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All content in this area was uploaded by Robert G Bingham on Jul 10, 2017
Content may be subject to copyright.
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Content may be subject to copyright.
A new volcanic province: an inventory of subglacial
volcanoes in West Antarctica
MAXIMILLIAN VAN WYK DE VRIES*, ROBERT G. BINGHAM & ANDREW S. HEIN
School of GeoSciences, University of Edinburgh, Drummond Street, Edinburgh EH8 9XP, UK
*Correspondence: gmaxvwdv@gmail.com
Abstract: The West Antarctic Ice Sheet overlies the West Antarctic Rift System about which, due
to the comprehensive ice cover, we have only limited and sporadic knowledge of volcanic activity
and its extent. Improving our understanding of subglacial volcanic activity across the province is
important both for helping to constrain how volcanism and rifting may have influenced ice-sheet
growth and decay over previous glacial cycles, and in light of concerns over whether enhanced geo-
thermal heat fluxes and subglacial melting may contribute to instability of the West Antarctic Ice
Sheet. Here, we use ice-sheet bed-elevation data to locate individual conical edifices protruding
upwards into the ice across West Antarctica, and we propose that these edifices represent subglacial
volcanoes. We used aeromagnetic, aerogravity, satellite imagery and databases of confirmed volca-
noes to support this interpretation. The overall result presented here constitutes a first inventory of
West Antarctica’s subglacial volcanism. We identified 138 volcanoes, 91 of which have not previ-
ously been identified, and which are widely distributed throughout the deep basins of West Antarc-
tica, but are especially concentrated and orientated along the >3000 km central axis of the West
Antarctic Rift System.
Gold Open Access: This article is published under the terms of the CC-BY 3.0 license.
West Antarctica hosts one of the most extensive
regions of stretched continental crust on the Earth,
comparable in dimensions and setting to the East
African Rift System and the western USA’s Basin
and Range Province (Fig. 1) (e.g. see Behrendt
et al. 1991; Dalziel 2006; Kalberg et al. 2015). Im-
proved knowledge of the region’s geological struc-
ture is important because it provides the template
over which the West Antarctic Ice Sheet (WAIS)
has waxed and waned over multiple glaciations
(Naish et al. 2009; Pollard & DeConto 2009; Jamie-
son et al. 2010), and this provides a first-order
control on the spatial configuration of the WAIS’
ice dynamics (Studinger et al. 2001; Jordan et al.
2010, Bingham et al. 2012). The subglacial region
today is characterized by an extensive and complex
network of rifts, which is likely to have initiated at
various times since the Cenozoic (Fitzgerald 2002;
Dalziel 2006; Siddoway 2008; Spiegel et al. 2016),
and which in some locations may still be active (Beh-
rendt, et al. 1998; LeMasurier 2008; Lough et al.
2013; Schroeder et al. 2014). Collectively, this series
of rifts beneath the WAIS has been termed the West
Antarctic Rift System (WARS), and is bounded by
the Transantarctic Mountains to the south (Fig. 1).
In other major rift systems of the world, rift
interiors with thin, stretched crust are associated
with considerable volcanism (e.g. Siebert & Simkin
2002). However, in West Antarctica, only a few
studies have identified subglacial volcanoes and/or
volcanic activity (e.g. Blankenship et al. 1993;
Behrendt et al. 1998, 2002; Corr & Vaughan 2008;
Lough et al. 2013), with the ice cover having deterred
a comprehensive identification of the full spread
of volcanoes throughout the WARS. Improving on
this limited impression of the WARS’distribution
of volcanism is important for several reasons. Firstly,
characterizing the geographical spread of volcanic
activity across the WARS can complement wider
efforts to understand the main controls on rift vol-
canism throughout the globe (Ellis & King 1991;
Ebinger et al. 2010). Secondly, volcanic edifices,
by forming ‘protuberances’at the subglacial inter-
face, contribute towards the macroscale roughness
of ice-sheet beds, which in turn forms a first-order
influence on ice flow (cf. Bingham & Siegert 2009).
Thirdly, volcanism affects geothermal heat flow
and, hence, basal melting, potentially also impacting
upon ice dynamics (Blankenship et al. 1993; Vogel
et al. 2006). Fourthly, it has been argued that sub-
glacial volcanic sequences can be used to recover
palaeoenvironmental information from Quaternary
glaciations, such as palaeo-ice thickness and thermal
regime (e.g. Smellie 2008; Smellie & Edwards 2016).
In this contribution, we present a new regional-
scale assessment of the likely locations of volca-
noes in West Antarctica based on a morphometric
(or shape) analysis of West Antarctica’s ice-bed
topography. Volcano shape depends on three prin-
cipal factors: (1) the composition of the magma
From:SIEGERT, M. J., JAMIESON,S.S.R.&WHITE, D. A. (eds) Exploration of Subsurface Antarctica: Uncovering
Past Changes and Modern Processes. Geological Society, London, Special Publications, 461,
https://doi.org/10.1144/SP461.7
© 2017 The Author(s). Published by The Geological Society of London.
Publishing disclaimer: www.geolsoc.org.uk/pub_ethics
erupted; (2) the environment into which the magma
has been erupted; and (3) the erosional regime to
which the volcano has been subjected since eruption
(Hickson 2000; Grosse et al. 2014; Pedersen &
Grosse 2014). Magma composition in large conti-
nental rifts generally has low–medium silica content
with some more alkaline eruptions (Ebinger et al.
2013). In West Antarctica, where most knowledge
of volcanoes is derived from subaerial outcrops in
Marie Byrd Land, volcanoes are composed of inter-
mediate alkaline lavas erupted onto a basaltic shield,
with smaller instances being composed entirely of
basalt and a few more evolved compositions (tra-
chyte, rhyolite: LeMasurier et al. 1990; LeMasurier
2013). We therefore consider it likely that many
structures in the WARS are also basaltic. Regard-
ing the environment of eruption, subaerial basaltic
eruptions typically produce broad shield-type cones
protruding upwards from the surrounding landscape
(Grosse et al. 2014). Under subglacial conditions,
monogenetic volcanoes often form steeper-sided,
flat-topped structures made up of phreatomagmatic
deposits draped on pillow lava cores and overlain
by lava-fed deltas known as tuyas (Hickson 2000;
Pedersen & Grosse 2014; Smellie & Edwards
2016). Larger, polygenetic volcanic structures give
rise to a range of morphometries reflecting the mul-
tiple events that cause their formation, but many
also have overall ‘conical’structures similar to stra-
tovolcanoes or shield volcanoes (Grosse et al. 2014;
Smellie & Edwards 2016).
