LEGAZPI CITY, Philippines—Sulfur dioxide emission and quakes showed clear signs the volcano continued to be on a heightened state of restiveness, said the Philippine Institute of Volcanology and Seismology on Monday.

A Phivolcs bulletin on Monday said the volcano released 853 tons of sulfur dioxide during the past 24 hours, a reading which was way above the 505 tons recorded on Sunday.

The sulfur dioxide disgorging from Mt. Mayon indicated a fluctuating trend ranging from 350 to 853 tons per day.

There were 505 tons per day recorded on Oct. 10; 761 tons on Oct. 8; and 350 tons on Oct. 7.

Ed Laguerta, Phivolcs resident volcanologist, said that “350 tons to 853 tons per day during the past five days is an indication that magma is intruding into the volcano’s vent.”

The agency’s seismic instruments detected 7 volcanic earthquakes which brought about a total of 43 quakes recorded during the past five days or a total of 106 earthquakes rocking the volcano since Oct. 1.

High and low frequency harmonic quakes detected by the instruments signified that magma intrusion is developing in the volcano’s crater vent.

Laguerta said the agency was still assessing the abnormal state of the volcano based on other parameters like ground deformation and crater glow.

In its latest bulletin, Phivolcs said the volcano did not exhibit crater glow due to cloudy sky prevailing in the volcano’s crater.

Alert level 2 remained hoisted over Mayon with Phivolcs strongly recommending that the 6-kilometer permanent danger zone, including the 7-km extended danger zones in the southeast flank, be off limits to any human activity due to threats from sudden explosions and rock falls from the volcano’s upper slopes.

In August, scientists kept watch for a feared collapse of a portion of Mayon’s crater, which holds about 200,000 cubic feet of rocks.