Glacier Velocity Research Articles

The south inylchek glacier activity analysis over a ten-year interval in surface velocity with multi-source spaceborne imagery

Glacier movement is one of the most important characteristics in describing mountain glacier activity, which is a sensitive natural indicator of climate change. However, the short-term glacier movement with a single data source could not precisely and sufficiently demonstrate the response of glaciers to climate change. In order to extract the reliable signal corresponding to climate change, the long-term monitoring of glacier movement should be widely exploited. This paper presents the glacier movement distribution of the South Inylchek Glacier by the improving pixel tracking algorithm with both synthetic aperture radar and optical satellite images in 2007–2008 and 2017–2018. The analysis in spatiotemporal characteristics of the glacier velocity indicates that the South Inylchek Glacier remained almost stable in a ten-year interval with the average velocity of 32 cm/d, which are computed with quasi-synchronization multi-source imagery. And the consistency of the velocity results was also verified with both optical and SAR imagery during the same period. Therefore, it would be valuable in expanding the research temporal cycle of glacier movement by uniting multi-source data. And the long-term glacier movement should be exploited for further analysis in mass balance prediction and assessing the climate change effects in the High Mountain Asia.

InSAR-based characterization of rock glacier movement in the Uinta Mountains, Utah, USA

Abstract. Rock glaciers are a prominent component of many alpine landscapes and constitute a significant water resource in some arid mountain environments. Here, we employ satellite-based interferometric synthetic aperture radar (InSAR) between 2016 and 2019 to identify and monitor active and transitional rock glaciers in the Uinta Mountains (Utah, USA), an area of ∼3000 km2. We used mean velocity maps to generate an inventory for the Uinta Mountains containing 205 active and transitional rock glaciers. These rock glaciers are 11.9 ha in area on average and located at a mean elevation of 3308 m, where mean annual air temperature is −0.25 ∘C. The mean downslope velocity for the inventory is 1.94 cm yr−1, but individual rock glaciers have velocities ranging from 0.35 to 6.04 cm yr−1. To search for relationships with climatic drivers, we investigated the time-dependent motion of three rock glaciers. We found that rock glacier motion has a significant seasonal component, with rates that are more than 5 times faster during the late summer compared to the rest of the year. Rock glacier velocities also appear to be correlated with the snow water equivalent of the previous winter's snowpack. Our results demonstrate the ability to use satellite InSAR to monitor rock glaciers over large areas and provide insight into the environmental factors that control their kinematics.

Debris Emergence Elevations and Glacier Change

Debris-covered glaciers represent potentially significant stores of freshwater in river basins throughout High Mountain Asia (HMA). Direct glacier mass balance measurements are extremely difficult to maintain on debris-covered glaciers, and optical remote sensing techniques to evaluate annual equilibrium line altitudes (ELAs) do not work in regions with summer-accumulation type glaciers. Surface elevation and glacier velocity change have been calculated previously for debris-covered glaciers across the region, but the response of debris cover itself to climate change remains an open question. In this research we propose a new metric, i.e. the debris emergence elevation (ZDE), which can be calculated from a combination of optical and thermal imagery and digital elevation data. We quantify ZDE for 975 debris-covered glaciers in HMA over three compositing periods (1985–1999, 2000–2010, and 2013–2017) and compare ZDE against median glacier elevations, modelled ELAs, and observed rates of both mass change and glacier velocity change. Calculated values of ZDE for individual glaciers are broadly similar to both median glacier elevations and modelled ELAs, but slightly lower than both. Across the HMA region, the average value of ZDE increased by 70 +/− 126 m over the study period, or 2.7 +/− 4.1 m/yr. Increases in ZDE correspond with negative mass balance rates and decreases in glacier velocity, while glaciers and regions that show mass gains and increases in glacier velocity experienced decreases in ZDE. Regional patterns of ZDE, glacier mass balance, and glacier velocities are strongly correlated, which indicates continued overall increases in ZDEE and expansion of debris-covered areas as glaciers continue to lose mass. Our results suggest that ZDE is a useful metric to examine regional debris-covered glacier changes over decadal time scales, and could potentially be used to reconstruct relative mass and ELA changes on debris-covered glaciers using historical imagery or reconstructed debris cover extents.

