Article

Thermal structure of Svalbard glaciers and implications for thermal switch models of glacier surging

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Abstract

Switches between cold- and warm-based conditions have long been invoked to explain surges of High Arctic glaciers. Here, we compile existing and new data on the thermal regime of six glaciers in Svalbard to test the applicability of thermal switch models. Two of the large glaciers of our sample are water-terminating while one is land-terminating. All three have a well-known surge history. They have a thick basal layer of temperate ice, superimposed by cold ice. A cold terminus forms during quiescence, but is mechanically removed by calving on tidewater glaciers. The other three glaciers are relatively small, and are either entirely cold or have a diminishing warm core. All three bear evidence of former warm-based thermal regimes and, in two cases, surge-like behavior during the Little Ice Age. In Svalbard, therefore, three types of glaciers have switched from slow to fast flow: (1) small glaciers that underwent thermal cycles during and following the LIA (switches between cold- and warm-based conditions), (2) large terrestrial glaciers which remain warm-based throughout the entire surge cycle but develop cold termini during quiescence, and (3) large tidewater glaciers that remain warm-based throughout the surge cycle. Our results demonstrate that thermal switching cannot explain the surges of large glaciers in Svalbard. We apply the concept of enthalpy cycling to the spectrum of surge and surge-like behavior displayed by these glaciers and demonstrate that all Svalbard surge-type glaciers can be understood within a single conceptual framework.

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... The temperature regime within a glacier determines its flow activity and affects the glacial hydrology and is therefore crucial to understand the glacier system (Hagen and Liestøl, 1990). Due to the fact that most of the glaciers in Svalbard are surge type glaciers, the climate change effects cannot just be deduced from the surface length change (Sevestre et al., 2015). Especially surge type glaciers are assumed to be sensitive towards temperature changes concerning the speed and initiation of surging. ...
... At the moment, Von Postbreen is not active. A radar survey performed by Sevestre et al. (2015) with a 100 MHz antenna revealed the same structure that was found by Dowdeswell (1984). A two layered thermal regime, with a cold layer in the ablation zone with a thickness of 70 -110 m and indications of completely cold glacier tongues. ...
... However, the rest of the glacier, is warm based and the warm ice is even up to 200 m thick. The study further showed that in the accumulation zone of Potpeschniggbreen (which is a name for a small glacier contributing to Von Postbreen, indicated as red star in Figure 9) the cool top layer just stops at an altitude of around 725 m above sea level (Sevestre et al., 2015). Von Postbreen corresponds to the polythermal glacier of type E meaning it is mainly temperate ice with a cold surface layer around the ablation zones (Pettersson et al., 2003). ...
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Research has shown that glaciers in Svalbard are very sensitive to the persistence of snow and firn and considerable knowledge gaps concerning the consequences of a changing climate and the effects on glacier accumulation processes are existent. Especially, empirical studies are necessary to update the knowledge by providing much-needed field data for monitoring and model validation. Therefore, this study aims to (i) identify the amount, distribution and properties of snow and firn in the accumulation zone and (ii) to estimate the amount of melt or rainwater which refreezes within the snow/firn. The field campaign for data collection was carried out in spring and summer 2019 in the accumulation zone of four arctic glaciers, Foxfonna, Nordenskiöldbreen, Drønbreen and Von Postbreen all located on the Svalbard archipelago. The snow and firn regime in the glacier accumulation zone were investigated using snow profiles, ground penetrating radar surveys, firn cores and snow depth probing’s. Additionally, an installation with iButtons (temperature loggers) was set up on Nordenskiöldbreen and a station with two highly sensitive thermistor strings were installed on Foxfonna. The temperature datasets were used to model the subsurface temperature evolution and the amount of melt or rainwater refreezing with MATLAB by using a thermodynamic equation and the density evolution modelled through meteorological parameters. Analysis of the obtained GPR data revealed similar accumulation characteristics throughout all collected radargrams. Further a trend of a densifying and thinning firn can be seen. Only the height of the Equilibrium line altitude and therefore also the elevation where the accumulation zone can be found varied. The total amount of refreezing on Foxfonna was modelled to be 593 mm for the first thermistor and 221 mm for the second thermistor string. On Nordenskiöldbreen, the refreezing amount was modelled to be 389 mm using the iButton data. The results of the refreezing modelling indicate that a lot of rainwater percolated into the snowpack and led to refreezing seen in the calculated datasets. Based on the results of this study, further investigations are recommended, especially towards long-time monitoring of the accumulation zone dynamics, to be able to identify trends. Additionally, to understand the effect of refreezing on the glacier mass balance, further research is needed with a broader focus on all melt enhancing processes on the glaciers surface and their mutual influence.
... It is especially crucial to determine glacier volume as precisely as possible, especially when small glaciers are considered [2,3]. Despite the long history of glacier studies in Svalbard, measurements of ice thickness of individual glaciers with geophysical methods or drillings are still scarce [4][5][6][7], etc., due to the remote location of the archipelago. The same can be stated about the determination of the distribution of cold and temperate ice [5][6][7], etc. ...
... Despite the long history of glacier studies in Svalbard, measurements of ice thickness of individual glaciers with geophysical methods or drillings are still scarce [4][5][6][7], etc., due to the remote location of the archipelago. The same can be stated about the determination of the distribution of cold and temperate ice [5][6][7], etc. ...
... Since the first attempts to apply GPR to glacier studies [24] (pp. [4][5][6], a range of its application has been found [3,4,7,14,[25][26][27]. Observing that water inclusions in temperate ice causes intense scattering of GPR signal [5,6,28] provided a powerful tool for detailed mapping of thermal structure of glaciers. ...
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Although measurements of thickness and internal structure of glaciers are substantial for the understanding of their evolution and response to climate change, detailed data about polythermal glaciers, are scarce. Here, we present the first ground-penetrating radar (GPR) measurement data of Irenebreen, and high-resolution DEM and orthomosaic, obtained from unmanned aerial vehicle (UAV) photogrammetry. A combination of GPR and UAV data allowed for the reconstruction of the glacier geometry including thermal structure. We compare different methods of GPR signal propagation speed determination and argue that a common midpoint method (CMP) should be used if possible. Our observations reveal that Irenebreen is a polythermal glacier with a basal temperate ice layer, the volume of which volume reaches only 12% of the total glacier volume. We also observe the intense GPR signal scattering in two small zones in the ablation area and suggest that intense water percolation occurs in these places creating local areas of temperate ice. This finding emphasizes the possible formation of localised temperate ice zones in polythermal glaciers due to the coincidence of several factors. Our study demonstrates that a combination of UAV photogrammetry and GPR can be successfully applied and should be used for the high-resolution reconstruction of 3D geometries of small glaciers.
... N and 17°43.27 E) is a polythermal glacier (Sevestre et al., 2015) located in the Tempelfjorden region of Svalbard. It is approximately 15 km in length and has an area of 168 km 2 (König et al., 2014). ...
... Bamber (1987) applied a reflection coefficient-based analysis of the uppermost internal scattering horizon on similar glaciers across Svalbard from the same surveys, and concluded that it represents a layer of temperate ice with a water content of approximately 3%. In 2012 and 2015, Sevestre et al. (2015) undertook an extensive GPR campaign at 100 MHz, successfully mapping the distribution of temperate ice within the glacier, but encountering strong scattering throughout the deepest ice, precluding the ability to pick the bed confidently throughout. ...
... With the assumption of a constant velocity field, Stolt (Hambrey et al., 2005;Murray et al., 1997;Navarro et al., 2014;Saintenoy et al., 2013) or Kirchhoff migrations (Arcone et al., 1995;Schannwell et al., 2014;Sevestre et al., 2015) have been commonly applied to similar glacier GPR surveys on polythermal glaciers. In exploration seismic imaging, depth migration or reverse time migration (RTM) is undertaken when there are lateral variations in interval velocity due to the effect of energy refraction with depth (Yilmaz, 2001). ...
Article
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Ground‐penetrating radar (GPR) is widely used on polythermal glaciers to image bed topography and detect internal scatter due to water inclusions in temperate ice. The glaciological importance of this is twofold: bed topography is a primary component for modeling the long‐term evolution of glaciers and ice sheets, and the presence of temperate ice and associated englacial water significantly reduces overall ice viscosity. Englacial water has a direct influence on radar velocity, which can result in incorrect observations of bed topography due to errors in depth conversion. Assessment of radar velocities often requires multi‐offset surveys, yet these are logistically challenging and time consuming to acquire, hence techniques to extract velocity from common‐offset data are required. We calculate englacial radar velocity from common offset GPR data collected on Von Postbreen, a polythermal glacier in Svalbard. We first separate and enhance the diffracted wavefield by systematically assessing data coherence. We then use the focusing metric of negative entropy to deduce a migration velocity field and produce a velocity model which varies spatially across the glacier. We show that this velocity field successfully differentiates between areas of cold and temperate ice and can detect lateral variations in radar velocity close to the glacier bed. This velocity field results in consistently lower ice depths relative to those derived from a commonly assumed constant velocity, with an average difference of 4.9 ± 2.5% of local ice depth. This indicates that diffraction focusing and velocity estimation are crucial in retrieving correct bed topography in the presence of temperate ice.
... Before the primary processing, each raw data profile was initialized at the preprocessing stage to ensure the correct positioning from the GPS data, to reset the time to zero and to remove repeated traces (see Table 6) (Sevestre et al., 2015). After that, the primary data processing was undertaken as follows : ...
... The thermal regime and internal structure of glaciers are the dominant factors to determine the flow speed, deformation and glaciers' characteristics (Sevestre et al., 2015). The GPR measurement is a reputable direct approach to examine glacier thermal regime, and Svalbard glaciers have been widely surveyed using this method. ...
... The presence or absence of scattering in the radargrams provides a way to interpret the glacier ice as being either temperate or cold, or a mixture of the two (Navarro and Eisen, 2010), allowing inference of the hydrothermal structure of the glaciers under study. Cold and pure ice is relatively transparent to electromagnetic waves, whereas temperate ice creates scatter as the result of diffractions from water-filled voids (Bamber, 1987;Sevestre et al., 2015). In this study, three types of internal structure and thermal regime were revealed from the radar echo soundings data: a clean-ice, debris-free poly-thermal structure at lower Foxfonna; a debris-free, cold ice-bed structure at Foxfonna icecap, and a post-surge, debris-rich, cold ice-bed structure at Riperbreen. ...
Thesis
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The dwindling volume of Arctic small-size (<30km2) Unmanned Aerial Vehicles (UAVs) photogrammetric reconstructions (3,552 images in September 2020) and Ground-Penetrating Radar (GPR) profiles (40.31km in April 2021) of Foxfonna & Rieperbreen glacier on Svalbard reveal that the total glacier extent is 6.46 km ) glaciers and icecaps provide valuable proxy information about the state of climate over more remote areas. 2 and about 55.08% of the areal extent have been lost since 1936. Comparisons to elevation data obtained from historical aerial photography indicate total mean surface elevation change is -20.50 ± 11.31m from 1961 to 2020, with a constantly accelerating rate of negative elevation change per year. Besides, A total of 56.68% of the ice volume has been lost over 60 years between 1961 and 2020. The presence of scattering zone in the radargram of lower Foxfonna showed a possible area of temperate ice close to the head of the glacier, up to 20 m thick and beneath approximately 100 m of ice. In contrast, the rest of the glacier system was entirely cold. The temperate ice was found to have formed recently, which may be related to the heavily crevassed zone in the uppermost part of lower Foxfonna, and the introduction of surface meltwater during an extreme melt year on the Foxfonna icecap. Thrusting features in Rieperbreen’s radargram revealed a historical surge, which was also indicated by surrounding landforms and historical elevation change. Both Foxfonna and Rieperbreen accumulation areas are too low to take advantage of any positive mass change from the ongoing precipitation increase. The linear extrapolation of estimated ice volume per year suggests that Foxfonna and Rieperbreen will be almost non-existent by the 2050s. These invaluable sources of additional information may be critical in predicting the future prospects of the high Arctic small-size glaciers, which may not exist in the near future.
... Near the terminus, mean annual surface velocities are persistently high (1.6-2.15 to m d −1 ) (Lefauconnier, 1987;Lefauconnier et al., 1994a;Kääb et al., 2005), and summer velocities peak up to 3.2 m d −1 . Such high velocities can only be achieved through basal sliding, which is consistent with the finding of widespread temperate basal conditions at several glaciers in the region (Björnsson et al., 1996;Sevestre et al., 2015). Kongsbreen has a more complex velocity pattern due to its split into two separate terminal branches: the northern, marine-terminating branch of the glacier is fast-flowing, with a maximal speed of 2.7 m d −1 (measured in 2012, Schellenberger et al., 2015), whereas the southern, partially land-terminating branch is slow-moving. ...
... Glaciers in Kongsfjord are polythermal, usually with basal temperatures at or close to the pressure melting point, meaning that water drains at their base all year through (Björnsson et al., 1996;Sevestre et al., 2015;Nuth et al., 2019). Glacial run-off is periodically released into the fjord, where it produces sediment-rich freshwater plumes that are of great importance for the glacio-marine dynamics and the ecosystem of Kongsfjorden (Svendsen et al., 2002;Everett et al., 2018). ...
