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YQRES-02617; No. of pages: 13; 4C: 6, 8
Quaternary Research xx (2005) xxx – xxx
www.elsevier.com/locate/yqres
Short Paper
Basal processes beneath an Arctic glacier and their geomorphic imprint
after a surge, Elisebreen, Svalbard
Poul Christoffersen a,*, Jan A. Piotrowski b, Nicolaj K. Larsen b
a
Centre for Glaciology, Institute of Geography and Earth Sciences, University of Wales, Aberystwyth, Ceredigion SY23 3DB, UK
b
Department of Earth Sciences, University of Aarhus, C.F. Møllers Allé 120, DK-8000, Aarhus C, Denmark
Received 24 March 2004
Abstract
The foreground of Elisebreen, a retreating valley glacier in West Svalbard, exhibits a well-preserved assemblage of subglacial landforms
including ice-flow parallel ridges (flutings), ice-flow oblique ridges (crevasse-fill features), and meandering ridges (infill of basal meltwater
conduits). Other landforms are thrust-block moraine, hummocky terrain, and drumlinoid hills. We argue in agreement with geomorphological
models that this landform assemblage was generated by ice-flow instability, possibly a surge, which took place in the past when the ice was
thicker and the bed warmer. The surge likely occurred due to elevated pore-water pressure in a thin layer of thawed and water-saturated till
that separated glacier ice from a frozen substratum. Termination may have been caused by a combination of water drainage and loss of
lubricating sediment. Sedimentological investigations indicate that key landforms may be formed by weak till oozing into basal cavities and
crevasses, opening in response to accelerated ice flow, and into water conduits abandoned during rearrangement of the basal water system.
Today, Elisebreen may no longer have surge potential due to its diminished size. The ability to identify ice-flow instability from
geomorphological criteria is important in deglaciated terrain as well as in regions where ice dynamics are adapting to climate change.
D 2005 University of Washington. All rights reserved.
Keywords: Till; Subglacial processes; Flutings; Surge; Svalbard; Landforms
Introduction
Glacier surges are highly dynamic events characterized
by an abrupt increase in ice-flow velocity by up to several
orders of magnitude. Surges are often considered a recurrent
instability of ice flow leading to bimodal glacier motion
(Meier and Post, 1969). The highly non-linear behavior of
surging glaciers stems from threshold conditions in the
control of basal motion. Much research has addressed the
role of subglacial water (Kamb, 1987; Engelhardt and
Kamb, 1997, 1998; Kavenaugh and Clarke, 2000, 2001) and
its lubricating effect on ice flow (Clarke, 1987; Kamb, 1991;
Fisher et al., 1999; Tulaczyk et al., 2000). Identification of a
single specific surge mechanism has been unsuccessful so
* Corresponding author.
E-mail addresses: [email protected] (P. Christoffersen),
[email protected] (J.A. Piotrowski).
far, partly because there are regional differences in surge
characteristics (Murray et al., 2003). Surges in Svalbard
build up gradually and terminate slowly over several years
(Murray et al., 1998). In contrast, surges in Alaska, as seen
in the particularly well-documented 1982 –1983 surges of
Variegated glacier, can buildup over a short period of a few
months and terminate very abruptly in just a few hours
(Kamb et al., 1985). The differences in basal conditions
(between polythermal and temperate glaciers) may well
explain why surge mechanisms seem different (Murray et
al., 2003). The thermal evolution of weak till beds may
control Svalbard surges (Murray et al., 2000; Fowler et al.,
2001) while subglacial water flow tortuosity (Kamb, 1987)
may control Alaskan surges. Release of englacially stored
meltwater may be a key factor in both regions (Lingle and
Fatland, 2003; Murray et al., 2003).
