; there were many people killed. In 1754, the whole barangay around Taal Lake, the old town of Taal, old town of Lipa, and old town of Tanauan were devastated,” Solidum said.
Alert Level 4 remained over Taal Volcano as of yesterday afternoon, meaning a hazardous eruption is possible within hours or days.
Solidum said this was the first time that Alert Level 4 was raised over Taal since the agency started using its alert level system for active volcanoes.
He said houses should no longer be built five meters from both sides of road fissures.
Phivolcs has already recommended a long-term land use plan that takes into consideration such hazards, he said.
For the past 24 hours, Taal Volcano’s activity has been characterized by “continuous but generally weaker” eruption of the main crater, Phivolcs said in its latest bulletin.
The eruption generated dark gray steam-laden plumes that reached approximately 1,000 meters high and dispersed ash to the southwest of the main crater.
Solidum said Taal Volcano’s restiveness could be declared to be slowing down only when “earthquakes have diminished and the trend is continuing.”
“The intense seismic activity signifies continuous magmatic intrusion beneath the Taal edifice, which may lead to further eruptive activity,” he said.