Report on Taal (Philippines) — August 2006
Bulletin of the Global Volcanism Network, vol. 31, no. 8 (August 2006)
Managing Editor: Richard Wunderman.
Taal (Philippines) Ongoing seismic unrest
Please cite this report as:
Global Volcanism Program, 2006. Report on Taal (Philippines) (Wunderman, R., ed.). Bulletin of the Global Volcanism Network, 31:8. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN200608-273070.
14.002°N, 120.993°E; summit elev. 311 m
All times are local (unless otherwise noted)
The Philippine Institute of Volcanology and Seismology (PHIVOLCS) notified the public on 26 September 2006 of ongoing seismic unrest at Taal. The Main Crater Seismic Station recorded 29 volcanic earthquakes during the 24-hour period from 0600 hours on 25 September. Five of these earthquakes, at 0233, 0234, 0242, 0247, and 0249 hours on 26 September, were felt at Modified Mercalli Intensities II to III by residents on Volcano Island. The earthquakes were accompanied by rumbling sounds. Initial locations showed epicenters generally dispersed in the vicinity of Daang Kastila (NE), Tibag (N), Tablas (NE), Mataas na Gulod (NE), and Panikihan (NW). This seismic activity was notably higher than the usual levels, generally only five or less events detected in 24 hours.
Surface thermal observations, however, did not indicate significant change in the thermal and steam emission manifestations of the Main Crater lake area. The increase in seismicity at Taal reflects a low-level episode of unrest. However, there is still no indication of an impending eruption. Possible precursors, such as increased steam emission, increased temperatures of steam vents at the Main Crater lake waters and adjacent areas are being monitored continuously. The ongoing seismic unrest could intensify in the coming days or weeks so that PHIVOLCS recommends appropriate vigilance by the public when visiting the island.
Geologic Background. Taal is one of the most active volcanoes in the Philippines and has produced some of its most powerful historical eruptions. Though not topographically prominent, its prehistorical eruptions have greatly changed the landscape of SW Luzon. The 15 x 20 km Talisay (Taal) caldera is largely filled by Lake Taal, whose 267 km2 surface lies only 3 m above sea level. The maximum depth of the lake is 160 m, and several eruptive centers lie submerged beneath the lake. The 5-km-wide Volcano Island in north-central Lake Taal is the location of all historical eruptions. The island is composed of coalescing small stratovolcanoes, tuff rings, and scoria cones that have grown about 25% in area during historical time. Powerful pyroclastic flows and surges from historical eruptions have caused many fatalities.
Information Contacts: Philippine Institute of Volcanology and Seismology (PHIVOLCS), University of the Philippines Campus, Diliman, Quezon City, Philippines (URL: http://www.phivolcs.dost.gov.ph/).