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Future mass loss projections of the Greenland ice sheet require understanding of the processes at a glacier terminus, especially of iceberg calving. We present detailed and high-rate terrestrial radar interferometer observations of Eqip Sermia and Bowdoin Glacier, two outlet glaciers in Greenland with comparable dimensions and investigate iceberg calving, surface elevation, velocity, strain rates and their links to air temperature, tides and topography. The results reveal that the two glaciers exhibit very different flow and calving behaviour on different timescales. Ice flow driven by a steep surface slope with several topographic steps leads to high velocities, areas of extension and intense crevassing, which triggers frequent but small calving events independent of local velocity gradients. In contrast, ice flow under smooth surface slopes leaves the ice relatively intact, such that sporadic large-scale calving events dominate, which initiate in areas with high shearing. Flow acceleration caused by enhanced meltwater input and tidal velocity variations were observed for terminus sections close to floatation. Firmly grounded terminus sections showed no tidal signal and a weak short-term reaction to air temperature. These results demonstrate reaction timescales to external forcings from hours to months, which are, however, strongly dependent on local terminus geometry. [ABSTRACT FROM AUTHOR]

Ice cliff distribution plays a major role in determining the melt of debris‐covered glaciers but its controls are largely unknown. We assembled a data set of 37,537 ice cliffs and determined their characteristics across 86 debris‐covered glaciers within High Mountain Asia (HMA). We find that 38.9% of the cliffs are stream‐influenced, 19.5% pond‐influenced and 19.7% are crevasse‐originated. Surface velocity is the main predictor of cliff distribution at both local and glacier scale, indicating its dependence on the dynamic state and hence evolution stage of debris‐covered glacier tongues. Supraglacial ponds contribute to maintaining cliffs in areas of thicker debris, but this is only possible if water accumulates at the surface. Overall, total cliff density decreases exponentially with debris thickness as soon as the debris layer reaches a thickness of over 10 cm. Plain Language Summary: Debris‐covered glaciers are common throughout the world's mountain ranges and are characterized by the presence of steep ice cliffs among the debris‐covered ice. It is well‐known that the cliffs are responsible for a large portion of the melt of these glaciers but the controls on their formation, development and distribution across glaciers remains poorly understood. Novel mapping approaches combined with high‐resolution satellite and drone products enabled us to disentangle some of these controls and to show that the ice cliffs are generally formed and maintained by the surface hydrology (ponds or streams) or by the opening of crevasses. As a result, they depend both at the local and glacier scale on the dynamic state of the glaciers as well as the evolution stage of their debris cover. This provides a pathway to better represent their contribution to glacier melt in predictive glacier models. Key Points: We derived an unprecedented data set of 37,537 ice cliffs and their characteristics across 86 debris‐covered glaciers in High Mountain AsiaWe find that 38.9% of the cliffs are stream‐influenced, 19.5% pond‐influenced and 19.7% are crevasse‐originatedIce cliff distribution can be predicted by velocity, as an indicator of the dynamics and state of evolution of debris‐covered glaciers [ABSTRACT FROM AUTHOR]

The dense mixture of iceberg of various sizes and sea ice observed in many of Greenland's fjords, called ice mélange (sikussak in Greenlandic), has been shown to have a significant impact on the dynamics of several Greenland tidewater glaciers, mainly through the seasonal support it provides to the glacier terminus in winter. However, a clear understanding of shorter-term ice mélange dynamics is still lacking, mainly due to the high complexity and variability of the processes at play at the ice–ocean boundary. In this study, we use a combination of Sentinel-1 radar and Sentinel-2 optical satellite imagery to investigate in detail intra-seasonal ice mélange dynamics and its link to calving activity at three major outlet glaciers: Kangerdlugssuaq Glacier, Helheim Glacier and Sermeq Kujalleq in Kangia (Jakobshavn Isbræ). In those fjords, we identified recurrent ice mélange weakening (IMW) episodes consisting of the up-fjord propagation of a discontinuity between jam-packed and weaker ice mélange towards the glacier terminus. At a late stage, i.e., when the IMW front approaches the glacier terminus, these episodes were often correlated with the occurrence of large-scale calving events. The IMW process is particularly visible at the front of Kangerdlugssuaq Glacier and presents a cyclic behavior, such that we further analyzed IMW dynamics during the June–November period from 2018 to 2021 at this location. Throughout this period, we detected 30 IMW episodes with a recurrence time of 24 d, propagating over a median distance of 5.9 km and for 17 d, resulting in a median propagation speed of 400 m d -1. We found that 87 % of the IMW episodes occurred prior to a calving event visible in spaceborne observations and that ∼75 % of all detected calving events were preceded by an IMW episode. These results therefore present the IMW process as a clear control on the calving activity of Kangerdlugssuaq Glacier. Finally, using a simple numerical model for ice mélange motion, we showed that a slightly biased random motion of ice floes without fluctuating external forcing can reproduce IMW events and their cyclic influence and explain observed propagation speeds. These results further support our observations in characterizing the IMW process as self-sustained through the existence of an IMW–calving feedback. This study therefore highlights the importance of short-term ice mélange dynamics in the longer-term evolution of Greenland outlet glaciers. [ABSTRACT FROM AUTHOR]

