The aim of this paper is to characterise the internal structures and ice-flow history of representative valley glaciers in Svalbard and infer from them dynamic changes over centennial timescales. Three polythermal and one cold valley glacier are investigated using field- and laboratory-based techniques and remote sensing. Structures along flow-unit boundaries indicate that ice-flow configuration in three of the glaciers has remained stable spanning the residence time of the ice. Deformation of a flow-unit boundary in the fourth reveals an ice-flow instability, albeit one that has been maintained since its most recent advance. Macro-crystallographic, sedimentological and isotopic analyses indicate that basal ice is elevated to the glacier surface, as shown by entrained sediments and enrichment in heavy isotopes. In narrow zones of enhanced cumulative strain, new ice facies are generated through dynamic recrystallisation. The surface density of longitudinal foliation is shown to represent the relative magnitude of cumulative strain. Geometric similarities between flow-unit boundaries in Svalbard valley glaciers and larger scale longitudinal surface structures in ice sheets suggest that deformation mechanisms are common to both.

We present a 1000 km transect of phase-sensitive radar measurements of ice thickness, basal reflection strength, basal melting and ice-column deformation across the Ross Ice Shelf (RIS). Measurements were gathered at varying intervals in austral summer between 2015 and 2020, connecting the grounding line with the distant ice shelf front. We identified changing basal reflection strengths revealing a variety of basal conditions influenced by ice flow and by ice–ocean interaction at the ice base. Reflection strength is lower across the central RIS, while strong reflections in the near-front and near-grounding line regions correspond with higher basal melt rates, up to 0.47 ± 0.02 m a−1 in the north. Melting from atmospherically warmed surface water extends 150–170 km south of the RIS front. Melt rates up to 0.29 ± 0.03 m a−1 and 0.15 ± 0.03 m a−1 are observed near the grounding lines of the Whillans and Kamb Ice Stream, respectively. Although troublesome to compare directly, our surface-based observations generally agree with the basal melt pattern provided by satellite-based methods but provide a distinctly smoother pattern. Our work delivers a precise measurement of basal melt rates across the RIS, a rare insight that also provides an early 21st-century baseline.

The accumulation area ratio (AAR) of a glacier reflects its current state of equilibrium, or disequilibrium, with climate and its vulnerability to future climate change. Here, we present an inventory of glacier-specific annual accumulation areas and equilibrium line altitudes (ELAs) for over 3000 glaciers in Alaska and northwest Canada (88% of the regional glacier area) from 2018 to 2022 derived from Sentinel-2 imagery. We find that the 5 year average AAR of the entire study area is 0.41, with an inter-annual range of 0.25–0.49. More than 1000 glaciers, representing 8% of the investigated glacier area, were found to have effectively no accumulation area. Summer temperature and winter precipitation from ERA5-Land explained nearly 50% of the inter-annual ELA variability across the entire study region (${R}^2=0.47$). An analysis of future climate scenarios (SSP2-4.5) projects that ELAs will rise by ∼170 m on average by the end of the 21st century. Such changes would result in a loss of 25% of the modern accumulation area, leaving a total of 1900 glaciers (22% of the investigated area) with no accumulation area. These results highlight the current state of glacier disequilibrium with modern climate, as well as glacier vulnerability to projected future warming.

Polar ice develops anisotropic crystal orientation fabrics under deformation, yet ice is mostly modelled as an isotropic fluid. We present three-dimensional simulations of the crystal orientation fabric of Derwael Ice Rise including the surrounding ice shelf using a crystal orientation tensor evolution equation corresponding to a fixed velocity field. We use a semi-Lagrangian numerical method that constrains the degree of crystal orientation evolution to solve the equations in complex flow areas. We perform four simulations based on previous studies, altering the rate of evolution of the crystal fabric anisotropy and its dependence on a combination of the strain rate and deviatoric stress tensors. We provide a framework for comparison with radar observations of the fabric anisotropy, outlining areas where the assumption of one vertical eigenvector may not hold and provide resulting errors in measured eigenvalues. We recognise the areas of high horizontal divergence at the ends of the flow divide as important areas to make comparisons with observations. Here, poorly constrained model parameters result in the largest difference in fabric type. These results are important in the planning of future campaigns for gathering data to constrain model parameters and as a link between observations and computationally efficient, simplified models of anisotropy.

