گروههای درسی زبان انگلیسی شهرستان بویین میاندشت

Evolution of high-Arctic glacial landforms during deglaciation

N.G. Midgley

a, ⁎ , T.N. Tonkin

a,b

, D.J. Graham

c

, S.J. Cook

d

a

School of Animal, Rural and Environmental Sciences, Nottingham Trent University, Brackenhurst Campus, Southwell, Nottinghamshire NG25 0AQ, UK

b

Department of Natural Sciences, University of Derby, Kedleston Road, Derby DE22 1GB, UK

c

Polar and Alpine Research Centre, Loughborough University, Leicestershire LE11 3TU, UK

d

School of Social Sciences, University of Dundee, Nethergate, Dundee DD1 4HN, UK

a b s t r a c t a r t i c l e i n f o

Article history:

Received 29 November 2017

Received in revised form 27 March 2018

Accepted 28 March 2018

Available online 29 March 2018

Glacial landsystems in the high-Arctic have been reported to undergo geomorphological transformation during

deglaciation. This research evaluates moraine evolution over a decadal timescale at Midtre Lovénbreen, Svalbard.

This work is of interest because glacial landforms developed in Svalbard have been used as an analogue for land-

forms developed during Pleistocene mid-latitude glaciation. Ground penetrating radar was used to investigate

the subsurface characteristics of moraines. To determine surface change, a LiDAR topographic data set (obtained

2003) and a UAV-derived (obtained 2014) digital surface model processed using structure-from-motion (SfM)

are also compared. Evaluation of these data sets together enables subsurface character and landform response

to climatic amelioration to be linked. Ground penetrating radar evidence shows that the moraine substrate at

Midtre Lovénbreen includes ice-rich (radar velocities of 0.17 m ns

−1

) and debris-rich (radar velocities of 0.1–

0.13 m ns

−1

) zones. The ice-rich zones are demonstrated to exhibit relatively high rates of surface change

(mean thresholded rate of −4.39 m over the 11-year observation period). However, the debris-rich zones

show a relatively low rate of surface change (mean thresholded rate of −0.98 m over the 11-year observation

period), and the morphology of the debris-rich landforms appear stable over the observation period. A complex

response of proglacial landforms to climatic warming is shown to occur within and between glacier forelands as

indicated by spatially variable surface lowering rates. Landform response is controlled by the ice-debris balance

of the moraine substrate, along with the topographic context (such as the influence of meltwater). Site-specific

characteristics such as surface debris thickness and glaciofluvial drainage are, therefore, argued to be a highly im-

portant control on surface evolution in ice-cored terrain, resulting in a diverse response of high-Arctic glacial

landsystems to climatic amelioration. These results highlight that care is needed when assessing the long-term

preservation potential of contemporary landforms at high-Arctic glaciers. A better understanding of ice-cored

terrain facilitates the development of appropriate age and climatic interpretations that can be obtained from

palaeo ice-marginal landsystems.

© 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/).

Keywords:

Unmanned aerial vehicle (UAV)

Structure-from-motion (SfM)

Ground penetrating radar (GPR)

Ice-cored moraine

Midtre Lovénbreen, Svalbard

1. Introduction

The aim of this research is to investigate the geomorphological evo-

lution of proglacial landforms during deglaciation in Svalbard. To

achieve this aim, data were collected — at Midtre Lovénbreen, Svalbard

(Fig. 1) — using a range of techniques, including (i) ground penetrating

radar (GPR) data collected in 2009 to assess moraine structure and com-

position; (ii) archive aerial imagery and LiDAR data, both acquired in

2003; and (iii) aerial imagery acquired in 2014 using an unmanned ae-

rial vehicle (UAV) to assess any change in moraine morphology over the

11-year period from 2003. This research also provides the opportunity

to contrast landform dynamics at adjacent glaciers with similar glacio-

logical conditions, following recent investigation of landforms at

neighbouring Austre Lovénbreen (Midgley et al., 2013; Tonkin et al.,

2016).

Neoglacial moraines in Svalbard have been used as analogues for

Pleistocene moraines in the mid-latitudes (e.g., Hambrey et al., 1997;

Bennett et al., 1998; Graham and Midgley, 2000); however, many con-

tain buried ice (e.g., Bennett et al., 1996, 2000; Lyså and Lønne, 2001;

Sletten et al., 2001; Lønne and Lyså, 2005; Schomacker and Kjær,

2008; Evans, 2009; Midgley et al., 2013; Ewertowski, 2014;

Ewertowski and Tomczyk, 2015; Tonkin et al., 2016), which means

that there is potential for significant landform change associated with

the ablation of buried ice. The validity of such analogues relies upon a

lack of buried ice in the proglacial area in order for the landforms to

be preserved through a period of complete deglaciation. Consequently,

the extent to which Neoglacial moraines in Svalbard serve as Pleisto-

cene analogues has been subject to debate (e.g., Lukas, 2005, 2007;

Graham et al., 2007).

Geomorphology 311 (2018) 63–75

⁎ Corresponding author.

