Carbon Dioxide in Taal Volcanic Lake: A Simple Gasometer for Volcano Monitoring

We report here an increase in the amount of carbon dioxide in Taal lake during the year preceding the January 2020 eruption. Starting in February 2019, the CO2emissions from the lake increased from background value (700 t day−1) to a flux close to 2,400 t day−1at the time of the eruption. We show that the lake acts as a highly sensitive gasometer where CO2 (aq)reflects the balance between CO2supplied to the lake (by hot springs) and CO2lost by diffusion at air‐water interface. The lake waters are extremely enriched in dissolved carbon dioxide with pCO2values as high as 0.35 atm (350,000 ppmV) equivalent to a CO2(aq)of 9.32 mmol l−1. The residence time of CO2in the lake is around 1 week which allows for fast detection of change in magma degassing and makes carbon dioxide a very promising tool for volcano monitoring.