CHAPTER
32
Remote sensing of glaciers of the
Subantarctic islands
J. Graham Cogley, Etienne Berthier, and Shavawn Donoghue
ABSTRACT
Through case studies, we summarize progress for
the Subantarctic in the drive to complete the World
Glacier Inventory. Most of the 29 Heard Island
glaciers have shrunk since the first observations in
1947, several having begun to retreat from former
tidewater termini. Total glacier area decreased from
288 km 2 in 1947 to 257 km 2 in 1988 and 231 km 2 in
2008. On Kerguelen, shrinkage has been more
dramatic. In 1963–1964, the date of the earliest
complete coverage, glacier extent was 703 km 2 . In
2001, it was 552 km 2 . We have compiled the first
objective topographic map of Montagu Island, the
largest of the South Sandwich Islands (glacierized
area 94 km 2 ), using the ASTER Global Digital
Elevation Model (version 1). We assess the shortcomings of this new tool, and conclude that it may
indeed prove valuable for first-time mapping. It will
also be useful as an aid in selecting accurately dated
scenes for estimation of multidecadal change. An
inventory based on cartographic sources yields an
estimate for total glacier area in the Subantarctic
during the late 20th century of 7,863 km 2 . Limited
measurements on other islands suggest that Heard
Island and Kerguelen are typical of glacier shrinkage, thinning, and negative mass balance across the
region.
32.1
INTRODUCTION
In this chapter we summarize progress for the
Subantarctic in the attempt to complete the World
Glacier Inventory (WGI; http://nsidc.org/data/docs/
noaa/g01130_glacier_inventory/ ), and illustrate
through case studies how progress in the systematic
monitoring of glaciological change is now accelerating.
Many Subantarctic islands are poorly surveyed
even today, and until recently there was little information about glacier change. Documenting change
is not a realistic ideal while information about the
first of the two required epochs remains uncompiled. Thus the aim of much glaciological work in
the Subantarctic is that originally articulated for the
WGI; namely, to develop a snapshot, necessarily
diachronous, of glacierization in the late 20th century. However, information about change is now
accumulating more rapidly. Here we present case
studies of glacier mapping and glacier change, relying on imagery from SPOT, ASTER, Landsat, and
other sensors, from Heard Island, Kerguelen, and
Montagu Island. We also summarize the results of
an almost complete map-based inventory of the
Subantarctic as a whole.
32.2
THE REGIONAL CONTEXT
We define the Subantarctic as in Fig. 32.1. The
northern boundary lies at 45 so as to include
the summit ice on Marion Island, but excludes
Patagonia and New Zealand. The boundary with
Antarctica is drawn to the north of islands that are
considered ‘‘close’’ to the mainland. Scott Island,
Peter I Island, the South Shetlands, the South
Orkneys, and the Balleny Islands are all regarded
760
Remote sensing of glaciers of the Subantarctic islands
Figure 32.1. The Subantarctic (white background) as defined for the present purpose. Islands with no glaciers are
in italics. Is ¼ Islands; Peter I ¼ Peter the First Island.
as Subantarctic, partly because they are at risk of
being neglected in studies focused on the much
larger Antarctic Ice Sheet.
The area of land in the Subantarctic is 30,160
km 2 , of which 26% is occupied by glacier ice (Section 32.4). Most of the islands lie on oceanic crust.
Many are volcanic, and several are currently active
or have been so recently (e.g., Bauer 1963, LachlanCope et al. 2001, López-Martı́nez et al. 2002,
Patrick et al. 2005, Stephenson et al. 2005).
The Subantarctic islands, scattered through 360
of longitude and 25 of latitude, have distinctly
different climates. Weather stations are few and
widely dispersed (Jacka et al. 2004). The main
features of the evolution of temperatures in the
Subantarctic during the 20th century can, however,
be seen in Table 32.1 and Fig. 32.2.
Mean annual temperature decreases polewards.
However, the potential for ablation by melting, as
measured by the positive degree-day sum at or close
to sea level (Fig. 32.2), remains substantial as far
south as the South Orkneys at latitude 61 . Subantarctic climate is strongly maritime. The mean
annual range of temperature is small, but increases
southwards from 4.6 C at Marion Island to 12.6 C
in the South Orkney Islands. There is evidence from
some islands of the expected contrast between
windward and leeward coasts. On Heard Island,
for example, föhn winds are documented on the
eastward side, in the lee of the main peak, and on
The regional context 761
Table 32.1. Temperature at subantarctic weather stations. Number of years of observation in parentheses; Heard
Island (proxy): based on Atlas Cove measurements and linear regression against measurements at Port aux Français
(Thost and Truffer 2008). Trends in bold type differ from zero by more than 2 standard errors.
Mean Tann
1951–1980
( C)
Mean Tann
1981–2007
( C)
Trend, period (no. of years)
Transvaal Cove, Marion Island
5.3 (30)
6.1 (26)
þ0.027, 1949–2006 (56)
Port aux Français, Kerguelen
4.5 (29)
4.9 (27)
þ0.010, 1951–2006 (56)
Atlas Cove, Heard Island
1.5 (7)
2.0 (12)
þ0.017, 1948–2006 (19)
Heard Island (proxy)
1.6 (30)
2.1 (22)
þ0.014, 1951–2002 (52)
Grytviken, South Georgia
2.0 (28)
—
þ0.014, 1951–1980 (28)
3.7 (30)
3.2 (26)
þ0.033, 1981–2007 (26)
—
7.1 (3)
Station
Orcadas, Laurie Island (South Orkney Islands)
Young Island, Balleny Islands
( C yr1 )
Figure 32.2. Annual positive degree-day sums based on records of near-surface air temperature from stations near
sea level: Transvaal Cove (Marion Island), Port aux Français (Kerguelen), Grytviken (South Georgia), Orcadas
(South Orkney Islands) and Young I (Balleny Islands) (Young I record from the Antarctic Meteorological Research
Center, University of Wisconsin-Madison, http://amrc.ssec.wisc.edu/stations.html ; other records from Turner et al.