E-mail address: nicholas.midgley@ntu.ac.uk. (N.G. Midgley).

https://doi.org/10.1016/j.geomorph.2018.03.027

0169-555X/© 2018 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Contents lists available at ScienceDirect

Geomorphology

journal homepage: www. elsevier. com/ locate/geomorph

Globally, paraglacial processes (e.g., Church and Ryder, 1972;

Ballantyne, 2002) are responsible for remobilising glacial sediment in

proglacial areas during and following deglaciation (Knight and

Harrison, 2009; Fame et al., 2018). Moraine slopes in proglacial areas

may adjust rapidly following deglaciation (e.g., Sharp, 1984; Curry,

1999; Curry et al., 2006). In polar regions characterised by the presence

of permafrost, rates of landsystem transformation are often expedited

by the disintegration of buried ice (Fitzsimons, 1996; Bennett et al.,

2000; Etienne et al., 2008; Oliva and Ruiz-Fernández, 2015). For exam-

ple, Mercier et al. (2009) reported that following deglaciation sediment

mantled slopes undergo significant transformation, with the formation

of gullies controlled by the ablation of buried ice. Conceptual pathways

of landsystem evolution predict that upon complete deglaciation, ice-

cored terrain will result in a ‘hummocky’ assemblage of landform

(Boulton, 1972), although preservation of buried ice is permitted

under an extensive sediment mantle. Controls on buried ice ablation

were reviewed in Schomacker (2008). Subsequent to the publication

of this review, a wider range of studies have provided insight into the

processes of buried ice ablation and paraglacial redistribution of

sediments following deglaciation (e.g., Irvine-Fynn et al., 2011;

Ewertowski, 2014; Ewertowski and Tomczyk, 2015; Tonkin et al., 2016).

At Midtre Lovénbreen, previous work has focused on ice-rich mo-

raine areas with low preservation potential over a 2-year period from

2003 to 2005 (Irvine-Fynn et al., 2011), hinting at the possibility that

Svalbard moraines undergo significant transformation during deglacia-

tion, which may last several decades or longer (e.g., Evans, 2009;

Ewertowski and Tomczyk, 2015). In this study, observations on moraine

transformation are extended beyond the 2-year study period previously

reported (Irvine-Fynn et al., 2011) to facilitate understanding of the

evolution of high-Arctic glacial landforms on a decadal scale through

the use of high-resolution LiDAR and UAV-SfM (structure-from-mo-

tion) derived topographic data sets (techniques demonstrated to be of

value in glacial environments by Bhardwaj et al., 2016a, 2016b). The

burial and long-term preservation of relict ice is of interest as a potential

palaeoglaciological and palaeoenvironmental archive (e.g., Sugden et

al., 1995; Schäfer et al., 2000; Murton et al., 2005; Waller et al., 2012).

In addition, understanding the preservation history of buried ice will

also assist with appropriate landform age determination (e.g.,

Kirkbride and Winkler, 2012; Çiner et al., 2015; Tonkin et al., 2017;

Crump et al., 2017) and assist with former glacier reconstruction (e.g.,

Benn and Hulton, 2010; Pellitero et al., 2016). This work is important be-

cause it advances our understanding of the buried ice ablation process

by providing insight into the deglaciation dynamics of a high-Arctic

glacier foreland over a decadal timescale and it contributes to our

knowledge of how debris-covered cryospheric systems respond to ame-

liorating climatic conditions.

2. Study site

Midtre Lovénbreen is a small valley glacier (currently ca. 4 km in

length, but ca. 5 km in length at the Neoglacial maximum) located in

the Norwegian high-Arctic (terminus ca. 78° 53.7′ N 12° 3.5′ E) around

4 km to the SE of Ny-Ålesund (Fig. 1). An arcuate moraine complex

shows that the glacier has receded by around 1 km since the Neoglacial

maximum (Fig. 2). Svalbard had 38,871 km

2

of glacier area at the

Neoglacial maximum and this has now decreased by 13.1% (Martín-

Moreno et al., 2017). Midtre Lovénbreen has a long mass balance record

dating back to 1968, with currently published data to 2015 (WGMS,

2017). These data demonstrate a mean mass balance of −0.39 m

water equivalent over the record period, with only 5 years showing a

positive annual balance. The west coast of Spitsbergen is warmed by

the West Spitsbergen Current and experiences a relatively mild climate

for its latitude. Ny-Ålesund (79° N) experienced a mean annual temper-

ature of −6.3 °C from 1961 to 1990, −5.2 °C from 1981 to 2010 (Førland

et al., 2011), −4.4 °C from 1979 to 2014 (Osuch and Wawrzyniak,

434000 436000 438000

8756000 8758000 8760000 8762000

0 2 1

km

Midtre

Lovénbreen

ML

K o n g s f jorden

10°E 20°E

78°N

80°N

SVALBARD

VL

AL

Contour (50 m interval)

Glaciers

Proglacial zone

VL = Vestre Lovénbreen

ML = Midtre Lovénbreen

AL = Austre Lovénbreen

Fig. 1. Study site location. (A) Midtre Lovénbreen on Svalbard in the Norwegian high-Arctic. (B) Midtre Lovénbreen on Brøggerhalvøya near Ny-Ålesund.

Data from the Norwegian Polar Institute (2014).

64 N.G. Midgley et al. / Geomorphology 311 (2018) 63–75

2017), and − 3.8 °C from 2003 to 2014 (data from the Norwegian Mete-

orological Institute downloaded via eKlima web portal).

The likely maximum Neoglacial extent of Midtre Lovénbreen was

photographed by Axel Hamberg in 1892 CE (Hamberg, 1894; picture

reproduced by Hambrey et al., 2005), mapped by Isachsen in 1906–

1907 CE (Isachsen, 1912), photographed by Sigvald Moa in spring

1918 CE (Fig. 3) (picture reproduced by Hanoa, 1993), and also

photographed by W. Mittelholzer in 1923 (De Geer, 1930). Midtre

Lovénbreen exhibits a near-vertical ice-margin at the outer-frontal mo-

raine in 1892 CE and 1918 CE (Hamberg, 1894; Hanoa, 1993). A number

of englacial debris bands are shown in the 1918 CE ice margin image

and are comparable to the debris bands that were also identified by

Hambrey et al. (2005) on the 1892 CE image. By 1936 CE, Norwegian

Polar Institute oblique aerial imagery shows that the glacier margin

had receded from its Neoglacial maximum and thinned significantly to

form a low-angle slope (Fig. 4; also see Midgley and Tonkin, 2017).

