Exception or Rule? The Case of Katla, One of Iceland’s Subglacial Volcanoes

Katla Volcano in Iceland on GlacierHub
Grasslands in the foreground, with Katla covered by clouds in the background (Source: Inga Vitola/Flickr).

A recent study in Geophysical Research Letters about Katla, a subglacial volcano in Iceland, revealed that Katla emits CO2 at a globally important level. Previously, Katla’s CO2 emissions were assumed to be negligible on a global scale.

In this study, conducted by Evgenia Ilyinskaya, a volcanologist at the University of Leeds, and her associate researchers, airborne measurements were carried out using gas sensors to obtain CO2 source and emission rates for Katla. In addition, the researchers used atmospheric dispersion modeling to identify the source of gas emissions and calculate gas emission rates.

A CO2 emission rate of 12-24 kilotons per day is considered significant on a global level. Ilyinskaya and coauthors’ measurements taken on the western side of Katla indicated significant CO2 flux levels in both 2016 and 2017. Also in 2017, the researchers identified another significant source of CO2 emissions, Katla’s central caldera.

Katla 1918 eruption on GlacierHub
Katla’s last eruption was in 1918 (Source: Creative Commons).

Emissions estimates that are both accurate and representative for subglacial volcanoes are challenging to obtain. According to the study, this is because these volcanoes are hard to access and “lack a visible gas plume.” The researchers noted that CO2 flux measurements are available for just two of Iceland’s 16 subglacial volcanoes, and these measurements indicate only modest emissions estimates. Further, these measurements were obtained by analyzing gas content dissolved in water, a method which likely underestimates CO2 flux. Ilyinskaya and her coauthors used a more precise estimate in this study than previous methods, such as the one discussed above.

Total CO2 emissions from passively degassing subaerial volcanoes are currently estimated at 1,500 kt/d, and CO2 flux is currently estimated at 540 kt/d. The results Ilyinskaya and the other researchers found indicate that Katla’s CO2 emissions would account for 2-4 percent of that total. However, they stipulated that subglacial volcanoes were underrepresented in the data collected to create this estimate. Measurements from 33 volcanoes were extrapolated to cover CO2 emissions of 150 volcanoes, but only three of the 33 were subglacial volcanoes.

Myrdalsjokull glacier covering Katla volcano on GlacierHub
View of the Myrdalsjokull glacier, which covers Katla (Source: Zaldun Urdina/Flickr).

Regarding Katla, Ilyinskaya and coauthors identified two possible implications of this information. First, Katla could be an exceptional emitter. Katla’s large size and recent heightened seismic activity make this possibility more plausible. But the researchers pointed out that measurements must be conducted at other subglacial volcanoes before this possibility can be corroborated.

A second possibility is that Katla’s CO2 emissions are representative of what other subglacial volcanoes emit. If this is true, estimates of CO2 emissions from subglacial volcanoes are grossly underestimated at present. Once measured properly, these volcanoes would make a much more significant contribution to global volcanic CO2 emissions. Currently, subaerial volcano CO2 emissions are assumed to be just 2 percent of anthropogenic CO2 emissions totals, but this could change with improved measurement practices.

Myrdalsjokull glacier above Katla volcano on GlacierHub
Atop the Myrdalsjokull glacier, with Katla beneath it (Source: Adam Russell/Flickr).

In the context of climate change, it is important that CO2 emissions from natural sources are adequately quantified alongside anthropogenic sources. As the results of this study suggest, subglacial volcanoes such as Katla could have emissions contributions that are more significant than originally thought. Ilyinskaya and her fellow researchers stressed the vital importance of conducting similar measurements at other subglacial volcanoes to ensure that their CO2 emissions are properly quantified in global estimates.

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