Metro Manila (CNN Philippines, February 5) — State volcanologists said the crater glow observed at Mayon Volcano in the last two days has most likely been caused by gases affecting the atmosphere, adding alert level 2 remains in place due to recent activity.

In its latest update, Phivolcs said while the volcano has calmed down since a magmatic eruption in 2018, slight changes have been observed since February 2019.

"These observations indicate that Mayon’s recent behavior has been mainly driven by changes occurring within magma already emplaced beneath the edifice rather than by renewed magma intrusion events," the agency said.

The crater glow seen was also explained as "likely caused by hot magmatic gases heating the overlying atmosphere."

Phivolcs said this could mean that "remnant magma" may be silently rising to the shallow levels of the volcano.

As Mayon was still showing "moderate levels of unrest," Phivolcs said alert level 2 was still over the volcano.

"It is therefore strongly recommended that entry into the six kilometer-radius Permanent Danger Zone or PDZ and a precautionary seven kilometer-radius Extended Danger Zone or EDZ in the south-southwest to east-northeast sector, stretching from Anoling, Camalig to Sta. Misericordia, Sto. Domingo, should be strictly prohibited," it said.

Doreen Abelinde, project assistant of Phivolcs' Volcano Monitoring and Eruption Prediction Division, told CNN Philippines Wednesday apart from the crater glow, they were also monitoring other characteristics such as sulfur dioxide emission, deflation, and acidity.

She added they were not able to monitor any crater glow tonight, as it was cloudy in the Mayon area.