The thermal regime of Midtre Lovénbreen has previously been reported

to be polythermal (Björnsson et al., 1996), but the warm-based zone has

reduced and the cold-based zone has increased in extent during the

twentieth century (Hambrey et al., 2005).

The whole moraine complex at Midtre Lovénbreen broadly com-

prises four components. Component 1: Lateral moraines that extended

along the sides of Midtre Lovénbreen at its Neoglacial maximum extent.

Component 2: A medial moraine located in the zone separating flow be-

tween the main flow unit of Midtre Lovénbreen and a former tributary.

The former tributary to the northeast of Berteltoppen is an unnamed

glacier that separated from the rest of Midtre Lovénbreen sometime be-

tween 1948 and 1966, based upon surface structural interpretation of

aerial images by Hambrey et al. (2005). Potential, although unlikely,

contribution to this flow unit may also have come from an unnamed

glacier to the south of Sherdahlfjellet shown on 1936 aerial imagery

(Fig. 4). By 2003 the medial moraine appears to be a relict feature that

now marks the lateral edge of Midtre Lovénbreen. Component 3: An ar-

cuate outer-frontal moraine marking the Neoglacial maximum extent of

Midtre Lovénbreen. Component 4: Comparatively low-relief ‘hum-

mocky moraine’ within the moraine-mound complex.

3. Methods

3.1. Subsurface characterisation

Ground penetrating radar has been shown to provide useful infor-

mation on subsurface composition and structure in glacial and

proglacial settings (e.g., Bennett et al., 2004; Lukas and Sass, 2011;

Midgley et al., 2013; Tonkin et al., 2017). In this study, a pulseEKKO

Pro ground penetrating radar (GPR) system was used with 100 MHz

centre frequency antennae to investigate the subsurface moraine char-

acteristics along two transects oriented parallel to inferred former ice

flow direction (Fig. 2B). This resulted in transect GPR1 being undertaken

parallel to the moraine crest orientation, whereas GPR2 was transverse

to the crest orientation. The GPR data sets were collected during winter

conditions to avoid the presence of liquid water, thus maximising pen-

etration and minimising signal attenuation. Antennae were stepped at

0.25-m intervals, with 1-m separation and a perpendicular broadside

configuration. Each trace was manually triggered, positioned along a

100-m tape with a 750–1000 ns time window and 36 stacks. The GPR

control unit was positioned at least 5 m away from the transmitter

and receiver to minimise signal interference. Change in topography

along each transect was surveyed using an automatic level. Radar veloc-

ities were obtained by matching hyperbolas to point diffractions in the

substrate (e.g., a technique previously applied to ice-cored terrain by

Brandt et al., 2007). The derived velocities were used to indicate subsur-

face composition.

Analysis of buried ice was undertaken within three shallow

trenches, of up to 5 m length, along transect GPR1. Samples of ice

were retrieved and described after having first removed the top 20–

30 cm of ice, following the procedures outlined by Toubes-Rodrigo et

al. (2016).

3.2. Surface characterisation: 2003

Aerial photographs and LiDAR data were collected on 9 August 2003

by the UK Natural Environment Research Council (NERC) Airborne Re-

search and Survey Facility (ARSF) and downloaded via the NERC Earth

Observation Data Centre (NEODC). The Agisoft Photoscan image pro-

cessing and 2003 orthomosaic production was generated using the

workflow documented in Midgley and Tonkin (2017). The LiDAR data

were collected using an Optech ALTM3033 laser scanner at an aircraft

A

B 0 500m N

GPR2

GPR1

B

S

Midtre

Lovénbreen

VL

Austre

Lovénbreen

Neoglacial

moraine limit 

medial

moraine

lateral

moraine

UAV

survey area

e

e

e

excavation Vestre Lovénbreen moraine

unnamed glacier below Sherdahlfjellet

unnamed glacier below Belteltoppen

VL

S

B

e 

Fig. 2. Geomorphological interpretation of Midtre Lovénbreen and the glacier foreland. (A)

Aerial orthomosaic imagery (from summer 2003) of the terminus of Midtre Lovénbreen

and the proglacial area (aerial data are from the UK Natural Environment Research

Council (NERC) Airborne Research and Survey Facility (ARSF) that are provided courtesy

of NERC via the NERC Earth Observation Data Centre); (B) summary map of the area

covered in part A with relevant features outlined, area surveyed by UAV in 2014

delimited, and ground penetrating radar transect locations identified (GPR1 and GPR2).

65 N.G. Midgley et al. / Geomorphology 311 (2018) 63–75

ground speed of ca. 77 ms

−1

and mean altitude of 1600 m asl. This re-

sulted in a resolution of around 1.1 points/m

2

over the proglacial area

(Irvine-Fynn et al., 2011). A DEM of the area of interest was produced

at 2 m/pixel resolution (e.g., Arnold et al., 2006) using linear

interpolation.

