Report on Taal (Philippines) — 25 May-31 May 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 25 May-31 May 2011
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2011. Report on Taal (Philippines). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 25 May-31 May 2011. Smithsonian Institution and US Geological Survey.
14.002°N, 120.993°E; summit elev. 311 m
All times are local (unless otherwise noted)
PHIVOLCS reported that field measurements conducted on 24 May at the E sector inside Taal's Main Crater Lake showed that the water temperature slightly increased from 32.5 to 32.8 degrees Celsius, the pH value became more slightly acidic decreasing from 2.83 to 2.67, and the water level increased by 4 cm. During 25-29 May, between 6 and 10 daily volcanic earthquakes were detected by the seismic network. Some of the earthquakes were felt by nearby residents on the SE part of the island. During 29-30 May, 115 earthquakes were recorded. Twelve of these events were felt at Intensity I-IV by residents of Pira-piraso, Alas-as, and Calauit located in the NE, SW, and SE sectors of Volcano Island, respectively. During 30-31 May there were 31 earthquakes noted. The Alert Level remained at 2 (on a scale of 0-5).
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 topography 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 has grown about 25% in area during historical time. Powerful pyroclastic flows and surges from historical eruptions have caused many fatalities.