The mass balance of lake-terminating glaciers responds to annual atmospheric variations, while calving-induced ice loss at the front is driven by local ice–water interactions. The current glaciological studies underestimate glacier response by neglecting the significant annual ice loss at the terminus through calving processes. This study integrates field measurements with remote sensing data to investigate the glaciological characteristics and proglacial lake evolution of the Gepang Gath glacier in the Chandra basin, Western Himalaya, India. Long-term observations reveal a continuous expansion of the proglacial lake from 0.21 ± 0.06 km2 (1962) to 1.21 ± 0.05 km2 (2023), along with terminus retreat of ∼2.76 km, attributed to calving at the ice–water interface. The glacier’s surface exhibits complex debris cover, with thicknesses up to 35 cm, creating significant spatial variations in surface mass balance. In-situ, glaciological measurements reveal a highly negative glacier-wide mass balance of −0.90 ± 0.30 m w.e. a−1 between the years 2014 and 2023. The geodetic estimates also reveal a negative mass balance of −0.61 ± 0.1 m w.e. a−1 over the past decade (2013–2023). The frontal area change (0.42 km2) and geodetic mass balance show a total volumetric ice loss of −21.77 × 106 m3 w.e. during the same period. Overall, the yearly frontal ice loss exacerbates the mass loss by 17–22%. These findings suggest that the presence of proglacial lakes plays a significant role in intensifying ice mass loss from Himalayan glaciers, strongly regulating their overall evolution.

As snowlines retreat, the bare ice of Central Asian glaciers is increasingly exposed to short-wave radiation and high temperatures. The importance of bare-ice albedo for glacier melt rates is thus rising. Little is known about the variability of bare-ice albedo, its drivers or its implications for glacier melt. We address this gap by presenting the sub-seasonal and interannual variability of bare-ice albedo of Abramov Glacier in Kyrgyzstan between 1999 and 2022. We derived albedo products from Landsat surface reflectance data, investigated the relationship between air temperature and bare-ice albedo variability and explored the implications of this variability for glacier melt. Our results indicate that bare-ice albedo undergoes a sub-seasonal cycle controlled by air temperature and elevation-dependent refreezing events. Bare-ice albedo decreased over the tongue in July and August between 1999 and 2017, while, in 2018, a lateral displacement of the ice resulted in a shift in the patterns of bare-ice albedo. We found significant correlations between bare-ice albedo variability and both temperature and glacier melt at various timescales. Rising temperatures are thus expected to lead to darker bare ice and amplified feedback melt cycles. Integrating albedo variability into glaciological models is thus crucial for accurate predictions of accelerated glacier response to intensifying climate change.

Cryoconite holes are supraglacial depressions containing water and microbe-mineral aggregates. Their autotrophic component plays a central role in reducing the albedo of glaciers and could contribute to sustaining the cryoconite food web. However, knowledge of its diversity is still limited, especially in Antarctica. Moreover, the study of cryoconite microalgae is challenging due to the limitations of molecular approaches, such as incomplete genetic databases and the semiquantitative nature of the data. Furthermore, it is equally difficult to examine the development of microalgae in sediment by using standard counting methods for water-living organisms. By using an adaptation of the high-speed density gradient centrifugation method, we provide a comprehensive description of the phenotypic characteristics, abundance and community structure of microalgae and Cyanobacteria in different cryoconite holes located in different glaciers of Northern Victoria Land, East Antarctica. We described 36 morphotypes belonging to Cyanobacteria, green algae and diatoms, revealing that cryoconite holes encompass a remarkably high diversity of photoautotrophs. The adapted protocol enabled the application of a standard microscopic approach, which provided crucial and comparable information on morphological characteristics, biovolume and community organization from a unique environment. The study poses the basis for the taxonomy of photoautotrophs as well as their diversity and distribution in cryoconite habitats.