The dense mixture of iceberg of various sizes and sea ice observed in many of Greenland's fjords, called ice mélange (sikussak in Greenlandic), has been shown to have a significant impact on the dynamics of several Greenland tidewater glaciers mainly through the seasonal support it provides to the glacier terminus in winter. However, a clear understanding of shorter-term ice mélange dynamics is still lacking, mainly due to the high complexity and variability of the processes at play at the ice-ocean boundary. In this study, we use a combination of Sentinel-1 radar and Sentinel-2 optical satellite imagery to investigate in detail intraseasonal ice mélange dynamics and its link to calving activity at three major outlet glaciers: Kangerdlugssuaq Glacier, Helheim Glacier and Sermeq Kujalleq in Kangia (Jakobshavn Isbræ). In those fjords, we identified recurrent ice mélange weakening (IMW) episodes consisting in the up-fjord propagation of a discontinuity between jam-packed and weaker ice mélange towards the glacier terminus. At a late stage, i.e. when the IMW front approaches the glacier terminus, these episodes were often correlated with the occurrence of large-scale calving events. The IMW process is particularly well visible at the front of Kangerdlugssuaq glacier and presents a cyclic behavior, such that we further analyzed IMW dynamics during the June–November period from 2018 to 2021 at this location. Throughout this period, we detected 30 IMW episodes with a recurrence time of 24 days, propagating over a median distance of 5.9 km and for 17 days, resulting in a median propagation speed of 400 m/d. We found that 87 % of the IMW episodes occurred prior to a calving event visible in spaceborne observations and that ~75 % of all detected calving events were preceded by an IMW episode. These results therefore present the IMW process as a clear control on the calving activity of Kangerdlugssuaq glacier. Finally, using a simple numerical model for ice mélange motion, we showed that a slightly biased random motion of ice floes without fluctuating external forcing can reproduce IMW events and their cyclic influence, and explain observed propagation speeds. These results further support our observations in characterizing the IMW process as self-sustained through the existence of an IMW-calving feedback. This study therefore highlights the importance of short-term ice mélange dynamics in the longer-term evolution of Greenland outlet glaciers. [ABSTRACT FROM AUTHOR]

Debris-covered glaciers are commonly found in alpine landscapes of high relief and play an increasingly important role in a warming climate. As a result of the insulating effect of supraglacial debris, their response to changes in climate is less direct and their dynamic behaviour more complex than for debris-free glaciers. Due to a lack of observations, here we use numerical modelling to explore the dynamic interactions between debris cover and geometry evolution for an idealized glacier over centennial timescales. The main goal of this study is to understand the effects of debris cover on the glacier's transient response. To do so, we use a numerical model that couples ice flow, debris transport, and its insulating effect on surface mass balance and thereby captures dynamic feedbacks that affect the volume and length evolution. In a second step we incorporate the effects of cryokarst features such as ice cliffs and supraglacial ponds on the dynamical behaviour. Our modelling indicates that thick debris cover delays both the volume response and especially the length response to a warming climate signal. Including debris dynamics therefore results in glaciers with extended debris-covered tongues and that tend to advance or stagnate in length in response to a fluctuating climate at century timescales and hence remember the cold periods more than the warm. However, when including even a relatively small amount of melt enhancing cryokarst features in the model, the length is more responsive to periods of warming and results in substantial mass loss and thinning on debris-covered tongues, as is also observed. [ABSTRACT FROM AUTHOR]

To improve knowledge of marine-terminating glaciers in western Greenland, marine sediment cores from the Ata Sund fjord system, hosting two outlet glaciers, Eqip Sermia and Kangilerngata Sermia, were investigated. The main objective was to reconstruct glacial activity and paleoceanographic conditions during the past 600 years. Ice-rafted debris (IRD) was quantified by wet-sieving sediment samples and by using a computed tomography scan. Variability in relative bottom water temperatures in the fjord was reconstructed using foraminiferal analysis. On the basis of this, three periods of distinct glacial regimes were identified: Period 1 (1380–1810 CE), which covers the culmination of the Little Ice Age (LIA) and is interpreted as having advanced glaciers with high IRD content. Period 2 (1810–1920 CE), the end of the LIA, which was characterised by a lowering of the glaciers' calving flux in response to climate cooling. During Period 3 (1920–2014 CE), both glaciers retreated substantially to their present-day extent. The bottom water temperature started to decrease just before Period 2 and remained relatively low until just before the end of Period 3. This is interpreted as a local response to increased glacial meltwater input. Our study was compared with a study in Disko Bay, nearby Jakobshavn Glacier and the result shows that both of these Greenlandic marine-terminating glaciers are responding to large-scale climate change. However, the specific imprint on the glaciers and the different fjord waters in front of them result in contrasting glacial responses and sediment archives in their respective fjords. [ABSTRACT FROM AUTHOR]

The recent rapid retreat of many Arctic outlet glaciers has been attributed to increased oceanic melt, but the relationship between oceanic melt and iceberg calving remains poorly understood. Here, we employ a transient finite element model that simulates oceanic melt and ice break‐off at the terminus. The response of an idealized tidewater glacier to various submarine melt rates and seasonal variations is investigated. Our modeling shows that for zero to low oceanic melt, the rate of volume loss at the front is similar or higher than that for intermediate oceanic melt rates. Only very high melt rates lead to increasing volume losses. These results highlight the complex interplay between oceanic melt and calving and question the general assumption that increased submarine melt leads to higher calving fluxes and enhanced retreat. Models for tidewater glacier evolution should therefore consider calving and oceanic melt as tightly coupled processes rather than as simple, additive parameterizations. Key Points: The effect of oceanic melt on tidewater glacier evolution is investigated using a transient calving model based on damage evolutionOceanic melt has a complex influence on tidewater glacier evolution and increased melt rates may not necessarily lead to more volume lossThe calving and oceanic melt processes are not additive, which has implications on the forcing of models for tidewater glacier evolution [ABSTRACT FROM AUTHOR]

