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A new concept for glacial geological investigations of surges, based on High-Arctic examples (Svalbard)
Abstract
Svalbard is a key area for the investigation of glacial surges, and almost two centuries worth of field observations exists from this region. Studies have shown that the course of a surge and the associated formation of landforms are strongly influenced by basinal factors, and that the broad range of variables involved can hamper interpretations and comparisons. Based on a review of surges in Svalbard, a new concept for glacial geological investigations has been developed that combines ice-flows, ice-front movements, and morphostratigraphy. The concept is comprised of the following four elements: 1) classification based on the configuration and characteristics of the receiving basin, 2) division of the surge cycle into six stages, 3) guidelines for morphological mapping, and 4) use of an allostratigraphic approach for interpreting ice-front movements. In this context, delineation of the active phase is critical, which include the history of terminus movements, and four main categories of receiving basins are recognized. These are (A) terrestrial basins with deformable substrates, (B) terrestrial basins with poorly deformable substrates, (C) shallow water basins, and (D) deep water basins. The ice-front movement history is reconstructed by coupling information from the proglacial moraines (syn-surge), the supraglacial moraines (post-surge), and the associated traces of meltwater to the surge stages (I-VI). This approach has revealed a critical relationship between the termination of the active phase and three morphological elements, namely, the maximum ice-front position, the maximum moraine extent and the youngest proglacial moraine, which are unique for each of the basins A-D. The concept is thus a novel and more precise approach for mapping the active phase and the active phase duration, as shown by the ~12-year long surge of Fridtjovbreen, where stage I was 30 months (inception), stage II was 54 months (ice-front advance), stage III was 12 months (stillstand), and stage IV was 48 months (retreat during active flow). The glacier has been in quiescent phase (stages V/VI) since 2002.
... Glacier cover in Svalbard has reduced by ∼13% since ∼1900 (Martín- Moreno et al., 2017), with widespread glacier recession revealing extensive and expanding glacial geomorphological records in terrestrial (e.g. Allaart et al., 2018;Christoffersen et al., 2005;Lønne, 2016) and marine (e.g. Dowdeswell et al., 2020;Forwick et al., 2016;Solheim & Pfirman, 1985) settings, recording past glacier characteristics and dynamics (e.g. ...
... Identification of geomorphological records formed by surging can thus improve understanding of the glaciers that have surged prior to the observational record (e.g. Farnsworth et al., 2016;Lovell et al., 2018b;Lovell & Boston, 2017;Lønne, 2016). This is important because surge-type glaciers are known to experience enhanced mass loss compared to non-surge-type glaciers (e.g. ...
... Composite ridges are also sometimes termed push-moraines (e.g. Hart & Watts, 1997;Kristensen et al., 2009;Lønne, 2016), but all cover the same formation mechanism of unconsolidated forefield sediments (glacial, glaciofluvial, glaciolacustrine or glaciomarine) being pushed and folded by an advancing glacier terminus during a surge. ...
This paper presents a map of terrestrial glacial geomorphology of eleven surge-type and non-surge-type glacier forefields in southwest and west Spitsbergen, Svalbard. Glacier forefields were mapped using a combination of field surveys and the use of an uncrewed airborne vehicle in September 2022 and satellite imagery captured in 2020, with mapping performed in ArcGIS Pro at a 1:5000 scale. Maps were constructed for glaciers in Van Kuelenfjorden and Van Mijenfjorden (southwest Spitsbergen), and in Isfjorden, Billefjorden a fjord branch of Isfjorden and St. Jonsfjorden (west Spitsbergen), to obtain a breadth of glacier types and features representative of glacial landsystems on Svalbard. The detailed landform inventory was divided into: (i) ice marginal, (ii) subglacial, (iii) glaciofluvial and glaciolacustrine, (iv) supraglacial and (v) other non-glacial and contemporary features. These detailed maps provide a geomorphological insight into the past and present characteristics of glaciers on Svalbard. ARTICLE HISTORY
... In its eastern end, Femmilsjøen receives direct runoff from Longstaffbreen (an outlet of Åsgardfonna) and icebergs calve into the lake. Longstaffbreen is a surge-type glacier, with its latest documented active phase in 1960 (Liestøl, 1993;Hagen et al., 1993;Lønne, 2016). The lake water is turbid from sediment in suspension during the icefree period (estimated to be July to September; Holm et al., 2012), and the water surface across the entire lake is opaque. ...
... Thus, glacier forelands have received a lot of research interest, resulting in maps of glacial landforms, landsystems, and glacial sedimentary processes across Svalbard (e.g., de Geer, 1896;Boulton, 1967Boulton, , 1999Szczęsny et al., 1989;Huddart and Hambrey, 1996;Hart and Watts, 1997;Glasser et al., 1999;Bennett et al., 1999Bennett et al., , 2000Glasser and Hambrey, 2001;van der Meer, 2004;Larsen et al., 2005;Schomacker and Kjaer 2008;Hanáček et al., 2011;Evans et al., 2012;Ewertowski et al., 2016;Farnsworth et al. 2016;Lønne, 2016;Lovell et al., 2018;Aradóttir et al., 2019;Fig. 1). ...
... High-resolution overview maps of the peri-and paraglacial processes influencing the terrestrial geomorphology exist from southern, central and western Svalbard (e.g., Åkerman, 1987;Karczewski et al., 1990;Tolgensbakk et al., 2001;Zwoliński et al., 2013;Miccadei et al., 2016;Rubensdotter et al., 2015a,b;2016;Lyså et al., 2018;Rouyet et al., 2019;Berthling et al., 2020; Fig. 1). Studies and geomorphological maps focusing on coastal processes exist from central and northern Svalbard (e.g., Brückner and Schellman, 2003;Sessford et al., 2015;Borriquen et al., 2018), and a highly detailed geomorphological map of an alluvial fan system exists from central Spitsbergen (Tomczyk et al., 2019; Fig. 1). ...
The Arctic regions are affected by the modern climate change to a greater extent than the global average. This effect is called the Arctic amplification and is reflected in air temperatures rising with double rate and increased precipitation compared to the global average. The climate of Svalbard is strongly related to variations in the atmospheric and oceanic circulation patterns, and the archipelago is, therefore, ideal location to study the climate sensitivity of the Arctic. This dissertation presents research on the Late Pleistocene and Holocene glacial history of Svalbard. Marine, lacustrine and terrestrial archives are assessed in a confined geographical area in northern Wijdefjorden, northern Spitsbergen, and the regional timing of the deglaciation, Holocene Thermal Maximum, Holocene Glacial Minimum as well as the onset of the Neoglacial are identified (Papers I-III). The research focus is on Wijdefjorden, Femmilsjøen and the NW part of the Åsgardfonna ice cap. The results are placed in a regional context and compared to studies across Svalbard. A review of the Holocene glacial history of Svalbard is presented in Paper IV, where all Holocene chronological data from Svalbard are re-calibrated or calculated and gathered in one database. The landforms in the fjord (Paper I) and the lowermost acoustic and sedimentary facies (Papers I-II) are interpreted to be indicative of grounded, warm-based ice occupied the fjord during the Last Glacial. By contrast, Paper III speculates that parts of the terrestrial terrain are similar to forelands of cold-based glaciers in Antarctica, which may have been covered by cold-based and little erosive glacier ice during the Last Glacial. Among the findings are that northern Svalbard deglaciated early. Wijdefjorden is inferred to deglaciate at least prior to 12.4 ± 0.3 cal. ka BP and potentially prior to 14.5 ± 0.3 cal. ka BP. Femmilsjøen deglaciated potentially prior to 16.1 ± 0.3 cal. ka BP. Deglaciation occurred in a stepwise manner and was characterised by fluctuating water temperatures and sea ice cover. Overarching, the Svalbard fjords deglaciated rapidly during the first half of the Early Holocene, however the overall retreat was punctuated by dynamic ice-advances of smaller tributary glaciers. Femmilsjøen was isolated from the marine environment c. 11.4 cal. ka BP. The regional Holocene glacial minimum coincided with the Holocene thermal maximum (between 10.1 ± 0.4 and 3.2 ± 0.2 cal. ka BP), during which time the ice cap Åsgardfonna was small or close to absent. Collectively in Svalbard, the Holocene glacial minimum most likely occurred between 8.0 and 6.0 cal. ka BP. Thus, the Holocene thermal maximum and Holocene glacial minimum in northern Wijdefjorden seems extended compared to the rest of Svalbard. In the fjord, seawater temperatures show a gentle decrease and the sea-ice proxy a gentle increase from c. 6.0 cal. ka BP, but values do not accelerate until c. 0.5 cal. ka BP. In Svalbard, Neoglacial glacier advances occurred generally from 4.0 to 0.5 cal. ka BP and with the Little Ice Age representing the last cold-spell of the Neoglacial. In Femmilsjøen, glacial influence recommenced from 3.2 ± 0.2 cal. ka BP, and glaciers in the catchment reached sizes no smaller than their current extent within c. 1.0 ka. The Holocene climate and glacial variability of Svalbard are strongly coupled to atmospheric and oceanic forcings.