3.3. Surface characterisation: 2014

The SfM photogrammetry, with imagery typically obtained using

small UAVs, is now commonplace for low-level aerial image acquisition

(e.g., Tonkin et al., 2014; Rippin et al., 2015; Ely et al., 2017; Rossini et al.,

2018). At Midtre Lovénbreen, a DJI S800 UAV was used to acquire aerial

images on 20 July 2014. A total of six flights, each 13 to 15 min in dura-

tion, with mean flight altitude of 110 m were undertaken in the area of

interest. A consumer-grade compact mirrorless camera (Canon EOS M)

with 18 MP resolution was used to obtain the images using an internal

intervalometer that resulted in an image being obtained approximately

every 5 s during each flight. Agisoft Photoscan was used to process a

total of 1042 images with 17 ground-control points (GCPs). The same

Agisoft Photoscan image processing workflow that was used with the

2003 aerial images was also used for the 2014 UAV imagery (workflow

described by Midgley and Tonkin, 2017). The GCPs were marked on the

ground using A4-sized targets that were surveyed with a Leica 1200

dGPS. The SfM processing of the UAV-derived imagery provided an

image resolution of 2.08 cm/pixel and a point cloud with 112.3 million

points over the survey area, resulting in a resolution of around 12.5

points/m

2

(an order of magnitude greater than the LiDAR resolution).

3.4. Surface change detection: 2003–2014

The 2014 UAV-derived DEM was compared to the 2003 LiDAR-de-

rived DEM for the purpose of assessing surface evolution over this

time period. The 2014 SfM DEM was resampled to the same resolution

as the LiDAR-derived DEM (2 m/pixel) to facilitate comparison between

the data sets. The 2.5D difference between the two data sets was

calculated by subtraction, and the resulting data subjected to error

thresholding using the Geomorphologic Change Detection plugin for

ArcGIS by Wheaton et al. (2010). Arnold et al. (2006) estimated that

the RMS (root mean square) error in the study area may exceed 0.2 m

for the LiDAR data. The 2014 SfM DEM is likely to represent a highly ac-

curate representation of the terrain (e.g., Tonkin et al., 2016) with the

resulting data well fitted to the 17 GCPs, providing a total RMSE value

of 0.052 m. Using a 0.2-m error value for the 2003 LiDAR DEM and a

0.05-m error value for the 2014 UAV DEM, a propagated error (after

Brasington et al., 2003) of 0.21 m is found. Using the survey setup de-

scribed above minor elevation errors are expected in areas of the 2014

SfM DEM not subject to ground control (e.g., Tonkin and Midgley,

2016). To avoid potentially spurious results, data located in excess of

100 m from the nearest GCP on the final DEM of Difference were re-

moved (Tonkin and Midgley, 2016).

4. Results

4.1. Subsurface characterisation

Within transect GPR1, three substrate zones are identified: substrate

zone 1 at 0–295 m; substrate zone 2 at 295–340 m; and substrate zone

3 at 340 m onward (Fig. 5). Substrate zone 1 (0–295 m) has numerous

up-glacier dipping reflectors with a high-density stacked appearance

between 0 and 25 m. A number of pronounced asymptotic-style up-gla-

cier dipping reflectors are also found, including one that extends from

around 15 m depth at 120 m to intersecting the surface at 215 m. This

zone has a low density of point diffractions but is sufficient to enable as-

sessment of subsurface velocity at 0.17 m ns

−1

(n 10). The substrate in

this zone also has low signal attenuation and typically returns reflectors

from up to 15 m depth and, in places, down to 20 m depth. A shallow

trench, excavated along the transect line, had a surface debris layer

thickness of ca. 0.25 m, consisting of an upper layer of coarse angular

gravel and a lower layer of coarse angular gravel mixed with a mud-

rich matrix. Buried ice below the debris layer from 20 m and 215–220

Slåttofjellet

Dolotoppen

Midtre Lovénbreen

outer-frontal

moraine

near-vertical

ice margin

outer-frontal moraine

Fig. 3. Historic image of Midtre Lovénbreen taken in spring 1918 with key elements delimited.

(adapted from Hanoa, 1993).

66 N.G. Midgley et al. / Geomorphology 311 (2018) 63–75

m along the transect is characterised by alternating layers of sediment

and clean ice on the scale of millimetres to centimetres in thickness. In-

cluded sediment ranges from clay/silt-size particles to centimetre-sized

clasts that are angular in nature. The clean ice between debris-bearing

layers is occasionally bubble-free, but millimetre-scale bubbles are

widespread within the clean and debris-bearing ice layers. Ice from

209 m along the transect is characterised by coarse, bubbly ice. Zone 2

(295–340 m) lacks clear reflectors but has numerous overlapping

point diffractions that indicate a velocity of 0.14 m ns

−1

(n 4) and has

low signal attenuation. Zone 3 (340–360 m) is characterised by high

signal attenuation, lacks clear reflectors, and has velocity characteristics

of 0.11 to 0.13 m ns

−1

(n 4).

Within transect GPR2, two substrate zones are identified: substrate

zone 1 at 0–330 m; and substrate zone 2 at 330 m onward (Fig. 6). Sub-

strate zone 1 (0–330 m) includes a range of reflector styles, up-glacier

and down-glacier dipping. Analysis of the point diffractions shows sub-

strate velocity characteristics of 0.10 to 0.12 m ns

−1

(n 4). Typically, re-

flectors from up to 7.5 m depth are found, although a prominent

continuous reflector is found within the outer ridge that is at 10-m

depth below the ridge crest. Overall, the substrate demonstrates high

signal attenuation. The moraine composition along this area of the tran-

sect has been described in detail by Midgley et al. (2007). Moraine com-

position, based upon seven excavated sections each typically around 1

m deep, comprises a number of facies types: diamicton (n 22), sandy

gravel (n 16) along with sand and mud (n 6) (Midgley et al., 2007). A

single excavation in this area revealed the presence of a buried ice facies

at 1.16 m with an ice depth of unknown thickness (Midgley et al., 2007).