Conventional and UAV-Based Aerial Surveys for Long-Term Monitoring (1954–2020) of a Highly Active Rock Glacier in Austria

Rock glaciers are creep phenomena of mountain permafrost. Speed-up has been observed on several rock glaciers in recent years and attributed to climate change. Although rare, related long-term studies are nevertheless essential to bring a climate perspective to creep velocity changes. In the present study, we focused on changes both in the surface creep velocity and volume of the Leibnitzkopf rock glacier (Hohe Tauern Range, Austria) in the period 1954–2020. We applied 3D change detection using aerial images of both conventional (12 epochs between 1954 and 2018) and unmanned aerial vehicle (UAV)-based aerial surveys (2 epochs, 2019 and 2020), and combined this with ground and air temperature data. Photogrammetric processing (structure-from-motion, multi-view stereo) of the multi-temporal dataset resulted in high-resolution digital orthophotos/DOPs (5–50 cm spatial resolution) and digital elevation models/DEMs (10–50 cm grid spacing). Georeferencing was supported by five externally triangulated images from 2018, bi-temporal aerial triangulation of the image data relying on stable ground around the rock glacier, measured ground control points (2019 and 2020), and measured camera locations (PPK-GNSS) of the UAV flight in 2020. 2D displacement vectors based on the multi-temporal DOPs and/or DEMs were computed. Accuracy analyses were conducted based on geodetic measurements (2010–2020) and airborne laser scanning data (2009). Our analyses show high multi-annual and inter-annual creep velocity variabilities with maxima between 12 (1974–1981) and 576 cm/year (2019–2020), always detected in the same area of the rock glacier where surface disintegration was first observed in 2018. Our volume change analyses of the entire landform for the period 1954–2018 do not indicate any significant changes. This suggests little permafrost ice melt and/or general low ice content of the rock glacier. Analyses of the temperature data reveal a close relationship between higher temperatures and rock glacier acceleration despite the high probability of low ice content. This suggests that hydrogeological changes play an important role in the rock glacier system. The paper concludes with a summary of technical improvements and recommendations useful for rock glacier monitoring and a general view on the kinematic state of the Leibnitzkopf rock glacier.

Surface composition of debris-covered glaciers across the Himalaya using linear spectral unmixing of Landsat 8 OLI imagery

Abstract. The Himalaya mountain range is characterized by highly glacierized, complex, dynamic topography. The ablation area of Himalayan glaciers often features a highly heterogeneous debris mantle comprising ponds, steep and shallow slopes of various aspects, variable debris thickness, and exposed ice cliffs associated with differing ice ablation rates. Understanding the composition of the supraglacial debris cover is essential for a proper understanding of glacier hydrology and glacier-related hazards. Until recently, efforts to map debris-covered glaciers from remote sensing focused primarily on glacier extent rather than surface characteristics and relied on traditional whole-pixel image classification techniques. Spectral unmixing routines, rarely used for debris-covered glaciers, allow decomposition of a pixel into constituting materials, providing a more realistic representation of glacier surfaces. Here we use linear spectral unmixing of Landsat 8 Operational Land Imager (OLI) images (30 m) to obtain fractional abundance maps of the various supraglacial surfaces (debris material, clean ice, supraglacial ponds and vegetation) across the Himalaya around the year 2015. We focus on the debris-covered glacier extents as defined in the database of global distribution of supraglacial debris cover. The spectrally unmixed surfaces are subsequently classified to obtain maps of composition of debris-covered glaciers across sample regions. We test the unmixing approach in the Khumbu region of the central Himalaya, and we evaluate its performance for supraglacial ponds by comparison with independently mapped ponds from high-resolution Pléiades (2 m) and PlanetScope imagery (3 m) for sample glaciers in two other regions with differing topo-climatic conditions. Spectral unmixing applied over the entire Himalaya mountain range (a supraglacial debris cover area of 2254 km2) indicates that at the end of the ablation season, debris-covered glacier zones comprised 60.9 % light debris, 23.8 % dark debris, 5.6 % clean ice, 4.5 % supraglacial vegetation, 2.1 % supraglacial ponds, and small amounts of cloud cover (2 %), with 1.2 % unclassified areas. The spectral unmixing performed satisfactorily for the supraglacial pond and vegetation classes (an F score of ∼0.9 for both classes) and reasonably for the debris classes (F score of 0.7). Supraglacial ponds were more prevalent in the monsoon-influenced central-eastern Himalaya (up to 4 % of the debris-covered area) compared to the monsoon-dry transition zone (only 0.3 %) and in regions with lower glacier elevations. Climatic controls (higher average temperatures and more abundant precipitation), coupled with higher glacier thinning rates and lower average glacier velocities, further favour pond incidence and the development of supraglacial vegetation. With continued advances in satellite data and further method refinements, the approach presented here provides avenues towards achieving large-scale, repeated mapping of supraglacial features.