Although much glaciological insight has been gained by
studies in front of glaciers known to have surged (Bennett et
0033-5894/$ - see front matter D 2005 University of Washington. All rights reserved.
doi:10.1016/j.yqres.2005.05.009
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al., 1999; Hambrey et al., 1999), it is still uncertain whether
surge mechanisms can be derived from geomorphological
studies alone. Geomorphological criteria for identification of
surging glaciers have been proposed among others by Evans
and Rea (1999) and it is becoming increasingly important to
test these criteria. The main objective of this study is to
identify ice-flow instability, e.g., surge-related events, for a
retreating glacier with unknown surge record. We compare
the landform assemblage from the foreground of Elisebreen
with hypothesized geomorphological criteria derived from
observations of surging glaciers elsewhere and find that iceflow instability can be inferred when geomorphological
criteria are combined with sedimentological data.
Changing dynamics of polythermal glaciers in Svalbard
In the maritime-arctic climate of Svalbard, glaciers need
to gain a thickness greater than about 100 m before warmbased conditions can arise (Hambrey et al., 1999; Murray
and Porter, 2001). Jiskoot et al. (1998, 2000) estimated that
a little over 10% of the glaciers in Svalbard have surge
potential and their statistical analysis showed that long
glaciers overlying weak sedimentary rocks, such as shale
and mudstone, have the highest probability of surging.
Murray et al. (2000) suggested that surge propagation in
Svalbard could be controlled by the transition between
unfrozen and frozen bed. Fowler et al. (2001) therefore
proposed thermally controlled surge mechanism for Svalbard glaciers. Investigations of Bakaninbreen showed that
surge propagation probably occurred as sliding and deformation of a thin layer of thawed sediment, just centimeters
to decimeters thick (Murray et al., 2000; Porter and Murray,
2001). Polythermal valley glaciers terminating on land may
have displayed similar characteristics in the past when ice
was thicker and the bed warmer (Hansen, 2003). Ice
dynamical regime may have subsequently changed due to
glacial recession following the end of the Little Ice Age ca.
100 yr ago and the progression of anthropogenic climate
warming (Hambrey et al., 2005; ACIA, 2004). Understanding the response of polythermal glaciers to climatic
variability is an integral part of assessing freshwater release
and contribution to sea-level rise from Svalbard.
Elisebreen and other glaciers in Kaffiøyra
There are six small valley glaciers in Kaffiøyra, a coastal
plain in West Svalbard bordered by two major tidewater
glaciers, Aavatsmarkbreen to the north and Dahlbreen to the
south (Fig. 1). The lengths of these valley glaciers are
approximately 2– 10 km and they retreat at a rate of 6 – 26 m
yr 1 (Lankauf, 2002). Kaffiøyra glaciers have been studied
for several decades, among others (Boulton, 1972) by
Forman (1989), Grzes and Lankauf (1997), Marciniak and
Marszelewski (1991), Olszewski (1977), and Zapolski
Figure 1. Study area showing location of Svalbard and approximate setting
of glaciers in Kaffiøyra.
(1977). To our knowledge, no surge has taken place during
this period.
Elisebreen is the largest of the six glaciers in Kaffiøyra
(Fig. 2a). A large network of moraine ridges crisscrosses its
glacially remoulded foreground (Figs. 2b and c). These
landforms and their abundance stand in striking contrast to the
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Figure 2. Oblique aerial photographs of Elisebreen’s foreground. (a) Streamlined till plain (photograph is a courtesy of M. Grzes). Arrows indicate view
direction of panels b and c, and white dot marks location of the river cut where geology was studied. The close-ups (b and c) show details of the subglacial
landscape. D = drumlinoids, S = supraglacial debris, F = ice-flow parallel ridges (flutings), CF = ice-flow oblique ridges (crevasse-fill ridges), MR =
meandering ridges (conduit infill).
barren foregrounds of the adjacent valley glaciers all of which
are smaller in size. Elisebreen is approximately 7 km long and
1.2 –1.8 km wide, and its surface area is around 12 km2. The
margin of Elisebreen is situated about 30– 60 m above sea
level. Studies of raised beach deposits have shown that the
Lateglacial ice retreat was followed by marine transgression
up to 48 m above the present sea level (Forman, 1989;
Niewiarowski et al., 1993). The coastal plain of Kaffiøyra is
thus composed of a succession of marine sediments that in
some places have been overridden by glaciers at least once
during the Little Ice Age. A prominent push moraine complex
marks the maximum advance of Elisebreen about 1.3 km
from its present margin. At present, the glacier retreats by
about 26 m yr 1 (Lankauf, 2002) and exposes a flat to gently
undulating till plain at 30 –40 m above sea level.