Subsequent to the publication of Midgley et al. (2007), three further ex-

cavations did not reveal any evidence of buried ice within three mo-

raines excavated down to 2.75, 3.0, and 3.3 m. Substrate zone 2 (300–

VL - Vestre Lovénbreen

ML - Midtre Lovénbreen B - unnamed glacier below Belteltoppen

S - unnamed glacier below Sherdahlfjellet

1936

2014

ML

VL

B

S lateral

moraine

medial

moraine

extent of outer

frontal moraine

lateral

moraine

medial

moraine

extent of outer

frontal moraine

VL

ML S

B

Fig. 4. Oblique aerial imagery obtained in approximately similar flight positions showing Midtre Lovénbreen in 1936 and 2014 (the 1936 image is part of aerial photograph S36 1552,

published with permission of the Norwegian Polar Institute).

67 N.G. Midgley et al. / Geomorphology 311 (2018) 63–75

360 m) is characterised by a distinct parallel reflector pattern, no point

diffractions, and a high signal attenuation.

4.2. Surface change detection: 2003–2014

In the frontal moraine zone, the mean depth of thresholded surface

change was −0.98 m (Table 1) over the observation period. Hummocks,

which attain several metres topographic prominence above the frontal

moraine surface, show less surface change (Fig. 7). The presence of

late-lying snow in the July 2014 survey is the primary cause of areas

of positive surface change. This is especially evident when surface

change is assessed alongside aerial imagery from the 2014 UAV survey

(Fig. 7), where snow patches are visible at various locations across the

study area, especially on the distal slopes of the moraine system.

Within the surveyed lateral moraine zone, a mean thresholded

surface change of −0.64 m between 2003 and 2014 was calculated

(Table 1). Whilst the amount of change appears to be less (mean sur-

face change) than in the frontal zone, small areas on the landform

have lowered by −4 m over the 11-year study period (Figs. 7, 8).

Two areas of surface increase were detected in the lateral zone. These

relate to (i) the presence of late-lying snow patches in the July 2014

survey; and (ii) geomorphological change associated with sediment re-

distribution. One area, which is located on the ice-proximal slope of the

Neoglacial lateral moraine, is snow free on the 2003 and on the 2014

250ns

0

250ns

0

0

250ns

former ice flow direction

zone 3

300m 250m 350m

0

10m

zone 2

zone 1

former ice flow direction 

200m 150m

0

10m

0m 100m 50m

former ice flow direction

0

10m

zone 1

Fig. 5. Ground penetrating radar transect (GPR1) obtained along the medial moraine at Midtre Lovénbreen, Svalbard.

68 N.G. Midgley et al. / Geomorphology 311 (2018) 63–75

250ns

0

250ns

0

0

250ns

former ice flow direction

zone 2

300m 250m 350m

0

10m

zone 1

former ice flow direction

200m 150m

0

10m

0m 100m 50m

former ice flow direction

0

10m

zone 1

Fig. 6. Ground penetrating radar transect (GPR2) obtained across the frontal moraine at Midtre Lovénbreen, Svalbard.

Table 1

Surface change for the study area segregated into five geomorphological zones.

Zone (as shown in Fig. 7) Total area

assessed (m

2

)

Mean depth of surface

lowering from 2003 to

2014 (m)

Total thresholded area

with detectable change (m

2

)

Annual mean thresholded

depth of surface lowering

between 2003 and 2014 (m)

Total volume of surface lowering

from 2003 to 2014 (m

3

)

Raw Thresholded Raw Thresholded

(i) Frontal 45,508 −0.84 −0.98 (±0.21) 37,304 −0.09 −35,920 −35,080 ± 7528

(ii) Lateral (ice-proximal slope) 23,184 −0.56 −0.64 (±0.21) 18,972 −0.06 −9926 −9603 ± 3133

(iii) Medial 79,440 −4.32 −4.39 (±0.21) 77,760 −0.40 −340,737 −340,564 ± 16,279

(iv) Outwash 3300 −0.22 −0.26 (±0.21) 2160 −0.02 −740 −556 ± 453

(v) Other (glacier foreland) 52,308 −0.25 −0.37 (±0.21) 26,172 −0.03 −11,981 −9211 ± 5189

69 N.G. Midgley et al. / Geomorphology 311 (2018) 63–75

aerial imagery, is located in an area well constrained by ground-control

points, and can be confidently related to the redistribution of sediment

on the ice-proximal slope of the moraine. This zone shows an increase

in surface elevation of up to +1.9 m over the 11-year study period. A

range of slope processes may be involved in this sediment

redistribution.

The medial moraine zone has the largest surface change, with a

mean thresholded depth of surface lowering of −4.39 m (Table 1),

which is equivalent to 340,564 m

3

of volume loss from 2003 to 2014.

The largest changes over the entire study area were detected on the me-

dial moraine ridge crest and in areas adjacent to standing water, with

change exceeding −14 m over the 11-year study period.

Fig. 7. Analysis of surface evolution from 2003 to 2011. (A) A UAV-derived orthorectified aerial image of the study site and associated ground control applied to the data. (B) A UAV-derived

surface model of the survey area obtained in 2014. (C) Surface evolution from 2003 and 2011 obtained by raster differencing. The study area is segregated into five geomorphological

zones.