2004; http://www.antarctica.ac.uk/met/READER/). Thick lines ¼ 5-year averages. Monthly mean temperatures
were corrected for within-month variability following Braithwaite (1984), a standard deviation of 4 C being
assumed.
South Georgia the equilibrium line altitude (ELA)
is higher in the lee (northeast) of the axial mountain
ranges (Clapperton et al. 1989).
Temperatures throughout the Subantarctic
have increased in recent decades. All of the trends
in Table 32.1 are statistically significant, some
strongly so, but interdecadal variability is also notable. For example, much of the warming at Port aux
Français, Kerguelen, happened between 1960 and
the early 1980s; since then temperatures have
762
Remote sensing of glaciers of the Subantarctic islands
Table 32.2. Precipitation at subantarctic weather stations. Data from the Global Historical Climate Network
(http://www.ncdc.noaa.gov/oa/climate/ghcn-monthly/index.php) except for Port aux Français (Berthier et al.
2009) and Arctowski (Marsz 2002).
Station
Mean annual precipitation
(mm)
Period
(no. of years)
Transvaal Cove, Marion Island
2294
1948–2009 (62)
Port aux Français, Kerguelen
759
1951–2005 (55)
Grytviken, South Georgia
1473
1906–1981 (65)
Arctowski, King George Island (South Shetland Islands)
507
1978–1996 (16)
Bellingshausen, King George Island (South Shetland Islands)
707
1968–2009 (40)
Arturo Prat, Greenwich Island (South Shetland Islands)
616
1966–2003 (32)
changed little (Berthier et al. 2009). The pattern of
interdecadal temperature variability shown by Berthier et al. is comparable with that in the annual
positive degree-day sum, as shown in Fig. 32.2, but
this is not true everywhere. The strong warming at
Orcadas (Table 32.1) is not mirrored in Fig. 32.2,
suggesting, consistent with the findings of Zazulie et
al. (2010), that much of the warming there is
wintertime warming.
Precipitation varies considerably from island to
island (Table 32.2). However, weather station
averages are not reliable as guides to accumulation
on glaciers. All of the stations are close to sea level,
and all are on the lee sides of islands. For example,
for 1995–2001 mean annual precipitation was 692
mm at Port aux Français, while 70 km to the west it
was 3,155 mm near to the eastern margin of Cook
Ice Cap (Institut Paul Émile Victor, dataset 136;
Berthier et al. 2009). On King George Island, for
1987–1991 mean annual precipitation was 472 mm
at Arctowski (Marsz 2002), while some 10 km to the
north, at 700 m asl, mean annual point mass balance was 2,480 mm water equivalent for the same
period (Wen et al. 1998).
The Antarctic Oscillation partly controls decadal
climate variability and glacier dynamics in New
Zealand (see Chapter 29 of this book on New Zealand’s glaciers by Chinn et al. and the summary,
Chapter 33, by Kargel et al.). Global warming,
the Antarctic Oscillation, and fluctuations in the
Antarctic Circumpolar Current can all be reasonably suspected as causes of glacier fluctuations in
the Subantarctic, but the geographic and temporal
coverage of the observations is insufficient to identify the most important factors or to order their
dynamical significance. Latitude alone is the
obvious major variable affecting static measures
of glacier characteristics, such as the ELA (Table
32.3).
Moving polewards, the ELA drops towards sea
level, and can be assumed to reach it somewhere
between latitudes 65 and 70 (Table 32.3).
Observations for South Georgia are partly cartographic; the substantial range reflects the contrast
between leeward and windward sides of the island.
Tidewater glaciers—those whose termini stand in
the sea—are known as far north as Kerguelen,
where, of two calving glaciers on the west coast in
1963, Pasteur Glacier was still at sea level as of
April 2009. Calving termini become the norm south
of 55 to 60 .
32.3
CASE STUDIES
32.3.1 Heard Island
Heard Island is a volcanically active island located
at 53.1 S, 73.5 E in the southern Indian Ocean
(Fig. 32.3). Heard Island’s position south of the
Polar Front is unique among the islands of the
southern Indian Ocean (e.g., Kerguelen, Crozet,
and Marion). This high-elevation roughly circular
island (367 km 2 ), culminating in Mawson Peak at
2,745 m asl on the Big Ben Plateau, had an estimated glacier cover of 288 km 2 in 1947 (Ruddell
2006).
The physiography and orographic effects of
the island have resulted in glaciers on the leeward
and windward sides reacting differently to climate
Case studies
763
Table 32.3. Observations of the equilibrium line altitude on subantarctic islands.
Island, glacier
Latitude
ELA
(m asl)
Source
Marion
46.9
>1,150
Sumner et al. (2004)
Kerguelen, Cook Ice Cap
49.4
700
Vallon (1977a)
Heard
53.1
100–700
Ruddell (2006)
Bouvet
54.4
200–350
Orheim (1981)
South Georgia
54.6
370–860
Clapperton et al. (1989)
Signy (South Orkney Islands)
60.7
200
King George, Little Dome
62.1
160
Wen et al. (1998)
Nelson
62.3
110
Wen et al. (1998)
Livingston, Rotch Ice Dome
62.6
140–170
Orheim and Govorukha (1982)
Deception, Glacier G1
62.9
275–330
Orheim and Govorukha (1982)
Cogley (unpublished)
Figure 32.3. The glacier boundaries of Heard Island from 1947 to 2008/2009, based on SPOT satellite imagery
acquired in 1988, aerial photos from 1987, QuickBird and Worldview satellite imagery from 2003, 2006, and 2008,
and International Space Station images from 2009. The red outlines represent extents in 2006–2009 (adapted from
Australian Antarctic Data Centre, Map Catalogue Number 13691, August 2009). Figure can also be viewed as
Online Supplement 32.1.