Article
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By regulating the amount, the timing, and the location of meltwater supply to the glacier bed, supraglacial hydrology potentially exerts a major control on the evolution of the subglacial drainage system, which in turn modulates ice velocity. Yet the configuration of the supraglacial hydrological system has received only little attention in numerical models of subglacial hydrology so far. Here we apply the two-dimensional subglacial hydrology model GlaDS (Glacier Drainage System model) to a Svalbard glacier basin with the aim of investigating how the spatial distribution of meltwater recharge affects the characteristics of the basal drainage system. We design four experiments with various degrees of complexity in the way that meltwater is delivered to the subglacial drainage model. Our results show significant differences between experiments in the early summer transition from distributed to channelized drainage, with discrete recharge at moulins favouring channelization at higher elevations and driving overall lower water pressures. Otherwise, we find that water input configuration only poorly influences subglacial hydrology, which instead is controlled primarily by subglacial topography. All experiments fail to develop channels of sufficient efficiency to substantially reduce summertime water pressures, which we attribute to small surface gradients and short melt seasons. The findings of our study are potentially applicable to most Svalbard tidewater glaciers with similar topography and low meltwater recharge. The absence of efficient channelization implies that the dynamics of tidewater glaciers in the Svalbard archipelago may be sensitive to future long-term trends in meltwater supply.
... signifies metres of water equivalent), for the period 2000-2019 (Schuler et al., 2020). The larger glaciers of SV are typically polythermal, with a temperate base and cold surface layer, whereas the small glaciers are predominantly cold, possibly with only patches of temperate bed (Hagen et al., 1993;Sevestre et al., 2015). Thus, mountain glaciers display low ice velocities, typically on the order of 1-15 m a −1 horizontally (e.g. ...
... However, glacier surges are common in SV (e.g. Jiskoot et al., 2000;Sevestre et al., 2015), but these have been seldom reported for local mountain glaciers over the past several decades. NZ comprises two main mountainous parts: Yuzhny Island and Severny Island. ...
Article
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Small land-terminating mountain glaciers are a widespread and important element of Arctic ecosystems, influencing local hydrology, microclimate, and ecology. Due to their relatively small ice volumes, this class of ice mass is particularly sensitive to the significant ongoing climate warming in the European sector of the Arctic, i.e. in the Barents Sea area. Archipelagos surrounding the Barents Sea, i.e. Svalbard (SV), Novaya Zemlya (NZ), and Franz Josef Land (FJ), host numerous populations of mountain glaciers, but their response to recent strong warming remains understudied in most locations. This paper aims to obtain a snapshot of their state by utilizing high-resolution elevation data (ArcticDEM) to investigate the recent (ca. 2011–2017) elevation and volume changes of 382 small glaciers across SV, NZ, and FJ. The study concludes that many mountain glacier sites across the Barents Sea have been in a critical imbalance with the recent climate and might melt away within the coming several decades. However, deviations from the general trend exist; e.g. a cluster of small glaciers in north SV has been experiencing thickening. The findings reveal that near-stagnant glaciers might exhibit contrasting behaviours (fast thinning vs. thickening) over relatively short distances, which is a challenge for glacier mass balance models but also an opportunity to test their reliability.
... The thermal regime of glaciers is important for several reasons. Warm-based ice can flow more quickly via basal flow or ice surging (e.g., Clarke, 1987;Sevestre et al., 2015), and also enables a range of subglacial hydrological processes that differ from cold-based ice (e.g., exchanges with the groundwater system; chemical weathering, erosion, and mobilisation of sediments in well-developed drainage systems; subglacial water storage). Warmer ice has a lower effective viscosity (Glen, 1955), with variations by a factor of ∼1,000 from temperatures of −50 to 0 • C (Marshall, 2005); hence, deformational velocities in temperate ice are much higher (e.g., Phillips et al., 2010;Bell et al., 2014). ...
... A transition from cold-to warm-based ice has been proposed as the trigger for deglaciation in the context of the 100-kyr glacial cycle (Marshall and Clark, 2002). The effects of basal flow have the potential to be dramatic, as observed in glacier surge cycles, since basal flow rates can greatly exceed those from internal ice deformation (e.g., Clarke, 1987;Sevestre et al., 2015). ...
Article
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Glaciers and ice sheets are experiencing dramatic changes in response to recent climate change. This is true in both mountain and polar regions, where the extreme sensitivity of the cryosphere to warming temperatures may be exacerbated by amplification of global climate change. For glaciers and ice sheets, this sensitivity is due to a number of non-linear and threshold processes within glacier mass balance and glacier dynamics. Some of this is simply tied to the freezing point of water; snow and ice are no longer viable above 0°C, so a gradual warming that crosses this threshold triggers the onset of melting or gives rise to an abrupt regime shift between snowfall and rainfall. Other non-linear, temperature-dependent processes are more subtle, such as the evolution from polythermal to temperate ice, which supports faster ice flow, a shift from meltwater retention to runoff in temperate or ice-rich (i.e., heavily melt-affected) firn, and transitions from sublimation to melting under warmer and more humid atmospheric conditions. As melt seasons lengthen, there is also a longer snow-free season and an expansion of glacier ablation area, with the increased exposure of low-albedo ice non-linearly increasing melt rates and meltwater runoff. This can be accentuated by increased concentration of particulate matter associated with algal activity, dust loading from adjacent deglaciated terrain, and deposition of impurities from industrial and wildfire activity. The loss of ice and darkening of glaciers represent an effective transition from white to grey in the world's mountain regions. This article discusses these transitions and regime shifts in the context of challenges to model and project glacier and ice sheet response to climate change.
... For some polythermal glaciers, a basal thermal transition has been established as a surge mechanism, where basal sliding increases as basal conditions transition from cold to temperate (Clarke et al., 1984;Fowler et al., 2001;Murray et al., 2000). In contrast, Sevestre et al. (2015) proposed a hydrological transition mechanism to explain surging in temperate and polythermal glaciers, in which a surge results from rapid sliding due to an increase in subglacial water flow (Björnsson, 1998;Kamb et al., 1985). A disturbance within till and more efficient water flow also have been proposed as influencing the nature and mechanisms of glacial surges (Boulton and Jones, 1979;Harrison and Post, 2003;Truffer et al., 2000). ...
... A disturbance within till and more efficient water flow also have been proposed as influencing the nature and mechanisms of glacial surges (Boulton and Jones, 1979;Harrison and Post, 2003;Truffer et al., 2000). In addition, a variety of positive feedback mechanisms for all conditions may enhance basal movement, such as deformation feedback and frictional heating (Clarke et al., 1984;Sevestre et al., 2015;Weertman, 1969). ...
Article
Unlike glaciers in other parts of the world, Karakoram glaciers seem to be stable or gaining in mass in response to global climate change, a phenomenon known as 'the Karakoram anomaly'. Many of the glaciers experience irregular, frequent, and sudden advances (surges) that pose an increasing threat of ice dam lake formation and subsequent outburst flooding throughout the region. In this study, we document 179 glacial lake outburst floods (GLOFs) that occurred from 1533 to 2020 in five major valleys. Sixty-four of the events took place after 1970, and 37 of these had remote sensing imagery that covered the GLOF formation to breaching sequence. Thirty-six glaciers were associated with GLOFS due to ice-front advance building ice barriers in rivers. The Kayger and Khurdopin glaciers are the most hazardous examples, being responsible for 31.8% of major GLOFs in the entire Karakoram. Using a cross-correlation feature-tracking technique on remote sensing imagery, we analyzed ten surge glaciers and documented six surge events from 1990 to 2019. Results show periodic surge cycles for the Khurdopin, Kyager, Shishper, and Chilinji glaciers of c. 15-20 years, with a surge velocity in the mid-2010s higher than that of the late 1990s for all studied glaciers. The higher velocity of a glacier increases the risk of flooding downstream of the terminus because the transfer of a huge ice mass towards the terminus during the surge is a key factor for formation and reformation of series of ice-dammed lakes, thus determining the magnitude and frequency of outburst flood events. The response of Karakorum glaciers to global warming and climate forcing, comprising a continuum of glacier mass gain, ice thinning and ice advance, has resulted in lake formation and ice dam failures. We predict the frequency of GLOFs will increase in the future. These findings support the increasing anomalous behavior of glaciers in the Karakoram region. To synthesize the detailed observations , a conceptual model is presented of ice-dammed lake formation and GLOF initiation in response to glacier surging.
... Intense scattering occurs within the transition layer between the ice, subglacial sediments, and bedrock, due to the inclusion of small amounts of water [16]. Therefore, temperate ice with electromagnetic wave creates scatter by numerous stacks of small hyperbolas, which is different from the relatively transparent reflection of cold ice [40]. The energy of the electromagnetic wave is attenuated and greatly decreases when it penetrates ice with melting water that reaches the bottom of the glacier. ...
... (2) Dewow (user's guide of the software) to suppress low-frequency energy emitted by the field near the transmitter, which acts on each trace independently; (3) a Butterworth bandpass filter set the frequency spectrum below and above a filter band to zero, which was set the optimal frequency range between 25 and 180 MHz; (4) automatic gain control (AGC) was applied to strengthen the signals with depth [18][19][20][21][40][41][42]. However, there was still no continuous clear ice-bedrock interface in the GPR data processing results. ...
Article
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Using ground-penetrating radar (GPR), we measured and estimated the ice thickness of the Baishui River Glacier No. 1 of Yulong Snow Mountain. According to the position of the reflected media from the GPR image, combined with the radar waveform amplitude and polarity change information, the ice thickness and the changing medium position at the bottom of this temperate glacier were identified. Water paths were found in the measured ice, including ice caves and crevasses. A debris-rich ice layer was found at the bottom of the glacier, which produces strong abrasion and ploughing action at the bedrock surface. This results in the formation of different detrital layers stagnated at the ice-bedrock interface and numerous crevasses on the bedrock surface. Based on the obtained ice thickness and differential GPS data, combined with Landsat images, the kriging interpolation method was used to obtain grid data. The average ice thickness was 52.48 m and between 4740 and 4890 m above sea level, with a maximum depth of 92.83 m. The bedrock topography map of this area was drawn using digital elevation model from the Shuttle Radar Topography Mission. The central part of the glacier was characterized by small ice basins with distributed ice steps and ice ridges at the upper and lower parts.
... Therefore, it is important to know the distribution of cold and temperate ice masses in glaciers and ice sheets in order to model their dynamics and bottom conditions and estimate their responses to climate change (Blatter and Greve 2015; Hewitt and Schoof 2017; Glazovsky and Macheret 2014). This is particularly important for modern glaciation in Svalbard, Norway -with 1,567 glaciers and a total ice-covered area of ~33,837.5 km 2 (Pfeffer et al. 2014; RGI Consortium 2017) -where 345 gla-ciers were attributed to the surge type (Sevestre et al. 2015). Switches between cold-and warm-based conditions have long been invoked to explain surges (i.e. ...
... The wide distribution of polythermal glaciers in Svalbard was shown by airborne RES measurements performed from 1970 to the 1980s, which detected anywhere from 50 (Jiscoot et al. 2000) to 85 (Glazovsky et al. 1988) glaciers with IRH. Later ground-based RES studies of hydrothermal structure were carried out at a number of Svalbard polythermal glaciers (Björnsson et al. 1996;Jania et al. 2005;Navarro et al. 2005Navarro et al. , 2016Baelum and Benn 2011;Martin-Español et al. 2013;Glazovsky and Macheret 2014;Sevestre et al. 2015). Changes in the hydrothermal structure of two glaciers in Nordenskiöld Land (NL) were discussed by Vasilenko et al. (2014). ...
Article
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The distribution of cold and temperate ice and water in polythermal glaciers is an important characteristic in studying their thermal regime, hydrology, and response to climate change. Data analysis of ground-based radio-echo sounding of 16 glaciers in Nordenskiöld Land in Spitsbergen shows that 5 of them are of cold type and 12 are of polythermal type. The mean thickness of cold and temperate ice in polythermal glaciers varies from 11±2 to 66±6 m and from 6±2 to 96±9 m, respectively, and their ratio varies from 0.30 to 5.31. The volume of temperate ice in polythermal glaciers varies from 0.0009 to 3.733 (±10%) km ³ . With water content of 2% in temperate ice in these glaciers they might contain in total up to ~93.5 × 106 m ³ of liquid water. Radar data suggest the greater water content or greater size of water inclusions in near-bottom temperate ice.
... High sedimentation rates in polythermal glacier catchments on Svalbard (e.g., Hallet et al., 1996;Hodgkins et al., 2003) can be attributed to previous surge activities and the sediment accumulation caused by this dynamic behavior (e.g., Lovell et al., 2015b;Lovell et al., 2018). Similarly high sedimentation rates in cold-based Svalbard glacier catchments can be linked to sediment accumulation during periods of more dynamic behavior and warm-based bed conditions in the Little Ice Age (e.g., Lovell et al., 2015a;Sevestre et al., 2015). In both cases, the sediment will be reworked by gravitational and fluvial processes, leading to high observable sedimentation rates. ...