Measuring the ice flow motion accurately is essential to better understand the time evolution of glaciers and ice sheets and therefore to better anticipate the future consequence of climate change in terms of sea level rise. Although there are a variety of remote sensing methods to fill this task, in situ measurements are always needed for validation or to capture high-temporal-resolution movements. Yet glaciers are in general hostile environments where the installation of instruments might be tedious and risky when not impossible. Here we report the first-ever in situ measurements of ice flow motion using a remotely controlled unmanned aerial vehicle (UAV). We used a quadcopter UAV to land on a highly crevassed area of Eqip Sermia Glacier, West Greenland, to measure the displacement of the glacial surface with the aid of an onboard differential GNSS receiver. We measured approximately 70 cm of displacement over 4.36 h without setting foot onto the glacier – a result validated by applying UAV photogrammetry and template matching techniques. Our study demonstrates that UAVs are promising instruments for in situ monitoring and have great potential for capturing continuous ice flow variations in inaccessible glaciers – a task that remote sensing techniques can hardly achieve. [ABSTRACT FROM AUTHOR]

Following the general warming trend in Greenland, an increase in calving rates, retreat and ice flow has been observed at ocean-terminating outlet glaciers. These changes contribute substantially to the current mass loss of the Greenland Ice Sheet. In order to constrain models of ice dynamics as well as estimates of mass change, detailed knowledge of geometry and ice flow is needed, in particular on the rapidly changing tongues of ocean-terminating outlet glaciers. In this study, we validate velocity estimates and spatial patterns close to the calving terminus of such an outlet derived from an iterative offset-tracking method based on synthetic aperture radar (SAR) intensity data with a collection of three independent reference measurements of glacier flow. These reference datasets are comprised of measurements from differential GPS, a terrestrial radar interferometer (TRI) and repeated unmanned aerial vehicle (UAV) surveys. Our approach to SAR velocity processing aims at achieving a relatively fine grid spacing and a high temporal resolution in order to best resolve the steep velocity gradients in the terminus area and aims to exploit the 12 d repeat interval of the single-satellite Sentinel-1A sensor. Results from images of the medium-sized ocean-terminating outlet glacier Eqip Sermia acquired by Sentinel-1A and RADARSAT-2 exhibit a mean difference of 11.5 % when compared to the corresponding GPS measurements. An areal comparison of our SAR velocity fields with independently generated velocity maps from TRI and UAV surveys showed good agreement in magnitude and spatial patterns, with mean differences smaller than 0.7 m d -1. In comparison with existing operational velocity products, our SAR-derived velocities show an improved spatial velocity pattern near the margins and calving front. There 8 % to 30 % higher surface ice velocities are produced, which has implications on ice fluxes and on mass budget estimates of similarly sized outlet glaciers. Further, we show that offset tracking from SAR intensity data at relatively low spatio-temporal sampling intervals is a valid method to derive glacier flow fields for fast-flowing glacier termini of outlet glaciers and, given the repeat period of 12 d of the Sentinel-1A sensor (6 d with Sentinel-1B), has the potential to be applied operationally in a quasi-continuous mode. [ABSTRACT FROM AUTHOR]

Iceberg calving, the detachment of an ice block at the glacier front, is the main process responsible for the dynamic mass loss from the ice sheets to the ocean. Understanding this process is essential to accurately predict ice sheet response to the future climate. We present a transient multiphysics finite‐element model to simulate iceberg break‐off and geometry evolution of a marine‐terminating glacier. The model solves the coupled equations of ice flow, damage mechanics, oceanic melt, and geometry evolution on the same Lagrangian computational grid. A modeling sensitivity analysis shows that the choice of stress measure used for damage evolution strongly influences the resulting calving front geometries. Our analysis suggests that the von Mises stress measures produce the most realistic calving front geometry evolutions for tidewater glaciers. Submarine frontal melt is shown to have a strong impact on the calving front geometry. The presented multiphysics model includes all processes thus far shown to be relevant for the evolution of tidewater glaciers and can be readily adapted for 3‐D and arbitrary bedrock geometries. Key Points: A couple transient ice flow model with damage and geometry evolution is developed to simulated iceberg break‐offCalving front geometries in two dimensions are emergent results of the modelThe choice of stress measure used for damage evolution strongly influences the calving front geometry [ABSTRACT FROM AUTHOR]