764
Remote sensing of glaciers of the Subantarctic islands
change. Understanding of change in the extent of
Heard Island glaciers has been derived from comparison of brief journal accounts, photos, and
drawings made during the early sealing period,
and later—as scientists began to explore this remote
island—from published reports, photos, satellite
images, and eventually mass balance studies. The
fluctuations of these glaciers have been discussed
by Budd and Stephenson (1970), Allison and
Keage (1986), Budd (2000), Ruddell (2006), and
Donoghue (2009).
Two SPOT images from January 1988 and
March 1991 were the first clear high-resolution
images of the majority of the island. Ruddell
(2006) used the SPOT images and aerial photographic surveys to estimate glacier extent between
1947 and 1988 and to provide the first complete
inventory of Heard Island’s glaciers. As of 1988,
there were 29 glacierized basins (41 termini) and 3
glaciated basins (which may have hosted glaciers
during the Last Glacial Maximum) on Heard Island
with a total area of 256.9 km 2 and an estimated
ice volume, by area–volume scaling, of 14.2 km 3
(Ruddell 2006).
The Australian Antarctic Data Centre analyzed a
Worldview-1 image from March 23, 2008 (Fig.
32.4). Glacier outlines were remapped, resulting in
a total glacierized area of 231 km 2 (Harris 2009,
Lucieer et al. 2009). A new DEM was created based
on this image (Brolsma 2010). It updated the 1997
(Ryan 2004) and 2002 (Brolsma and Smith 2008)
Radarsat DEMs.
We have divided the glaciers on Heard Island
into four regions, Laurens Peninsula, northern
Big Ben, eastern Big Ben, and southwestern Big
Ben. The temperate glaciers of Heard Island were
first systematically observed in the early 1900s. The
majority of these glaciers were stable or slightly
thinning until a marked retreat began in the early
1960s (Ruddell 2006). Retreat since the 1960s has
continued through the last recorded observation in
2009 (Donoghue 2009).
Recent (1947–2009) changes in the eastern Big
Ben glaciers are known in more detail than for
the other regions of Heard Island due to relatively
cloud-free satellite images and glacier-based field
surveys in 2000/2001 and 2003/2004 (Donoghue
2009). These eastern Big Ben glaciers include
larger glaciers that extend from the summit of Big
Ben to the coast (Compton, Stephenson, and Winston) and smaller glaciers that extend from around
1,000 m asl to the coast (Brown, AU1121, and
AU1141).
The first flight over Heard Island in 1947 indicated that Winston Glacier had already retreated
from the coastline. Between 1947 and 1963 Winston
retreated 1.6 km (Budd and Stephenson 1970) and
therefore appeared to have the most rapid retreat
during that interval. However, this was followed by
a period of advance in the 1970s, which was later
lost again in the 1980s (Ruddell 2006). This oscillation suggests that Winston Glacier has a response
time of the order of a decade and argues against
former calving dynamics as a cause of the oscillation. However, it is not clear whether the advance
was climatically driven or not. It is interesting that
glaciers in New Zealand also advanced starting in
the 1970s.
By the 1960s several of the other glaciers along
the east coast of Heard Island had begun to retreat
(Budd and Stephenson 1970). For example,
AU1121 had retreated to a stagnant ice field, and
Brown and Stephenson had begun to retreat. By the
1980s Compton Glacier had experienced the most
substantial retreat of any of the glaciers on Heard
Island. It was then 1.6 km inland from its 1947
tidewater glacier front (Allison and Keage 1986)
and was 2.5 km inland by 1987 (Ruddell 2006).
The fact that former calving glaciers have continued
to retreat for decades after losing connection to the
sea shows that calving dynamics are not the root
cause of the retreat.
By the mid-1980s Brown and Stephenson were
beginning to show signs of increased retreat. Both
had developed proglacial lagoons. Brown Glacier’s
terminus retreated a total of 1.7 km from the
coast between 1947 and 2004 at an average rate
of 30 m yr1 (Thost et al. 2004). GPS surveys from
2000 and 2003 indicate significant thinning of
Brown Glacier, by up to 11.7 m on the lower
glacier and 8.5 m on the upper glacier (Thost
and Truffer 2008).
Between 1947 and 1987 Stephenson Glacier
decreased in area by 18% (Ruddell 2006) although
this shrinkage was not steady; instead, there was a
dramatic acceleration (of 100 m yr1 ) in retreat of
the northern margin from 1987 to 2000 (Kiernan
and McConnell 2002). This increased retreat continued with the opening of a waterway by 2006
between the two proglacial lagoons that had formed
near the terminus of Stephenson Glacier. By 2010
the glacier had retreated even further from its 1987
terminus.
QuickBird images were used to measure the
changes in eastern glaciers between January 2004
and January 2006 (Donoghue 2009; Fig. 32.4).
Case studies
765
Figure 32.4. QuickBird and Worldview images of Heard Island, all provided by the Australian Antarctic Data
Centre. (A) January 17, 2003 Quickbird image; (b) January 23, 2006 Quickbird image with the area of retreat
outlined (Donoghue 2009); (c) March 23, 2008 Worldview-1 panchromatic image; (d) February 4, 2009 Quickbird
image. Figure can also be viewed as Online Supplement 32.2.
