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Global and Planetary Change xx (2006) xxx – xxx
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Palaeosurfaces in central West Greenland as reference for
identification of tectonic movements and estimation of erosion
Johan M. Bonow a,b,⁎, Karna Lidmar-Bergström b , Peter Japsen a
a
Department of Physical Geography and Quaternary Geology, Stockholm University, SE-10691 Stockholm, Sweden
b
Geological Survey of Denmark and Greenland (GEUS), Øster Voldgade 10 DK-1350 Copenhagen, Denmark
Received 14 April 2004; accepted 20 December 2005
Abstract
Landform analysis of basement rocks has been undertaken with the aid of digital elevation data, aerial photographs and field
observations in central West Greenland (69°15′N–66°00′N). Palaeosurfaces have been identified, dated relatively to each other,
used to quantify uplift and fault movements and also used to estimate differential erosion. Two types of palaeosurfaces were
mapped across the Precambrian basement: a surface at low elevation with distinct hills (hilly relief), and two planation surfaces
formed across different types of basement rocks. The hilly relief surface emerges as an inclined surface from Cretaceous cover
rocks in Disko Bugt and is interpreted as a stripped late Mesozoic etch surface. This surface is cut off towards the south by a less
inclined planation surface, which is younger and thus of Cenozoic age. It is similar to the post-Eocene (Miocene?) planation
surfaces identified on Disko and Nuussuaq in other studies. The planation surface splits in two southwards towards high areas
around Nordre Isortoq and Sukkertoppen Ice Cap. The upper planation surface forms near-summit areas of tectonic blocks dipping
in different directions and with different tilts. The uplift centres define the crests of two mega blocks, separated by the ‘Sisimiut
Line’ which coincides with the Precambrian Ikertôq thrust zone. A partially developed lower planation surface indicates a first
uplift of maximum 500 m followed by a second uplift of maximum 1000 m. We infer that these uplift events occurred during the
late Neogene based on correlation with similar surfaces on Nuussuaq and the timing of exhumational events estimated from apatite
fission track analyses of samples from a deep borehole on Nuussuaq (reported elsewhere). The difference between a reconstruction
of the upper planation surface across the entire area and the present topography was used as an estimate of erosion of basement rock
since the formation of the upper planation surface. The erosion is unevenly distributed and varies from almost none on the wellpreserved planation surfaces to 800–1300 m along valleys, and even more in the fjords. Erosion is less within areas of gneiss in
granulite facies, than in areas of gneiss in amphibolite facies.
© 2006 Published by Elsevier B.V.
Keywords: palaeosurface; West Greenland; uplift; tectonic movements; differential erosion; Neogene; planation surface; etch surface; hilly relief;
Landform analysis
1. Introduction
⁎ Corresponding author. Present address: Geological Survey of
Denmark and Greenland (GEUS), Øster Voldgade 10 DK-1350
Copenhagen, Denmark. Tel.: +45 38142251; fax: +45 38142050.
E-mail address: [email protected] (J.M. Bonow).
The relationships between uplift, erosion and
sedimentation along the elevated passive continental
margins of the North Atlantic and which the driving
forces are, tectonic or climatic, have become a key
0921-8181/$ - see front matter © 2006 Published by Elsevier B.V.
doi:10.1016/j.gloplacha.2005.12.011
GLOBAL-01044; No of Pages 21
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issue for geomorphologists, geophysicists and geologists (Japsen and Chalmers, 2000; Doré et al., 2002).
Important questions are when the areas have risen, if
the uplift was simultaneous across the region, and how
much different areas were uplifted. Other questions are
from where the offshore sediments emanate and how
much is eroded where? Central West Greenland was
chosen for a pilot study, in which the landforms are
used as a data set for conclusions on uplift and
erosion.
West Greenland is part of a passive margin east of the
Davis Strait, where N–S faults connect extinct NW–SE
oriented Palaeogene sea-floor spreading axes in the
Labrador Sea and Baffin Bay (Chalmers and Pulvertaft,
2001). Separate uplift events of the Nuussuaq Basin in
the Palaeogene (Dam et al., 1998; Dam, 2002) as well as
in the late Neogene (Mathiesen, 1998; Chalmers, 2000;
Japsen et al., 2005) have been documented.
The relationships between denudation surfaces in
basement (denuded rocks from old orogenies) and
cover rocks (undeformed sedimentary strata or volcanic
rocks directly on basement) (Lidmar-Bergström and
Näslund, 2005) have turned out to be a most important
research field to reveal the denudational and diastrophic history of an area (Lidmar-Bergström, 1988, Hall,
1991; Lidmar-Bergström, 1993, 1995; Demoulin,
1995; Peulvast et al., 1996; Lidmar-Bergström, 1996,
1999; Hall and Bishop, 2002; Japsen et al., 2002a;
Hall, 2003; Bonow, 2004). In central West Greenland
the Precambrian basement is exposed over large areas
(Fig. 1), but Cretaceous strata are preserved in the
Nuussuaq Basin, which extends from the Melville Bay
in the north to approximately 62°N in the south
(Chalmers et al., 1999). Palaeogene volcanics rest both
on Cretaceous strata and directly on basement, both
offshore and onshore (Chalmers et al., 1999; Henriksen
et al., 2000).
The aim of the present study is to use these
conditions in identifying and mapping denudation
surfaces on central West Greenland, in determining
their relative ages, and to use the mapped surfaces as
reference for identification of tectonic movements and
estimations of amounts of uplift and erosion.
Fig. 1. Regional map of basement and cover rocks in the Nuussuaq
Basin, central West Greenland, containing Cretaceous and Paleocene
sediments and Palaeogene volcanic rocks presently exposed on Disko,
Nuussuaq and Svartenhuk. Basement is in certain areas covered by
Cretaceous sedimentary rocks while in other areas it is covered by
Palaeogene basalt. The black lines show faults. CBFS — Cretaceous
Boundary Fault System. MB — Melville Bay. SIC — Sukkertoppen
Ice Cap. Geology after Chalmers et al. (1999), Chalmers and Pulvertaft
(2001) and Pulvertaft and Larsen (2002).
