Volcano experts started Sunday their close watch on Mayon Volcano in Legazpi City, Albay, showing signs of unrest, the Philippine Institute of Volcanology and Seismology (Phivolcs) said Sunday.

Phivolcs Director Renato Solidum said Mayon is still at “Alert Level 1 with 13 volcanic quakes, moderate steaming, and Intensity II crater glow observed for past 24 hours.”

Earlier, Ed Laguerta, resident volcanologist of Phivolcs, said his office is closely watching Mayon, following observations that its crater glow has become brighter compared to that in previous months.

The Phivolcs had conducted an aerial survey and continuously monitoring the seismic activity around the volcano, he said, to see whether there is a need to raise the alert status of the volcano.

Phivolcs said with an Alert Level 1 status, a hazardous eruption is unlikely, but reminded the public “that the seven-kilometer Extended Danger Zone (EDZ) at the southeastern flank of the volcano and the six-kilometer radius Permanent Danger Zone (PDZ) in other areas remain off-limits due to the continuing threat from sudden small explosions and rockfalls from the upper slopes.”

“Active river channels and those areas, perennially identified as lahar-prone around the volcano, should be avoided when there is heavy and prolonged rainfall,” Philvolcs said in its 8 a.m. update on Mayon Volcano.

“Phreatic” explosions are also possible, Phivolcs said. Jojo Cordon, a science research specialist of Phivolcs, explained that a phreatic explosion occurs when rising magma makes contact with ground or surface water.

Phivolcs Alert system for Mayon Volcano states that “Alert Level 1 means that there is low-level unrest with slight increase in seismicity.”

There is also a "slight increase in sulfur dioxide gas output above the background level. A very faint glow at the crater may occur, but no conclusive evidence of magma ascent.”

Mayon Volcano has been on Alert Level 1 since October, 2006. It reached a Level 3 alert status in July, 2006, when it had a silent type of eruption in the form of lava extrusion.

Phivolcs’ last advisory on Mayon was dated Aug. 10, 2008. The volcano at 9:12 a.m. of that daye had an ash ejection that reached 200 meters above summit crater. Mayon had an explosion-type earthquake which lasted one minute.

Also known as Mount Mayon, the volcano popular for its near- perfect cone shape has had 47 eruptions in the past 400 years.