... A further alternative approach that is yet to be investigated fully is the geomorphology of composite ridge systems. It has been demonstrated that different phases of the surge cycle can be identified from the geomorphological record based on reconstructing former ice-contact faces and therefore ice front positions (Lønne, 2016). Large multicrested composite ridge systems can form during a single surge advance caused by longitudinal transmission of stresses in front of the rapidly advancing margin (e.g., Croot, 1987Croot, , 1988bHagen, 1988;Boulton et al., 1999;Benediktsson et al., 2010), or they could form from several ridge-building advances to successively less-extensive positions (e.g., Hart and Watts, 1997;Lønne, 2016). ...
... It has been demonstrated that different phases of the surge cycle can be identified from the geomorphological record based on reconstructing former ice-contact faces and therefore ice front positions (Lønne, 2016). Large multicrested composite ridge systems can form during a single surge advance caused by longitudinal transmission of stresses in front of the rapidly advancing margin (e.g., Croot, 1987Croot, , 1988bHagen, 1988;Boulton et al., 1999;Benediktsson et al., 2010), or they could form from several ridge-building advances to successively less-extensive positions (e.g., Hart and Watts, 1997;Lønne, 2016). Lønne (2016) used detailed geomorphological mapping from aerial photographs to identify the termination of the surge active phase(s) as recorded within the proglacial geomorphology. ...
... Two possible explanations for the formation of BFAs are consistent with processes of formation during a single episode of rapid ice advance ( Fig. 8A): (1) channel abandonment and truncation during the advance caused by (a) seasonal reorganisation of meltwater drainage routes (e.g., Boulton et al., 1999;Lønne, 2016) and/or (b) different phases and styles of glacitectonic deformation (e.g., Boulton et al., 1999;Benediktsson et al., 2010); and (2) channels developing from blowouts of overpressurised water within the moraine complex (e.g., Benediktsson et al., 2008Benediktsson et al., , 2010. ...
Some surge-type glaciers on the High-Arctic archipelago of Svalbard have large glacitectonic
composite ridge systems at their terrestrial margins. These have formed by rapid glacier
advance into proglacial sediments during the active surge phase, creating multicrested moraine
complexes. Such complexes can be formed during single surge advances or multiple surges to
successively less-extensive positions. The few existing studies of composite ridge systems have
relied on detailed information on internal structure and sedimentology to reconstruct their
formation and links to surge processes. However, natural exposures of internal structure are
commonly unavailable, and the creation of artificial exposures is often problematic in fragile
Arctic environments. To compensate for these issues, we investigate the potential for
reconstructing composite ridge system formation based on geomorphological evidence alone,
focusing on clear morphostratigraphic relationships between ridges within the moraine
complex and relict meltwater channels/outwash fans. Based on mapping at the margins of
Finsterwalderbreen (in Van Keulenfjorden) and Grønfjordbreen (in Grønfjorden), we show that
relict meltwater channels that breach outer parts of the composite ridge systems are in most
cases truncated upstream within the ridge complex by an inner pushed ridge or ridges at their
ice-proximal extents. Our interpretation of this relationship is that the entire composite ridge
system is unlikely to have formed during the same glacier advance but is instead the product
of multiple advances to successively less-extensive positions, whereby younger ridges are
emplaced on the ice-proximal side of older ridges. This indicates that the Finsterwalderbreen composite ridge system has been formed by multiple separate advances, consistent with the
cyclicity of surges. Being able to identify the frequency and magnitude of former surges is
important as it provides insight into the past behaviour of surge-type glaciers and, if absolute
dating is possible, allows for the assessment of surge-type glacier response to climate change
on decadal to centennial timescales. Although further investigations into the internal structure
of these deposits should be sought where possible, our study demonstrates that geomorphology
could be an invaluable tool for reconstructing the formation of composite ridge systems.
... Due to the multi-decadal return periods of glacier surges and the remote nature of the archipelago, many surges are likely to have gone undetected [23,35,65], and thus the figure quoted above represents a minimum value for the surge-type glacier total. It is also recognised that some glaciers may have surged in the past (e.g. during the Little Ice Age maximum *1900 AD) but are no longer in the surge cycle (e.g. ...
... This distinction reflects the difference between composite ridge systems, formed in a proglacial position, and de-icing forelands comprising sub-/supraglacial deposits left-behind by glacier recession during the quiescent phase of the surge cycle (e.g. [65]). The few studies that have investigated the internal structure of glacitectonic composite ridge systems in Svalbard report stacked and contorted sequences consisting of predominantly sorted and fine-grained sediment, typically with varying compositions of mud, sand and gravel (e.g. ...
... In order to reduce the chance of missing any composite ridge systems, the Croot [18] composite ridge system and Hagen et al. [42] push moraine inventories were examined in detail, alongside all glaciers documented as surge-type ( [18,35]; and references therein) and those likely to have surged based on the presence of CSR networks [35]. Table 1 Geomorphological criteria for identifying composite ridge systems in Svalbard from aerial photographs and links to inferred processes of formation during surges, including observations in Aber et al. [1], Croot [18], Hart and Watts [48], Boulton et al. [14] and Lønne [65] Key feature Description Interpretation ...
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.
... The method is useful in the almost vegetation-free Svalbard landscape, where lineation patterns are used to distinguish bedrock and ice-and sediment-covered surfaces. Although these early studies were promising, the potential has really become apparent with the recent series of images (2008-2013, resolution 20-50 cm), 2 where lineation maps from a number of terrains appear to have distinct signatures (Lønne, 2014a(Lønne, , 2014bLønne, 2016). ...
... For example, the pattern of supraglacial meltwater ( Fig. 2A) is controlled by the gradients and character of the glacier surface. Water running from the ice and into the adjacent landscape often form a distinct signature (runoffpoint, Lønne, 2016), which may appear as drainage "without" catchment when the ice has melted (Fig. 2B). Supra-to subglacial sediment surfaces and proglacial moraines also have distinct patterns (Figs. ...
... Moraines in this landscape are chiefly supraglacial in origin and disintegrate by meltdown and release of the debris Mercier et al., 2009), except for push moraines (Boulton, 1986;Bennett, 2001), which locally form in lowland terrains during rapid advance (Croot, 1988;Lønne, 2016). Former ice margins are thus often associated with traces of running water, and supraglacial runoff points may provide information on glaciodynamic conditions. ...
High-Arctic terrestrial slopes have received limited systematic research interest, but increased vulnerability related to regional warming has driven the call for better knowledge of the dynamics of these systems. Studies of sediment transport from a plateau area in Adventdalen, Svalbard, and associated slopes extending to sea level demonstrate that glacial processes play a more prominent role than earlier anticipated, − especially the impact of glacial meltwater. Traces of drainage at the plateau and the dissection of the plateau edge and upper slope were clearly initiated during various stages of Late Glacial runoff. Further, there is a close association between the sediment distribution and composition at the plateau and the evolution of various types of slopes. The reconstructed sedimentation history shows that the landscape will undergo four stages with contrasting modes of sediment transport: 1) subglacial processes related to active ice, 2) processes related to the margin of active ice, 3) processes related to the melting of inactive ice, and 4) nonglacial processes. These stages form four successions, referred to as supply regimes A–D, which control the supply of water and sediments to a given slope segment. In this landscape, traces of glacial meltwater occur at most altitudes, in “odd” positions and in slope segments “without” catchments. The associated depocenters (isolated, composite or coalescing into aprons), are often outsized compared to the apparent slope catchment. Reworked glacial sediments form a significant part of the slope-debris but are covered partly or entirely by products of physical weathering. Colluvium, senso stricto, thus masks a distinct system shift related to the local termination of glacial meltwater. Consequently, the weathering part of the slope sediment budget in this region is considerably overestimated.
... Observations of surge events are relatively rare in Svalbard because of the remoteness of many glaciers and the extended surge cycles characteristic of the cold, dry region (Dowdeswell et al., 1991;Lønne, 2016). Commonly, surge-type glaciers are identified by the presence of specific landforms characteristic of a surge (Benn and Evans, 2010). ...
... Lønne (2016) discusses how variations in available sediment and deformable beds can aid or hinder the preservation of sediment morphology. Lønne (2016) describes 'Type B' glaciers as land-terminating basins with poorly deformable substrate and low probability of proglacial moraine formation because of the coarse-grained debris. She notes that in these types of basins, the glacier debris rapidly transforms to alluvial or colluvial facies (Lønne, 2016). ...