Glacier Velocity Changes in the Himalayas in Relation to Ice Mass Balance

Glacier evolution with time provides important information about climate variability. Here, we investigated glacier velocity changes in the Himalayas and analysed the patterns of glacier flow. We collected 220 scenes of Landsat-7 panchromatic images between 1999 and 2000, and Sentinel-2 panchromatic images between 2017 and 2018, to calculate surface velocities of 36,722 glaciers during these two periods. We then derived velocity changes between 1999 and 2018 for the early winter period, based on which we performed a detailed analysis of motion of each individual glacier, and noted that the changes are spatially heterogeneous. Of all the glaciers, 32% have sped up, 24.5% have slowed down, and the rest 43.5% have remained stable. The amplitude of glacier slowdown, as a result of glacier mass loss, is significantly larger than that of speedup. At regional scales, we found that glacier surface velocity in winter has uniformly decreased in the western part of the Himalayas between 1999 and 2018, while increased in the eastern part; this contrasting difference may be associated with decadal changes in accumulation and/or melting under different climatic regimes. We also found that the overall trend of surface velocity exhibits seasonal variability: summer velocity changes are positively correlated with mass loss, i.e., velocity increases with increasing mass loss, whereas winter velocity changes show a negative correlation. Our study suggests that glacier velocity changes in the Himalayas are spatially and temporally heterogeneous, in agreement with studies that previously highlighted this trend, emphasising complex interactions between glacier dynamics and environmental forcing.

Geometric Evolution of the Chongce Glacier during 1970–2020, Detected by Multi-Source Satellite Observations

Glacier surge, which causes a quick movement of ice mass from high to low elevation, is closely associated to the glacial hazards of debris flows and glacial lake outburst floods. Over the West Kunlun Shan, surge events have been detected for some glaciers, however, the characteristics (e.g., the active phase) of the identified surge-type glaciers are not fully understood due to the paucity of long-term observations of glacier changes. In this study, we investigated the geometric evolution of the Chongce Glacier (a surge-type glacier) over the past five decades. Glacier elevation changes were observed by comparing topographic data from different times. Surface velocity and terminus position were derived using a cross-correlation algorithm and band ratio method, respectively. A decreasing rate of glacier surface thinning was found for the Chongce Glacier during the studied period. Glacier elevation changes of −0.46 ± 0.12, −0.12 ± 0.05, and 0.27 ± 0.11 m yr−1 were estimated for the periods of 1970–2000, 2000–2012, and 2012–2018, respectively. Moreover, this glacier experienced obvious surface lowering over the terminus zone and clear surface thickening over the upper zone during 1970–2000, and the opposite during 2000–2018. Surface velocity of the Chongce Glacier was less than 300 m yr−1 in 1990–1993, and then quickly increased to more than 1000 m yr−1 between 1994 and 1998, and dropped to less than 50 m yr−1 in 1999–2020. Over the past five decades, the Chongce Glacier generally experienced a slight retreat, except for a terminus advance from 1995 to 1999. According to the spatial pattern of glacier elevation changes in 1970–2000 and the long-term changes of glacier velocity and terminus position, the recent surge event at the Chongce Glacier likely initiated in winter 1993 and terminated in winter 1998. Furthermore, the start date, end date, and duration of the active phase indicate that the detected surge event was likely triggered by a thermal mechanism.

