June 2016 – PHILIPPINES – The
Philippine Institute of Volcanology and Seismology yesterday warned
residents living near Mount Bulusan in Sorsogon of the possibility of
more steam-driven eruptions, following an explosion last Friday. Thin
ash caused by the steam-driven eruption in Mount Bulusan last Friday was
observed in Casiguran and Juban in Sorsogon. Ash fell over Barangays
Añog, Juban, and Mabini in Casiguran. Traces of volcanic ash were
observed in Barangays Casay, Casiguran proper, Escuala, Inlagadian, San
Antonio, and San Juan in Casiguran, and Barangays Aroroy, Juban proper,
Puting Sapa, and Rangas in Juban.
Steam-driven explosion, also called
phreatic explosion, happens when groundwater is heated by magma. The
eruption that occurred at 11:35 a.m. Friday was observed on the
west-northwest vent of the volcano. A two-kilometer-high grayish ash
plume, which drifted to the northwest, was visible after the explosion.
Phivolcs recorded an explosion-type earthquake that lasted approximately
five minutes, which was accompanied by rumbling sound reportedly heard
at Barangays Puting Sapa, Ranga, and Añog in Juban, and Barangays Mabini
and Inlagadian in Casiguran.
From 8 a.m. Friday to 8 a.m. Saturday,
Bulusan’s seismic monitoring network recorded a total of five volcanic
earthquakes, including the explosion-type earthquake Friday. Phivolcs
said weak to moderate emission of white steam plumes that rose up to 150
meters and drifted towards north-northwest remain visible. Alert Level
1, which is the lowest of five-tier level of volcanic unrest, remains in
effect over Mount Bulusan. This indicates that hydrothermal processes
are ongoing beneath the volcano that may lead to steam-driven eruptions,
Phivolcs said.
It warned local government units and
the public from entering four-kilometer permanent danger zone
surrounding the volcano due to possible sudden and hazardous
steam-driven eruptions. Civil aviation authorities were advised to warn
pilots to from flying close to the volcano’s summit as ash from any
sudden phreatic eruption can be hazardous to aircraft. People living
within valleys and along river or stream channels, especially on the
southwest and northwest sector of the edifice, were also advised to be
vigilant from sediment-laden stream flows and lahars in the event of
heavy and prolonged rainfall. –Tempo
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