In the WARS, the macrogeomorphology is
dominated by elongate landforms resulting from
geological rifting and subglacial erosion. We
Fig. 1. (a) Location of the main components of the West Antarctic Rift System and confirmed volcanoes (red circles:
after LeMasurier et al. 1990; Smellie & Edwards 2016). (b) Location of Holocene volcanoes (red circles) in the
Ethiopia/Kenya branch of the East African Rift (red shaded area). The majority of this activity is aligned along the
rift axis with occasional flank volcanism. Data from Siebert & Simkin (2002) and Global Volcanism Program (2013).
M. VAN WYK DE VRIES ET AL.
propose here that, in this setting, the most reasonable
explanation for any ‘cones’being present is that they
must be volcanic in origin. We define ‘cones’as any
features that have a low length/width ratio viewed
from above; hence, for this study, we include cones
even with very low slope angles. Thus, we use
cones in this subglacial landscape as diagnostic of
the presence of volcanoes. We note that identifying
cones alone will by no means identify all volcanism
in the WARS. For example, volcanic fissures erup-
tions, a likely feature of rift volcanism, will yield
ridge forms, or ‘tindars’(Smellie & Edwards 2016),
rather than cones. Moreover, in the wet basal envi-
ronment of the WAIS, the older the cone the more
likely it will have lost its conical form from sub-
glacial erosion. Therefore, cones present today are
likely to be relatively young –although we cannot
use our method to distinguish whether or not the
features are volcanically active.
Methods
Our underpinning methodology was to identify
cones that protrude upwards from a digital elevation
model (DEM) of Antarctica’s subglacial topography,
and to assess the likelihood that each cone is a vol-
canic edifice. We undertook our analysis on the
Bedmap2 DEM (Fretwell et al. 2013) domain
encompassed by the WARS, which incorporates all
of West Antarctica, the Ross Ice Shelf and the Trans-
antarctic Mountains fringing East Antarctica that
flank the WARS (Elliott 2013). Importantly, while
Bedmap2 represents the state-of-the-art knowledge
of West Antarctica’s subglacial landscape, it is
derived from variable data coverage, the vast major-
ity of the data being sourced from airborne radar-
sounding acquired along one-dimensional tracks.
Along the radar tracks the horizontal spacing of
bed-elevation data points can reach a few metres,
but between tracks the spacing is often several kilo-
metres. The DEM itself is presented as a 1 km
gridded product, although the raw data were initially
gridded at 5 km (Fretwell et al. 2013). Therefore,
while the DEM cannot capture the fine-scale topog-
raphy now routinely acquired by satellite and air-
borne altimetry, and which has been exploited for
multiple morphometric analyses (e.g. Pedersen &
Grosse 2014; Lindback & Pettersson 2015; Ely
et al. 2016), it nevertheless presents a workable start-
ing point for identifying volcanic edifices. We con-
sider how some of the DEM’s limitations can be
overcome in our analysis below.
We defined a cone as an upwards protuberance
from the DEM whose elongation ratio (width
v. length) <1.5. Over the domain, but excluding non-
grounded ice (primarily the Ross Ice Shelf) where
the subglacial topography is poorly characterized,
we first extracted cones protruding at least 100 m
from the surrounding terrain. The bed-elevation un-
certainties within the DEM prevent reliable identifi-
cation of smaller edifices. Elevation profiles across
each cone were then extracted from Bedmap2 at
multiple angles with respect to the current ice-flow
direction (taken from Rignot et al. 2011). Where
radar profiles directly traversed a cone, we further
cross-checked the shape of the bed directly from
the raw data. This is part of our procedure for
accounting for any artefacts in Bedmap2, which
involves corroborating our identified volcanoes
with auxiliary datasets. To assess the likelihood
that the Bedmap2-extracted cones were (a) not
merely interpolation-induced artefacts and (b) likely
represent volcanoes, we implemented a scheme
wherein points were awarded where auxiliary data
ground-truthed the bed DEM and/or gave greater
confidence in a volcanic interpretation. The assess-
ment criteria are as follows, with points awarded
for each and data-source references given in Table 1:
(1) Whether a cone is found within 5 km of the
nearest raw ice-thickness data.
(2) Whether a cone is overlain by an upwards-
protruding prominence in the surface of the
ice draped over it. This criterion takes advan-
tage of the fact that, under the right balance
between ice thickness and ice-flow speed, sub-
glacial topographical prominences can be
expressed at the ice surface (e.g. De Rydt
et al. 2013).
(3) Whether a cone is discernible as a feature at the
ice surface in visible satellite imagery. Various
recent studies have demonstrated that subgla-
cial features can be outlined by visible expres-
sions in surface imagery (e.g. Ross et al. 2014;
Chang et al. 2015; Jamieson et al. 2016).
(4) Whether a cone is associated with a clear con-
centric magnetic anomaly. This depends on
the potential volcano having a pillow-lava
core, rather than being composed solely of
tuff. This is consistent with the thickness
of ice overlying the cones and the erodibility
of tuff/tephra deposits. Strong geomagnetic
anomalies have long been suggested as evi-
dence of subglacial volcanism in the WARS
(e.g. Behrendt et al. 1998, 2002).
(5) Whether a cone is associated with a concentric
free-air and/or Bouguer anomaly.
Each cone was assigned a final confidence factor
value of between 0 and 5 by summing up the points
from the five indicators described above (Table 1).
Results
Our morphometric analysis of subglacial West Ant-
arctica recovers a total of 178 conical structures
SUBGLACIAL VOLCANOES IN WEST ANTARCTICA
Table 1. Classification scheme used in assessing confidence that a cone extracted from Bedmap2 (Fretwell et al. 2013) can be interpreted as a volcano
Confidence assessment criterion Dataset/source Confidence score
0 0.5 1
(1) Distance to nearest raw ice-thickness
measurement Figure 3 in Fretwell et al. (2013) >15 km 5–15 km <5 km
(2) Expression in ice-surface DEM overlying
identified subglacial cone Bedmap2 ice-surface DEM: Fretwell
et al. (2013) No expression Associated but off-
centre anomaly Direct overlying
anomaly
(3) Expression in MODIS imagery of the ice
surface overlying the identified
subglacial cone
MODIS Mosaic of Antarctica:
Scambos et al. (2007) No expression Weak expression Clear expression
(4) Magnetic anomaly data ADMAP: Kim et al. (2007) No anomaly Weak anomaly Clear anomaly
(5) Gravity anomaly data Studinger et al. (2002); Damiani et al.
