Geochemical evidence of magma intrusion inferred from diffuse CO2 emissions and fumarole plume chemistry: the 2010-2011 volcanic unrest at Taal Volcano, Philippines

We report herein significant increases in the diffuse CO2 emission through the lake and soils of the Taal Volcano Main Crater (Philippines), during a volcano-seismic unrest period in April 2010-June 2011. Monitoring of CO2 emissions fromthe Taal Main Crater Lake and soils in the fumarole areas started in 2008 with a collaborative project between ITER and PHIVOLCS. In August 2010, the total diffuse CO2 emission from the Taal Main Crater Lake increased almost three times from a previously measured baseline emission value similar to 1,000 t day(-1) to 2,716 +/- 54 t day(-1). This increase occurred during anomalous seismic activity which started in April 2010. The highest CO2 emission value in the crater lake was measured in March 2011 at 4,670 +/- 159 t day(-1) when the volcano was still showing signs of unrest. Significant changes in the CO2/SO2, CO2/H2O, and SO2/H2S ratios in the fumarole gases suggest the occurrence of a magmatic injection several weeks before the onset of the volcano-seismic unrest period. These observed changes in the CO2 emission rate and the fumarole gas composition as the result of magmatic activity were likely caused by magma moving from a deep reservoir to a shallow reservoir.