... Lønne (2016) describes 'Type B' glaciers as land-terminating basins with poorly deformable substrate and low probability of proglacial moraine formation because of the coarse-grained debris. She notes that in these types of basins, the glacier debris rapidly transforms to alluvial or colluvial facies (Lønne, 2016). This type of glacier seems to correspond to higher alpine basins that do not form CSRs despite documented surge advances. ...
... In the case of sparse archival data, the application of surging glacier landsystem models based on characteristic landform assemblages in the terrestrial (Evans andRea, 1999, 2003) and submarine forefields (Ottesen and Dowdeswell, 2006;Ottesen andothers, 2008, 2017) allows the detection of surge-like behaviour of glaciers with no documented surging history (Christoffersen and others, 2005;Farnsworth andothers, 2016, 2017;. The landforms are a record of a fully active surge with glacier advance (stage 3 according to Sund and others, 2009) marked with pro-and supraglacial moraines and characteristic meltwater drainage patterns (Lønne, 2016). One of the key features of the surge landsystems are crevasse-squeeze ridges (CSRs), which indicate basal crevassing and saturated basal sediments during the active surge phase, while the preservation of the ridges implies abrupt surge termination and ice stagnation during the quiescent phase (Evans and Rea, 1999;Ben-Yehoshua and others, 2023). ...
... A restricted extent or absence of CSRs on the fjord floor, but occurrence on land, were evidenced in the forefield of surge-type Blomstrandbreen (Burton and others, 2016; Farnsworth and others, 2016) and the glacial system of Trygghamna (Aradóttir and others, 2019). Hansbreen has not developed a terrestrial thrust-block moraine diagnostic of surging, but such landforms are not widespread in the lateral forefields of surge-type tidewater glaciers in Svalbard (Lønne, 2016;Lovell and Boston, 2017). The slightly curvilinear ridges of the lateral terminal moraines and the submarine large terminal moraine indicate the radial expansion of the glacier snout when entering the Hornsund Fjord (Figs 2, 3, 9). ...
This paper presents geomorphological and historical records of the surge-type behaviour of Hansbreen, one of the most studied tidewater glaciers in Svalbard. The surge-type behaviour of the glacier has not been considered before due to the lack of evidence of this phenomenon. We integrate geomorphological mapping of the terrestrial and submarine forefields with historical data from the 19th and 20th centuries to reconstruct the glacier dynamics and identify the possible timing of surging. Landform assemblages are representative of the surging glacier land-system, including crevasse-squeeze ridges (CSRs) and submarine streamlined glacial lineations. Abundant CSRs in the outer part of the terrestrial forefield were also documented in the 1980s, but most have been obliterated since then. We suggest the identified surge landsystem was produced during a surge of Hansbreen detected from photographs taken during the Austro-Hungarian expedition in 1872. Historical photogrammetric photos from the Norwegian expedition in 1918 revealed surge-diagnostic features in the glacier surface, including a folded medial moraine and a dense, complex network of crevasses. A potential next surge remains questionable in the following decades due to the low-lying accumulation area of the main stream hindering the mass build-up, but potential surges of the tributary glaciers should not be excluded.
... Several of these moraines originate from quasi-periodic dynamic surge advances, not directly related to mass balance (Meier and Post, 1969;Sharp, 1988;Sevestre and Benn, 2015;Lovell and Boston, 2017). The glacial forelands of Svalbard have received a lot of research interest, resulting in maps of glacial landforms, landsystems, and glacial sedimentary processes across Svalbard (e.g., de Geer, 1896;Boulton, 1967;Szczęsny et al., 1989;Huddart and Hambrey, 1996;Hart and Watts, 1997;Bennett et al., 1999;Boulton et al., 1999;Glasser et al., 1999;Bennett et al., 2000;Glasser and Hambrey, 2001;van der Meer, 2004;Larsen et al., 2005;Schomacker and Kjaer, 2008;Hanáček et al., 2011;Evans et al., 2012;Ewertowski et al., 2016;Farnsworth et al., 2016;Lønne, 2016;Allaart et al., 2018;Lovell et al., 2018;Aradóttir et al., 2019;Fig. 1). ...
... The few and faint moraine ridges on the bedrock plateau suggest that Midtsundstadbreen was cold-based during its most recent advances. Comparing the aerial images of the area from 1936 and 2010, the location of the thrust moraine on Midtsundstadbreen has not changed, indicating no modification by the 1960s surge of Longstaffbreen ( Fig. 2; Hagen et al., 1993;Lønne, 2016). The lack of change in frontal position could reflect that the glacier is in steady state. ...
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.
... This highlights the importance of identifying surge-type glaciers and understanding the reason behind individual glacier advances (Lefauconnier and Hagen, 1991;Yde and Paasche, 2010;Farnsworth et al., 2016). Landsystem models have been developed to help identify undocumented surge-type glaciers (Evans andRea, 1999, 2003;Ottesen and Dowdeswell, 2006;Ottesen et al., 2008) and then modified to better depict the preservation potential and formation of sediments and landforms (Brynjólfsson et al., 2012(Brynjólfsson et al., , 2014Schomacker et al., 2014;Brynjólfsson, 2015;Flink et al., 2015;Lønne, 2016). ...
... The absence of diagnostic surge-type landforms in the terrestrial archive could owe to generally coarse and thin cover of subglacial sediments (Lønne, 2016), intense fluvial erosion, high amount of supraand englacial debris (Brynjólfsson et al., 2012(Brynjólfsson et al., , 2014Brynjólfsson, 2015) and degradation due to permafrost thawing (Schomacker and Kjaer, 2008). These characteristics all correspond well with the landform assemblage in the forefield of Protektorbreen and we propose that they could be the reason for the absence of certain landforms, such as CSRs and concertina eskers. ...
... Vere and Benn (1989) argued that these models were best regarded as fundamental classes that would contribute to specific medial moraine aggregations in the field. The debris concentration in medial moraines results in differential ablation and a gradual increase in moraine relief downglacier, causing the moraines to stand above the surrounding clean ice (Anderson, 2000;Kirkbride and Deline, 2013;Schomacker et al., 2014;Lønne, 2016). Once the ice melts, subtle traces of the medial moraines can be found in contemporary glacier forelands and formerly glaciated areas in the form of thin and diffuse concentrations of debris that bear the characteristics of supraglacial deposits (Sharp, 1958;Danson, 1979;Smiraglia, 1989;Evans and Twigg, 2002;Schomacker et al., 2014;Lønne, 2016). ...
... The debris concentration in medial moraines results in differential ablation and a gradual increase in moraine relief downglacier, causing the moraines to stand above the surrounding clean ice (Anderson, 2000;Kirkbride and Deline, 2013;Schomacker et al., 2014;Lønne, 2016). Once the ice melts, subtle traces of the medial moraines can be found in contemporary glacier forelands and formerly glaciated areas in the form of thin and diffuse concentrations of debris that bear the characteristics of supraglacial deposits (Sharp, 1958;Danson, 1979;Smiraglia, 1989;Evans and Twigg, 2002;Schomacker et al., 2014;Lønne, 2016). Thus the preservation potential of medial moraines is generally low. ...
Rockfalls and avalanches, medial moraines, and englacial debris bands are the most common sources of supraglacial debris on glacier and ice sheet surfaces, but tephra and meteorites may be the main source in specific areas. Supraglacial processes comprise melting of debris-covered ice and resedimentation of the sediment cover. The final products of the melt-out of debris-covered dead-ice are hummocky moraines, kames, and eskers. Supraglacial deposits are of little palaeoclimatic significance because studies in modern glacial environments reveal that identical processes operate in a broad range of climatic settings and conspicuous moraines in glacier forelands may represent the delivery of significant rockfall deposits to the ice margin. Glaciodynamically, ancient supraglacial deposits indicate that debris-covered stagnant glacier ice existed at the time of formation. Hummocky moraine at the margins of Pleistocene ice sheets reveals that large areas were debris-covered and melted out as dead-ice rather than by the retreat of a clean, well-defined ice margin. The main processes of dead-ice melting are downwasting, i.e., the melting at (sub-)horizontal
top and bottom surfaces, and backwasting of near-vertical ice faces. Resedimentation of the debris-cover characterizes the supraglacial environment mainly by sediment gravity flows. Repeated resedimentation cycles remove fines from the sediment and might lead to topographical inversion.
