Report on Taal (Philippines) — April 1991
Bulletin of the Global Volcanism Network, vol. 16, no. 4 (April 1991)
Managing Editor: Lindsay McClelland.
Taal (Philippines) Continued seismicity and changes to crater lake
Please cite this report as:
Global Volcanism Program, 1991. Report on Taal (Philippines) (McClelland, L., ed.). Bulletin of the Global Volcanism Network, 16:4. Smithsonian Institution. https://doi.org/10.5479/si.GVP.BGVN199104-273070.
14.002°N, 120.993°E; summit elev. 311 m
All times are local (unless otherwise noted)
High seismicity continued as of early May, with the daily number of earthquakes varying from 15 to 30 (figure 4). Felt earthquakes reached intensity IV. Acidity and chloride content of the volcano's crater lake continued to fluctuate, ranging from 2.4-2.8 and 9,630-11,720 ppm, respectively. Lake temperature increased slightly from 30° to 31°C, and lake level rose by 4 cm.
On 26 April, strong bubbling and increased steaming were observed in the N sector of the crater and at the base of the wall. Geysering, to 1.2 m height, was also noted near the NNE shore of the lake, where water temperatures of 99°C were measured.
Deformation measurements on Taal Volcano Island have found no inflation or swelling of the volcanic edifice.
Volcano Island has been partly evacuated since 23 March, but a small number of residents have remained, particularly near the PHIVOLCS station at the N end of 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: R. Punongbayan, PHIVOLCS.