(2014); Scheinert et al. (2016) No anomaly Weak anomaly Clear anomaly
Full scores are given in Table 2.
M. VAN WYK DE VRIES ET AL.
located beneath the grounded WAIS and along the
WARS (Fig. 2; Table 2). Of these, 80% are located
within 15 km of the raw ice-thickness data measure-
ments (Fretwell et al. 2013) and 30% are identified
from the DEM at sites where volcanoes, either active
or inactive, have previously been identified (LeMa-
surier et al. 1990; LeMasurier 2013; Wardell et al.
2014). Many cones were crossed directly by radio-
echo-sounding flightlines, allowing verification of
their profiles (e.g. Fig. 3) –thus, while there is, inev-
itably, some smoothing in the Bedmap2 interpola-
tion, the major features of interest are largely
captured. One of our confidence tests for volcanic
interpretation of cones also takes into account prox-
imity to the raw ice-thickness measurements, further
discounting DEM interpolation as a disproportionate
influence on the results.
The identified cones range in height between 100
and 3850 m, with an average relief of 621 m, includ-
ing 29 structures >1 km tall that are mainly situated
in Marie Byrd Land and the central rift zone. The
basal diameter of the cones ranges between 4.5 and
58.5 km, with an average diameter of 21.3 km.
Most of the cones have good basal symmetry, with
63% of the long to short axis ratios being <1.2.
Table 3 presents a more in-depth statistical analysis
of the morphology of these features and compares
them to a global volcanic database (Grosse et al.
2014). Figure 4 shows 1:1 cross-sections of three
of the newly identified cones along with three prom-
inent shield volcanoes for comparison.
Seventy-eight per cent of the cones achieve a
confidence score (from our five-point scheme) >3,
and we therefore consider it reasonable to interpret
these 138 cones henceforth as subglacial volcanoes.
(We note that 98% of the 47 previously identified
volcanoes in West Antarctica (visible at the surface
and listed by LeMasurier et al. 1990) achieved a con-
fidence score >3.) The volcanoes are distributed
across subglacial West Antarctica, but are especially
concentrated in Marie Byrd Land (one cone per 11
200 ± 600 km
2
); and along a central belt roughly
corresponding to the rift’s central sinuous ridge
(Behrendt et al. 1998), with one cone per 7800 ±
400 km
2
. For comparison, the overall volcanic edi-
fice concentration along the East African Rift is
roughly one volcano per 7200 km
2
, rising to one vol-
cano per 2000 km
2
in the densest regions (Global
Volcanism Program 2013).
Discussion
Morphometry as a tool for identifying
subglacial volcanoes
We consider here three main implications that
arise from our findings. Firstly, our approach
demonstrates that it is possible to use morphometry
on Antarctica’s subglacial DEM, crucially together
with relevant auxiliary information, to identify
potential subglacial volcanic edifices beneath West
Antarctica. Secondly, it highlights that subglacial
West Antarctica –and, in essence, the WARS –
comprises one of the world’s largest volcanic prov-
inces (cf. LeMasurier et al. 1990; Smellie & Edwards
2016), and it provides basic metrics concerning the
locations and dimensions of the main volcanic
zones. Thirdly, it serves to highlight the wide spread
of subglacial volcanism beneath the WAIS, which
may impact upon its response to external forcing
through affecting coupling of the ice to its bed, and
may have implications for future volcanic activity
as ice cover thins.
To our knowledge, our study here is the first to
use morphometry to identify volcanic edifices on
the continental scale beneath Antarctica. The extent
of this volcanism has only previously been inferred
from geophysical studies (Behrendt et al. 2002).
Morphometry has been used widely elsewhere in
volcanology: for example, to catalogue volcanic
parameters, such as height, base width and crater
width (e.g. McKnight & Williams 1997; Pedersen
& Grosse 2014), or to reconstruct eroded volcanic
edifices (Favalli et al. 2014). It has been applied to
resolve volcanic characteristics in subaerial, subma-
rine (e.g. Stretch et al. 2006) and extraterrestrial (e.g.
Broz et al. 2015) settings. However, in all such cases
volcanic morphometry has been applied to DEMs
assembled from evenly distributed elevation mea-
surements derived from sensors viewing unobscured
surfaces. For subglacial Antarctica, having confi-
dence that the subglacial DEM that has been con-
structed from non-random elevation measurements
has sufficient resolution for the applied interpretation
is key. Recent years have witnessed increasing glaci-
ological recovery of subglacial information from
morphometry. For example, seeding centres for gla-
ciation of the WAIS (Ross et al. 2014) and the East
Antarctic Ice Sheet (Bo et al. 2009; Rose et al. 2013)
have been identified by the preponderance of sharp
peaks, cirque-like features and closely spaced val-
leys relative to other parts of the subglacial land-
scape. Elsewhere, landscapes of ‘selective linear
erosion’, diagnostic of former dynamism in now-
stable regions of ice, have been detected from the
presence of significant linear incisions (troughs)
into otherwise flat higher surfaces (plateaux)
(Young et al. 2011; Jamieson et al. 2014; Rose
et al. 2014). All of these studies have in common
that they have closely considered auxiliary evidence
to the morphometry and, hence, have not relied on
the surface shape alone in coming to interpretations
concerning landscape formation. We have shown
here that such a combined approach is also valid
for locating and mapping numerous previously
SUBGLACIAL VOLCANOES IN WEST ANTARCTICA
Fig. 2. Location map of conical edifices (circles) identified from Bedmap2 (greyscale background) across the West Antarctic Rift System. The data are tabulated in Table 2. The
circle colour represents the confidence factor used to assess the likelihood of cones being subglacial volcanoes, and the circle size is proportional to the cone’s basal diameter.
Circles with black rims represent volcanoes that have been confirmed in other studies (LeMasurier et al. 1990; Smellie & Edwards 2016), generally those that have tips which
protrude above the ice surface.
