Showing papers on "Accumulation zone published in 2023"

Dynamic Changes of a Thick Debris-Covered Glacier in the Southeastern Tibetan Plateau

Abstract: Debris-covered glaciers have contrasting melting mechanisms and climate response patterns if compared with debris-free glaciers and thus show a unique influence on the hydrological process. Based on high-resolution satellite images and unpiloted aerial vehicle surveys, this study investigated the dynamic changes of Zhuxi Glacier, a thick debris-covered glacier in the southeastern Tibetan Plateau. Our result shows that the whole glacier can be divided into the active regime and stagnant regime along the elevation of 3400 m a.s.l. The mean surface velocity of the active regime was 13.1 m yr−1, which was five times higher than that of the stagnant regime. The surface-lowing rate of this debris-covered glacier reaches more than 1 m yr−1 and displays an accelerating trend. The majority of ice loss concentrates around ice cliffs and supraglacial ponds, the ablation hotspots. These hotspots can be roughly classified into three types, including persistent, expanding, and shrinking patterns, at different dynamic regimes on the Zhuxi Glacier. With the evolution of these hotpots and glacier dynamic changes, the supraglacial ponds showed significant change, with the total number fluctuating from 15 to 38 and the total area increasing from 1128 m2 to 95790 m2 during the past decade. The recent exponential expansion of the proglacial lake and the significant downwasting of stagnant ice inside the dammed terminus moraine possibly trigger the glacial lake outburst flood and thus threaten the security of livelihoods and infrastructure downstream.

Climatic control on seasonal variations in mountain glacier surface velocity

Abstract: Abstract. Accurate measurements of ice flow are essential to predict future changes in glaciers and ice caps. Glacier displacement can in principle be measured on the large scale by cross-correlation of satellite images. At weekly to monthly scales, the expected displacement is often of the same order as the noise for the commonly used satellite images, complicating the retrieval of accurate glacier velocity. Assessments of velocity changes on short timescales and over complex areas such as mountain ranges are therefore still lacking but are essential to better understand how glacier dynamics are driven by internal and external factors. In this study, we take advantage of the wide availability and redundancy of satellite imagery over the western Pamirs to retrieve glacier velocity changes over 10 d intervals for 7 years and for a wide range of glacier geometry and dynamics. Our results reveal strong seasonal trends. In spring/summer, we observe velocity increases of up to 300 % compared to a slow winter period. These accelerations clearly migrate upglacier throughout the melt season, which we link to changes in subglacial hydrology efficiency. In autumn, we observe glacier accelerations that have rarely been observed before. These episodes are primarily confined to the upper ablation zone with a clear downglacier migration. We suggest that they result from glacier instabilities caused by sudden subglacial pressurization in response to (1) supraglacial pond drainage and/or (2) gradual closure of the hydrological system. Our 10 d resolved measurements allow us to characterize the short-term response of glaciers to changing meteorological and climatic conditions.

The Changes of Hailuogou Glacier in the Southeastern Tibetan Plateau and the Impacts on Glacier Dynamics from the Mechanical Ablation

Abstract: Glaciers in the Tibetan Plateau are melting at an unprecedented rate in the context of global warming. Hailuogou (HLG) Glacier, a rapidly receding temperate land-terminating glacier in the southeastern Tibetan Plateau, has been observed to lose mass partly through ice frontal mechanical ablation (i.e., ice collapse).In this study, we present analysis from Uncrewed Aerial Vehicles (UAV) surveys conducted over nine field campaigns to the HLG Glacier, providing evidence of glacier change and frontal ice collapse between 2017 and 2021. Structure from Motion with Multi-View Stereo was applied to produce multi-temporal Digital Surface Models (DEMs) and orthophoto mosaics, from which geomorphological maps and DEMs of Difference were derived to quantify the changes of the glacier snout and the ice loss from frontal ice collapse. Based on that, a linear correlation of Area-Volume for frontal ice collapse was subsequently built. Planet images were used to identify additional ice collapse events (i.e., 2017 to 2021) and to extract time-sequenced glacier extents. ASTER-derived DEMs generated by NASA Ames Stereo Pipeline (ASP) were then differenced to calculate the ice volume changes in the period. Combined with frontal ice collapse events identified from Planet, the contribution of that to the glacier mass balance can be estimated from the established Area-Volume correlation.These analyses reveal that at the margins of the glacier terminus retreated 132.1 m over the period of analysis, and that in the area specifically affected by collapsing (i.e., the glacier collapsed terminus), it retreated 236.4 m. Overall the volume lost in the terminal area was of the order of 184.61 ± 10.32 x 104 m3, within which the volume change due to observed collapsing events comprises approximately 28%. We show that ice volume changes at the terminus due to a single ice collapse event may exceed the interannual level of volume change, and the daily volume of ice loss due to ice calving exceeds the seasonal and interannual level by a factor of ~ 2.5 and 4. The contribution to the mass balance change of the entire glacier that is attributed to frontal ice collapse is limited (i.e., ranges from 0.48% to 1.12% from 2017 to 2021). However, the mechanical ablation (e.g., frontal ice collapse and subglacial/englacial conduit’s roof collapse) has probably changed the way of losing ice mass to some extent.Our results suggest that the evolution of the HLG Glacier terminus is dominantly controlled by the frontal ice collapse. The projection of the recession rate of the HLG Glacier may well be underestimated if based on surface mass balance alone, as the frontal ice collapsing might be more frequent and larger under the context of warming. If the future evolution of glaciers such as HLG Glacier is to be robustly predicted, the contribution of mechanical ablation should be accounted for by numerical models.