0

5000

10000

15000

-20 -15 -10 -5 0 5

Volume (m 3 )

Elevation change (m)

0

5000

10000

15000

-20 -15 -10 -5 0 5

Volume (m 3 )

Elevation change (m)

0

5000

10000

15000

-20 -15 -10 -5 0 5

Volume (m 3 )

Elevation change (m)

0

5000

10000

15000

-20 -15 -10 -5 0 5

Volume (m 3 )

Elevation change (m)

(A) Medial zone (B) Lateral zone

(D) Other (C) Frontal zone

Fig. 8. Histograms of surface change for: (A) the medial moraine; (B) the lateral moraine; (C) the frontal moraine; and (D) other areas of the glacier foreland.

70 N.G. Midgley et al. / Geomorphology 311 (2018) 63–75

The outwash zone was found to have undergone very limited geo-

morphological change (−0.26 m thresholded mean surface lowering).

Other off-moraine areas of the glacier foreland (see Fig. 7) were also

covered by the survey. In this area (ca. 52,000 m

2

), a thresholded

mean surface change of −0.37 m over the observation period was

found.

5. Discussion

5.1. Subsurface characterisation

Within transect GPR1, substrate zone 1 (0–295 m) (Fig. 5), the high

radar velocities, low signal attenuation, and trench excavation (reveal-

ing a shallow surface debris cover) highlight that the majority of this

zone is composed of buried ice. The coarse bubbly ice facies found at

209 m is interpreted as firnified glacier ice. The ice facies found at 20

m and from 215 to 220 m is interpreted as showing rockfall debris

entrained at the glacier surface, then buried by further snowfall and

firnification. Within substrate zone 2 (295–340 m) (Fig. 5), the lower

radar velocities indicate a higher debris concentration within the ice.

Within substrate zone 3 (340–360 m) (Fig. 5), the low radar velocities

and high signal attenuation indicate a debris-rich substrate. This zone

has a high-preservation potential in response to further climatic amelio-

ration and is contiguous with the outer-frontal moraine surveyed along

transect GPR2. A similar sequence consisting of an ice-rich zone, transi-

tion zone and a debris-rich zone was also recognised at the lateral-fron-

tal moraine of adjacent Austre Lovénbreen (Midgley et al., 2013).

Within transect GPR2, the radar velocities, high signal attenuation,

and numerous excavations previously undertaken in the area demon-

strate that substrate zone 1 is dominated by a high-debris and low-ice

component. Preservation potential, in response to further climatic ame-

lioration, along this transect is high because of the high debris content.

Substrate zone 2 covers the proglacial outwash area, beyond the outer

moraine marking the Neoglacial maximum. The radar transect in this

zone, with parallel reflectors, is a clearly distinguishable radar facies

from the moraine found in substrate zone 1. Substrate zone 2 is

interpreted as stratified glaciofluvial outwash sediment.

5.2. Surface change detection: 2003–2014

The surface elevation changes documented in this study demon-

strate the ablation of buried ice over an 11-year period at this high-Arc-

tic site. The values reported here are similar to studies undertaken at

other high-Arctic glaciers (Table 2), where vertical rates of surface low-

ering up to −1.8 ma

−1

have been reported (Schomacker and Kjær,

2008; Irvine-Fynn et al., 2011; Ewertowski, 2014; Ewertowski and

Tomczyk, 2015; Tonkin et al., 2016).

Specifically, Irvine-Fynn et al. (2011) reported a surface lowering

rate of −0.65 (±0.2) ma

−1

on the ‘western lateral moraine’ (which is

interpreted as a relict medial moraine in this study) at Midtre

Lovénbreen between 2003 and 2005. Over the 11-year study period in-

vestigated here, the medial moraine zone had a spatially averaged

(mean) change of −4.39 m, which is equivalent to a mean yearly sur-

face change of −0.40 ma

−1

. However, 4488 m

2

of the medial moraine

zone was found to have lowered at a mean rate exceeding −1 ma

−1

over the 11-year study period. The findings indicate the progression of

buried ice ablation, resulting in a significant landscape response to cli-

matic amelioration, with some localised areas demonstrating high

rates of change and other localised areas demonstrating low rates of

change.

The low rates of change that were detected on the frontal moraine

system (Table 1) may relate to either (i) stabilised buried ice, below

the depth of seasonal thaw, thus permitting limited or negligible rates

of ablation (e.g., Etzelmüller and Hagen, 2005); or (ii) limited buried

ice within the frontal moraine (e.g., Section 4.1). The second scenario

is most likely, given the low radar velocities and high signal attenuation

found along GPR2, indicative of a debris-rich composition. Similarly, the

moraine system at the neighbouring Austre Lovénbreen was found to be

debris-rich within frontal zones and ice-rich in lateral zones (Midgley et

al., 2013), which has resulted in variable rates of surface change across

the moraine system between 2003 and 2014 (Tonkin et al., 2016).

5.3. Influence of glaciofluvial systems and standing water on moraine

degradation

Areas with higher rates of surface change (such as on the medial mo-

raine) can most likely be attributed to the development and evolution of

glaciofluvial drainage systems, including standing water — both of

which represent an important driver of surface change. On debris-cov-

ered glaciers, ice cliffs and ponded water are linked to high rates of ab-

lation (e.g., Sakai et al., 2000; Benn et al., 2001, 2012; Juen et al., 2014).

In the study by Immerzeel et al. (2014), repeat UAV-derived DEMs were

used to measure the evolution of a debris-covered glacier terminus in

the Himalaya, showing that 24% of ice-melt could be linked to the pres-

ence of supraglacial ponds and ice-cliffs. In this study, glaciofluvial run

off was found to incise ice-cored terrain and areas of standing water

have developed on the western slope of the medial moraine, resulting

in the development of exposed ice-cliffs, which coincide with high

rates of surface evolution.