Article
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Cold glacier beds, i.e., where the ice is frozen to its base, are widespread in polar regions. Common theories state that stable permafrost should exist under glacier beds on shorter timescales, varying from years to decades. Presently, only a few direct measurements of both sub-glacial permafrost and the processes influencing its thermal regime exist. Here, we present subglacial permafrost and active layer measurements obtained from within the basal drainage systems of two cold-based glaciers on Svalbard during the summer melt season. Temperature observations were obtained from subglacial sediment that was accessed through the drainage systems of the two glaciers in the previous winters. The temperature records cover the periods from spring to autumn in 2016 and 2019 at the glaciers Lars-breen and Tellbreen in central Svalbard. The ground temperature below Larsbreen indicates colder ground conditions, whereas the temperatures of the Tellbreen drainage system show considerably warmer conditions, close to the freezing point. We suggest the latter is due to the presence of liquid water all year round inside the Tellbreen drainage system. Both drainage systems investigated show an increase in subglacial sediment temperatures after the disappearance of snow bridges and the subsequent connection to surface melt-water supply at the start of the summer melt season. Temperature records show influence of sudden summer water supply events, when heavy melt and rain left their signatures on the thermal regime and the erosion of the glacier bed. Observed vertical erosion can reach up to 0.9 m d −1 at the base of basal drainage channels during summer. We also show that the thermal regime under the subglacial drainage systems is not stable during summer but experiences several freeze-thaw cycles driven by weather events. Our results show the direct importance of heavy melt events and rain on the thermal regime of subglacial permafrost and the erosion of the glacier bed in the vicinity of subglacial drainage channels. Increased precipitation and surface melt, as expected for future climate, will therefore likely lead to increased degradation of subglacial permafrost, as well as higher subglacial erosion of available sediment around the preferential hydrological paths. This in turn might have significant impacts on proglacial and fjord ecosystems due to increased sediment and nutrient input.
... However, compared to the typical polythermal surge-type glaciers in Svalbard, the Monomah Glacier exhibited a shorter quiescent period (less than 20 years) [21]. The surge cycle can be affected by the local climate [52]. The climate wetting in the Bukatage Massif allowed glaciers to gain mass faster in the upper reaches. ...
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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.
... These surges can begin or end at any seasonal time of year. Hydrological control can explain surging for temperate glaciers and many polythermal glaciers that are already temperate at the base [76]. The subglacial drainage system becomes inefficient during the winter months, increasing the subglacial water pressure and facilitating rapid liding [77,78]. ...
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The inner Tibetan Plateau is a glacierized region where glaciers show heterogeneous change. The Xinqingfeng and Malan ice caps are located in this region, and a transition zone exists with shifting influences between the westerlies and Indian summer monsoon. However, there is a lack of detailed information regarding glacier area and mass changes in this region before 2000. In the present study, we describe an integrated view of the glacier area and its mass changes for Mt. Xinqingfeng and Mt. Malan as derived from topographic maps, Landsat, ASTER, SRTM DEM, and TerraSAR-X/TanDEM-X from 1970 to 2012 and from 1970 to 2018, respectively. Our results show that the glaciers experienced a slight shrinkage in area by 0.09 ± 0.03% a-1 from 1970 to 2018 with a median mass loss rate of 0.22 ± 0.17 m w.e. a-1 and 0.29 ± 0.17 m w.e. a-1 between 1999 and 2012 at Mt. Xinqingfeng and Mt. Malan, respectively. The glaciers of Mt. Malan had a total mass loss of 0.19 ± 0.14 m w.e. a-1 during the period 1970–1999. A minimum of seven glaciers at Mt. Xinqingfeng and Mt. Malan showed heterogeneous variations with either surging or advancing during the observation period. Among them, the West Monuomaha Glacier, Monuomaha Glacier, and Zu Glacier were identified as surging glaciers, and the others may also be surging glaciers, although more evidence is required. These glaciers showed a long active period and low velocities. Therefore, we suggested that thermal controls are important for surge initiation and recession.
... The sediment-bedrock boundary underneath the ice core of the terminal moraine was mapped this way, which was not possible using other geophysical methods. The potential use of antennas with higher frequencies (100 Mhz and higher) in the imaging of the active layer is high, but at the cost of depth resolution and the visualisation of moraine structures (Sevestre et al. 2015;Zhao et al. 2016). In addition, the scattering of GPR waves by loose rock, unconsolidated sediment and water in a partially or fully frozen state further limits the imaging potential. ...
Article
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This article presents the results of a geophysical survey from which detailed images of glacial and periglacial landforms and subsurface structures were obtained. Sediments and landforms on newly deglaciated terrain can be used to reconstruct the extent and character of glaciers in the past and add to the understanding of their response to climate and environmental changes. To derive spatial information from complex geomorphological terrain, joint interpretation of three non-intrusive geophysical methods were applied: Electrical Resistivity Tomography (ERT), Ground Penetrating Radar (GPR), and time-lapse Seismic Tomography. These were used to identify subsurface structures in the forefield of the retreating Hans Glacier in SW Spitsbergen, Svalbard. Three main zones were distinguished and described: outwash plain, terminal moraine from the last glacial maximum, and glacial forefield proximal to the glacier front. Geophysical profiles across these zones reveal information on glacio-fluvial sediment thickness and structure, ice thickness and structure, and bedrock topography. The freezing-thawing effect of the active layer has a strong and deep impact, as demonstrated by variations in P-wave velocity in the obtained outcomes. The results are discussed in the context of the current climate in Svalbard. This study provides a snapshot of ground parameters and the current state of the subsurface in southern Spitsbergen. The boundary between sediment-bedrock layers was estimated to be from 5 to 20 m in depth. It is the first such extensive description of periglacial structures in the forefield of the Hans Glacier, utilising the longest ERT profile (1500 m) in Svalbard together with deep GPR and precise seismic tomography.
... 10). Surging is common during melting events, especially in temperate-based or polythermal Arctic glaciers (Fowler et al., 2001;Sevestre et al., 2015), due to gravitational spreading of the inland ice sheet with the development of tidal calving and ice-stream thinning (Fig. 10). A volcanogenic water supply may have also helped the surging (Björnsson, 2009). ...
Article
Southern Iceland is one of the main outlets of the ice-sheet, and is subject to seismicity of both tectonic and volcanic origins, along the South Iceland Seismic Zone (SISZA sedimentary complex spanning Marine Isotopic Stage 6 to the present includes evidence of both activities. It includes a continuous sedimentary record since the Eemian interglacial period, controlled by a rapid deglaciation, followed by two marine glacioisostasy-forced transgressions, separated by a regression phase connected to an intra-MIS 5e glacial advance. This record has been constrained by tephrostratigraphy and dating. Analysis of this record has provided better insights into the interconnections between hydrology, volcanic and tectonic activity during deglaciations, and glaciations. Low-intensity earthquakes recurrently affected the water-laid sedimentation during the early stages of unloading, accompanying rifting events, dyke injection, and fault reactivations. During full interglacials periods, earthquakes were significantly less frequent, but of higher magnitudes, along the SISZ, in consequence to stress accumulation, favoured by low groundwater levels and more limited magma production. Occurrence of volcanism and seismicity in Iceland is mostly related to rifting events, but subglacial one seems to have been moreover related to stress unlocking related to limited or full unloading/deglaciation events. Major eruptions were mostly located at the melting margin of the ice-sheet.
... These soft-bed configurations can also sustain high water pressure over distributed areas to weaken the till layer and reduce basal resistance to ice flow. Current field observations do not seem able to distinguish the hard-bed and soft-bed configurations or whether there exists a single mechanism for surges (Harrison & Post, 2003;Murray et al., 2003;Pritchard, 2005;Sevestre et al., 2015). ...
Article
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Subglacial drainage systems are known to critically control ice flows, but their spatial configuration and temporal evolution are poorly constrained due to inaccessibility. Here we report a twelve‐year long monitoring of the drainage underneath Bering Glacier, Alaska, by correlating ambient noise recorded at two seismic stations on the sides of the glacier. We find that the seismic surface waves traveling across Bering Glacier slowed down by 1~2% during its latest 2008‐2011 surge, likely due to the switch of the subglacial drainage from a channelized system to a distributed system. In contrast to current models, the relative amplitude of velocity reductions for Rayleigh and Love waves requires the distributed drainage to be highly anisotropic and aligned perpendicular to the ice flow direction. We infer that the subglacial water flow is mainly through a network of transverse basal crevasses during surges, thus can sustain the high water pressure and ice flow speed.
... The surface of the glacier tongue is oriented mainly towards E and NE and is typically inclined at 3-9 . Consistent with other similarly sized glaciers in central Spitsbergen (e.g., Sobota, 2009;Sevestre et al., 2015), Svenbreen is predominantly cold with an ice temperature of ca. −4 C at 8 m below the surface, with slight variation throughout the year, as revealed by borehole thermistor monitoring (J. ...
Article
Arctic glaciers have been, and are predicted to remain, an important sea‐level rise contributor over the 20th and 21st centuries. However, multi‐annual observations of their basic meteorological characteristics, which drive melt processes, are very sparse, contributing to uncertainties in sea‐level rise projections. This paper presents a methodology to process and analyse six years (September 2011–September 2017) of glacier meteorology data collected by an automatic weather station on the ablation zone of a small valley glacier in Svalbard (~79°N). The study focuses on the microclimate of the study glacier and its differences with that of large glaciers in the region, namely slightly increased summer air temperature with steep near‐surface lapse rates, frequently superadiabatic, reduced wind speed and incoming shortwave radiation flux. These differences are likely related to the adjacent complex relief and non‐ice‐covered surfaces within the basin of the study glacier and, as such, pose a challenge for accurate simulation of alpine glacier microclimates in regional melt assessments in the Arctic. The processing routine applied in this paper might serve as a reference for future similar studies. This article is protected by copyright. All rights reserved.
... Potential triggers for surges have been suggested, including the reorganization of the basal hydrological system (Kamb et al., 1985), switching of thermal regime (Fowler et al., 2001;Sevestre et al., 2015) as well as sediment deformation on the glacier bed (Clarke et al., 1984;Björnsson, 1998). East of Lake Viedma, a combination of a source of soft erodible sedimentary rocks and sediments, the presence of a proglacial lake in contact with the glacier and the morphologicaltopographical features of the valley could have contributed to the surge activity of the Lake Viedma Lobe. ...
Article
The valley of Lake Viedma represents one of the main ice flow axes during the Quaternary glaciations of Patagonia. Geomorphological mapping of the eastern sector of the lake, between the shoreline and the end moraine systems attributed to the Last Glaciation, allowed us to recognize a large number of ice-marginal and subglacial landforms. The landform assemblage of this area matches with previous models of surging glacier landsystems around the world. We identified the three geomorphological zones that characterise surging glacier landsystems, with some mixing of the zones, possibly related to multiple surges. The outer zone includes push moraines, thrust-block moraines, overridden moraines and hummocky moraines. In the middle zone, overridden moraines and hummocky moraines were developed. Finally, the inner zone is composed of megaflutes, crevasse-squeeze ridges, eskers and till eskers in a till plain. We interpreted these geomorphological features as evidence of surge activity of the Lake Viedma Lobe. A combination of topographic setting, soft-bedrock and the presence of a proglacial lake in contact with ice could have contributed to the development of surge activity in the Viedma paleoglacier. It could have been triggered by a change in the glacial thermal regime of the Viedma paleoglacier from polar during the Last Glacial Maximum to polythermal or temperate during the beginning of the Late Glacial.
... Most glaciers in Svalbard today are classified as polythermal, i.e., they are cold-based at their margins and depending on their thickness, temperate at the base in central parts of the glacier (Hagen et al., 1993). It has also been argued that several smaller glaciers in the central part of Svalbard underwent a thermal cycle during the "Little Ice Age" (LIA) (Sevestre et al., 2015) shifting from an early-LIA cold-based state, to a temperate state during the LIA maximum before returning to a cold-based state post-LIA (Lovell et al., 2015). Such changes could have led to surge-type behavior when the glaciers changed from an initial cold-based state to a temperate state, with increased sliding before returning to a cold state. ...
Article
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A process-based understanding of lacustrine deposited sediments in Arctic lakes is essential to set the present warming and hydroclimatic shift into perspective. From such a perspective, we can enhance our understanding of the natural climate variability in the Arctic. Here, we present work from the northern coast of Spitsbergen in which we unravel the sediment sequence from a distal glacier-fed lake, Vårfluesjøen. Utilizing recent methodological and technological developments, we base our interpretation on new tools that better visualize and characterize the sediments cores. High-resolution X-ray Computed Tomography (X-ray CT) is used to visualize the lake sediments and quantify the sand-sized particles found in the 210Pb- and radiocarbon-dated sediments, together with a multi-proxy approach including measurement of their physical, geochemical, and magnetic properties. Our findings suggest that Vårfluesjøen (6 m a.s.l.) was isolated from Woodfjorden at c. 10200 ± 260 cal. yr. BP. During the early Holocene, the glaciers in the Vårfluesjøen catchment were considerably smaller than today or had even melted completely. At the start of the Neoglacial period (c. 3500 cal. yr. BP), we find increased glacier activity in the catchment of the lake. X-ray CT reveals an increased frequency of sand-sized particles from 3500 to 1750 cal. yr. BP, suggesting greater wintertime aeolian activity. Starting c. 2250 years ago, we find a progressive increase in snowmelt runoff in the Vårfluesjøen catchment, with peak runoff from 1000 to 750 cal. yr. BP. This coincides with a drop in sand-sized particles, hence less favorable environment for aeolian activity, and implying wetter conditions. During the last 2000 years, there is evidence for high glacier activity between c. 2000 to 900 and 750–350 cal. yr. BP. In between these time spans, less activity is recorded in the periods 1900–1800, 1000–800, and 350–150 cal. yr. BP.
