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Phivolcs lowers Mayon’s alert level to 2

December 19, 2014 8:26am Tags: Mayon volcano , Phivolcs

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Citing the lower activity levels there in recent weeks, the Philippine Institute of Volcanology and Seismology on Friday lowered the alert level at Mayon Volcano to "2."
 
Phivolcs, in a bulletin on Friday, noted a "general decline" in the volcano's overall activity since the last recorded seismic swarm last Nov. 29.
 
"(Phivolcs) is now lowering the alert status of Mayon from Alert Level 3 to Alert Level 2.  This means that the likelihood of hazardous eruption within days to weeks has lessened," it said.
 
But it stressed this should not be taken to mean the volcano’s unrest has ceased, saying eruptible magma has already accumulated deeper beneath it.
 
"If there is a resurgence of volcanic unrest based on any one or combination of the above monitoring parameters, the alert status may step up to Alert Level 3 again. On the other hand, if there is a noticeable return to baseline levels of ground deformation and sustained low levels of other parameters, then the Alert Level may further step down," it said.
 
Phivolcs maintained its warning to the public to avoid entry into the six-kilometer permanent danger zone due to the hazards of rockfalls, avalanche, ash puffs and sudden steam-driven or phreatic eruptions at the summit area.
 
It also reminded people living in valleys and active river channels to remain vigilant against sediment-laden stream flows and lahar in prolonged and heavy rainfall.
 
Lower activity
 
Phivolcs said volcanic seismic activity declined in the last three weeks to an average of two to three mostly volcano-tectonic earthquakes, attributed to rock fracturing beneath the northern flank of the edifice.
 
It also noted lesser low frequency earthquakes associated with magma or volcanic gas movement, and few minor rockfall events more likely enhanced by intense rainfall over the volcano summit rather than by lava extrusion at the crater.
 
"Such overall low-level seismicity indicates that there is currently no active transport of eruptible magma to the shallow levels of the volcano," it said.
 
On ground deformation, it said Mayon’s edifice has been inflating or swelling due to very slow intrusion of subsurface magma beneath the northern flank of the edifice since June 2014.
 
Sulfur dioxide emission or SO2 flux from Mayon crater has declined since October 2 to below 500 tons a day, which is the baseline value during quiescence.
 
It said SO2 flux levels have decreased from a high of 2,360 t/d on September 6 to 259 t/d Dec. 9.
 
"The low levels of SO2 flux indicate that shallow magma degassing has declined, due to either the progressive loss of volcanic gas from shallow magma, or the generally low volcanic gas content of magma intruded at deeper levels beneath the edifice, or both," it said.
 
As for visual observation of the summit, Phivolcs said that since the last observation of lava flow on October 19, no new lava material has been observed at Mayon’s summit crater.
 
"Crater glow, which is incandescence associated with superheated gas emission at the summit vent, has not been observed since 28 November. The decline in observable parameters at the summit is consistent with the cessation of magma supply to the shallow levels of the volcanic edifice," it said.
 
Mayon raised the alert level to 3 in mid-September, saying an eruption is likely in weeks.
 
But last Nov. 3, the Office of Civil Defense allowed residents in the seven- to eight-kilometer extended danger zone to return home for now.
 
On Nov. 4, many families whose homes were within the seven- to eight-kilometer extended danger zone were allowed to go home. —Joel Locsin/KG, GMA News


source: http://www.gmanetwork.com/news/story/393264/news/regions/phivolcs-lowers-mayon-s-alert-level-to-2

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