Energy and mass balance of Mera glacier (Everest region, Central Himalaya) and its sensitivity to climate

Abstract: Recent glacier mass changes are very heterogeneous in High Mountain Asia, owing to climatic variability and the mass balance sensitivity to climate, which may differ from one region to another. Mera glacier in the Everest region is one of the longest field-based monitored and well-studied glaciers of the Central Himalaya. In this study, we examine the sensitivity of Mera glacier mass balance to climate variables using the COupled Snowpack and Ice surface energy and mass balance model in PYthon (COSIPY), using 4 years (2016-2020) of in-situ meteorological data recorded at different elevations in the ablation and accumulation zones of the glacier. This shows that the net short-wave radiation is the main energy input at the surface, and in turn albedo is a key parameter controlling the glacier mass balance. As a result, at 5360 m asl, in the ablation zone, surface melt accounts for 90% of mass loss whereas sublimation and subsurface melt account for less than 10%. This analysis is performed at point scale at 5360 and 5770 m asl, in the ablation and accumulation zones respectively, as well as in a distributed way. We produce and analyze 88 distinct climatic scenarios, varying from dry and warm to wet and cold conditions. Dry conditions, primary during the pre-monsoon and secondary during the monsoon, strongly decrease the glacier mass balance, revealing that the annual amount and the seasonal distribution of snowfalls primary drives the glacier-wide mass balance of Mera Glacier.   

Reply on RC2

Abstract: Abstract. Debris-covered glaciers are a common feature of the mountain cryosphere in the southeastern Tibetan Plateau. A better understanding of these glaciers change is necessary to reduce the uncertainties of the regional water resource variability, and to anticipate potential cryospheric risks. In this study, we quantify seasonal thinning (dh) and surface mass balance (SMB) patterns of two neighboring debris-covered glaciers (23 K Glacier and 24 K Glacier) in the southeastern Tibetan Plateau with repeated unpiloted aerial vehicle (UAV) surveys and in-situ measurements. We observe that the dh pattern of 23 K Glacier is distinct from that of 24 K Glacier, despite their proximity. The dh magnitude of the 23 K Glacier is ~1.4–3.0 times greater than that of the 24 K Glacier at all periods, which is mainly driven by the stronger dynamic state of 24 K Glacier. The contrasted behaviour between the two glaciers is also valid in the early twenty-first century. In contrast, the SMB patterns of the two glaciers are generally in agreement at different periods. The debris thickness distribution correlates with the SMB spatial distribution for both glaciers, while the supraglacial ice cliffs and ponds area density distribution is not correlated with SMB spatial distribution. This high-resolution comparison study of two neighboring glaciers confirms the significance of both glacier dynamic and debris thickness in controlling the thinning and melt for the different type debris-covered glaciers of the southeastern Tibetan Plateau in the context of climate change.

Automated ice ablation readings reveal the significance of summer heat waves for glacier melt