M. VAN WYK DE VRIES ET AL.
Table 2. Tabulation of subglacial cone coordinates, dimensions and volcanic-interpretation confidence factors (see Table 1)
Number Height
(m) Average
diameter
(km)
Elongation
ratio Volume
(km
3
)Latitude Longitude Volcano confidence factor Previously
identified
12345Sum
1 800 26 1.08 106 −74.00 −80.38 0.5 1 1 0.5 0.5 3.5 Yes
2 600 14 1.15 23 −75.60 −81.60 1 1 0 1 0.5 3.5 No
3 300 7.5 1.14 3 −76.13 −83.53 1 0.5 0 1 0.5 3 No
4 300 18.5 1.18 20 −76.80 −85.27 1 0 0 1 0.5 2.5 No
5 650 24.5 1.04 77 −74.47 −86.40 0.5 0.5 0.5 0.5 0.5 2.5 No
6 350 17.5 1.19 21 −76.74 −87.50 1 0 0.5 1 0.5 3 No
7 250 17 1.27 14 −76.97 −87.89 1 0 0 1 0.5 2.5 No
8 950 29 1.07 157 −77.37 −88.10 1 0 1 0.5 0.5 3 No
9 300 19.5 1.05 22 −77.40 −89.38 1 0.5 1 0.5 0.5 3.5 No
10 350 15.5 1.07 17 −77.32 −90.34 1 0.5 1 0.5 0.5 3.5 No
11 600 32.5 1.17 124 −74.27 −89.58 0.5 0.5 0 0.5 0.5 2 No
12 550 36 1.06 140 −74.07 −91.18 0.5 0 1 0.5 0.5 2.5 No
13 450 27.5 1.20 67 −72.90 −91.30 0 1 0.5 0.5 0.5 2.5 No
14 500 22.5 1.25 50 −74.05 −92.90 1 1 0.5 1 0.5 4 No
15 1400 22.5 1.25 139 −73.73 −93.68 0.5 1 1 1 0.5 4 Yes
16 1450 19.5 1.29 108 −70.03 −125.97 1 1 1 1 0.5 4.5 Yes
17 1300 27 1.25 186 −73.89 −94.64 0.5 1 1 1 0.5 4 Yes
18 400 20 1.11 31 −78.03 −92.95 1 1 0 0.5 0.5 3 No
19 325 18.5 1.18 22 −78.21 −93.20 1 1 0 0.5 0.5 3 No
20 200 9.5 1.11 4 −78.20 −93.82 1 0.5 0 0.5 0.5 2.5 No
21 600 20.5 1.16 49 −78.15 −94.62 1 1 0 0.5 0.5 3 No
22 375 18.5 1.06 25 −78.68 −95.65 1 0 0.5 0.5 0.5 2.5 No
23 250 19 1.11 18 −78.52 −96.16 1 0.5 1 1 0.5 4 No
24 700 26.5 1.30 96 −78.13 −96.36 1 0.5 0 0.5 0.5 2.5 No
25 450 22.5 1.25 45 −78.00 −97.16 1 1 0 0.5 0.5 3 No
26 250 13.5 1.25 9 −78.67 −97.68 1 1 0 1 1 4 No
27 500 24.5 1.13 59 −74.97 −96.54 0.5 1 1 1 0.5 4 No
28 400 16.5 1.36 21 −74.86 −97.42 1 1 0 1 0.5 3.5 No
29 550 16 1.13 28 −75.07 −99.54 1 1 1 1 0.5 4.5 Yes
30 820 20.5 1.16 68 −74.73 −99.04 1 1 1 1 0.5 4.5 Yes
31 650 29 1.15 107 −75.07 −99.54 0.5 1 1 1 0.5 4 Yes
32 750 31 1.07 141 −74.03 −98.83 0.5 0 0 1 0.5 2 No
33 950 26 1.17 126 −74.21 −100.19 1 1 1 0.5 0.5 4 No
34 900 30 1.14 159 −74.51 −99.94 1 0 1 0.5 0.5 3 Yes
(Continued)
SUBGLACIAL VOLCANOES IN WEST ANTARCTICA
Table 2. Tabulation of subglacial cone coordinates, dimensions and volcanic-interpretation confidence factors (see Table 1) (Continued )
Number Height
(m) Average
diameter
(km)
