LEGAZPI CITY, Sept. 30 (PNA) -- A scientist of the Philippine Institute of Volcanology and Seismology (Phivolcs) said Tuesday that what Mayon Volcano is releasing are still remnants of the September 2009 vulcanian eruption.
Paul Karson Alanis, Phivolcs science research specialist, said the volcanic materials that have come out initially -- particularly the 855,000 cubic meters in volume of lava dome, which is equivalent to more than 85,000 truckloads of rocks -- may still be remnants or material remains of the previous eruption.
"The remnants of 2009 eruption cause volcanic plug, which means the crater has been blocked. Before eruption happens, the lava dome at the crater must first be cleared or what we call vent clearing. The new magma can't go out if there's still old materials hardened and plugged the crater," Alanis explained.
He said a volcanic plug is when the magma hardens (called lava dome) and trapped at the crater -- like in human, the throat still needs to be cleared before phlegm comes out.
"The lava dome that makes the crater partially closed is not advantageous because sometimes, it can lead to an explosive eruption as the magma can build-up more pressure inside," the Phivolcs scientist said.
Sept. 30 bulletin shows that magma is still moving slowly as Phivolcs detected only one volcanic earthquakes and three rockfall events during the past 24-hour observation period while sulfur dioxide (SO2) flux increased to 1,421 tons per day compared to 1,265 tons per day on Sept. 28.
"In the present situation, the decrease of some movements is not significant because of the increase of sulfur dioxide emission, which means the magma is extruding -- and based on the tilt data, there is an indication that Mayon is still inflated. The changes must be consistent before we consider it as significant," Alanis explained.
He said that there are four parameters in monitoring the volcano: the rockfall events, volcanic earthquakes, sulfur dioxide emission and result of ground deformation survey, if there's an inflation based on the tilt data.
Alanis said if the movement of the volcano continuously decreases and if deflated in two weeks, that's the time they will lower the alert level of Mayon.
"We are considering the so called 'lull before the storm effect' (a period of mild activity for Mayon Volcano before the big one) amid minimum activity of Mayon. We are maintaining the alert status to avoid evacuees returning to their home, especially in danger zone. At the very least, we need one week or two to see the consistent changes as it continually decreases, but as of now there's still high activity considering the parameters," he added.
Mayon Volcano has again shown magma movement since last Sept. 15, after a week of slumber. (PNA) CTB/FGS/AMM/CBD/UTB