Abstract: Summer heat waves have a substantial impact on glacier melt as emphasized by the extreme summer of 2022 that caused unprecedented mass losses to the Swiss glaciers. Despite the dramatic impact on glaciers, the summer of 2022 offered a unique opportunity to analyze the implications that such extraordinary events have on glacier melt and related runoff release.This study presents a novel approach based on computer-vision techniques for automatically determining daily mass balance variations at the local scale. The approach is based on the automated recognition of color-taped ablation stakes from camera images acquired at six sites on three Alpine glaciers in the period 2019-2022. The validation of the method revealed an uncertainty of the automated readings of ±0.81 cm d-1. By comparing the automatically retrieved mass balances at the six sites with the average mass balance of the last decade derived from seasonal in situ observations, we detect extreme melt events in the summer seasons of 2019-2022.The in-depth analysis of summer 2022 allows us to assess the impact that the summer heat waves have on glacier melt. With our approach we detect 23 days with extreme melt over the summer, emphasizing the strong correspondence between heat waves and extreme melt events. The Swiss-wide glacier mass loss during the 25 days of heat waves in 2022 is estimated as 1.27 ± 0.10 Gt, corresponding to 35% of the overall glacier mass loss in the summer of 2022. As compared to the 2010-2020 average glacier mass change, days with extreme melt in 2022 correspond to 56% of the mass change during the summer period, thus demonstrating the significance of heat waves for seasonal melt.

Dynamics throughout a complete surge of Iceberg Glacier on western Axel Heiberg Island, Canadian High Arctic

Abstract: This study provides the first comprehensive reconstruction of the dynamics of Iceberg Glacier, located on western Axel Heiberg Island, and reveals detailed observations of a complete surge for the first time in the Canadian Arctic. Historical aerial photographs, declassified intelligence satellite photographs, optical satellite imagery and synthetic aperture radar data were used to quantify changes in terminus position, ice velocity and glacier thickness since the 1950s. A surge initiated at the terminus in 1981 and terminated in 2003, suggesting a 22-year active phase. High surface velocities, reaching ~2300 m a−1 in 1991, were accompanied by a maximum terminus advance of >7 km and a large transfer of mass down-glacier, causing significant median trunk-wide surface elevation changes attaining >3 ± 1 m a−1. We suggest that the retreat from a pinning point, flotation of the terminus, the removal of sea-ice from the ice front, and an increase in subglacial meltwater availability from relatively high air temperatures in 1981 likely contributed to surge initiation. The ensuing quiescent period has seen a continual decrease in surface flow rates to an average centreline velocity of 11.5 m a−1 in 2020–21, a gradual steepening of the glacier surface and a > 2.5 km terminus retreat.

Climatic control on seasonal variations of moutain glacier surface velocity

Abstract: Glacier displacement can in principle be measured at the large-scale by cross-correlation of satellite images. At weekly to monthly scales, the expected displacement is often of the same order as the noise for the commonly used satellite images, complicating the retrieval of accurate glacier velocity. Assessments of velocity changes on short time scales and over complex areas such as mountain ranges are therefore still lacking, but are essential to better understand how glacier dynamics are driven by internal and external factors. In this study, we take advantage of the wide availability and redundancy of satellite imagery over the Western Pamir to retrieve glacier velocity changes over 10 days for 7 years for a wide range of glacier geometry and dynamics. Our results reveal strong seasonal trends. In spring/summer, we observe velocity increases of up to 300% compared to a slow winter period. These accelerations clearly migrate upglacier throughout the melt-season, which we link to changes in subglacial hydrology efficiency. In autumn, we observe glacier accelerations that have rarely been observed before. These episodes are primarily confined to the upper ablation zone with a clear downglacier migration. We suggest that they result from glacier instabilities caused by sudden subglacial pressurization in response to (1) supraglacial pond drainage and/or (2) gradual closure of the hydrological system. Our 10-day resolved measurements allow us to characterize the short-term response of glacier to changing meteorological and climatic conditions.

Examining the impact of climatic and non-climatic attributes on glacier mass budget and surging in Alaknanda Basin, India

Abstract:  Glacier meltwater is a significant component of the regional runoff In High Mountain Asia (HMA),. However, the majority of the HMA's glaciers are rapidly losing their mass, putting the long-term viability of meltwater as a component of river flow at risk. It is, hence, crucial to comprehend the long-term glacier response to climate change at the regional scale as well as the impact of non-climatic characteristics like morpho-topographic factors on ice loss. We estimate changes for 445 glaciers in the upper Alaknanda basin and neighboring transboundary glaciers using multi-temporal optical satellite images from 1973 to2020. Our measurements indicate a mean annual area change of −1.14 ± 0.07 m a–1 and a geodetic glacier mass balance of −0.34 ± 0.08 m w.e.a–1 for the whole period. Before 2000 (1973-2000), the mean regional glacier mass loss rate was -0.30 ± 0.07 m w.e.a-1, which increased to -0.43 ± 0.06 m w.e.a-1 during 2000-2020. The mass loss increased further (-0.68 ± 0.09 m w.e.a-1) in the recent period (2015-2020) and we observed heterogeneous mass loss both in spatial and temporal scales. Our analysis revealed that the current significant glacier imbalance is probably a result of the rising temperature trend as revealed from the ERA5 Land reanalysis data. An extended ablation season due to the strong seasonal temperature increase has further accelerated glacial mass loss. Steep and higher elevation glaciers were less affected by negative mass budget. This can be explained beside the lower average temperatures at higher elevation by a rapid transfer of snow and ice that helped them to readjust their geometry compared to glaciers at lower elevation, having more gentle slopes and lower dynamics. Such low elevation glaciers are unlikely to recover in coming decades if the current trend of warming continues. We also identified a surging glacier draining onto the Tibetan Plateau that advanced rapidly by around 800 m within three months in Sep-Dec 2019. The advance is still ongoing, though at a much-reduced rate. Our temporally detailed measurements of glacier change provide an in-depth view of glacier evolution in the Alaknanda Basin and will improve the estimation of meltwater run-off component of the hydrological cycle. 

