Three minor explosions woke up residents living near Mount Mayon in Albay province early Tuesday morning, which the Philippine Institute of Volcanology and Seismology (PHIVOLCS) said was an indication of increased activity of the world-famous volcano.

In a notice to the public and concerned authorities, PHIVOLCS said the three minor explosions occurred at 5:37 a.m. Tuesday, producing brownish ash columns that rose to a maximum height of about 700 meters for three minutes before drifting towards the southwest.

But Julio Sabit, supervising science researcher at PHIVOLCS, said the minor eruptions should not be a cause for alarm since it did not include the emission of lava or other volcanic materials.

“It was pure vertical emission, which means that there was no volcanic materials spewed in the eruption that could affect the residents. Most of it was composed of water vapor and very minimal brownish ash columns,” Sabit told the Manila Bulletin in a phone interview.

“But this is not normal. It indicates increased volcanic activities, which is abnormal under Alert Level II status,” he added.

Sabit said the steam emission had very minimal force, ranging from weak to moderate, while the rate of sulfur dioxide emission decreased to 50 tons per day compared to the previous reading of 818 tons on September 12.

He also said a faint crater glow at intensity I was observed the night before the explosion.

For his part, PHIVOLCS director Renato Solidum said they had to maintain an Alert Level 2 or a state of unrest, saying that more field observers will arrive to monitor Mayon early next week.

PHIVOLCS has recommended the implementation of the six-kilometer radius Permanent Danger Zone around the volcano and another seven-kilometer Extended Danger Zone, particularly on the southeast flank of the volcano.

Solidum explained that the 13-kilometer danger zone around the volcano should be off limits due to threat from more explosions that could eventually lead to hazardous magmatic eruptions as well as rock falls from under the slopes.

“Active river channels and those perennially identified as lahar prone in the southeast sector should also be avoided especially during bad weather condition or when there is heavy and prolonged rainfall,” he said.