The University of Manchester Research
Globally Significant CO2 Emissions From Katla, a
Subglacial Volcano in Iceland
DOI:
10.1029/2018GL079096
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Citation for published version (APA):
Ilyinskaya, E., Mobbs, S., Burton, R., Burton, M., Pardini, F., Pfeffer, M. A., Purvis, R., Lee, J., Bauguitte, S.,
Brooks, B., Colfescu, I., Petersen, G. N., Wellpott, A., & Bergsson, B. (2018). Globally Significant CO2 Emissions
From Katla, a Subglacial Volcano in Iceland. Geophysical Research Letters, 45(19), 10,332-10,341.
https://doi.org/10.1029/2018GL079096
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Geophysical Research Letters
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Download date:10. Aug. 2022
Globally Significant CO
2
Emissions From Katla, a Subglacial
Volcano in Iceland
Evgenia Ilyinskaya
1
, Stephen Mobbs
2
, Ralph Burton
2
, Mike Burton
3
, Federica Pardini
3
,
Melissa Anne Pfeffer
4
, Ruth Purvis
5
, James Lee
5
, Stéphane Bauguitte
6
, Barbara Brooks
2
,
Ioana Colfescu
2
, Gudrun Nina Petersen
4
, Axel Wellpott
6
, and Baldur Bergsson
4
1
School of Earth and Environment, University of Leeds, Leeds, UK,
2
National Centre for Atmospheric Science, Fairbairn
House, University of Leeds, Leeds, UK,
3
School of Earth and Environmental Sciences, Williamson Building, University of
Manchester, Manchester, UK,
4
Icelandic Meteorological Office, Reykjavik, Iceland,
5
National Centre for Atmospheric Science,
Innovation Way, University of York, York, UK,
6
Facility for Airborne Atmospheric Measurements, Cranfield University,
Cranfield, UK
Abstract Volcanoes are a key natural source of CO
2
, but global estimates of volcanic CO
2
flux are
predominantly based on measurements from a fraction of world’s actively degassing volcanoes. We
combine high-precision airborne measurements from 2016 and 2017 with atmospheric dispersion modeling
to quantify CO
2
emissions from Katla, a major subglacial volcanic caldera in Iceland that last erupted
100 years ago but has been undergoing significant unrest in recent decades. Katla’s sustained CO
2
flux,
12–24 kt/d, is up to an order of magnitude greater than previous estimates of total CO
2
release from Iceland’s
natural sources. Katla is one of the largest volcanic sources of CO
2
on the planet, contributing up to 4% of
global emissions from nonerupting volcanoes. Further measurements on subglacial volcanoes worldwide are
urgently required to establish if Katla is exceptional, or if there is a significant previously unrecognized
contribution to global CO
2
emissions from natural sources.
Plain Language Summary We discovered that Katla volcano in Iceland is a globally important
source of atmospheric carbon dioxide (CO
2
) in spite of being previously assumed to be a minor gas
emitter. Volcanoes are a key natural source of atmospheric CO
2
, but estimates of the total global amount of
CO
2
that volcanoes emit are based on only a small number of active volcanoes. Very few volcanoes that
are covered by glacial ice have been measured for gas emissions, probably because they tend to be difficult
to access and often do not have obvious degassing vents. Through high-precision airborne measurements
and atmospheric dispersion modeling, we show that Katla, a highly hazardous subglacial volcano that last
erupted 100 years ago, is one of the largest volcanic sources of CO
2
on Earth, releasing up to 4% of total
global volcanic emissions. This is significant in a context of a growing awareness that natural CO
2
sources
have to be more accurately quantified in climate assessments, and we recommend urgent investigations of
other subglacial volcanoes worldwide.