Spatial response of Greenland's firn layer to NAO variability

Abstract: Firn on the Greenland Ice Sheet (GrIS) buffers meltwater, and has a variable thickness, complicating observations of volume change to mass change. In this study, we use a firn model (IMAU-FDM v1.2G) forced by a regional climate model (RACMO2.3p2) to investigate how the GrIS firn layer thickness and pore space have evolved since 1958 in response to variability in the large-scale atmospheric circulation. On interannual timescales, the firn layer thickness and pore space show a spatially heterogeneous response to variability in the North Atlantic Oscillation (NAO). Notably, a stronger NAO following the record warm summer of 2012 led the firn layer in the south and east of the ice sheet to regain thickness and pore space after a period of thinning and reduced pore space. In the southwest, a decrease in melt dominates, whereas in the east the main driver is an increase in snow accumulation. At the same time, the firn in the northwestern ice sheet continued to lose pore space. The NAO also varies on intra-annual timescales, being typically stronger in winter than in summer. This impacts the amplitude of the seasonal cycle in GrIS firn thickness and pore space. In the wet southeastern GrIS, most of the snow accumulates during the winter, when melting and densification are relatively weak, leading to a large seasonal cycle in thickness and pore space. The opposite occurs in other regions, where snowfall peaks in summer or autumn. This dampens the seasonal amplitude of firn thickness and pore space.

The Glacier-climate Interaction over the High-Mountain Asia during the Last Glacial Maximum

Abstract: Glacier advances affect the local climate, and in turn, can either promote or prohibit its own growth. Such feedback has not been considered in modeling the High-Mountain Asia (HMA) glaciers during the Last Glacial Maximum (LGM; ~28-23 ka), which may contribute to the large spread in some of the published modeling work, with some notable discrepancy with existing reconstruction data. By coupling an ice sheet model (ISSM) with a climate model (CESM1.2.2), we find that the total glacial area is reduced by 10% due to the glacier-climate interaction; glacier growth is promoted along the western rim of HMA, and yet reduced in the interior. Such changes in spatial pattern improve model-data comparison. Moreover, the expansion of glaciers causes an increase in the winter surface temperature of the eastern Tibetan Plateau by more than 2 K, and a decrease of precipitation almost everywhere, especially the Tarim basin, by up to 60%. These changes are primarily due to the increase in surface elevation, which blocks the water vapor brought by westerlies and southwesterlies, reducing precipitation and increasing surface temperatures to the east and northeast of the newly grown glaciers.

Reply on RC1

Abstract: Abstract. The Greenland Ice Sheet's (GrIS) firn layer buffers the ice sheet's contribution to sea level rise by storing meltwater in its pore space. However, available pore space and meltwater retention capability is lost due to ablation of the firn layer and refreezing of meltwater as near-surface ice slabs in the firn. Understanding how firn properties respond to climate is important for constraining the GrIS's future contribution to sea level rise in a warming climate. Observations of firn density provide detailed information about firn properties, but they are spatially and temporally limited. Here we use two firn models, the physics-based SNOWPACK model and the semi-empirical Community Firn Model (CFM) to quantify firn properties across the GrIS from 1980 through 2020. We use an identical forcing (MERRA-2 atmospheric reanalysis) for SNOWPACK and the CFM in order to isolate model differences. To evaluate the models, we compare simulated firn properties, including firn air content (FAC), to measurements from the SUMup dataset of snow and firn density. Both models perform well, though their performance is hindered by meltwater percolation and the spatial resolution of the atmospheric forcing. In the full ice-sheet simulations, the spatially-integrated FAC (i.e., air volume in the firn) for the upper 100 m is 34,645 km³ from SNOWPACK and 28,581 km³ from the CFM. The discrepancy in the magnitude of the modeled FAC stems from differences in densification with depth and variations in the models' treatment of atmospheric input. In more recent years (2005–2020), both models simulate substantial depletion of pore space. During this period, the spatially-integrated FAC across the entire GrIS decreases by 2.8 % and 1.2 % in SNOWPACK and the CFM, respectively. The differing magnitudes of the 2005–2020 spatially-integrated FAC of -66.6 km³ yr^-1 in SNOWPACK and -17.4 km³ yr^-1 in the CFM demonstrate how model differences propagate throughout the FAC record. Over the full modeled record (1980–2020), SNOWPACK simulates a loss of pore space equivalent to 3 mm of sea level rise buffering, while the CFM simulates a loss of 1 mm. The greatest depletion in FAC is along the margins, and especially along the western margin where observations and models show the formation of near-surface, low-permeability ice slabs that inhibit meltwater storage.

