Getting to know Taal’s possible hazard: What is base surge?

Volcanologists have warned that a base surge may affect the communities surrounding Taal Volcano should the expected hazardous eruption occur.

According to the Philippine Institute of Volcanology and Seismology (PHIVOLCS), a base surge is a special class of pyroclastic density currents (PDC) which are "mixtures of fragmented volcanic particles, hot gases and ash that rush down the volcanic slopes or rapidly outward from a source vent at high speeds."

What does it look like?

Base surges—mobile and water vapor-rich—are generated when explosive phreatomagmatic eruptions take place, according to PHIVOLCS.

The United States Geological Survey said that phreatomagmatic eruption "involves both magma and water, which typically interact explosively, leading to concurrent ejection of steam and pyroclastic fragments."

PHIVOLCS Volcano Monitoring and Eruption Prediction Division chief Mariton Bornas said that base surges are ring-shaped spreading out from the base of the eruption column.

"Mayroon kang matayog na eruption column tapos mayroong ring na kumakalat mula doon sa base ng eruption column," she said during a press conference.

In the case of the restive Taal Volcano, the possible base surge may affect the communities surrounding its lake.

"Itong ring na ito, ito 'yung base surge, tumatawid siya ng lawa at tinatamaan niya ang mga pamayanan sa paligid ng lawa. 'Yung base surge po talaga ang primary hazard," she said.

What can it do?

A base surge could travel horizontally at 80 kilometers/hour and can instantly destroy and kill anything on its way.

This volcanic hazard could be fatal as it can cause incineration, suffocation, abrasion, dynamic pressure impact and burial in hot volcanic material, according to PHIVOLCS.

Did this happen before?

PHIVOLCS Director Renato Solidum said that base surges had been the cause of death of most victims in the previous eruptions of Taal Volcano.

"'Yung nangyari noong 1965, tumawid po 'yung deposito sa Agoncillo, noong 1911 nag-base surge sa buong isla, maraming namatay doon at umabot pa sa lakeshore. Noong 1754, 'yung buong barangay sa gilid ng Taal Lake—'yung dating bayan ng Taal, dating bayan ng Lipa at dating bayan ng Tanauan ay nasalanta," he said in an interview on State of the Nation with Jessica Soho.

More than 1,500 people perished when Taal Volcano violently erupted in the said years.

The total evacuation of the Taal Volcano Island, as well as the areas within the 14-kilometer radius of the main crater was strongly advised because these are susceptible to base surge.

Over 40,000 people are now taking refuge in 189 evacuation centers in Batangas and Cavite, according to the National Disaster Risk Reduction and Management Council.

"Ang susunod nating hinaharap na kailangan masigurong maiwasan ay maabutan ang mga kababayan natin sa mga lugar na malapit sa lake at maabutan ng tinatawag na base surge," Solidum said.

"Marapat na sumunod tayo sa mga kinauukulan upang mas ligtas ang ating mga lokasyon," he added.

Alert Level 4 remains over Taal Volcano as its intense seismic activity continues, probably signifying magmatic intrusion beneath the Taal edifice which may lead to further eruptive activity. — RSJ, GMA News