Essential study of Karakoram glacier velocity products extracted using various techniques

The present study focuses on using remote sensing techniques to estimate the Karakoram glacier velocity that emulates glacier’s reaction to climate warming. Proposed study is essential and critical due to the vast spatial and temporal variability of the Karakoram Glaciers, fieldwork difficulties, and the lack of in situ data in the Karakoram. It focuses on assessing the robustness in extracting the velocity products of the Rimo Glacier, Karakoram using DInSAR, Intensity tracking, and Normalized Cross-Correlation. The results indicate that the average velocity of the Rimo glacier estimated from DInSAR and correlation techniques are around 22.4 cm/day and 5.2 cm/day respectively which is similar to earlier studies. Intensity tracking based average velocity is found to be around 18 cm/day. Results obtained are also compared with field-based measurements for corroboration. Continuous monitoring of the velocity of Karakoram glaciers is necessary to understand the complex and evolving trends of surging in the future.

Monitoring glacier surges in the Kongur Tagh area of the Tibetan Plateau using Sentinel-1 SAR data

Accurate identification of glacier surges aids in promoting a better understanding of the mechanisms of rapid glacier movement and predicting possible surge-related hazards. Surges of 10 glaciers in the Kongur Tagh area of the Tibetan Plateau were examined based on 128 scenes of Sentinel-1 Synthetic Aperture Radar (SAR) imagery with 12-day and 24-day time intervals from 2015 to 2019. To identify the surges, a set of quantifiable multi-feature criteria was used, including higher glacier velocity, surge front position movement and continuous higher velocity at contiguous time intervals based on surge-type glacier characteristics. The results showed that the Karayaylak Glacier surge reported in May 2015 was more likely initiated in summer 2014, and an unreported pulse event occurred in 2019. Another new and complete surge in the Jangmanjiar Glacier from 2016 to 2018 was further identified. Another two pulse events in the Jangmanjiar Glacier and the Kokodak Glacier in 2015 were discovered. The elevation changes from ASTER images and glacier terminus evolution based on Landsat 8 images also provided positive evidence for the occurrence of two surges. In the Kongur Tagh area, the surge-type glaciers might have larger areas (above 40 km2), longer lengths (above 13 km), lower slopes (below 10°) and higher mean quiescent velocities (above 0.1 ± 0.05 m d−1) than non-surging glaciers. The temperature and precipitation data of ECMWF Re-Analysis 5 (ERA5) showed that the surges in the Kongur Tagh area were mainly induced by thermal and hydrological trigger mechanisms together.

High-resolution monitoring of debris-covered glacier mass budget and flow velocity using repeated UAV photogrammetry in Iran

Iran's glaciers are commonly debris-covered. Due to climate changes, the frequency of glacial hazards such as glacial lake outbursts floods is increasing, and consequently, the mass of Iran's glaciers is decreasing. Fieldwork in high-altitude mountains is difficult, thus, the dynamics of debris–covered glaciers and their associated driving factors are poorly studied. In this study, changes in the elevation and the surface flow speed of the largest and most dynamic debris-covered glacier in Iran (Alamkouh glacier) are evaluated during 2018 to 2020 for the first time. For this purpose, images from a high-resolution unmanned aerial vehicle (UAV) are used. Additionally, the spatial distribution of glacier ice thickness is estimated based on the principles of ice-flow and glacier surface velocity data. The distribution of ice thickness is evaluated with in-situ Ground Penetration Radar (GPR) data. The acquired high-resolution images from UAV are processed into a digital elevation model (with a spatial resolution of about 15 cm) and orthoimages (with a spatial resolution of about 8 cm), and glacier ice thickness change and surface flow velocity are derived. In order to estimate glacier surface velocity, a frequency cross-correlation model was applied using the COSI-Corr module. Our results show that the mean glacier ice thinning during the study period 2018–2020 is about −0.23 ± 0.03 m yr−1 and it reaches about −5 ± 0.65 m yr−1 at the terminus and accumulation areas. The observed variations in ice thinning are best explained by the existence of debris cover (and their corresponding insulating effects), the existence of ice cliffs, and their associated supraglacial lakes. We found that ice cliffs and supraglacial lakes show mass losses that can be an order of magnitude higher than average. Moreover, the mean surface velocity of Alamkouh glacier is about 1.1 ± 0.06 m yr−1 from 2018 to 2020 with considerable spatial variation in surface velocities. The maximum surface velocity (about 4.5 ± 0.27 m yr−1) belongs to its upper regions, and lower and marginal areas are nearly stagnant. The slow movement of the glacier, along with a continuous increase in debris and ice thinning, provides a suitable condition for supraglacial pond development, which decreases glacier mass. Total volume of glacier was estimated to be ~102 × 106 m3 in 2020, corresponding to an average ice thickness of ~31.3 ± 7.5 m. Moreover, the average ice thinning rate is 0.66% yr−1 in 2018 to 2020. According to this reduction rate, it is expected that more than 51.7% of the glacier will be lost by the end of the 21st century.