Comment on tc-2022-231

Abstract: Abstract. Debris-covered glaciers are a common feature of the mountain cryosphere in the southeastern Tibetan Plateau. A better understanding of these glaciers change is necessary to reduce the uncertainties of the regional water resource variability, and to anticipate potential cryospheric risks. In this study, we quantify seasonal thinning (dh) and surface mass balance (SMB) patterns of two neighboring debris-covered glaciers (23 K Glacier and 24 K Glacier) in the southeastern Tibetan Plateau with repeated unpiloted aerial vehicle (UAV) surveys and in-situ measurements. We observe that the dh pattern of 23 K Glacier is distinct from that of 24 K Glacier, despite their proximity. The dh magnitude of the 23 K Glacier is ~1.4–3.0 times greater than that of the 24 K Glacier at all periods, which is mainly driven by the stronger dynamic state of 24 K Glacier. The contrasted behaviour between the two glaciers is also valid in the early twenty-first century. In contrast, the SMB patterns of the two glaciers are generally in agreement at different periods. The debris thickness distribution correlates with the SMB spatial distribution for both glaciers, while the supraglacial ice cliffs and ponds area density distribution is not correlated with SMB spatial distribution. This high-resolution comparison study of two neighboring glaciers confirms the significance of both glacier dynamic and debris thickness in controlling the thinning and melt for the different type debris-covered glaciers of the southeastern Tibetan Plateau in the context of climate change.

The Infierno Glacier (Pyrenees, Aragon, Spain): Evolution 2016–2022

Abstract: The Infierno Glacier is located in Aragon (Spain), Pyrenees Mountain range, the only one in this country that still preserves white glaciers. These are the southernmost glaciers in Europe and are currently in rapid decline. The work analyzes the evolution of the glacier between 2016 and 2022 and provides data, for this period, which lacked this information, in an area bordering the glacial ice survival. In addition to the observations on the glacier itself, the variables (precipitation, temperature, snow volume and thickness) that allow an understanding of this evolution are studied. The results show a setback of the glacier (thickness losses: 4.6 m; front retreat; 14.9 m). The evolution has frequent trend changes, linked to the interannual climatic irregularity characteristic of the Pyrenees. The main explanatory factor is the thermal increase. The thermal anomalies with respect to the average reference values have increased, in this period, by +0.55 °C. The year 2022 has been particularly warm and has recorded the greatest losses for this glacier. With respect to precipitation, it has an irregular behavior and shows a tendency to decrease (−9% in the same period). This work has the additional interest of analyzing a glacier in the terminal phase, which if current trends continue, evolves into dead ice.