Brown Glacier, and Compton Glacier along most
of its lagoon-based terminus, each retreated by less
than 0.1 km. The northern terminus of Stephenson
Glacier, which has broken up into the lagoon,
retreated by 0.25 km, and the southern terminus
by more than 0.75 km. Winston Glacier retreated
by 0.2 km.
32.3.2
Kerguelen
The Kerguelen Islands (49 S, 69 E) are a group
(7,215 km 2 ) of isolated islands in the southern
Indian Ocean. They were discovered in 1772 by
Yves de Kerguelen. Here, we summarize and
update some recently published results of glacier
766
Remote sensing of glaciers of the Subantarctic islands
Table 32.4. Changes in Kerguelen ice cover. Isolated glaciers (covering 18 km 2
in 1963–1964) are not tabulated.
Region
Year
Area
(km 2 Þ
Ice loss
(km 2 , %)
Cook Ice Cap
1963
2001
500.9
410.0
90.9 (18.2)
Rallier du Baty Peninsula
1964
2001
102.3
79.2
23.1 (22.5)
Mont Ross
1964
2001
59.3
35.1
24.2 (40.8)
Presqu’ı̂le de la Société de Géographie
1964
1994
14.7
4.7
10 (68)
change on the Kerguelen Islands (Berthier et al.
2009).
We measured the extent of glaciers and ice caps
on these islands by digitizing and comparing successive glacier outlines on a map and satellite
images. Our oldest dataset is a map published by
the Institut Géographique National (IGN) at a
scale of 1:200,000. It was produced using end-ofsummer aerial photos taken in 1963 of Cook Ice
Cap and in 1964 of other glaciated areas, and
appears to represent glacier outlines reliably. SPOT
(1991, 1994, and 2003), Landsat (November 2001),
and ASTER (2005, 2006, 2009) images were used to
generate a time series of ice cap extent. Our glacier
inventory has been incorporated into the Global
Land Ice Measurements from Space (GLIMS)
Glacier Database (http://nsidc.org/glims/ ).
Area change for the four main glacierized regions
on the Kerguelen Islands is summarized in Table
32.4. Between 1963–1964 and 2001, the total icecovered area on the Kerguelen Islands shrank from
703 51 to 552 11 km 2 .
Between 1963 and 2001, Cook Ice Cap shrank by
18% (Fig. 32.5a) due to major retreat of all outlet
glacier fronts and the growth and appearance of
nunataks (isolated rock outcrops within the ice
cap). We estimated the overall rate of contraction
for two time periods (Figure 32.5b). Area loss was
1.9 1.3 km 2 yr1 between 1963 and 1991 and
increased to 3.8 0.7 km 2 yr1 after 1991. Thus,
in recent years, nearly 1% of the ice cap has disappeared annually. The temporal resolution of our
data on glacier change is rather low and does not
permit us to observe interannual or decadal variability of area loss. However, we detect a recent
acceleration of area loss by comparing losses over
these two periods.
Ampère Glacier is the largest outlet glacier of
Cook Ice Cap and, because of its relatively good
accessibility, has received most attention in previous studies (Vallon et al. 1977a, b, Frenot et al.
1993). Between 1963 and 2006, the terminus
retreated at a mean rate of 70 3.7 m yr1 , the
glacier length decreased from 15.3 to 12.5 km,
and the glacier contracted by 18.3 5.1 km 2 (Figure 32.6b). Area loss was mainly restricted to the
glacier front, where a proglacial lake (Ampère
Lake) appeared in the 1960s and covered 1.6 km 2
in 1991 and 3.5 km 2 in 2006.
A longer time series of terminus change for
Ampère Glacier was compiled by mapping seven
frontal moraines (Frenot et al. 1993). These moraines were dated using the radial growth of Azorella
selago Hooker, a cushion-forming plant of the
Umbelliferae (Apiaceae) group. The moraines were
deposited between 1799 and 1962 following a maximum Little Ice Age advance in 1799, and indicate a
total (but irregular) retreat of about 1 km over 160
years, at a slow mean rate of 6 m yr1 . One can thus
conclude that there has been an order-of-magnitude
acceleration in the retreat of the Ampère Glacier
front after 1963.
More recent work to validate the use of A. selago
as a phytochronometer confirmed linearity of
growth rates with cushion size and validated the
basic concept of this technique at a given site and
environment; however, this newer work pointed up
inconsistent growth rates for different environments
(le Roux and McGeoch 2004), which, as we have
noted, vary considerably on and across individual
Case studies
767
Figure 32.5. Retreat of Cook Ice Cap between 1963 and 2001. (a) 2001 Landsat image with the 1963 (white) and
2001 (black) glacier outlines. (b) Temporal changes of the ice-covered area. The rates of glacier shrinkage (km 2
yr1 ) are indicated for 1963–1991 and 1991–2003 (from Berthier et al. 2009, & 2009 American Geophysical Union;
reprinted with permission). Figure can also be viewed as Online Supplement 32.3.
islands. To the extent that glacier retreat and fluctuations are a response to climatic variability, the
detailed timeline developed by Frenot et al. (1993)
can be considered a valuable extension of the length
of the record. The rapid acceleration of retreat is so
striking that it is difficult to explain in other than
climatic terms.
An April 2009 ASTER image was used to update
the outlines of Ampère Glacier (Fig. 32.6a). The
most striking feature is the disappearance of the
part of the glacier tongue that previously existed
in the lower reaches of the Nunatak de Lapparent.
A lake is now found instead with a high density of
icebergs, indicating that calving has become an
important component of the mass balance. Intensification of calving and erosion of the glacier front
by proglacial lake water are most likely responsible
for the accelerating rate of area loss, which doubled
Figure 32.6. Retreat of Ampère Glacier between 1963 and 2009. (a) Location of the glacier front in 1963 (yellow)
and 2003 (blue). The background image is an ASTER image acquired in April 2009. (b) Temporal changes of the
Ampère Glacier area. Average rates of area change are indicated during 1963–1991, 1991–2001, and 2001–2009.