Debris-covered glaciers generally exhibit large, gently sloping, slow-flowing tongues. At present, many of these glaciers show high thinning rates despite thick debris cover. Due to the lack of observations, most existing studies have neglected the dynamic interactions between debris cover and glacier evolution over longer time periods. The main aim of this study is to reveal such interactions by reconstructing changes of debris cover, glacier geometry, flow velocities, and surface features of Zmuttgletscher (Switzerland), based on historic maps, satellite images, aerial photographs, and field observations. We show that debris cover extent has increased from ∼13 % to ∼32 % of the total glacier surface since 1859 and that in 2017 the debris is sufficiently thick to reduce ablation compared to bare ice over much of the ablation area. Despite the debris cover, the glacier-wide mass balance of Zmuttgletscher is comparable to that of debris-free glaciers located in similar settings, whereas changes in length and area have been small and delayed by comparison. Increased ice mass input in the 1970s and 1980s resulted in a temporary velocity increase, which led to a local decrease in debris cover extent, a lowering of the upper boundary of the ice-cliff zone, and a strong reduction in ice-cliff area, indicating a dynamic link between flow velocities, debris cover, and surface morphology. Since 2005, the lowermost 1.5 km of the glacier has been quasi-stagnant, despite a slight increase in the surface slope of the glacier tongue. We conclude that the long-term glacier-wide mass balance is mainly governed by climate. The debris cover governs the spatial pattern of elevation change without changing its glacier-wide magnitude, which we explain by the extended ablation area and the enhanced thinning in regions with thin debris further up-glacier and in areas with abundant meltwater channels and ice cliffs. At the same time rising temperatures lead to increasing debris cover and decreasing ice flux, thereby attenuating length and area losses. [ABSTRACT FROM AUTHOR]

Measuring the ice flow motion accurately is essential to better understand the time evolution of glaciers and ice sheets, and therefore to better anticipate the future consequence of climate change in terms of sea-level rise. Although there exist a variety of remote sensing methods to fill this task, in-situ measurements are always needed for validation or to capture high temporal resolution movements. Yet glaciers are in general hostile environments where the installation of instruments might be tedious and risky when not impossible. Here we report the first-ever in-situ measurements of ice flow motion using a remotely controlled Unmanned Aerial Vehicle (UAV). We used a multicopter UAV to land on a highly crevassed area of Eqip Sermia Glacier, West Greenland, to measure the displacement of the glacial surface with the aid of an on-board differential GNSS receiver. Despite the unfortunate loss of the UAV, we measured approximately 70 cm of displacement over 4.36 hours without setting foot onto the glacier - a result validated by applying UAV photogrammetry and template matching techniques. Our study demonstrates that UAVs are promising instruments for in-situ monitoring, and have a great potential for capturing short-term ice flow variations in inaccessible glaciers - a task that remote sensing techniques can hardly achieve. [ABSTRACT FROM AUTHOR]

Ocean-terminating glaciers in Arctic regions have undergone rapid dynamic changes in recent years, which have been related to a dramatic increase in calving rates. Iceberg calving is a dynamical process strongly influenced by the geometry at the terminus of tidewater glaciers. We investigate the effect of varying water level, calving front slope and basal sliding on the state of stress and flow regime for an idealized grounded ocean-terminating glacier and scale these results with ice thickness and velocity. Results show that water depth and calving front slope strongly affect the stress state while the effect from spatially uniform variations in basal sliding is much smaller. An increased relative water level or a reclining calving front slope strongly decrease the stresses and velocities in the vicinity of the terminus and hence have a stabilizing effect on the calving front. We find that surface stress magnitude and distribution for simple geometries are determined solely by the water depth relative to ice thickness. Based on this scaled relationship for the stress peak at the surface, and assuming a critical stress for damage initiation, we propose a simple and new parametrization for calving rates for grounded tidewater glaciers that is calibrated with observations. [ABSTRACT FROM AUTHOR]

Accelerated discharge through marine-terminating outlet glaciers has been a key component of the rapid mass loss from Arctic glaciers since the 1990s. However, glacier retreat and its climatic controls have not been assessed at the pan-Arctic scale. Consequently, the spatial and temporal variability in the magnitude of retreat, and the possible drivers are uncertain. Here we use remotely sensed data acquired over 273 outlet glaciers, located across the entire Atlantic Arctic (i.e. areas potentially influenced by North Atlantic climate and/or ocean conditions, specifically: Greenland, Novaya Zemlya, Franz Josef Land and Svalbard), to demonstrate high-magnitude, accelerating and near-ubiquitous retreat between 1992 and 2010. Overall, mean retreat rates increased by a factor of 3.5 between 1992 and 2000 (−30.5 m a−1) and 2000–10 (−105.8 m a−1), with 97% of the study glaciers retreating during the latter period. The Retreat was greatest in northern, western and south-eastern Greenland and also increased substantially on the Barents Sea coast of Novaya Zemlya. Glacier retreat showed no significant or consistent relationship with summer air temperatures at decadal timescales. The rate of frontal position change showed a significant, but weak, correlation with changes in sea-ice concentrations. We highlight large variations in retreat rates within regions and suggest that fjord topography plays an important role. We conclude that marine-terminating Arctic outlet glaciers show a common response of rapid and accelerating retreat at decadal timescales. [ABSTRACT FROM AUTHOR]

Rapid dynamic changes of ocean-terminating outlet glaciers of the Greenland ice sheet are related to atmospheric and oceanic warming but the detailed link to external forcing is not well understood. Observations show high variability in dynamic changes and are mainly limited to the past three decades with dense satellite observations. Here we compile a long-term record of dynamic changes of Eqip Sermia Glacier, West Greenland. Starting in 1912, we combine historical measurements of terminus positions, ice-surface elevation and flow velocity together with more recent in-situ and remote-sensing observations. In the 20th century, the glacier underwent small variations in terminus position and flow speed. Between 2000 and 2003, the terminus retreated substantially, but stabilized thereafter. In 2009, the northern terminus lobe started to retreat very rapidly; the southern lobe collapsed in 2013. The present terminus position, which has retreated by 4 km since 1920, is unprecedented in the historical record. Flow velocities were relatively stable until 2010. The recent acceleration reached threefold velocities in 2014 and rapidly affected the whole terminus region up to 15 km inland. Comparison with forcings from the atmosphere and the ocean over the past century shows that no dominant cause can be identified, and that local effects of bed geometry modulate the glacier response. [ABSTRACT FROM AUTHOR]

