Four volcanoes in the country —Taal, Kanlaon, Mayon, Bulusan —remain under Alert 1, the Philippine Institute of Volcanology and Seismology (Phivolcs) said on Monday.

Kanlaon Volcano in Negros Island, in a state of unrest and in an abnormal condition following a minor steam explosion last week, was recorded having 11 volcanic earthquakes since Sunday.

Weak to moderate emission of white steam plumes that rose up to 50-meter high above the summit crater has been monitored.

PHIVOLCS has strictly enforced the 4-kilometer radius Permanent Danger Zone (PDZ) in areas around and near the four volcanoes due to further possibilities of sudden and hazardous steam-driven or phreatic eruptions.

Civil aviation authorities were also asked to advise pilots to avoid flying close to the volcanoes’ summit as airborne ash from a sudden eruption can be hazardous.

Mayon Volcano in Albay Province, meanwhile, had one volcanic earthquake recorded since Sunday with moderate emission of white steam plumes was also observed.

Although alert level 1 in Mayon volcano means that no magmatic eruption is imminent, PHIVOLCS strongly advised the public to keep the 6-kilometer radius PDZ due to the perennial life-threatening dangers of rockfalls, landslides in the middle and upper slopes, sudden ash puffs and steam-driven or phreatic eruptions from the summit.

Likewise Mount Bulusan in Sorsogon and Taal Volcano in Batangas were also observed in an abnormal condition.

The alert in Bulusan indicates that hydrothermal processes are underway beneath the volcano that may lead to steam-driven eruptions.

People living within valleys and along river or stream channels, especially on the southwest and northwest sector of the volcano should be vigilant against sediment-laden stream flows and lahars in the event of heavy and prolonged rainfall.

Meanwhile, the alert level in Taal Volcano means that hazardous eruption is not imminent.

The public is reminded that the entire Taal Volcano Island is a permanent danger zone and settlement in the island is strongly not recommended.