Philippines: Mayon volcano update 09 Mar 2000

News and Press Release
Originally published
Since the last eruption of 01 March 2000, a waning trend in its overall activity has been evident. The number of volcanic earthquakes has decreased and has remained at unremarkable levels for the past days. In addition, tremor associated with emission of lava from the crater has ceased and this condition indicates that this quiet phase of extrusion has ended. Seismic activity now only reflects sporadic and surface disturbances such as occasional rockfalls caused by oversteepened slopes. The Electronic Distance Meter (EDM) and precise leveling surveys also show a return to the baseline indicating a probable deflation of the edifice. In terms of gas output, Mayon continues to vent a large amount of steam but the Sulfur Dioxide (SO2) component measured by the Correlation Spectrometer (COSPEC) has decreased progressively.
In summary, the critical parameters defining the overall status of volcanic activity apparently point to an abatement of the eruptive period towards quiet conditions. Seismic, ground deformation and COSPEC data obtained during the past seven days suggest no renewed active magma intrusion towards the shallow levels of the volcanic cone. Although the tip of the volcano and isolated spots from the new lava flow deposits continue to glow at night, this incandescence is attributed to residual heat and will eventually diminish as these deposits cool down.

In view of these recent developments at Mayon, PHIVOLCS is therefore lowering the volcano status to Alert Level 4. Corollary to Alert Level 4 is the reduction of the 8-kilometer radius extended danger zone in the southeast quadrant to 7 kilometers. PHIVOLCS emphasizes that the 6-kilometer radius Permanent Danger Zones should remain evacuated at all times because of instability of new pyroclastic and lava deposits that may be dislodged towards the lower slopes with resultant secondary explosions and life-threatening secondary pyroclastic flows. PHIVOLCS also reminds the public that the lowering of alert status does not necessarily mean that volcanic activity will continue to decrease and finally die out. The possibility of having another Vulcanian eruption still exists. Should there be a reversal in prevailing trends such as acceleration of seismicity, ground deformation and increase in Sulfur Dioxide outputs, then PHIVOLCS will provide the appropriate notice and warning.

Although volcanic activity is considered to have decreased, it should be realized that lahars may occur whenever pyroclastic flow deposits are remobilized during heavy rainfall in the volcano's slopes and middle slopes. The channels in which lahar flows may occur include 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. Authorities are advised to monitor the condition of major roads crossing the above mentioned channels specially those channels radiating southeast of Mayon Volcano. People residing adjacent to riverbanks and low-lying areas are also reminded to be extra alert as these sites are most prone to the danger of these destructive and life-threatening flows. Temporary evacuation may be necessary in case of prolonged and sustained intense rainfall over the edifice of Mayon. ( from Phivolcs)