Report on Taal (Philippines) — 6 April-12 April 2011
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 6 April-12 April 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, 6 April-12 April 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 observations of Taal conducted at the E sector inside the main crater lake on 5 April 2011 showed that steaming at the thermal area was weak. The water level had receded 3 mm and the water temperature slightly increased from 30 to 30.5 degrees Celsius. Since the previous measurement on 29 March, the pH value increased indicating that the water had become slightly less acidic. Gas measurements conducted last January, February, and March yielded carbon dioxide emission values (in tonnes per day) of 2,250, 1,875, and 4,670, respectively.
On 9 April PHIVOLCS noted that after 31 March the number of earthquakes gradually rose and the depths become more shallow (1-4 km). Steaming at the N and NE sides of the main crater occasionally intensified and was occasionally accompanied by hissing sounds. The Alert Level was raised to 2 (on a scale of 0-5) because of increased seismicity and carbon dioxide emissions. PHIVOLCS warned tourists and residents to avoid Volcano Island. According to news articles, about 100 families had volunteered to evacuate; about 7,000 people remained.
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.