Glacier calving can cause violent tsunami waves which, upon landfall, can cause severe destruction. Here we present data acquired during a calving event from Eqip Sermia, an ocean-terminating glacier in west Greenland. During an exceptionally well-documented event, the collapse of 9 × 105 m³ ice from a 200m high ice cliff caused a tsunami wave of 50m height, traveling at a speed of 25-33ms-1. This wave was filmed from a tour boat at 800m distance from the calving face, and simultaneously measured with a terrestrial radar interferometer and a tide gauge. Tsunami wave run-up height on the steep opposite shore at a distance of 4 km was 10-15 m, destroying infrastructure and eroding old vegetation. These observations indicate that such high tsunami waves are a recent phenomenon in the history of this glacier. Analysis of the data shows that only moderately bigger tsunami waves are to be expected in the future, even under rather extreme scenarios. [ABSTRACT FROM AUTHOR]

Discharge from marine-terminating outlet glaciers accounts for up to half the recent mass loss from the Greenland ice sheet, yet the causal factors are not fully understood. Here we assess the factors controlling the behaviour of Humboldt Glacier (HG), allowing us to evaluate the influence of basal topography on outlet glacier response to external forcing since part of HG's terminus occupies a large overdeepening. HG's retreat accelerated dramatically after 1999, coinciding with summer atmospheric warming of up to 0.19°C a-1 and sea-ice decline. Retreat was an order of magnitude greater in the northern section of the terminus, underlain by a major basal trough, than in the southern section, where the bedrock is comparatively shallow. Velocity change following retreat was spatially non-uniform, potentially due to a pinning point near HG's northern lateral margin. Consistent with observations, numerical modelling demonstrates an order-of-magnitude greater sensitivity to sea-ice buttressing and crevasse depth (used as a proxy for atmospheric warming) in the northern section. The trough extends up to 72km inland, so it is likely to facilitate sustained retreat and ice loss from HG during the 21st century. [ABSTRACT FROM AUTHOR]

Substantial ice loss has occurred in the Russian High Arctic during the past decade, predominantly on Novaya Zemlya, yet the region has been studied relatively little. Consequently, the factors forcing mass loss and the relative contribution of ice dynamics versus surface melt are poorly understood. Here we evaluate the influence of atmospheric/oceanic forcing and variations in fjord width on the behaviour of 38 glaciers on the northern ice cap, Novaya Zemlya. We compare retreat rates on land- versus marine-terminating outlets and on the Kara versus Barents Sea coasts. Between 1992 and 2010, 90% of the study glaciers retreated and retreat rates were an order of magnitude higher for marine-terminating outlets (52.1ma-1) than for land-terminating glaciers (4.8ma-1). We identify a post-2000 acceleration in marine-terminating glacier retreat, which corresponded closely to changes in sea-ice concentrations. Retreat rates were higher on the Barents Sea coast, which we partly attribute to lower sea-ice concentrations, but varied dramatically between individual glaciers. We use empirical data to categorize changes in along-flow fjord width, and demonstrate a significant relationship between fjord width variability and retreat rate. Results suggest that variations in fjord width exert a major influence on glacier retreat. [ABSTRACT FROM AUTHOR]

The geomorphology of the south-western and central Lake District, England is used to reconstruct the mountain palaeoglaciology pertaining to the Lateglacial and Younger Dryas. Limitations to previous ice-mass reconstructions and consequent palaeoclimatic inferences include: (i) the use of static (steady-state) glacier reconstructions, (ii) the assumption of a single-stage Younger Dryas advance, (iii) greatly varying ice-volume estimates, (iv) inexplicable spatial variations in ELA ( Equilibrium Line Altitude), and (v) a lack of robust extent chronology. Here we present geomorphological mapping based on aerial photography and the Next Map Britain Digital Elevation Model, checked by ground survey. Former glacier extents were inferred and ELAs were calculated using the Balance Ratio method of Osmaston. Independently, a time-dependant 2-D ice-flow model was forced by a regional ELA history that was scaled to the GRIP record. This provided a dynamic reconstruction of a mountain ice field that allowed for non-steady-state glacier evolution. Fluctuations in climate during the Younger Dryas resulted in multiple glacial advance positions that show agreement with the location of mapped moraines, and may further explain some of the ELA variations found in previous local and static reconstructions. Modelling based on the GRIP record predicts three phases: an initial maximum extent, a middle minor advance or stillstand, and a pronounced but less extensive final advance. The comparisons find that the reconstructions derived from geomorphological evidence are effective representations of steady-state glacier geometries, but we do propose different extents for some glaciers and, in particular, a large former glacier in Upper Eskdale. [ABSTRACT FROM AUTHOR]