Figure can also be viewed as Online Supplement 32.4.
768
Remote sensing of glaciers of the Subantarctic islands
from 0.35 km 2 yr1 during 1963–1991 to 0.69
km 2 yr1 during 2001–2009 (Fig. 32.6b).
Our analysis of area change has been complemented by estimates of the volume balance of Cook
Ice Cap since 1963 using (i) area–volume scaling
relationships, (ii) sequential DEM analysis (Berthier et al. 2004), and (iii) the integration of sparse
but reliable measurements of ice elevation changes
over the ice cap (Berthier et al. 2009). Although they
are all highly uncertain, we obtained three independent and consistent measurements between 1963
and 2000, in the range of 25–30 km 3 of ice loss.
This is equivalent to an area average thinning rate
of 1.4–1.7 m yr1 .
The accelerated rates of ice loss observed since
the 1990s suggest that ice masses in the Kerguelen
Islands have not yet reached a steady state. New
satellite acquisitions are needed to assess whether
the apparent acceleration of ice loss is maintained.
A better understanding of the dynamics of glaciers
and ice caps on the Kerguelen Islands is also needed
to predict how quickly they will react to the 1–2 C
warming predicted in this region by the end of the
21st century.
32.3.3 Montagu Island
The first ASTER global DEM, a product of METI
(Ministry of Economy, Trade and Industry, Japan)
and NASA that was released in June 2009 (Hayakawa et al. 2008, ASTER 2009), has attributes and
shortcomings that will require considerable processing before it can be put to use in the estimation of
glacier elevation change. It can, however, be
expected to be valuable in the topographic mapping
of certain remote glacierized areas for the first time.
In this section we assess the ASTER GDEM1 of
one such area, Montagu Island in the South Sandwich Islands. We have not reassessed Montagu
Island with GDEM2 (a more recently released
and updated global ASTER-derived DEM), but
would expect that some incremental and perhaps
important improvements have been made relative
to GDEM1. Fig. 32.7a shows Montagu Island
according to the best available pre-ASTER map
(Holdgate and Baker 1979). The highest elevation,
1,370 m, is taken from Kemp and Nelson (1931),
while that of Mt. Oceanite in the southeast was
estimated from a helicopter altimeter. According
to Holdgate and Baker, the general topography is
‘‘not accurately laid down’’.
Fig. 32.7b shows the ASTER GDEM1 product
for Montagu Island, without editing. Figs. 32.7a
and 32.7b were georeferenced approximately to
each other, relying on shaded relief images of
GDEM1. The shoreline and ice margin from Fig.
32.7a are 4 km north-northeast of their apparent
positions in GDEM1. The ASTER position, with
accuracy better than 50 m (Fujisada et al. 2005), is
clearly the more accurate.
There are obvious artifacts in the ASTER topography. The irregular truncation of the southern
limit of coverage is probably due to masking of
the surrounding ocean based on the inaccurate
Holdgate and Baker position. The numerous offshore ‘‘islets’’ must be ice floes, misinterpreted by
the GDEM1 processing algorithms. On the ‘‘mainland’’, elevation errors are common. At the northeastern limit of coverage, spurious elongate ridges
appear to rise to 2,000 m. In the southeast, Mt.
Oceanite has been misinterpreted as sea. On the
summit plateau, several pits and bumps can be
seen. Close-ups with finer contour intervals (not
shown), and comparison with Fig. 32.7c, suggest
strongly that these irregular details are artifacts.
Pits and bumps were found in ‘‘virtually every
ASTER GDEM[1] tile’’ examined during validation
(ASTER 2009).
GDEM1 elevations are obtained by ‘‘stacking’’
stereo image pairs with dates between 1999 and
2008. Averaging the results reduces root-meansquare errors significantly (ASTER 2009). For
Montagu Island the number of image pairs ranges
from 1 to 10, and is typically 3 or 4. Evidently this
amount of averaging has not sufficed to reduce pitand-bump noise below the threshold implied by the
100 m contour interval of Fig. 32.7b. Indeed, stacking may be partly responsible for the noise: no
cloud-free image has been acquired since the launch
of the satellite in 1999.
However, a problem peculiar to Montagu Island
is that Mt. Belinda has been erupting more or
less continuously since 2001 (see Fig. 32.7c). The
MODIS Thermal Alert System (MODVOLC;
Wright et al. 2004) recorded a highly variable heat
source at the location of Mt. Belinda between 2001
and 2004 (Patrick et al. 2005), and an intensification
of activity in September 2005 is documented by
NASA (2005) from ASTER imagery. Inspection
of MODVOLC suggests that eruptive activity continued at least to 2007; ASTER TIR imagery
impressively shows the high rate of eruptive activity
from 2003 to late 2006, and possible hydrothermal
activity within the caldera in late 2008 (see Online
Supplement 32.5). Eruptive plumes are visible in all
ASTER images examined for this study, and doubt-
Case studies
769
Figure 32.7. Montagu Island, the largest (area 101 km 2 ) of the South Sandwich Islands, mapped in UTM
projection (zone 26S). (a) A representation of the best map published (Holdgate and Baker 1979), based on
shipboard observations and helicopter reconnaissance in 1964, with scale adjusted following Patrick et al. (2005);
(upper left inset) position of Montagu I within the South Sandwich chain; (lower left inset) position of the South
Sandwich Islands within the Subantarctic. ‘‘Contours’’ are actually crude formlines; summit of Mt. Belinda is
assigned the elevation measured in 1930, but the position measured from panel (c). (b) ASTER Global GDEM1generated map, unedited except for projection into UTM zone 26S; contour interval is 100 m. Shoreline (black) and
ice margin (red) from panel (a). Panels also available as Online Supplement 32.6a–d.