Geological and geomorphological investigations of the
proglacial terrain were performed during two field seasons.
The geology of the study area was established from a 70m-long and 5-m-deep river section in the central till plain
(Fig. 2a) as well as from several smaller sections through
the terminal moraine. Two radiocarbon datings were done
on shell fragments from the marine gravel. The location,
size, and orientation of different types of proglacial ridges
were mapped with GPS and compass. A series of small pits
(>10) were excavated at selected sites in the ridges.
Sedimentological and structural descriptions of glacial
deposits, beyond what is presented here, are subject of
work in progress.
Geological setting
Four major sedimentary units were mapped in a river
section dissecting a gentle hillock in the central part of the
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glacier foreground (Fig. 3). The lowermost unit (unit 1)
overlying the bedrock is a 0.4-m-thick, occasionally
laminated, greyish-green clayey silt (19% sand, 67% silt,
and 14% clay) with marine shells and shell fragments. It is
overlain by an up to 0.5-m-thick well-sorted, well-rounded
openwork gravel (unit 2) grading upwards into a clastsupported gravely sand with abundant fragments of redeposited mollusc shells (unit 3). The gravely sand is
parallel bedded with individual beds usually decimeters
thick. The beds dip in accord with the ground surface of the
hillock, giving the appearance of an onion-like structural
arrangement. Shell fragments from unit 3 were dated to
10,980 T 60 14C yr B.P. (Poz-700) and 10,820 T 65 14C yr
B.P. (Poz-694), which is in the bracket of radiocarbon dates
on marine shells from other parts of Kaffiøyra (Niewiarowski et al., 1993). In the topmost 30 cm, this deposit is
cryoturbated and contains frost-shattered boulders. The
periglacial structures are well preserved and display no
signs of glacier-induced deformation despite being overridden by ice. The uppermost unit (unit 4) is a stony
diamicton with fine-grained matrix (37% coarser than sand,
28% sand, 26% silt, and 9% clay). This unit constitutes a
thin drape of glacially re-deposited sediment with erratics
from the local bedrock composed of the Precambrian
Haeklahook Formation with characteristic tillites, and
various tertiary formations consisting of sedimentary rocks
as mudstone, siltstone, limestone, and shale (Hjelle, 1993).
We interpret units 1, 2, and 3 as a concession of marine
sediments deposited during the Lateglacial/early Holocene
transgression. Unit 4 is a layer of basal till, which is the
source material of the landform assemblage described
below. Texture of this till is largely the same regardless of
the landform it occurs in (Fig. 4).
Landforms
The foreground of Elisebreen reveals a high concentration of distinctly different landforms. Several hundred
small moraine ridges, approximately 0.1 –1 m in height and
up to 200 m in length, protrude from the ground surface
(Figs. 2b and c). The ridges are composed of the same till
source (Fig. 4b) and they can be divided into groups based
on geomorphic appearance.
Ice-flow parallel ridges (flutings)
The most prominent landforms in front of Elisebreen are
linear moraine ridges oriented parallel to ice-flow direction.
Several hundreds of these closely spaced and easily
discernible ridges are distributed throughout the foreground
(Figs. 2b and c). They vary in height from just a few
centimeters to a little more than 1 m (Figs. 5a, b, c, and e)
and in length from a few meters to almost 200 m. The ridges
have a relatively constant width/height ratio of about 5, but
their lengths vary extensively. Length/width ratios are
Figure 3. Photograph (a) and drawing (b) of a river cut through
proglacial sedimentary succession in front of Elisebreen. A thin drape
of till (shaded) covers stratified units of sand and gravel, which overlie
a layer of clayey silt. View is towards SE and location is given in
Figure 2a. Synthetic log (c) shows the major lithological units (1 – 4) of
this site.