... In its eastern end, Femmilsjøen receives direct runoff from Longstaffbreen (an outlet of Åsgardfonna) and icebergs calve into the lake. Longstaffbreen is a surge-type glacier, with its latest documented active phase in 1960 (Liestøl, 1993;Hagen et al., 1993;Lønne, 2016). The lake water is turbid from sediment in suspension during the icefree period (estimated to be July to September; Holm et al., 2012), and the water surface across the entire lake is opaque. ...
The response of glaciers and ice caps to past climate change provides important insight into how they will react to ongoing and future global warming. In Svalbard, the Holocene glacial history has been studied for many cirque and valley glaciers. However, little is known about how the larger ice caps in Svalbard responded to Late Glacial and Holocene climate changes. Here we use lake sediment cores and geophysical data from Femmilsjøen, one of Svalbard's largest lakes, to reconstruct the glacial history of the Åsgardfonna Ice Cap since the last deglaciation. We find that Femmilsjøen potentially deglaciated prior to 16.1 ± 0.3 cal ka BP and became isolated from the marine environment between 11.7 ± 0.3 to 11.3 ± 0.2 cal ka BP. Glacial meltwater runoff was absent between 10.1 ± 0.4 and 3.2 ± 0.2 cal ka BP, indicating that Åsgardfonna was greatly reduced or disappeared in the Early and Middle Holocene. Deposition of glacial-meltwater sediments re-commenced in Femmilsjøen at c. 3.2 ± 0.2 cal ka BP, indicating glacier re-growth in the Femmilsjøen catchment and the onset of the Neoglacial. The glacier(s) in the Femmilsjøen catchment area reached sizes no smaller than their modern extents already at c. 2.1 ± 0.7 cal ka BP. Our results suggest that larger Svalbard ice caps such as Åsgardfonna are very sensitive to climate changes and probably melted completely during the Holocene Thermal Maximum. Such information can be used as important constraints in future ice-cap simulations.
... Boulton et al. 1999;Benediktsson et al. 2010), the dual-crested morphology of the terminal moraine and particularly the patches of CSRs between the crests suggest that they originate from two different surges. Similar conclusions have been reached in studies of glacier surging processes and resulting landforms in terrestrial settings (Croot 1988;Lønne 2016;Lovell et al. 2018a). The zone of large icemarginal moraine ridges on the proximal flank of the TMC is separated from the terminal moraine by another patch of CSRs suggesting that these end-moraines are also a product of a separate surge (Figs 3, 7, 8). ...
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.
... It is possible that the englacial temperature also increased [2,10]. In addition, in Svalbard the positive feedback from deformable till was thought to be an important factor that initiates the glacier surge [7,53], and the prevalent proglacial moraine and supraglacial drainage can support this view [54,55]. However, the Monomah glacier is debris-free. ...
Several glaciers in the Bukatage Massif are surge-type. However, previous studies in this region focused on glacier area and length changes, and more information is needed to support the deep analysis of glacier surge. We determined changes in glacier thickness, motion, and surface features in this region based on TanDEM-X, ALOS/PRISM, Sentinel-1A, and Landsat images. Our results indicated that the recent surge of the Monomah Glacier, the largest glacier in the Bukatage Massif, started in early 2009 and ceased in late 2016. From 2009 to 2016, its area and length respectively increased by 6.27 km2 and 1.45 km, and its ice tongue experienced three periods of changes: side broadening (2009–2010), rapid advancing (2010–2013), and slow expansion (2013–2016). During 2000–2012, its accumulation zone was thinned by 50 m, while its ice tongue was thickened by 90 m. During 2015–2017, its flow velocity reduced from 1.2 to 0.25 m/d, and the summer velocities were much higher than winter velocities. We conclude that the recent Monomah Glacier surge is thermal-controlled. The subglacial temperature rose to the pressure-melting point because of substantial mass accumulation, and then the increased basal meltwater caused the surge.
... Crevasse-squeeze ridges have not previously been identified in other glaciated valleys in New Zealand, possibly due to a lack of highresolution imagery similar to that employed in this study. Recognition of these crevasse-squeeze ridges, especially within cross-cutting networks, is particularly notable because they are diagnostic of a surging glacier process-form regime Rea, 1999, 2003;Evans et al., 2007Evans et al., , 2016Benediktsson et al., 2015;Farnsworth et al., 2016;Lønne, 2016;Lovell et al., 2018). Glacier surges have not previously been recognised in New Zealand in either ancient or modern landsystems. ...
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.
... Fig. 6A& B;Flink et al. 2015;Lønne 2016;Flink et al. 2017;, a documented exception to this is Nathorstbreen(Sund et al. 2014). These recessive surge moraines have been mapped and described across Svalbard with the most frequent series of events identified in front of Tunabreen and Paulabreen (Fig. 6A & B;Flink et al. 2015;. ...
Identifying the key factors that influence the global cryosphere and eustatic sea level are critical in today’s populated world characterized by a changing climate. Within the Arctic, which has recently experienced amplified warming, and located between the Polar Northern Atlantic and the Arctic seasonal sea-ice, the Svalbard archipelago experiences a heightened sensitivity to climate change. Studying the processes, dynamics and historic fluctuations of Svalbard’s glaciers and climate is critical. Understanding these elements allows us to place current rates of change into longer-term perspective and ultimately to better model future climatic conditions. This study synthesizes the state of the art of Svalbard’s Holocene glacial and climate history. Chapters (i) introduce new findings of Holocene glaciers and climate; (ii) discuss the factors influencing Svalbard ice margins; (iii) summarize accumulated knowledge in the perspective of today’s paradigm; and (iv) outline potential approaches to address further unknowns regarding the Holocene on Svalbard.
Through the Holocene, Svalbard glaciers have exhibited at least two phases of widespread re-advances, one during the Early Holocene and another throughout the entire Late Holocene. No geomorphological features have been identified corresponding to glacier re-advances between 9.0 – 4.5 ka BP. The Early Holocene glacier re-advances are identified across Svalbard and correspond to a diverse range of glacier sizes. With our current level of age constraint, these ice marginal fluctuations do not appear synchronous. Furthermore, the Early Holocene climate is believed to have been warm, unfavorable for glacier growth, and characterized by deglaciation. Early Holocene glacier re-advances appear to relate to the time-transgressive nature of deglaciation. Thus, the re-advances correspond to glacio-dynamics (not mass balance) and reflect the complex style of icemass-loss during a changing climate.
Landforms and deposits from glaciers re-advancing during the Late Holocene have been the primary focus of Holocene glacial studies. Glacier re-advances and corresponding deposits have been attributed to episodic Neoglacial cooling and the Little Ice Age (LIA). The majority of Late Holocene glacier re-advances have been dated to between 4.0 – 0.5 ka BP with the highest frequency of re-advances constrained to 1.0 – 0.5 ka BP, during the first half of the LIA. It has been suggested that glacial landforms and deposits from LIA re-advances indicate rapid and dynamic glacier behavior, and in some cases surge-type events.
During the 20th century (i.e. post-LIA), Svalbard glaciers have exhibited widespread negative mass balance, ice marginal retreat, and glacier thinning. This phase of retreat has had a direct influence on glacier thermal regime, hydrologic system and surface profile. Through the 20th century, some Svalbard glaciers have continued to exhibit surge-type re-advances. Several glaciers have surged numerous times. These glacio-dynamic re-advances have been un-sustained and each subsequent surge has been less extensive then prior surges. Consequently, and despite re-advance, glaciers reflect a continual phase of ice-mass-loss in a periodic fashion.
Our understanding of Svalbard’s Holocene glaciers and climate has progressed but critical components remain obscure. For example, although our understanding of the timing of the Holocene glacial minimum has improved, we lack detailed constraints on the extent of ice retreat across Svalbard during the Mid-Holocene. As reconstructions of palaeo-temperatures develop, the improvement of palaeo-precipitation proxies (e.g., leaf wax hydrogen isotopes) should continue. Additionally, as we approach further unknowns of Svalbard’s Holocene history, it is evident that studies must take a holistic approach. Combining a mixture of archives, geochronological methods and emerging techniques will enhance the accuracy of reconstructions detailing Svalbard’s glacial history.
... Also, several studies have analyzed the suite of glacial landforms related to the surging landsystem (e.g. Evans and Rea, 1999;Benediktsson et al., 2015;Farnsworth et al., 2016;Lønne, 2016;Lovell et al., 2018). These landforms are generally assumed to have formed during the surge event and are exposed in the proglacial area during the quiescent phase when the glaciers recede. ...
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.
