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Abstract

The englacial entrainment of basal debris during surges presents an opportunity to investigate processes acting at the glacier bed. The subsequent melt-out of debris-rich englacial structures during the quiescent phase produces geometrical ridge networks on glacier forelands that are diagnostic of surge activity. We investigate the link between debris entrainment and proglacial geomorphology by analyzing basal ice, englacial structures, and ridge networks exposed at the margins of Tunabreen, a tidewater surge-type glacier in Svalbard. The basal ice facies display clear evidence for brittle and ductile tectonic deformation, resulting in overall thickening of the basal ice sequence. The formation of debris-poor dispersed facies ice is the result of strain-induced metamorphism of meteoric ice near the bed. Debris-rich englacial structures display a variety of characteristics and morphologies and are interpreted to represent the incorporation and elevation of subglacial till via the squeezing of till into basal crevasses and hydrofracture exploitation of thrust faults, reoriented crevasse squeezes, and preexisting fractures. These structures are observed to melt-out and form embryonic geometrical ridge networks at the base of a terrestrially grounded ice cliff. Ridge networks are also located at the terrestrial margins of Tunabreen, neighboring Von Postbreen, and in a submarine position within Tempelfjorden. Analysis of network characteristics allows these ridges to be linked to different formational mechanisms of their parent debris-rich englacial structures. This in turn provides an insight into variations in the dominant tectonic stress regimes acting across the glacier during surges.

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... Interpretation. -The geometric networks of ridges have similar patterns and dimensions as earlier described crevasse-squeeze ridges observed in both terrestrial as well as submarine settings (Boulton et al. 1996;Christoffersen et al. 2005;Ottesen & Dowdeswell 2006;Ottesen et al. 2008;Flink et al. 2015;Lovell et al. 2015). The ridges are therefore suggested to be crevasse-squeeze ridges, formed by the upward injection of deformable, subglacial debris into basal crevasses (Rea & Evans 2011;Lovell et al. 2015). ...
... -The geometric networks of ridges have similar patterns and dimensions as earlier described crevasse-squeeze ridges observed in both terrestrial as well as submarine settings (Boulton et al. 1996;Christoffersen et al. 2005;Ottesen & Dowdeswell 2006;Ottesen et al. 2008;Flink et al. 2015;Lovell et al. 2015). The ridges are therefore suggested to be crevasse-squeeze ridges, formed by the upward injection of deformable, subglacial debris into basal crevasses (Rea & Evans 2011;Lovell et al. 2015). Basal crevasses in turn have been proposed to form during surge stagnation, in a zone of longitudinal extension or intense compression, when basal water pressures are close to ice overburden pressures and allow for the propagation of basal crevasses (Larsen et al. 2010;Kristensen & Benn 2012;Lovell et al. 2015). ...
... The ridges are therefore suggested to be crevasse-squeeze ridges, formed by the upward injection of deformable, subglacial debris into basal crevasses (Rea & Evans 2011;Lovell et al. 2015). Basal crevasses in turn have been proposed to form during surge stagnation, in a zone of longitudinal extension or intense compression, when basal water pressures are close to ice overburden pressures and allow for the propagation of basal crevasses (Larsen et al. 2010;Kristensen & Benn 2012;Lovell et al. 2015). The presence of crevasse-squeeze ridges therefore suggests high basal water pressures and fast glacier flow usually associated with surge activity (Solheim & Pfirman 1985;Boulton et al. 1996;Kjaer et al. 2008;Rea & Evans 2011). ...
Article
Submarine geomorphology is one of the main tools for understanding past fluctuations of tidewater glaciers. In this study we investigate the glacial history of Mohnbukta, on the east coast of Spitsbergen, Svalbard, by combining multibeam-bathymetric data, marine sediment cores and remote sensing data. Presently, three tidewater glaciers, Heuglinbreen, Königsbergbreen and Hayesbreen calve into Mohnbukta. Hayesbreen surged at the end of the Little Ice Age, between 1901 and 1910. The submarine landform assemblage in Mohnbukta contains two large transverse ridges, interpreted as terminal moraines, with debrisflow lobes on their distal slopes and sets of well-preserved geometric networks of ridges, interpreted as crevasse-squeeze ridges inshore of the moraines. The arrangement of crevasse-squeeze ridges suggests that both landform sets were produced during surge-type advances. The terminus position of the 1901–1910 Hayesbreen surge correlates with the inner (R.2) terminal moraine ridge suggesting that the R.1 ridge formed prior to 1901. Marine sediment cores display 14C ages between 5700–7700 cal. a BP derived from benthic foraminifera, from a clast-rich mud unit. This unit represents pre-surge unconsolidated Holocene sediments pushed in front of the glacier terminus and mixed up during the 1901 surge. An absence of retreat moraines in the deeper part of the inner basin and the observation of tabular icebergs calving off the glacier front during retreat suggest that the front of Hayesbreen was close to flotation, at least in the deeper parts of the basin. As the MOH15-01 core does not penetrate into a subglacial till and the foraminifera in the samples were well preserved, the R.1 ridge is suggested to have formed prior to the deposition of the foraminifera. Based on these data we propose that a surge-type advance occurred in Mohnbukta in the early Holocene, prior to 7700 cal. a BP, which in turn indicates that glaciers can switch to and from surge mode.
... Numerous studies have investigated englacial, geomorphological and sedimentological evidence exposed at the receding margins of quiescent phase surge-type glaciers in Svalbard in order to better understand the processes that occur during surges (e.g. Boulton et al., 1996Boulton et al., , 1999Glasser et al., 1998a;Bennett et al., 1999;Christoffersen et al., 2005;Larsen et al., 2006;Ottesen et al., 2008Ottesen et al., , 2017Kristensen et al., 2009a;Lovell et al., 2015;Sobota et al., 2016;Larsen et al., 2018;Lyså et al., 2018). For tidewater glacier surges, this evidence is typically recorded on the sea floor (e.g. ...
... King et al., 2009); (ii) a large terminal moraine located just beyond the northern extents of Nordre and Søre Nathorstmorenen ( Fig. 1), interpreted to be glaciotectonic in origin (Ottesen et al., 2008); (iii) geometrical ridges, interpreted as crevasse-squeeze ridges formed by the injection of seafloor sediments into basal crevasses (e.g. Lovell et al., 2015); and (iv) annual retreat moraines, marking minor winter readvances during terminus retreat in the quiescent phase (e.g. Flink et al., 2015). ...
... The geometrical ridge networks are interpreted as crevassesqueeze ridges, commonly observed at the submarine and terrestrial margins of surge-type glaciers (e.g. Sharp, 1985;Boulton et al., 1996;Evans and Rea, 1999;Ottesen and Dowdeswell, 2006;Ottesen et al., 2008Ottesen et al., , 2017Lovell et al., 2015;Farnsworth et al., 2016;Ing olfsson et al., 2016). Crevasse-squeeze ridges are formed by the injection of deformable basal debris into vertical and near-vertical crevasses, as observed at the active ice margin (Fig. 6b). ...
Article
Most large tidewater glaciers in Svalbard are known to have surged at least once in the last few hundred years. However, very little information exists on the frequency, timing or magnitude of surges prior to the Little Ice Age (LIA) maximum in ∼1900. We investigate the sediment-landform assemblages produced by multiple advances of the Nathorstbreen glacier system (NGS) in order to reconstruct its Late Holocene surge history. The glacier has recently undergone one of the largest surges ever observed in Svalbard, advancing ∼16 km from 2008 to 2016. We present flow velocities and ice-marginal observations (terminus change, proglacial geomorphological processes) from the later stages of this surge. A first detailed assessment of the development of a glaciotectonic mud apron within the fjord during a surge is provided. Geomorphological and sedimentological examination of the terrestrial moraine areas formed prior to the most recent surge reveals that at least two advances were responsible for their formation, based on the identification of a previously unrecognised ice-contact zone recorded by the distribution of sediment facies in coastal exposures. We distinguish between an outer, older advance to the distal part of the moraine system and an inner, younger advance to a position ∼2 km upfjord. Radiocarbon dating of shells embedded in glaciotectonic composite ridges formed by the onshore bulldozing of marine mud during the outer (older) of the two advances shows that it occurred at some point during the interval 700–890 cal. yr BP (i.e. ∼1160 AD), and not during the LIA as previously assumed. We instead attribute the inner (younger) advance to the LIA at ∼1890. By combining these data with previous marine geological investigations in inner and outer Van Keulenfjorden, we demonstrate that NGS has advanced at least four times prior to the recent 2008–2016 surge: twice at ∼2.7 kyr BP, at ∼1160 AD, and in ∼1890. This represents a unique record of the timing and magnitude of Late Holocene tidewater glacier surges in Svalbard.
... The most detailed structural study of foliation in a surge-type glacier was undertaken on Variegated Glacier in Alaska (see Lawson et al., 1994;Lawson, 1996), but surge-type glaciers in Svalbard are receiving increasing amounts of structural attention (e.g. Hambrey and Dowdeswell, 1997;Fleming et al., 2013;King et al., 2015;Lovell et al., 2015). In contrast to the other Brøggerhalvøya glaciers included in this study, there is structural evidence to suggest that Pedersenbreen has surged in the past. ...
... More recently, Svalbard surge-type glaciers have been receiving increasing amounts of attention, especially with regard the glacier structure (e.g. Hambrey and Dowdeswell, 1997;Fleming et al., 2013;King et al., 2015;Lovell et al., 2015). These studies have revealed a complex array of structures and a variety of structural assemblages that are associated with surge-type glaciers. ...
... European Alps - Milnes, 1975, 1977;Hambrey, 1977a;Hambrey et al., 1980;Goodsell et al., 2002Goodsell et al., , 2005aRoberson, 2008;Jennings et al., 2014. Svalbard -Hambrey andHambrey et al., 1999Hambrey et al., , 2005Glasser and Hambrey, 2001;Roberson and Hubbard, 2010;Fleming et al., 2013;Jennings et al., 2015;King et al., 2015;Lovell et al., 2015. Norway -Hambrey, 1976a, b. ...
Thesis
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This study examines how longitudinal foliation develops in glaciers and ice sheets in a wide range of topographic, climatic, and dynamic settings, at a variety of spatial scales. Study locations include four valley glaciers in Svalbard (Austre Brøggerbreen, Midtre Lovénbreen, Austre Lovénbreen, and Pedersenbreen), a valley glacier in Canada (Sermilik Glacier), and seven outlet glaciers in Antarctica (Hatherton Glacier, Taylor Glacier, Ferrar Glacier, Lambert Glacier, Recovery Glacier, Byrd Glacier, and Pine Island Glacier). Detailed structural mapping of the valley glaciers from satellite imagery and field-based measurements were used to document the formation of longitudinal foliation in small-scale ice masses. These findings were ‘up-scaled’ and applied to much larger glaciers and ice streams. Longitudinal foliation develops in concentrated bands at flow unit boundaries as a result of enhanced simple shear. However, longitudinal foliation is not directly observable from satellite imagery at the surface of larger-scale valley glaciers. The longitudinal structures visible at the surface of larger-scale glaciers form at flow-unit boundaries and are composed of bands of steeply dipping longitudinal foliation; however, they appear as individual linear features on satellite imagery as a result of the comparatively low spatial resolution of the imagery. The persistence of flowlines in the Antarctic Ice Sheet through areas of crevassing and net ablation (blue-ice areas) suggests that they are the surface representation of a three-dimensional structure. Flowlines are therefore inferred to be the surface expression of flow-unit boundaries composed of bands of steeply dipping longitudinal foliation. The survival and deformation of flowlines in areas of ice flow stagnation indicates that flowlines form in their initiation zones and not along their entire length. Furthermore, these ice stagnation areas indicate that flowlines record past ice dynamics and switches in ice flow.
... Concertina eskers, also referred to as 'zigzag, eskers by Benn and Evans (2010), have been regarded as a unique landform left by surge-type glaciers since they were first described from Brúarjökull by Knudsen (1995) and included in the surge-type glacier landsystem model of . However, they are not common features in the foreland of surge-type glaciers, and have hitherto only been described from Eyjabakkajökull and Brúarjökull (Knudsen, 1995;Kjaer et al., 2008), from three surge-type glaciers on Svalbard (Hansen, 2003;Lovell et al., 2015) and Novaya Zemlya (Grant et al., 2009), as well as from a deglaciation setting at a presently submarine setting in the Baltic Sea (Feldens et al., 2013). Knudsen (1995) originally proposed that concertina eskers were formed by shortening of pre-surge sinuous eskers by compression in the glacier snout during surging. ...
... Studies from Svalbard surge-type glaciers have invoked englacial thrusting mechanisms for producing the CSR, suggesting they being derived from debris-bearing thrust faults (Hambrey and Huddart, 1995;Bennett et al., 1996;Glasser et al., 1998). Lovell et al. (2015) found that debris-rich englacial structures observed at surge-type tidewater glaciers in Svalbard display a variety of characteristics and morphologies, which they interpreted to represent the incorporation and elevation of subglacial till via squeezing into basal crevasses and hydrofracture exploitation of thrust faults, reoriented crevasse squeezes, and pre-existing fractures. These structures were observed to melt-out and form embryonic geometrical ridge networks during quiescent phase ice stagnation and ice-margin recession. ...
... Cross cutting relationships between flutes and CSR have neither been widely studied nor well explained, and the processes operating between infilling of basal fractures by till and CSR becoming exposed on the foreland during the quiescent phase melting out of dead-ice are not clear. Thorough sedimentological studies, linked to detailed observations of processes operating during surges (Kristensen and Benn, 2012;Lovell et al., 2015), could further highlight the processes explaining the CSR-flute relationships and thus increase our understanding of subglacial ice-flow mechanisms at work during surging. ...