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2. Study area
2.1. Location and major physiographic features of West
Greenland
The study area is located along the west coast of
Greenland, between Sukkertoppen Ice Cap in the south
and Disko Bugt in the north (Figs. 1 and 2). The area is
limited by the Greenland ice sheet in the east and by
Davis Strait in the west. The distance from the coast to
the ice sheet is up to 150 km, whereas the N–S extent of
the study area is up to 350 km. The area is thus one of
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the largest continuous ice-free areas in Greenland.
Greenland is approximately an asymmetric plateau
with high rims, higher on the eastern side than on the
western side (Weidick, 2000). A major drainage route
has a water divide situated along the eastern rim of
Greenland and a watershed draining the major parts of
southern and central Greenland. The depositional
pattern of fluvial Cretaceous sediments in the Nuussuaq
Basin shows that this major drainage system was
already established in the Cretaceous (Funder, 1989;
Pedersen and Pulvertaft, 1992; Dam et al., 1998). At
present it is a major drainage outlet into Disko Bugt
Fig. 2. Geology of the study area (simplified). Geology after Henriksen et al. (2000). Position for topographical profiles in Figs. 4 and 6 is indicated.
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(bay), occupied by the Jakobshavn Isbræ immediately
north of the study area (Fig. 1).
2.2. Glacial record
Greenland was completely, or almost completely,
covered by ice during parts of the Pliocene and most of
the Quaternary, and glacial deposits are widespread on
ice-free land areas and on the adjacent shelf (e.g.,
Funder, 1989). Climatic cooling started in the Late
Miocene with full glacial conditions of Greenland at
7 Ma (Larsen et al., 1994). The glaciation with the
largest recorded aerial extent occurred near the end of
the Pliocene and is evidenced on the shelf (Funder,
1989). During the Eemian the ice sheet was significantly
reduced, followed by large variations of the ice margin
during the latest glacial cycle. The latest deglaciation
began 14,000–10,000 years ago, with various oscillations. A minimum position was reached approximately
5000 years ago, when the ice margin was up to 50 km
inland of its present position in southwest Greenland
(Huybrechts, 2002) and at least 15 km in West
Greenland (Weidick et al., 1990).
2.3. Tectonic development, volcanism and Neogene
uplift
Sedimentary rift basins started to form outside West
Greenland probably during the Palaeozoic and developed during the Mesozoic and Cenozoic with maximum
total sediment thicknesses of around 10 km (Chalmers et
al., 1999; Chalmers and Pulvertaft, 2001). A continental
margin developed in the Paleocene when seafloor
spreading took place in Baffin Bay and the Labrador
Sea, areas separated by a major strike-slip fault system
in Davis Strait (Chalmers and Pulvertaft, 2001). The
impact of the Iceland Plume is recorded in Cretaceous–
Paleocene strata on Nuussuaq. Here extensive erosion
together with development and reactivation of faults
took place in latest Cretaceous times followed by uplift
and incision of valley systems in the Cretaceous rocks
during the early Paleocene (Dam et al., 1998; Dam,
2002). The valleys were subsequently drowned and
filled with marine Paleocene sediments prior to eruption
of thick sub-aqueous basalt, which extruded over large
parts of the Nuussuaq Basin later in the Paleocene. The
volcanism became later generally sub-aerial and the
basalt onlapped also the basement areas in the east
(Pedersen et al., 2002). Volcanism continued until the
Eocene in the eastern areas of the Nuussuaq Basin
(Storey et al., 1998). Offshore West Greenland,
Cenozoic sediments reach thicknesses of more than
4 km (Rolle, 1985; Piasecki et al., 1992; Nøhr-Hansen,
2003; Piasecki, 2003). A mid-Eocene unconformity
probably marks the end of major fault movements and
can be correlated to slowing rates of sea-floor spreading
in the Labrador Sea (Chalmers, 2000; Dalhoff et al.,
2003).
Uplift of the Nuussuaq Basin in the Neogene has
been concluded from the fission track record acquired
from the 3 km deep, hydrocarbon exploration well
GRO#3 (Mathiesen, 1998; Japsen et al., 2005). The
fission track record shows three distinct episodes of
cooling, that began between 40 and 30, 11 and 10 as
well as 7 and 2 Ma (Japsen et al., 2005). The two latter
episodes surely included exhumation of rocks and
were interpreted as uplift events. They are in
agreement with the observations offshore by Chalmers
(2000), who found that a > 3 km thick, post-midEocene, seaward dipping section is truncated by an
erosional unconformity close to sea bed west of
Nuussuaq, and concluded it had formed substantially
after the mid-Eocene and probably during the
Neogene. These studies suggest uplift and erosion
offshore as well as on the landmass on Nuussuaq
during the Neogene.
A coherent erosion surface formed across large
distances has been identified on Nuussuaq (Bonow,
2004). This surface is close to the summits, dips in
different directions, and changes of tilt occur abruptly
across major faults. The surface is post-Eocene and its
formation has been independent of rock types as it cuts
across both resistant Precambrian basement and more
easily eroded Eocene and Paleocene volcanic rocks. Its
final shape must have been obtained before the 11 to
10 Ma uplift event occurred (see above) and it is thus
suggested to be of middle Miocene age (Bonow et al.,
in press). The formation of a lower planation surface
and valley generation is interpreted to be a result of this
uplift and the youngest valley generation is correlated
with the 7–2 Ma event (Bonow et al., in press).
2.4. Basement and cover rocks
The study area is part of a Precambrian shield (Figs. 1
and 2) and is crossed by the Ikertôq thrust zone (van
Gool et al., 2002), which roughly coincides with a
topographic feature, in this paper called the Sisimiut
Line. The shield was probably denuded and covered by
sedimentary strata in the Ordovician. “Loose blocks” of
Phanerozoic sandstone are present in the study area
(Peel and Secher, 1979; Fig. 2) and an Ordovician
outlier is located at Fossilik just south of the study area
(Stouge and Peel, 1979). Ordovician strata occur at sea
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bed in the western part of the Davis Strait (Chalmers and
Pulvertaft, 2001).
