Taal volcano

An aquatic view of magmatic CO₂ degassing at Taal volcano, Philippines

On 9 April 2011, the Philippine Institute of Volcanology and Seismology (PHIVOLCS) raised the Alert Level status of Taal Volcano to Alert Level 2. The most alarming parameter detected was a spectacular increase in the rate of carbon dioxide emissions from the main crater lake (MCL) where CO₂ fluxes have more than doubled between January and March 2011. The fact that lake temperatures did not increase suggest that the discharge rate of hydrothermal waters remains unchanged and that this CO₂ increase is not related to a change in hydrodynamic processes within the hydrothermal system (i.e. opening of fracture) but has a deeper magmatic origin.

The active vent complex (the volcano island) lies in the middle of a large (15X22 km) prehistoric caldera filled with Lake Taal. The main crater of the volcanic island contains a volcanic lake termed MCL with a volume of 41-45 millions m³. About 6,000 people are living on the volcano island.

View of MCL lake from the East rim of the crater. The lake is slightly acidic with pH around 2.9 and a temperature (30°C) a few degrees warmer than the average ambient atmosphere. This lake seems to be very placid but look at the current underwater activity!! (scroll down to the next image).

Lake's floor degassing activity recorded on 24 January 2011. The vertical tracks above the bottom (brown-red) are trains of CO₂ bubbles ("flares") rising to the surface. Colour scale in decibels (dB) reflects variable intensities of the backscattering of the sound wave by the gas bubbles which are roughly proportional to bubble density in the water column. Echograms recorded with a SIMRAD ES60 single beam sonar equipped with a dual frequency (50 and 200 kHz) transducer. Echograms processed with SonarData Echoview software. Horizontal grid spacing = 50 meters and vertical (depth) spacing = 10 meters. Field work carried by Alain Bernard (ULB), Corentin Caudron (ORB-ULB) and PHIVOLCS (ULB: Université Libre de Bruxelles, ORB: Observatoire Royal de Belgique).

co2all40

Evolution of CO₂ fluxes (tons per day) as measured by PHIVOLCS in collaboration with ITER (Instituto Tecnolóo y de energí renovables, Spain), ULB (Université Libre de Bruxelles, Belgium) and EMSEV. Figure courtesy of Nemesio Perez (ITER). CO₂ fluxes were measured with the "floating accumulation chamber" method (see Kelud for more details).

Echosounder can be used to evaluate the activity of gas vents at the lake floor by measuring the backscattering intensity (Sv). Sv is roughly proportional to bubble density in the water column. In order to minimize the effect of dissolution of CO₂ bubbles during their rise to the surface, Sv are measured in individual cells close to the lake's floor i.e. 2 meters above the bottom ( 50kHz data processed with Sonar 4 software).

Map of the degassing activity from the lake bottom obtained from the integration of 23 km of echosounder profiles covering the all lake (almost). Sv is the mean backscattering strength of the water column, (dB) are decibels. No degassing is observed for Sv < -70 dB. More than 50% of the lake's floor is degassing.