1. Introduction
Volcanoes are one of the most important natural sources of carbon dioxide (CO
2
), but empirical measure-
ments are available for only ~20% of major volcanic gas emission sources (reviewed in Burton et al.,
2013). Extrapolations of these measurements give an estimated a global subaerial geological emission rate
of ~1,500-kt/d CO
2
(Burton et al., 2013), which is ~2% of the anthropogenic emission rate of ~96,000 kt/d
(Friedlingstein et al., 2010). Updated measurements of degassing from arc volcanoes, for example, Aiuppa
et al. (2017), demonstrate that there are still large uncertainties. The quanti fication of CO
2
emissions from
previously unmeasured volcanic sources is therefore critical. While subglacial volcanoes are numerous, they
are grossly underrepresented in terms of volcanic gas measurements (3 out of the 33 volcanoes reviewed in
Burton et al., 2013), potentially because they often lack a visible gas plume and/or are more difficult to
access. In Iceland, gas measurements of CO
2
fluxes from the 32 active volcanic systems are sparse, and only
2 out of its 16 subglacial volcanoes (Grímsvötn and Eyjafjallajökull) have been measured (Table 1). The
reported fluxes CO
2
from nonerupting volcanoes are relatively low, with a maximum of 0.5 kt/d from
Grímsvötn (Ágústsdóttir & Brantley, 1994). Due to the low number of available measurements, the estimates
of total volcanic CO
2
flux in Iceland, 2.7–5.8 kt/d (Arnórsson & Gislason, 1994; Hernández et al., 2012;
ILYINSKAYA ET AL. 10,332
Geophysical Research Letters
RESEARCH LETTER
10.1029/2018GL079096
Key Points:
• Subglacial volcanoes are
underrepresented in terms of gas
monitoring, but we show that they
can be major emitters of CO
2
• Katla volcano is found to be one of
largest volcanic sources of CO
2
on
the planet, contributing up to 4% of
all nonerupting volcanoes
• High-precision airborne
measurements combined with
atmospheric modeling are a
powerful method to monitor poorly
accessible volcanoes
Supporting Information:
• Supporting Information S1
Correspondence to:
E. Ilyinskaya,
e.ilyinskaya@leeds.ac.uk
Citation:
Ilyinskaya, E., Mobbs, S., Burton, R.,
Burton, M., Pardini, F., Pfeffer, M. A., et al.
(2018). Globally significant CO
2
emissions from Katla, a subglacial
volcano in Iceland. Geophysical Research
Letters, 45, 10,332–10,341. https://doi.
org/10.1029/2018GL079096
Received 5 JUN 2018
Accepted 10 SEP 2018
Accepted article online 17 SEP 2018
Published online 7 OCT 2018
©2018. American Geophysical Union.
All Rights Reserved.
Pálmason et al., 1985), are poorly constrained and are likely too low (Ármannsson et al., 2005). The CO
2
flux
from Grímsvötn and Eyjafjallajökull were estimated by analyzing gas content dissolved in melt water accu-
mulating under the ice that likely underestimates the flux as CO
2
degasses very rapidly when the water is
depressurized. Our study is the first to report the CO
2
flux from a subglacial volcano in Iceland by measuring
the gas directly in the atmosphere.
Measurements of gas emissions from subglacial volcanic systems are important for understanding the under-
lying magma systems and, subsequently, for forecasting their eruptions, which are typically highly hazardous
due to the generation of ash and jökulhlaups (flash floods of glacial melt water). Recent studies across differ-
ent tectonic and geographical settings have demonstrated that increases in CO
2
output can precede erup-
tions by months to years, for example, at Redoubt in the Aleutians (Werner et al., 2012), Kilauea in Hawaii
(Poland et al., 2012), and Villarica in Chile (Aiuppa et al., 2017) but it is not yet known if this applies to any
of the Icelandic volcanoes.
1.1. Katla Volcanic System
The subglacial Katla volcanic system is one of the largest and most active ones in Iceland and has erupted 1–3
times per century since the settlement of Iceland 1,100 years ago (Larsen, 2000), and up to 6 times per
century in prehistoric times (Óladóttir et al., 2008). The current repose period is the longest one on record,
with the last confirmed eruption in 1918 C.E. Katla system consists of a central volcano (max altitude
1,500 m above sea level [asl]) and 80-km long fissure system. The central volcano is partially covered by
the vast 590-km
2
Mýrdalsjökull glacier, which is on average ~200 m thick, reaching 700-m thickness in
Table 1
CO
2
Flux (kt/d With Standard Error) From Katla Volcano Compared With Other Volcanoes in Iceland (kt/d, Minimum and Maximum Values) for Which Data Have
Been Published
Methods
Katla only
Volcano
Date (flight
number for Katla)
CO
2
flux
(kt/d) Approach
Number
of flight
tracks
CO
2
max
(ppm)
Altitude of
CO
2
plume
(m above
sea level)
Flux
calculation
method
Katla, western flank 18 Oct 2016 (B987) 19.6 ± 3.2 Airborne direct
observations
12 432 100–600 IDW
15 Simulation SMF
20 Oct 2016 (B989) 14.6 ± 3.2 Airborne direct
observations
13 413 840–1,200 IDW
11.9 ± 5.4 Gaussian
5–10 Simulation SMF
04 Oct 2017 (C060) 12.8 ± 1.3 Airborne direct
observations
3 432 890–970 IDW
5–10 Simulation SMF
Katla, central caldera 04 Oct 2017 (C060) 11.4 ± 2.7 Airborne direct
observations
7 415 380–650 IDW
5–10 Simulation SMF
Grímsvötn (Ágústsdóttir &
Brantley, 1994)
1954–1991 0.53 Subglacial melt water
from the caldera
Eyjafjallajökull (Gíslason, 2000) 2000 0.007–0.070 Subglacial melt water
from the caldera
Hekla (Gislason et al., 1992) 1988–1991 0.19 Gas dissolved in
groundwater
Hekla (Ilyinskaya et al., 2015) 2012–2013 0.044 Diffuse soil emissions
Reykjanes (Fridriksson et al., 2006,
Fridriksson et al., 2010)
2004–2009 0.012–0.019 Diffuse soil emissions
Hengill (Hernández et al., 2012) 2006 0.45 Diffuse soil emissions
Krafla (Ármannsson et al., 2007) 2004–2006 0.23 Diffuse soil emissions
Note. For Katla airborne measurements, the table shows the number of flight tracks that passed through the plume, the max CO
2
concentration measured on each
flight, and the altitude at which the CO
2
plume was found. Methods used for Katla CO
2
flux calculations: IDW, inverse distance weighting; Gaussian, fitting of a
Gaussian plume dispersion model; SMF, specified mass flux.
