Ice skates are remarkably slippery across a wide range of conditions. We propose, based on earlier observations and new modeling, that an ice-rich slurry forms rapidly beneath a skate blade during each stride to lubricate the interface. Crushing from normal load and abrasion from sliding provide ice particles and heat to the slurry, with average contact pressures approaching melting pressures for the bulk ice. Shearing of the slurry by forward motion generates additional heat to melt the ice particles at the pressure-reduced temperature. We model these mechanics and link the viscosity of the resulting slurry to its ice fraction, which controls slurry-film thickness via lateral squeeze-flow. The slurry properties quickly converge to establish a highly efficient lubricating film that provides the characteristically low skate friction across a wide range of conditions. Although our 1D model greatly simplifies the complex interaction mechanics, its predictions are insensitive to most assumptions other than the average contact pressure. The presence of ice-rich slurries supporting skates merges pressure-melting, crushing, abrasion and lubricating films as a unified hypothesis for why skates are so slippery across broad ranges of speeds, temperatures and normal loads.

On the Kamchatka Peninsula in the Russian Far East, 405 glaciers with an estimated total mass of 49 Gt were reported in the 1970s. These have been retreating at an accelerated rate since the start of the 21st century. Because glacier studies in this region are scarce, ice loss and its influence on sea level rise and regional environments is poorly understood. In this study, we analyzed satellite data to quantify glacier mass change from 2000 to 2016 in six major glacier-covered regions on the peninsula. The mean rate of the glacier mass change over the study period was −0.46 ± 0.01 m w.e. a−1 (total mass change was −4.9 ± 0.1 Gt, −304.2 ± 9.1 Mt a−1), which is slightly lower than other regions in mid-latitude and subarctic zones. The mass loss accelerated from >−0.33 ± 0.02 m w.e. a−1 in the period 2000–2006/2010 to <−1.65 ± 0.12 m w.e. a−1 in 2006/2010–2015/16. The increase in mass loss is attributed to a rise in average decadal summer temperatures observed in the region (+0.68°C from 1987–99 to 2000–13). Moreover, a recent trend in Pacific decadal oscillation suggests future acceleration of mass loss due to a decline in winter precipitation.

Glacier change in Kenai Fjords National Park in southcentral Alaska affects local terrestrial, fresh water and marine ecosystems and will likely impact ecotourism. We used Landsat 4–8 imagery from 1984 through 2021 to manually map lower glacier ice margins for 19 maritime glaciers in Kenai Fjords National Park. Of these glaciers, six are tidewater, three are lake-terminating, six are land-terminating and four terminated in more than one environment throughout the study period. We used the mapped ice margins to quantify seasonal terminus position and areal change, including distinguishing between ice loss at glacier termini and along glacier margins. Overall, 13 glaciers substantially retreated (more than 2σ), 14 lost substantial area and only two underwent both net advance and area gain. The glaciers that had insubstantial length and area changes were predominantly tidewater. Cumulatively, the lower reaches of these 19 glaciers lost 42 km2 of ice, which was nearly evenly distributed between the terminus and the lateral margins. The rapid rate of glacier change and subsequent land cover changes are highly visible to visitors and locals at Kenai Fjords National Park, and this study quantifies those changes in terms of glacier length and area.

The Tian Shan mountain range, known as the water towers of Central Asia, plays a key role in local water supply, yet large uncertainties remain about the amount of water that is stored in its glaciers. In this study, we assess the impact of the boundary conditions on ice thickness estimates using two inversion models: a mass conservation (MC) model and a basal shear stress (BS) model. We compare the widely used Randolph Glacier Inventory version 6 with the updated Glacier Area Mapping for Discharge from the Asian Mountains glacier inventory, as well as two digital elevation models (SRTM DEM and Copernicus DEM). The results show that the ice volume (in ~2000 CE) in the Tian Shan range is 661.0 ± 163.5 km3 for the MC model and 552.8 ± 85.3 km3 for the BS model. There are strong regional differences due to inventory, especially for glaciers in China (17–25%). However, the effect of different DEM sources on ice volume estimation is limited. By the end of the 21st century, the projected mass loss differences between inventories are higher than between adjacent emission scenarios, illustrating the vital importance of high-quality inventories. These differences should be carefully considered during water resource planning.