The results contrast with findings at the neighbouring Austre

Lovénbreen (Table 2) where repeat SfM DEMs were used to quantify

lateral-frontal moraine evolution, highlighting lower rates of surface

evolution over the same time period (2003–2014) as this study

(Tonkin et al., 2016). The well-drained, elevated position of the ice-

cored landforms at Austre Lovénbreen, which are detached from the

main glaciofluvial system, were argued to limit the impact of thermo-

erosion by run off and standing water, resulting in no exposed ice at

the moraine surface. In contrast, glaciofluvial discharge at Midtre

Table 2

A comparison of the vertical rate of moraine degradation quantified in this study with other sites in Svalbard.

Study Study site Time period

(CE)

Method Landform – area Rate of vertical

change (ma

−1

)

Schomacker and Kjær (2008) Holmströmbreen 1984–2004 Total station survey Ice-cored moraine −0.9

Ewertowski (2014) Ragnarbreen 1990–2009 Repeat photogrammetric

DEMs

Lateral moraine −0.08

‘End’ moraine −0.003

Ewertowski and Tomczyk (2015) Ragnarbreen and

Ebbabreen

2012–2014 Repeat DEMs (Topcon

Imaging Station)

Ice-cored moraine

(passive down-wastage)

Up to −0.3

Ice-cored moraine

(active mass movements)

Up to −1.8

Tonkin et al. (2016) Austre Lovénbreen 2003–2014 Repeat DEMs

(SfM photogrammetry)

Lateral-frontal moraine Variable: e.g. –0.04

to −0.23

Irvine-Fynn et al. (2011) Midtre Lovénbreen 2003–2005 Repeat DEMs (LiDAR) ‘Western lateral moraine’

(medial moraine)

−0.65

This study – see Table 1 Midtre Lovénbreen 2003–2014 Repeat DEMs

(LiDAR/SfM photogrammetry)

Frontal moraine −0.09

Medial moraine −0.40

71 N.G. Midgley et al. / Geomorphology 311 (2018) 63–75

Lovénbreen is routed over ice-cored terrain, resulting in high rates of

thermo-erosion. Site-specific characteristics are, therefore, argued to

be a highly important control on surface evolution in ice-cored terrain,

resulting in the diverse response of high-Arctic glacial landsystems to

climatic amelioration. These findings indicate that a diverse response

of ice-cored landforms to deglaciation can be anticipated, even for

sites with similar glaciological characteristics, or in close proximity to

each other. Rates of change on ice-cored moraine appear to be variable,

even locally, and represent complex topographic controls on moraine

degradation (e.g., Schomacker, 2008).

5.4. Implications of subsurface observations on long-term landscape

evolution

Given the strong contrast between the subsurface characteristics de-

tected within the ice-rich zone of GPR1 and the debris-rich zone of GPR1

(where the medial moraine becomes frontal moraine) and along the full

length of GPR2, a higher preservation potential of the debris-rich zones

is envisaged following complete deglaciation (Fig. 9). However, land-

scape response to climatic amelioration is dampened by the release of

debris from buried ice, which contributes to a thickening surface debris

layer that provides underlying ice within greater protection from atmo-

spheric warming (e.g., Østrem, 1959; Nicholson and Benn, 2006). The

high debris component in GPR2 may permit zones of stabilised glacier

ice within the moraine. However, this is dependent on the relationship

between debris thickness and the response of the active layer to future

warming, with permafrost degradation over the twenty-first century

principally expected at coastal sites with low elevations (Etzelmüller

et al., 2011).

Moraine genesis and degradation rates are also closely linked and re-

quire consideration. Medial moraines can develop as the folded limbs of

primary stratification and rockfall debris. Material is predominantly

transported passively and emerges at the glacier terminus as a thin, lin-

ear supraglacial drape of coarse angular debris (Hambrey et al., 1999). In

a proglacial setting, the moraines are manifested as linear landforms,

oriented parallel to glacier flow, and are volumetrically principally com-

posed of dead/stagnant glacier ice that is typically protected by a thin

veneer of sediment (Hambrey and Glasser, 2003). In contrast, the ice

content may be more restricted in the frontal moraine, which again, is

related to the mode of moraine genesis.

Englacial and proglacial thrusting of subglacial sediment have been

discussed as an important moraine-forming process at many high-Arc-

tic glaciers, including Midtre Lovénbreen (Hambrey et al., 1997, 1999;

Bennett et al., 1999; Midgley et al., 2007), resulting in a hummocky as-

semblage of landforms with steep ice-distal slopes and in gentler recti-

linear and curvilinear ice-proximal slopes (Glasser and Hambrey, 2003).

The long-term preservation potential of such landforms has been de-

bated owing to the potential ice component within the landforms

(Lukas, 2005; Graham et al., 2007; Lukas, 2007; Evans, 2009). In the

frontal zone, moderate rates of surface lowering are detected overall

0

10

height

(m)

glaciofluvial

outwash

zone 1 zone 3 zone 2

buried ice (limited debris)

buried ice

(moderate debris)

debris-rich

ice-poor

ice-cored medial moraine / supraglacial debris

moraine

(outer-frontal)

thin surface debris layer

GPR1:

0 100 200 300 400

Distance along transect (m)

contemporary

profile

anticipated profile following

complete climatic amelioration

0

10

20

height (m)

zone 1 zone 2

debris-rich ice-poor substrate

moraine (outer-frontal)

glaciofluvial

outwash

GPR2:

0 100 200 300 400

Distance along transect (m)

contemporary profile and anticipated profile

following complete climatic amelioration

A

B

Fig. 9. Schematic model of contemporary moraine and moraine evolution at Midtre Lovénbreen, Svalbard.