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Figure 4. Mean grain-size distribution of (a) different sedimentary units (with standard deviation whiskers), and (b) material in different types of landforms.
Note that till texture is largely the same in all landforms studied.
spread from about 5 to >100 with average around 25. A
comparison to landform geometries measured at other
glaciers is shown in Figure 6. The ridges have two
subforms: they come with or without a boulder on their
ice-proximal end. Boulders located in front of the ridges are
polished and striated parallel to the ridge orientation (Fig.
5d). There is no direct correlation between boulder size and
landform geometry. Most of the boulders are found at the
end of ploughing trails (Fig. 5d), which deepen progressively towards the boulders. The ploughing marks are
largely filled with till.
The ridges are mainly composed of material from the
adjacent, thin till layer, which overlies marine sediments
along a subhorizontal contact surface (Figs. 7a– c). The
landform relief is therefore given predominantly by varia-
tions in till thickness. A string of test pits excavated on two
separate sites revealed diapirs or up-thrusts of marine gravel
immediately down-ice from the boulders (Fig. 7d), and
tongues of till intruded from the sides. Till and marine
sediment become progressively mixed down-ice from the
boulders (Fig. 7c), but we observed centimeter- to decimeter-large inclusions of marine sediment transported more
than 50 m from the boulder site. Till fabric measured on 14
sites in one fluting reveals a strong ridge-parallel orientation
(mean S1 = 0.833) and low dip angles evenly distributed
either in up-ice or down-ice direction (Fig. 8). Fabric at the
transition between till plain and landform is weaker (mean
S1-value from 11 sites is 0.760).
The ice-flow parallel ridges with boulders on their
proximal ends are interpreted as classic flutings (e.g., Benn
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Figure 5. Subglacial landforms in front of Elisebreen: (a) oblique aerial photograph of the till plain showing ice-flow parallel ridges (flutings; in the view
direction) superimposed by ice-flow oblique ridges (crevasse-fill); (b) small flutings without initiating boulders on till plain; (c) a fluting (about 90 m long) with
person standing on the initiating boulder; note also a crevasse-fill ridge in lower-right corner; (d) a boulder with a ploughing groove behind it (view down-ice);
(e) a fluting with initiating boulder; note also other parallel ridges and grooves giving the till plain its distinct linear pattern (view down-ice); (f) a crevasse-fill
ridge emerging at the glacier surface close to the terminus due to ablation (view down-ice); (g) contrasting morphology of a fluting (on the left; linear), a
meandering ridge (on the right), and a small crevasse-fill ridge (obliquely superimposed on the former ridges). This landform assemblage is elaborated in
Figure 7.
and Evans, 1998, p. 426). The measured clast fabric is
consistent with observations of flutings in other field sites
(e.g., Rose, 1989; Benn, 1994; Eklund and Hart, 1996). Iceflow parallel ridges without initiating boulders are also
interpreted as flutings, although they contain no evidence of
ploughing or thrusting. These flutings (Fig. 5b) are likely
formed by sediment infill of basal ice cavities, which may
have formed by ice sliding over an irregular surface, e.g.,
bedrock protrusions. This mechanism is similar to the
groove-ploughing theory for production of large glacial
lineations by fast ice-stream flow (Clark et al., 2003).
The subglacial conditions from which flutings develop
are uncertain. Their elongation ratios exceed values pro-
posed to be indicative of fast ice flow (Stokes and Clark,
2001, 2002), and fast ice flow depends on warm-based
conditions (Clarke et al., 1984; Clarke, 1987). Yet, the
landform is observed in both warm-based and cold-based
environments (Gordon et al., 1992; Evans and Twigg,
2002). Structural data from our field site indicate two
separate mechanisms whereby sediment accumulated in the
lee of the lodged boulders. These are up-thrusting from
below and inflow from the sides. We speculate that while
thrusting can occur under any subglacial thermal field,
oozing-in from the sides depend on warm-based conditions
and high pore-water pressure, which yields low basal shear
strength.