Accurate ice flow velocity data are essential for studying the mass balance of the Antarctic ice sheet. However, there is a lack of ice velocity maps of 1960s–80s in basin-wide regions or the entire ice sheet. In this study, an enhanced hierarchical network densification approach is developed for basin-wide Antarctic velocity mapping using historical ARGON and Landsat images. The produced multiple historical velocity maps from 1963 to 1989 in the region of the Fimbul and Jelbart ice shelves, East Antarctica, achieved an accuracy better than 29 m a−1. They revealed that the ice flow velocity had no significant changes over the period. Combining the surface mass balance estimate with the ice discharge estimated from our historical velocity maps and recently published velocity maps, we estimated a positive mass balance of 8.6 ± 3.9 Gt a−1 in the study area from 1963 and 2015. Our results indicate that the region's positive mass balance, as estimated in recently published studies, has been maintained since the 1960s. It is also in concordance with the low level of mass balance from 1992 to 2017 in East Antarctica. This suggests that the study area has been stable since the 1960s.

Glacier monitoring has been internationally coordinated for more than 125 years. Despite this long history, there is no authoritative answer to the popular question: ‘Which glaciers are the largest in the world?’ Here, we present the first systematic assessment of this question and identify the largest glaciers in the world – distinct from the two ice sheets in Greenland and Antarctica but including the glaciers on the Antarctic Peninsula. We identify the largest glaciers in two domains: on each of the seven geographical continents and in the 19 first-order glacier regions defined by the Global Terrestrial Network for Glaciers. Ranking glaciers by area is non-trivial. It depends on how a glacier is defined and mapped and also requires differentiating between a glacier and a glacier complex, i.e. glaciers that meet at ice divides such as ice caps and icefields. It also depends on the availability of a homogenized global glacier inventory. Using separate rankings for glaciers and glacier complexes, we find that the largest glacier complexes have areas on the order of tens of thousands of square kilometers whereas the largest glaciers are several thousands of square kilometers. The world's largest glaciers and glacier complexes are located in the Antarctic, Arctic and Patagonia.

The interior of an ice sheet consists of layers of accumulated snow, which contain important information on accumulation and ice dynamics that are imprinted on layer shapes over time. This work describes how changes in accumulation influence the stratigraphy of an ice sheet. The thickness of each layer at present day depends both on accumulation and on the effect of dynamic thinning after its deposition. An isochronal numerical model is used to simulate the evolution of a 2-D, idealized ice sheet while explicitly representing the layers. A series of simulations was carried out to quantify the changes that anomalous accumulation at different locations and times has on the stratigraphy. These simulations form the basis of a linear response function. A second set of simulations with more sustained changes in accumulation is then used to describe large-scale and long-term impacts on the layering of the ice sheet as well as to test the quality of the linear approximation. The aim is to examine whether long-term effects can be extrapolated from small differential changes. The result confirms a certain degree of linearity between changes in accumulation and layer thickness that may be exploited for future inverse modeling applications.

Sea-level projections depend sensitively on the parameterization used for basal slip in glacier flow models. During slip over rock-beds, ice-bed separation increases with slip velocity and basal water pressure. We present a method for using these variables and measured bed topography to estimate the average bed slope in contact with ice, ${\bar m}$. Three-dimensional numerical modeling of slip over small areas of former beds has shown that changes in ${\bar m}$ with increasing slip velocity and water pressure mimic changes in basal drag. Computed values of ${\bar m}$ can thus provide the form of the slip law that relates drag to velocity and water pressure, avoiding computationally expensive numerical modeling. The method is applied to 618 sections from four former glacier beds. Results generally show an increase in ${\bar m}$, and hence inferred basal drag, with slip velocity up to a limiting value, consistent with a regularized Coulomb slip law.