In Disko Bugt, at least 2 km of Cretaceous
sediments rest directly on basement. The Cretaceous
sediments are bounded in the east by the Cretaceous
Boundary Fault System (CBFS) and in the west by a
N–S trending basement ridge. This ridge is exposed in
Disko Bugt on several small islands and skerries and
also at sea bed (Chalmers et al., 1999). On the
northward continuation of the ridge below Disko,
basalt of Paleocene age (Storey et al., 1998) rests
directly on the basement.
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reshaping of the flat sub-Cambrian peneplain is
negligible (Johansson et al., 2001). Another important
condition, when interpreting glaciated areas, is the
protecting effect of ice sheets and ice caps during most
of the glaciations due to cold based conditions (e.g.,
Sugden, 1978; Kleman, 1994). These conditions have
been at hand in many high areas during the whole
period with Late Cenozoic glaciations (Kleman and
Hättestrand, 1999), while glacial erosion has been most
effective in low areas (Sugden, 1978; Glasser, 1995;
Näslund, 1997).
3.2. Definitions
3. Landform analysis
3.1. Background
The relation between re-exposed relief, new relief,
and cover rocks of different age within areas of
basement rocks in southern Fennoscandia has turned
out to be a key for analysis of relief development on a
shield (Lidmar-Bergström, 1988, 1995, 1996). Particularly the effect of Mesozoic deep weathering for shaping
a hilly relief with up to 200 m high hills could be
acknowledged by studying the regional distribution and
local position of remnants of both thick kaolinitic
saprolites and Mesozoic cover rocks (Lidmar-Bergström, 1982, 1989). The striking difference between the
hilly landscape and the totally flat sub-Cambrian
peneplain was useful in this analysis as also the
difference in tilt of the identified surfaces. Together
with a literature review on the surrounding sedimentary
strata it was possible to define periods during the
Phanerozoic when deep weathering (etching) and
stripping on the one hand and stripping and pedimentation on the other dominated basement denudation in
northern and central Europe (Lidmar-Bergström, 1982
table 11 p. 172).
It is a common assumption, though not written in
any scientific paper, that bedrock hills within former
glaciated areas are caused and totally formed by glacial
erosion. On the contrary many studies on relief
development in Fennoscandia had given support for
the opposite conclusions, viz. that preglacial weathering and fluvial erosion are main causes for the origin of
the present landforms also outside the exhumed
surfaces (Björnsson, 1937; Nordenskjöld, 1944; Mattsson, 1962; Lidmar-Bergström, 1997; Olvmo et al.,
2005). Glacial erosion can cause substantial reshaping,
particularly within hilly relief by abrasion on top of
hills and plucking on lee sides (Olvmo et al., 1999;
Migón and Lidmar-Bergström, 2001), while the glacial
The following terminology is used in the present
study: Denudation surface is used as a general term
for a landscape feature of wide extent formed across
the bedrock. If it is characterised by low relief, it is
called a planation surface and if it is characterised by
distinct bedrock hills we call it a hilly relief. Exhumed
or re-exposed surfaces are surfaces that have been
exposed by erosion of protective cover rocks. Such
surfaces are common over basement rocks (Twidale,
1985, 1999). Erosion surface is here used for surfaces
constrained by a common base level for the fluvial
system.
The described surfaces are palaeosurfaces, defined as
landforms not in accordance with present climatic or
tectonic conditions. They are partly destructed or
reshaped, but still recognizable. Their former wider
extent may be reconstructed (cf. Widdowson, 1997).
Envelope surface is used to denote an imagined
surface across summits. Even if imaginary it can be
useful in general discussions. In Scandinavia the
envelope surface is often close to either the subPalaeozoic peneplain or any sub-Mesozoic surface.
The envelope surface does not depict any particular
palaeosurface.
3.3. Identification of palaeosurfaces in the study area
No studies of the large scale geomorphology had
been done before in the area. A general topographical
overview was obtained by a preliminary study based on
a field trip and digital elevation data (Japsen et al.,
2002b), and documentation of landforms in the southern
part of the study area in 2003.
The relief is depicted in a digital elevation model
(DEM) in a 250 × 250 m resolution square grid,
constructed by National Survey and Cadastre (Kort og
Matrikelstyrelsen), Copenhagen (Ekholm, 1996; Bamber et al., 2001). The data set includes the
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Sukkertoppen Ice Cap and minor ice caps. By
comparison with topographical maps and aerial
photographs, the topographical effect of ice was
evaluated. In general the ice is thought not to affect
the overall interpretation of surfaces, due to their
limited extent and thickness. However the Sukkertoppen Ice Cap is of substantial extent and thickness,
which was taken into consideration during interpretation and reconstruction of surfaces.
An elevation/slope map was constructed according to
Bonow et al. (2003) (Fig. 3). Slopes were calculated in
four groups, > 25°, 25–12°, 12–6.5° and < 6.5°. Areas
with an inclination < 6.5°, the common inclination for
pediments (Dohrenwend, 1994), were defined as flat.
We think that at high elevations these areas rather well
depict planation surfaces graded to former common base
levels.
The coastal area is characterised by a narrow coastal
plain in front of a great escarpment with two high areas,
one in the south between Kangerlussuaq and Itilleq
fjords (maximum altitude 1848 m a.s.l.) and one around
Nordre Isortoq fjord in the central study area (max
1597 m a.s.l.) (Fig. 3). Both high areas can be regarded
as alpine landscapes (Sugden, 1974) with horns, arêtes
and local glaciers, but some flat summits are still
present. Sukkertoppen Ice Cap in the south generally
terminates at about 1400 m a.s.l., but several outlet
glaciers reach sea-level. Further inland a low-relief
highland at 1400 to 1000 m a.s.l., the Angujaatorfiup
Nunaa (Fig. 2), lies between the Sukkertoppen Ice Cap
and the ice sheet in the east.
North of Nassuttooq the summit plateaus become
progressively lower and flat summits are less frequent,
and the landscape gradually changes to an undulating
terrain with hills of irregular size. Towards the north the
coastal escarpment fades away.