... Clusters of surge-type glaciers are found in mountain regions around the world, including the Tibetan Plateau 7,9,11 . Processes involved in the lowering of basal friction required for surging include abnormally high water pressure 8,11,12 , change in the thermal regime 10,11,13,14 and complex responses of subglacial till rheology to increasing shear stress and water input 6,8,11,12,[15][16][17] . ...
Article
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Surges and glacier avalanches are expressions of glacier instability, and among the most dramatic phenomena in the mountain cryosphere. Until now, the catastrophic collapse of a glacier, combining the large volume of surges and mobility of ice avalanches, has been reported only for the 2002 130 × 10^6 m3 detachment of Kolka Glacier (Caucasus Mountains), which has been considered a globally singular event. Here, we report on the similar detachment of the entire lower parts of two adjacent glaciers in western Tibet in July and September 2016, leading to an unprecedented pair of giant low-angle ice avalanches with volumes of 68 ± 2 × 10^6 m3 and 83 ± 2 × 10^6 m3. On the basis of satellite remote sensing, numerical modelling and field investigations, we find that the twin collapses were caused by climate- and weather-driven external forcing, acting on specific polythermal and soft-bed glacier properties. These factors converged to produce surge-like enhancement of driving stresses and massively reduced basal friction connected to subglacial water and fine-grained bed lithology, to eventually exceed collapse thresholds in resisting forces of the tongues frozen to their bed. Our findings show that large catastrophic instabilities of low-angle glaciers can happen under rare circumstances without historical precedent.
... This could increase basal water pressures and reduce till strength in the glacier tongue areas. Through these seemingly contrasting mechanisms of increased basal freezing and enhanced meltwater production, both imposed by atmospheric warming, changes in climate could therefore orchestrate a temporal clustering of surging on decadal timescales, providing a viable explanation for the rather large number of Svalbard tidewater glacier surge events at the end of the Little Ice Age 22,40 , and now also more recently 42 . The similarity between the mechanism here with the binge-purge oscillations described for ice stream behavior 43,44 , for example in Heinrich events, is fascinating as both are controlled by basal freezing. ...
Article
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Glacier flow instabilities can rapidly increase sea level through enhanced ice discharge. Surge-type glacier accelerations often occur with a decadal to centennial cyclicity suggesting internal mechanisms responsible. Recently, many surging tidewater glaciers around the Arctic Barents Sea region question whether external forces such as climate can trigger dynamic instabilities. Here, we identify a mechanism in which climate change can instigate surges of Arctic tidewater glaciers. Using satellite and seismic remote sensing observations combined with three-dimensional thermo-mechanical modeling of the January 2009 collapse of the Nathorst Glacier System (NGS) in Svalbard, we show that an underlying condition for instability was basal freezing and associated friction increase under the glacier tongue. In contrast, continued basal sliding further upstream increased driving stresses until eventual and sudden till failure under the tongue. The instability propagated rapidly up-glacier, mobilizing the entire 450 km2 glacier basin over a few days as the till entered an unstable friction regime. Enhanced mass loss during and after the collapse (5–7 fold compared to pre-collapse mass losses) combined with regionally rising equilibrium line altitudes strongly limit mass replenishment of the glacier, suggesting irreversible consequences. Climate plays a paradoxical role as cold glacier thinning and retreat promote basal freezing which increases friction at the tongue by stabilizing an efficient basal drainage system. However, with some of the most intense atmospheric warming on Earth occurring in the Arctic, increased melt water can reduce till strength under tidewater glacier tongues to orchestrate a temporal clustering of surges at decadal timescales, such as those observed in Svalbard at the end of the Little Ice Age. Consequently, basal terminus freezing promotes a dynamic vulnerability to climate change that may be present in many Arctic tidewater glaciers.
... The ice within a polythermal glacier can be classified according to its temperature: it is "cold" when its temperature is below the pressure melting point, while it is "warm" if at the pressure melting point (Lorrain and Fitzsimmons, 2011). The presence and distribution of such types of ice result in a complex glacier thermal regime which affects many aspects of glaciers' dynamics, such as its hydrology (Irvine-Fynn et al., 2011), water supply, and rapid hydrological events (Sevestre et al., 2015). So, it is essential to improve the characterization of the internal structure of glaciers to better understand the mechanisms leading to changes in their thermal regime. ...
Conference Paper
We exploit the attribute analysis of GPR data to analyze the different EM responses of the ice of two alpine glaciers. We focus on frequency-related attributes to identify zones with higher attenuation of EM signal, which could be further related to higher water content and higher electrical conductivity. We succeeded in associating the scattering facies to warm ice zones of the Marmolada glacier, further linked to the thickness of the snow cover, and to a layer of mixed debris and ice of the Eastern Gran Zebrù glacier. Moreover, we conducted automated diffraction hyperbolas analyses to gain insight into the basal thermal conditions and glaciological facies.
... The GrIS has active subglacial hydrology with extensive regions of saturated sediments (Jordan et al., 2018;MacGregor et al., 2016), which allows for microbial activity and may contribute more aromatic DOM signatures at the onset of melt (Kellerman et al., 2020b;O'Donnell et al., 2016). Svalbard glaciers, on the other hand, are a mixture of cold-and polythermal-based glaciers (Sevestre et al., 2015). Outflow from cold-based glaciers originates from direct supraglacial inputs and ice-marginal flow, whereas the warm bases of polythermal glaciers allow for the interaction of supraglacial water with the basal environment as it is routed through subglacial channels to the outflow portal ( tential sources for each glacier may further explain the larger compositional variance in Svalbard rivers, compared to the similarity of outflow from Russell Glacier (Figures 4 and 5). ...
Article
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Glaciers and ice sheets cover over 10 % of Earth's land surface area and store a globally significant amount of dissolved organic matter (DOM), which is highly bioavailable when exported to proglacial environments. Recent rapid glacier mass loss is hypothesized to have increased fluxes of DOM from these environments, yet the molecular composition of glacially derived DOM has only been studied for a handful of glaciers. We determine DOM composition using ultrahigh resolution mass spectrometry from a diverse suite of Arctic glacial environments, including time series sampling from an ice sheet catchment in Greenland (Russell Glacier) and outflow from valley glaciers in catchments with varying degrees of glacial cover in Svalbard. Samples from the Greenland outflow time series exhibited a higher degree of similarity than glacier outflow between glaciers in Svalbard; however, supraglacial meltwater samples from Greenland and Svalbard were more similar to each other than corresponding glacial outflow. Outflow from Russell Glacier was enriched in polyphenolic formulae, potentially reflecting upstream inputs from plants and soils, or inputs from paleosols overridden by the ice sheet, whereas Svalbard rivers exhibited a high level of molecular richness and dissimilarity between sites. When comparing DOM compositional analyses from other aquatic systems, aliphatic, and peptide-like formulae appear particularly abundant in supraglacial meltwater, suggesting the DOM quickly metabolized in previous incubations of glacial water originates from energy-rich supraglacial sources. Therefore, as glaciers lose mass across the region, higher-quality fuel for microbial degradation will increase heterotrophy in coastal systems with ramifications for carbon cycling.
... 4 For example, due to the low frequencies often used in ground-based glaciological radio-echo sounding (Scott et al., 2010;Sevestre et al., 2015;King et al., 2016), lengthy dipole antennas are often towed in-line to the survey direction and as such cannot be modeled accurately using 2D FDTD algorithms. ...
Article
Finite-difference time-domain (FDTD) forward modeling is often used to gain a more quantitative understanding of the interactions between electromagnetic fields and targets. To undertake full 3D simulations the computational demands are challenging, so simulations are often undertaken in 2D where assumptions in the propagation of electromagnetic fields and source type can result in errors. We develop the concept of a sliced-3D simulation, wherein a thin slice of a 3D domain with strictly 2D geometry is used to minimize computational demands while obtaining synthetic waveforms that contain full 3D propagation effects. This approach requires optimization of perfectly matched layer (PML) boundary condition parameters so as to minimize the errors associated with the source being located close to the boundary, and as a result of grazing-incident angle wave conversion to evanescent energy. We explore the frequency dependence of PML parameters, and establish a relationship between complex frequency stretching parameters and effective wavelength. The resultant parameter choice is shown to minimize propagation errors in the context of a simple radioglaciological model, where 3D domains may be prohibitively large, and for a near-surface cross-borehole survey configuration, a case where full waveform inversion may typically be used.
... The distribution of warm and cold ice results in complex and still not fully understood thermal regime, which affects glaciers' hydrology and drainage system (Irvine-Fynn et al., 2011) and is responsible for surging events (Fowler et al., 2001). Thermal characterization of glaciers is a highly investigated issue, especially in Swiss Alps (Eisen et al., 2009;Rutishauser et al., 2016), Scandinavia (Pettersson et al., 2003;Gusmeroli et al., 2012;Reinardy et al., 2019), Svalbard (Sevestre et al., 2015), Canadian Arctic (Blatter and Hutter, 1991;Delcourt et al., 2013) and Chilean Andes (Gacitùa et al., 2015), among the other zones. In any case, it is essential to highlight that the number of scattering events depends not only on the water and/or debris content, but also on the frequency (or, better, on the spectral content) of the antennas used to perform the GPR survey (Björnsson et al., 1996). ...
Article
In GPR profiles, ice is usually imaged as a mostly electromagnetic transparent facies. However, diffraction events, as well as internal layering, can be also observed. In some cases, the bedrock below glaciers is masked by dense diffractions usually interpreted as the effect of liquid water pockets inside the so-called warm ice. However, the actual physical meaning of such GPR facies is not always obvious, because it can be related also to mixed debris and ice deposits. We adopted a strategy well known in medical sciences and referred as “differential diagnosis” in order to infer which is the actual meaning of a high scattering facies imaged within the Eastern Gran Zebrù glacier (Central Italian Alps) and, more generally, of all the internal glacier features. In fact, in many cases, there is no direct information to limit the subjectivity of geophysical interpretation; therefore, we provide all the discriminative hypotheses based on both independent and integrated criteria including GPR attribute analysis, imaging effects, reflection analysis, GPR frequency evaluations combined with geomorphological and remote sensing data obtained by two photogrammetric UAV and thermal infrared surveys. On the basis of the differential diagnosis, we concluded that the high scattering zone embedded within the studied glacier is most likely related to a mixture of ice and debris probably formed during a past shrinking phase. Beside this case study, this approach could be helpful in other GPR glaciological surveys, in which the target is related not only to the bedrock detection, but also to a detailed analysis of the internal facies of a glacier.
... Дополнительные источники тепла в самой его толще -диссипативный разогрев изза деформации льда, трение ледника о ложе, трение текущей воды во внутриледниковых каналах, по вторное замерзание воды в порах снега и фирна, геотермический поток тепла. Эти источники во многом определяют распределение холодного и тёплого льда и воды в толще и у ложа ледника и влияют на их гидротермическую структуру и ди намику [1][2][3][4]. Сосуществование холодного и тёп лого льда в политермических ледниках заметно влияет на их механические и гидрологические свойства [5]. В частности, термический барьер из холодного льда на языке препятствует стоку под ледниковых вод, создавая угрозу их прорыва [4]. ...
... Overall, glaciers of SV are known to lose mass over many past decades, recently at -8 Gt a -1 , equivalent to ca. -0.23 m w.e. a -1 (2000( , Schuler et al., 2020. Larger glaciers of SV are typically polythermal, with a temperate base and cold surface layer, whereas small glaciers are predominantly cold, possibly with only patches of temperate bed (Hagen et al., 1993;Sevestre et al., 2015). Thus, mountain glaciers display low ice velocities, typically 90 on the order of 1-15 m a -1 horizontally (e.g. ...
Preprint
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Small land-terminating mountain glaciers are a widespread and important element of Arctic ecosystems, influencing local hydrology, microclimate, and ecology, among others. Due to little ice volumes, this class of ice masses is very sensitive to climate warming, the latter of which is extremely well manifested in the European sector of the Arctic, i.e. in the Barents Sea area. Archipelagos surrounding the Barents Sea, i.e. Svalbard (SV), Novaya Zemlya (NZ), and Franz Josef Land (FJ), host numerous populations of mountain glaciers, but their response to recent strong warming remains understudied in most locations. This paper aims to obtain a snapshot of their state by utilizing high-resolution elevation data (ArcticDEM) to investigate the recent (ca. 2011–2017) elevation and volume changes of 382 small glaciers across SV, NZ, and FJ. The study concludes that many mountain glacier sites across the Barents Sea have been in a critical imbalance with the recent climate and might melt away within the coming several decades. However, deviations from the general trend exist, e.g. a cluster of small glaciers in north SV experiencing thickening. The findings reveal that near-stagnant glaciers might exhibit contrasting behaviours (fast thinning vs. thickening) over relatively short distances, being a challenge for climate models, but also an opportunity to test their reliability.
