Report on Mayon (Philippines) — September 2003
Bulletin of the Global Volcanism Network, vol. 28, no. 9 (September 2003)
Managing Editor: Edward Venzke.
Mayon (Philippines) Elevated sulfur-dioxide flux after mid-September; crater glow in October
Please cite this report as:
Global Volcanism Program, 2003. Report on Mayon (Philippines). In: Venzke, E. (ed.), Bulletin of the Global Volcanism Network, 28:9. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200309-273030.
13.257°N, 123.685°E; summit elev. 2462 m
All times are local (unless otherwise noted)
The Philippine Institute of Volcanology and Seismology (PHIVOLCS) reported on 18 September 2003 that earthquake activity at Mayon had been within background levels (< 5 events/day) since 14 August with no volcanic earthquakes over the previous five days and moderate volcanic gas outputs. However, the sulfur dioxide (SO2) flux at 1,237 metric tons per day (t/d) was above baseline levels, having increased from 829 t/d since 5 September. In view of increased SO2 gas emissions, and recent significant earthquake occurrences, PHIVOLCS set the hazard status at Alert Level 1 (on a scale of 0-5).
For the period 29 September-5 October, 16 low-frequency volcanic earthquakes (19.0 mm amplitude), five high-frequency volcanic earthquakes (26.0 mm amplitude), and four high-frequency short-duration volcanic earthquakes (2.5 mm amplitude) were recorded, accompanied by weak to moderate steaming and no visible crater glow. During 6-12 October, 29 low-frequency volcanic earthquakes (14.0 mm amplitude), four high-frequency volcanic earthquakes (6.2 mm amplitude), and two high-frequency short duration volcanic earthquakes (2.0 mm amplitude) were recorded, with moderate steaming and faint crater glow.
PHIVOLCS reported on 9 October that a faint glow had been seen by telescope at the inner E portion of the summit crater between 2330 on 8 October and 0048 on 9 October, and again between 1630 and 1650 on 9 October. Low-frequency volcanic earthquakes occurred four and six times, respectively, during 8 and 9 October. Steam emission remained moderate, with visible plumes barely rising above the crater rim. Mayon's SO2 flux on 9 October rose to 2,386 t/d from 1,616 t/d on 1 October.
On 11 October PHIVOLCS noted persistent and significant incandescence inside the summit crater, apparently from lava in the E portion of the volcano's conduit. Seismicity over the previous 24 hours was relatively low (three low-frequency volcanic earthquakes). The Alert Level was raised to 2, signifying instability that may lead to ash explosions or a magmatic eruption.
Geologic Background. Beautifully symmetrical Mayon, which rises above the Albay Gulf NW of Legazpi City, is the Philippines' most active volcano. The structurally simple edifice has steep upper slopes averaging 35-40 degrees that are capped by a small summit crater. Historical eruptions date back to 1616 and range from Strombolian to basaltic Plinian, with cyclical activity beginning with basaltic eruptions, followed by longer term andesitic lava flows. Eruptions occur predominately from the central conduit and have also produced lava flows that travel far down the flanks. Pyroclastic flows and mudflows have commonly swept down many of the approximately 40 ravines that radiate from the summit and have often devastated populated lowland areas. A violent eruption in 1814 killed more than 1,200 people and devastated several towns.
Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), Department of Science and Technology, PHIVOLCS Building, C.P. Garcia Avenue, University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs. dost.gov.ph/).