Elongation
ratio Volume
(km
3
)Latitude Longitude Volcano confidence factor Previously
identified
12345Sum
35 300 15.5 1.21 14 −74.72 −100.09 1 0 1 0.5 0.5 3 No
36 325 11.5 1.30 8 −75.24 −96.95 1 1 1 0.5 0.5 4 No
37 500 34 1.13 113 −72.19 −97.70 0 1 1 1 0.5 3.5 Yes
38 1025 40.5 1.19 330 −72.54 −97.61 0 0 0.5 1 0.5 2 Yes
39 400 20.5 1.16 33 −72.51 −98.38 0 1 1 1 0.5 3.5 Yes
40 525 28 1.15 81 −72.42 −99.23 0.5 1 1 1 0.5 4 Yes
41 325 20.5 1.16 27 −72.47 −99.94 0 1 1 1 0.5 3.5 Yes
42 550 33.5 1.16 121 −72.32 −101.07 0.5 1 1 0.5 0.5 3.5 Yes
43 225 11.5 1.30 6 −73.87 −103.30 0 0.5 1 1 0.5 3 No
44 675 26.5 1.12 93 −75.45 −103.29 1 1 1 0.5 1 4.5 No
45 350 9.5 1.38 6 −78.41 −101.96 1 0 0 0.5 0.5 2 No
46 575 23 1.19 60 −79.65 −101.80 1 0.5 0 1 0.5 3 No
47 275 12 1.18 8 −80.03 −101.60 1 0.5 0 0.5 0 2 No
48 250 13 1.17 8 −80.15 −101.46 1 0.5 0 0.5 0 2 No
49 175 21.5 1.15 16 −80.17 −103.39 0.5 0.5 0.5 0.5 2 No
50 325 22 1.20 31 −78.87 −102.91 1 0.5 0.5 0.5 0 2.5 No
51 225 27 1.16 32 −80.40 −105.61 0.5 1 0 1 0.5 3 No
52 1175 23 1.19 122 −78.74 −104.24 1 1 1 0.5 1 4.5 No
53 125 15 1.14 6 −77.61 −103.56 1 0.5 0.5 0.5 1 3.5 No
54 225 11.5 1.30 6 −82.05 −111.42 1 0.5 1 1 0.5 4 No
55 175 23 1.19 18 −77.43 −105.77 1 1 1 1 0.5 4.5 No
56 150 9 1.25 2 −77.70 −74.55 1 0.5 0 0.5 0 2 No
57 275 13.5 1.25 10 −78.46 −107.77 1 0.5 1 0.5 0 3 No
58 175 11 1.44 4 −76.72 −106.61 1 1 1 1 0.5 4.5 No
59 150 12.5 1.27 5 −76.87 −106.38 1 1 1 1 1 5 No
60 1200 33.5 1.16 264 −79.15 −111.05 1 0 1 1 1 4 No
61 450 14.5 1.23 19 −79.60 −111.45 1 0 0 1 0.5 2.5 No
62 200 6 1.40 1 −80.42 −114.00 1 0.5 0 1 0 2.5 No
63 425 10 1.22 8 −75.22 −106.92 0 0.5 0.5 0.5 0.5 2 No
64 450 18 1.12 29 −75.71 −108.40 1 0 1 0.5 1 3.5 No
65 375 14.5 1.23 15 −76.11 −107.68 1 0 1 0.5 1 3.5 No
66 400 17 1.27 23 −76.38 −109.78 1 0.5 1 1 1 4.5 No
67 325 10.5 1.33 7 −74.60 −110.62 0.5 1 1 0.5 0.5 3.5 No
68 400 19 1.24 28 −74.81 −110.57 1 1 1 0.5 0.5 4 No
69 350 14 1.33 13 −75.00 −110.43 0.5 1 1 0.5 0.5 3.5 No
70 750 30 1.14 132 −74.89 −111.26 1 1 1 0.5 0.5 4 No
71 2300 51.5 1.15 1197 −75.60 −110.70 1 1 1 0.5 1 4.5 Yes
M. VAN WYK DE VRIES ET AL.
72 3200 58.5 1.13 2149 −76.52 −112.02 1 1 1 1 1 5 Yes
73 250 15.5 1.07 12 −77.21 −111.92 1 0 0.5 0.5 1 3 No
74 1025 36 1.00 261 −77.72 −112.64 1 0.5 1 1 0.5 4 No
75 300 16 1.13 15 −77.67 −114.04 1 0.5 1 0.5 1 4 No
76 625 26 1.17 83 −77.80 −115.00 1 1 1 0.5 1 4.5 No
77 650 12 1.18 18 −78.08 −115.37 1 0 0.5 0.5 0 2 No
78 400 10.5 1.33 9 −78.11 −115.93 1 1 0.5 0.5 0 3 No
79 350 13.5 1.25 13 −78.93 −115.69 1 0 0.5 1 1 3.5 No
80 325 20.5 1.28 27 −79.68 −113.53 1 1 0 1 1 4 No
81 200 6 1.40 1 −80.38 −115.11 1 0.5 0 1 1 3.5 No
82 125 4.5 1.25 0 −80.38 −115.11 1 0.5 0 1 1 3.5 No
83 150 10 1.22 3 −80.34 −116.40 1 1 0 1 1 4 No
84 1750 31.5 1.10 341 −80.30 −117.49 1 1 1 1 1 5 No
85 800 20 1.22 63 −80.37 −118.90 1 0.5 1 1 1 4.5 No
86 750 18.5 1.31 50 −80.73 −117.56 1 1 1 1 1 5 No
87 150 10.5 1.33 3 −80.81 −118.65 1 1 0 1 1 4 No
88 225 13 1.36 7 −80.87 −120.70 1 0 0 1 1 3 No
89 100 9 1.25 2 −80.27 −117.62 1 1 0 0 0 2 No
90 150 10.5 1.33 3 −80.41 −118.65 1 1 1 1 0.5 4.5 No
91 550 29.5 1.19 94 −80.62 −120.12 1 0.5 1 1 1 4.5 No
92 250 12.5 1.27 8 −79.96 −120.20 1 1 1 1 0.5 4.5 No
93 150 10 1.22 3 −79.24 −119.18 1 1 0 1 0 3 No
94 100 8 1.00 1 −79.37 −119.00 1 1 0 0 0 2 No
95 125 7.5 1.14 1 −79.78 −115.18 1 0 0 0.5 0.5 2 No
96 100 8.5 1.13 1 −78.46 −120.28 1 0 0.5 1 1 3.5 No
97 1000 28.5 1.19 159 −77.54 −118.28 0.5 1 0.5 0.5 0.5 3 No
98 2600 49.5 1.11 1250 −76.96 −117.78 1 1 1 0.5 1 4.5 Yes
99 3850 58 1.11 2542 −76.07 −115.94 0.5 1 1 1 1 4.5 No
100 1350 27.5 1.29 200 −76.73 −125.76 1 1 1 1 0.5 4.5 Yes
101 1100 21 1.21 95 −76.93 −125.73 1 1 1 1 0.5 4.5 Yes
102 1050 20 1.11 82 −77.11 −125.89 0.5 1 1 0.5 0.5 3.5 Yes
103 2400 39 1.17 716 −77.32 −125.97 1 1 1 0.5 0.5 4 Yes
104 1100 22 1.20 104 −77.46 −126.85 0.5 1 1 0.5 0.5 3.5 Yes
105 550 29 1.15 91 −79.24 −128.12 0.5 0 1 0.5 0.5 2.5 No
106 600 17 1.27 34 −81.34 −125.35 1 0.5 0 1 1 3.5 No
107 150 11.5 1.30 4 −82.36 −127.50 1 1 1 1 1 5 No
108 600 25.5 1.13 77 −83.98 −133.02 1 0 1 0.5 0.5 3 No
109 500 39 1.11 149 −84.31 −131.87 1 0.5 1 0.5 0.5 3.5 No
110 125 11.5 1.30 3 −81.82 −128.45 1 0.5 1 1 1 4.5 No
111 100 8 1.29 1 −81.20 −129.58 1 1 0 0 0 2 No
112 550 42 1.15 190 −81.62 −130.38 1 0 1 1 1 4 No