Understanding deformation and slip at ice streams, which are responsible for 90% of Antarctic ice loss, are vital for accurately modelling large-scale ice flow. Ice crystal orientation fabric (COF) has a first-order effect on ice stream deformation. For the first time, we use shear-wave splitting measurements of basal icequakes at Whillans Ice Stream (WIS), Antarctica, to determine a shear-wave anisotropy with an average delay time of 7 ms and fast S-wave polarisation (φ) of 29.3°. The polarisation is expected to align perpendicular to ice flow, whereas our observation is oblique to the current ice flow direction (${\sim}280^{\circ}$). This suggests that ice at WIS preserves upstream fabric caused by palaeo-deformation developed over at least the past 450 years, which provides evidence of the concept of microstructural fading memory. Our results imply that changes in the shape of WIS occur on timescales shorter than COF re-equilibration. The ‘palaeo-fabric’ can somewhat control present-day ice flow, which we suggest may somewhat contribute to the long-term slowdown at WIS. Our findings suggest that seismic anisotropy can provide information on past ice sheet dynamics, and how past ice dynamics can play a role in controlling current deformation.

Ice cliffs on debris-covered glaciers act as melt hotspots that considerably enhance glacier ablation. However, studies are typically limited in time and space; glacier-scale studies of this process of ice cliff melt are rare, and their varying seasonal energy balance remains largely unknown. In this study, we combined a process-based ice cliff backwasting model with high-resolution (1.0 m) photogrammetry-based terrain data to simulate the year-round melt of 479 ice cliffs on Trakarding Glacier, Nepal Himalaya. Ice cliff melt accounted for 26% of the mass loss of the glacier from October 2018 to October 2019, despite covering only 1.7% of the glacier surface. The annual melt rate of ice cliffs was 2.7 cm w.e. d−1, which is 8–9 times higher than the sub-debris melt rate. Ice cliff melt rates were significantly controlled by their aspects, with south-facing ice cliffs showing a melt rate 1.8 times higher than that of north facing ones. The results revealed that the aspect dependence of ice cliff melt rate was amplified in winter and decreased/disappeared toward the monsoon season. The seasonal changes in melt characteristics are considered to be related to variations in direct shortwave radiation onto the cliff surface, which are dependent on changes in solar altitude and monsoonal cloud cover.

Recent observations have shown a fast decrease in thickness and area of Pyrenean glaciers in some cases leading to a stagnation of ice flow. However, their transition to a new paraglacial stage is not well understood. Through the combination of uncrewed aerial vehicles imagery, airborne LiDAR, ground-penetrating radar and ground temperature observations, we characterized the recent evolution of Infiernos Glacier. In 2021, this glacier had small sectors thicker than 25 m, but most of area did not exceed 10 m. The thickness losses from 2011 to 2023 reached 9 m in average, of which 5 m occurring during the period 2020–23. This trend demonstrates the significant ice melt under current climatic conditions. In the last years, the glacier has also shown a remarkable increase of debris cover extent. In these areas, the ice loss was reduced by half when compared to the thickness decrease in the entire glacier. Sub-freezing ground temperatures evidence the highly probable presence of permafrost or buried ice in the surroundings of the glacier. The clear signs of ice stagnation and the magnitude of area and thickness decrease support the main hypothesis of this work: After 2023, the Infiernos Glacier can no longer be considered a glacier and has become an ice patch.

To investigate dislocation densities of deformed polycrystalline ice the modified Warren-Averbach and modified Williamson-Hall plots of X-ray line broadening have been applied to artificial ice with and without silica particles, which model microparticles in ice sheets. This also provides us with the dislocation velocity during creep. Creep tests were conducted at −20ºC and 2 MPa by altering the strains using the artificial ice. In the primary creep region the ice with microparticles is remarkably deformed, and the strain rate is suppressed because of high dislocation densities. At 10% strain the dislocation density shows the maximum value due to the continuous dislocation pile-ups in the silica-containing ice: the dislocation density in the pure ice remains almost constant within the maximum strain used in this study. As the strains continuously decrease, microparticles pin the grain boundaries, leading to small grain sizes. Such small grain sizes provide sinks for dislocation annihilations, resulting in decrease in the dislocation densities in the silica-containing ice.