Velocity Anomaly of Campbell Glacier, East Antarctica, Observed by Double-Differential Interferometric SAR and Ice Penetrating Radar

Regional changes in the flow velocity of Antarctic glaciers can affect the ice sheet mass balance and formation of surface crevasses. The velocity anomaly of a glacier can be detected using the Double-Differential Interferometric Synthetic Aperture Radar (DDInSAR) technique that removes the constant displacement in two Differential Interferometric SAR (DInSAR) images at different times and shows only the temporally variable displacement. In this study, two circular-shaped ice-velocity anomalies in Campbell Glacier, East Antarctica, were analyzed by using 13 DDInSAR images generated from COSMO-SkyMED one-day tandem DInSAR images in 2010–2011. The topography of the ice surface and ice bed were obtained from the helicopter-borne Ice Penetrating Radar (IPR) surveys in 2016–2017. Denoted as A and B, the velocity anomalies were in circular shapes with radii of ~800 m, located 14.7 km (A) and 11.3 km (B) upstream from the grounding line of the Campbell Glacier. Velocity anomalies were up to ~1 cm/day for A and ~5 cm/day for B. To investigate the cause of the two velocity anomalies, the ice surface and bed profiles derived from the IPR survey crossing the anomalies were analyzed. The two anomalies lay over a bed hill along the glacial valley where stick-slip and pressure melting can occur, resulting in temporal variation of ice velocity. The bright radar reflection and flat hydraulic head at the ice bed of A observed in the IPR-derived radargram strongly suggested the existence of basal water in a form of reservoir or film, which caused smaller friction and the reduced variation of stick-slip motion compared to B. Crevasses began to appear at B due to tensile stress at the top of the hill and the fast flow downstream. The sporadic shift of the location of anomalies suggests complex pressure melting and transportation of the basal water over the bed hill.

A Landsat-based dataset of glacier velocity in Eastern Pamir from 1989 to 2020

A Landsat-based dataset of glacier velocity in Eastern Pamir from 1989 to 2020

Evolution of Surface Characteristics of Three Debris-Covered Glaciers in the Patagonian Andes From 1958 to 2020

A number of glaciological observations on debris-covered glaciers around the globe have shown a delayed length and mass adjustment in relation to climate variability, a behavior normally attributed to the ice insulation effect of thick debris layers. Dynamic interactions between debris cover, geometry and surface topography of debris-covered glaciers can nevertheless govern glacier velocities and mass changes over time, with many glaciers exhibiting high thinning rates in spite of thick debris cover. Such interactions are progressively being incorporated into glacier evolution research. In this paper we reconstruct changes in debris-covered area, surface velocities and surface features of three glaciers in the Patagonian Andes over the 1958–2020 period, based on satellite and aerial imagery and Digital Elevation Models. Our results show that debris cover has increased from 40 ± 0.6 to 50 ± 6.7% of the total glacier area since 1958, whilst glacier slope has slightly decreased. The gently sloping tongues have allowed surface flow velocities to remain relatively low (<60 m a−1) for the last two decades, preventing evacuation of surface debris, and contributing to the formation and rise of the ice cliff zone upper boundary. In addition, mapping of end of summer snowline altitudes for the last two decades suggests an increase in the Equilibrium Line Altitudes, which promotes earlier melt out of englacial debris and further increases debris-covered ice area. The strongly negative mass budget of the three investigated glaciers throughout the study period, together with the increases in debris cover extent and ice cliff zones up-glacier, and the low velocities, shows a strong linkage between debris cover, mass balance evolution, surface velocities and topography. Interestingly, the presence of thicker debris layers on the lowermost portions of the glaciers has not lowered thinning rates in these ice areas, indicating that the mass budget is mainly driven by climate variability and calving processes, to which the influence of enhanced thinning at ice cliff location can be added.