Depth-integrated (1-D) flowline models have been widely used to simulate fast-flowing tidewater glaciers and predict change because the continuous grounding line tracking, high horizontal resolution, and physically based calving criterion that are essential to realistic modeling of tidewater glaciers can easily be incorporated into the models while maintaining high computational efficiency. As with all models, the values for parameters describing ice rheology and basal friction must be assumed and/or tuned based on observations. For prognostic studies, these parameters are typically tuned so that the glacier matches observed thickness and speeds at an initial state, to which a perturbation is applied. While it is well know that ice flow models are sensitive to these parameters, the sensitivity of tidewater glacier models has not been systematically investigated. Here we investigate the sensitivity of such flowline models of outlet glacier dynamics to uncertainty in three key parameters that influence a glacier's resistive stress components. We find that, within typical observational uncertainty, similar initial (i.e., steady-state) glacier configurations can be produced with substantially different combinations of parameter values, leading to differing transient responses after a perturbation is applied. In cases where the glacier is initially grounded near flotation across a basal over-deepening, as typically observed for rapidly changing glaciers, these differences can be dramatic owing to the threshold of stability imposed by the flotation criterion. The simulated transient response is particularly sensitive to the parameterization of ice rheology: differences in ice temperature of ∼2 °C can determine whether the glaciers thin to flotation and retreat unstably or remain grounded on a marine shoal. Due to the highly non-linear dependence of tidewater glaciers on model parameters, we recommend that their predictions are accompanied by sensitivity tests that take parameter uncertainty into account. [ABSTRACT FROM AUTHOR]

This paper presents a glacial geomorphological map of over 17,000 landforms on the bed of a major palaeo-ice stream in Marguerite Bay, western Antarctic Peninsula. The map was compiled using various geophysical datasets from multiple marine research cruises. Eight glacial landform types are identified: mega-scale glacial lineations, crag-and-tails, whalebacks, gouged, grooved and streamlined bedrock, grounding-zone wedges, subglacial meltwater channels, gullies and channels, and iceberg scours. The map represents one of the most complete marine ice-stream signatures available for scrutiny, and these data hold much potential for reconstructing former ice sheet dynamics, testing numerical ice sheet models, and understanding the formation of subglacial bedforms beneath ice streams. In particular, they record a complex bedform signature of palaeo-ice stream flow and retreat since the last glacial maximum, characterised by considerable spatial variability and strongly influenced by the underlying geology. The map is presented at a scale of 1: 750,000, designed to be printed at A2 size, and encompasses an area of 128,420 km2. [ABSTRACT FROM AUTHOR]

Observations of ocean-terminating outlet glaciers in Greenland and West Antarctica indicate that their contribution to sea level is accelerating as a result of increased velocity, thinning and retreat. Thinning has also been reported along the margin of the much larger East Antarctic ice sheet, but whether glaciers are advancing or retreating there is largely unknown, and there has been no attempt to place such changes in the context of localized mass loss or climatic or oceanic forcing. Here we present multidecadal trends in the terminus position of 175 ocean-terminating outlet glaciers along 5,400 kilometres of the margin of the East Antarctic ice sheet, and reveal widespread and synchronous changes. Despite large fluctuations between glaciers-linked to their size-three epochal patterns emerged: 63 per cent of glaciers retreated from 1974 to 1990, 72 per cent advanced from 1990 to 2000, and 58 per cent advanced from 2000 to 2010. These trends were most pronounced along the warmer western South Pacific coast, whereas glaciers along the cooler Ross Sea coast experienced no significant changes. We find that glacier change along the Pacific coast is consistent with a rapid and coherent response to air temperature and sea-ice trends, linked through the dominant mode of atmospheric variability (the Southern Annular Mode). We conclude that parts of the world's largest ice sheet may be more vulnerable to external forcing than recognized previously. [ABSTRACT FROM AUTHOR]

Until relatively recently, it was assumed that Arctic ice masses would respond to climatic/oceanic forcing over millennia, but observations made during the past two decades have radically altered this viewpoint and have demonstrated that marine-terminating outlet glaciers can undergo dramatic dynamic change at annual timescales. This paper reviews the substantial progress made in our understanding of the links between marine-terminating Arctic outlet glacier behaviour and the ocean-climate system during the past 20 years, when many ice masses have rapidly lost mass. Specifically, we assess three primary climatic/oceanic controls on outlet glacier dynamics, namely air temperature, ocean temperature and sea ice concentrations, and discuss key linkages between them. Despite recent progress, significant uncertainty remains over the response of marine-terminating outlet glaciers to these forcings, most notably: (1) the spatial variation in the relative importance of each factor; (2), the contribution of glacier-specific factors to glacier dynamics; and (3) the limitations in our ability to accurately model marine-terminating outlet glacier behaviour. Our present understanding precludes us from identifying patterns of outlet glacier response to forcing that are applicable across the Arctic and we underscore the potential danger of extrapolating rates of mass loss from a small sample of study glaciers. [ABSTRACT FROM AUTHOR]