The hilly relief immediately south of Disko Bugt
extends from below Cretaceous and Palaeogene cover
rocks. The occurrence of kaolinitic saprolites in the
basement on Nuussuaq (Pulvertaft, 1979) and central
Disko below Cretaceous strata (Chalmers et al., 1999),
on southern Disko below Palaeogene strata (Bonow,
2005), and offshore in a well SW of the study area (e.g.,
Bate, 1997), indicates that deep weathering and
subsequent stripping were the major processes in
formation of this relief, and similar to conditions in
Fennoscandia.
Flat areas occur both in low positions as plains
(covered by Quaternary sediments) or as glacially
widened valley floors, and in high positions as large
plateaus and shallow valleys. The summit plateaus with
shallow valleys could, by our definition, be palaeosur-
faces and of interest for mapping. They are partly
dissected by deeply incised valleys.
3.4. Mapping of palaeosurfaces
Based on the information given above a detailed
analysis has been performed according to the methods
developed for mapping of palaeosurfaces in Scandinavia
by Lidmar-Bergström (1988, 1995, 1996) and Bonow et
al. (2003). The landforms were analysed in two steps.
First, three palaeosurfaces were mapped (see below), an
upper and a lower planation surface, and a surface with
distinct hills at low elevations (Fig. 4). The mapping
resulted also in a description of the envelope surface and
identification of fault blocks. In a second step the former
extent of the upper planation surface was reconstructed
and used for estimation of erosion since its formation.
3.4.1. Hilly relief areas
Bedrock hills limited by fractures were mapped by
interpretation of aerial photographs at the scale
1:150,000 in a Zeiss–Jena interpretoscope. All together
415 hills were mapped in the study area. The
approximate border between the hilly relief areas and
the planation surface is marked as the hilly relief
boundary (HRB).
South of Nassuttooq hills occurs on a coastal plain
below a high escarpment. The hills here are more
sparsely distributed than to the north. Between Sisimiut
and Itilleq the escarpment is mainly obliterated by
glacial erosion (see below) but the hills are still present
at the western end of protective ridges in lee-side
positions for eroding ice. The appearance of hills does
not obviously change from one area to the other.
3.4.2. Planation surfaces
A combination of a contour map (100 m contour
interval) and a grid of topographical profiles 20 km apart
(Fig. 5), was used to map the sub-horizontal and/or
inclined surfaces. The relative relief was denoted by
using a 20 km wide corridor divided into 250 m long
sections. The result of the mapping was checked against
the bedrock map for control of bedrock influence on
surface appearance.
The major upper surface is best preserved in the
southeast part of the study area, which was used as a key
area for its identification. The lower surface has
developed as a valley generation along a rectangular
fracture system and is only slightly incised in the upper
surface. The two surfaces are inclined and merge more
or less northwards and eastwards. They split into two
surfaces in the central and south-western parts of the
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Fig. 3. Elevation and slope map from a digital elevation model (DEM) with 250 m grid. Areas with slope angle less than 6.5° have been coloured
according to height above present-day sea level. Areas with slopes >6.5° have been coloured in grey scale. Elevation data obtained from Kort and
Matrikelstyrelsen, Denmark.
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Fig. 5. All profiles used for correlation of palaeosurface remnants. Crossing profiles were used in combination with a contour map (100 m interval) to
get a three-dimensional picture, which made it possible to map both inclined and sub-horizontal surfaces as well as faults.
study area, where the land surface has a higher
elevation. Four profiles are selected to illustrate the
mapping (Fig. 6).
The N–S profile [a] is drawn along areas with well
preserved planation surfaces making up a plateau
landscape at about 500 m in the north. At the crossing
Fig. 4. Palaeosurface map of the study area with an upper and a lower planation surface and a hilly relief surface (etch surface). The upper planation
surface with a few residual massifs is a major feature, and is preserved mainly in areas underlain by gneisses in granulite facies. The lower surface is
only slightly incised in the upper surface and mainly forms a valley generation (profile d). The hilly relief surface is cut of by the planation surface at
low angle (profile e). The surfaces are offset by fault scarps.
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Fig. 6. Topographical profiles (shaded area) with minimum and maximum profiles covering a 20 km wide corridor centred along the topographic
profile. The palaeosurfaces dip in different directions and are occasionally offset by faults. The lower surface (dashed line) is only identified in
the higher areas. In the north the planation surface cuts off the tilted hilly relief surface at low angle [d], cf. Fig. 4, profile e. See Figs. 2 and 4
for location.
with the Sisimiut Line there is a clear break in the
summit surface. South of the Sisimiut Line the surface
rises and splits into two. Coincidence of the summit
profile and the topographical profile denotes areas
where the upper planation surface is well preserved.
This is the case in areas with Archaean gneisses of
granulite facies, while the surface is eroded in areas with
Archaean gneisses of amphibolite facies and of gabbroanorthosite (Figs. 2 and 6).
Profile [b] illustrates the situation close to the coast
with two high areas. The upper surface starts at about
250 m a.s.l. in the north, where it cuts off the hilly
relief surface with a low angle. This condition is also
clear from east–west profiles (Fig. 4, profile e). In
profile [b] the upper surface rises slowly towards the
south and splits into two surfaces. They are offset
along structural lines that delimit the Nordre Isortoq
high area where the two surfaces are clearly apart. A
low-lying area is delimited by the Sisimiut Line to the
north and by the structurally controlled Itilleq fjord to
the south. Further south is a high area where the two
surfaces are clearly separated, but their exact position
was difficult to ascertain and therefore their position in
the profile is marked with question marks. The summit
plateaus here show no glacial reshaping (Sugden,
1974) and are therefore important for the validity of the
reconstruction.
The east–west profiles cross the low plateaus in the
east and high areas along the coast. Close to the
Sukkertoppen Ice Cap, the upper surface is well
preserved also in the gneisses in amphibolite facies
(profile [d]). In the high area, west of the Sisimiut Line,
the two surfaces are clearly separated, but along the
eastern part of profile [c] only one surface was identified
(cf. crossing of profile [a]). Here the profile crosses the
gneiss in amphibolite facies and most of the planation
surface is obliterated.
The two planation surfaces are best preserved in two
areas: in Angujaatorfiup Nunaa, east of Sukkertoppen
Ice Cap and in the Nordre Isortoq area (Fig. 4). The
surfaces and incised valleys as identified in the profiles
are illustrated in the eastern part of profile [d] in Fig. 4
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(cf. profile [d] in Fig. 6). The surfaces in Angujaatorfiup
Nunaa seem to continue beneath Sukkertoppen Ice Cap.