Pigmented microalgae inhabiting snow and ice environments lower the albedo of glacier and ice-sheet surfaces, significantly enhancing surface melt. Our ability to accurately predict their role in glacier and ice-sheet surface mass balance is limited by the current lack of empirical data to constrain their representation in predictive models. Here we present new empirical optical properties for snow and ice algae and incorporate them in a radiative transfer model to investigate their impact on snow and ice surface albedo. We found ice algal cells to be more efficient absorbers than snow algal cells, but their blooms had comparable impact on surface albedo due to the different photic conditions of their habitats. We then used the model to reconstruct the effect of ice algae on bare ice albedo spectra collected at our field site in southern Greenland, where blooms dropped the albedo locally by between 3 and 43%, equivalent to 1–10 L m$^{-2}$ d$^{-1}$ of melted ice. Using the newly parametrized model, future studies could investigate biological albedo reduction and algal quantification from remote hyperspectral and multispectral imagery.

Understanding the dynamic behaviour of ice shelves, specifically the controls on their ability to buttress the flow of ice into the ocean, is critical for predicting future ice-sheet contributions to sea level rise. Many large ice shelves, which are predominantly composed of meteoric ice, have a basal layer of marine ice (formed from accumulated platelets at the ice–ocean interface), comprising up to 40% of their thickness locally. Differences in temperature, chemistry and microstructure between marine and meteoric ice mean the rheological properties of the ice vary throughout the ice shelf. These differences are not explicitly accounted for in ice-sheet modelling applications, and may have an important influence on ice shelf dynamics. We tested the sensitivity of a model of an idealised ice shelf to variations in temperature distribution and flow enhancement, and found that incorporating a realistic thermal profile (where the marine ice layer is isothermal) had an order of magnitude greater effect on ice mass flux and thinning than incorporating the mechanical properties of the marine ice. The presence of marine ice at the ice shelf base has the potential to significantly increase deviatoric stresses at the surface and ice mass flux across the front of an ice shelf.

Debris-covered glaciers are an important component of the mountain cryosphere and influence the hydrological contribution of glacierized basins to downstream rivers. This study examines the potential to make estimates of debris thickness, a critical variable to calculate the sub-debris melt, using ground-based thermal infrared radiometry (TIR) images. Over four days in August 2019, a ground-based, time-lapse TIR digital imaging radiometer recorded sequential thermal imagery of a debris-covered region of Peyto Glacier, Canadian Rockies, in conjunction with 44 manual excavations of debris thickness ranging from 10 to 110 cm, and concurrent meteorological observations. Inferring the correlation between measured debris thickness and TIR surface temperature as a base, the effectiveness of linear and exponential regression models for debris thickness estimation from surface temperature was explored. Optimal model performance (R2 of 0.7, RMSE of 10.3 cm) was obtained with a linear model applied to measurements taken on clear nights just before sunrise, but strong model performances were also obtained under complete cloud cover during daytime or nighttime with an exponential model. This work presents insights into the use of surface temperature and TIR observations to estimate debris thickness and gain knowledge of the state of debris-covered glacial ice and its potential hydrological contribution.

Glacial hydraulic tremor (GHT) can be monitored to observe changes in location and distribution of water flow beneath glacial ice, allowing the spatiotemporal evolution of subglacial hydrology to be studied continuously and remotely. We use frequency-dependent polarization analysis (FDPA) to classify types of GHT and assess its spatio-temporal extent beneath Rhonegletscher, Switzerland, in a continuous seismic record through 2018 and 2019 at three ice-proximal bedrock-based seismometers. We determine the frequency bands composing the GHT and calculate back azimuth angles pointing to a previously known subglacial channel. We also inspect the relationship between GHT seismic power and water discharge from the glacier to compare daily and seasonal shifts with the observed GHT. We observed the seasonal shift from a distributed system to a channelized system, and our dataset allowed comparison of channel locations within and across seasons, with implications for sediment evacuation and bed erosion. The successful use of this method to assess GHT previously on Taku glacier (the methods of which this project follows) and now Rhonegletscher shows that existing ice-proximal passive seismic installations can be used to easily and continuously monitor subglacial hydraulic activity.