Characterizing the behaviour of surge-type glaciers in the Geladandong Mountain Region, Inner Tibetan Plateau, from 1986 to 2020

Although surging glaciers in the Geladandong Mountain region represent a small percentage of the Qinghai-Tibet Plateau's glacier population, they can provide valuable insight into the glacier processes, flow instabilities, and fast glacier flow. Here we identify 11 surge-type glaciers and reported the observations of surging behaviour in this region by mapping changes in the terminus position, surface velocity, and elevation of glaciers, using a combination of Landsat and ASTER satellite imagery from 1986 to 2020, TerraSAR-X/TanDEM-X, NASADEM, and topographic maps. Among the 11 surge-type glaciers, nine glaciers started to surge in the 1980s and 1990s, and two glaciers began to surge after 2000. In total, we present 22 surface velocity data sets, which show that the active phases usually last 10–19 years and peak surge velocities are between 30 ± 1.26 m a−1 and 100 ± 1.26 m a−1. The acceleration phases at the beginning can last for several years, and the deceleration phases at the end last for a maximum of 2 years, and the flow velocity in summer is greater than that in winter. Under the background of global climate warming, no single process is responsible for glacier surges in the Geladandong Mountain region. The dynamic evolution of glacier surges does not fit neatly within either of the classically cited thermal or hydrological models of surging. We hypothesize that the recent glacier surges may be caused by multiple factors.

Rock glaciers throughout the French Alps accelerated and destabilised since 1990 as air temperatures increased

Rock glaciers—ice-rich creeping landforms typical of permafrost mountain ranges—can develop an anomalous landslide-like behaviour called destabilisation. This behaviour is characterised by failure mechanisms (including cracks and crevasses) and increases in displacement rates by one to two orders of magnitude. Existing studies of this phenomenon have been limited to a small number of landforms and short time spans. Here, we systematically investigate the evolution of rock glacier kinematics over the past seven decades for the entire French Alps by combining observations of landform features indicative of the onset of destabilisation with data on displacements rates using aerial orthoimagery. We show that rock glacier velocities have significantly increased since the 1990s, concurrent with the development of destabilisation in 18 landforms that represent 5% of the 337 active rock glaciers. This pattern of activity correlates with rising air temperatures in the region, which suggests that a warming climate may play a role in this process.

Glacier Image Velocimetry: an open-source toolbox for easy and rapid calculation of high-resolution glacier velocity fields

Abstract. We present Glacier Image Velocimetry (GIV), an open-source and easy-to-use software toolkit for rapidly calculating high-spatial-resolution glacier velocity fields. Glacier ice velocity fields reveal flow dynamics, ice-flux changes, and (with additional data and modelling) ice thickness. Obtaining glacier velocity measurements over wide areas with field techniques is labour intensive and often associated with safety risks. The recent increased availability of high-resolution, short-repeat-time optical imagery allows us to obtain ice displacement fields using “feature tracking” based on matching persistent irregularities on the ice surface between images and hence, surface velocity over time. GIV is fully parallelized and automatically detects, filters, and extracts velocities from large datasets of images. Through this coupled toolchain and an easy-to-use GUI, GIV can rapidly analyse hundreds to thousands of image pairs on a laptop or desktop computer. We present four example applications of the GIV toolkit in which we complement a glaciology field campaign (Glaciar Perito Moreno, Argentina) and calculate the velocity fields of small mid-latitude (Glacier d'Argentière, France) and tropical glaciers (Volcán Chimborazo, Ecuador), as well as very large glaciers (Vavilov Ice Cap, Russia). Fully commented MATLAB code and a stand-alone app for GIV are available from GitHub and Zenodo (see https://doi.org/10.5281/zenodo.4624831, Van Wyk de Vries, 2021a).

Changes in Ground Temperature and Dynamics in Mountain Permafrost in the Swiss Alps

Rising air temperatures and increasingly intense precipitation are being observed in the Swiss Alps. These changes strongly affect the evolution of the temperature regime and the dynamics of mountain permafrost. Changes occur at different rates depending on ground ice content. Long-term monitoring reveals progressive warming and degradation of permafrost and accelerating rock glacier velocities. This study analyses changes occurring in ice-rich (excess-ice) and ice-poor mountain permafrost in Switzerland between 1997 and 2019 on the basis of ground temperature and rock glacier dynamics measurements carried out by the WSL Institute for Snow and Avalanche Research SLF at seven sites. Long-term borehole data indicate an increase of ground temperatures at all depths, in particular at ice-poor and nearly snow-free sites. Active layers are thickening at most sites and prolonged periods of active layer thaw are observed. Long autumn zero curtains are observed in ice-rich permafrost, possibly leading to an overall acceleration of rock glaciers. All these changes point towards ongoing permafrost warming and permafrost degradation in future.