Over the past decade, ice loss from the Greenland Ice Sheet increased as a result of both increased surface melting and ice discharge to the ocean. The latter is controlled by the acceleration of ice flow and subsequent thinning of fast-flowing marine-terminating outlet glaciers. Quantifying the future dynamic contribution of such glaciers to sea-level rise (SLR) remains a major challenge because outlet glacier dynamics are poorly understood. Here we present a glacier flow model that includes a fully dynamic treatment of marine termini. We use this model to simulate behaviour of four major marine-terminating outlet glaciers, which collectively drain about 22 per cent of the Greenland Ice Sheet. Using atmospheric and oceanic forcing from a mid-range future warming scenario that predicts warming by 2.8 degrees Celsius by 2100, we project a contribution of 19 to 30 millimetres to SLR from these glaciers by 2200. This contribution is largely (80 per cent) dynamic in origin and is caused by several episodic retreats past overdeepenings in outlet glacier troughs. After initial increases, however, dynamic losses from these four outlets remain relatively constant and contribute to SLR individually at rates of about 0.01 to 0.06 millimetres per year. These rates correspond to ice fluxes that are less than twice those of the late 1990s, well below previous upper bounds. For a more extreme future warming scenario (warming by 4.5 degrees Celsius by 2100), the projected losses increase by more than 50 per cent, producing a cumulative SLR of 29 to 49 millimetres by 2200. [ABSTRACT FROM AUTHOR]

The article discusses a research study on the impact of large calving events in 2010 on Peterman Glacier in Greenland, its future stability and the interaction of the glacier with climate and ocean system components. Researchers investigated the dynamic response of ice-sheet to the retreat of ice-shelf by measuring upstream and downstream velocities of the Peterman Glacier grounding line using a numerical ice-flow model. It mentions the observation of seasonal velocity cycles for assessing mechanisms that drive glacier speed seasonal changes. Results showed the highest flow speed of Peterman Glacier near the grounding line than the floating ice-shelf. It also notes the observation on very minor near-terminus acceleration after the 2010 calving event.

Recent dramatic acceleration, thinning and retreat of tidewater outlet glaciers in Greenland raises concern regarding their contribution to future sea-level rise. These dynamic changes seem to be parallel to oceanic and climatic warming but the linking mechanisms and forcings are poorly understood and, furthermore, large-scale ice sheet models are currently unable to realistically simulate such changes which provides a major limitation in our ability to predict dynamic mass losses. In this paper we apply a specifically designed numerical flowband model to Jakobshavn Isbrae (JIB), a major marine outlet glacier of the Greenland ice sheet, and we explore and discuss the basic concepts and emerging issues in our understanding and modelling ability of the dynamics of tidewater outlet glaciers. The modelling demonstrates that enhanced ocean melt is able to trigger the observed dynamic changes of JIB but it heavily relies on the feedback between calving and terminus retreat and therefore the loss of buttressing. Through the same feedback, other forcings such as reduced winter sea-ice duration can produce similar rapid retreat. This highlights the need for a robust representation of the calving process and for improvements in the understanding and implementation of forcings at the marine boundary in predictive ice sheet models. Furthermore, the modelling uncovers high sensitivity and rapid adjustment of marine outlet glaciers to perturbations at their marine boundary implying that care should be taken in interpreting or extrapolating such rapid dynamic changes as recently observed in Greenland. [ABSTRACT FROM AUTHOR]

The article discusses a study on the ability of a physically based iceberg calving model to generate realistic patterns of glacier advance and retreat and the influence of bed topography on flow dynamics and terminus stability. The crevasse-depth calving model and the ice-flow model used to evolve the glacier through time are examined. Significant progress on the so-called calving problem is expected to be gained from model simulations and observations. It points out the importance of the choice of calving model in numerical prognostic ice-flow models in determining behaviour and stability of the model glacier. Also stressed is the necessity for observations to validate proposed models.

The article presents a numerical study of glacier advance over a deforming sediment layer. It cites the three modes of advances which are observed in the relative viscosities of ice and till including overriding, plug-flow and mixed-flow. It shows the contrast in effective viscosity between ice and till as the most important model parameter defining the mode of advance and the resulting thickness distribution of the till.

The article discusses the shrinking of the world's mountain glaciers in mass and extent due to atmospheric warming. It reports that the issue is discussed with reference to a modeling framework by G.K.C. Clarke that simulates the evolution of glaciers in Western Canada at high resolution and accounts for glacier flow. It suggests the framework includes full ice flow physics and predicts that mountain glaciers in this region will mostly be restricted to the coastal areas by 2100.

Abstract: Digital elevation models of the area around the Solway Lowlands reveal complex subglacial bedform imprints relating the central sector of the LGM British and Irish Ice Sheet. Drumlin and lineation mapping in four case studies show that glacier flow directions switched significantly through time. These are summarised in four major flow phases in the region: Phase I flow was from a dominant Scottish dispersal centre, which transported Criffel granite erratics to the Eden Valley and forced Lake District ice eastwards over the Pennines at Stainmore; Phase II involved easterly flow of Lake District and Scottish ice through the Tyne Gap and Stainmore Gap with an ice divide located over the Solway Firth; Phase III was a dominant westerly flow from upland dispersal centres into the Solway lowlands and along the Solway Firth due to draw down of ice into the Irish Sea basin; Phase IV was characterised by unconstrained advance of Scottish ice across the Solway Firth. Forcing of a numerical model of ice sheet inception and decay by the Greenland ice core record facilitates an assessment of the potential for rapid ice flow directional switching during one glacial cycle. The model indicates that, after fluctuations of smaller radially flowing ice caps prior to 30kaBP, the ice sheet grows to produce an elongate, triangular-shaped dome over NW England and SW Scotland at the LGM at 19.5kaBP. Recession after 18.5kaBP displays a complex pattern of significant ice flow directional switches over relatively short timescales, complementing the geomorphologically-based assessments of palaeo-ice dynamics. The palaeoglaciological implications of this combined geomorphic and modelling approach are that: (a) the central sector of the BIIS was as a major dispersal centre for only ca 2.5ka after the LGM; (b) the ice sheet had no real steady state and comprised constantly migrating dispersal centres and ice divides; (c) subglacial streamlining of flow sets was completed over short ... [Copyright &y& Elsevier]