Article
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Surging glaciers are potential analogues for land-terminating palaeo-ice streams and surging ice sheet lobes, and research on surge-type glaciers is important for understanding the causal mechanisms of modern and past ice sheet instabilities. The geomorphic signatures left by the Icelandic surge-type glaciers vary and range from glaciotectonic end moraines formed by folding and thrusting, crevasse-squeeze ridges, concertina eskers, drumlins and fluted forefields, to extensive dead-ice fields and even drift sheets where fast ice-flow indicators are largely missing. We outline some outstanding research questions and review case studies from the surge-type outlets of Brúarjökull, Eyjabakkajökull and Tungnaárjökull (Vatnajökull ice cap), Múlajökull and Sátujökull (Hofsjökull ice cap), Hagafellsjökull and Sudurjökull (Langjökull ice cap), Kaldalónsjökull, Leirufjardarjökull and Reykjarfjardarjökull (Drangajökull ice cap), as well as the surge-type cirque glaciers in northern Iceland. We review the current understanding of how rapid ice flow is sustained throughout the surge, the processes that control the development of the surge-type glacier landsystem and the geological evidence of surges found in sediments and landforms. We also examine if it is possible to reconstruct past surge flow rates from glacial landforms and sediments and scale-up present-day surge processes, landforms and landsystems as modern analogues to past ice streams. Finally, we also examine if there is a climate/mass-balance control on surge initiation, duration and frequency.
... They might represent proglacial geometrical ridge networks (cf. Bennett et al., 1996;Evans & Rea, 1999Lovell et al., 2015) potentially originating from debris-rich englacial structures. Such debris-rich structures are often linked with surge behaviour Lønne, 2006;Roberts, Yde, Knudsen, Long, & Lloyd, 2009) and the main mechanism proposed to be responsible for their origin is squeezing of debris into crevasses (Rea & Evans, 2011); thrust faulting related to longitudinal compression Lovell et al., 2015); reorientation of vertical crevasses, which facilitates subsequent thrusting (Evans & Rea, 1999;Rea & Evans, 2011) and hydrofracturing (Denis, Buoncristiani, & Guiraud, 2009;Lovell et al., 2015;Roberts et al., 2009). ...
... Bennett et al., 1996;Evans & Rea, 1999Lovell et al., 2015) potentially originating from debris-rich englacial structures. Such debris-rich structures are often linked with surge behaviour Lønne, 2006;Roberts, Yde, Knudsen, Long, & Lloyd, 2009) and the main mechanism proposed to be responsible for their origin is squeezing of debris into crevasses (Rea & Evans, 2011); thrust faulting related to longitudinal compression Lovell et al., 2015); reorientation of vertical crevasses, which facilitates subsequent thrusting (Evans & Rea, 1999;Rea & Evans, 2011) and hydrofracturing (Denis, Buoncristiani, & Guiraud, 2009;Lovell et al., 2015;Roberts et al., 2009). However, no surge behaviour has been observed in the historical records for Nordenskiöldbreen, which suggest that potential surge behaviour had to occur prior to 1882. ...
... Bennett et al., 1996;Evans & Rea, 1999Lovell et al., 2015) potentially originating from debris-rich englacial structures. Such debris-rich structures are often linked with surge behaviour Lønne, 2006;Roberts, Yde, Knudsen, Long, & Lloyd, 2009) and the main mechanism proposed to be responsible for their origin is squeezing of debris into crevasses (Rea & Evans, 2011); thrust faulting related to longitudinal compression Lovell et al., 2015); reorientation of vertical crevasses, which facilitates subsequent thrusting (Evans & Rea, 1999;Rea & Evans, 2011) and hydrofracturing (Denis, Buoncristiani, & Guiraud, 2009;Lovell et al., 2015;Roberts et al., 2009). However, no surge behaviour has been observed in the historical records for Nordenskiöldbreen, which suggest that potential surge behaviour had to occur prior to 1882. ...
Article
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A 1:4000 scale map of the terrestrial margins of the foreland of Nordenskiöldbreen depicts a polythermal glacial landsystem containing a record of the landform signatures of individual ice flow units that operate within the glacier snout. A 1:700 map provides a detailed overview of fluted terrain, based on unmanned aerial vehicle images captured in 2014. The pattern of landforms lying inside the Little Ice Age (LIA) latero-frontal moraine on the northern side of the fjord comprises a fluted till surface, which in turn grades into ice-moulded bedrock. This signature records the recession of a single, wide ice flow unit, which was characterised by limited incorporation of subglacial material and restricted delivery of supraglacial debris. Inside the latero-frontal moraine on the south side of the fjord, a fluted surface is subordinate to a pronounced and large ice-cored moraine complex related to the confluence of five narrower ice flow units, each of which transported significant quantities of englacial and supraglacial debris at their suture zones as a series of longitudinal debris stripes. The suite of foreland landforms is diagnostic of both temperate subglacial and frozen-snout conditions, indicating the operation of a warm polythermal glacier fed by multiple flow units during the LIA.
... of a poorly connected subglacial drainage system (high P w has been observed in drill hole C in Greenland; Iken et al., 1993 ), then water can migrate upwards against gravity either by percolation or possibly by hydraulic fracturing. Water may also migrate as bubbles during ductile deformation, as suggested by the experiments of Wilson et al. (1996). Lovell et al. (2015suggested that the " dispersed " basal ice facies found close to the base in surge glaciers may form by shear deformation and partial melting along grain boundaries, resulting in an upward flux of liquid and gas along grain boundaries. Although temperate ice has a low permeability (Lliboutry, 1971), even a small water flux is very effect ...
... Temperate ice in Alpine glaciers can contain 1–2 % water (Vallon et al., 1976 ), which has been observed in experiments to gather along grain triple junctions (Barnes and Tabor, 1966; Wilson et al., 1996), so that it is likely that a vein network along triple junctions exists (Nye and Frank, 1973; Mader, 1992). Partial melting of a deforming temperate layer is furthermore suggested by the formation of bubble-free ice, both in experiments (Barnes and Tabor, 1966) as well as in Alpine and surging Svalbard glaciers (Tison and Hubbard, 2000; Lovell et al., 2015 ). The dominant deformation mechanism for temperate ice, however, is uncertain and it is possible that different deformation mechanisms operate simultaneously . ...
... De La Chapelle, 1995Chapelle, , 1999). Grain boundary melting is supported by the formation of bubble-poor ice at the base of temperate glaciers: both Tison and Hubbard (2000) and Lovell et al. (2015) show that such ice is not formed by direct freeze-on (regelation ice) but by a metamorphic process involving partial melting. Grain boundary melting is loosely analogous to pressure solution (solution-precipitation creep) observed in salts and limestone, insofar that material changes from solid to liquid or vice versa along grain boundaries in different stress states (Pharr and Asby, 1983; McClay, 1977; Rutter, 1983 ), but differs in that grain boundary melting creates its own liquid. ...
Article
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Basal ice motion is crucial to ice dynamics of ice sheets. The classic Weertman model for basal sliding over bedrock obstacles proposes that sliding velocity is controlled by pressure melting and/or ductile flow, whichever is the fastest; it further assumes that pressure melting is limited by heat flow through the obstacle and ductile flow is controlled by standard power-law creep. These last two assumptions, however, are not applicable if a substantial basal layer of temperate (T � Tmelt/ ice is present. In that case, frictional melting can produce excess basal meltwater and efficient water flow, leading to near-thermal equilibrium. High-temperature ice creep experiments have shown a sharp weakening of a factor 5–10 close to Tmelt, suggesting standard power-law creep does not operate due to a switch to melt-assisted creep with a possible component of grain boundary melting. Pressure melting is controlled by meltwater production, heat advection by flowing meltwater to the next obstacle and heat conduction through ice/rock over half the obstacle height. No heat flow through the obstacle is required. Ice streaming over a rough, hard bed, as possibly in the Northeast Greenland Ice Stream, may be explained by enhanced basal motion in a thick temperate ice layer.
... The geometric ridge networks are interpreted as crevasse-squeeze ridges, based on their varied orientation, intersecting nature and similarity to previously described crevasse-squeeze ridges (Boulton et al., 1996;Rea and Evans, 2011;Lovell et al., 2015). Crevasse-squeeze ridges form as soft subglacial sediments are squeezed upward into basal crevasses during surge stagnation (Kristensen and Benn, 2012;Lovell et al., 2015). ...
... The geometric ridge networks are interpreted as crevasse-squeeze ridges, based on their varied orientation, intersecting nature and similarity to previously described crevasse-squeeze ridges (Boulton et al., 1996;Rea and Evans, 2011;Lovell et al., 2015). Crevasse-squeeze ridges form as soft subglacial sediments are squeezed upward into basal crevasses during surge stagnation (Kristensen and Benn, 2012;Lovell et al., 2015). High basal water pressures, close to ice overburden, coupled with high extensional strain rates in turn enable bottom-up crevasse propagation or hydrofracturing and subsequent sediment squeeze into the basal crevasses (Rea and Evans, 2011;Lovell et al., 2015). ...
... Crevasse-squeeze ridges form as soft subglacial sediments are squeezed upward into basal crevasses during surge stagnation (Kristensen and Benn, 2012;Lovell et al., 2015). High basal water pressures, close to ice overburden, coupled with high extensional strain rates in turn enable bottom-up crevasse propagation or hydrofracturing and subsequent sediment squeeze into the basal crevasses (Rea and Evans, 2011;Lovell et al., 2015). Crevasse-squeeze ridges in a landform assemblage have been used as a characteristic criterion for identifying surging glacier (Solheim and Pfirman, 1985;Evans and Rea, 1999;Farnsworth et al., 2016). ...
Article
Vaigattbogen is located in northern Svalbard. The area is currently affected by several tidewater glaciers. This study uses multibeam-, sub-bottom acoustic data, and four sediment cores to reconstruct the Late Weichselian and Holocene glacial history in Vaigattbogen. During the last glacial, ice flowed northwards through Vaigattbogen and fed into the Hinlopen Strait Ice Stream. Streamlined bedforms indicate relatively fast ice flow and their increasing elongation ratios towards the north suggest increasing flow velocities. De Geer moraines in the shallower parts of Vaigattbogen imply that multiple halts and/or re-advances interrupted the ice retreat in these areas. A sediment core suggests that the north basin deglaciated prior to 9.1 cal. ka BP. In the south basin, two large moraine ridges and networks of crevasse-squeeze ridges suggest that at least two surge-type advances occurred during the Holocene. The Hinlopenbreen glacier surged in the early 1970s and deposited the inner (R.2) of the two large moraine ridges. Radiocarbon ages from a sediment core recovered from the crest of the outer (R.1) ridge yield a basal age of 2.6 cal. ka BP. However, the core did not sample subglacial diamict and the age of the ridge could be anything between 2.6 cal. ka BP and early Holocene. The R.1 ridge formed prior to the Little Ice Age (LIA), implying that more than one tidewater glacier has experienced a pre-LIA surge on the east coast of Spitsbergen, suggesting that surging during the Holocene was a regional phenomenon. The R.1 ridge is double-crested with small crevasse-squeeze ridges between the crests suggesting that more than one surge-type advance occurred during the Holocene reaching approximately the same location. Data from eastern Svalbard indicate differences in surge-landform assemblages suggesting that different mechanisms could have governed surge-cycles throughout the Holocene.
... The thermal state of Svalbard glaciers has been documented to switch from polythermal to cold-based during retreat and thinning, as thinning allows for penetration of cold atmospheric temperatures to the bed of the ice (e.g., Hagen et al., 1993;Lovell et al., 2015;Farnsworth et al., 2020b). Midtsundstadbreen could have switched from warm to cold after the LGM, and as the ice sheet in the northern sector had already started thinning c. 25 ka ago, the switch may have occurred early . ...
... Midtsundstadbreen could have switched from warm to cold after the LGM, and as the ice sheet in the northern sector had already started thinning c. 25 ka ago, the switch may have occurred early . However, while most of the case studies of thermal switch are from small valley glaciers, we assume that it would also occur within large ice caps (e.g., Humlum et al., 2005;Lovell et al., 2015). ...
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Climate change is amplified in the Arctic, and establishing baseline data for its current character is important. Here we present a map of the geomorphology of the Femmilsjøen area, Spitsbergen, northern Svalbard. The regional physiography is characterised by a low-relief, high elevation mountain plateau, its high-relief steep slopes, and low-relief coastal lowlands. The results indicate that glaciers were most likely warm-based and erosive in the low terrain, whereas there are signatures of colder, less erosive ice on the plateaus during the Late Weichselian. Our study highlights the ongoing glacial and periglacial morphological processes in an area of hard and weathering-resistant bedrock, situated in northern Svalbard.
... The relationship between the CSR and fluted till plain suggests several possible modes of formation (Sharp, 1985b;Bjarnadóttir, 2007;Ferguson et al., 2009). Similar morphological structures can form from subaerial infill of moraine sediments (Morawski, 2005) or debrisrich thrust-faults (Glasser et al., 1998) but are not usually arranged in interconnected rhombohedral networks (Lovell et al., 2015b). Generally CSRs are believed to form by local saturated sediment infilling, from the bed upward, into basal crevasses during the latter part of a surge and subsequently meltout. ...
... 14 result of the different methods used for identifying surge behavior. Crevasse squeeze ridges have been interpreted from fjord bathymetry (Flink et al., 2015;Lovell et al., 2015b), and many tidewater glaciers have relatively long observation histories (Liestøl, 1993). Surging tributary glaciers at higher elevations have been mainly identified by geodetic changes (Sund et al., 2009). ...
... Forwick & Vorren 2007;Dowdeswell et al. 2016). Glacier surging is believed to be particularly widespread in Svalbard, where up to 90% of glaciers are suggested to have exhibited surge-type behaviour (Lefauconnier & Hagen 1991;Flink et al. 2015;Lovell et al. 2015Lovell et al. , 2018bFarnsworth et al. 2016Farnsworth et al. , 2017. Many surge-type glaciers drain into the fjords (or have drained in the past) in Svalbard forming tidewater margins (cf. ...
... The geometric network of small ridges was most likely formed by squeezing of subglacial sediments into the basal crevasses during the surge of Hambergbreen. Similar networks of small ridges have previously been described from a number of fjords and adjacent coastal plains in Svalbard (Ottesen & Dowdeswell 2006;Flink et al. 2015;Lovell et al. 2015;Farnsworth et al. 2016Farnsworth et al. , 2017. Their formation has been attributed to the fast advance of the glaciers, usually surge, when the glacier becomes stagnant at the end of the surge and the deformable bed is injected into the basal crevasses that opened up during the surge (Sharp 1985;Rea & Evans 2011;Kristensen & Benn 2012). ...