The higher surface is a major erosion surface (light
green in Fig. 4), covering vast areas and has few residual
massifs. Most massifs appear to consist of the same type
of bedrock as underlies of the surrounding surface. The
lower surface (dark green in Fig. 4) is mainly a valley
generation, developed along the edges of the primary
surface. In some cases the exact position of the surfaces
11
was difficult to ascertain, but the correlations from
profile to profile with the crosscutting analyses (Fig. 5)
make us think that we have given a fairly good picture of
the position for the different palaeosurfaces.
In summary the mapping gave the following result:
an upper planation surface has been formed across
different types of bedrock. The surface is best preserved
in areas with Archean gneisses in granulite facies and,
east of Sukkertoppen Ice Cap also in other types of
Fig. 7. 3D-map of the southern part of the study area. The planation surfaces in the Angujaatorfiup Nunaa area are well preserved in the southeast,
while in the northern areas the planation surfaces are mainly obliterated. The high area in the southwest shows mainly alpine relief, but with planation
surface remnants. Photograph a: the upper planation surface makes up the skyline. To the left is a valley incised in the upper planation surface,
glacially reshaped, but closely following the fracture pattern, which guided the original fluvial incision. Both left and right of this valley are minor
remnants of the lower planation surface (cf. Fig. 4). A deeply incised and glacially reshaped valley (Sarfartoq) is seen at the background. Photograph
b: a shallow valley within the upper planation surface. Photographs: J.M. Bonow, 2003.
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bedrock. A 3D picture combined with landscape views
illustrates its dominance in the skyline and shows the
shallow valleys of the lower planation surface, as well as
the deeply incised valleys (Fig. 7).
3.5. Landform development
3.5.1. Relative timing of surface development
The hilly relief in the northern part of the study area
extends from a Cretaceous cover offshore and is
interpreted as an exhumed surface (Bonow, 2005). The
planation surface (only one here) cuts off the more
inclined surface with hilly relief and is therefore
interpreted to be younger and of Cenozoic age. In the
eastern part of the study area the upper planation surface
is at about 500 m a.s.l. and the surface continues
northwards and can be followed on Nuussuaq across
both Precambrian basement and Palaeogene basalt
(Bonow et al., in press). This observation supports a
Cenozoic age of the planation surface.
The relationship between the hilly relief and the
planation surfaces at high elevations becomes unclear
south of Nassuttooq, where a coastal escarpment
delimits the hilly relief to the east (see Section 3.4.1).
A coastal plain with residual hills with the character of a
strandflat has developed. The origin of strandflats is
problematic (Guilcher et al., 1994). Studies of its
relation to offshore cover rocks are needed to ascertain
if it is partly an exhumed feature as parts of the
Norwegian strandflat is (Holtedahl, 1998), or if it is a
totally new feature. This problem will not be treated in
this paper.
3.5.2. Tectonic blocks and the envelope surface
The result of the palaeosurface mapping in West
Greenland is different from that obtained for the
Southern Scandes, where four well developed surface/
valley generations were identified between 1000 and
2000 m a.s.l. (Bonow et al., 2003). The valleys in the
present study area cut each other more or less
perpendicular and the valley systems show a strong
structural control. The situation is similar to what is
observed across flat relief in the Precambrian rock of
southern Sweden, where rock blocks are clearly
defined (Lidmar-Bergström, 1991; Tirén and Beckholmen, 1992; Lidmar-Bergström, 1993, 1994). The
mapping of the palaeosurfaces showed clear jumps
or change of inclination across some major structurally
controlled valleys, indicating faults or breaks after
surface formation. One of the most prominent jumps is
across the Sisimiut line (Fig. 6), where also the
palaeosurfaces change inclination. This indicates that
the palaeosurfaces here have been offset by a
reactivated fault. Thus a major result of the palaeosurface mapping is identification of fault scarps and
breaks separating tectonic blocks.
To further outline major tectonic blocks, two
summit envelope maps were constructed from the
DEM by extracting the maximum height value from
rectangular calculation in windows with 4 and 10 km
side respectively. The resulting maps show different
degree of surface generalisation (Fig. 8a, b). The most
generalised map (Fig. 8a) clearly denotes two mega
blocks, one around Nordre Isortoq and one around
Sukkertoppen Ice Cap, which are separated by the
Sisimiut Line. The more detailed map (Fig. 8b)
indicates that the mega blocks are subdivided into
minor blocks.
The fault lines separating individual blocks were then
used in a reconstruction of the former shape of the upper
planation surface over the whole study area in the form
of a contour map (Fig. 8c). A grid, 20 by 20 km, was
created with calculated height values for the position of
the upper planation surface as interpreted in the profiles.
The fault lines were inferred to depict the contours of the
planation surfaces of the different tectonic blocks as
correctly as possible. However it was noted that the
20 km grid was too sparse in the two high areas and it
did not satisfactorily show obvious tectonic blocks (Fig.
8a, b). A denser net of height values (10 km spacing)
was therefore created in two east–west profiles covering
these areas. The total number of height values for the
grid was 157.
The combination of the envelope maps (Fig. 8a, b)
and the reconstructed upper planation surface (Fig. 8c)
is the base for interpretation of individual tectonic
blocks in Fig. 8d. The southern mega block consists of
three minor blocks. A major E–W fault scarp along
Itilleq crosscuts the western part of this block with a
down-throw to the north (Figs. 6b and 8d). The two
southern blocks reach over 1800 m a.s.l. in the west. The
surface of the larger block slopes down to about 600 m
a.s.l. in the northeast. The northern mega block reaches
1600 m in the southwest, in an area crosscut by tectonic
lines, some with fault scarps limiting individual blocks
with a NE to ENE tilt. The summit surfaces of the blocks
slope down to about 600 m in the northeast.