Observations of ice deformation patterns at the front of an actively calving glacier during five summer field seasons allow us to relate ice flow patterns to glacier calving. Ice geometry and displacement were measured every minute with a terrestrial radar interferometer (GPRI) during 10 days per field season. The investigated tidewater glacier, Eqip Sermia in West Greenland, features calving front sections that are in very shallow water or near-floating, and glacier thinning with a nearly constant calving front position yield measurements at different ice thicknesses. We used this data set for a parameter study on the influence of ice thickness, front geometry and external forcing on the calving process. We present limits on critical strain rate for iceberg calving in dependence on front height and water depth. [ABSTRACT FROM AUTHOR]

A warming climate not only affects the glacier melt rates and mass balance, but also favours the formation of supraglacial debris cover on glacier tongues. Debris cover in turn affects melt rates and melt patterns and can thus influence glacier geometry in the long run. Therefore, knowledge about the processes that govern the formation, transport and distribution of debris cover can assist in predicting glacier evolution. The spatial distribution of debris covers is a function of the debris origin and deposition on the glacier ice and the debris transport away from the deposition location. Few studies have investigated debris extent and thickness distribution holistically, i.e. by including the context of debris origin and deposition as well as debris transport. This study presents an integral assessment of the debris cover of Zmuttgletscher in the western Swiss Alps by combining remote sensing and mass transport modelling for the debris origin and deposition as well as the debris transport paths. These observations are combined with statistically analysed field measurements for the debris thickness distribution.This study shows that the correct determination of the glacier transport paths is crucial, which act as debris transport units. Only then, integral conclusions about the evolution of a supraglacial debris cover are possible. The debris input via snow avalanches is higher for avalanche deposition areas with a higher relative amount of bare rock wall area in their contributing headwall area. Extracted debris concentrations for these avalanche cones determine the variations in debris thickness patterns on the glacier tongue. Furthermore, decreasing debris emergence rates downglacier are calculated. The statistical analysis of the debris cover thickness measurements yields thicker debris on south-exposed flanks on the glacier tongue compared to north-exposed flanks, as well as increasing debris thicknesses towards the terminus in line with literature.The findings obtained in this study improve our knowledge of supraglacial debris and contribute important information to the modelling of supraglacial debris cover evolution and dynamics. [ABSTRACT FROM AUTHOR]

We observed an outlet glacier in West-Greenland over five years by using a terrestrial radar interferometer, pressure sensors in the fjord and a time-lapse camera. A combination of these technologies provides us with displacement and topographical data with a spatial resolution of 5 meters in one minute intervals during five multi-day field campaigns, water level data in the fjord with a temporal resolution of several seconds over five years and images of the glacier front every 10 seconds for four days. This very detailed dataset enables us to get new insights of the calving process and changes in the front geometry. We use these data to establish detailed calving event statistics over five years, which are compared to environmental forcings like tides or weather conditions. By identifying source areas and ice volumes of individual calving events we quantitatively investigate the relationship between calving front geometry, calving rate and potential drivers. Additionally, identifying changes in the front geometry, the ice flow velocity pattern and the crevasse characteristics and comparing them with potential drivers enables us to improve our understanding of the ongoing observed changes of calving glaciers. [ABSTRACT FROM AUTHOR]

Debris-covered glaciers receive increasing attention during the current period of sustained negative mass balance and expanding debris cover. The debris cover induces various feedback mechanisms that shape the evolution of the glacier geometry, and also the glacier surface. Although the surface morphology of many debris-covered glaciers is markedly different from that of debris-free glaciers, only a few studies have combined different processes to investigate these characteristic glacier surfaces in order to improve our knowledge of glacier evolution on a wider spatial and temporal scale. Debris-covered glacier tongues can consist of parts with a smooth surface as well as surfaces of high local relief with abundant ice cliffs in the lower end. In this study we analysed the evolution of the surface features of Zmuttgletscher, a debris-covered glacier in Switzerland, over a period of 140 years using time series of historic maps, high resolution digital elevation models and glacier velocities, as well as data on debris cover extent and thickness. Our results reveal insights into the up-glacier expansion of the debris cover over time and the formation of medial moraines in the prolongation of the uppermost areas where debris emerged on the glacier surface. Moraine ridge prominence increased during periods of negative mass balance, and troughs developed in debris-free areas between ridges, persisting even after a continuous debris cover had developed. The changing surface morphology inhibits across-glacier meltwater flow, both supra- and subglacially. Accordingly, we found that large cryo-valleys with ice cliffs have formed down-glacier of the troughs where meltwater runoff accumulates. The meanders of these valleys have enlarged over time, especially by ice cliff backwasting at steep slopes, and most of the glacier width today is affected by such high-relief erosion features. We find that about 75% of all ice cliffs are located in this high-relief zone. The volume lost at these erosion features has increased by a factor of five since the 1980s, but is still very small in comparison to the high glacier-wide thinning rates. [ABSTRACT FROM AUTHOR]