Article
The submarine landforms and shallow sediment record are presented from Hambergbukta, southeastern Spitsbergen using swath‐bathymetric, subbottom acoustic, and sediment core data. The mapped landforms include large terminal and end‐moraines with associated debrisflow aprons on their distal flanks, drumlinized till surface, glacial lineations, medial and retreat moraines, crevasse squeeze ridge networks, eskers, as well as iceberg‐produced terraces and plough‐marks. Analysis of the landforms and landform assemblages in combination with the sediment core data and aerial imagery studies reveal a complex and dynamic glacial history of Hambergbukta. We present a detailed history of Hambergbreen glacier indicating two previously unknown surges as well as new details on the nature of the subsequent ice‐margin retreat. The results from two gravity cores combined with the shallow acoustic stratigraphy and high‐resolution bathymetry suggest that the c. AD 1900 surge was less extensive than previously thought and the retreat was most likely rapid after the c. AD 1900 and 1957 surges of the Hambergbreen. Mixed benthic foraminifera collected from the outer fjord basin date to 2456 cal. a BP, suggesting older sediments were re‐worked by the c. AD 1900 surge. This highlights the importance of exercising caution when using foraminifers for dating surge events in fjord basins enclosed by prominent end‐moraines.
... Basal crevasses are not observed as easily as the surface crevasses (Harper et al., 2010;Walter et al., 2010) but are known to exist widely in surging glaciers. Actually, crevasse squeeze ridges near glacier terminus are unique indicators of surge-type glaciers (Farnsworth et al., 2016;Lovell et al., 2015;Sharp, 1985). They form when soft sediment is squeezed into the basal crevasses near the end of surges and get preserved after glaciers retreat. ...
... Therefore, water would flow transversely to ice flows and has inefficient downstream component. After surge stops, sediments and water filling the crevasses would warm the bottom ice layer (Barrett et al., 2008;Murray et al., 2000) and eventually produce crevasse squeeze ridges once the advanced glacier terminus retreats (Lovell et al., 2015;Sharp, 1985). The bimonthly average applied in our seismic observations does not allow us to resolve the process at the surge front on how the switch of drainage system happens. ...
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Subglacial drainage systems are known to critically control ice flows, but their spatial configuration and temporal evolution are poorly constrained due to inaccessibility. Here we report a twelve‐year long monitoring of the drainage underneath Bering Glacier, Alaska, by correlating ambient noise recorded at two seismic stations on the sides of the glacier. We find that the seismic surface waves traveling across Bering Glacier slowed down by 1~2% during its latest 2008‐2011 surge, likely due to the switch of the subglacial drainage from a channelized system to a distributed system. In contrast to current models, the relative amplitude of velocity reductions for Rayleigh and Love waves requires the distributed drainage to be highly anisotropic and aligned perpendicular to the ice flow direction. We infer that the subglacial water flow is mainly through a network of transverse basal crevasses during surges, thus can sustain the high water pressure and ice flow speed.
... The CSRs are only present proximal to the wide marginal moraines (Fig. 4). The landforms have low preservation potential and are often reworked by meltwater and dead-ice melt (Lovell et al. 2015b). The ridges consist of matrix-supported diamict sediments and are often preserved in geometric networks located on raised till plains protected from meltwater erosion (Schomacker et al. 2014). ...
... Crevasse-squeeze ridges. -A geometric ridge network has been mapped and interpreted as crevasse-squeeze ridges in inner St. Jonsfjorden (Lovell et al. 2015b;Figs 3, 7). The rhombohedral structures are present on a flat basin along with streamlined glacial features (Fig. 7D). ...
Article
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Evidence of a dynamic Holocene glacial history is preserved in the terrestrial and marine archives of St. Jonsfjorden, a small fjord-system on the west coast of Spitsbergen, Svalbard. High-resolution, remotely sensed imagery from marine and terrestrial environments was used to construct geomorphological maps that highlight an intricate glacial history of the entire fjord-system. The geomorphology and stratigraphy indicate an early Holocene local glacier advance constrained to the Lateglacial–early Holocene transition. Identification and 14Cdating of the thermophilous bivalve mollusc Modiolus modiolus to 10.0�0.12 cal. ka BP suggest a rapid northward migration of the species shortly after deglaciation. Further evidence enhances the understanding of the onset and subsequent climax of the Neoglacial - Little Ice Age in inner St. Jonsfjorden.The present-day terminus of Osbornebreen, the dominating glacier system in St. Jonsfjorden, is located over 8.5 km up-fjord from its Neoglacial maximum extent. Cross-cutting relationships suggest subsequent advances of all the smaller glaciers in the area following the break-up of Osbornebreen. Glacial deposits, landforms and their cross-cutting relationships observed in both terrestrial and marine settings imply a complex and highly dynamic environment through the later part of the Holocene.
... Please cite as: Submarine landforms and glacimarine sedimentary processes in Lomfjorden, East Spitsbergen. Marine Geology.DOI: 10.1016DOI: 10. /j.margeo.2017 of the ridges in inner Lomfjorden, as their indistinct appearance is different 303 to the well-developed, sharp-crested crevasse-squeeze ridges in other Spitsber-304 gen fjords(Ottesen et al., 2008;Flink et al., 2015). This could be related to 305 the presence of an undersaturated, less deformable subglacial till in Lomfjorden 306 (cf. ...
... This could be related to 305 the presence of an undersaturated, less deformable subglacial till in Lomfjorden 306 (cf. e.g.Lovell et al., 2015), to poorly-developed crevasses within the glacier,307 or to post-glacial sediment infill between individual ridges masking their true 308 appearance. The predominantly transverse orientation of the ridges and the 309 lack of cross-cutting relationships between individual ridges are consistent with 310 formation of the ridges as glacier end moraines. ...
Article
Understanding the role of fjords in modulating the long-term interaction between ice sheets and glaciers with the surrounding ocean requires the investigation of glacigenic landform and sediment archives. In Svalbard, there is a wealth of data from fjords in west Spitsbergen that constrains the glacial history of this sector of the Svalbard-Barents Sea Ice Sheet (SBIS) since the Last Glacial Maximum (LGM), and the nature and timing of subsequent ice retreat. In contrast, however, very little is known about the glacial history of fjords in east Spitsbergen.
... Blaszczyk et al. [6] specifically described Svalbard's tidewater glaciers with emphasis on flow velocity, calving fluxes, and mass loss. Many tidewater glaciers in Svalbard have experienced surge events during the last 150 years [13,[35][36][37][38][39][40]. Such activity is described for most of the glaciers in this study [6,13], even though there is only one reported surge event on Markhambreen from around 2010. ...
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Tidewater glaciers on the east coast of Svalbard were examined for surface elevation changes and retreat rate. An archival digital elevation model (DEM) from 1970 (generated from aerial images by the Norwegian Polar Institute) in combination with recent ArcticDEM were used to compare the surface elevation changes of eleven glaciers. This approach was complemented by a retreat rate estimation based on the analysis of Landsat and Sentinel-2 images. In total, four of the 11 tidewater glaciers became land-based due to the retreat of their termini. The remaining tidewater glaciers retreated at an average annual retreat rate of 48 m year􀀀1, and with range between 10–150 m year􀀀1. All the glaciers studied experienced thinning in their frontal zones with maximum surface elevation loss exceeding 100min the ablation areas of three glaciers. In contrast to the massive retreat and thinning of the frontal zones, a minor increase in ice thickness was recorded in some accumulation areas of the glaciers, exceeding 10 m on three glaciers. The change in glacier geometry suggests an important shift in glacier dynamics over the last 50 years, which very likely reflects the overall trend of increasing air temperatures. Such changes in glacier geometry are common at surging glaciers in their quiescent phase. Surging was detected on two glaciers studied, and was documented by the glacier front readvance and massive surface thinning in high elevated areas.
... It is widely accepted that, although individual CSRs are not necessarily diagnostic of surging per se, their arrangement in dense networks at glacier margins is. These networks are characterised by multiple ridges oriented oblique and transverse (and occasionally normal) to ice flow [29,30,34,35,58,67,75,78,80]. ...
Article
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Glacitectonic composite ridge systems are found at the margins of a number of surge-type glaciers globally. On the High-Arctic archipelago of Svalbard, the pioneering work of Croot (Glaciotectonics: forms and processes. Balkema, Amsterdam, 1988) highlighted the coincidence between composite ridge systems and surge-type glaciers on the island of Spitsbergen. These observations have contributed significantly to our understanding of the links between glacier surges and the landforms they produce. We update this work and expand it to the whole archipelago using the Norwegian Polar Institute’s TopoSvalbard aerial photograph archive to identify 50 composite ridge systems. These are found on all four of the largest islands: Spitsbergen, Nordaustlandet, Edgeøya and Barentsøya, and at the margins of both tidewater and land-terminating glaciers. Of the 50 composite ridge systems, 49 are associated with glaciers that have either been documented as surge-type or contain indicative geomorphological evidence of surging in the form of crevasse-squeeze ridge (CSR) networks. This provides further support for the established link between composite ridge systems and surging. Based on the proportion of glaciers that are documented as being of surge-type and those that display indicative evidence of surging (but have not been observed to surge), we conclude that at least 32.6% of all glaciers in Svalbard surge or are likely to have surged. This study contributes to the understanding of the links between glacier surging and specific landforms/landform assemblages (composite ridge systems and CSR networks), which has applications in other modern glacial environments and at the margins of former ice masses in palaeoglaciological settings.
... Their similar dimensions and geometrical pattern of the ridges in the T.5 landsystem to earlier described crevassesqueeze ridges (Ottesen and Dowdeswell, 2006;Ottesen et al., 2008a;Flink et al., 2015;Lovell et al., 2015) allows us to interpret these as the same submarine landforms. In the T.5 landsystem the crevasse-squeeze ridges intersect with retreat moraines, making it sometimes difficult to distinguish these ridges from each other. ...
Article
Wahlenbergfjorden is a fjord situated in the western part of Nordaustlandet in northern Svalbard. It leads into the 400 m deep Hinlopen Strait located between Nordaustlandet and Spitsbergen. High-resolution multibeam bathymetric and sub-bottom data, as well as sediment cores are used to study the past extent and dynamics of glaciers in Wahlenbergfjorden and western Nordaustlandet. The submarine landform assemblage in Wahlenbergfjorden consists of landforms characteristic of subglacial, ice marginal and proglacial conditions. Glacial lineations indicate that Wahlenbergfjorden was occupied by streaming ice during the LGM and most likely acted as an ice stream onset zone. Westward ice flow in the fjord merged with the ice stream in Hinlopen Strait. Absence of ice recessional landforms in outer Wahlenbergfjorden suggests relatively fast deglaciation, possibly by flotation of the glacier front in the deeper parts of the fjord. The inner part of Wahlenbergfjorden and Palanderbukta are characterized by De Geer moraines, indicating episodic retreat of a grounded glacier front. In Palanderbukta, longer still stands of the glacier terminus resulted in the formation of larger terminal moraine ridges. The inner part of Wahlenbergfjorden was deglaciated prior to 11.3 ± 55 Cal. ka BP. The submarine landform assemblages in front of Bodleybreen, Etonbreen, Idunbreen, Frazerbreen and Aldousbreen confirm that these glaciers have surged at least once during the Holocene.
... Spitzbergen) eine Bildung im Zusammenhang mit schnell vorstoßenden Gletschern (sog. surging glaciers) nahe (Lovell 2014, Lovell et al. 2015. Die komplex aufgebauten Block-Stauchkörper (engl. ...
