Philippines

Philippines: Mayon volcano update 12 Mar 2000

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An ash puff with height of about one kilometer was observed on March 11 at 0903H,. The ash column was drifted to the northwest direction. The ash ejection was caused by water that comes in contact with the still hot lava deposits at the summit. And at 1242H, another minor billowing ash was seen descending the Bonga Gully due to the detachment of the new lava deposit at the upper slope. The elutriated ash cloud drifted to the west-southwest by the prevailing winds.
During the rest of the past observation period the volcano was relatively quiet. This was manifested by faint crater glow at the tip of the cone and weak to moderate emission of steam. Sulfur Dioxide (SO2) emission rate decreased from the previous reading of 4,300 tonnes per day (t/d) to 4,000 t/d.

Seismic activity consisted of 5 low-frequency volcanic quakes and 7 episodes of short-duration tremors. Slight deflation of the volcano edifice continued to be recorded by ground deformation measurements via precise leveling.

PHIVOLCS considers the moderate seismic levels, deflation of the volcanic cone, moderate steam ad SO2 outputs including crater glow to be part of the volcanic processes involving the gradual return to quiet conditions. At this stage, however, these parameters are still above normal repose levels such that Alert Level 4 remains hoisted over the volcano. It is therefore necessary to keep the six (6) kilometers radius Permanent Danger Zone around the volcano and the seven (7) kilometers Extended Danger Zone in the southeast quadrant free from permanent human activity in case resurgence should occur. If the trend of decreasing activity continues, it is probable that a further lowering of Alert Level can be made. Regardless of alert level, a significant volume of pyroclastic deposits is still susceptible to erosion and subsequent remobilization as secondary pyroclastic flows, lahars or debris flows. The areas in which volcanic flows may occur are lowlands fronting the Mabinit and Buyuan-Padang river channels in Legazpi City; Miisi, Tumpa, Anoling and Quirangay channels in Camalig; Maninila and Upper Nabonton channels in Guinobatan; Basud-Lidong channel in Sto. Domingo, Bulawan channel in Malilipot, San Vicente and Buang channels in Tabaco and Upper Nasisi in Ligao. Residents adjacent to these channels are advised to be alert and ready to evacuate should there be intense and prolonged rainfall and/or large magnitude earthquakes. ( from PHIVOLCS)