3.5.3. Conclusions on uplift and block tilting
The identified palaeosurfaces are used to set up a
relative chronology of events after the formation of the
upper planation surface. The lower surface is developed
on the expense of the upper, which is thus left more or
less dissected. The present position of the two planation
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13
Fig. 8. Summit envelope surface maps for identification of tectonic blocks, constructed from a rectangle with a) 10 km side b) 4 km side. Note that the
ice surface of Sukkertoppen Ice Cap is part of the data base, but that the ice thickness is mainly not very great. c) Reconstruction of the upper planation
surface over the whole study area. Crosses mark the grid net. d) Interpretation of tectonic blocks. The north and south mega blocks are separated by
the Sisimiut Line (S.L.) (thick line), approximately along an early Proterozoic structure (cf. Fig. 2).
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surfaces, with a lower surface incised in an upper
surface and on blocks differently tilted, suggests a first
uplift and tilting after formation of the upper planation
surface. A planation surface, which is inclined more
than 0.4% will not survive (Rudberg, 1970; Spönemann,
1979). All erosion governed by gravity aims at
horizontality, and thus a planation surface cannot form
as an inclined surface across regions of large extent with
several fluvial systems. It must have formed at a uniform
level and the sea is the most probable base level. To
achieve such a wide surface as the extensive and
regionally developed upper planation surface, stable
tectonic conditions must have prevailed for a very long
time. The rearrangement of this surface to a high
position is therefore indicative of a period of active
tectonic movements.
This first uplift has had a magnitude of less than
500 m, which is the approximate height difference
between the two planation surfaces in the areas of
maximum uplift (Fig. 6). A second major event raised
the two surfaces an additional 1000 m in the two uplift
centres and less along their flanks. The Sisimiut Line
seems to have been reactivated during these uplift events
and the mapped fault scarps to have formed as a
consequence (Fig. 8). The uplift also initiated the
erosion processes that led to the removal of Cretaceous
or Palaeogene cover rocks and re-exposure of an etched
surface with hilly relief in the north.
The upper and lower planation surfaces can be
correlated with similar surfaces on Nuussuaq and Disko
described in Section 2.3. If our study area experienced
the same uplift events the upper planation surface is of
middle Miocene age, the lower planation surface
developed after uplift starting at 11–10 Ma and the
deep valley incision is connected to a major uplift event
starting at 7–2 Ma.
3.5.4. Dissection of palaeosurfaces
The western part of Angujaatorfiup Nunaa is a key
area for analysing the successive dissection of the
planation surfaces by valley incision. The tributary
running north to the Sarfartoq valley has a fluvially
formed canyon (Figs. 4[d], 6, 7)), between the two
glacially shaped valleys, Tasesiaq and Sarfartoq. The
upper valley is formed by glacial reshaping of a shallow
fluvial palaeovalley. The step from the upper to the
lower valley is caused by fluvial incision. The present
Sarfartoq valley is glacially widened and lowered but its
original incision and the formation of a step we think
was triggered by the preglacial uplift. The present
position of the step has moved backwards in interaction
between glacial lowering of the main valley and fluvial
backward erosion. In this way the two upper planation
surfaces have been partly destroyed north of Angujaatorfiup Nunaa (Fig. 7).
The palaeosurfaces in the two high areas close to
the coast have, besides being dissected by valleys,
partly been obliterated by erosion from cirque glaciers,
resulting in a characteristic alpine landscape (Fig. 7).
3.6. The upper planation surface − a reference surface
for estimation of erosion
3.6.1. Method
The map (Fig. 8c) with the reconstructed shape of the
upper planation surface (see Section 3.5.2) was used as
reference for estimation of erosion since its formation. A
map of erosion was obtained (Fig. 9) by subtracting the
present topography from the reconstructed upper
planation surface. As no information about depth in
fjords has been used, the map only reflects erosion
above present sea level. The position of the upper
planation surface along the west coast is not known and
therefore there is no estimation of erosion here. The
estimated amount of erosion is dependent on the correct
identification of the upper planation surface on
differently tilted tectonic blocks. The area marked with
a question mark in Fig. 8c, has bended contours and this
either marks a downfaulted block or that the identification of the palaeosurface is incorrect.
3.6.2. Result
The map of erosion (Fig. 9) shows clear differences
in amount of erosion of the upper planation surface. It
has in certain areas experienced almost no erosion since
formation, while in other areas it has been totally
obliterated. Most erosion, 800–1300 m, since its
formation has occurred in the area of highest uplift.
The summit surface of the low lying block to the south
of the Sisimiut Line has suffered deeper erosion (up to
400 m) than other inland areas. Areas underlain by
amphibolite gneiss are much more eroded than areas
underlain by granulite gneiss, e.g. the area south of
Sisimiut Line. The exception to this is the high coastal
areas eroded by cirque and valley glaciers, where both
rock types are eroded, although minor flat remnants of
the planation surface do occur (Fig. 4). On the other
hand areas underlain by amphibolite gneiss are well
preserved close to the present border of the Sukkertoppen Ice Cap indicating its protective role.
We think that the validity of the erosion map is
fairly good (with exception of the area with question
mark: Fig. 8c). This is a first attempt to estimate
differentiated erosion over a large area in West
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15
Fig. 9. Absolute amount of erosion since uplift, calculated as the difference between the reconstructed upper planation surface (Fig. 8c) and the
present relief.
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Greenland, and the method can be refined by still better
landform analysis.
3.6.2.1. Relative effect of glacial erosion. The relative
effect of glacial erosion versus fluvial erosion in the
study area has not been evaluated in detail. The areas
of preserved planation surfaces at high elevation have
only experienced limited erosion (green to yellow
areas in Fig. 9), while erosion has been more
pronounced in other parts of the landscape. The
identification of two distinct erosion generations, a
fully developed upper planation surface and a lower
generation, mainly represented by wide valleys,
possible to correlate with the aid of an inclined plane
and distinct from the deeply incised valleys, gives
reasons to regard erosion from the upper to the lower
planation surface as mainly fluvial. Where the
palaeosurfaces are obliterated between valleys, erosion
must have been mainly glacial, while along the incised
valleys erosion has been both fluvial and glacial. Even
if in detail the preserved planation surfaces are
characterised by glacial scouring (Sugden, 1974; Fig.