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Die glazialgeomorphologische und -sedimentologische Terminologie hat in den vergangenen zwei Jahrzehnten international eine starke Weiterentwicklung erfahren und die Nutzung der Begrifflichkeiten folgt seit geraumer Zeit einheitlichen Richtlinien. Grundsätzlich ist bei der Aufnahme glazialer Ablagerungen auf eine saubere Trennung zwischen Beschreibung und Interpretation zu achten, insbesondere sollten geomorphologische Begrifflichkeiten stets klar von sedimentären Prozessen und den sedimentären Produkten unterschieden werden, um eine terminologisch-interpretative Vermengung von Form (Landform) und Inhalt (Sediment) zu vermeiden. Glaziale Sedimente sollten zunächst ausschließlich aufgrund ihrer lithofaziellen Eigenschaften und unter Nutzung strikt lithologischer Begriffe (wie Diamikton, schräggeschichtete Sande, laminierte Schluffe etc.) beschrieben werden. Erst im nächsten Schritt, und nach eingehender Untersuchung, sollten genetische Begriffe (wie Till, Schmelzwassersande, glaziolimnische1 Warvensedimente etc.) zur Interpretation der zuvor beschriebenen Einheiten genutzt werden. Die empfohlene Trennung glazialgeomorphologischer und -sedimentärer Begriffe ist bis heute im deutschsprachigen Raum nicht immer gewährleistet. Dies betrifft v.a. den Begriff der ‚Moräne‘, der einerseits als sedimentäre Sammelbezeichnung für glaziale Ablagerungen verschiedenster Herkunft dient (z.B. ,Moränenmaterial‘), anderseits aber auch den durch den Gletscher aktuell transportierten Gesteinsschutt beschreibt (z.B. ‚Obermoräne‘). Desweiteren wird der Moränenbegriff gleichermaßen sowohl für die Ansprache glazialer Landformen (z.B. Endmoräne) als auch für die Beschreibung von Eigenschaften des Geschiebespektrums genutzt (z.B. Lokalmoräne). Diese Praxis führt nicht nur bei Einsteigern zu Verwirrungen, sondern erschwert auch die Verständigung unter Fachleuten, da diese multifunktionale Nutzung des Moränenbegriffs international seit geraumer Zeit nicht mehr üblich ist. Weitere terminologische Probleme ergeben sich aus den voneinander abweichenden Nomenklaturansätzen, die innerhalb der verschiedenen deutschsprachigen Staaten im Gebrauch sind, sowie der Praxis, dass z.B. in Deutschland quartärgeologische Aufnahmen in den Aufgabenbereich der einzelnen Bundesländer fallen und damit eigene begriffliche Traditionen fortbestehen. Der vorliegende Artikel hat das Ziel, einen systematischen Überblick über die Genese glazialer Sedimente zu liefern und Empfehlungen für die zukünftige Beschreibung, Benennung und Interpretation solcher Sedimente in der deutschsprachigen Literatur zu liefern, die den internationalen Definitionen entsprechen. Der Begriff ‚Moräne‘, einschließlich der Variante ‚Grundmoräne‘, sollte fortan lediglich für die Einordnung glazialer Landformen bzw. Landformenvergesellschaftungen verwendet werden, jedoch nicht für die Ansprache glazialer Sedimente. Letztere sollten künftig erst nach genauerer lithologischer Beschreibung und nach den hier definierten diagnostischen Kriterien benannt und geogenetisch interpretiert werden. Die in diesem Artikel präsentierte Zusammenstellung der wichtigsten Kriterien für eine sichere Unterscheidung diverser glazialer Diamikte richtet sich nach dem aktuellen internationalen Forschungsstand. Danach wird ein primärer Till als ein ausschließlich subglaziales und durch direkte Ablagerung vom Eis gebildetes Sediment definiert. Ein solcher in der ‚Traktionszone‘ eines basal gleitenden Gletschers entstandener Till wird als ‚subglazialer Traktionstill‘ (engl. subglacial traction till) bezeichnet. Traktionstills sind von gletscherüberfahrenen prä-existenten Sedimenten (z.B. deformierte Schmelzwassersande) zu unterschieden, welche künftig als ‚Glaziotektonit‘ (engl. glaciotectonite) angesprochen werden sollten und nicht zu den primären Tills sensu stricto gerechnet werden. Eine Weiterverwendung der älteren, stark prozessspezifisch geprägten Till-Begriffe wie Lodgement till und Deformation till ist nach aktuellem Forschungsstand nicht mehr sinnvoll, da zwischen beiden Tilltypen in der Realität ein genetisches Prozesskontinuum besteht und keine gesicherten diagnostischen Kriterien für eine zuverlässige Einzelansprache im Gelände vorliegen. Andere diamiktische Sedimente, die häufig in glazialen Ablagerungsräumen auftreten und meist supra- bzw. proglazialer Herkunft sind, sollten nicht als Till, sondern nach dem jeweils dominanten Ablagerungsprozess benannt werden (z.B. Schlammstrom(-ablagerung), debris flow (deposit); Abtropfdiamikt, dropstone diamict). Unter Anwendung dieser Kriterien stellen die Autoren fest, dass subglazial gebildeter Till weit weniger verbreitet ist als bislang angenommen. Vor allem glaziale Landformen wie Endmoränen enthalten bei genauer Betrachtung nur selten größere Anteile primärer glaziale Sedimente (Till). Stattdessen setzen sie sich zumeist aus einer Vielzahl verschiedenartiger und deformierter Sedimente zusammen, die im ehemaligen Gletschervorfeld abgelagert und im Zuge eines Vorstoßes zusammengestaucht wurden.
... Additionally, Lovell et al. (2012) raised the possibility for surge-like behaviour of the Otway lobe based partly on this landform evidence. Our study confirms that many of the landforms associated with surging activity are exhibited in the study area, including thrust moraines, highly elongate flutings, hummocky terrain and crevasse-squeeze ridges, which are often viewed as diagnostic of surge activity Rea, 1999, 2003;Schomacker et al., 2014;Lovell et al., 2015). As such, we suggest the ice lobes may have periodically displayed rapid ice-flow and possible surge-like behaviour. ...
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Reconstructions of former ice masses from glacial geomorphology help to constrain the nature and timing of glaciation in relation to climatic forcing. This paper presents a new reconstruction of the glacial history of five ice lobes in southernmost South America: the Bahía Inútil − San Sebastián, Magellan, Otway, Skyring and Río Gallegos ice lobes. We use previous geomorphological mapping of glacial landforms to reconstruct former glacial limits and proglacial lakes, demarcate flow-sets from the distribution of glacial lineations, and evaluate glacial landsystem signatures and their palaeoglaciological implications. Evidence suggests that the ice lobes predominantly reflect active temperate glacial landsystems, which may have switched to polythermal systems when periods of cold-based ice developed ephemerally. This complex landsystem signature implies that the ice lobes were sensitive to regional climate variability, with active re-advances during overall retreat of the ice margins. There is also evidence for periods of fast ice flow and possible surge-like activity in the region, followed by the rapid retreat or even collapse of some of the ice lobes in association with proglacial lakes. Constraining our new reconstruction with published chronological information suggests that at least some of the ice lobes advanced before the global Last Glacial Maximum (gLGM: ca. 26.5–19 ka) during the last glacial cycle. Our new reconstruction demonstrates a more complex picture of ice dynamics than has previously been portrayed, and one in which the advance and retreat of the ice lobes was likely to have been primarily driven by changes in climate. As such, ice advances before the gLGM in the southernmost part of the Patagonian Ice Sheet are likely to indicate a wider climatic forcing at this time.
... It is instructive to indicate that not all supraglacial debris is necessarily angular. It is not uncommon in boulder trains and as ablation deposits in many glaciated areas to find well-rounded clasts and boulders transported and deposited from supraglacial environments depending on bedrock sources, and ice basal scavenging (debris entrainment) by removal of rock and debris causing, through debris entrainment, clasts to rise within the ice to the supraglacial (Shilts, 1973;DiLabio and Shilts, 1979;Lawson, 1995;Darvill et al., 2015;Lovell et al., 2015). (A) Folding of basal debris leading to thickening of the basal debris layer; rock in centre is ca. ...
Chapter
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Subglacial sediments are among the most prevalent sediments in glaciated terrains. The environments and processes that erode, transport and deposit/emplace subglacial sediments and landforms are described in the light of recent research developments. Tills and deforming beds and thermal/rheological conditions in subglacial environments are elucidated. The characteristics and origins of subglacial landforms such as drumlin, Rogen, fluted and hummocky moraine and eskers are discussed. Finally, future perspectives, challenges and possible new research opportunities in subglacial environments are considered.
... Alternatively, top-down infilling can occur by the accumulation of supraglacial debris or glaciofluvial material but this mechanism would make the preservation of CSRs less likely (Evans et al. 2016). The possibility of CSRs to develop from englacial debris-rich structures has been noted as well (Bennett et al. 1996;Rea, Evans 2011;Lovell et al. 2015). Unfortunately, it is difficult to evaluate the possible englacial transport of sediment-filled fractures or thrust faults at the paleo-ice streams but, for example, Ankerstjerne et al. (2015) who did detailed analyses of the properties of sediments constructing CSRs concluded that the formation of CSRs was assisted by basal ice motion and occurred prior to complete ice stagnation during the late stages of surge. ...
Article
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Glacial geomorphological mapping of western Latvia using a 1-m-resolution digital elevation model generated from airborne LiDAR data has revealed two sets of mega-scale glacial lineations (MSGLs), one of which is superimposed by crevasse-squeeze ridges (CSRs). CSRs occur as a dense ridge network with a dominant orientation of ridges perpendicular to the ice flow direction. The landform assemblage is interpreted as evidence for two separate phases of fast ice flow with different ice flow directions during the overall deglaciation of the Fennoscandian Ice Sheet (FIS). The first fast ice flow phase occurred from the northwest by the Usma Ice Lobe that extended in the Eastern Kursa Upland. The second fast ice flow occurred from the north by the Venta Ice Tongue in a narrow flow corridor limited mainly to the Kursa Lowland. Active ice streaming caused ice crevassing perpendicular to the ice flow direction and formation of CSRs by squeezing of subglacial till into basal crevasses. A good preservation of the CSRs and general lack of recessional moraines suggest widespread stagnation and ice mass melting after the shutdown of the Venta Ice Tongue followed by the formation of the Venta-Usma ice-dammed lake and glaciolacustrine deposition in the lowest areas of lowland. Our data provide the first evidence of CSRs in the southeastern terrestrial sector of the FIS suggesting the dynamic ice streaming or surging behaviour of the ice lobes and tongues in this region during deglaciation.
... The surge may also have been influential in the creation of large ice-cored moraines, hummocky terrain, and crevasse squeeze ridges (cf. Evans and Rea, 2003;Roberts et al., 2009;Evans et al., 2012;Lovell et al., 2015Lovell et al., , 2018, the latter emerging within a dense geometric ridge network that appears to be centred on a zone of linear esker ridges. This landform assemblage comprises small eskers, crevasse-squeeze ridges, and hydrofracture fills and might more realistically relate to the rapid release of pressurised meltwater from the temperate ice zone of the glacier snout and its injection into the cold-based snout ice rather than surge-induced crevassing. ...
Article
The assessment of multidecadal scale change in a polythermal glacial landsystem in the high Arctic is facilitated by a quantitative approach that utilises time series of aerial photographs, satellite images, digital elevation models, and field geomorphological mapping. The resulting spatiotemporal analysis illustrates a transition from glacial to proglacial/paraglacial conditions indicating that (1) the areal coverage of ice between the maximum LIA extent and 2013 decreased from 29.35 to 16.07 km², which is a reduction in the glacierized area in the catchment from 62% to 34%; (2) the ice volume loss in the proglacial area amounted to 214.9 (±3%) million m³, which was attributed mostly to ablation of the glacier snout but to a lesser extent the degradation of ice-cored landforms; (3) the transition from areas formerly covered by glacier ice to ice-cored moraines, glacifluvial deposits, and other landforms was the most intense in the period 1990–2013; (4) two end member scenarios (polythermal glacial landsystem domains) evolve during glacier recession, each one dictated by the volume of debris in englacial and supraglacial positions, and include (a) subglacial surfaces (limited englacial and supraglacial debris) related to temperate basal ice and (b) ice-cored lateral moraines and moraine-mound complexes (significant supraglacial debris accumulations) related to marginal cold-based ice. An additional assemblage of geometric ridge networks (discrete or linear englacial and supraglacial debris concentrations) relates to crevasse and hydrofracture infill branching out from an esker complex and is indicative of either surging or later rapid release of pressurised meltwater from temperate to cold-based parts of the former glacier snout.
... A new surge diagnostic landform that appeared between 2005 and 2015 is crevasse-squeeze ridges (Fig. 8a). These features develop when saturated sediment is squeezed into subglacial crevasses during the surge phase (Sharp, 1985a(Sharp, , 1985bSharp, 1988;Rea and Evans, 2011;Lovell et al., 2015). They occur as elongated transverse ridges with a height up to about 3 m, and are common features in the proglacial area of surge-type glaciers (Bennett et al., 1996;Evans and Rea, 1999;Farnsworth et al., 2016). ...
Article
Kuannersuit Glacier in west Greenland experienced a major surge in 1995–1998, where the glacier advanced 10.5 km down-valley. In this paper, we examine how the quiescent phase has progressed until 2015 with respect to ice dynamics, landform formations and glaciomorphological changes. In the initial quiescent phase (2001–2005), ice velocities along the center flowline were 37–55% higher than ice velocities (6.3–9.0 m yr⁻¹) in 2005–2015, and a linear relationship between ice velocity and distance from the glacier front, which existed during the initial quiescent phase, had disappeared in 2005–2015. Between 2001 and 2015, the post-surge glacier tongue thinned by 84.0 ± 6.3 m, equal to 6.0 ± 0.5 m yr⁻¹. The 30-m high terminal moraine detached from the active glacier along the uppermost thrust band between 2005 and 2015, after which the glacier front receded 1.5 km. Between the terminal moraine and the glacier front, observations suggested that a proximal outwash plain was forming on top of glacier ice and that glacier naled (icing, aufeis) was incorporated into the outwash plain. In less dynamic areas with gently sloping topography along the lateral glacier margins, crevasse-squeeze ridges were melting out. The most prominent glaciomorphological feature in 2015 was a c. 1-km long gorge with c. 30–40 m high ice cliffs. This gorge had formed into the glacier front, following the collapse of a series of chasms above the main subglacial channel. Roof collapse processes above subglacial channels had a significant impact on the glacier's mass loss and on the glaciomorphology during the quiescent phase. Earlier observations from 1913 suggest that the formation of this gorge is a reoccurring phenomenon during the quiescent phase. A lower pothole field on the glacier tongue that existed during the initial quiescent phase had completely disappeared in 2015, while a larger upper pothole field in the reservoir area prevailed. During the initial quiescent phase, the subglacial drainage system developed into a stable channelized network, although a jökulhlaup from a large ice-dammed lake occurred. This single event was dated to have occurred between 11 and 13 August 2006, and the lake did not refill. The spatiotemporal association and evolution of glacial and glaciomorphological landforms at Kuannersuit Glacier are likely similar to processes at many other surging and rapidly receding glaciers of similar size.
... Clasts shapes are predominantly subangular and subrounded, and some clasts are striated. The structures closely resemble those described in surge-type Tunabreen in Svalbard (Lovell, Fleming, Benn, Hubbard, Lukas, Rea, et al., 2015). ...
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Interpreting the relationships among the internal processes of glaciers and their mesoscale structural products has been a long-standing challenge for glaciologists. Trapridge Glacier is a small polythermal surge-type valley glacier that has been studied for 40 years. It offers an opportunity to investigate the structural evolution of a glacier through a series of surges and to apply novel modeling approaches to gain physical insight as to how different structures are formed. Following the glacier's most recent slow surge, the structural attributes were documented, with emphasis on their three-dimensional geometry and sequential development: ice stratification (S 0 ), longitudinal foliation (S 1 ), and associated medial moraine, folding of stratification (F 1 ), transverse foliation (S 2 ), thrusts (S 3 ), and recumbent folds (F 3 ), fractures (surface crevassing and crevasse traces; S 4 ). Efforts to represent these structures using models of glacier flow dynamics remain at an early stage but provide informative tests of model skill and of current understanding of the processes that control structure generation. Using field interpretations as a guide to the relevant processes of formation, structures on Trapridge Glacier are compared with computer-simulated structures for the same glacier. Modeling achieved the greatest success in simulating moraine patterns, ice stratification, longitudinal foliation, and the downglacier decrease in the density of surface crevasse traces. The least successful effort was to simulate the orientation of crevasse traces.