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Figure 6. Comparison of elongation ratios and lengths for flutings in front of Elisebreen flutings and flutings observed elsewhere. Flutings in front of
Hagafellsjokull and Columbia Glacier have been interpreted as a signature of fast ice flow.
Ice-flow oblique ridges (crevasse-fill ridges)
Another prominent network of moraine ridges has
orientation oblique to ice-flow direction (Figs. 5a and g)
with an offset of about 20 –30- (Fig. 9). These landforms
(Figs. 7a and e) are regularly distributed throughout the
proglacial till plain and superimpose the ice-flow parallel
landforms described above. The ridges range from 0.3 to
0.6 m in height and from 10 to 50 m in length. They often
have slightly undulating crests and lack the perfect
linearity typical for flutings. They are nonetheless composed of the same basal till. Formation of the oblique
ridges can be observed at present at the retreating ice
terminus (Fig. 5f).
Ice-flow oblique ridges are interpreted as crevasse-fill
ridges, which have either basal or supraglacial source of
debris (Sharp, 1985; Bennett et al., 2000). Here, compositional similarity to the surrounding basal till shows that the
former source is most likely. Fracture mechanical analysis
demonstrates that basal crevasses can form when basal
water pressure is close to the ice overburden pressure
(Weertman, 1980; van der Veen, 1998). Pore-water pressure
a few bars below the ice overburden pressure was observed
during the 1982 –1983 surge of Variegated Glacier (Kamb
et al., 1985) and similar conditions are found beneath ice
streams in Antarctica (Engelhardt and Kamb, 1997, 1998).
Crevasse-fill ridges composed of basal sediment may be a
diagnostic feature of past surges if they are found in front
of surge-type glaciers. Basal crevasses are, however, not
easily identified due to their subglacial origin and their
closure from compressional stresses arising in the slowmoving quiescent phase. Basal crevasse-fill has nonetheless
been interpreted from studies at other localities in Svalbard
(Woodward et al., 2002) as well as studies in Canada
(Clarke et al., 1984), Alaska (Ensminger et al., 2001), and
Iceland (Sharp, 1985).
There is also morphological evidence of till ridges
orientated transverse to ice-flow direction in the study area.
These ridges are, however, much more subdued and less
frequent than the landforms described above. Their height is
typically 0.1 – 0.3 m and their length is generally less than
20 m. We interpret these ridges as a result of melt-out of
debris-rich thrust faults (Hambrey et al., 1999). Observations from the glacier terminus show that thrust faults have a
gentle dip and tend to strike perpendicular to ice-flow
direction due to high compressional stresses arising at the
warm/cold thermal transition near the terminus.
Meandering ridges (conduit infill)
This type of ridges is characterized by a meandering
shape quite similar to that of an esker (Figs. 5g, 7a, and e).
The undulating crests of these ridges are typically less than
0.5 m high. Their lengths range from a few meters to
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Figure 8. Fabric measurements from locations shown in Figure 7a. Lower hemisphere equal-area projection, 25 – 40 stones measured on each site. S1
eigenvalues indicate fabric strength (Mark, 1973). Symbols denote fabric measurements in fluting (F), meandering ridge (M), and till plain (P).
Figure 7. Sediment structural data from a fluting-meandering ridge-crevasse-fill ridge assemblage. (a) Landform spatial arrangement and cross sections
observed in excavated trenches. Numbers refer to fabric measurements shown in Figure 8. View direction in cross sections is down-ice. (b – d) Geological
composition seen in cross sections with view direction up-ice. Note the gravel diapir projecting through the till behind the initiating boulder in panel d; (e)
landform assemblage viewed down-ice before excavation. The same assemblage is shown in the opposite direction in Figure 5g.