7a), our quantification shows a great variation in the
erosional effect. Shallow valleys in the planated relief
show minor glacial modification (Fig. 7b). Heavy
erosion has affected the upper planation surface at the
eastern part of the low-lying tectonic block south of
Sisimiut Line (Figs. 4, 6, 9). The block is underlain by
amphibolite gneiss and the erosion is interpreted as
mainly glacial. An argument for this is the preservation
of the preglacial surface on this type of gneiss below
the Sukkertoppen Ice Cap (see above). Thus the glacial
erosion here could be caused by a combination of
mechanically easily erodible bedrock (cf. Olvmo and
Johansson, 2002) and by the position between two
high areas with merging ice flows. Glacial erosion has
also been severe in the western part of this block,
which can be explained by confluent ice in combination with easily erodible amphibolite gneiss. Severe
glacial erosion has also affected the main valleys that
hosted outlet glaciers.
4. Discussion
4.1. Formation and preservation of palaeosurfaces
4.1.1. A former sub-Ordovician peneplain?
Tiny remnants of Lower Palaeozoic rocks (Secher
and Larsen, 1980; Pedersen and Peel, 1985; Larsen and
Rex, 1992; Larsen et al., 1999) give reasons to believe
that central West Greenland had long-lasting Palaeozoic covers like Northern Greenland (e.g., Henriksen et
al., 2000) and the Baltic (Lidmar-Bergström, 1995) and
Canadian shields (Ambrose, 1964). In these areas
remnants of Palaeozoic covers are present across low
relief in basement rocks. Ordovician rock fragments in
intrusive rocks at Fossilik (south of Sukkertoppen Ice
Cap) show the presence of an Ordovician cover during
the Jurassic intrusive event in that area (L.M. Larsen,
pers. comm. 2002). In the northern part of the study
area any Palaeozoic cover was removed before the
deposition of the Cretaceous or Palaeogene cover
rocks. It is, however, likely that the highest massifs in
at least the southern part of the study area (Fig. 4)
could be close to a sub-Ordovician planation surface
from which the present relief has developed (cf.
primary peneplain in Scandinavia, Lidmar-Bergström,
1996).
4.1.2. A stripped Late Mesozoic etch surface
The northern part of the study area is the
continuation of the basement ridge exposed at southern
Disko (Fig. 1). At Disko the basement exhibits
structurally controlled hills and weathered forms with
associated saprolite remnants close to and even below a
Palaeocene basalt cover (Bonow, 2005). The northeastern part of the study area is close to the erosional
boundary of Cretaceous cover rocks. A former extent in
over the study area of these sediments is likely (Fig. 1).
The erosional boundary of the basalt is fairly close in
the west (Fig. 1), and the basalt may thus have covered
parts of the study area as well.
The landform analysis led to the identification of a
hilly relief along the coast, particularly well developed
in the northern part of the study area. It was observed
that the distribution of hills is highly dependent on host
rock and density of joints and fractures and it is known
that deep weathering exploits structural weaknesses in
bedrock and enhances landform patterns controlled by
fractures and joints (Thomas, 1966; Kroonenberg and
Melitz, 1983; Thomas, 1994). Thus there are reasons to
believe that the present landforms in the northern part of
the study area, although glacially altered, have their
origin in a Mesozoic and/or early Palaeocene deeply
weathered surface. The hilly relief has been preserved
due to protective cover rocks, that have been removed
fairly recently, caused by a combination of fluvial
processes triggered by Neogene uplift and of glacial
erosion. The origin and age of the hilly coastal plain
south of Nassuttooq is however unclear.
4.1.3. The Cenozoic planation surfaces
The analysis of landforms in the study area resulted
in identification of two planation surfaces at high
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17
altitude. Very little relief rises above the upper planation
surface but the existing residual massifs (Fig. 4) may
reach the level of a lost sub-Ordovician peneplain. The
lower surface is mainly a valley generation, which only
in restricted areas has grown to wider plains. The
planation surfaces are under destruction. They must
have formed by a fluvial system to former common base
levels and subsequently been uplifted (cf. Section 3.5.3).
The largely intact planation surfaces in the study area
show that the fluvial system was not efficient enough to
dissect the surfaces after uplift in preglacial times, and
therefore that uplift must have occurred late. The highly
situated planation surfaces are better preserved where
the gneiss is in granulite facies. The surfaces are also
well preserved in more easily eroded rock types near the
Sukkertoppen Ice Cap. It seems that ice-sheets during
the Late Cenozoic have contributed in preserving the
planation surfaces.
In the present study area the planation surfaces have
partly been dissected by fluvial and glacial erosion.
Kangerlussuaq, Nordre Isortoq and Itilleq fjords all cut
water gaps across areas with preserved planation
surfaces above 1000 m a.s.l. The step from the lower
erosion surface to the valley bottoms is interpreted as
originally caused by fluvial incision (cf. Section 3.5.4).
The valleys have been deepened and widened by glacial
erosion to different degrees depending on location (Fig.
7). Interaction of fluvial and glacial erosion along
valleys during repeated glaciations and interglacials
have contributed in the backward retreat of the step.
Fluvial and glacial interactions have been a common
phenomenon in reshaping preglacial landscapes in
formerly glaciated areas (Rudberg, 1993; Kleman and
Stroeven, 1997).
4.2. Fluvial valley incision and glacial erosion
4.3.1. Palaeosurfaces for identification of tectonic
movements
In this study we have been able to confirm a
landscape development by fluvial incision in a valleyin-valley system as was concluded for southern Norway
(Bonow et al., 2003). From our studies we have got
input for the formulation of a landscape development
model, which integrate different parts of older models.
First, we adapt the Baulig (1935) idea of a valley-invalley system often forced by land uplift. Second, we
adopt the idea of formation of valley bottoms with low
inclination, which we call pediment (King, 1967; 1976;
Ahnert, 1998: rock-floored terraces p.183–184, pediments and piedmonttreppen p.223–227). It was noted in
the study from southern Norway (Bonow et al., 2003)
that slopes are maintained between surface and therefore
we adopt a model with slope retreat (with its exact form
depending on bedrock) and not slope decline as
proposed by Davis (1899). The Davis model does not
allow the formation of stepped surfaces (Twidale, 1976)
and is therefore not applicable. Ideas similar to our way
of thinking we find in Ahnert (1982), Demoulin (1995)
and Huguet (1996). The formation of large flat surfaces
we think largely have occurred in semi-humid and semiarid climates during the late Palaeogene and the
Neogene. Regarding the dissection of the flat surfaces
we also think that uplift has been more important than
climate change for triggering enhanced fluvial incision
(cf. Ahnert, 1970), and that climate change in certain
cases may be caused by uplift.