... Their formation is generally thought to be by upward infilling of saturated sediments into basal crevasses that form in association with the ongitudinal and extensional stress during a surge. The process happens towards the termination of the surge and subsequent meltout (Rea and Evans, 2011;Lovell et al., 2015). The complex network of CSRs in the forefield of Kjerulfbreen indicates that the base of the glacier was heavily crevassed in multiple directions. ...
... The presence of crevassesqueeze ridges in the Tekapo Valley, and their cross-cutting relationships however, indicates that the glacier margin was highly fractured by crevasses whose pattern is more diagnostic of a surge origin than radial crevasse infilling (cf. Sharp, 1985aSharp, , 1985bEvans et al., 2007Evans et al., , 2016Evans et al., , 2017aRea and Evans, 2011;Lovell et al., 2015). The complex, reticulate networks typical of crevasse-squeeze ridges in the Tekapo Valley were therefore likely produced by till squeezing upwards into open basal crevasses and likely formed where there was soft, readily deformable sediment at the ice-bed interface, either during or immediately after a surge (Sharp, 1985a(Sharp, , 1985bRea, 1999, 2003;Benediktsson et al., 2009;Rea and Evans, 2011;Evans et al., 2016; ...
Article
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Quaternary glaciations have created impressive landform assemblages that can be used to understand palaeo-glacier extent, character and behaviour, and hence past global and local glacier forcings. However, in the southern hemisphere and especially in New Zealand, the Quaternary glacial landform record is relatively poorly investigated with regard to glaciological properties. In this study, a 1 m digital elevation model (DEM) was generated from airborne LiDAR data and supplemented with aerial imagery and field observations to analyse the exceptionally well-preserved glacial geomorphology surrounding Lake Tekapo, New Zealand. We describe a rich suite of Last Glacial Maximum (LGM) and recessional ice-marginal, subglacial, supraglacial, glaciofluvial and glaciolacustrine landform assemblages. These represent two landsystems comprising i) fluted till surfaces with low-relief push moraine ridges; and ii) crevasse-squeeze ridges, ‘zig-zag’ eskers and attenuated lineations. The former landsystem records the behaviour of an active temperate glacier and the latter landsystem, which is superimposed upon and inset within the former, strongly suggests intermittent surge phases. The two landsystem signatures indicate a sequential change in ice-marginal dynamics during recession that was likely to have been partially non-climatically driven. Overall, we present the first evidence of surge-type glacier behaviour in New Zealand.
... High sedimentation rates in polythermal glacier catchments on Svalbard (e.g., Hallet et al., 1996;Hodgkins et al., 2003) can be attributed to previous surge activities and the sediment accumulation caused by this dynamic behavior (e.g., Lovell et al., 2015b;Lovell et al., 2018). Similarly high sedimentation rates in cold-based Svalbard glacier catchments can be linked to sediment accumulation during periods of more dynamic behavior and warm-based bed conditions in the Little Ice Age (e.g., Lovell et al., 2015a;Sevestre et al., 2015). ...
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... Geometric ridge networks have also been described from the proglacial area of two other surge-type glaciers in Svalbard, Tunabreen, and Von Postbreen, but a modified process of formation has been ascribed to them (Lovell, Fleming, Benn, Hubbard, Lukas, Rea, et al., 2015). Englacial structures include basal crevasse-squeezes containing deformation till. ...
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The aims of this review are to: (i) describe and interpret structures in valley glaciers in relation to strain history; and (ii) to explore how these structures inform our understanding of the kinematics of large ice masses, and a wide range of other aspects of glaciology. Structures in glaciers give insight as to how ice deforms at the macroscopic and larger scale. Structures also provide information concerning the deformation history of ice masses over centuries and millennia. From a geological perspective, glaciers can be considered to be models of rock deformation, but with rates of change that are measurable on a human time-scale. However, structural assemblages in glaciers are commonly complex, and unravelling them to determine the deformation history is challenging; it thus requires the approach of the structural geologist. A wide range of structures are present in valley glaciers: (i) primary structures include sedimentary stratification and various veins; (ii) secondary structures that are the result of brittle and ductile deformation include crevasses, faults, crevasse traces, foliation, folds, and boudinage structures. Some of these structures, notably crevasses, relate well to measured strain-rates, but to explain ductile structures analysis of cumulative strain is required. Some structures occur in all glaciers irrespective of size, and they are therefore recognizable in ice streams and ice shelves. Structural approaches have wide (but as yet under-developed potential) application to other sub-disciplines of glaciology, notably glacier hydrology, debris entrainment and transfer, landform development, microbiological investigations, and in the interpretation of glacier-like features on Mars.
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Thesis
Abstract This thesis presents a reconstruction of the late Weichselian, deglacial and Holocene glacial history of the Svalbard fjords, focusing on eastern Svalbard. The study is based on high-resolution multibeam data, shallow acoustic (chirp) data, marine sediment cores, historical maps and aerial- satellite images. During the Last Glacial Maximum the Svalbard Barents Sea ice sheet reached the shelf edge around Svalbard and was drained by large ice streams along its western and northern margins, located in the same areas as the present day cross-shelf troughs. In northeastern Svalbard, fastflowing ice converged into the Hinlopen Strait ice stream from the surrounding fjords. Submarine landforms indicate that ice flow velocities increased as ice flowed from the inner- to the outer fjords and the shelf. The deglaciation from the northeastern shelf edge proceeded rapidly by ice lift-off in the troughs and deeper parts of the fjords, whereas the shallower areas experienced slower retreat with minor re-advances. The inner fjords around Nordaustlandet were ice free prior to 11.3-10.5 ka BP years. During early- to mid-Holocene tidewater glaciers in Mohnbukta and Vaigattbogen experienced at least one surge-type advance. These pre-Little Ice Age surges differentiate the east coast glaciers from the west coast glaciers. The early Holocene advance in Mohnbukta has been attributed to rapid climatic and environmental change at the end of the deglaciation, leading to dynamic disequilibrium and an environmentally induced jump into surge-mode. This suggests a more dynamic Holocene glacial history in Svalbard than previously stated, also indicating that the role of climate is more important in the evolution of general surge patterns than previously presumed. Similarly, climatic and environmental changes at the end of the Little Ice Age could explain why many Svalbard glaciers, both on the west and east coasts surged in that time period. Today, the majority of Svalbard’s fjords accommodate tidewater glaciers, of which several have been recorded to surge. Commonly the glaciers have surged at least twice during the Holocene. The surging tidewater glacier landform assemblages share many similarities and can be used to identify past surges in the geological record. In this study the submarine morphology has been used to identify three new surge-type glaciers in Wahlenbergfjorden. The surge history of the Svalbard glaciers is diverse and even though the landform assemblages share many similarities, they all feature differences, suggesting that local conditions are important in the evolution of glacial surges.
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The evolution of glaciers and ice sheets depends on processes in the subglacial environment. Shear seismicity along the ice–bed interface provides a window into these processes. Such seismicity requires a rapid loss of strength that is typically ascribed to rate-weakening friction, i.e., decreasing friction with sliding or sliding rate. Many friction experiments have investigated glacial materials at the temperate conditions typical of fast flowing glacier beds. To our knowledge, however, these studies have all found rate-strengthening friction. Here, we investigate the possibility that rate-weakening rock-on-rock friction between sediments frozen to the bottom of the glacier and the underlying water-saturated sediments or bedrock may be responsible for subglacial shear seismicity along temperate glacier beds. We test this ‘entrainment-seismicity hypothesis’ using targeted laboratory experiments and simple models of glacier sliding, seismicity and sediment entrainment. These models suggest that sediment entrainment may be a necessary but not sufficient condition for the occurrence of basal shear seismicity. We propose that stagnation at the Whillans Ice Stream, West Antarctica may be caused by the growth of a frozen fringe of entrained sediment in the ice stream margins. Our results suggest that basal shear seismicity may indicate geomorphic activity.
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This study focuses on the glacial landform record associated with recent surge events of Tunabreen - a calving tidewater glacier in Tempelfjorden, Spitsbergen. Submarine geomorphology and recent terminal fluctuations of Tunabreen's glacier front were studied using high-resolution multibeam-bathymetric data and a range of published and remote-sensing sources, including topographic maps, satellite images and aerial photographs. The retreat moraines in the inner part of Tempelfjorden have been correlated with glacier terminus positions during retreat from the 2004 surge maximum. Glacier surface velocity and ice-front positions derived from high-resolution TerraSAR-X satellite data show ice movements at the glacier front during minor advances of the front in winter when calving is suppressed. This suggests that the moraines have formed annually during quiescent phase winter advances. Tunabreen has experienced three surges since the Little Ice Age (LIA). This is in contrast with most Svalbard surging glaciers which have long quiescent phases and have typically only undergone one or two surges during this time. The landform record in Tempelfjorden is distinguished from previously studied glacier-surge landsystems by four, well-preserved sets of landform assemblages generated by the LIA advance and three subsequent surges, all of which partly modify earlier landform records. Based on the unique landform record in Tempelfjorden, a new conceptual landsystem model for frequently surging glaciers has been put forward improving our understanding of the dynamics of the surging glaciers and, most importantly, how they can be distinguished from the climatically-controlled glaciers in the geological record.
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Basal ice is formed by regelation as a consequence of both pressure-melting and freezing-on at the glacier sole. A study of D/H and 18O/16O ratios in basal ice from five Arctic outlet glaciers indicates that a co-isotopic signature exists for these two mechanisms of formation. The dispersed and stratified facies of basal ice present in these glaciers are related respectively to the occurrence of regelation and to freezing-on at the glacier base. Their origin is tentatively connected with the onset of basal sliding and the zone of bed decoupling due to basal water pressure in these Arctic outlet glaciers.
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The basal ice layer of surge-type Variegated Glacier, Alaska, appears to have formed by a combination of (i) open-system freezing of subglacial meltwaters over both rigid and unconsolidated substrates; (ii) apron over-riding during surge-induced glacier advance; (iii) incorporation of glacier ice by recumbent folding, thrust-faulting and nappe over-riding during down-glacier propagation of a surge front; and (iv) post-formational metamorphism involving recrystallization, partial internal melting and squeezing out of meltwaters and dissolved gases. Structural evidence and the characteristics of debris entrained in ice facies formed by basal freezing suggest that the layer includes a lower element formed under surge conditions and an upper element formed during the quiescent phase of a surge cycle. The lower element is depleted in comminution products and enriched in medium gravel, while the upper element contains comminution products but virtually no medium gravel. This distinction is attributed to the efficiency of bedrock fracture and meltwater flushing of comminution products under surge conditions. The basal ice layer thickens from 13 m down-glacier in a manner consistent with the magnitude of horizontal shortening induced by the 1982–83 surge. Thickening is largely tectonic in origin, and the style and intensity of folding and thrust faulting change down-glacier as the magnitude of horizontal shortening increases. Tectonic processes associated with the down-glacier propagation of surge fronts therefore appear to be capable of creating thick basal ice layers which allow extensive supraglacial sedimentation of subglacially derived debris.
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A model for the isotopic composition in δD and δ 18O of ice formed by refreezing at the glacier sole is developed. This model predicts relatively well the distribution of points representing samples from basal layers of an Arctic and an Alpine glacier on a δD–δ 18O diagram. The frozen fraction which is the part of the liquid that refreezes can be determined for each basal ice layer. This may have implications on the study of the ice–water system at the ice–rock interface.
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This paper combines a study of the rock debris and δD/δ18O isotopic characteristics of basal ice sequences in three representative glaciers in South Georgia and concludes that the debris and ice has been entrained mainly by basal freezing. The size distribution of the rock debris is typical of crushing and abrasion, and reflects transport at the ice–rock interface. The δD/δ18O relationships show that clear ice associated with the debris has accreted through freezing. The white bubbly glacier ice has δD/δ18O relationships typical of precipitation which demonstrates an altitudinal effect between glaciers.
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Experiments on progressive unidirectional freezing are conducted to determine the evolution in δD and δ 18O of successive water samples and ice layers taken during the course of freezing. Results indicate that this evolution takes place, in a δD–δ 18O diagram, along a straight line with a characteristic slope. This slope, different from that due to the precipitation effect, gives a finger-print of the occurrence of a freezing or of a melting–refreezing process in the studied reservoir.
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ABSTRACT. Large numbers of small valley glaciers on Svalbard were thicker and more extensive during the Little Ice Age (LIA), demonstrated by prominent ice-cored moraines up to several kilometres beyond present-day margins. The majority of these glaciers have since experienced a long period of strongly negative mass balance during the 20th century and are now largely frozen to their beds, indicating they are likely to have undergone a thermal transition from a polythermal to a cold-based regime. We present evidence for such a switch by reconstructing the former flow dynamics and thermal regime of Tellbreen, a small cold-based valley glacier in central Spitsbergen, based on its basal sequence and glaciological structures. Within the basal sequence, the underlying matrix-supported diamict is interpreted as saturated subglacial traction till which has frozen at the bed, indicating that the thermal switch has resulted in a cessation of subglacial sediment deformation due to freezing of the former deforming layer. This is overlain by debris-poor dispersed facies ice, interpreted to have formed through strain-induced metamorphism of englacial ice. The sequential development of structures includes arcuate fracture traces, interpreted as shear planes formed in a compressive/transpressive stress regime; and fracture traces, interpreted as healed extensional crevasses. The formation of these sediment/ice facies and structures is indicative of dynamic, warm-based flow, most likely during the LIA when the glacier was significantly thicker. KEYWORDS: Arctic glaciology, basal ice, ice dynamics, structural glaciology, subglacial sediments
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We present observations of a surge of the glaciers Skobreen-Paulabreen, Svalbard, during 2003-05, including a time-lapse movie of the frontal advance during 2005, Advanced Spaceborne Thermal Emission (ASTER) imagery and oblique aerial photographs. The surge initiated in Skobreen, and then propagated downglacier into the lower parts of Paulabreen. ASTER satellite images from different stages of the surge are used to evaluate the surge progression. Features on the glacier surface advanced 2800 m over 2.4 yr, averaging 3.2 m/day, while the front advanced less (ca. 1300 m) due to contemporaneous calving. The surge resulted in a lateral displacement of the medial moraines of Paulabreen of ca. 600 m at the glacier front. The time-lapse movie captured the advance of the frontal part of the glacier, and dramatically illustrates glacier dynamic processes in an accessible way. The movie documents a range of processes such as a plug-like flow of the glacier, proglacial thrusting, incorporation of old, dead ice at the margin, and calving into the fjord. The movie provides a useful resource for researchers, educators seeking to teach and inspire students, and those wishing to communicate the fascination of glacier science to a wider public.
