The emission rate of carbon dioxide (CO 2 ) is one of the less obvious—but nevertheless significant—measures of volcanic activity. Volcanic CO 2 emissions are also important for understanding the preindustrial climate balance. To date, estimates of global volcanic CO 2 emissions have been extrapolated primarily from measurements collected at a small number of active sources. Ice-covered volcanic centers are prevalent, but they are often difficult to access, and their vents are difficult to discern, so they are rarely included in these calculations.

To address this gap, Ilyinskaya et al. recorded the first atmospheric gas emission rate measurements from Katla, one of Iceland’s largest active volcanoes. This massive ice-covered caldera, which last erupted a century ago, was previously assumed to be a relatively minor emitter of CO 2 , but the new results suggest otherwise.

The team detected CO 2 emitted by Katla by analyzing airborne gas emission measurements made in October 2016 and October 2017. These observations were combined with gas dispersion modeling to calculate the volcano’s total emissions. The results indicate that Katla emits 12–24 kilotons of CO 2 per day, which is more than double previous estimates of the emission rate of CO 2 from all volcanic and geothermal sources in Iceland combined (2.7–5.8 kilotons per day). Although the large CO 2 emission rate may suggest the presence of magma in the roots of Katla volcano, regular monitoring is needed to establish whether there is a link between the CO 2 emission and any future eruptions.

These findings suggest that subglacial volcanoes—the emissions of which have not been considered in much detail, historically—may be major emitters of carbon dioxide. Because of this, their contributions to the global volcanic CO 2 budget may have been underestimated. Future work will determine whether Katla is representative of other ice-covered volcanoes. (Geophysical Research Letters, https://doi.org/10.1029/2018GL079096, 2018)

—Terri Cook, Freelance Writer