(Continued)
SUBGLACIAL VOLCANOES IN WEST ANTARCTICA
Table 2. Tabulation of subglacial cone coordinates, dimensions and volcanic-interpretation confidence factors (see Table 1) (Continued )
Number Height
(m) Average
diameter
(km)
Elongation
ratio Volume
(km
3
)Latitude Longitude Volcano confidence factor Previously
identified
12345Sum
113 275 28.5 1.19 44 −81.87 −130.76 1 0 0 1 1 3 No
114 350 29 1.07 58 −82.41 −134.85 1 1 1 0.5 0.5 4 No
115 150 10.5 1.33 3 −81.10 −132.52 1 0.5 1 1 1 4.5 No
116 400 31.5 1.25 78 −81.36 −133.60 1 1 1 0 0.5 3.5 No
117 100 6 1.40 1 −81.64 −134.55 1 0 0 0 1 2 No
118 250 15.5 1.07 12 −81.55 −135.48 1 0 1 1 0.5 3.5 No
119 550 21.5 1.15 50 −80.35 −131.14 1 1 1 0 1 4 No
120 250 11.5 1.30 6 −80.50 −134.03 1 0 1 1 1 4 No
121 950 36 1.12 242 −80.23 −134.29 1 0.5 1 1 0 3.5 No
122 250 30.5 1.03 46 −79.57 −132.88 1 0 0 0.5 0.5 2 No
123 325 23.5 1.24 35 −80.40 −136.32 0.5 0 1 1 1 3.5 No
124 400 29 1.00 66 −80.08 −138.89 0.5 0.5 0 1 0.5 2.5 No
125 275 32.5 1.10 57 −79.39 −137.82 0.5 0.5 1 1 0.5 3.5 No
126 125 17.5 1.19 8 −79.67 −138.15 0.5 0 1 0.5 0.5 2.5 No
127 250 19 1.11 18 −79.76 −139.69 1 0 0 0.5 0.5 2 No
128 400 24 1.18 45 −78.70 −137.18 0.5 1 0 0.5 0.5 2.5 No
129 300 10.5 1.33 6 −78.61 −137.87 0.5 0 1 0.5 0.5 2.5 No
130 600 25.5 1.13 77 −78.39 −139.25 1 0.5 1 1 0.5 4 No
131 425 39.5 1.08 130 −79.00 −142.10 1 0.5 0 0.5 0.5 2.5 No
132 700 31 1.00 132 −78.15 −140.91 1 0.5 1 0.5 0.5 3.5 No
133 675 22 1.00 64 −77.91 −140.89 1 1 1 0.5 0.5 4 No
134 2600 52.5 1.06 1406 −73.71 −126.54 0 1 1 1 0.5 3.5 Yes
135 400 28 1.15 62 −74.69 −127.78 0.5 1 1 0.5 0.5 3.5 No
136 200 4.5 1.25 1 −75.98 −128.21 0 1 1 1 0.5 3.5 Yes
137 1700 47.5 1.16 753 −76.11 −128.64 0 1 1 1 0.5 3.5 No
138 325 16 1.13 16 −75.80 −128.57 0 1 1 1 0.5 3.5 No
139 1500 19.5 1.17 112 −75.98 −129.11 0 1 1 1 0.5 3.5 Yes
140 450 5.5 1.20 3 −75.90 −129.29 0 1 1 1 0.5 3.5 No
141 1800 36 1.06 458 −75.98 −132.31 0.5 1 1 0.5 0.5 3.5 Yes
142 900 21 1.00 78 −76.24 −132.63 0.5 1 1 0.5 0.5 3.5 Yes
143 400 5 1.00 2 −76.22 −133.14 0 1 1 0.5 0.5 3 No
144 600 13 1.17 20 −76.27 −135.11 0 1 1 0.5 0.5 3 Yes
145 950 18.5 1.18 64 −76.27 −136.12 0 1 1 0.5 0.5 3 Yes
146 800 9.5 1.11 14 −75.88 −137.95 0 1 1 0.5 0.5 3 No
147 275 19.5 1.17 21 −75.62 −138.08 0 1 1 0.5 0.5 3 No
148 600 8.5 1.13 9 −78.09 −153.87 1 1 1 1 0.5 4.5 No
149 450 21.5 1.15 41 −78.13 −155.26 1 1 1 1 0.5 4.5 No
M. VAN WYK DE VRIES ET AL.
150 775 23 1.19 80 −77.88 −153.60 1 1 1 1 0.5 4.5 No
151 275 16.5 1.06 15 −77.89 −154.81 1 1 1 1 0.5 4.5 No
152 100 7 1.33 1 −78.19 −157.00 0 1 1 0.5 0.5 3 No
153 125 18 1.25 8 −82.11 −154.71 0 0 1 0.5 0.5 2 No
154 100 16.5 1.06 5 −81.96 −157.64 0 0 1 0.5 0.5 2 No
155 150 24 1.18 17 −81.53 −163.39 1 1 1 0.5 0.5 4 No
156 225 15 1.00 10 −78.00 −165.52 0 0.5 0.5 1 0.5 2.5 No
157 100 12 1.18 3 −77.18 −164.77 0 0.5 0.5 1 0.5 2.5 No
158 1400 34 1.13 318 −85.96 −163.98 0.5 1 1 0.5 0.5 3.5 Yes
159 400 10.5 1.33 9 −78.39 167.56 0.5 1 1 1 0.5 4 Yes
160 325 16.5 1.20 17 −78.50 166.04 0 1 1 1 0.5 3.5 Yes
161 1600 29 1.07 264 −78.61 165.08 0 1 1 1 0.5 3.5 Yes
162 2050 39.5 1.14 628 −78.73 163.67 0 1 1 1 0.5 3.5 Yes
163 2250 33 1.13 481 −77.78 168.67 0 1 1 1 0.5 3.5 Yes
164 1800 29.5 1.19 307 −77.70 166.83 0 1 1 1 0.5 3.5 Yes
165 1250 21 1.10 108 −77.49 166.78 0 1 1 1 0.5 3.5 Yes
166 425 22.5 1.14 42 −77.23 167.68 0 1 1 1 0.5 3.5 Yes
167 350 20.5 1.16 29 −77.18 166.94 0 1 1 0.5 0.5 3 Yes
168 750 16.5 1.20 40 −74.58 164.22 1 1 1 1 0.5 4.5 Yes
169 600 26.5 1.21 83 −73.80 169.69 0.5 1 1 1 0.5 4 Yes
170 950 33.5 1.09 209 −73.42 164.70 0 1 1 1 0.5 3.5 Yes
171 1550 34.5 1.16 362 −72.78 169.89 0 1 1 0.5 0.5 3 Yes
172 750 17.5 1.19 45 −71.93 170.41 0 1 1 1 0.5 3.5 Yes
173 500 25.5 1.13 64 −76.45 −165.16 0 0.5 0.5 0.5 0.5 2 No
174 450 34.5 1.09 105 −76.37 −166.16 0 0.5 0.5 0.5 0.5 2 No
175 450 13.5 1.25 16 −76.12 −72.41 0.5 1 1 1 0.5 4 Yes
176 400 9.5 1.38 7 −73.68 −78.91 0 1 1 0.5 0.5 3 No
177 550 20 1.22 43 −73.70 −79.43 0.5 1 1 1 0.5 4 Yes
178 300 17 1.27 17 −74.67 −78.72 0.5 1 1 1 0.5 4 Yes
Average 621 21.3 1.18 121 −77.56 −120.28 0.69 0.69 0.71 0.74 0.57 3.40
The final column identifies whether the cone was a previously recognized volcano (Yes) or a new discovery (No). Most of the previously identified volcanoes are catalogued in LeMasurier et al. (1990).