We perform Bayesian inference of the parameters of a time-dependent model of ice flow and calving at Helheim Glacier, East Greenland. We find that, while a time-independent calving parameterization can recover the mean observed terminus position, such a model is unable to recover sub-annual variability, even when forced with seasonally varying climate. To address this, we develop a simple stochastic model relating surface runoff rates and calving threshold. Again inferring model parameters from observations, we find that this parameterization is able to reproduce observations with respect to both mean position and characteristic temporal variability. This result demonstrates the importance of considering potential sub-annual controls on calving rates in numerical models, which may include variable undercutting rates or surface runoff-dependent surface crevasse propagation.

We use a mathematical model to investigate the effect of basal topography and ice surface slope on transport and deposition of sediment within a water-filled subglacial channel. In our model, three zones of different behaviour occur. In the zone furthest upstream, variations in basal topography lead to sediment deposition under a wide range of conditions. In this first zone, even very small and gradually varying basal undulations (~5 m amplitude) can lead to the deposition of sediment within a modelled channel. Deposition is concentrated on the downstream gradient of subglacial ridges, and on the upstream gradient of subglacial troughs. The thickness and steepness of the ice sheet has a substantial impact on deposition rates, with shallow ice profiles strongly promoting both the magnitude and extent of sediment deposition. In a second zone, all sediment is transported downstream. Finally, a third zone close to the ice margin is characterised by high rates of sediment deposition. The existence of these zones has implications for esker formation and the dynamics of the subglacial environment.

Tasman Glacier, a temperate maritime glacier in the New Zealand Southern Alps, is rapidly receding. Climate warming is resulting in lengthening of the ablation season, meaning crevasses in the accumulation area are becoming exposed at the surface for longer. We combine measurements of air temperature and wind speed from inside crevasses with surface meteorological data, finding that during summer, in-crevasse air temperature is frequently positive, and can at times exceed surface air temperature. Greatest warming occurred in the widest crevasses during clear-sky conditions, but full depth warming of crevasses also occurred at night. Net shortwave radiation contributes to heating of air in the upper regions of crevasses, but turbulent sensible heat transfer was responsible for driving warm air deeper into crevasses. Crevasses orientated to maximise radiation retrieval, and running parallel to wind flow, have the greatest potential for warming and heat storage. We hypothesise a positive feedback loop in the surface energy-balance system, where crevasses entrain and trap heat, which enhances melting, that in turn enlarges the crevasses, enabling greater heat storage and further melting. Energy-balance models that treat accumulation areas of alpine glaciers as homogeneous surfaces will therefore underestimate snow melt and overestimate mass balance.

We quantify the surface elevation changes along Yala Glacier in Langtang Valley, Nepal Himalaya, since 1981 using geodetic methods to understand the recent evolution and current state of small debris-free glaciers across the region. We analyse differential global positioning system measurements and aerial stereo imagery that were acquired along Yala Glacier in 2007, 2009, 2012 and 2015 to generate digital elevation models for each calculation period. Continuous surface lowering has mainly been observed across the down-glacier area during the calculation periods, although a large degree of variability exists, with this lowering trend propagating up-glacier in recent years. The area-weighted glacier mass balances range from −0.98 ± 0.27 to −0.26 ± 0.30 m w.e. a−1 for the five calculation periods (1981–2007, 2007–2009, 2009–2012, 2012–2015 and 2007–2015). These calculated mass-balance data reveal that Yala Glacier has undergone accelerated mass loss since the late 2000s, which is consistent with the results of previous in situ measurement and remote-sensing studies.