Reply on RC2

Abstract: Abstract. The Greenland Ice Sheet's (GrIS) firn layer buffers the ice sheet's contribution to sea level rise by storing meltwater in its pore space. However, available pore space and meltwater retention capability is lost due to ablation of the firn layer and refreezing of meltwater as near-surface ice slabs in the firn. Understanding how firn properties respond to climate is important for constraining the GrIS's future contribution to sea level rise in a warming climate. Observations of firn density provide detailed information about firn properties, but they are spatially and temporally limited. Here we use two firn models, the physics-based SNOWPACK model and the semi-empirical Community Firn Model (CFM) to quantify firn properties across the GrIS from 1980 through 2020. We use an identical forcing (MERRA-2 atmospheric reanalysis) for SNOWPACK and the CFM in order to isolate model differences. To evaluate the models, we compare simulated firn properties, including firn air content (FAC), to measurements from the SUMup dataset of snow and firn density. Both models perform well, though their performance is hindered by meltwater percolation and the spatial resolution of the atmospheric forcing. In the full ice-sheet simulations, the spatially-integrated FAC (i.e., air volume in the firn) for the upper 100 m is 34,645 km³ from SNOWPACK and 28,581 km³ from the CFM. The discrepancy in the magnitude of the modeled FAC stems from differences in densification with depth and variations in the models' treatment of atmospheric input. In more recent years (2005–2020), both models simulate substantial depletion of pore space. During this period, the spatially-integrated FAC across the entire GrIS decreases by 2.8 % and 1.2 % in SNOWPACK and the CFM, respectively. The differing magnitudes of the 2005–2020 spatially-integrated FAC of -66.6 km³ yr^-1 in SNOWPACK and -17.4 km³ yr^-1 in the CFM demonstrate how model differences propagate throughout the FAC record. Over the full modeled record (1980–2020), SNOWPACK simulates a loss of pore space equivalent to 3 mm of sea level rise buffering, while the CFM simulates a loss of 1 mm. The greatest depletion in FAC is along the margins, and especially along the western margin where observations and models show the formation of near-surface, low-permeability ice slabs that inhibit meltwater storage.

Reply on RC1

Abstract: Abstract. Accurate measurements of ice flow are essential to predict future changes in glaciers and ice caps. Glacier displacement can in principle be measured at the large-scale by cross-correlation of satellite images. At weekly to monthly scales, the expected displacement is often of the same order noise for the commonly used satellite images, which limits the retrieval of accurate glacier velocity. Assessments of velocity changes on short time scales and over complex areas such as mountain ranges are therefore still lacking, but are essential to better understand how glacier dynamics are driven by internal and external factors. In this study, we take advantage of the wide availability and redundancy of satellite imagery over the Western Pamir to retrieve 10-day glacier velocity changes over 7 years for a wide range of glacier geometry and dynamics. Our results reveal strong seasonal trends. In spring/summer, we observe velocity increases of up to 300 % compared to a slow winter period. These accelerations clearly migrate upglacier throughout the melt-season, which we link to changes in subglacial hydrology efficiency. In autumn, we observe glacier accelerations that have rarely been observed before. These episodes are primarily confined to the upper ablation zone with a clear downglacier migration. We suggest that they result from glacier instabilities caused by sudden subglacial pressurization in response to (1) supraglacial pond drainage and/or (2) gradual closure of the hydrological system. Our 10-day resolved measurements allow us to characterize the short-term response of glacier to changing meteorological and climatic conditions.

Characterization of Three Surges of the Kyagar Glacier, Karakoram

Abstract: Glaciers experience periodic variations in flow velocity called surges, each of which influences the glacier’s characteristics and the occurrence of downstream disasters (e.g., ice-dammed lake outburst floods). The Karakoram region contains many surging glaciers, yet there are few comprehensive studies of multiple surge cycles. In this work, Landsat, topographic map, Shuttle Radar Topography Mission (SRTM), TerraSAR-X/TanDEM-X, ITS_LIVE, and Sentinel-1 glacier velocity data were used to systematically analyze the characteristics of Kyagar Glacier since the 1970s. Three surging events were identified, with active phases in 1975–1978, 1995–1997, and 2014–2016. The timing of these surges was similar, with a cycle of 19–20 years, an active phase of 3–4 years, and a quiescent phase of 16–17 years. During the quiescent phase, a large amount of ice accumulates in the lower part of the accumulation zone, and the terminal of the tongue thins significantly. According to the most recent surge event (2014–2016), glacier flow accelerated suddenly in the active phase and reached a maximum velocity of 2 ± 0.08 m d−1. Then, the glacier terminal thickened sharply, the reservoir zone thinned by 12 ± 0.2 m, and the terminal receiving zone thickened by 28 ± 0.2 m. The glacier may have entered a quiescent phase after July 2016. The glacier surge causes a large amount of material to transfer from upstream to downstream, forming an ice dam and creating conditions for a glacial lake outburst flood (GLOF). At the termination of the active phase, the subglacial drainage channel became effective, triggering the GLOF. For a period of the quiescent phase, the glacier ablation intensifies and the GLOF repeats constantly. One surge caused 7–8 GLOFs, and then a continuous reduction in the ice dam elevation. Eventually, the ice dam disappeared, and the GLOF no longer continued before the next glacier-surging event.