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Cook, S. J., Robinson, Z. P., Fairchild, I. J., Knight, P. G., Waller, R. I. & Boomer, I. 2009: Role of glaciohydraulic supercooling in the formation of stratified facies basal ice: Svínafellsjökull and Skaftafellsjökull, southeast Iceland. Boreas, 10.1111/j.1502-3885.2009.00112.x. ISSN 0300-9483. There is need for a quantitative assessment of the importance of glaciohydraulic supercooling for basal ice formation and glacial sediment transfer. We assess the contribution of supercooling to stratified facies basal ice formation at Svínafellsjökull and Skaftafellsjökull, southeast Iceland, both of which experience supercooling. Five stratified basal ice subfacies have previously been identified at Svínafellsjökull, but their precise origins have not been determined. Analysis of stratified basal ice stable isotope compositions (δ18O and δD), spatial distribution and physical characteristics demonstrates that two subfacies present at both glaciers are consistent with supercooling. These ‘supercool’ subfacies account for 42% of stratified facies exposed at Svínafellsjökull, although estimates at Skaftafellsjökull are precluded by limited basal ice exposure. Owing to their high debris contents, supercooling-related facies contribute a debris flux of 4.8 to 9.6 m3 m−1 a−1 at Svínafellsjökull (83% of the stratified facies debris flux). Other stratified subfacies, formed by non-supercooling processes, account for 58% of the stratified basal ice at Svínafellsjökull, but only contribute a debris flux of 1.0 to 2.0 m3 m−1 a−1 (17% of the stratified facies debris flux). We conclude that supercooling has a significant role in glacial sediment transfer, although in stratified basal ice formation its role is less significant at these locations than has been reported elsewhere.
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We present a comprehensive new inventory of surge-type glaciers on the Novaya Zemlya archipelago, using high-resolution (up to 4 m) satellite imagery from 1976/77 (Hexagon), 1989 (Landsat TM), 2001 (Landsat ETM+) and 2006 (ASTER). A total of 692 glaciers and their forelands were observed for glaciological and geomorphological criteria indicative of glacier surging (e.g. looped moraines, heavy surface crevassing, surface potholes, thrust-block moraines, concertina eskers). This enabled the identification of 32 potential surge-type glaciers (compared with four previously identified) representing 4.6% of the total but 18% by glacier area. We assess the characteristics of surge-type glaciers. Surge-type glaciers are statistically different from non-surge-type glaciers in terms of their area, length, surface slope, minimum elevation, mid-range elevation and terminus type. They are typically long (median length 18.5 km), large (median area 106.8 km2) outlet glaciers, with relatively low overall surface slopes (median slope 1.7°) and tend to terminate in water (marine or lacustrine). They are predominantly directed towards and located in the more maritime western region of the Russian Arctic, and we suggest that surge occurrence might be related to large and complex catchment areas that receive increased delivery of precipitation from the Barents Sea.
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Abstract – The geomorphology and sedimentology of the Teigarjökull and Búrfellsjökull, two small surge-type cirque glaciers at the Tröllaskagi peninsula, northern Iceland was explored for improved understanding of their surge imprints. Geomorphological, geological and remote sensing data on sediments and landforms were used for developing a geomorphological model for surge-type cirque glaciers in Iceland. Most surge moraines identified are in the form of uneven small ridges or debris sheets that constitute a boulder-rich hummocky terrain. The size and structures of two moraines in front of Teigarjökull are interpreted as suggesting that the glacier has in the past switched between surge and non-surge behavior. Hummocky surfaces, small medial moraines and crevasse-fill ridges are common, as are landforms suggesting dead-ice melting, such as backslumping, extension cracks and sinkholes. The surface sediments are rich in subangular and angular pebbles, cobbles, and boulders. This distinct geomorphology of the glacier forefields results from ample supply of coarse and angular sediments originating from the steep mountain slopes bordering the glaciers and subsequently carried to the marginal zone via englacial and supraglacial transport. Key words: Surge-type glaciers, glacial geomorphology, Búrfellsjökull, Teigarjökull
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[1] Anisotropy of magnetic susceptibility (AMS) has been shown to provide specific useful information regarding the kinematics of deformation within subglacially deformed sediments. Here we present results from debris-rich basal glacier ice to examine deformation associated with glacier motion. Basal ice samples were collected from Tunabreen, a polythermal surge-type glacier in Svalbard. The magnetic fabrics recorded show strong correlation with structures within the ice, such as sheath folds and macroscopic stretching lineations. Thermomagnetic, low-temperature susceptibility, varying field susceptibility, and isothermal remanent magnetism acquisition experiments reveal that the debris-rich basal ice samples have a susceptibility and anisotropy dominated by paramagnetic phases within the detrital sediment. Sediment grains entrained within the basal ice are inferred to have rotated into a preferential alignment during deformation associated with flow of the glacier. An up-glacier directed plunge of magnetic lineations and subtle deviation from bulk glacier flow at the margins highlight the importance of noncoaxial strain during surge propagation. The results suggest that AMS can be used as an ice petrofabric indicator for investigations of glacier deformation and interactions with the bed.
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A simple model is developed to simulate the isotopic fractionation which accompanies Weertman regelation at the bed of temperate-based glaciers. The fractionation equations of Jouzel and Souchez (1982) are applied to multiple refreezing events over measured glacier-bed profiles, and mass balance is maintained as the basal ice and meltwater produced at one bedrock hummock enter the next. Simulation results indicate that undeformed regelation ice layers are on the order of millimetres to centimetres thick, often being completely melted at the stoss face of certain hummocks and exceptionally reaching a thickness in excess of 10 cm. Neither the internal morphology nor the isotopic composition of these layers is constant, but both vary down-glacier in accordance with bedrock configuration. A glacier-wide fractionation process is identified whereby heavy isotopes are preferentially removed from the basal meltwater film and incorporated into the basal ice. This process might go some way to explaining the anomalously "light' isotopic composition measured in base-flow waters leaving some glaciers. Heavy isotope enrichment of this magnitude and consideration of the thickness of the basal ice layers concerned may explain the absence of recorded basalt ice samples heavy enough to have been formed in equilibrium with subglacial precipitates sampled at one of the sites (Glacier de Tsanfleuron) and reported in an earlier paper. -from Authors
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Hessbreen is a small valley glacier which last surged in 1974, and is typical of many polythermal glaciers in Svalbard. The present ice surface displays a wide range of structures that can be attributed to either quiescent-phase or surge-phase deformation. During quiescent-phase flow, primary stratification becomes slightly deformed into low-amplitude open folds, while a completely new structure, longitudinal foliation, develops in axial-planar relationship to these folds. The propagation of a surge front is associated with the formation of thrusts; however, not all of these break through to the surface. As the surge progresses, and the ice behind the surge front becomes extensional, the surface of the glacier breaks up into numerous crevasses, of which several hundred metre long transverse crevasses, convex up-glacier, are dominant. After a period of quiescence, these become degraded into crevasse traces, planar structures which are steeply dipping and have many different orientations. Overall, most ice which reaches the snout has not undergone significant cumulative strain, as indicated by the lack of deformation of both the primary structures and the later crevasse traces. The distribution of debris in Hessbreen is controlled strongly by the development of some of these structures. Angular supraglacial debris is intimately associated with stratification, while basal debris is lifted to en- and supraglacial positions in association with thrusting.
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The basal ice layer of surge-type Variegated Glacier, Alaska, appears to have formed by a combination of 1) open-system freezing of subglacial meltwaters over both rigid and unconsolidated substrates; 2) apron over-riding during surge-induced glacier advance; 3) incorporation of glacier ice by recumbent folding, thrust-faulting and nappe over-riding during down-glacier propagation of a surge front; and 4) post-formational metamorphism involving recrystallization, partial internal melting and squeezing out of meltwaters and dissolved gases. Structural evidence and the characteristics of debris entrained in ice facies formed by basal freezing suggest that the layer includes a lower element formed under surge conditions and an upper element formed during the quiescent phase of a surge cycle. Tectonic processes associated with the down-glacier propagation of surge fronts appear to be capable of creating thick basal ice layers which allow extensive supraglacial sedimentation of subglacially derived debris. -from Authors
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This paper combines a study of the rock debris and δD/δ ¹⁸ O isotopic characteristics of basal ice sequences in three representative glaciers in South Georgia and concludes that the debris and ice has been entrained mainly by basal freezing. The size distribution of the rock debris is typical of crushing and abrasion, and reflects transport at the ice–rock interface. The δD/δ ¹⁸ O relationships show that clear ice associated with the debris has accreted through freezing. The white bubbly glacier ice has δD/δ ¹⁸ O relationships typical of precipitation which demonstrates an altitudinal effect between glaciers.
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Debris-laden ice accretes to the base of Matanuska Glacier, Alaska, U.S.A., from water that supercools while flowing in a distributed drainage system up the adverse slope of an overdeepening. Frazil ice grows in the water column and forms aggregates, while other ice grows on the glacier sole or on substrate materials. Sediment is trapped by this growing ice, forming stratified debris-laden basal ice. Growth rates of >0.1 m a-1 of debris-rich basal ice are possible. The large sediment fluxes that this mechanism allows may have implications for interpretation of the widespread deposits from ice that flowed through other overdeepenings, including Heinrich events and the till sheets south of the Laurentian Great Lakes.
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Dipping, arcuate bands of debris-rich ice outcropping near the margins of glaciers are often interpreted as thrust faults, assumed to originate in zones of longitudinal compression. Identification of thrusts is typically based either on the geometry and sedimentology of the debris bands or on the crystal fabric of surrounding ice, but the physical processes necessary to generate thrusts are rarely evaluated. Herein, we combine a numerical model of compressive ice flow near a glacier margin with theoretical stress and strain rate criteria for ice fracture and stress criteria for frictional slip to determine the conditions necessary for thrust faulting in glaciers. This model is applied to two different glaciological settings where longitudinal compression has been documented: (1) the transition between warm-based and cold-based ice near the terminus of Storglaciären, Sweden, and (2) the downglacier extent of the 1983 surge front of Variegated Glacier where surging ice encountered stagnant ice. Simulations representing the margin of Storglaciären indicate that peak compressive strain rates are six orders of magnitude too small to induce fracture, whereas at Variegated Glacier, strain rates were an order of magnitude too small for compressive fracture. In both groups of simulations, preexisting fractures governed by Coulomb friction are susceptible to slip if they span the ice thickness, are oriented close to the optimal fracture angle, and, in the case of Storglaciären, are subject to water pressures that are a large fraction of ice overburden pressure. Variations about the optimal fracture orientation, low or zero water pressure, high sliding friction coefficient, and limited vertical or lateral fracture extent each tend to suppress thrusting.
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Thrust-block naled in front of Kuannersuit Glacier, West Greenland, appears to have formed during the termination of a terrestrial surge event by a combination of enhanced winter runoff, rapid advance of the glacier terminus, and proglacial stress release by thrusting and stacking of naled blocks. This process is equivalent to the formation of thrust-block moraines. The thrust-block naled consists of at least seven thrust sheets, which are characterized by stratified ice with beds composed of a lower debris-rich lamina, an intermediate dispersed lamina and a top clean-ice lamina, and underlain by frozen outwash deposits. The thrust-block naled differs from basal stratified ice in the absence of internal deformation structures, a relatively low debris concentration, a clay-rich particle-size distribution and a preferential sorting of lighter minerals. The oxygen isotope composition of the thrust-block naled is indistinguishable from delta18O values from meteoric glacier ice and bulk meltwater, but different from basal stratified ice facies. The d-deltaD relationship indicates that thrust-block naled has been formed by freezing of successive thin layers of bulk waters with variable isotopic composition, whereas basal stratified ice has developed in a subglacial environment with regelation. This work shows that the association between proglacial naled and rapidly advancing glaciers may have significant consequences for the proglacial geomorphology and the interpretation of basal ice layers.
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High-resolution swath bathymetry from the marine margins of several Svalbard tidewater glaciers shows an assemblage of submarine landforms that is probably linked to glacier surging. These landforms are essentially unmodified since their initial deposition over the past hundred years or so because they have not been subjected to subaerial erosion or periglacial activity. Swath images comprise an assemblage of superimposed landforms, allowing reconstruction of relative age of deposition: (1) large transverse ridges, interpreted as recessional moraines overridden by a subsequent ice advance; (2) a series of curvilinear streamlined bedforms orientated parallel to former ice flow, interpreted as lineations formed subglacially during rapid advance; (3) large terminal ridges, marking the farthest extent of ice at the last advance, with flow lobes immediately beyond interpreted as submarine debris flows; (4) a series of interconnected rhombohedral ridges, interpreted as a product of soft sediment squeezing into crevasses formed at the glacier bed, probably formed during immediate post-surge stagnation; and (5) a series of fairly evenly spaced small transverse ridges, interpreted as push moraines produced annually at tidewater glacier termini during retreat. A simple descriptive landsystem model for tidewater glaciers of probable surge type is derived from these observations. We also show that megascale glacial lineations can form not only beneath large ice streams, but are also produced beneath surging tidewater glaciers lying on deforming sedimentary beds.
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Till ridges at Eyjabakkajökull, Iceland, are considered to be 'crevasse-fill’ ridges formed by the flow of sediments from the dilatant horizon of subglacial lodgement tills into open crevasses in response to local variations in overburden pressure. Crevasses are formed during the active phase of a surge cycle, and are filled with sediment during the early part of the quiescent phase as the stagnant glacier sinks into its bed. The resultant ridges form a network covering the whole of the area in which crevassing penetrated to the bottom of the glacier during the surge. Nowhere are they associated with till ridges formed at and parallel to the glacier margin. Since similar ridges have been observed at a number of other surging glaciers, it is suggested that lodgement till surfaces crossed by networks of ‘crevasse-fill’ ridges may be characteristic of surging glaciers.