Temporal fluctuations of siachen glacier velocity: a repeat pass sar interferometry based approach

Glacier velocity, the glacier's health indicator, is an emerging research interest in global warming among the scientific community over the current decade. As per scientific reports, due to their stable and advanced nature, the glaciers of Karakoram are exclusive. The present study focuses on understanding the temporal velocity variability of the Siachen Glacier, Shyok Basin, Karakoram using SAR datasets, in the perspective of the difficulties in estimating the glacier velocity over the inaccessible Karakoram Mountain. For the hydrological year 2017-18, 30 sentinel-1 derived interferograms using the DInSAR technique were analyzed to obtain Line Of Sight velocity. The transient velocity of the glacier reflects separate patterns within the glacier for different seasons due to the thermodynamic and orographic system over the glacier surface. In azimuth and range direction, the projected annual LOS velocity to a two-dimensional surface velocity is estimated to be around 103.8 ± 3.1 m/year.

Hydrological and Kinematic Precursors of the 2017 Calving Event at the Petermann Glacier in Greenland Observed from Multi-Source Remote Sensing Data

Both a decrease of sea ice and an increase of surface meltwater, which may induce ice-flow speedup and frontal collapse, have a significant impact on the stability of the floating ice shelf in Greenland. However, detailed dynamic precursors and drivers prior to a fast-calving process remain unclear due to sparse remote sensing observations. Here, we present a comprehensive investigation on hydrological and kinematic precursors before the calving event on 26 July 2017 of Petermann Glacier in northern Greenland, by jointly using remote sensing observations at high-temporal resolution and an ice-flow model. Time series of ice-flow velocity fields during July 2017 were retrieved with Sentinel-2 observations with a sub-weekly sampling interval. The ice-flow speed quickly reached 30 m/d on 26 July (the day before the calving), which is roughly 10 times quicker than the mean glacier velocity. Additionally, a significant decrease in the radar backscatter coefficient of Sentinel-1 images suggests a rapid transformation from landfast sea ice into open water, associated with a decrease in sea ice extent. Additionally, the area of melt ponds on the floating ice tongue began to increase in mid-May, quickly reached a peak at the end of June and lasted for nearly one month until the calving occurred. We used the ice sheet system model to model the spatial-temporal damage and stress on the floating ice, thereby finding an abnormal stress distribution in a cracked region. It is inferred that this calving event may relate to a weakening of the sea ice, shearing of the tributary glacier, and meltwater infiltrating crevasses.

Spatiotemporal Variability of Velocity and Influence of Glacier Thickness Using Landsat Imagery: Hunza River Basin, Karakoram Range

The Karakoram Anomaly has been intensively investigated, but the factors that control this anomaly, such as the glacier velocity, topography, and mass balance, remain poorly understood. To improve our understanding of the velocity, topography, and mass balance of the Karakoram Glacier, in this study, the spatiotemporal variability of four glacier velocities in the Hunza Basin of the Karakoram range were surveyed using co-registration of optically sensed images and correlation (COSI-Corr) on Landsat imagery from 1993–2019. The results show that the velocity of the Gulmit Glacier increases with a rising altitude from the glacier terminal. The three other glaciers initially display high velocity, followed by a decrease from the glacier terminal, with the maximum velocity attained in the middle of the glacier. In addition, the Karakoram glaciers produced a slight mass gain, with all mountain glaciers exhibiting clear regional acceleration from 1993–2019. The ice deformation velocity of the Batura Glacier diminished at an average rate of 8.49 %. However, the topography of the glacier base and physical factors require further analysis to determine their contribution to the observed changes in glacier velocity. In the present work, multi-temporal remote sensing image interpretations were carried out to determine glacier kinematics, which could enhance our understanding of glacier change mechanisms.