Rain-induced transient variations in glacier dynamics characterized by a continuous and dense GPS network at the Glacier d’Argentière

Abstract: The motion of glaciers with a temperate base is highly variable in time and space, mainly as a result of glacier basal sliding being strongly modulated by subglacial hydrology. Although transient friction laws have recently been established in order to predict short-term sliding velocity changes in response to water input changes, yet little observations enable fully constraining these laws. Here we investigate short-term changes in glacier dynamics induced by transient rainwater input on the Glacier d’Argentière (French Alps) using up to 13 permanent GPS stations. We observe strong surface acceleration events materialized by maximum downglacier velocities on the order of 2 to 3 times background velocities and associated with significant glacier surface uplift of 0.03 m to 0.1 m. We demonstrate that uplift strikingly coincides with water discharge. In contrast, horizontal speed-up occurs over a timescale shorter than discharge and uplift changes, with a maximum occurring concomitantly with maximum water pressure but prior to maximum discharge or uplift. Our findings suggest that transient acceleration and uplift of the glacier are not necessarily modulated by the same mechanism. We also observe that the horizontal speed-ups propagate downglacier at migrating speeds of 0.04 m s-1 to 0.13 m s-1, suggesting an underlying migration of subglacial water flows through the inefficient, distributed system. We demonstrate that the temporal relationship between water discharge, water pressure, and three-dimensional glacier motions are complex and cannot be directly interpreted by changes in the subglacial water pressure through cavity formation and water storage. 

Monitoring glacier fade out in Austrian Eastern Alps

Abstract: <p>In the Austrian Alps, recent rapid glacier melt affected the glaciers up to the summits. Glacier disintegration, debris flows, rock falls and increased melt rates are challenging glacier monitoring. Apart from the technical and safety issues arising, the scientific question arises how long a glacier fade out can and should be observed.</p> <p>From a technical perspective, direct mass balance monitoring is hampered by destruction of stakes by rock fall and snow pressure mounted on the increasingly steep glacier surfaces. Glacier changes require a frequent repositioning of stakes. Deep parts of the glaciers where stakes were not mounted in the past because the area was heavily crevassed remain longer that the thinner parts where stakes were operated in past decades, for example on Jamtalferner/Silvretta.</p> <p>Area loss meanwhile has a significant impact on glacier wide specific mass balance, but an annual resurvey of glacier area by terrestrial photogrammetry, airborne LiDAR or UAV rises the monitoring costs and effort considerably, while the uncertainty of mapping glacier area from remote sensing images is hampered by resolution and/or debris cover.  </p> <p>Subglacial melt in large cavities which developed during the last years so far is not quantified, but estimated from thickness loss data suggest that the contribution of basal mass loss to total mass loss can be as large as surface mass balance.</p> <p>Common definitions of a glacier imply ice formation from snow and firn, ice dynamics and a runoff system. For several Austrian glaciers, snow and firn cover is entirely gone. There, no new ice can form during the next decades even in case accumulation of snow would take place in future. In addition to that, flow velocities drop to <5 m/year, which is a similar magnitude than that measured for rock glaciers. From a glaciological perspective, those (former?) glaciers rather meet the definition of dead ice, especially when covered by debris.</p> <p>From a hydrological perspective, monitoring of those glacier remnants still makes sense, as they are still part of the local hydrological system. From the perspective of hazard monitoring, glacier remnants are also worth monitoring as they are relevant for generation of debris flows and englacial/thermokarst lakes.</p> <p>To continue local glacier monitoring and contribute to a global database, a joint global monitoring strategy and methodology would be beneficial. For example, a definition of ‘transient glaciers’ in fade out with a specification of monitoring methods would be helpful to prolongate mass balance time series when direct measurements become impossible for the total area. That could be single stakes, geodetic methods when glacier margins are still clear, or hydrological methods.   </p>

Glacier retreat with optical and radar images: Olivares Glacier and Juncal sur

Abstract: Most of the glaciers in Chile have experienced strong retreats and surface reductions from historical times to the present in response to global climate changes (1). Climate change is not the only factor, given that both the Anthropic intervention and/or natural factors may contribute to accelerating glacial shrinkage. Studies and measurements carried out by researchers have revealed that the Andean glaciers of the central zone are increasingly vulnerable to processes of mass loss and fragmentation as a result of the darkening of the ice and its effect on the absorption of solar radiation, a phenomenon known as the albedo effect. Not only are they losing surface, but they are also thinning up to two meters per year, a figure that is no less, since a large part of the glaciers in the central zone, and in particular in the Metropolitan Region, are no more than a few tens of meters Tall. Having knowledge of the variation of the glacial area is essential for the decision-making process in the management and conservation of solid water reserves and thus face potential water crises in the region over time. Through remote sensing techniques and the use of Geographic Information Systems (GIS), the aim is to determine the variation in area and volume that the Olivares Alfa, Beta, Gamma and Juncal Sur glaciers have experienced and at the same time calculate the current speed of movement Juncal Sur Glacier.