... That is not to say that seafloor sediments would have necessarily been pushed above the waterline during the formation of surge terminal moraines in these other examples d this will depend on water depth. Aside from Van Keulenfjorden, to our knowledge the only other report of mud pushed above the waterline at an advancing glacier margin in Svalbard is from the 2002-2010 surge of Comfortlessbreen, which advanced~700 m into the shallow water of Engelskbukta (King et al., 2016;Lønne, 2016). However, such processes have been inferred during past surges of Sefstr€ ombreen (Boulton et al., 1996), Paulabreen (Kristensen et al., 2009a; and Osbornebreen (Evans and Rea, 2005;Farnsworth et al., 2017) based on terrestrial geomorphological evidence. ...
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.
... With improvements in technology, high-resolution (ground resolution < 0.5 m per pixel) digital copies of aerial photographs have become widely available and used for glacial geomorphological mapping (e.g. Brown et al., 2011a;Bradwell et al., 2013;Brynjólfsson et al., 2014;Jónsson et al., 2014;Pearce et al., 2014;Schomacker et al., 2014;Chandler et al., 2016a;Evans et al., 2016c;Lardeux et al., 2015;Lønne, 2016;Allaart et al., 2018). Indeed, digital aerial photographs, along with scanned copies of archival aerial photographs, are now more widely used than hard-copy stereoscopic aerial photographs, particularly in modern glacial settings. ...
Geomorphological mapping is a well-established method for examining earth surface processes and landscape evolution in a range of environmental contexts. In glacial research, it provides crucial data for a wide range of process-oriented studies and palaeoglaciological reconstructions; in the latter case providing an essential geomorphological framework for establishing glacial chronologies. In recent decades, there have been significant developments in remote sensing and Geographical Information Systems (GIS), with a plethora of high-quality remotely-sensed datasets now (often freely) available. Most recently, the emergence of unmanned aerial vehicle (UAV) technology has allowed sub-decimetre scale aerial images and Digital Elevation Models (DEMs) to be obtained. Traditional field mapping methods still have an important role in glacial geomorphology, particularly in cirque glacier, valley glacier and icefield/ice-cap outlet settings. Field mapping is also used in ice sheet settings, but often takes the form of necessarily highly-selective ground-truthing of remote mapping. Given the increasing abundance of datasets and methods available for mapping, effective approaches are necessary to enable assimilation of data and ensure robustness. This paper provides a review and assessment of the various glacial geomorphological methods and datasets currently available, with a focus on their applicability in particular glacial settings. We distinguish two overarching ‘work streams’ that recognise the different approaches typically used in mapping landforms produced by ice masses of different sizes: (i) mapping of ice sheet geomorphological imprints using a combined remote sensing approach, with some field checking (where feasible); and (ii) mapping of alpine and plateau-style ice mass (cirque glacier, valley glacier, icefield and ice-cap) geomorphological imprints using remote sensing and considerable field mapping. Key challenges to accurate and robust geomorphological mapping are highlighted, often necessitating compromises and pragmatic solutions. The importance of combining multiple datasets and/or mapping approaches is emphasised, akin to multi-proxy approaches used in many Earth Science disciplines. Based on our review, we provide idealised frameworks and general recommendations to ensure best practice in future studies and aid in accuracy assessment, comparison, and integration of geomorphological data. These will be of particular value where geomorphological data are incorporated in large compilations and subsequently used for palaeoglaciological reconstructions. Finally, we stress that robust interpretations of glacial landforms and landscapes invariably requires additional chronological and/or sedimentological evidence, and that such data should ideally be collected as part of a holistic assessment of the overall glacier system.
... Surges can advance an ice front by a kilometre per year, so it could have covered the distance from Escrick to Lindholme and Wroot rapidly. Surges are also known to stop rapidly (Lønne, 2016), and ice reaching Lindholme may not have lasted long before it became unsustainable. ...
The limits of the glacier that occupied the southwest part of the southern Vale of
York at the Last Glacial Maximum are defined in relation to recent temporary exposures at
Lindholme and previous regional mapping by Geoff Gaunt. Erratic content of associated
diamicts indicates sources in the Yorkshire Dales, over Stainmore and along the Permo-
Triassic outcrops on the west side of the Vale of York. The advance is dated to an episode
associated with a high level of pro-glacial Lake Humber within the Last Glacial Maximum.
Lidar imagery suggests that the northeastern ice limit is concealed beneath later alluvium of
the rivers Ouse and Trent.
Central Tianshan (CTS) plays a prominent role in maintaining the vulnerable ecosystem in Central Asia. Rivers originating from it have high proportions of the runoffs contributed by glacier meltwater. In this study, the glacier mass balance in the catchments of Muzart and Karayulun rivers, CTS, was estimated by a geodetic method based on Advanced Land Observing Satellite/Panchromatic Remote-sensing Instrument for Stereo Mapping images and Shuttle Radar Topography Mission (SRTM) digital elevation model (DEM). The results revealed that at the west and east glacial centers in the study area, the 2000–2011 mass loss rates were −0.03 ± 0.17 and −0.06 ± 0.17 m w.e./a, respectively, considerably lower than other CTS zones. In order to ascertain this stable glacier state, we also performed a geodetic measurement based on TerraSAR-X add-on for Digital Elevation Measurement (TanDEM-X) images and SRTM DEM (2000–2012), and the results are similar (0.01 ± 0.17 and −0.04 ± 0.17 m w.e./a, respectively). The glacier thickness change around the regional snowline was close to zero. The strong capability of cold storage and the temperature drop in the early 21st century may account for the anomalous mass changes. Despite slight overall mass changes, obvious thinning was observed on many exposed glacier feet. This study indicates that the glacier melting can be effectively controlled if the rising trend of temperatures is reversed; furthermore, the land surface hydrological model should be calibrated with geodetic glacier mass balance measurement when it is used to simulate the streamflow trend in the headwater basin.
Describes part of the forefield of a small cirque glacier in the Swiss Alps. Frozen sediments are deformed in what seems to be a push moraine. Such forms are not common in the Alps, and it may be that many ice cored moraines are in fact push moraines. -Keith Clayton
Bakaninbreen, a 17 km long glacier terminating in fjord waters in central Spitsbergen (77°45′ N, 17°20′E), began to surge between the springs of 1985 and 1986. By summer 1994 the surge front had reached a position 3 km from the terminus and had almost ceased propagation. Structural investigations were undertaken to characterise the tectonic evolution of this thermally complex surge-type glacier, and the role played by thrusting and its effect on debris entrainment. Much of the glacier surface, particularly within and below the surge front, displayed transverse high-angle thrusts, defined by discrete fractures bounded by coarse clear ice. Some fractures were associated with a film of mud, whereas in others a discrete laver of diamicton, with interstitial ice several decimetres thick, was evident. Within the surge front, and genetically related to the thrusts, was a number of shear zones several metres wide. These were defined by fine-grained ice that was the product of the grinding up of crystals during shear (mylonitization). Three main sedimentary facies are associated with the thrusts: mud, gravelly mud and clast-rich muddy diamicton. The diamicton has the character of basal glacial debris: grain-size distribution ranging from clay to cobble size, clasts with a predominance in the sub-angular and sub-rounded classes, and striated and faceted clasts. Hot-water drilling through the glacier revealed several englacial layers above the surge front, and debris brought up on the drill stem suggests a basal origin. At least some of these englacial layers are probably the sub-surface continuations of the thrusts. The observed facies indicate that the glacier is moving over a soft, deformable bed and that thrusting is an important process in transferring debris to the surface, especially when the surge front is propagating down-glacier.
Finsterwalderbreen is a 35 km2, polythermal glacier in southern Spitsbergen, which last surged at around the start of the 20th century, and is still in the quiescent phase. Surface elevations measured several times since 1898 show strong thinning and retreat at the front, and gradual build-up in the accumulation area. Present-day annual velocities increase from about 1 m a–1 at the snout to a maximum of 13 m a–1 near the equilibrium line, then drop to 5 m a–1 at the bergschrund. Summer velocities are higher than the annual average, and winter velocities are lower (10–60% of summer velocities, where both are measured over several months). Velocities measured along the glacier centre line in 1950–52 are higher than those measured in 1994–95 in the upper basin, but are lower in the ablation area, which may be attributable to changes in surface profile on recovery from the surge. The measured modern ice flux (≈2.5 x 10–3 km3 a–1 w.e.) is only about 60% of the flux required to maintain balance (≈4.1 x 10–3 km3 a–1 w.e.), as determined from continuing mass-balance studies. Multi-frequency radar profiles show that most of the glacier is at the pressure-melting point at the base. This is consistent with hydrological studies showing high suspended-sediment loads, and hydro-chemical evidence of high sulphate levels, both indicating a well-developed basal drainage system during the summer which probably accounts for the seasonal velocity variations. Since the glacier still has a temperate bed, and appears to be building up in the accumulation area, it may be developing towards another surge.