Article
From observations on the sub-polar glaciers of Phillips Inlet, north-west Ellesmere Island, neither complex basal thermal regimes nor internal thrusting need be invoked to explain all types of debris distribution in the basal ice of sub-polar glaciers. Debris is present in the terminal ice cliffs as: (1) debris-poor folia expressing internal flow patterns; (2) debris-rich bands of various thickness; and (3) augens or clots. Debris-rich bands and augens are concentrated predominantly in the basal ice, contain a wide range of grain-sizes, cut across debris-poor folia, rarely extend >1 m laterally, and are irregularly spaced. Observations on patterns of entrainment and contemporary processes at ice margins, together with clast-shape analyses, suggest that the recycling and re-incorporation of fluvial/deltaic sediment, aprons, and pro-glacially thrusted blocks at the ice face are an alternative process of debris entrainment to basal plucking and large-scale freeze-on at the base of the glacier. The most active processes observed at the glacier margins are fluvial, and the origins of some debris-rich bands and augens are linked to thermal-erosional niches and abandoned meanders in the base of the glacier cliff face. Because the large-scale accumulation of ice-cored debris at glacier snouts represents periods of increased run-off and snout recession (specifically during the early Holocene), basal and englacial debris concentrations resulting from glacial over-riding and re-incorporation have great palaeoclimatic significance.
Article
A new mechanism is described which explains the formation of moraines in the ablation areas of cold ice sheets. The mechanism involves the freezing of water onto the bottom surface of an ice sheet. This water comes from regions of the bottom surface where the combination of the geothermal heat and the heat produced by the sliding of ice over the bed is sufficient to melt ice. A number of criticisms are made of the shear hypothesis, which has been advanced to explain moraines occurring on Baffin Island and near Thule, Greenland. It is concluded that this older hypothesis may be inadequate to account for these moraines. Although in theory the mechanism proposed in this paper undoubtedly will lead to the formation of moraines, the existing field data are insufficient to prove conclusively that actual moraines have originated by means of this mechanism.
Article
At the head of a tunnel driven to bedrock in Blue Glacier, Washington, the mechanism of sliding of the glacier over bedrock has been investigated. This mechanism involves (1) regelation-slip, which operates through the combined action of heat transport and mass transport (liquid and solid) in the immediate neighborhood of the glacier sole; (2) plastic flow, promoted by stress concentrations in the basal ice. We have observed and/or measured the following features of the basal slip process: 1. Slip rate in relation to internal deformation of the ice; 2. Time-variations of the slip rate; 3. Freezing of basal ice to bedrock upon release of overburden pressure; 4. Formation of a regelation layer in the basal ice, and detailed behavior of this layer in relation to bedrock obstacles and to incorporated debris particles; 5. Local separation of ice from bedrock and continuous formation of regelation spicules in the open cavities thus created; 6. Plastic deformation of basal ice as recorded in the warping of foliation planes and of the regelation layer. Simple experiments to test our interpretation of the regelation layer have been carried out, in which regelation flow of solid cubes of different materials frozen into blocks of ice was produced. The field measurements and laboratory results are used to test the theory by Weertman (1957, 1962) of the basal slip mechanism. It is found that the theoretical “controlling obstacle size” and “controlling obstacle spacing” that should correspond to our observations are about an order of magnitude too small. This quantitative failure represents an overemphasis in the theory on the importance of plastic flow as compared to regelation. A new theory has been constructed which gives results in better agreement with observation.
Article
At the head of a tunnel driven to bedrock in Blue Glacier, Washington, the mechanism of sliding of the glacier over bedrock has been investigated. This mechanism involves (1) regelation-slip, which operates through the combined action of heat transport and mass transport (liquid and solid) in the immediate neighborhood of the glacier sole; (2) plastic flow, promoted by stress concentrations in the basal ice. We have observed and/or measured the following features of the basal slip process: 1. Slip rate in relation to internal deformation of the ice; 2. Time-variations of the slip rate; 3. Freezing of basal ice to bedrock upon release of overburden pressure; 4. Formation of a regelation layer in the basal ice, and detailed behavior of this layer in relation to bedrock obstacles and to incorporated debris particles; 5. Local separation of ice from bedrock and continuous formation of regelation spicules in the open cavities thus created; 6. Plastic deformation of basal ice as recorded in the warping of foliation planes and of the regelation layer. Simple experiments to test our interpretation of the regelation layer have been carried out, in which regelation flow of solid cubes of different materials frozen into blocks of ice was produced. The field measurements and laboratory results are used to test the theory by Weertman (1957, 1962) of the basal slip mechanism. It is found that the theoretical “controlling obstacle size” and “controlling obstacle spacing” that should correspond to our observations are about an order of magnitude too small. This quantitative failure represents an overemphasis in the theory on the importance of plastic flow as compared to regelation. A new theory has been constructed which gives results in better agreement with observation.
Article
Experiments on progressive unidirectional freezing are conducted to determine the evolution in δ D and δ¹⁸ O of successive water samples and ice layers taken during the course of freezing. Results indicate that this evolution takes place, in a δ D– δ¹⁸ O diagram, along a straight line with a characteristic slope. This slope, different from that due to the precipitation effect, gives a finger-print of the occurrence of a freezing or of a melting–refreezing process in the studied reservoir.
Article
The Irish Sea ice stream was the largest ice stream to drain the last British ice sheet, and around the margins of the Celtic Sea it deposited a shelly diamict facies that has been variously interpreted as subglacial till or distal glacial marine mud. We present new observations on the sedimentology of the shelly diamict and overlying sediments from the south coast of Ireland, and demonstrate that the shelly diamict facies is a subglacial deformation till deposited during onshore movement of a grounded Irish Sea ice stream. Stratigraphic and chronological data indicate that this occurred during the last glaciation, and this is regionally consistent with marine geological evidence from the Celtic Sea. We propose that the deforming bed tills along the south coast of Ireland are the onshore record of a rapid advance of an unstable Irish Sea ice stream into the Celtic Sea. This advance was facilitated, at least in part, by a saturated substrate of readily deformable, fine-grained, marine sediment. This implies an unstable and dynamic Irish Sea ice stream during oxygen isotope stage 2, and therefore extension of the last British ice sheet into the Celtic Sea far south of its traditionally interpreted limits.
Article
Experimental results indicate that wet-based, soft-bedded glaciers may penetrate their substrates by regelation (melting and refreezing) and thereby entrain sediment. In principle, there should be a steady depth of penetration at which the downward regelation speed, driven by the interfacial effective pressure, equals the basal melt rate. Herein, the magnitude and distribution of penetration are estimated for the case of a glacier resting on a deformable bed with channelized basal drainage. The distance between channels and the distribution of effective pressure across the bed are calculated, and special attention is paid to the interdependence of the basal melt rate and effective pressure. A major uncertainty is whether fine-grained tills may impede or prevent regelation as a result of high surface tension at the ice/water interface. Predicted penetration depths range from millimetres to a few decimetres, and thus, dirty basal ice layers of such thicknesses might be expected. Predicted distances between channels agree well with those indicated by borehole measurements at Ice Stream B, West Antarctica. Effective pressures, and hence penetration depths, increase toward channels. Therefore, the edges of interfluves, bounded by anastomosing subglacial channels, should be eroded preferentially. This motivates the testable hypothesis that such erosion contributes to the formation of streamlined landforms, such as drumlins. Copyright (C) 2000 John Wiley & Sons, Ltd.
Article
A model for the isotopic composition of ice formed by refreezing at the glacier sole is developed. This model predicts relatively well the distribution of points representing samples from basal layers of an Arctic and an Alpine glacier. The frozen fraction which is the part of the liquid that refreezes can be determined for each basal ice layer.-from Authors
Chapter
Glaciohydrologic supercooling at Matanuska Glacier results in abundant and conspicuous summer ice growth even when air temperatures are constantly and significantly above freezing. Ice grows as frazil ice and anchor ice. Frazil ice grows unattached in high-velocity discharge water. Anchor ice grows at vent orifices, in subglacial conduits and canals, in moulins, and in fractures. Anchor ice can grow as large, debris-free platy crystals or, more commonly, as fine-grained, debris-rich laminated ice. To date, these types of summer ice growth have been reported at few glaciers and studied in detail at the Matanuska Glacier but we anticipate that glaciohydrologic supercooling and the associated ice growth are operating at numerous other glaciers with the appropriate geometries. The objective of this paper is to provide a photographic atlas, and brief explanation, of the ice growth forms and features observed at the Matanuska Glacier. We hope that it will enable other researchers to recognize the evidences of glaciohydrologic supercooling at additional glaciers and eventually establish glaciohydrologic supercooling, and the associated basal freeze-on, as a major debris entrainment and transportation mechanism.
Article
Results indicate that evolution takes place, in a dD-d18O diagram, along a straight line with a characteristic slope. This slope, different from that due to the precipitation effect gives a finger-print of the occurrence of a freezing or of a melting-refreezing process in the studied reservoir.-from Authors
Article
This study focuses on the glacial landform record associated with recent surge events of Tunabreen - a calving tidewater glacier in Tempelfjorden, Spitsbergen. Submarine geomorphology and recent terminal fluctuations of Tunabreen's glacier front were studied using high-resolution multibeam-bathymetric data and a range of published and remote-sensing sources, including topographic maps, satellite images and aerial photographs. The retreat moraines in the inner part of Tempelfjorden have been correlated with glacier terminus positions during retreat from the 2004 surge maximum. Glacier surface velocity and ice-front positions derived from high-resolution TerraSAR-X satellite data show ice movements at the glacier front during minor advances of the front in winter when calving is suppressed. This suggests that the moraines have formed annually during quiescent phase winter advances. Tunabreen has experienced three surges since the Little Ice Age (LIA). This is in contrast with most Svalbard surging glaciers which have long quiescent phases and have typically only undergone one or two surges during this time. The landform record in Tempelfjorden is distinguished from previously studied glacier-surge landsystems by four, well-preserved sets of landform assemblages generated by the LIA advance and three subsequent surges, all of which partly modify earlier landform records. Based on the unique landform record in Tempelfjorden, a new conceptual landsystem model for frequently surging glaciers has been put forward improving our understanding of the dynamics of the surging glaciers and, most importantly, how they can be distinguished from the climatically-controlled glaciers in the geological record.
Article
Till ridges at Eyjabakkajokull, Iceland, are considered to be 'crevasse-fill' ridges formed by the flow of sediments from the dilatant horizon of subglacial lodgement tills into open crevasses in response to local variations in overburden pressure. Crevasses are formed during the active phase of a surge cycle, and are filled with sediment during the early part of the quiescent phase as the stagnant glacier sinks into its bed. -from Author
Article
The glacial coastal exposures of north Norfolk are a type site for subglacial glaciotectonic deforming bed sediments. This investigation of the lower stratified diamict within the North Sea Drift at West Runton reveals two distinct lamina types. Type 1 laminae are the product of primary extensional glaciotectonism, with ductile, intergranular pervasive shear predominating over brittle shear. Type 2 laminae also exhibit structures that can be attributed to ductile, intergranular pervasive shear and brittle shear, but the lateral continuity of Type 2 laminae and the presence of dropstone—like structures supports a primary subaqueous origin with secondary subglacial deformation.When coupled with micromorphological analysis, these findings show that ductile, viscous creep mechanisms control sedimentary architecture, and that ‘shear stratification’ in particular, has the potential to affect the rheological properties of the sediment pile and the hydraulic routing of basal water, ultimately influencing critical effective pressure fluctuations and the thresholds controlling the subglacial drainage system.
Article
A photogrammetric survey of the movement of supraglacial boulders together with field survey of surface markers has revealed the spatial and temporal change in velocity on the debris-mantled tongue of Tasman Glacier, New Zealand. Between 1957 and 1986 a general reduction of glacier velocity is recorded, and towards the terminus the local effects of thermokarst erosion on flow vectors became more influential as the downvalley component of velocity decreased. Only ca. 2% of the debris-covered glacier area had no measurable movement, and mature thermokarst sinkholes formed on ice moving at >24 ma-1. Increases in ice velocity and surface elevation 10 km above the terminus were not recorded 2.5 km above the terminus in 1986. Changes in ice volume have been manifested by changes to ice levels and velocity, not by fluctuations of the terminus. The study shows that extensive supraglacial debris mantles and thermokarst forms can exist on actively-moving ice in alpine regions of high debris supply and ablation, and that shear-zone formation is not necessary to explain debris-mantling of such glaciers.
Article
The Irish Sea ice stream was the largest ice stream to drain the last British ice sheet, and around the margins of the Celtic Sea it deposited a shelly diamict facies that has been variously interpreted as subglacial till or distal glacial marine mud. We present new observations on the sedimentology of the shelly diamict and overlying sediments from the south coast of Ireland, and demonstrate that the shelly diamict facies is a subglacial deformation till deposited during onshore movement of a grounded Irish Sea ice stream. Stratigraphic and chronological data indicate that this occurred during the last glaciation, and this is regionally consistent with marine geological evidence from the Celtic Sea. We propose that the deforming bed tills along the south coast of Ireland are the onshore record of a rapid advance of an unstable Irish Sea ice stream into the Celtic Sea. This advance was facilitated, at least in part, by a saturated substrate of readily deformable, fine-grained, marine sediment. This implies an unstable and dynamic Irish Sea ice stream during oxygen isotope stage 2, and therefore extension of the last British ice sheet into the Celtic Sea far south of its traditionally interpreted limits.