72 N.G. Midgley et al. / Geomorphology 311 (2018) 63–75

(Table 1). Lowering is, however, limited on areas of topographic prom-

inence (e.g., the hummocks; Fig. 7). As structural glaciology and mo-

raine evolution are linked (e.g., Evans, 2009), debris concentrations

within stagnant/dead ice exert an important control with regard to

landform preservation potential. For example, the Neoglacial ice-mar-

gin of Midtre Lovénbreen was near vertical, promoting the flowage of

debris emerging at the terminus from a supraglacial to proglacial posi-

tion (Hamberg, 1894; Hambrey et al., 2005). Such a scenario would re-

sult in the development of debris-rich zones within the moraine system.

Furthermore, high debris concentrations (e.g., hummocks of glacigenic

sediment) will permit the development of a thick debris mantle to sta-

bilise the landform.

Evans (2009) highlighted that the presence of kettle lakes within the

Midtre Lovénbreen proglacial area indicates that ablation of buried ice is

occurring. The results of our subsurface characterisation indicate a de-

bris-dominant composition for this Neoglacial frontal moraine. Whilst

our results show that the moraine system does appear to be responding

to deglaciation, a higher preservation potential is possible as a conse-

quence of the debris-rich subsurface composition. Ultimately, complex

debris-rich and ice-rich landform assemblages at adjacent sites

(Midgley et al., 2013; Tonkin et al., 2016; this study) highlight the

need for care when assessing the palaeoglaciological significance and

likely long-term preservation potential of ice-marginal landscapes in

the geomorphological record. Appropriate understanding of landform

character and landform censoring or degradation history is an impor-

tant consideration for obtaining appropriate ages for glacial landforms

(e.g., Kirkbride and Winkler, 2012; Çiner et al., 2015; Crump et al.,

2017; Tonkin et al., 2017) and for glacier reconstructions (e.g., Benn

and Hulton, 2010; Pellitero et al., 2016) where moraines are used to

constrain the extent and vertical dimensions of former glaciers. As

such, a better understanding of this landform type with a mix of de-

bris-rich and ice-rich substrate will prove valuable to assessing age

and palaeoclimatic interpretations.

6. Conclusions

The research reported here advances our understanding of the var-

ied ice-debris composition of the proglacial setting and the evolution

of proglacial landscape over a decadal timescale in a warming climate.

It highlights the complex response of glacial geomorphological systems

to climatic change, with spatially variable surface lowering rates de-

tected within and between adjacent glacier forelands; Austre

Lovénbreen (Midgley et al., 2013; Tonkin et al., 2016) and the research

presented in this study on Midtre Lovénbreen. This study provides in-

sight into the dynamics of a deglaciating high-Arctic landscape over a

decadal timescale. Specifically, GPR is used to demonstrate that the

composition of ice-marginal landforms is variable. Velocities deter-

mined from the GPR surveys demonstrate that the frontal moraine

zones of the moraine system are debris-rich (radar velocities of 0.1–

0.13 m ns

−1

), whereas the medial moraine zones are ice-rich (radar ve-

locities of 0.17 m ns

−1

). The DEM differencing of LiDAR- (2003) and

UAV-derived elevation data (2014) are used to quantify landscape re-

sponse to climatic amelioration. The complex response of the

landsystem relates not only to the ice and sediment composition of

the landforms but also to the topographic context. The medial moraine

zone is undergoing a larger magnitude of change than the frontal and

lateral moraine zones as a result of debris thickness and the presence

of glaciofluvial drainage and standing water. Site-specific characteristics

are, therefore, argued to be a highly important control on surface evolu-

tion in ice-cored terrain, with the findings indicating that even at adja-

cent sites with similar glaciological characteristics, a diverse response of

ice-cored landforms to deglaciation can be anticipated. The accessibility

of new tools (UAV and SfM) to generate high-resolution topographic

data sets is now allowing for the geomorphological response of ice-mar-

ginal landsystems to deglaciation to be better understood. A better un-

derstanding of contemporary ice-marginal landsystems will assist

with the determination of age and climatic interpretations of the palaeo

ice-marginal landsystems that are found in the landform record.

Acknowledgements

The fieldwork was funded by grants from the Royal Society (2007/

R2 to DJG and NGM), Nottingham Trent University (NGM and TNT),

the Manchester Geographical Society (SJC), and TNT was also in receipt

of a Nottingham Trent University VC bursary postgraduate studentship.

The winter fieldwork benefited from logistical support provided by

Steinar Aksnes at Sverdrup Station (Norwegian Polar Institute) and

summer fieldwork benefited from logistical support provided by Nick

Cox at Harland Huset (Arctic Office – NERC) with accommodation also

provided at Harland Huset during summer fieldwork courtesy of the

Arctic Office (NERC). Anya Wicikowski and Lloyd Stanway are thanked

for assistance with fieldwork and both received financial support from

Nottingham Trent University. The 2003 aerial data are from the UK Nat-

ural Environment Research Council (NERC) Airborne Research and Sur-

vey Facility (ARSF) that are provided courtesy of NERC via the NERC

Earth Observation Data Centre (NEODC). Part of archive aerial

photograph S36 1552 from 1936 is published with permission of the

Norwegian Polar Institute. A climate data set from the Norwegian Mete-

orological Institute was downloaded via the eKlima web portal. The re-

viewers and Richard Marston are thanked for their constructive

comments of an earlier version of our manuscript.

Appendix A. Supplementary data

Supplementary data associated with this article can be found in the

online version, at https://doi.org/10.1016/j.geomorph.2018.03.027.

These data include the Google map of the most important areas de-

scribed in this article.

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