The geographical distribution of surge-type glaciers worldwide displays a remarkably non-random pattern. Surge-type glaciers tend to be concentrated in certain glacierized areas and to be completely absent in others. This observation suggests that special conditions are required for surges to occur. However, the factors controlling the spatial occurrence of surge-type behaviour are not known. To investigate this problem we performed probability statistical analysis on a sample population of 615 glaciers in Svalbard. The probability that a glacier in the sample population is surge-type is 36.4%. Within the sampled area there is a spatial variation in the concentration of surge-type glaciers. Several geometric and environmental factors associated with glaciers in the sample population were measured and tested to determine if they are related to the probability of surging. Of the geometric factors tested (length, slope, elevation, orientation and presence or absence of tributaries), only glacier length is related to surging, with surge probability increasing with increasing length. Elevated probabilities of surging were also found for glaciers associated with sedimentary subglacial rocks and sub-polar thermal regimes. The distributions of related factors were used to predict the spatial distribution of surge-type glaciers. However, in each case the individual factors were unable to reproduce the observed pattern of surge-type glacier distribution.
Active push moraines are not well-investigated glacial features. They develop in arctic regions as the glacier advances into frozen glaciofluvial sediments. The moraine grows at the front while additional frozen blocks are raised in the outwash plain and incorporated into the moraine. Thus, glacier and moraine advance as one unit. Thrust plains occur throughout the moraine. Different areas of activity show that most of the subsurface activity occurs in the frontal part. Permafrost is affected in several ways. Most important is the stacking of permafrost due to the stacking of frozen gravel blocks. -Author
An end moraine (Vassryggen) and associated sandur, described by Jens Esmark as early as 1824, was the first pre-Neoglacial glacigenic landform association to be recognised as such. It forms the most important element of a range of evidence used by Esmark in support of his continental-scale glaciation hypothesis. The career of Esmark, who became a foundation professor of the Royal Frederick University in Christiania (Oslo) is outlined, and his influence on the development of the glacial theory in Britain is appraised, as is the role of his associate Robert Jameson in Edinburgh. A sketch of the glacial geology of the Forsand area of southwest Norway examines Vassryggen and its allied landforms in the context of déglaciation and sea-level change at the close of the Younger Dryas stadial.
A surge cycle of the Bering Glacier system, Alaska, is examined using observations of surface velocity obtained using synthetic aperture radar (SAR) offset tracking, and elevation data obtained from the University of Alaska Fairbanks LiDAR altimetry program. After 13 yr of quiescence, the Bering Glacier system began to surge in May 2008 and had two stages of accelerated flow. During the first stage, flow accelerated progressively for at least 10 months and reached peak observed velocities of similar to 7md(-1). The second stage likely began in 2010. By 2011 velocities exceeded 9md(-1) or similar to 18 times quiescent velocities. Fast flow continued into July 2011. Surface morphology indicated slowing by fall 2011; however, it is not entirely clear if the surge is yet over. The quiescent phase was characterized by small-scale acceleration events that increased driving stresses up to 70 %. When the surge initiated, synchronous acceleration occurred throughout much of the glacier length. Results suggest that downstream propagation of the surge is closely linked to the evolution of the driving stress during the surge, because driving stress appears to be tied to the amount of resistive stress provided by the bed. In contrast, upstream acceleration and upstream surge propagation is not dependent on driving stress evolution.
The understanding of climate and climate change is fundamentally concerned with two things: a well-defined and sufficiently complete climate record to be explained, for example of observed temperature, and a relevant mechanistic framework for making closed and consistent inferences concerning cause-and-effect. This is the case for understanding observed climate, as it is the case for historical climate as reconstructed from proxy data and future climate as projected by models. The present study offers a holistic description of northern maritime climate – from the Last Glacial Maximum through to the projected global warming of the 21st century – in this context. It includes the compilation of the most complete temperature record for Norway and the Norwegian Sea to date based on the synthesis of available terrestrial and marine paleoclimate reconstructions into continuous times series, and their continuation into modern and future climate with the instrumental record and a model projection. The scientific literature on a variable northern climate is reviewed against this background, and with a particular emphasis on the role of the Norwegian Atlantic Current – the Gulf Stream's extension towards the Arctic. This includes the introduction of an explicit and relatively simple diagnostic relation to quantify the change in ocean circulation consistent with reconstructed ocean temperatures. It is found that maritime climate and the strength of the Norwegian Atlantic Current are closely related throughout the record. The nature of the relation is however qualitatively different as one progresses from the past, through the present, and into the future.
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.
Geometric changes on a sample of Svalbard glaciers were studied using subtraction of repeat digital terrain models to determine early surge-stage dynamics. Changes in surface features were also analyzed. A number of new surges were found for glaciers not known to have surged previously. The surge development could be followed through three stages, of which the first two had not been previously described in Svalbard. The first two stages are mainly identified from glacier thickness changes and showed little visual evidence. In stage 1, initial surface lowering was found in the upper part of the glacier, followed by a thickening further downglacier in stage 2. Stage 3 represents the period of well-developed surge dynamics that is usually reported. Some surges ceased at stage 2 as a partial surge and never developed into a fully active surge. These partial surges could be misinterpreted as rapid response to climate change. The results of this study further support previous findings that the majority of Svalbard glaciers are of surge type.
See also conference paper:
Nemec (1993), The concept and definition of a fan delta: review and discussion.
There was a new focus on “processes” within sedimentary geology from the 1960s.
It was initially driven by alluvial-channel and fl ow-regime experiments, but led to the
concept of facies succession for all depositional environments and eventually, on the
larger scale, to a new stratigraphy in which base-level change was the key ingredient.
Systematic study of modern environments led to a marked improvement in our
know ledge of alluvial to deepwater sedimentary systems and how they are linked. New
access to seismic data, especially on shelf margins and deep marine environments, was
critical for further great changes in our understanding of marine processes and basinscale
products. Integration of new knowledge on rates and time scales in tectonics,
climate dynamics, and sea-level change has been important for gleaning the signals of
these drivers from the accumulated sedimentary successions. Current research, not
least from geomorphic and stratigraphic experiments, is suggesting that autogenic
responses in stratigraphy are more common and occur on longer time scales than formerly
thought and will cause a rethink in sequence stratigraphy.
The past half-century of work in siliciclastic petrology has benefi ted from a broad
consensus on classifi cations for sandstones and limestones that provided clarity on
the roles of detrital and diagenetic components in compositional heterogeneity. Subsequent
advances in provenance and diagenetic studies have both been driven by the
availability of microanalytical tools for imaging and analysis of elements and isotopes.
A petrographically based appreciation of the role of pervasive non-equilibrium and
chemical kinetics underpins our current capabilities to make predictions of siliciclastic
rock properties in the subsurface, creating a strong link between siliciclastic petrology
and the global petroleum industry. Community consensus has yet to converge on
classifi cation for fi ne-grained siliciclastic rocks (shales, mudrocks, mudstones), but
the compelling need for prediction of rock properties in unconventional reservoirs is
presently driving much research into the causes of heterogeneity in this great class of
sedimentary materials.
We present a multi-temporal digital inventory of Svalbard glaciers with
the most recent from the late 2000s containing 33 775 km2 of
glaciers, or 57% of the total land area of the archipelago. At present,
68% of the glaciated area of Svalbard drains through tidewater glaciers
that have a summed terminus width of ~ 740 km. The glaciated area over
the entire archipelago has decreased by an average of 80 km2
a-1 over the past ~ 30 yr, representing a reduction of 7%.
For a sample of ~ 400 glaciers (10 000 km2) in the south and
west of Spitsbergen, three digital inventories are available from
1930/60s, 1990 and 2007 from which we calculate average changes during 2
epochs. In the more recent epoch, the terminus retreat was larger than
in the earlier epoch while area shrinkage was smaller. The contrasting
pattern may be explained by the decreased lateral wastage of the glacier
tongues. Temporal retreat rates for individual glaciers show a mix of
accelerating and decelerating trends, reflecting the large spatial
variability of glacier types and climatic/dynamic response times in
Svalbard. Last, retreat rates estimated by dividing glacier area changes
by the tongue width are larger than centerline retreat due to a more
encompassing frontal change estimate with inclusion of lateral area
loss.