Thesis
Accurately predicting the future dynamic contribution to mass loss from the ice caps of the High Arctic requires an improved understanding of the basal conditions of these ice bodies. An adjoint method numerical inversion is therefore applied to elucidate the basal and englacial conditions of Devon Ice Cap in the Canadian Arctic Archipelago, which exhibits a variety of changes to flow dynamics in recent years. These include the surge of Southeast1 and Southeast2 Glaciers, which is suggested to be thermally-regulated. A cryo-hydraulic warming feedback may contribute to the acceleration during this surge as an additional source of heat or water is required for the base of sliding areas to reach pressure melting point. During the active phase of the surge, freezing rates increase as the basal temperature gradient increases dramatically, leading to enhanced conductive heat loss which is not countered by additional frictional heating as the weakened till provides less resistance to flow. The termination of this surge could therefore result from water withdrawal from the underlying till without the need for changes to geometry. Glaciers defined as pulsing consistently had lower basal shear stresses when velocities were higher, but different pulses produced different changes to the basal conditions, making it difficult to suggest a mechanism for these events. The cause of the unequal periods of faster and slower flow observed on the Croker Bay Glaciers also remains uncertain. However, changes to water storage in the till layer are far smaller than interannual variability in surface meltwater reaching the bed, suggesting this could play some role in modulating till strength, thus flow speeds. The bed of Belcher Glacier provides very little resistance to flow near the terminus, supporting the hypothesis that its acceleration is a result of the thinning and retreat of the terminus reducing resistive stresses.
Article
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Understanding glacier drainage system behaviour and its response to increased meltwater production faces several challenges in the High Arctic because many glaciers are transitioning from polythermal to almost entirely cold thermal structures. We, therefore, used ground-penetrating radar data to investigate the thermal structure and drainage system of Waldemarbreen in Svalbard: a small High Arctic glacier believed to be undergoing thermal change. We found that Waldemarbreen retains up to 80 m of temperate ice in its upper reaches, but this thickness most likely is a relict from the Little Ice Age when greater ice volumes were insulated from winter cooling and caused greater driving stresses. Since then, negative mass balance and firn loss have prevented latent heat release and allowed near-surface ice temperatures to cool in winter, thus reducing the thickness of the temperate ice. Numerous reflectors that can be traced up-glacier are interpreted as englacial channels formed by hydrofracturing in the crevassed upper region of the glacier. The alternative cut and closure mechanism of conduit initiation only forms conduits in parts of the lower ablation area. Consequently, Waldemarbreen provides evidence that hydrofracturing at higher elevations can play a major role in englacial water drainage through cold ice.
Article
There have been numerous reports that surges of tidewater glaciers in Svalbard were initiated at the terminus and propagated up-glacier, in contrast with downglacier-propagating surges of land-terminating glaciers. Most of these surges were poorly documented, and the cause of this behavior was unknown. We present detailed data on the recent surges of two tidewater glaciers, Aavatsmarkbreen and Wahlenbergbreen, in Svalbard. High-resolution time series of glacier velocities and evolution of crevasse patterns show that both surges propagated up-glacier in abrupt steps. Prior to the surges, both glaciers underwent retreat and steepening, and in the case of Aavatsmarkbreen, we demonstrate that this was accompanied by a large increase in driving stress in the terminal zone. The surges developed in response to two distinct processes. (1) During the late quiescent phase, internal thermodynamic processes and/or retreat from a pinning point caused acceleration of the glacier front, leading to the development of terminal crevasse fields. (2) Crevasses allowed surface meltwater and rainwater to access the bed, causing flow acceleration and development of new crevasses up-glacier. Upward migration of the surge coincided with stepwise expansion of the crevasse field. Geometric changes near the terminus of these glaciers appear to have led to greater strain heating, water production, and storage at the glacier bed. Water routing via crevasses likely plays an important role in the evolution of surges. The distinction between internally triggered surges and externally triggered speedups may not be straightforward. The behavior of these glaciers can be understood in terms of the enthalpy cycle model.
Article
Ice dammed glacial lake outburst floods (GLOFs) associated with surge glaciers are increasing in response to climate change. Predicting the phenomenon to protect downstream communities remains challenging around the globe. Surge-type glaciers are characterized by unsteady movements and frequent frontal advances, which cause natural hazards by obstructing river channels, forming ice-dammed lakes, which can cause GLOFs, posing threats downstream. The determination of the surge characteristics, timing and evolution of lakes and GLOFs is fundamental to flood control and disaster management. In this study, the case of the Khurdopin Glacier (Karakoram) is used to elucidate key behavioral characteristics of surging glaciers that usefully can be applied to understand the GLOF hazard from glaciers worldwide. Seven surge periodical cycles associated with the Khurdopin Glacier that occurred at intervals of 19–20 years between 1880 and 2020 were investigated using a GLOF dataset. The ice flow dynamics of three surge events that occurred between 1970 and 2020 were analyzed using high-resolution satellite imagery. The results indicate that the maximum and minimum surge velocities control the conduit development that drains lakes resulting in a number of GLOFs. A surge between 1998 and 2002 generated six GLOFs. A subglacial drainage model was developed to estimate the timing of the peak discharge in GLOF hydrographs. The results show that conduit melt enlargement becomes the dominant drainage process at one-third of the rising limb. These floods' high peak discharges and short durations are primarily due to the higher lake water temperature, which controls the conduit enlargement rate. Based on the current study results, the proposed model can be adopted worldwide for surge-type glaciers. The initiation of the main surge period, which leads to lake formation, can be anticipated, as the pre-surge period can be identified using remote-sensing analysis. The timing of ice-dammed lake formation and GLOFs can be estimated, providing residents and authorities time to take precautionary measures and thus limiting damage downstream.
Thesis
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Glacier hydrology describes water movement around, on, in and under glaciers. It plays an important role for glacier flow and thus ice transport into the sea and the associated sea level rise. It is further relevant for nutrient transport and release into ecosystems, for hydropower, and for drinking water supply in glaciated regions. Glacier related flood events are additionally a frequent geohazard, emphasizing the importance of accurate knowledge of glacier hydrology. This knowledge is, however, very limited due to general inaccessibility of glacial subsurface flows and thus lack of direct observations and technologies that could provide them. The present thesis therefore develops novel technologies, allowing to observe and study water flow inside glacial channels in detail, and applies them on Svalbard glaciers. For this, sensing drifters are proposed and their statistical repeatability tested. The instruments are then used to study water flow over glacier surfaces. Further, a method to reconstruct flow paths from drifter data is proposed and showcased with the example of a channel within a glacier. Additional speleological investigations provide permafrost temperatures under Svalbard glaciers and highlight the importance of meteorological glacier surface conditions for temperature and erosion of the glacier bed.
Article
Kuannersuit Glacier in west Greenland experienced a major surge in 1995–1998, where the glacier advanced 10.5 km down-valley. In this paper, we examine how the quiescent phase has progressed until 2015 with respect to ice dynamics, landform formations and glaciomorphological changes. In the initial quiescent phase (2001–2005), ice velocities along the center flowline were 37–55% higher than ice velocities (6.3–9.0 m yr⁻¹) in 2005–2015, and a linear relationship between ice velocity and distance from the glacier front, which existed during the initial quiescent phase, had disappeared in 2005–2015. Between 2001 and 2015, the post-surge glacier tongue thinned by 84.0 ± 6.3 m, equal to 6.0 ± 0.5 m yr⁻¹. The 30-m high terminal moraine detached from the active glacier along the uppermost thrust band between 2005 and 2015, after which the glacier front receded 1.5 km. Between the terminal moraine and the glacier front, observations suggested that a proximal outwash plain was forming on top of glacier ice and that glacier naled (icing, aufeis) was incorporated into the outwash plain. In less dynamic areas with gently sloping topography along the lateral glacier margins, crevasse-squeeze ridges were melting out. The most prominent glaciomorphological feature in 2015 was a c. 1-km long gorge with c. 30–40 m high ice cliffs. This gorge had formed into the glacier front, following the collapse of a series of chasms above the main subglacial channel. Roof collapse processes above subglacial channels had a significant impact on the glacier's mass loss and on the glaciomorphology during the quiescent phase. Earlier observations from 1913 suggest that the formation of this gorge is a reoccurring phenomenon during the quiescent phase. A lower pothole field on the glacier tongue that existed during the initial quiescent phase had completely disappeared in 2015, while a larger upper pothole field in the reservoir area prevailed. During the initial quiescent phase, the subglacial drainage system developed into a stable channelized network, although a jökulhlaup from a large ice-dammed lake occurred. This single event was dated to have occurred between 11 and 13 August 2006, and the lake did not refill. The spatiotemporal association and evolution of glacial and glaciomorphological landforms at Kuannersuit Glacier are likely similar to processes at many other surging and rapidly receding glaciers of similar size.
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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.
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Although many convincing, diverse, and sometimes competing models of glacier surging have been proposed, the observed behavior of surging glaciers does not fit into distinct categories, and suggests the presence of a universal mechanism driving all surges. On the one hand, recent simulations of oscillatory flow behavior through the description of transient basal drag hint at a fundamental underlying process. On the other hand, the proposition of a unified model of oscillatory flow through the concept of enthalpy adopts a systems based view, in an attempt to rather unify different mechanisms through a single universal measure. While these two general approaches differ in perspective, they are not mutually exclusive, and seem likely to complement each other. A framework incorporating both approaches would see the mechanics of basal drag describing ice flow velocity and surge propagation as a function of forcing by conditions at the glacier bed, in turn modulated through the unified measure of enthalpy.
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Analysis of a recent surge of Morsnevbreen, Svalbard, is used to test predictions of the enthalpy balance theory of surging. High-resolution time series of velocities, ice thickness and crevasse distribution allow key elements of the enthalpy (internal energy) budget to be quantified for different stages of the surge cycle. During quiescence (1936–1990), velocities were very low, and geothermal heat slowly built-up enthalpy at the bed. Measurable mass transfer and frictional heating began in 1990–2010, then positive frictional heating-velocity feedbacks caused gradual acceleration from 2010 to 2015. Rapid acceleration occurred in summer 2016, when extensive crevassing and positive air temperatures allowed significant surface to bed drainage. The surge front reached the terminus in October 2016, coincident with a drop in velocities. Ice plumes in the fjord are interpreted as discharge of large volumes of supercooled water from the bed. Surge termination was prolonged, however, indicating persistence of an inefficient drainage system. The observations closely match predictions of the theory, particularly build-up of enthalpy from geothermal and frictional heat, and surface meltwater, and the concomitant changes in ice-surface elevation and velocity. Additional characteristics of the surge reflect spatial processes not represented in the model, but can be explained with respect to enthalpy gradients.
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By regulating the amount, the timing and the location of meltwater supply to the glacier bed, supraglacial hydrology potentially exerts a major control on the evolution of the subglacial drainage system, which in turn modulates sliding. Yet the configuration of the supraglacial hydrological system has received only little attention in numerical models of subglacial hydrology so far. Here we apply the two dimensional subglacial hydrology model GlaDS to a Svalbard glacier basin with the aim of investigating how the spatial distribution of meltwater recharge affects the characteristics of the basal drainage system. We design four experiments with various degrees of complexity in the way that meltwater is delivered to the subglacial drainage model. Our results show significant differences between experiments in the early-summer transition from distributed to channelized drainage, with discrete recharge at moulins favouring channelization and driving earlier rise in basal water pressure. Otherwise, we find that water input configuration only poorly influences subglacial hydrology, which is controlled primarily by subglacial topography. All experiments fail to develop channels of sufficient efficiency to substantially reduce summertime water pressures, which we impute to small surface gradients and short melt seasons. The findings of our study may be extended to most Svalbard tidewater glaciers with similar topography and low meltwater recharge. The absence of efficient channelization implies that the dynamics of tidewater glaciers in the Svalbard archipelago may be sensitive to future long-term trends in meltwater supply.
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This study examines how longitudinal foliation develops in glaciers and ice sheets in a wide range of topographic, climatic, and dynamic settings, at a variety of spatial scales. Study locations include four valley glaciers in Svalbard (Austre Brøggerbreen, Midtre Lovénbreen, Austre Lovénbreen, and Pedersenbreen), a valley glacier in Canada (Sermilik Glacier), and seven outlet glaciers in Antarctica (Hatherton Glacier, Taylor Glacier, Ferrar Glacier, Lambert Glacier, Recovery Glacier, Byrd Glacier, and Pine Island Glacier). Detailed structural mapping of the valley glaciers from satellite imagery and field-based measurements were used to document the formation of longitudinal foliation in small-scale ice masses. These findings were ‘up-scaled’ and applied to much larger glaciers and ice streams. Longitudinal foliation develops in concentrated bands at flow unit boundaries as a result of enhanced simple shear. However, longitudinal foliation is not directly observable from satellite imagery at the surface of larger-scale valley glaciers. The longitudinal structures visible at the surface of larger-scale glaciers form at flow-unit boundaries and are composed of bands of steeply dipping longitudinal foliation; however, they appear as individual linear features on satellite imagery as a result of the comparatively low spatial resolution of the imagery. The persistence of flowlines in the Antarctic Ice Sheet through areas of crevassing and net ablation (blue-ice areas) suggests that they are the surface representation of a three-dimensional structure. Flowlines are therefore inferred to be the surface expression of flow-unit boundaries composed of bands of steeply dipping longitudinal foliation. The survival and deformation of flowlines in areas of ice flow stagnation indicates that flowlines form in their initiation zones and not along their entire length. Furthermore, these ice stagnation areas indicate that flowlines record past ice dynamics and switches in ice flow.
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Recent speleological surveys of meltwater drainage systems in cold and polythermal glaciers have documented dynamic englacial and in some cases subglacial conduits formed by the ‘cut-and-closure’ mechanism. Investigations of the spatial distribution of such conduits often require a combination of different methods. Here, we studied the englacial drainage system in the cold glacier Longyearbreen, Svalbard by combining speleological exploration of a 478 m long meltwater conduit with a high-resolution ground penetrating radar (GPR) survey with two different centre-frequencies (25 and 100 MHz). The results yielded a 3-D documentation of the present englacial drainage system. The study shows that the overall form of englacial conduits can be detected from velocity−depth converted GPR data, and that the 3-D model can facilitate a method to pinpoint the reflections in a radargram corresponding with the englacial drainage system, although fine detail cannot be resolved. Visible reflections approximately parallel to the mapped englacial water drainage system likely result from sediment incorporated in the ice or from abandoned parts of the englacial drainage system.