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several tens of meters. Despite similarity to eskers we
found no fluvial sediment in these landforms. They are,
just like the other ridges described above, composed of
basal till that overlies marine gravel along a subhorizontal
interface (Fig. 7a). Till fabric measured at 14 locations in
one meandering ridge is strong (mean S1 = 0.808; Fig. 8)
and uniformly ice-flow parallel, which indicates that it
exhibits an active-ice signature similar to the flutings and
the flat ground-moraine surface. Meandering ridges are
often superposed by the crevasse-fill ridges and located
alongside the flutings (Fig. 7).
We interpret this group of ridges as infill of an abandoned
water conduit system. Their composition and structure,
together with the absence of fluvial sediment, indicate that
meltwater became distributed within the till and that porewater pressure rose to the point where material behavior
became fluid-like, i.e., water content above the liquid limit
of the sediment (Mitchell, 1993). Till thus started to ooze
into the abandoned water conduit system following an
instantaneous cessation of water flow and pressure drop in
the channel. A similar observation of conduit infill was
made in front of an Icelandic glacier that surged in 1991
(Bennett et al., 2000).
Other landforms
A large terminal moraine complex, approximately 20 m
high and 50 to >100 m wide (Fig. 10a), marks the maximum
extent of Elisebreen. The complex is composed of multiply
stacked but internally intact, fossil-bearing marine sediments similar to those exposed in the river section shown in
Figure 3. A large ice-cored moraine and hummocky terrain
Figure 10. Other proglacial landforms in front of Elisebreen. (a) Terminal
moraine complex composed of stacked succession of the sedimentary units
shown in their original position in Figure 3 (view towards SE); (b) ice-cored
moraine and hummocky topography in the northern part of the foreground
(view towards NE).
with multiple topographic highs are found immediately upice from the thrust moraine (Fig. 10b). The till plain, which
is located between the hummocky terrain and the ice
margin, features several drumlinoid hills. The drumlinoids,
which lack a typical stoss-and-lee-side asymmetry, are about
100 m long, 20 m wide, and 3 –5 m high (Fig. 2a).
Preservation of original strata in the stacked succession of
the terminal moraine complex indicates that glaciotectonic
thrusting (also noted by Niewiarowski et al., 1993;
Olszewski, 1977) occurred under permafrozen conditions.
Given thawed conditions, the clay layer in the marine
succession (Fig. 3) would most likely be too weak to remain
intact during displacement. The moraine complex may have
been deposited around or just after the Little Ice Age when
Elisebreen was larger.
Discussion
Figure 9. Rose diagram showing direction of 20 flutings and 200 crevassefill ridges, which are offset to ice-flow direction by ca. 20-.
Surge-related landforms have mainly been explored in
front of glaciers with a known surge record. It remains
uncertain whether these landforms can be used to infer iceflow instability for glaciers with no such record. Our
observations comply with existing geomorphological cri-
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teria developed for surge-type glaciers elsewhere (Glasser et
al., 1998a,b; Bennett et al., 1999; Hambrey et al., 1997,
1999; Fuller and Murray, 2002). The landform assemblage
in front of Elisebreen fits particularly well with the landsystem model proposed by Evans and Rea (1999), in which
diagnostic features of contemporary surging glaciers were
compiled from geological observations in the marginal zone
of glaciers in Svalbard, Iceland, and North America known
to have surged in the past. The key limitation of using
geomorphic criteria to infer changes in ice dynamical
regime is that none of the specifications is a single piece
of evidence for ice-flow instability. It is the combination of
landforms and their assemblage that must provide sufficient
support for correct inference.
Common to the landform assemblage outlined above is
formation by lateral entrainment of soft, deformable till into
basal ice cavities, crevasses, and water conduits abandoned
in response to a rearrangement of the basal water system,
possibly to a linked cavity configuration (Kamb, 1987). It is
probable that Elisebreen experienced a surge (or a series of
surges) during the Little Ice Age or shortly thereafter, ca.