Multiproxy analyses including hydrographical, geochemical, foraminferal, lithological and geophysical data reveal variable influences of the glaciers Tunabreen and von Postbreen as well as the river Sassenelva on the sedimentary environment in two Spitsbergen fjords during the Late Weichselian and the Holocene. Grounded ice covered the study area during the last glacial. The glacier fronts retreated stepwise during the latest Weichselian/earliest Holocene, and the glaciers were probably small during the early Holocene. A growth of Tunabreen occurred between 6 and 4 cal ka BP. Reduced input from Tunabreen from c. 3.7 cal ka BP was probably a result of suppressed iceberg rafting related to the enhanced formation of sea ice and/or reduced meltwater runoff. During the past two millennia, the glacier fronts advanced and retreated several times. The maximum Holocene glacier extent was reached at the end of a surge of von Postbreen in AD 1870. Characteristics of the modern glaciomarine environment include: (1) different colours and bulk-mineral assemblages of the turbid waters emanating from the main sediment sources; (2) variable locations of the turbid-water plumes as a consequence of wind forcing and the Coriolis effect; (3) stratified water masses during summers with interannual variations; (4) increasing productivity with increasing distance from the glacier fronts; (5) foraminifera-faunal assemblages typical for glacierproximal settings; and (6) periodical mass-transport activity.
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.
A temperate glacier ending in water advances by depositing a moraine shoal, which “dams” tidewater calving, and then recycling this shoal in conveyor-belt fashion. A simple model suggests that conveyor-belt recycling of the shoal must continue until calving stops and all ice flux is removed by surface ablation, or until the glacier retreats rapidly from the shoal; retreat can occur without external forcing if the glacier advances into deepening water and if sediment recycling is rapid compared to supply of new sediment to the moraine shoal.
In the summers of 1993, 1994 and 1995, video and Global Positioning System location data and 35 mm photographs were collected in a series of systematic survey flights undertaken over the Bering Glacier and Bagley Ice Field system (Alaska) in an effort to characterize surge-crevasse patterns and surge propagation. During survey flights in late August 1995, we observed that the 1993–94. Bering Glacier surge was continuing and still expanding affecting new areas farther up in Bagley Ice Field. New crevasse fields, similar in pattern to the first surge crevasses we had observed in June 1993 below Khitrov Hills and in other isolated areas of central Bering Glacier and in July 1994 near the head of Bering Glacier (near the junction of Bering Glacier and Bagley Ice Field, in both upper Bering Glacier and Bagley Ice Field), were opening in eastern Bagley Ice Field and in the “Stellet” side of Bagley Ice Field. The type of crevasses seen in the new fields suggested that the surge was propagating into these areas. By analysis and interpretation of the brittle-deformation patterns apparent in the crevasse patterns, some aspects of the past kinematic framework of the surge can be deduced. This approach may lead to a more general classification of ice-surface structures and to their linkage to ongoing processes.
The vast Bering piedmont glacier, which has large folds in the medial moraines in its terminal lobe, recently experienced two surges with a combined ice displacement of as much as 13 km. Vertical aerial photographs taken before and after the surges disclose the direction and magnitude of ice flow in various parts of the piedmont lobe. The ice moved toward the terminus and expanded in a normal, radial pattern with no evidence of unusual shearing that would result in the formation of large folds. Many surging glaciers display repeated lateral displacements in their medial moraines which result from periodic surging of the main glacier past non-surging tributaries. Moraines of Bering Glacier display small periodic irregularities of this nature. The large “accordion” folds in the moraines in the piedmont lobe are judged to be due to the combined effects of compressive flow and lateral or transverse expansion of these previously formed irregularities. The initially small pre-existing perturbations in the moraines are simply spread laterally and shortened radially into large folds as the ice spreads out.
A very large debris band composed of repeatedly folded medial moraines extends across the center of the Bering Glacier lobe. These remarkable folds are thought to result from the deformation of surge-related irregularities in medial moraines as they pass through the zone of intensive shear near the glacier’s margin.
Many glaciers in Svalbard and in other glacierized areas of the world are known to surge. However, the time series of observations required to assess the duration of fast motion is very restricted. Data on active-phase duration in Svalbard come from aerial photographs, satellite imagery, field surveys and airborne reconnaissance. Evidence on surge duration is available for eight Svalbard ice masses varying from 3 to 1250 km2. Worldwide, active-phase duration is recorded for less than 50 glaciers. Few observations are available on high polar ice masses. The duration of the active phase is significantly longer for Svalbard glaciers than for surge-type glaciers in other areas from which data are available. In Svalbard, the active phase may last from 3 to 10 years. By contrast, a surge duration of 1–2 years is more typical of ice masses in northwest North America, Iceland and the Pamirs. Ice velocities during the protracted active phase on Svalbard glaciers are considerably lower than those for many surge-type glaciers in these other regions. Mass is transferred down-glacier more slowly but over a considerably longer period. Svalbard surge-type glaciers do not exhibit the very abrupt termination of the active phase, over periods of a few days, observed for several Alaskan glaciers. The duration of the active phase in Svalbard is not dependent on parameters related to glacier size. The quiescent phase is also relatively long (50–500 years) for Svalbard ice masses. Detailed field monitoring of changing basal conditions through the surge cycle is required from surge-type glaciers in Svalbard in order to explain the significantly longer length of the active phase for glaciers in the archipelago, which may also typify other high polar ice masses. The finding that surge behaviour, in the form of active-phase duration, shows systematic differences between different regions and their environments has important implications for understanding the processes responsible for glacier surges.
Fridtjovbreen is an actively surging tidewater glacier in western Spitsbergen, Svalbard. This paper presents observations made at the western flank of the glacier in July 1997, when the glacier front was still advancing rapidly and was characterised by steep lateral ice cliffs. The geomorphological consequences of the surge include the formation of push moraines from toppled ice blocks along this ice cliff and the development of debris-rich thrusts. There is also evidence of glaciotectonic deformation within deformed debris-rich thrusts. Thrusts are restricted to the lateral margins and are not seen in the terminal calving cliff. On its western flank, Fridtjovbreen is over-riding Sagabreen, a small-tributary glacier. Large facies variations in this area are a result of recycling by Fridtjovbreen of material originally transported as medial moraines on Sagabreen. There are few observations of landform development at actively surging glaciers in Svalbard. The Fridtjovbreen descriptions provide documentation for post-surge landform development. More observations are required at the margins of actively surging glaciers to determine how representative Fridtjovbreen is of a surge event.
The temperature, flow and marginal fluctuation of glaciers in the Kongsfjorden area of Svalbard are examined. Large areas of the glacier above the equilibrium line are at melting point yet permafrost exists in front of the glaciers. The heat capacity of water-saturated snow is thought to prevent deep winter freezing. During winter, large tidewater glaciers produce water which flows to the surface producing thicker fjord ice. The flow velocities of the small thinner glacier is about 1 cm.day⁻¹ in the centre yet Kronebreen flows at 3-4m.day⁻¹ with mean winter velocities of 1.5m.day⁻¹. A map of glacier front positions is presented which shows continual recession from the extended position reached in 1869-70 and evidence is presented which suggests that these maxima are related to surging behaviour between 1860 and 1880. Since then some of the smaller glaciers have lost 50% of their volume. -J.D.Hansom
The results of a Norwegian Polar Research Institute programme are reported, providing a list of potential future surging glaciers that could affect offshore oil exploration operating in the Barents Sea. Mapping was performed through the analysis of available aerial photographs and satellite images as well as through a literature search, and a map of former front positions of the glaciers was constructed. Changes of glacial and proglacial morphology and the responses of ice sheets to current climate were also studied. After an introduction and some examples of air photos, individual glaciers are examined by area with the aid of illustrations, stating maximum extension, current state and surges. -J.W.Cooper
Surging glaciers are not found to produce sediments unique to this environment, but taken together, the combination and variations in sediment types, physical properties, sedimentation rates, and morphology can be diagnostic and used in the interpretation of older sequences and areas where surges are not documented. -from Author
A recent re-advance resulted in a 5-10 m high push moraine complex at the glacier's western frontal margin. This complex mainly consists of outwash sediments and appears to be partly ice-cored. Measurement of both ice flow velocities and movements within the push moraine complex combined with sedimentological observations in basal ice as well as with and in front of the push moraine complex led to a possible explanation of the process of formation of the push moraine in question. -from Author
Climate is the first-order control on fluctuations of glacial tidewater termini. However, factors affecting relative water depth such as eustasy, isostasy, and sediment yield are important second-order controls on termini fluctuations. Deposition of grounding-line systems, which include ice-contact deltas, morainal banks, and grounding-line fans, can change relative water depth and consequently alter the stability of tidewater termini independent of climate. Therefore, the rate at which sediment accumulates in these grounding-line systems can control the rate of terminus movement. Modern temperate glaciers at Glacier Bay, Alaska, on average produce about 10 6 M3/yr of sediment, most of which accumulates at grounding lines. Sediment volume decreases logarithmically downfjord from a grounding line. In Glacier Bay, readvance rates that average about 10 m/yr are one to two orders of magnitude slower than retreat rates. Rates of glacial advance may be a function of sediment yield (determined by drainage area and rates of glacial erosion, transportation and debris release), total sediment volume of grounding-line systems (determined by fjord width, fjord depth less the maximum water depth for terminus stability, and angle of repose of sediment making the system), and sediment dispersal patterns (determined by process of debris release and dispersion, type of sediment, and marine currents). Consequently, average rates of advance are slower than retreat rates because of the time required for sediment to accumulate as a bathymetric high at a grounding line, which effectively decreases relative water depth and increases terminus stability. Retreat rates are faster because they occur during terminus instability in deep water and cannot be altered by sediment accumulation rates until quasi-stability of the terminus is caused by other means, such as bedrock pinning-points or a decrease in ablation area. As marine-ending glaciers expand, total sediment delivered to a grounding line increases; as they retreat, sediment volume decreases because of the change in size of the drainage basin. Grounding lines are the major depocenters receiving this sediment, and resulting lithofacies packages and geometries are primarily controlled by grounding-line movement over a glacial advance-retreat cycle. During glacial minima, fjords trap sediment while the continental shelf and slope are starved. During glacial advances and retreats, fjords are eroded while the continental shelf receives sediment and the slope may remain starved. At glacial maxima, fjords and commonly the shelf are eroded, and the continental slope receives sediment. Because grounding-line advance and retreat may or may not coincide with eustatic sea-level changes, the sedimentary record may vary depending on environmental settings and the magnitude of glacial cycles.