770
Remote sensing of glaciers of the Subantarctic islands
Figure 32.7. (c) ASTER image of the continuing eruption of Mt. Belinda, September 23, 2005, georeferenced to
the ASTER global DEM1 using shaded relief images of the latter (image courtesy of J.L. Smellie, color processing by
M.R. Patrick). Shoreline (white) is traced from the ASTER image; ice margin (red) is adjusted from panel (a). (d)
ASTER Global DEM1 map, clipped against shoreline (black) from panel (c); ice margin in red. Glacier ice covers
93% of the island. Panels also available as Online Supplement 32.6a–d.
Cartographic Inventory of the Subantarctic
less contaminated the topographic results. In fact,
the plume of grayish steam off the north coast in
Fig. 32.7c is recognizable in Fig. 32.7b, and the lava
stream flowing northeastwards down the flank of
Mt. Belinda appears as a number of spurious high
spots in Fig. 32.7b.
Fig. 32.7c (NASA 2005) shows the best single
ASTER image of Montagu Island. Both the shoreline and the ice margin were transferred from Fig.
32.7a to this image, but the approximate nature of
the georeferencing meant that no reliable conclusions could be drawn about changes in glacier
terminus positions. Instead, we accept Fig. 32.7c as
the most reliable source for the shoreline while Fig.
32.7a remains the best source for the ice margin
because Fig. 32.7c is snow covered. Minor adjustments were made by eye to match the Holdgate and
Baker ice margin to the ASTER shoreline.
The result of this merger of information is shown
in Fig. 32.7d, the first objective topographic map of
Montagu Island. Truncation of the south coast
could presumably be remedied rather easily, and
flaws such as the misinterpretation of Mt. Oceanite
could be corrected by detailed analysis of suitable
image pairs, although this would tend to nullify the
convenience of GDEM1. A broader conclusion is
that a general solution of the pit-and-bump problem will be essential if GDEM1 is to fulfill its
promise as an analytical tool. As mentioned, a more
recent global DEM, GDEM2, has been released
and in some parts of the world has reduced the
problems associated with GDEM1, but many of
the same problems identified here remain significant
in the newer product.
Certain features of the topography are now
clearer. The formlines of Fig. 32.7a suggest a conical mountain, but in Fig. 32.7d the summit region
is recognizable as the caldera that Fig. 32.7c shows
it to be. Most notably, GDEM1 shows that the
peak of Mt. Belinda is 2 km to the north of its
formline position in Fig. 32.7a, and that its maximum elevation, 1,070 m, is 300 m less than previously estimated.
32.4
CARTOGRAPHIC INVENTORY OF
THE SUBANTARCTIC
Fig. 32.7a is taken from a study of Montagu Island
(unpublished work), which aims to inventory Subantarctic glaciers from cartographic sources. The
work, summarized in Table 32.5, is incomplete,
but provides a regional perspective for Section
771
32.3, further insight into the potential of GDEM1,
and an estimate of total glacierized area. This total,
7,863 km 2 , derives from maps published over several decades, mostly based on aerial photos but in
some cases on little more than ground surveys or
even explorers’ sketches.
The inventory of the most extensively glacierized
island, South Georgia, is incomplete, and the information presented here is from Smith (1960).
For King George Island in the South Shetlands,
information in Table 32.5 is from a complete inventory compiled by the King George Island GIS
Project. For Deception Island, also in the South
Shetlands, information is from López-Martı́nez
and Serrano (2002). Elsewhere, Table 32.5 summarizes on-screen digitizing of scanned paper maps,
all transformed to the WGS 84 datum and the
UTM projection.
The quality of these maps varies greatly. Maps of
Kerguelen at 1:200,000 scale are good enough to
yield acceptable estimates of elevation changes
when compared with modern satellite images (Section 32.3.2). Measurements of Kerguelen glacier
area in 1963–1964 given in Table 32.5 (698 km 2 )
and in Section 32.3.2 (703 51 km 2 ) were obtained
by different operators working on the same map.
They are within 1% of each other, illustrating the
agreement that is possible between duplicate cartographic measurements. Comparable agreement is
seen between duplicate measurements of Heard
Island glacierization, respectively 257 km 2 (Section
32.3.1) and 254 km 2 (Table 32.5) for 1988.
The map of Peter I Island in 1987 at 1:50,000
scale (NPI 1988) is as good as maps of any glacierized region can get. It was used as the basis for an
inventory (Fig. 32.8) in which the ice cover was
subdivided into 26 glaciers with a total area of
151 km 2 . Unfortunately, the ASTER GDEM1 of
Peter I Island is unusable as a result of being based
on a single image pair that was almost completely
cloud covered.
At the opposite extreme, the best map of the
Balleny Islands (Fig. 32.9) is a crude sketch. Cartographic details are from the Soviet Atlas Antarktidy
(ADD 2000; shorelines and ice margins) and
Hatherton et al. (1965; conjectural formlines).
Two of the largest islands have formlines, but on
the third there is only a single spot height. Here
the ASTER GDEM1 would represent a major
advance in elementary knowledge, but it has no
coverage at all of Sturge Island and Buckle Island.