Understanding glacier retreat in the Bhutan Himalaya through regional inventory and influence of glacial lakes.

Abstract: Abstract The present study demonstrates the importance of glacier inventories in understanding and managing glaciers in the Himalayan region, specifically in the Pho Chu Basin (PCB) of Bhutan Himalaya. The study utilised, Sentinel-2A imagery of 2021 to create a novel inventory of glaciers in the PCB, and further modified the boundaries of 35 (area > 1 km2) glaciers for the years 1991 and 2006. The results suggest, 184 glaciers covering an area of 192.07 + 15.50 km2 in the PCB, with the areal extent of the 34 glaciers (excluding Thorthormi Glacier) decreasing from 153.32 + 8.60 km2 to 139.97 + 8.44 km2 (1991-2021), indicating an area loss of 8.7 % in the basin. Further, we have observed the topographic parameters of each glacier. Interestingly, the glaciers retreated at a rate of -14.62 + 11.39 ma-1 (1991-2021), and small glaciers retreat much faster than large glaciers in PCB. Our observation reveals that glacier with lakes in this region are subjected to more retreat when compared to clean and debris covered glaciers. The alarming retreat of the Thorthormi Glacier has been the subject of multiple GLOF events and is analysed separately in the present study. Overall, the study demonstrates the importance of glacier inventories as a database for researchers, policymakers, and local communities about the location, extent, area, length, orientation, and other characteristics of glaciers.

Post-Little Ice Age Glacier Recession in the North-Chuya Ridge and Dynamics of the Bolshoi Maashei Glacier, Altai

Abstract: The glacier recession of the North-Chuya ridge, Altai, after the maximum of the Little Ice Age (LIA) is estimated based on remote sensing and in situ studies of the Bolshoi Maashei glacier. The glacier area decreased from 304.9 ± 23.49 km2 at the LIA maximum to 140.24 ± 16.19 km2 in 2000 and 120.02 ± 16.19 km2 in 2021. The average equilibrium-line altitude (ELA) rise after the LIA was 207 m. The reduction of glaciers was caused by the warming trend, most rapid in the 1990s, and by the decrease in precipitation after the mid-1980s. The volume of glaciers decreased from approximately 16.5 km3 in the LIA maximum to 5.6–5.8 km3 by 2021. From the LIA maximum to 2022, the Bolshoi Maashei glacier decreased from 17.49 km2 to 6.25 km2, and the lower point rose from 2160 m to 2225 m. After the LIA, the glacial snout retreat was about 1 km. The fastest retreat of the glacier terminus was estimated in 2010–2022 as 14.0 m a−1 on average. The glacier mass balance index was calculated, with the results showing a strong negative trend from the mid-1980s until now. Strong melt rates caused the increase in the area of the Maashei lake, which could lead to the weakening of its dam, and prepared for its failure in 2012. The current climatic tendencies are unfavorable for the glaciers.

Rapid and massive 335 million m3 glacier bed erosion after detachment of the Sedongpu Glacier (Tibet)

Abstract: Following the 130 106 m3 detachment of the Sedongpu Glacier (south-eastern Tibet) in 2018, the Sedongpu valley underwent drastic and rapid large-volume landscape changes. Between 2018 and 2022, and in particular during summer 2021, an enormous volume of in total ~335 106 m3 was eroded from the former glacier bed, forming a new canyon of up to 300 m depth, 1 km width and almost 4 km length. The mass was transported into the Yarlung Tsangpo (Brahmaputra) River and further. Several rock-ice avalanches of in total ~150 106 m3 added to the total rock, sediment and ice volume of over 0.6 km3 that were exported from the basin since around 2017. The recent events at Sedongpu Glacier represent a rapid and irreversible process of landscape transformation from a sediment-filled glacier valley to a glacier-free one with a deeply incised canyon, impressively confirming that glaciers are able to protect their soft beds against massive erosion. Once uncovered, the erosion potential of soft glacier beds is here demonstrated to be possibly enormous for some glaciers in terms of volumes and rates. Such erosion could be particularly extreme for fine-grained subglacial sediments and for elevated glacier beds where large amounts of subglacial sediments are stored. The 2018–2022 landscape development at Sedongpu represents an extreme example of rapid paraglacial slope response highlighting extreme glacier erosion potentials and related hazards from debris flows and impacts on rivers. Such consequences of climate change in glacierized mountains have so far not been considered at this magnitude.