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Glacier surges are cyclic oscillations of velocity and mass resulting from internal dynamic instabilities. For surge-type glaciers, cycles of advance and retreat are decoupled from climate forcing, so it is important to consider the possibility that former glaciers may have been surge-type when making climatic inferences from their dimensions and chronologies. In this paper, climatic and glacier geometric data are used to show that Scotland was likely the location of a surge cluster during the Loch Lomond Stade (∼12.9–11.7 ka), with high probabilities of surging for outlets of the West Highland Icefield and the larger glaciers in the Inner Hebrides and Northern Highlands. Terrestrial and marine landforms consistent with surging occur in all of these areas, and it is proposed that surge-type glaciers existed on the Islands of Skye and Mull, in the Northern Highlands, and in a ‘surging arc’ along the western, southern and south-eastern margins of the West Highland Icefield. The possibility that surge-type glaciers were widespread in Scotland during the Loch Lomond Stade offers a fresh perspective on some long-standing issues, including the relationship between style of deglaciation and climate change, the climatic significance of glacial chronologies, palaeoclimatic reconstructions, and the interpretation of numerical model results.
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Negribreen, a tidewater glacier located in central eastern Svalbard, began actively surging after it experienced an initial collapse in summer 2016. The surge resulted in horizontal surface velocities of more than 25 m d ⁻¹ , making it one of the fastest-flowing glaciers in the archipelago. The last surge of Negribreen likely occurred in the 1930s, but due to a long quiescent phase, investigations of this glacier have been limited. As Negribreen is part of the Negribreen Glacier System, one of the largest glacier systems in Svalbard, investigating its current surge event provides important information on surge behaviour among tidewater glaciers within the region. Here, we demonstrate the surge development and discuss triggering mechanisms using time series of digital elevation models (1969–2018), surface velocities (1995–2018), crevasse patterns and glacier extents from various data sources. We find that the active surge results from a four-stage process. Stage 1 (quiescent phase) involves a long-term, gradual geometry change due to high subglacial friction towards the terminus. These changes allow the onset of Stage 2, an accelerating frontal destabilization, which ultimately results in the collapse (Stage 3) and active surge (Stage 4).
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In this study, 110 tidewater glaciers from Spitsbergen were studied to characterize the frontal zone using morphometric indicators. In addition, their time variability was also determined based on features of the active phase of glacier surges. Landsat satellite imagery and topographic maps were used for digitalization of the ice-cliffs line. In recent years (2014–2017) all the glaciers studied can be thus classified as: stagnant (33%), retreating and deeply recessing (33%), starting to move forward/fulfilling the frontal zone (23%), and surging (11%). Indicators of the glacier frontal zone (CfD and CfE) allow to identify the beginning and the end of the active phase through changes in their values by ca. 0.05–0.06 by the year and get even bigger for large glaciers as opposed to typical interannual differences within the limits of ±0.01 to 0.02. The active phase lasted an average of 6–10 years. The presence of a “glacier buttress system” and the “pointed arch” structure of the ice-cliff seem to be an important factor regulating the tidewater glacier stability.
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The detachment of large parts of low-angle mountain glaciers, resulting in massive ice-rock avalanches, have so far been believed to be a unique type of event, made known to the global scientific community first for the 2002 Kolka Glacier detachment, Caucasus Mountains, and then for the 2016 collapses of two glaciers in the Aru range, Tibet. Since 2016, several so-far unknown glacier detachments have been discovered and described, and new ones occurred. In the current contribution, we compile, compare and discuss 19 actual or possible large-volume detachments of low-angle mountain glaciers at nine different sites in the Caucasus, the Pamirs, Tibet, Alaska’s St. Elias mountains, and the Southern Andes. Many of the detachments reached volumes in the order of 10–100 million m3. Commonalities and differences between the cases investigated suggest that a set of different conditions drives a transient combination of factors related to low basal friction, high driving stress, concentration of shear stress, and low resistance to exceed stability thresholds. Particularly, soft bedrocks below the detached glaciers seem to be a common condition among the observed events, as they offer smooth contact areas between the glacier and its substratum while being prone to till-strength weakening and eventually basal failure under high pore-water pressure. Surface slopes of the detached glaciers range between around 10° and 20°, possibly on the one hand low enough to enable development of thick and thus large-volume glaciers, and on the other hand steep enough to allow critical basal stresses to build up. Most of the ice-rock avalanches resulting from the detachments in this study have a particularly low angle of reach, down to around 0.1 (apparent friction angle), likely due to their high ice content and connected liquefaction potential, the ready availability of soft basal slurries and large amounts of basal water, and the smooth topographic setting typical for glacial valleys. Low-angle glacier detachments combine elements, and likely also physical processes of glacier surges and ice break-offs from steep glaciers. The surge-like temporal evolution ahead of several detachments or their geographic proximity to other surge-type glaciers suggests the glacier detachments investigated can be interpreted as end-members of the continuum of surge-like glacier instabilities. Though rare, glacier detachments appear more frequent than previously thought and disclose, despite local differences in conditions and precursory evolutions, the fundamental and critical potential of low-angle soft glacier beds to fail catastrophically.
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Understanding fast ice flow is key to assess the future of glaciers. Fast ice flow is controlled by sliding at the bed, yet that sliding is poorly understood. A growing number of studies show that the relationship between sliding and basal shear stress transitions from an initially rate-strengthening behavior to a rate-independent or rate-weakening behavior. Studies that have tested a glacier sliding law with data remain rare. Surging glaciers, as we show in this study, can be used as a natural laboratory 5 to inform sliding laws because a single glacier shows extreme velocity variations at a sub-annual timescale. The present study has two parts: (1) we introduce a new workflow to produce velocity maps with a high spatio-temporal resolution from remote sensing data combining Sentinel-2 and Landsat 8 and use the results to describe the recent surge of Shisper glacier, and (2) we present a generalized sliding law and provide a first-order assessment of the sliding-law parameters using the remote sensing dataset. The quality and spatio-temporal resolution of the velocity timeseries allow us to identify a gradual amplification of 10 spring speed-up velocities in the two years leading up to the surge that started by the end of 2017. We also find that surface velocity patterns during the surge can be decomposed in three main phases, and each phase appears to be associated with hydraulic changes. Using this dataset, we are able to constrain the sliding law parameter range necessary to encompass the sliding behavior of Shisper glacier, before and during the surge. We document a transition from rate-strengthening to rate-independent or rate-weakening behavior. A range of parameters is probably necessary to describe sliding at a single glacier. 15 The approach used in this study could be applied to many other sites in order to better constrain glacier sliding in various climatic and geographic settings.
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The detachment of large parts of low-angle mountain glaciers resulting in massive ice–rock avalanches have so far been believed to be a unique type of event, made known to the global scientific community first for the 2002 Kolka Glacier detachment, Caucasus Mountains, and then for the 2016 collapses of two glaciers in the Aru range, Tibet. Since 2016, several so-far unrecognized low-angle glacier detachments have been recognized and described, and new ones have occurred. In the current contribution, we compile, compare, and discuss 20 actual or suspected large-volume detachments of low-angle mountain glaciers at 10 different sites in the Caucasus, the Pamirs, Tibet, Altai, the North American Cordillera, and the Southern Andes. Many of the detachments reached volumes in the order of 10–100 million m3. The similarities and differences between the presented cases indicate that glacier detachments often involve a coincidental combination of factors related to the lowering of basal friction, high or increasing driving stresses, concentration of shear stress, or low resistance to exceed stability thresholds. Particularly soft glacier beds seem to be a common condition among the observed events as they offer smooth contact areas between the glacier and the underlying substrate and are prone to till-strength weakening and eventually basal failure under high pore-water pressure. Partially or fully thawed glacier bed conditions and the presence of liquid water could thus play an important role in the detachments. Surface slopes of the detached glaciers range between around 10∘ and 20∘. This may be low enough to enable the development of thick and thus large-volume glaciers while also being steep enough to allow critical driving stresses to build up. We construct a simple slab model to estimate ranges of glacier slope and width above which a glacier may be able to detach when extensively losing basal resistance. From this model we estimate that all the detachments described in this study occurred due to a basal shear stress reduction of more than 50 %. Most of the ice–rock avalanches resulting from the detachments in this study have a particularly low angle of reach, down to around 5∘, likely due to their high ice content and connected liquefaction potential, the availability of soft basal slurries, and large amounts of basal water, as well as the smooth topographic setting typical for glacial valleys. Low-angle glacier detachments combine elements and likely also physical processes of glacier surges and ice break-offs from steep glaciers. The surge-like temporal evolution ahead of several detachments and their geographic proximity to other surge-type glaciers indicate the glacier detachments investigated can be interpreted as endmembers of the continuum of surge-like glacier instabilities. Though rare, glacier detachments appear to be more frequent than commonly thought and disclose, despite local differences in conditions and precursory evolutions, the fundamental and critical potential of low-angle soft glacier beds to fail catastrophically.
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Over the last decades, glaciers on Svalbard were shrinking in response to the current climate change. Most of them decreased in size, area, and surface height with a stable negative or even accelerated changes in the mass balance. Many of them belong to the polythermal type, and as they shrink, their thermal regime can also change significantly depending on the climate and local parameters such as the ice facies distribution, the firn thickness, and others that affect the hydrology and movement of glaciers. Data from repeated GPR surveys in 1999 and 2018–2019 were used to identify changes in the thermal regime of the polythermal Aldegondabreen, Svalbard. The glacier has undergone a significant reduction of its temperate ice core, as a consequence of steadily negative mass balance, decreasing thickness, and the tongue retreat. The results show that over a 19‑year period, the total area of the glacier has decreased by 23.1% (from 6.94 to 5.34 km2), and the total volume of ice – by 36.4% (from 0.437 to 0.278 km3). At the same time, the area of its temperate core has decreased by 32.7% (from 1.196 to 0.804 km2), and the core volume – by 42.5% (from 0.035 to 0.02 km3). In this way, the relative rates of internal glacier changes associated with the warm core exceeded the external changes of the entire glacier. The share of temperate ice in the total volume of the glacier ice decreased from 8% to 7%. The glacier shrinking in response to rise of the air temperature was accompanied by its gradual internal «cooling». In the near future, this can result in a rapid transition of the glacier from a polythermal type into a cold one. Regular repeated geophysical surveys of the internal structure of the Svalbard polythermal glaciers can become an important element in the system of long-term monitoring of changes in climate and the natural environment of the archipelago, along with already existing observations of other sensitive natural indicators such as the size and mass balance.
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We present a theoretical framework that integrates the dynamics of glaciers with and without the topographic confinement. This Part 1 paper concerns the former, which may exhibit surge cycles when subjected to thermal switches associated with the bed condition. With the topographic trough setting the glacier width and curbing the lateral drainage of the meltwater, the problem falls under the purview of the undrained plastic bed (UPB) formalism. Employing the UPB, we shall examine the external controls of the glacial behavior and test them against observations. Through our non-dimensionalization scheme, we construct a 2-D regime diagram, which allows a ready prognosis of the glacial properties over the full range of the external conditions, both climate- and size-related. We first discern the boundaries separating the glacial regimes of steady-creep, cyclic-surging and steady-sliding. We then apply the regime diagram to observed glaciers for quantitative comparisons. These include the Svalbard glaciers of both normal and surge types, Northeast Greenland Ice Stream characterized by steady-sliding, and Hudson Strait Ice Stream exhibiting cyclic surges. The quantitative validation of our model containing no free parameters suggests that the thermal switch may unify the dynamics of these diverse glaciers.
Thesis
Abstract This thesis presents a reconstruction of the late Weichselian, deglacial and Holocene glacial history of the Svalbard fjords, focusing on eastern Svalbard. The study is based on high-resolution multibeam data, shallow acoustic (chirp) data, marine sediment cores, historical maps and aerial- satellite images. During the Last Glacial Maximum the Svalbard Barents Sea ice sheet reached the shelf edge around Svalbard and was drained by large ice streams along its western and northern margins, located in the same areas as the present day cross-shelf troughs. In northeastern Svalbard, fastflowing ice converged into the Hinlopen Strait ice stream from the surrounding fjords. Submarine landforms indicate that ice flow velocities increased as ice flowed from the inner- to the outer fjords and the shelf. The deglaciation from the northeastern shelf edge proceeded rapidly by ice lift-off in the troughs and deeper parts of the fjords, whereas the shallower areas experienced slower retreat with minor re-advances. The inner fjords around Nordaustlandet were ice free prior to 11.3-10.5 ka BP years. During early- to mid-Holocene tidewater glaciers in Mohnbukta and Vaigattbogen experienced at least one surge-type advance. These pre-Little Ice Age surges differentiate the east coast glaciers from the west coast glaciers. The early Holocene advance in Mohnbukta has been attributed to rapid climatic and environmental change at the end of the deglaciation, leading to dynamic disequilibrium and an environmentally induced jump into surge-mode. This suggests a more dynamic Holocene glacial history in Svalbard than previously stated, also indicating that the role of climate is more important in the evolution of general surge patterns than previously presumed. Similarly, climatic and environmental changes at the end of the Little Ice Age could explain why many Svalbard glaciers, both on the west and east coasts surged in that time period. Today, the majority of Svalbard’s fjords accommodate tidewater glaciers, of which several have been recorded to surge. Commonly the glaciers have surged at least twice during the Holocene. The surging tidewater glacier landform assemblages share many similarities and can be used to identify past surges in the geological record. In this study the submarine morphology has been used to identify three new surge-type glaciers in Wahlenbergfjorden. The surge history of the Svalbard glaciers is diverse and even though the landform assemblages share many similarities, they all feature differences, suggesting that local conditions are important in the evolution of glacial surges.