For Young Island, as for Montagu Island (Section
32.3.3), the GDEM1 ocean mask is based on an
South Orkney Islands
6C20101
6C20102
6C20103
6C20104
6C20105
6C20106
6C20107
6C20108
6C20109
6C20110
6C20111
Elephant
Gibbs Islands
King George
Nelson
Robert
Greenwich
Livingston
Deception
Snow
Low
Smith
6C20200
6C20201
6C20202
6C20203
6C20204
6C20205
Laurie
Saddle
Powell
Robertson
Coronation
Signy
6C202
6C20100
6C201
South Shetland Islands
Clarence
6C10200
Peter I Island
Inventory
code
6C10100
Island
Scott
Region
55
0.23
67.40
68.85
61.70
61.25
61.48
61.48
62.00
62.32
62.40
62.40
62.60
62.95
62.80
63.30
63.00
60.70
60.77
60.62
60.67
60.74
60.58
60.72
179.93
90.80
57.40
54.10
55.25
55.75
58.30
59.06
59.45
59.85
60.10
60.55
61.40
62.15
62.48
45.00
44.75
44.80
45.03
45.12
45.50
45.63
6.5
404
2.3
18
486
121.6
130.4
117.6
62.3
756.6
145.4
148.1
156.6
1,085
16.2
458.6
116.1
3,314
151.0
0.05
(km 2 )
(deg)
(deg)
Glacierized
area
Latitude
Longitude
1968
1979
1979
1979
1979
1979
1957
1957
1956
1979
1957
1957
1957
1957
2000
1957
1957
1957
1987
2002
Date of
glacierized
area
21
446
5.9
25
3
74
575
145.2
135.0
124.9
109.3
849.7
155.3
154.2
164.8
1,150
25.2
468.0
121.8
3,603
156.0
0.10
(km 2 )
Area
Table 32.5. Cartographic glacier inventory of the Subantarctic (WGI region 6C).
31.0
90.6
39.0
72.0
7.7
74.3
84.5
83.8
96.6
94.2
57.0
89.0
93.6
96.0
95.0
94.4
64.3
98.0
95.3
92.0
96.8
50
(%)
Glacier cover
288
1,265
346
550?
427
550?
1,265
2,100
<250
320
539
1,700
600
385
325
700
734
973
1,924
2,100
1,640
60
(m asl)
Maximum
elevation
772
Remote sensing of glaciers of the Subantarctic islands
All
6C50101
6C50102
Buckle
Sturge
6C
6C50100
Young
6C501
6C203072
Thule
Balleny Islands
6C203071
Cook
6C404
6C203070
Bellingshausen
Heard
6C20306
Bristol
6C403
6C20305
Montagu
Kerguelen Island
6C20304
Saunders
6C401
6C203031
Vindication
Marion
6C203030
Candlemas
6C301
6C20302
Visokoi
Bouvet
6C20301
Leskov
6C204
6C20300
Zavodovski
6C203
South Georgia
South Sandwich Islands
46.5
1
698
254
660
183
113
364
56.70
57.08
57.10
57.76
58.42
59.03
59.43
59.47
59.47
54.33
54.42
46.89
49.30
53.08
66.78
66.40
66.78
67.50
27.17
26.67
26.78
26.45
26.33
26.58
27.10
27.17
27.33
36.67
164.60
163.10
162.40
163.10
73.50
69.00
37.72
3.33
1975
56.67
28.13
7,863
15.1
20.1
0.1
94.5
93.5
25.6
0.3
4.2
24.1
0.0
(0.1)
56.30
27.58
277.6
57.76
26.45
1961
1961
1961
1988
1963–1964
1966
1985
1964
1964
1964
1964
1964
1964
1964
1964
1962
1962
1962
16,816
376
124
202
701
365
7,215
290
50.0
3,525
17.9
22.2
1.4
97.7
101.4
34.7
3.1
10.2
30.7
0.3
15.5
335.1
46.8
96.8
91.1
90.6
94.2
69.6
9.7
0.3
93.0
56.0
84.4
90.5
7.1
96.7
92.2
73.8
9.7
41.2
78.5
0.0
0.6
82.8
2,934
1,524
1,239
1,340
1,524
2,755
1,865
1,230
780
2,934
725
1,075
253
1,100
1,370
990
442
550
1,005
190
551
1,370
Cartographic Inventory of the Subantarctic
773
774
Remote sensing of glaciers of the Subantarctic islands
Figure 32.8. Peter I Island, mapped in UTM projection (zone 15S, with ticks every 5 km). Shoreline, ice margin,
contours at 100 m intervals, and glacier names from NPI (1988), based on air photography in 1987. Glacier
boundaries (dark blue lines) and numbers (red italic type) constitute a glacier inventory prepared as described by
Cogley (2009; see also Haeberli et al. 1989). The WGI region code assigned to Peter I Island is AQ6C10200. Island
area is 156.0 km 2 , of which 151.0 km 2 (97%) is glacierized. (Inset) Location of Peter I Island. Figure can also be
viewed as Online Supplement 32.7.
estimate of position that is incorrect and only a
small part of the western side of the island appears
in GDEM1.
However, not all of the Subantarctic is represented disappointingly by ASTER GDEM1. Fig.
32.10a shows Laurie Island in the South Orkney
Islands from a 1:100,000-scale map based on January 1979 photography and older ground surveys
(BAS 1988). The amount of detail is adequate for
inventory purposes. A shaded relief image of the
ASTER GDEM1 shows pits and bumps like those
visible in Fig. 32.7b, but they are few. Fortunately,
none have magnitudes detectable with the 50 m
contour interval adopted for Fig. 32.10b. The
1979 position of the island is about 2 km east of
the ASTER position, and as for Montagu Island it
was necessary to eliminate a large number of ice
floes. In fact, Figs. 32.4 and 32.7 show that a shoreline mask from an independent source is essential
when using GDEM1.