SUBGLACIAL VOLCANOES IN WEST ANTARCTICA
unknown volcanic edifices across the ice-shrouded
WARS.
Extent and activity of subglacial volcanism
We have identified at least 138 likely volcanic
edifices distributed throughout the WARS. This
represents a significant advance on the total of 47
identified volcanoes across the whole of West Ant-
arctica, most of which are visible at the surface and
are situated in Marie Byrd Land and the Transantarc-
tic Mountains (LeMasurier et al. 1990). The wide
distribution of volcanic structures throughout the
WARS, along with the presence of clusters of
Fig. 3. The upper panel shows an echogram from NASA’s Icebridge mission (NSIDC 2014) that shows generally
good agreement between a cone on the echogram and on the Bedmap2 data. The lower panel shows an echogram
from Corr & Vaughan (2008) with basal topography picking out two cones; the dark layer above the bed is tephra
believed to have erupted around 2000 years ago.
Table 3. Statistical comparison of the morphologies of the cones identified in this study identified as volcanoes
Height
(m) Average
diameter (km) Axis
ratio Volume
(km
3
)Confidence
factor
(a) (b) (a) (b) (a) (b) (a) (b) (a)
Average 701 940 21.9 17.1 1.19 2.11 144 150 3.75
Standard Deviation 641 670 10.7 11.6 0.09 0.81 345 371 0.56
Median 475 810 20.5 15.3 1.17 1.98 42 31 3.5
Minimum 100 100 4.5 2.3 1.00 1.13 0.5 0.2 3
Maximum 3850 3030 58.5 63.3 1.44 5.23 2542 3086 5
Comparison with: (a) those from a global database of shield volcanoes; and (b) Grosse et al. (2014). The two are similar, apart from the
long-short axis ratio; our cones are, on average, more circular than shield volcanoes elsewhere. This could be linked to specific glaciovol-
canic eruption mechanisms, but is most likely a data bias due to our detection methods excluding more elliptical edifices.
M. VAN WYK DE VRIES ET AL.
volcanism concentrated within the Marie Byrd
Land dome, is markedly similar to the East African
Rift System, which is also >2000 km in length and
flanked by the Ethiopian and Kenyan domes (Fig.
1b) (Siebert & Simkin 2002; Ebinger 2005). Mor-
phologically, the volcanoes have volume–height
characteristics and basal diameters that closely
match those of rift volcanoes around the world
(Fig. 5; Table 3). Bearing in mind that data paucity
beneath the Ross Ice Shelf precluded meaningful
analysis of a significant terrain also considered to
be part of the WARS, the total region that has expe-
rienced volcanism is likely to be considerably larger
than that we have identified here.
Cone 91
Cone 60
Cone 21
Mouna Kea, Hawaii
Erta Ale, Ethiopia
Marsabit, Kenya
5 km 10 km 15 k m 20 km 25 km 30 km
1000 m
1000 m
1000 m
1000 m
1000 m
1000 m
Fig. 4. Cross-sections of three cones from this study (numbers 21, 60 and 91: see Fig. 2 and Table 2 for more details
and locations) and three prominent shield volcanoes, namely Mauna Kea (Hawaii), Erta Ale and Marsabit (East
African Rift).
Fig. 5. Volume/height chart of the cones from this study (crosses) superimposed over data from volcanoes
worldwide (Grosse et al. 2014). The cones closely fit the morphology data for shield volcanoes, as would be expected
for basalt-dominated rift volcanism.
SUBGLACIAL VOLCANOES IN WEST ANTARCTICA
The activity of the WARS has been the subject of
a longstanding debate, with one side advocating a
largely inactive rift (LeMasurier 2008) and others
suggesting large-scale volcanism (Behrendt et al.
2002). The arguments in favour of an inactive rift
are based on the anomalously low elevation of the
WARS compared to other active continental rifts
(Winberry & Anandakrishnan 2004; LeMasurier
2008) and the relative absence of basalt pebbles
recovered from boreholes (LeMasurier pers. comm.
2015). Conversely, high regional heat fluxes (Sha-
piro & Ritzwoller 2004; Schroeder et al. 2014), geo-
magnetic anomalies (Behrendt et al. 2002) and
evidence of recent subglacial volcanism (Blanken-
ship et al. 1993; Corr & Vaughan 2008) suggest
that the rift is currently active. This study provides
evidence of a large number of subglacial volcanoes,
with their quasi-conical shield volcano type geome-
tries still intact. The largely uneroded nature of the
cones suggests that many may be of Pleistocene
age or younger, which supports the argument that
the rift remains active today.
From this study, we are not able to determine
whether the different volcanoes are active or not;
however, the identification of multiple new volcanic
edifices, and the improved regional sense of their
geographical spread and concentration across the
WARS, may guide future investigation of their
activity. Several previous studies have suggested
that the Marie Byrd Land massif is supported by
particularly low-density mantle, possibly compris-
ing a volcanic ‘hotspot’(Hole & LeMasurier
1994; Winberry & Anandakrishnan 2004). Tephra
layers recovered from the Byrd Ice Core near the
WAIS divide suggest that multiple Marie Byrd
Land volcanoes were active in the Late Quaternary
(Wilch et al. 1999), while recent seismic activity
in Marie Byrd Land has been interpreted as cur-
rently active volcanism (Lough et al. 2013). In the
Pine Island Glacier catchment, strong radar-sounded
englacial reflectors have been interpreted as evi-
dence of a local eruption that occurred approxi-
mately 2000–2400 years ago (Fig. 3) (see Corr &
Vaughan 2008) while, on the opposite rift flank in
the Transantarctic Mountains, Mount Erebus com-
prises a known active volcano located above another
potential volcanic hotspot (Gupta et al. 2009). Vol-
canism across the region is also likely to contribute
to the elevated geothermal heat fluxes that have been
inferred to underlie much of the WAIS (Shapiro &
Ritzwoller 2004; Fox Maule et al. 2005; Schroeder
et al. 2014). The deployment of broadband seismics
to recover the mantle structure beneath the WAIS is
now showing great promise (e.g. Heeszel et al.