Article
Palaeo-records of rapid ice stream retreat are important as they can be used to identify the processes involved, and inform investigations of present-day ice masses. Here we document a previously unknown retreat stage in northernmost Bjørnøyrenna (Bear Island Trough) in the northern Barents Sea, representing the youngest stage in a stepwise retreat of the Bjørnøyrenna Ice Stream. We present a descriptive landsystem model for retreat of a marine-based ice stream, which provides new insights into the glacial dynamics of the episodic retreat stages. This model captures the landforms produced during a cycle of 1) fast ice stream flow, 2) intense calving of large icebergs locked in a dense matrix of smaller icebergs, probably from a collapsed ice shelf, 3) ice-stream stagnation, 4) ice-stream floating off, forming an ice shelf as the grounding line retreats, and eventually 5) ice-shelf disintegration. We hypothesize that the presented ice-stream retreat model reflects glacial surging. The formation of corrugated furrows in the study area is consistent with interpretation of similar features in Pine Island Bay, West Antarctica, which are interpreted to have been formed during a massive ice shelf break-up and associated grounding line retreat. Two directions of past ice flow are indicated from streamlined glacial landforms in the study area. Ice flow from north north-east is indicated for the Last Glacial Maximum and an early phase of deglaciation, whereas a shift to flow from north north-west, from an ice dome located over Hinlopenstretet, Svalbard is indicated for the latest deglaciation phases of the Bjørnøyrenna Ice Stream.
Article
KEYWORDS: surge-type glaciers; crevasse-fill ridges; geometrical ridge networks; Svalbard Traditionally, geometrical ridge networks are interpreted as the product of the flow of subglacial sediment into open basal crevasses at the cessation of a glacier surge (‘crevassefill’ ridges). They are widely regarded as a characteristic landform of glacier surges. Understanding the range of processes by which these ridge networks form is therefore of importance in the recognition of palaeosurges within the landform record. The geometrical ridge network at the surge-type glacier Kongsvegen in Svalbard, does not form by crevasse filling. The networks consist of transverse and longitudinal ridges that can be seen forming at the current ice margin. The transverse ridges form as a result of the incorporation of basal debris along thrust planes within the ice. The thrusts were apparently formed during a glacier surge in 1948. Longitudinal ridges form through the meltout of elongated pods of debris, which on the glacier surface are subparallel to the ice foliation and pre-date the surge. This work adds to the range of landforms associated with glacier surges.
Article
This paper presents a detailed palaeoglaciological reconstruction of ice sheet dynamics in the Seno Skyring, Seno Otway and Strait of Magellan region of the former Patagonian Ice Sheet, with a particular focus on previously hypothesised zones of rapid ice flow and the evolution of proglacial lakes. Geomorphological mapping from a combination of satellite imagery and oblique and vertical aerial photographs reveals a variety of glacial landforms that are grouped into several discrete flow-sets and associated ice margin positions. The most distinct features are represented by flow-sets of highly elongate streamlined glacial lineations on both sides of the Strait of Magellan. Based on the shape and dimensions of the flow-sets and their abrupt lateral margins, a transverse and longitudinal variation in glacial lineation length and elongation ratio, and the reported presence of a potentially deformable bed and thrust moraines, the flow-sets are interpreted as zones of rapid ice flow within the Otway and Magellan lobes. We hypothesise that this provides evidence for contemporaneous surge-like advances within the lobes, which may explain the asymmetry in the lobate margin positions on either side of the strait. The mechanisms that initiated rapid flow are unclear, but are likely to have been influenced by internal factors such as a change in thermal/hydrological conditions at the bed. The topography of the region suggests ice-dammed lakes would have formed as the ice lobes retreated. The westernmost of the former lakes, Lake Skyring, is delimited by a series of palaeo-shorelines surrounding the present-day lake Laguna Blanca and we reconstruct lake evolution based on manipulation of a digital elevation model. The size and orientation of meltwater channels and a large outwash plain indicate that Lake Skyring drained eastwards towards the Strait of Magellan, probably quite rapidly. We conclude that the potential for quasi-independent surge-like behaviour within adjacent lobes raises the possibility that, during climate-driven ice expansion, some advances in this region may have been partly controlled by secondary internal feedback mechanisms. Copyright © 2012 John Wiley & Sons, Ltd.
Article
The glacier Holmstrømbreen, in Spitsbergen, surged into the ice contact scarp of a proglacial outwash sequence at some time during its Neoglacial maximum. The outwash sediments were pushed along a decollement to produce a moraine in which deformation extended for 1.5 km beyond the furthest extent of the glacier front. The style of folding and faulting and the nature of the pre-, syn- and post-tectonic sedimentary sequence across the whole push moraine is described from a continuously exposed section of the push moraine which extends from its proximal to distal extremities. The precise extent of incremental compressive shortening of the pushed sediments, of some 900 m, is established. The depth to the underlying decollement is inferred to be an average of about 30 m, indicating that stresses and movement were transmitted through a thin nappe with an aspect ratio of about 1 in 30. It is suggested that this nappe was frozen and that an artesian water pressure head of 60 m immediately beneath it reduced friction along its base to a very low value. It is calculated that a glacially generated force of about 1.5×107 kN was responsible for pushing the sediment nappe. The nature of the glacially controlled groundwater flow system rather than the magnitude of longitudinal forces generated by the glacier is the principle determinant of large-scale push moraine characteristics.
Article
Thick exposures of debris-rich ice at various Icelandic glaciers are central to the debate over the prevalence of glacial sediment transfer by glaciohydraulic supercooling. We present physical analyses of ice and debris at Kvíárjökull, a temperate glacier in southeast Iceland with a terminal glacier-bed overdeepening, where stratified debris-rich ice forms up to metre-thick transverse englacial bands. Our results are not consistent with debris-rich ice formation predominantly by supercooling because: (1) 137Cs was absent from sediment filtered from debris-rich ice; (2) isotopic analysis (deltaD and delta18O) demonstrated no clear pattern of isotopic enrichment of debris-rich ice with respect to englacial ice; and (3) melt-out debris from debris-rich ice included large striated clasts from both fluvial and basal sources. We support transverse englacial debris-rich ice band formation by the thickening and elevation of basal materials in a region of longitudinally compressive ice flow situated between the reverse slope of the overdeepening and the base of an ice fall. Debris band form and distribution are likely to be controlled by thrusting along transverse englacial foliae associated with the formation of band ogives on the glacier surface.
Article
From observations on the sub-polar glaciers of Phillips Inlet, north-west Ellesmere Island, neither complex basal thermal regimes nor internal thrusting need be invoked to explain all types of debris distribution in the basal ice of sub-polar glaciers. Debris is present in the terminal ice cliffs as: (1) debris-poor folia expressing internal flow patterns; (2) debris-rich bands of various thickness; and (3) augens or clots. Debris-rich bands and augens are concentrated predominantly in the basal ice, contain a wide range of grain-sizes, cut across debris-poor folia, rarely extend >1 m laterally, and are irregularly spaced. Observations on patterns of entrainment and contemporary processes at ice margins, together with clast-shape analyses, suggest that the recycling and re-incorporation of fluvial/deltaic sediment, aprons, and pro-glacially thrusted blocks at the ice face are an alternative process of debris entrainment to basal plucking and large-scale freeze-on at the base of the glacier. The most active processes observed at the glacier margins are fluvial, and the origins of some debris-rich bands and augens are linked to thermal-erosional niches and abandoned meanders in the base of the glacier cliff face. Because the large-scale accumulation of ice-cored debris at glacier snouts represents periods of increased run-off and snout recession (specifically during the early Holocene), basal and englacial debris concentrations resulting from glacial over-riding and re-incorporation have great palaeoclimatic significance.
Article
Bakaninbreen, Svalbard, started to surge during 1985–86, and developed a surge front up to 60 m high. Associated with down-glacier propagation of this surge front was the formation of shear zones and thrust faults, some of which revealed basally derived debris at the glacier surface. Hot water drilling and sampling of basal material showed the glacier bed to be soft sediment more than 1 m thick. A high-resolution ground-penetrating radar (GPR) survey at 100 MHz was conducted along three 500 m lines parallel to glacier flow on the surge front. The aims were to investigate the internal geometry of the thrust features, and the processes of entrainment of basal debris into bulk glacier ice. A strong linear reflector was seen on the survey, but it is about 15–20 m above the bed as identified from drilling depths. It probably represents the upper interface of a layer of debris-rich basal ice. Several extensive englacial reflectors were interpreted as debris-laden emergent thrust features, varying in thickness from 0.1 to 1.1 m. These features were mapped at the glacier surface, and drilling and sediment sampling verified the interpretation. Other englacial features included regions of incipient thrusting at the basal reflector, and an extensive region of scattering up to 30 m above the basal reflector that we interpret as folds, or blind thrusts that terminate englacially. Our results clearly demonstrate the potential of GPR for mapping internal glacial structure, and suggest that thrusting is an important process by which sediment is incorporated into glacier ice in the highly compressive region at the surge front.
Article
Experimental results indicate that wet-based, soft-bedded glaciers may penetrate their substrates by regelation (melting and refreezing) and thereby entrain sediment. In principle, there should be a steady depth of penetration at which the downward regelation speed, driven by the interfacial effective pressure, equals the basal melt rate. Herein, the magnitude and distribution of penetration are estimated for the case of a glacier resting on a deformable bed with channelized basal drainage. The distance between channels and the distribution of effective pressure across the bed are calculated, and special attention is paid to the interdependence of the basal melt rate and effective pressure. A major uncertainty is whether fine-grained tills may impede or prevent regelation as a result of high surface tension at the ice/water interface.Predicted penetration depths range from millimetres to a few decimetres, and thus, dirty basal ice layers of such thicknesses might be expected. Predicted distances between channels agree well with those indicated by borehole measurements at Ice Stream B, West Antarctica. Effective pressures, and hence penetration depths, increase toward channels. Therefore, the edges of interfluves, bounded by anastomosing subglacial channels, should be eroded preferentially. This motivates the testable hypothesis that such erosion contributes to the formation of streamlined landforms, such as drumlins. Copyright © 2000 John Wiley & Sons, Ltd.
Article
Temperate glacier ice is neither dry nor impermeable, as the standard theory of glacier sliding assumes. This fact leads to the already published concept of locally stress-controlled temperatures. Why the temperature is determined by the highest principal pressure, why the microscopic stress equals more or less the macroscopic one, and why water may flow in the capillary network even when water lenses at grain boundaries are freezing is explained. The new concept is applied to ice sliding on a hard bed having a sine profile, without cavitation. -from Author
Article
Mapping of the structural glaciology of Kongsvegen, Svalbard, reveals evidence for four main deformational structures. These are stratification, longitudinal foliation, thrusts and crevasse traces. These structures are considered in terms of their contribution to debris entrainment, transport and subsequent landform development. Stratification is associated with small amounts of supraglacial debris that has been folded with flow-parallel axes; longitudinal foliation in places incorporates basal glacial sediments along folds with flow-parallel axes; and thrusts transport basal debris to the glacier surface. Crevasse traces are not significant in terms of debris entrainment. The entrainment of basal debris along longitudinal foliation is not a universally recognised process. At Kongsvegen this process is attributed to the development of a transposition foliation, in combination with incorporation of debris-rich basal ice or soft basal sediment in the fold complex. Mapping of the landforms in the proglacial area shows that debris incorporated along longitudinal foliation is released as 'foliation-parallel ridges' and that transverse ridges mark debris-bearing thrusts. The role of longitudinal foliation in landform development has never been documented in this manner. Although the preservation potential of such ridges may be limited, recognition of foliation-parallel ridges in the Pleistocene landform record has important implications for the interpretation of the dynamics of former ice masses.
Article
In 1995-1998, Han 11 km terrestrial surge of Kuannersuit Glacier, an outlet glacier of the largest ice cap on Disko Island, West Greenland, affected the catchment dramatically. In order to estimate solute fluxes and provenances, bulk meltwaters were sampled at the main subglacial outlet during the initial part of the quiescent phase. The hydrochemistry is significantly influenced by a subglacial basaltic weathering regime with absence of carbonate minerals. The results show that marine and aerosol derived solutes have minimal contribution to the total ion content, whereas sequestration of atmospheric CO2 associated with carbonation of Ca-rich feldspar and reactive volcanic glass is more dominant than previously reported from glacierized catchments. Application of a sampling strategy dividing water samples into four groups to determine the content of dissolved HCO3- and CO32- shows that the cationic equivalent weathering rate range is 683-860 Sigmameq(+) a(-1) and solute flux ranges between 76 and 98 t km(-2) a(-1). The crustal denudation rate is estimated to 26 t km(-2) a(-1), and the transient CO2 drawdown amounts to 8500-13700 kg C km(-2) a(-1).
Article
Evidence for extensive crevassing is preserved on the deglaciated forelands of many surging glaciers as crevasse squeeze ridges (CSRs). At some point these crevasses make direct connection with the bed in order to become sediment filled, and full-depth connections have been inferred from turbid water up-wellings in crevasses and the formation of concertina eskers. The dynamics of seven surging glaciers are assessed, using a linear elastic fracture mechanics approach, to determine the likely directions of fracture and controlling parameters for Mode I crevasses. Extensional surface strain rates are insufficient to promote top-down full-depth penetration. For small crevasse spacing (<5 m), surface strain rates are sufficient for top-down crevassing to depths of 4-12 m, explaining the extensive surface crevassing associated with glacier surging. As has been shown in other settings, top-down, full-depth crevassing is only possible when water is added and approaches 97% of the crevasse depth. The provision of sufficient meltwater to facilitate this is problematic due to the extensive surface crevassing, unless water can move along connected crevasses to a dominant water capturing crevasse. For ice thicknesses greater than ∼200 m, basal water pressures in excess of 80-90% of flotation are required for full-depth, bottom-up crevassing. Field evidence suggests that this is the default for surging glaciers and that, on occasion, water pressures may even become artesian. CSRs, found across many surging glacier forelands and ice margins, most likely result from the infilling of basal crevasses, driven for the most part, bottom-up, by high basal water pressures.
Article
The bottom 15.7m of the Camp Century core contain over 300 alternating bands of clear and debris-laden ice. The size of the included debris ranges from particles less than 2 micrometers in diameter to particle aggregates which are a maximum of 3cm in diameter; the average debris concentration is 0.24% by weight. The debris size, concentration, and composition indicate that the debris originates from the till-like material directly below the debris-laden ice. Ice texture and ice-fabric analyses of the lowermost 10m of the core indicate a zone of high deformation. -from Authors