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Proglacial icings accumulate in front of many High Arctic glaciers during the winter months, as water escapes from englacial or subglacial storage. Such icings have been interpreted as evidence for warm-based subglacial conditions, but several are now known to occur in front of cold-based glaciers. In this study, we investigate the drainage system of Tellbreen, a 3.5 km long glacier in central Spitsbergen, where a large proglacial icing develops each winter, to determine the location and geometry of storage elements. Digital elevation models (DEMs) of the glacier surface and bed were constructed using maps, differential GPS and ground penetrating radar (GPR). Rates of surface lowering indicate that the glacier has a long-term mass balance of −0.6 ± 0.2 m/year. Englacial and subglacial drainage channels were mapped using GPR, showing that Tellbreen has a diverse drainage system that is capable of storing, transporting and releasing water year round. In the upper part of the glacier, drainage is mainly via supraglacial channels. These transition downglacier into shallow englacial "cut and closure" channels, formed by the incision and roof closure of supraglacial channels. Below thin ice near the terminus, these channels reach the bed and contain stored water throughout the winter months. Even though no signs of temperate ice were detected and the bed is below pressure-melting point, Tellbreen has a surface-fed, channelized subglacial drainage system, which allows significant storage and delayed discharge.
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Controls on the global distribution of surge-type glaciers hold the keys to a better understanding of surge mechanisms. We investigate correlations between the distribution of surge-type glaciers and climatic and glacier geometry variables, using a new global geodatabase of 2317 surge-type glaciers. The highest densities of surge-type glaciers occur within an optimal climatic envelope bounded by temperature and precipitation thresholds. Across all regions with both surge-type and normal glaciers, the former are larger, especially at the cold, dry end of the climatic spectrum. A species distribution model, Maxent, accurately predicts the major clusters of surge-type glaciers using a series of climatic and glacier geometry variables, but under-predicts clusters found outside the climatically optimal surge zone. We interpret the results in terms of a new enthalpy cycle model. Steady states require a balance between enthalpy gains generated by the balance flux and losses via heat conduction and meltwater discharge. This condition can be most easily satisfied in cold, dry environments (thin, low-flux glaciers, efficient conductive heat losses) and warm, humid environments (high meltwater discharges). Intermediate conditions correspond to the optimal surge zone, where neither heat conduction nor runoff can effectively discharge enthalpy gains, and dynamic cycling can result.
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The tectonic effects of a glacier surge differ from those of steady state because flow is driven by longitudinal stresses rather than shear stresses. The orientations of recently formed crevasses, indicating the directions of the principal stresses, have been used to investigate tectonic processes in glacier surges recorded by repeat aerial photography. Long-term, large-magnitude shifts in stress regime are demonstrated, as are short-term propagation features. Two types of tide-water glacier advance are identified, depending on the position of the surge front relative to a low effective-pressure zone at the glacier terminus. -Authors
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ABSTRACT. Large numbers of small valley glaciers on Svalbard were thicker and more extensive during the Little Ice Age (LIA), demonstrated by prominent ice-cored moraines up to several kilometres beyond present-day margins. The majority of these glaciers have since experienced a long period of strongly negative mass balance during the 20th century and are now largely frozen to their beds, indicating they are likely to have undergone a thermal transition from a polythermal to a cold-based regime. We present evidence for such a switch by reconstructing the former flow dynamics and thermal regime of Tellbreen, a small cold-based valley glacier in central Spitsbergen, based on its basal sequence and glaciological structures. Within the basal sequence, the underlying matrix-supported diamict is interpreted as saturated subglacial traction till which has frozen at the bed, indicating that the thermal switch has resulted in a cessation of subglacial sediment deformation due to freezing of the former deforming layer. This is overlain by debris-poor dispersed facies ice, interpreted to have formed through strain-induced metamorphism of englacial ice. The sequential development of structures includes arcuate fracture traces, interpreted as shear planes formed in a compressive/transpressive stress regime; and fracture traces, interpreted as healed extensional crevasses. The formation of these sediment/ice facies and structures is indicative of dynamic, warm-based flow, most likely during the LIA when the glacier was significantly thicker. KEYWORDS: Arctic glaciology, basal ice, ice dynamics, structural glaciology, subglacial sediments
Conference Paper
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Controls on the global distribution of surge-type glaciers hold the keys to a better understanding of surge mechanisms. Our study represents the first investigation of the correlations between the global distribution of surge-type glaciers and climatic and geometric variables, using a new geodatabase inventorying all surge-type glaciers in the world. The highest densities of surge-type glaciers occur within an optimal climatic envelope bounded by temperature and precipitation. Across all regions with both surge-type and normal glaciers, the former are larger, especially at the cold, dry end of the climatic spectrum. Climate change can also alter the distribution of surge-type glaciers. A species distribution model, Maxent, accurately depicts the major clusters of surge-type glaciers using three variables: temperature, precipitation and glacier area, but under-predicts clusters found outside of the climatically optimal surge zone. We interpret the results in terms of a new enthalpy cycle model. Steady states require a balance between enthalpy gains generated by the balance flux and losses via heat conduction and meltwater discharge. This condition can be most easily satisfied in cold, dry environments (thin, low-flux glaciers, efficient conductive heat losses), and warm, humid environments (high meltwater discharges). Intermediate conditions correspond with the optimal surge zone, where neither heat conduction nor runoff can effectively discharge heat gains, and enthalpy cycling can result.
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We present observations of a surge of the glaciers Skobreen-Paulabreen, Svalbard, during 2003-05, including a time-lapse movie of the frontal advance during 2005, Advanced Spaceborne Thermal Emission (ASTER) imagery and oblique aerial photographs. The surge initiated in Skobreen, and then propagated downglacier into the lower parts of Paulabreen. ASTER satellite images from different stages of the surge are used to evaluate the surge progression. Features on the glacier surface advanced 2800 m over 2.4 yr, averaging 3.2 m/day, while the front advanced less (ca. 1300 m) due to contemporaneous calving. The surge resulted in a lateral displacement of the medial moraines of Paulabreen of ca. 600 m at the glacier front. The time-lapse movie captured the advance of the frontal part of the glacier, and dramatically illustrates glacier dynamic processes in an accessible way. The movie documents a range of processes such as a plug-like flow of the glacier, proglacial thrusting, incorporation of old, dead ice at the margin, and calving into the fjord. The movie provides a useful resource for researchers, educators seeking to teach and inspire students, and those wishing to communicate the fascination of glacier science to a wider public.
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We present ground-penetrating radar (GPR)–based volume calculations, with associated error estimates, for eight glaciers on Wedel Jarlsberg Land, southwestern Spitsbergen, Svalbard, and compare them with those obtained from volume-area scaling relationships. The volume estimates are based upon GPR ice-thickness data collected during the period 2004–2013. The total area and volume of the ensemble are 502.91 ± 18.60 km2 and 91.91 ± 2.75 km3, respectively. The individual areas, volumes, and average ice thickness lie within 0.37–140.99 km2, 0.01–31.98 km3, and 28–227 m, respectively, with a maximum recorded ice thickness of 619 ± 13 m on Austre Torellbreen. To estimate the ice volume of unsurveyed tributary glaciers, we combine polynomial cross-sections with a function providing the best fit to the measured ice thickness along the center line of a collection of 22 surveyed tributaries. For the time-to-depth conversion of GPR data, we test the use of a glacierwide constant radio-wave velocity chosen on the basis of local or regional common midpoint measurements, versus the use of distinct velocities for the firn, cold ice, and temperate ice layers, concluding that the corresponding volume calculations agree with each other within their error bounds.
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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.
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Nathorstbreen glacier system (NGS) recently experienced the largest surge in Svalbard since 1936, and this was examined using spatial and temporal observations from DEM differencing, time series of surface velocities from satellite synthetic aperture radar (SAR) and other sources. The upper basins with maximum accumulation during quiescence corresponded to regions of initial lowering. Initial speed-up exceeded quiescent velocities by a factor of several tens. This suggests that polythermal glacier surges are initiated in the temperate area before mass is displaced downglacier. Subsequent downglacier mass displacement coincided with areas where glacier velocity increased by a factor of 100–200 times (stage 2). After more than 5 years, the joint NGS terminus advanced abruptly into the fjord during winter, increasing velocities even more. The advance was fol-lowed by up-glacier propagation of crevasses, indicating the middle and subsequently the upper part of the glaciers reacting to the mass displacement. NGS advanced ∼15 km, while another ∼3 km length was lost due to calving. Surface lowering of ∼50 m was observed in some up-glacier areas, and in 5 years the total glacier area increased by 20 %. Maximum measured flow rates were at least 25 m d −1 , 2500 times quiescent velocity, while average velocities were about 10 m d −1 . The surges of Zawadzkibreen cycle with ca. 70-year periods.
Article
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Nathorstbreen glacier system (NGS) recently experienced the largest surge in Svalbard since 1936, and is examined using spatial and temporal observations from DEM differencing, time-series of surface velocities from satellite synthetic aperture radar (SAR) and other sources. The upper basins with maximum accumulation during quiescence correspond to regions of initial lowering. Initial speed-up exceeds quiescent velocities by a factor of several tens of times. This suggests that polythermal glaciers surges are initiated in the temperate area before mass is displaced downglacier. Subsequent downglacier mass displacement coincides with areas of 100-200 times increased velocities (stage 2). After > 5 yr the joint NGS terminus advanced abruptly into tidewater during winter. The advance was followed by upglacier propagation of crevasses, indicating a re-action following from the already displaced mass and extending flow. NGS advanced ca. 15 km, while another ca. 3 km length was lost due to calving. Surface lowering of ca. 50 m was observed in some upglacier areas and during 5 yr the total area increased by 20%. Maximum measured flow rates were at least 25 m d-1, 2500 times quiescence, while average velocities were about 10 m d-1. The surges of Zawadzkibreen cycle with ca. 70 yr periods.
Article
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Most polythermal glaciers in Svalbard, other than those of surge type, have receded steadily since the early 20th century. Midre Lovénbreen, a slow-moving, 4-km-long valley glacier terminating on land, is a typical example, and its internal structures reflect changing dynamics over this period. The three-dimensional structural style of this glacier and the sequential development of structures have been determined from surface mapping, ground-penetrating radar, and numerical flow modeling. In order of formation the structures observed today at the glacier surface are (1) primary stratification that has become folded about flow-parallel axes; (2) axial plane longitudinal foliation associated with this folding; (3) several sets of intersecting crevasse traces; (4) arcuate upglacier-dipping fractures developed as part of a thrust complex near the snout; and (5) longitudinal splaying fractures in the snout area. The long-term evolution and dynamic significance of these structures can be ascertained from historical ground and aerial photographs. Modeling indicates that stratification and foliation continue to evolve today as a result of internal deformation, especially in zones of converging flow, where simple shear is most pronounced, but within the tongue are carried passively toward the snout. Crevasse traces appear to be no longer actively forming but are interpreted as relict structures when the ice was more dynamic and mostly wet based. The interpretation of arcuate fractures near the snout as thrusts is supported by the matching orientations of modeled strain ellipses, which illustrate the importance of longitudinal compression.
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One of the few long instrumental records available for the Arctic is the Svalbard Airport composite series that hitherto began in 1911, with observations made on Spitsbergen, the largest island in the Svalbard Archipelago. This record has now been extended to 1898 with the inclusion of observations made by hunting and scientific expeditions. Temperature has been observed almost continuously in Svalbard since 1898, although at different sites. It has therefore been possible to create one composite series for Svalbard Airport covering the period 1898–2012, and this valuable new record is presented here. The series reveals large temperature variability on Spitsbergen, with the early 20th century warming as one striking feature: an abrupt change from the cold 1910s to the local maxima of the 1930s and 1950s. With the inclusion of the new data it is possible to show that the 1910s were colder than the years at the start of the series. From the 1960s, temperatures have increased, so the present temperature level is significantly higher than at any earlier period in the instrumental history. For the entire period, and for all seasons, there are positive, statistically significant trends. Regarding the annual mean, the total trend is 2.6°C/century, whereas the largest trend is in spring, at 3.9°C/century. In Europe, it is the Svalbard Archipelago that has experienced the greatest temperature increase during the latest three decades. The composite series may be downloaded from the home page of the Norwegian Meteorological Institute and should be used with reference to the present article.
