"Each volcano has its own magma chamber and these are not physically connected. There is no relation, even if the volcanoes are near (each other) like Bulusan and Mayon (that are both in Bicol)," said Phivolcs director Renato Solidum.
Solidum said ground water and rainwater could have come in contact with hot rocks on the surface "so the sudden conversion of water into steam triggered the ash emission."
Phivolcs monitored Kanlaon to have exhibited minor steam-ash emissions from 4:10 to 4:44 p.m. and from 5:36 to 5:50 p.m. last Tuesday. The volcano also spewed ashes from 5:09 to 5:30 a.m. yesterday.
"The grayish steam clouds rose to about 900 meters above the active crater and drifted to the northeast and northwest. However, no volcanic earthquakes coincident with the ash puffs were recorded," Phivolcs said in a bulletin.
Phivolcs said only traces of ash deposits were observed on the northern upper slopes of the volcano. There has been no report of any ashfall in low-lying areas.
Alert level one remains hoisted around Kanlaon. Phivolcs cautioned residents against venturing into the four-kilometer radius permanent danger zone.
Meanwhile, Solidum said they have monitored that the magma inside Mt. Bulusan has been rising.
"Magma is rising but there is no evidence that it is very near the surface," he said.
He said the interval of ash explosions in Bulusan is getting shorter so a "hazardous eruption" in the future is possible.
At about 7:04 p.m. Tuesday, Bulusan exhibited steam and ash explosions, followed by small volcanic quakes. This was the seventh ash explosion since the volcano became restive last March 21.
"The nature of these micro earthquakes suggests a shallow source beneath the volcano and may be associated with magmatic movement. The surface activity yesterday was characterized by moderate to voluminous volcanic gas emission from the western fissure but weak discharge from the active central summit vent," Phivolcs said in a bulletin.
The agency also observed that the sulfur dioxide contained in the volcanic plume rose slightly to 423 tons per day from 295 tons.
"Last (Tuesday) night’s explosion and relatively voluminous ash emission indicated that Bulusan Volcano is undergoing a period of elevated unrest, distinct from the early explosions from March to May," Phivolcs said. — With Celso Amo and Cet Dematera