100 yr ago, when ice was thicker and the bed warmer. The
overall smoothness of Elisebreen’s foreground including
ice-flow parallel lineaments stands in distinct contrast to
other valley glaciers in Kaffiøyra, which have rugged
foregrounds mainly composed of chaotically scattered
angular debris. Such different appearances of glacier foregrounds may result from different ice-flow regimes with fast
flow in the former case (Hart, 1999). In contrast to ice-flow
parallel lineaments and conduit infill, which are individually
ambiguous indicators of fast ice-motion, crevasse-fill ridges
with a subglacial source may act as a more direct piece of
evidence of past ice-flow instability as basal crevasses only
form when glaciers are close to flotation due to subglacial
pore-water pressure close to the ice overburden pressure
(Weertman, 1980; van der Veen, 1998).
Historical accounts of surges in Iceland indicate reduced
surge potential in response to glacial recession since the early
1900. The same may be the case in Svalbard. A transition
from surge to non-surge glacier potential was for instance
identified on Midre Loevenbreen, which is a small valley
glacier ca. 25 km northeast of Elisebreen (Hansen, 2003;
Hambrey et al., 2005). The absence of surges in recent time
together with ongoing glacial retreat at a rate of ca. 26 m yr 1
suggests that Elisebreen’s surge potential may no longer
exist. The glacier appears to be thinning rather than
rebuilding mass and this may be related, at least partly, to
the Arctic amplification of global warming. The projected
warming of the Arctic is 4 – 7-C over the next 100 yr with an
increase in precipitation falling mainly as rain (ACIA, 2004).
Polythermal valley glaciers will become thinner and increasingly cold based, and thus more stagnant, due to increase in
loss of heat from the bed. Coastal valley glaciers in Svalbard,
such as the ones in Kaffiøyra, may eventually waste away
causing sea level rise and increased release of freshwater to
the Arctic Ocean (Hagen et al., 2003).
11
Conclusions
Fast glacier flow is commonly associated with basal
lubrication arising from pore-water build-up in fine-grained
subglacial sediment (Clarke et al., 1984; Kamb, 1991;
Tulaczyk et al., 2000). Bedrock composed of fine-grained
sedimentary material is thus likely to generate surgefavorable conditions (Jiskoot et al., 2000). However, with
its ¨65% of sand and gravel, and ¨35% of silt and clay, the
Elisebreen till is very different from the fine-grained West
Antarctic sub-ice stream tills in which the content of sand
and gravel is ¨45%, while silt and clay constitute ¨55%
(Tulaczyk et al., 1998). This indicates that fast glacier flow
may also occur from sliding over coarse-grained sediment.
The well-preserved sedimentary structures in the marine
deposits underlying the thin till layer support the potential
role of subglacial permafrost beneath surging glaciers in
Svalbard. It is likely that Elisebreen surged over a thin layer
of thawed till while the underlying marine sediments
remained largely frozen and thus undisturbed apart from
scattered ploughing by boulders that were large enough to
penetrate through the till layer. A very thin till layer was also
observed beneath Bakaninbreen (Murray and Porter, 2001;
Murray et al., 2000), whose surge may have terminated from
a drop in water pressure associated with loss of basal
meltwater into permafrost discontinuities (Smith et al.,
2002). Termination of a surge of Elisebreen may also have
been caused by (1) loss of basal lubricant into basal cavities
and bottom crevasses opening in response to accelerated ice
flow, and (2) drop in subglacial pore-water pressure from
collapse of a linked cavity system and a return to a
channelized subglacial drainage system (Kamb, 1987).
Acknowledgments
We thank N. Copernicus University, Poland, for
permission of using their Polar Field Station in Kaffiøyra
during fieldwork in 2001 and 2002, and W. Wysota, K.
Lankauf, I. Sobota, and M. Grzes for the hospitality and
on-site discussions. SNF grant 51-00-0410 to JAP, Erik
Hegenhofts grant to PC, and Knud Hojgaard Fond grant to
NKL are acknowledged. Fieldwork was carried out when
PC was a PhD student at the Technical University of
Denmark. We are grateful to reviewers and the editor for
helpful comments.
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