Summary and conclusion 775
Figure 32.9. The Balleny Islands, mapped in UTM projection (zone 58S, with a 20 km grid). Shoreline, ice margin,
formlines, spot heights, and place names from ADD (2000) and Hatherton et al. (1965). The three largest islands
have areas of 202 (Young I, 183 glacierized), 124 (Buckle I, 113 glacierized) and 376 (Sturge I, 364 glacierized)
km 2 , respectively. ‘‘UWis 8980’’ marks the location, measured by GPS, of an automatic weather station at the
northern tip of Young Island, and suggests that mapped positions are in error by several kilometers. (Inset) Location
of the Balleny Islands, for which the assigned WGI region code is AQ6C501. Figure can also be viewed as Online
Supplement 32.8.
32.5
SUMMARY AND CONCLUSION
Glaciers on Heard Island shrank at rates of 0.18%
yr1 between 1948 and 1980, 0.68% yr1 between
1980 and 1988, and 0.51% yr1 between 1988 and
2008 (Ruddell 2006; Section 32.3.1). On Kerguelen,
Cook Ice Cap shrank at 0.38% yr1 between 1963
and 1991 and at 0.85% yr1 between 1991 and
2003 (Section 32.3.2). Scattered measurements
elsewhere tend to corroborate these results. For
example, the summit glacier on Marion Island
had an area of about 1 km 2 in 1961 (Langenegger
and Verwoerd 1971). Sumner et al. (2004) report
that it ceased to exist during the 1990s, although
they describe remnants of ice buried beneath scoria.
In the South Shetland Islands, Calvet et al. (1999)
documented shrinkage of the ice cover of Livingston Island between five dates spanning 1956 to
776
Remote sensing of glaciers of the Subantarctic islands
Figure 32.10. (a) Laurie Island, South Orkney Islands, mapped in UTM projection (zone 23S, with ticks every 5
km). Shoreline, ice margin, contours at 100 m intervals, and place names from BAS (1988), based on air photography in 1979 and older ground surveys. Glacier boundaries (dark blue lines) and numbers (red italic type)
constitute a glacier inventory prepared as described by Cogley (2009; see also Haeberli et al. 1989). The WGI
region code assigned to Laurie Island is AQ6C20200. Island area is 74 km 2 , of which 55 km 2 (74%) is glacierized.
(Inset) Location of Laurie Island. (b) ASTER GDEM1 map of Laurie Island, with contour intervals of 50 m. Ice
margins (red) from panel (a). Panels also available as Online Supplement 32.9a, b.
References 777
Table 32.6. Mass balance measurements on Subantarctic glaciers. Superscript G denotes a geodetic measurement, in each case assuming a density of 900 kg m 3 when converting volume balance to mass balance.
Glacier
Island
Area
(km 2 )
Period
(no. of years)
Balance
(kg m 2 yr1 )
Hodges
South Georgia
0.27
1958 (1)
150
Smith (1960)
Hamberg
South Georgia
11.40
1958 (1)
254
Smith (1960)
Little Dome
King George
14.00
1992 (1)
þ163
Wen et al. (1998)
Flagstaff
King George
0.09
1958 (1)
537
Noble (1965)
G1
Deception
0.42
1969–1974 (6)
412
Orheim and Govorukha (1982)
Hurd G
Livingston
5.24
1956–2000 (44)
74
Molina et al. (2007)
Johnsons G
Livingston
5.62
1956–1998 (42)
161
Molina et al. (2007)
Brown G
Heard
6.18
1947–2004 (57)
450
Thost and Truffer (2008)
4.40
2000–2003 (3)
1,644
500.90
1963–2000 (37)
1,400
Cook Ice Cap G
Kerguelen
1996. The loss over the whole period was 31.6 km 2
from a 1956 area of 734.1 km 2 , a rate of 0.11%
yr1 . The ice cover of Greenwich Island decreased
from 145.4 km 2 in 1957 to 136.7 km 2 in 1991 (Ballester et al. 1993), a rate of 0.18% yr1 . Neither of
these estimates includes changes in the extent of
nunataks. Braun and Gossmann (2002) measured
the retreat of glacier termini in Admiralty Bay,
King George Island, between 1956 and 1995. The
21 glaciers drained an area of 237.7 km 2 in 1956 and
222.4 km 2 in 1992, a decrease of 15.1 km 2 at
0.18% yr1 . All of these rates are for tidewater
glaciers without floating tongues, and are therefore
roughly comparable with rates for Heard Island,
where several glaciers remain in contact with the
sea. The shrinkage rate on Kerguelen is hardly
influenced at all by the presence of stable calving
termini. The accelerating shrinkage of Cook Ice
Cap is therefore noteworthy, although on Heard
Island retreat appears to have been fastest in the
1980s.
Mass balance measurements are few in the Subantarctic. Table 32.6 is a complete list. The recent
geodetic measurements of Cook Ice Cap, Brown
Glacier, and two glaciers on Livingston Island are
significant additions. All but one of the measurements is negative.
There is thus no evidence that the remote and
little-known glaciers of the Subantarctic are exceptions to the rule, widely observed elsewhere,
Source
Section 32.3.2
that glaciers are shrinking and losing mass. Where
they have been observed, Subantarctic rates of
glacier retreat, shrinkage, and mass balance are
comparable with those of better known regions.
Future monitoring will inevitably have to rely
heavily on remote sensing. Measurements of shrinkage (reduction of area) are valuable in themselves,
but future work should focus more aggressively on
the measurement of elevation changes by subtraction of sequential DEMs obtained from radar
and optical stereo imagery. In this regard the measurements reported here are notable early contributions.
32.6
ACKNOWLEDGMENTS
We thank Gregory Leonard (University of Arizona) for contribution of Online Supplement 32.5
showing the Mt. Belinda ASTER time series.
ASTER data courtesy of NASA/GSFC/METI/
Japan Space Systems, the U.S./Japan ASTER
Science Team, and the GLIMS project.
32.7
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