2016), and our map of potential volcanic locations
could help target further installations directed to-
wards improved monitoring of the continent’s sub-
glacial volcanic activity.
Implications for ice stability and future
volcanism
The wide spread of volcanic edifices and the possi-
bility of extensive volcanism throughout the
WARS also provides potential influences on the
stability of the WAIS. Many parts of the WAIS over-
lie basins that descend from sea level with distance
inland, lending the ice sheet a geometry that is
prone to runaway retreat (Bamber et al. 2009;
Alley et al. 2015). Geological evidence points to
the likelihood that the WAIS experienced extensive
retreat during Quaternary glacial minima (Naish
et al. 2009) and concurrently contributed several
metres to global sea-level rise (O’Leary et al.
2013). Currently, the WAIS may be undergoing
another such wholesale retreat, as ice in the Pacific-
facing sector has consistently been retreating from
the time of the earliest aerial and satellite observa-
tions (Rignot 2002; McMillan et al. 2014; Mouginot
et al. 2014). We do not consider it likely that volca-
nism has played a significant role in triggering
the current retreat, for which there is compelling
evidence that the forcing has initiated from the mar-
gins (Turner et al. 2017), but we do propose that
subglacial volcanism has the potential to influence
future rates of retreat by (1) producing enhanced
basal melting that could impact upon basal ice
motion and (2) providing edifices that may act to
pin retreat.
On the first of these possibilities, some authors
have suggested that active subglacial volcanism,
through providing enhanced basal melting that
might ‘lubricate’basal motion, could play a role in
WAIS instability (Blankenship et al. 1993; Vogel
et al. 2006; Corr & Vaughan 2008). A possible anal-
ogy is provided by subglacial volcanism in Iceland,
where subglacial eruptions have been known to
melt basal ice, flood the basal interface and induce
periods of enhanced ice flow (e.g. Magnússon
et al. 2007; Einarsson et al. 2016); however, in Ice-
land’s ice caps the ice is considerably thinner than in
the WAIS and, hence, more prone to subglacial-
melt-induced uplift. Nevertheless, there is evidence
to suggest that changes to subglacial water distribu-
tion can occur beneath the WAIS, and that they can
sometimes have profound impacts on ice dynamics:
examples are ice-dynamic variability over subglacial
lakes (e.g. Siegfried et al. 2016) or the suggestion
that subglacial water pulses may have been responsi-
ble for historical occurrences of ice-stream piracy
(e.g. Anandakrishnan & Alley 1997; Vaughan et al.
2008). Much recent attention has focused on the
drainage of subglacial lakes comprising plausible
triggers of such dynamic changes, but subglacial
eruptions may represent another pulsed-water source
whose occurrence has rarely, if ever, been factored
into ice-sheet models. Even inactive or dormant
M. VAN WYK DE VRIES ET AL.
volcanism has the potential to influence ice flow by
increasing heat flux to the subglacial interface; this
may generate a basal melt cavity and enhance ice
flow (Bourgeois et al. 2000; Schroeder et al. 2014).
On the other hand, volcanic edifices, whether
active or not, stand as significant protuberances
which may act geometrically as stabilizing influ-
ences on ice retreat. Numerical models used to pro-
ject potential rates of WAIS retreat show that, once
initiated, ice retreat will continue unabated as long
as the ice bed is smooth and downslopes inland,
but that any increase in roughness or obstacle in
the bed can act to delay or stem retreat (Ritz et al.
2015; Nias et al. 2016). We have identified here
a number of volcanic edifices sitting within the
WAIS’deep basins; these edifices, which are likely
to owe their existence to volcanism, could represent
some of the most influential pinning points for past
and future ice retreat.
Looking ahead, the thinning and potential
removal of ice cover from the WARS volcanic prov-
ince could have profound impacts for future volcanic
activity across the region. Research in Iceland has
shown that with thinning ice cover, magma pro-
duction has increased at depth as a response to
decompression of the underlying mantle (Jull &
McKenzie 1996; Schmidt et al. 2013). Moreover,
there is evidence that, worldwide, volcanism is
most frequent in deglaciating regions as the overbur-
den pressure of the ice is first reduced and then
removed (Huybers & Langmuir 2009; Praetorius
et al. 2016). Unloading of the WAIS from the
WARS therefore offers significant potential to
increase partial melting and eruption rates through-
out the rifted terrain. Indeed, the concentration of
volcanic edifices along the WARS could be con-
strued as evidence that such enhanced volcanic activ-
ity was a feature of Quaternary minima. This raises
the possibility that in a future of thinning ice cover
and glacial unloading over the WARS, subglacial
volcanic activity may increase and this, in turn,
may lead to enhanced water production and contrib-
ute to further potential ice-dynamical instability.
Conclusions
By applying morphometric analysis to a digital ele-
vation model of the West Antarctic Rift System,
and assessing the results with respect to auxiliary
information from ice-surface expressions to aero-
geophysical data, we have identified 138 subglacial
volcanic edifices spread throughout the rift. The
volcanoes are widely distributed in the broad rift
zone, with particular concentrations in Marie
Byrd Land and along the central WARS axis. The
results demonstrate that the West Antarctic Ice
Sheet shrouds one of the world’s largest volcanic
provinces, similar in scale to the East African
Rift System. The overall volcano density beneath
West Antarctica was found to be one edifice per
18 500 ± 500 km
2
, with a central belt along the
rift’s central sinuous ridge containing one edifice
per 7800 ± 400 km
2
. The presence of such a volcanic
belt traversing the deepest marine basins beneath the
centre of the West Antarctic Ice Sheet could prove to
be a major influence on the past behaviour and future
stability of the ice sheet.
We would like to thank John Smellie and Matteo Spagnolo
for insightful and thorough reviews of a first draft of this
manuscript that contributed, we hope, to a much improved
paper.
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