Other researchers favour a dynamic approach and try
to establish “variations in rates of denudation across
landscapes, rather than attempting to diagnose the
It has often been taken for granted that glacial erosion
was the main cause for valley incision in formerly
glaciated areas. However, studies of U-shaped valleys in
recently uplifted areas in New Zealand (Kirkbride and
Matthews, 1997), Washington, USA (Montgomery,
2002) and Scandinavia (Bonow et al., 2003) indicate
that major river systems were incised and graded prior to
onset of glaciations.
The central parts of southern Norway have experienced long periods with cold based ice sheets during
the Cenozoic glaciations and much of the preglacial
landscape is preserved (Sollid and Sørbel, 1994). Here
Bonow et al. (2003) chose an area where the preglacial
fluvial landscape development was analysed. The major
valley, Gudbrandsdalen, is wide but clearly glacially
reshaped, however it has a tributary valley (Lordalen)
of the same wideness but with almost no glacial
reshaping. Further, resistant rocks have at two locations
along the main valley preserved its old valley bottom.
These valley benches were correlated with valley
benches further upstream, beyond the present water
divide. This reconstructed valley floor fitted the
connection to the wide fluvial Lordalen. Thus, the
incision of Gudbrandsdalen in the uplifted palaeosurface was shown to originally have been fluvial.
Lordalen was used as reference in evaluating the glacial
effect in other parts of the river system. It was
concluded that the glacial erosion of the main valley
Gudbrandsdalen was up to 150 m (valley fill not
included) but over 300 m (valley fill not included) in a
neighbouring major tributary.
4.3. Palaeosurfaces as geomorphological markers
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amount and timing of tectonic uplift on the basis of
correlating erosion-surface remnants” (Brown et al.,
2000). The importance of former base levels for the
fluvial system that once shaped now uplifted landscapes
was, however, acknowledged by Schoenbohm et al.
(2004), Sugden and Denton (2004), and Clark et al.
(2005), and the former base level positions were used as
evidence for late uplift.
Sea level has been the most probable general base
level for surface formation in the study area. Consequently, identification and mapping of planation surfaces turned out to be important tools for conclusions on
both block tilting and amounts of uplift.
4.3.2. Palaeosurfaces as reference for fluvial and
glacial erosion
Sugden and Denton (2004) use the existence of
erosion surfaces with upstanding inselbergs and valley
benches backed by rectilinear slopes as strong evidence
for preservation of former fluvial landscapes in
Antarctica and for only limited glacial erosion. There
is always a risk for circularity in the reasoning of what is
glacial and what is pre-glacial, but there are today much
independent evidences for the selectivity of glacial
erosion (Sugden, 1978) from both paleoglaciologists
(e.g., Kleman and Hättestrand, 1999) and from studies
of preserved palaeosurfaces of different shape and
inclination (e.g., Lidmar-Bergström, 1988), that nonglacial explanations cannot be ignored. The two
planation surfaces in central West Greenland, the fully
developed and the partly developed, are evidences of
preglacial fluvially formed palaeosurfaces. As we have
shown, the surfaces can be used as markers for
estimation of erosion and qualitative judgements of
the glacial impact.
5. Conclusions
A major planation surface cuts across different types
of basement rocks in central West Greenland south of
Disko Bugt. In the northern parts of the study area the
planation surface cuts off an inclined surface with hilly
relief, exhumed from Upper Cretaceous cover rocks,
which determines the age of the planation surface to the
Cenozoic. South of Nassuttooq, the hilly relief surface is
delimited by a coastal escarpment in the east, and here
its age is unclear. The planation surface was broken and
tilted in different directions during two uplift events,
concentrated around two centra, Nordre Isortoq and
Sukkertoppen Ice Cap. A partially developed lower
planation surface indicates a first uplift of maximum
500 m followed by a second uplift of maximum 1000 m.
Correlation with similar erosion surfaces on Nuussuaq
suggests that uplift in the study area occurred in the late
Neogene, as the onset of two exhumation events at 11–
10 and 7–2 Ma, have been interpreted from analysis of
fission track data from Nuussuaq.
Differential erosion has affected the area since
formation of the upper planation surface, which is best
preserved in areas with Archean gneisses in granulite
facies. The highest amount of erosion (800–1300 m) has
occurred in the areas of maximum uplift, while highly
situated plateaus are partly not at all affected. Fluvial
processes are considered responsible for most of the
erosion to the level of the lower planation surface.
Fluvial processes, triggered by uplift, were also
responsible for the initial incision of deep valleys. The
exhumation of the etch surface in the north was caused
by a combination of fluvial processes due to uplift and
the late Cenozoic glaciations. Glacial erosion has had a
great effect on low lying areas and especially within
areas underlain by amphibolite gneisses.
The mapping of planation surfaces in central West
Greenland, by landform analysis in combination with
elevation data, provided a direct measure of the lateral
variation of uplift, recognition of block movements, and
estimation of amounts of erosion since the formation of
the upper planation surface.
Acknowledgements
We acknowledge the support of the Danish Natural
Science Research Council, GEUS, the Swedish Research Council, the Carlsberg Foundation, Arktisk
Station, Stiftelsen Margit Althins stipendiefond
(KVA), John Söderbergs stiftelse and Svenska Sällskapet för Antropologi och Geografi (Andreéfonden). We
want to thank James A. Chalmers, Clas Hättestrand,
Jens-Ove Näslund, Asger Ken Pedersen and Chris
Pulvertaft for fruitful discussions. Challenging and
provoking comments by Paul Bishop, Mauro Coltorti
and one anonymous referee forced us to clarify our
views, and thus the paper was significantly enhanced.
The digital elevation model is with courtesy from KMS,
Copenhagen. The paper is published with permission of
the Geological Survey of Denmark and Greenland.
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