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[1] Anisotropy of magnetic susceptibility (AMS) has been shown to provide specific useful information regarding the kinematics of deformation within subglacially deformed sediments. Here we present results from debris-rich basal glacier ice to examine deformation associated with glacier motion. Basal ice samples were collected from Tunabreen, a polythermal surge-type glacier in Svalbard. The magnetic fabrics recorded show strong correlation with structures within the ice, such as sheath folds and macroscopic stretching lineations. Thermomagnetic, low-temperature susceptibility, varying field susceptibility, and isothermal remanent magnetism acquisition experiments reveal that the debris-rich basal ice samples have a susceptibility and anisotropy dominated by paramagnetic phases within the detrital sediment. Sediment grains entrained within the basal ice are inferred to have rotated into a preferential alignment during deformation associated with flow of the glacier. An up-glacier directed plunge of magnetic lineations and subtle deviation from bulk glacier flow at the margins highlight the importance of noncoaxial strain during surge propagation. The results suggest that AMS can be used as an ice petrofabric indicator for investigations of glacier deformation and interactions with the bed.
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This paper presents the changes in the thermal structure of the polythermal glacier Storglaciären, northern Sweden, over the 20 year period 1989-2009 derived by comparing maps of the depth of the englacial transition between cold ice (permanently frozen) and temperate ice (which contains water inclusions). The maps are based on interpreted ice-penetrating radar surveys from 1989, 2001 and 2009. Complex thinning of the cold layer, first identified between 1989 and 2001, is still ongoing. A volume calculation shows that Storglaciären has lost one-third of its cold surface layer volume in 20 years, with a mean thinning rate of 0.80 ± 0.24 m a ⁻¹ . We suggest that the thinning of the cold layer at Storglaciären is connected to the climatic warming experienced by sub-Arctic Scandinavia since the 1980s and we argue that repeated ice-penetrating radar surveys over the ablation area of polythermal glaciers offer a useful proxy for evaluating glacier responses to changes in climate.
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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.
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Geodetic measurements indicate that a number of glaciers in western Svalbard ranging in size from 5-1000 km2 are losing mass at an accelerating rate. The average thinning rate for Midtre Lovénbreen, the glacier with the best data coverage, has increased steadily since 1936. Thinning rates for 2003-2005 are more than 4 times the average for the first measurement period 1936-1962 and are significantly greater than presented previously. On Slakbreen, thinning rates for the latest measurement period 1990-2003 are more than 4 times that of the period 1961-1977. Thinning of several glaciers along a previously measured airborne lidar profile in Wedel Jarls Land has also increased, doubling between the period 1990-1996 and 1996-2002. Our results imply an increased sea level contribution from Svalbard. In addition, the mass loss is an important influence on measured rates of rebound on western Svalbard and should be factored into analysis of GRACE results.
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A deep-ice temperature measurement program has been conducted on Trapridge Glacier, Yukon Territory. Large regions of temperate ice are predicted at the base of the otherwise cold glacier, The glacier snout, frozen to bedrock, appears to act as an ice dam allowing the build up of an ice reservoir in the upper regions. Thermal regulation of the surges of Trapridge Glacier is suggested and the relevance of basal temperatures in large surging glaciers is discussed.
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Radio echo soundings on Rusty Glacier, a small surge-type glacier in Yukon Territory reveal that the ice is considerably thicker than previously believed. A reinterpretation of deep ice-temperature measurements made in 1969 and 1970 suggests that a large zone of temperate basal ice exists. This result supports thermal instability as the surge mechanism for Rusty Glacier.
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Surging outlet glaciers are important in draining large ice caps, but the mechanisms controlling surge periodicities are poorly known. We investigated a sediment sequence from the glacier-fed Lake Lögurinn in eastern Iceland, and our unique annually resolved data, based on sedimentary varves, imply that Eyjabakkajökull, an outlet glacier of Vatnajökull, began surging about 2200 cal a BP (before 1950 AD). Approximately 1700 cal a BP, the glacier started to surge at a uniform 34- to 38-year periodicity that prevailed until the coldest part of the Little Ice Age when the periodicity almost halved to 21–23 years. Since the late 1800 s the surge periodicity of Eyjabakkajökull has returned to a longer period of 35–40 years. We suggest that surge periodicities of Eyjabakkajökull are forced by climatically driven mass balance changes, which may be a common forcing factor for similar surge-type outlet glaciers. Copyright © 2011 John Wiley & Sons, Ltd.
Article
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A necessary condition for a glacier to surge by thermal instability is that the glacier be cold with basal ice at or near the melting point. Deep temperature measurements show that two small surge-type glaciers in the Yukon Territory meet this requirement, but shallow measurements in three other surge-type glaciers suggest a temperate regime. If the latter observations are accepted, not all surges are thermally controlled: if a single mechanism accounts for all surges it cannot be thermal instability. In this paper it is argued that thermal instability remains a viable mechanism for explaining surges of many cold glaciers, and that regardless of the underlying mechanism, thermal processes must at least have a major influence on the surge behavior of cold glaciers. Two numerical modelling experiments are described. The first involves a one-dimensional model which shows that thermal control can account for the remarkably constant surge cycle found in some glaciers. The second, a two-dimensional model of the time-dependent temperature structure of a surge-type glacier, shows that the relative amounts of temperate and cold basal ice can change considerably as the surge cycle progresses. This variation alone may be sufficient to explain surges, but even if this is not the case, thermal processes must affect the timing of surges in many cold glaciers. A compelling feature of the thermal instability mechanism is that it offers an explanation of the factors controlling the non-random geographical distribution of surge-type glaciers. For a glacier to have a cold surface and near-temperate bed, the ice thickness, temperature, and geothermal flux must be fortuitously related.
Article
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Trapridge Glacier, Yukon, Canada, is a polythermal, soft-bedded surge-type glacier. As revealed by a 1951 aerial photograph, an important surge occurred in the 1940s, leaving the glacier heavily crevassed and at least 1 km downstream from the 1941 position. It is our conclusion that another surge, albeit far less dramatic, has been taking place over the last three decades and is now terminated. To quantify the changes in ice geometry, ground survey measurements were coupled with aerial photogrammetry to yield digital elevation models of the glacier from 1951 to present. For 1951, 1970, 1972, 1977 and 1981, years for which ground data are scarce or unavailable, DEMs were generated from stereographic analysis of aerial photographs. For the subsequent years, DEMs are obtained from ground survey data using our implementation of a Bayesian Kriging algorithm. For each year, the topography of the previous year is used as a background model and updated by the available survey data. This chain is initiated by the 1981 DEM obtained from aerial photogrammetry. Using exposed sections of the bed from the 1981 DEM and radar data, a map of the bed topography is obtained. Changes in the flow patterns are also investigated using an extended but variable array of flow markers. The results of this work indicate that the period from the previous surge to the present was characterized by two processes: 1) the deglaciation of the 1940s surge `receiving area' and 2) the slow advance of a mass wave from the upper reaches of the glacier. While it was previously believed that this mass reorganization was to precede a fast surge, it is now obvious that such a surge is not to happen. Ice velocity peaked at nearly 40 m/yr in the mid 1980s, fluctuated for the next 15 years and then dropped ca 2000 to reach ~10 m/yr in 2005. The bulge that formed in the 1980s at the transition between warm- and cold-based ice continued to propagate beyond the limits of the 1981 glacier. The glacier snout is currently ~200 m downstream from the 1981 terminus and not advancing. Together the DEMs and bed topography map enable us to characterize changes in the distribution and volume of ice, hydrological potential, and basal stress that accompanied the slow surge.
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Changes in driving and resistive stresses play an essential role in governing the buoyancy forces that are important controls on the speed and irreversibility of tidewater glacier retreats. We describe changes in geometry, velocity and strain rate, and present a topdown force balance analysis performed over the lower reach of Columbia Glacier. Our analysis uses new measurements and estimates of basal topography and photogrammetric surface velocity measurements made between 1977 and 2001, while assuming depth-independent strain. Sensitivity tests show that the method is robust and insensitive to small changes in the calculation parameters. Spatial distributions of ice speed show little correspondence with driving stress. Instead, spatial patterns of ice speed exhibit a nonlinear correspondence with basal drag. Primary resistance to flow comes from basal drag, but lateral drag becomes increasingly more important throughout the retreat, which may account for observed increases in speed. Maximum basal drag is always located in a prominent constriction located ~12 km upstream from the pre-retreat terminus. Once the terminus retreated into deep water off the terminal moraine marking the modern maximum extent, the upstream location of this maximum basal drag helped to promote thinning and decrease effective pressure in the lower region by limiting replenishing ice flow from upstream. An increase in both ice velocity and calving resulted, initiating what appears to be an irreversible retreat.
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The end of the Little Ice Age (LIA) in Svalbard (76-81°N), a climate-sensitive region at the northern extreme of strong poleward heat transfer, was marked by an abrupt increase in mean annual air temperature of up to 5°C around 1920. Glacier mass balance has been consistently negative since this time, and large cumulative net losses of mass have occurred at most glaciers. Energy-balance modelling confirms the sensitivity of Svalbard glaciers to climate change, predicting a negative shift in net mass balance of up to 0.8 m a-1 (water equivalent) per degree temperature rise. This climate-related shift in glacier mass balance has reduced the intensity of glacier surge activity in Svalbard. One glacier, known to have surged since the end of the LIA, has since failed to accumulate the mass required to re-initiate the surge cycle, and is also now cold at its base and incapable of rapid flow by basal sliding. Three overviews of the total number of actively-surging glaciers in Svalbard between 1936-90 show a decrease from 18 to 5. This is significant compared with the expected numbers of surges based on LIA conditions. Post-LIA climate change in Svalbard has therefore affected not only glacier extent, but also ice dynamics. This is trend will probably continue given CO2-induced climate-warming.
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Trapridge Glacier, a polythermal surge-type glacier located in the St. Elias Mountains, Yukon Territory, Canada, passed through a complete surge cycle between 1951 and 2005. Air photos (1951–1981) and ground-based optical surveys (1969–2005) are used to quantify the modifications in flow and geometry that occurred over this period. Yearly averaged flow records suggest that the active phase began ∼1980, and lasted until ∼2000. The average velocity in the central area of the glacier went from 16 m yr−1 in 1974 to 39 m yr−1 in 1980; it peaked at 42 m yr−1 in 1984, and remained above 25 m yr−1 until 2001. Over that interval, the flow decelerated by steps, in 4-year pulses. After a particularly vigorous acceleration in 1997–1999, the glacier gradually slowed to presurge velocities. In 2005, the flow was less than 9 m yr−1. Digital elevation models are generated by stereographic analysis of air photos for 1951, 1970, 1972, 1977, and 1981. These models are updated annually using ground-based survey data and a novel implementation of Bayesian kriging. Over the course of the surge, the front of active ice advanced 450 m and the glacier area increased by 10%, with an associated thinning of the ice. The previous surge of Trapridge Glacier, starting before 1939 and ending before 1951, led to a terminus advance of ∼1 km. Comparison of the two surges suggests that the 1930s surge started with a slow progression similar to what we observed in the 1980s and 1990s, and switched to a faster flow mode after 1941. This second phase was never attained in the recent surge, probably owing to a lack of mass.
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A characteristic feature of ground penetrating radar (GPR) surveys on polythermal glaciers is an internal reflection presumably caused by the cold temperate transition surface (CTS), hence providing a possible tool for mapping thermal structure with high accuracy. Comparison of detailed temperature measurements in bore holes and GPR profiles at 345 MHz and 800 MHz center frequencies on Storglaciären, Sweden, show that the CTS can be detected and mapped with an accuracy of about ±1 m at both frequencies. A comparison between comprehensive GPR surveys of the cold surface layer, separated by 12 years (1989–2001), shows a substantial and complex thinning of the cold layer. An overall decrease of 8.3 m (22% of average thickness) of the CTS depth is much larger than uncertainties in CTS depth determinations. The stability of the cold surface layer depends on the net ice ablation at the surface and the downward migration of CTS. There is no evidence of substantial increased net ablation between the survey dates that could explain the observed thinning. However, small increase in average winter air temperature, a limiting factor for the temperature gradient through the cold surface layer, may provide a partial explanation. The weaker temperature gradient reduces the transport of latent heat from the CTS, thus slowing down its downward migration.
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The ice masses of Svalbard cover an area of ca. 36 600 km2, and are thus among the largest glaciated areas in the Arctic. Annual mass balance measurements have been carried out on several Svalbard glaciers over up to 30 yr. However, these glaciers extend over only 0.5% of the total ice-covered area. The measured mean net balance has been negative and no changing trend has been observed. On some glaciers and larger ice caps, the mean net balance has also been measured at different altitudes by detecting radioactive reference layers from nuclear fallouts in 1963 and 1986 in shallow ice cores. The net balance/altitude curves have been estimated for thirteen different regions in Svalbard, and combined with digital elevation models of all Svalbard ice masses used to calculate the net balance in each 100-m altitude interval. The net loss of mass through iceberg calving was estimated and appears to be an important component of the net mass loss from Svalbard ice masses. The overall total net balance is slightly negative, � 4:5 6 1k m3 yr� 1; giving a specific net balance of ca. � 120 630 mm yr� 1 over the archipelago. The contribution of ice caps and glaciers on Svalbard to global sea-level change is, therefore, close to 0.01 mm yr� 1 as an average value over the last 30 years, which is less negative than former estimates.
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Temperature measurements in a subpolar surge-type glacier reveal a distinctive thermal structure associated with the boundary between the ice reservoir and receiving areas. In the receiving area the glacier is cold based, but bottom temperature has increased as much as 0.5 °C between 1981 and 1982, and the basal heat flux is roughly 10 times the expected geothermal flux. Water percolation through permeable subglacial material is the probable energy source. Deformation of the substrate could destroy this drainage system and trigger a surge.