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ILYINSKAYA ET AL. 10,333
places. The central volcano contains a large, ice-filled caldera (110 km
2
, Figure 1). The eruptions within the
glaciated part are typically accompanied by tephra generation (bulk volume 0.02–2km
3
) and jökulhlaups
due to the magma-ice interaction (Larsen, 2000). The fissure swarm has produced large effusive basaltic
eruptions with lava volumes ≥18 km
3
(Thordarson et al., 2003). The size and proximity to populations of
Katla mean that the next eruption will likely have major local and possibly regional impacts, whether it
occurs within the glaciated or nonglaciated part of the system. Disturbance to international aviation by
ash is likely, even if the eruption is small in size (Biass et al., 2014).
Katla has had recurring geophysical unrest (seismicity and ground deformation), but the presence of glacial ice
makes the subsurface signals difficult to interpret. Previous studies have disagreed on whether unrest in differ-
ent parts of the system is caused by movements of magma (e.g., Soosalu et al., 2006; Sturkell et al., 2008), or
movements of glacial ice and its seasonal changes (e.g., Jónsdóttir et al., 2009; Spaans et al., 2015). Katla has
an annual average of ~300 earthquakes (Icelandic Met Office monitoring data) and periodic escalations of
up to a few thousand earthquakes. The majority of the earthquakes are at 0- to 5-km depth and <2.5 in mag-
nitude, with rarer occurrences of deeper (up to 20-km depth) and larger events (magnitude ≥ 4). There are two
main areas of geophysical unrest—within the caldera, and near the Goðabunga rise on the western part of the
central volcano (e.g., Jónsdóttir et al., 2009). The largest unrest periods since the last confirmed eruption have
occurred in 1955, 1999, and 2011 C.E. These periods had increased seismicity for months to years, increased
geothermal activity, and significant jökulhlaups that caused damage to infrastructure (Sturkell et al., 2008). It
has not been conclusively shown whether these episodes were associated with small subglacial eruptions.
Katla has no obvious degassing vents or areas, or visible gas plumes. Presence of subglacial activity is man-
ifested by 20 ice cauldrons, which are 10- to 50-m deep depressions in the glacier surface (Figure 1) caused by
geothermal melting of the glacier base. Geothermal melt water escapes through the glacier drainage systems
and is periodically flushed out from the outlet rivers (Figure 1). The number, size, and shape of Katla ’s ice caul-
drons and the activity of the outlet rivers change over time as the subglacial system is highly dynamic
(Guðmundsson et al., 2007), likely influenced both by the state of the volcanic system, and short- and long-term
variations in weather and climate. The smell of hydrogen sulfide (H
2
S) is commonly reported near the outlet
rivers, in particular during major and minor jökulhlaups (Bergsson, 2016). Conversely, there are no known reports
of visible gas plumes or gas smell in the vicinity of the ice cauldrons. A DOAS UV spectrometer installed on the
flanks of Katla since July 2017 has never detected sulfur dioxide (SO
2
)(IcelandicMetOffice monitoring data).
The only eruption of Katla where gas release has been estimated using the petrological method is the Eldgjá
flood basalt eruption 934–40 C.E. (Thordarson et al., 2003). Its current gas emission rate has not been
Figure 1. (a) Map and (b) photograph of Katla. The map shows the outlines of the subglacial caldera and locations of glacier river outlets (n = 8), ice cauldrons (n = 20),
Goðabunga rise (God), and Austmannsbunga rise (Aust). For model simulations of the gas source, the 20 ice cauldrons were combined into seven clusters (A–G).