Firn, an interannual layer made of a seasonal snow, covers the vast majority of the Greenland ice sheet. Firn holds the potential to buffer meltwater runoff by refreezing in its pore space. However, recent intensive summer melt and refreezing have led to the development of low-permeability ice slabs several metres thick in the shallow firn of the percolation zone, in areas that now often undergo visible surface runoff. Here, we analyse ice slab thickness retrievals from Operation IceBridge Accumulation Radar together with visible runoff limits derived from Landsat imagery. We constrain the minimum average ice slab thickness over spatial scales of kilometres that can support visible surface water flow as lying between 2.8 m and 3.5 m. We highlight that there is substantial heterogeneity in ice slab thickness, much of which can be explained by visible lateral meltwater flow over the slab and subsequent localised refreezing. Our findings provide a basis for improving how firn models partition between meltwater retention and runoff, by providing constraints on when simulated ice layers become impermeable enough to support lateral water flow over scales of several kilometres.

Glacier dirt cones are meter-scale cones of ice covered with sediment and rock. The cones develop through a process known as differential melt, whereby ice underlying thick debris melts more slowly than bare ice. We report observations of dirt cones on the Kuskulana Glacier, Alaska and develop a model that simulates the growth of dirt cones from debris-filled pits in the ice. With this model, we vary ice melt rates, hillslope debris diffusion rates and pit geometry. Cone heights scale with the square root of debris volume and growth occurs in three distinct stages: emergence, flux-controlled growth and melt-controlled growth. Using dimensional analysis, we derive a characteristic length composed of the ratio of the debris diffusion rate (D) and the bare ice melt rate (b0). Shorter characteristic lengths produce taller, steeper cones. The characteristic length ($\ell = D/b_0$) determines, in part, the relative duration of each growth stage because it controls debris flux as relief increases. These experiments suggest increasing melt rates and low-mobility debris increase relief on hummocky debris-covered glaciers. Furthermore, the modeling approach demonstrates a method for handling debris transport over an irregular ice surface and could serve as a component in more comprehensive debris-covered glacier models.

Glacier ice flux is a key indicator of mass balance; therefore, accurate monitoring of ice dynamics is essential. Satellite-based methods are widely used for glacier velocity measurements but are limited by satellite revisit frequency. This study explores using seismic station internal GPS data to track glacier movement. While less accurate than differential GPS, this method offers high-temporal resolution as a by-product where seismic stations are deployed. Using a seismic station on Borebreen, Svalbard, we show that internal GPS provides reliable surface velocity measurements. When compared with satellite-inferred velocities, the results show a strong correlation, suggesting that the internal GPS, despite its inherent uncertainty, can serve as an efficient tool for glacier velocity monitoring. The high-temporal sampling reveals short-term dynamics of speed-up events and underscores the role of meltwater in driving these processes. This approach augments glacier observation networks at no additional cost.

Numerous supraglacial lakes form on the Greenland Ice Sheet (GrIS) during the summer, and accurately estimating their depth is crucial for understanding GrIS water storage. In this study, we estimate the depth of 35 representative GrIS supraglacial lakes using ICESat-2, Sentinel-2 imagery and ArcticDEM data. ICESat-2-derived lake depth is used to validate the performance of three remote sensing methods, namely empirical formula method (EFM), radiative transfer method (RTM) and depression topography method (DTM). EFM relies on ICESat-2-derived lake depth to construct empirical formulas, while RTM and DTM do not. The results show that (1) the green band EFM performs best; the DTM performs secondarily but tends to consistently underestimate depths; the green-band RTM has lower accuracy and overestimates depths, while the red-band RTM also has lower accuracy but underestimates depths. (2) Temporal changes of depression topography have limited impacts on the performance of DTM, whereas the uncertainties caused by lake shoreline height estimates should be considered. (3) The performance of RTM is significantly influenced by the spectral attenuation coefficient. We further identify the factors that affect spatiotemporal extrapolation of these methods and recommend prioritizing the use of the EFM when near-simultaneous ICESat-2 data are available; otherwise, DTM is recommended, yet an underestimation ratio should be used.