Many glaciers in Svalbard and in other glacierized areas of the world are known to surge. However, the time series of observations required to assess the duration of fast motion is very restricted. Evidence on surge duration is available for eight Svalbard ice masses varying from 3 to 1250km2. In Svalbard, the active phase may last from 3 to 10 yr. By contrast, a surge duration of 1-2 yr is more typical of ice masses in northwest North America, Iceland and the Pamirs. The finding that surge behaviour, in the form of active-phase duration, shows systematic differences between different regions and their environments has important implications for understanding the process responsible for glacier surges. -from Authors
Glacial surges in Svalbard are protracted and characterized by individual dynamic evolution, in contrast to many other areas, which calls for a subdivision of the classic two-phased surge cycle. A dominating part of the ice masses seem to have a surge potential and this represents a considerable challenge for palaeoclimatic studies. Glaciological and geological models therefore need to be coupled. The issue is discussed with Fridtjovbreen glacier as an example. This ice mass is one of few glaciers studied throughout a surge cycle. It was active for 12 years (1991–2002) and represents the most protracted surge documented. The maximum advance rate was 4.2 m day−1, its maximum extent was reached after seven years, its run-out distance was 4 km, and the relocated ice filled 5 km2 of the fjord. Intense subglacial thrusting occurred during various stages, including part of the ice-front retreat, as shown by sub-bottom profiling data from 2002. A six-stage model is presented and processes are discussed with emphasis on the ice-front retreat with transition to the quiescent phase. Although the surge mechanism itself is unrelated to climate, climatic conditions obviously play a major role in the course of a surge. During the surge, the ice mass made a dramatic impression in the landscape, but 10 years after the maximum extent, there is little onshore evidence of the event.
Glacial surges are periods of fast flow, often limited in space and time, and driven by internal conditions which are not fully explained. The quantity and variety of documented case-studies and settings demonstrate that the critical variables are difficult to isolate. In an alternative approach, two surges from the same basin were compared at Fridtjovhamna; one of the few known sites where this is possible. Fridtjovbreen is a polythermal glacier that has been through two recent surges: the last event (1991–2002) occurred during an unusually warm period in the high Arctic, whereas the previous surge culminated in 1861, around the Little Ice Age when many Svalbard-glaciers had their maximum Holocene extent. Based on a multi-disciplinary study, processes and landforms from the two episodes were compared with respect to ice-front movement rates, formation and decay of ice-cored moraines and glacial meltwater drainage patterns. The study demonstrates that moraines and meltwater traces from the oldest surge, locally well preserved, provide excellent opportunities for reconstructing the behavior of the ice-mass. The last surge, however, took place during a period with ablation rates never seen at this latitude, and 10 years after the maximum extent, the deglaciated areas onshore hardly show traces from the event.
This paper describes the landform and sediment assemblage produced by a surge (in 1948) of the Kongsvegen/Kronebreen tidewater glacier complex in northwest Spitsbergen. The main geomorphological products of this advance are two large thrustmoraine complexes on opposite sides of the fjord, and a system of geometrical ridges revealed on glacier decay. The thrust-moraines are composed largely of diamicton, sandy and muddy gravel, gravelly sand, sand and mud, with minor laminites. All of these appear to be derived from the fjord floor and represent both fine fjord basin sediments and coarse grounding-line fan deposits. Thrusting was the principal mode of emplacement of the sediment onto the adjacent land areas during the 1948 advance. However, the geomorphology of the thrust-moraine complexes on either side of the fjord is quite different, reflecting a transpressive regime on the southwest side (mainly long ridges) and a normal compressive regime on the northeast side (short ridges and pinnacles of a ‘hummocky’ nature). The advance which produced the moraine complex has previously been attributed to a surge of Kongsvegen, but the glaciological and geomorphological evidence suggests that the advance involved both Kongsvegen and Kronebreen. Comparison of the landform assemblage produced by this event with that produced by other tidewater glacier surges demonstrates the diverse range of landform assemblages associated with glacier surges, or other episodes of rapid flow, within glaciomarine environments.
A river crossing a coastal plain is assigned a zone of influence within which it may abruptly move and construct new channel sand-bodies following avulsion. Assuming uniform and steady subsidence at a fixed site, the alluvium formed beneath the zone is constructed over a series of equal time-steps, at the start of each of which an avulsion occurs, and during each of which an increment of sediment is accumulated beneath the plain. Each increment comprises an overbank sequence of a thickness proportional to subsidence rate and avulsion period, laterally equivalent to a generally weakly multi-storey sand body of a thickness proportional to channel depth, avulsion period, and subsidence rate. The choice of sand-body width is determined by stream size and mode of behaviour. The new position of the river after an avulsion is chosen using random-number tables combined with rules for the avoidance of older, relief-creating sand bodies. The model otherwise ignores sequence compaction, and so is valid only when operated for comparatively short periods.In accordance with a theoretical model of sand-body connectedness, in which uniform bodies are regularly packed, experimental sand bodies are virtually unconnected in those alluvial suites containing 50% or more of overbank fines. The degree of connectedness grows very rapidly as the proportion of sand bodies increases above 50%. The use of rules for avoidance does not prevent the experimental suites from being somewhat disordered internally, as shown by the wide variation in the composition of one-dimensional profiles through individual sequences. The results obtained from the model suggest that coarsening-upward alluvial suites of coastal origin may owe their character as much to progressively decreasing subsidence as to any independent decline in channel sinuosity.
A temperate glacier ending in water advances by depositing a moraine shoal, which "dams' tidewater calving, and then recycling this shoal in conveyor-belt fashion. A simple model suggests that conveyor-belt recycling of the shoal must continue until calving stops and all ice flux is removed by surface ablation, or until the glacier retreats rapidly from the shoal; retreat can occur without external forcing if the glacier advances into deepening water and if sediment recycling is rapid compared to supply of new sediment to the moraine shoal. -Author
In the summers of 1993, 1994 and 1995, video and Global Positioning System location data and 35 mm photographs were collected in a series of systematic survey flights undertaken over the Bering Glacier and Bagley Ice Field system (Alaska) in an effort to characterize surge-crevasse patterns and surge propagation. During survey flights in late August 1995, we observed that the 1993-94 Bering Glacier surge was continuing and still expanding, affecting new areas farther up in Bagley Ice Field. New crevasse fields, similar in pattern to the first surge crevasses we had observed in June 1993 below Khitrov Hills and in on other isolated areas of central Bering Glacier and in July 1994 near the head of Bering Glacier (near the junction of Bering Glacier and Bagley Ice Field, in both upper Bering Glacier and Bagley Ice Field), were opening in eastern Bagley Ice Field and in the "Steller" side of Bagley Ice Field. The type of crevasses seen in the new fields suggested that the surge was propagating into these areas. By analysis and interpretation of the brittle-deformation patterns apparent in the crevasse patterns, some aspects of the past kinematic framework of the surge can be deduced. This approach may lead to a more general classification of ice-surface structures and to their linkage to ongoing processes.
The results of observations bearing on the fast motion during a glacial surge are discussed. The characteristics of the surge cycle are described, and the processes of surge behavior are examined, including the basic mechanisms of surge motion, the role of longitudinal stress gradients in surge motion, constraints on sliding behavior during surge motion, initiation and termination of surge motion. Unresolved questions concerning bed structure, sliding process, basal water flow, and surges are addressed.