Magmas degas volatiles such as H2O, CO2 and SO2 as they rise to the Earth’s surface. Sulfur dioxide levels are commonly used for monitoring volcanic activity, as this gas effectively absorbs ultraviolet radiation and has a trace atmospheric background level, so increased SO2 levels can be relatively easily detected. However, detecting changes in CO2 levels are challenging to monitor owing to their high background concentrations in the atmosphere, and previously could only be indirectly estimated via the SO2 flux and CO2/SO2 ratios of volcanic gases. As such, the CO2 budget of many volcanic areas is inaccurately known.
Alain Bernard from Université Libre de Bruxelles, Belgium, and colleagues, found that pCO2 levels at the Taal Volcano crater lake in the Philippines could be an additional tool to help monitor volcanic activity and volcanic CO2 flux. Monitoring surface lake CO2 levels throughout the 2013–2020 period showed that CO2 is primarily transferred in a dissolved state from hydrothermal systems directly into the crater lake and becomes homogenized over the lake surface. As the residence time of CO2 in the lake is approximately one week, it allows for fast detection of changes in magma degassing. From February 2019, pCO2 levels at the crater lake surface began to increase, reaching more than three times the background level before the onset of the eruption in January 2020, which impacted over 380,000 local people.
Taal crater lake volcanic CO2 measurements are the longest continuous record of volcanic CO2 emissions to date, providing important insights into eruption monitoring, magma degassing and volcanic CO2 budgets. However, it remains to be seen whether this method can be applied to other active volcanic crater lakes, which should be a target for future work. Nevertheless, these results indicate the promising potential for crater lake pCO2 levels as an additional tool to help understand the natural warning signs before volcanic eruptions.
Bernard, A. et al. Carbon dioxide in Taal volcanic lake: a simple gasometer for volcano monitoring. Geophys. Res. Lett. https://doi.org/10.1029/2020GL090884 (2020)