The photograph, taken in November 2017, shows ice cauldrons 10 and 11 (K10 and K11, respectively) and Goðabunga rise. The cauldrons are several hundreds of
meters in diameter. The summit of the neighboring Eyjafjalljökull volcano is seen behind the Katla caldera.
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ILYINSKAYA ET AL. 10,334
quantified. Here we measured Katla’s gas emissions from an aircraft in October 2016 and October 2017.
This work builds on previous airborne measurements of CO
2
-rich plumes in other countries using in situ
sensors (Delgado et al., 1998; Doukas & McGee, 2007; Gerlach et al., 1999, 1997; Werner et al., 2006, 2008,
2012, 2013) and serves as a proof-of-concept for monitoring gas emissions from other Icelandic
volcanic systems.
2. Methods
2.1. Airborne Observations
The airborne observations were made using the atmospheric research aircraft (a highly modified BAE-146
aircraft) of the Facility for Airborne Atmospheric Measurements (http://www.faam.ac.uk). Details about the
instrumentation are in Text S1 in the supporting information. Flight paths were selected based on the preva-
lent wind direction in order to obtain downwind measurements of active volcanoes. Low-altitude cloud dis-
tribution and topography influenced the flight path planning for safety reasons. No flights traversing the
subglacial caldera were possible in 2016 or 2017 due to cloud cover over the glacier. The full tracks of the
flights reported in this paper are shown in Figure S1 in the supporting information.
2.2. Gas Source Modeling
In order to identify the source of the excess CO
2
, we applied two approaches. The first was to use back-
trajectories based on simple, low-resolution forecast wind fields; we used the Hybrid Single-Particle
Lagrangian Integrated Trajectory (HYSPLIT) Lagrangian dispersion model driven by GFS forecast winds (full
details about the model in Text S1). The second involved simulating the effects of a variety of plausible
sources within a very high resolution numerical weather prediction model (Weather Research and
Forecasting model [WRF]; full details about the model Text S1) and comparing the distribution of dispersed
gases within the model with the observations. HYSPLIT was run from numerous measurement points along
the aircraft track for 12 hr back in time in order to determine which trajectories coincided with likely sources.
The relatively long run time was chosen so that there were no initial constraints on the gas source within
Iceland (e.g., other volcanic systems and anthropogenic activities). Results of HYSPLIT are included in support-
ing information (Figure S2). For the sources in the WRF simulations we initially used the 32 volcanic systems in
Iceland (Figure S1) and ran the WRF model with CO
2
as a passive tracer. This confirmed unequivocally that the
source was in the region of Katla, leading us to make further measurement flights in 2017, and more detailed
simulations of the Katla region in order to identify the source of the gas. For these simulations, we specified as
potential sources 8 glacier outlet rivers from Katla, 20 ice cauldrons within the caldera that were combined
into 7 cauldron clusters (A–G), and Goðabunga rise (a location of long-term seismic activity on the volcano’s
west fl ank), giving a total of 16 sources (Figure 1). All sources were treated as a point release of a dense gas
with a specified emission rate (full details in Text S1). For most of the simulated cases, HYSPLIT and WRF indi-
cated the same source locations; notable differences are described in section 3.
2.3. Gas Emission Rate Calculations
As the exact location and number of the degassing sources within the large glacier (590 km
2
) overlying Katla
were unknown, the calculation of the CO
2
emission rate (“flux”) presented a challenge not previously
reported in studies using airborne measurements. We calculated the CO
2
flux using two independent
methods, direct calculations and model simulations. The model simulations provided an independent means
of mass flux estimation and hence a corroboration of the principal findings of the paper.
The first method was a direct calculation of the measured mass flux by integration of interpolations of the
measured wind and CO
2
concentration fields (we used two different interpolation techniques). The interpo-
lation techniques were inverse distance weighting (IDW in Table 1) for all of the flights and fitting of a
Gaussian plume dispersion model (Gaussian in Table 1). The Gaussian method provided an independent flux
estimate in addition to IDW. Several restrictions on its use (the requirement for a Gaussian plume, the need
for wind speeds above 5 m/s, and the wind direction and flight track alignment to be perpendicular) meant
that the Gaussian method could only be used for flight B989 (Table 1). It is included here for completeness.
See Text S1 for further details about both interpolation techniques.
Motivated by the large emission rates given by IDW and Gaussian calculations (11–20 kt/d of CO
2
, Table 1), we
designed the second method of estimating emission rates using a state-of-the-art numerical model, WRF (the
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ILYINSKAYA ET AL. 10,335