Glacier surges are episodes of significantly increased ice flow due to ice-dynamical feedbacks, and are often repeated in a quasi-periodical manner. Ice mass is redistributed during a surge, which leads to surface lowering at high elevation as ice is transferred down-glacier and thickening nearer the terminus. In this paper, we review different approaches for monitoring and detecting glacier surges in Svalbard, one of the most prominent global clusters of surge-type glaciers. Current surge detection is mainly based upon tracking the speed of glaciers over time, measuring elevation and frontal changes, and more recently automatically detecting surface changes such as increased crevassing. Thermal and hydrological changes near the glacier bed drive surge dynamics and can be measured using geophysical sensors such as ground-penetrating radar (GPR) and seismometers. When glaciers surge, they often produce diagnostic landforms in subglacial and proglacial environments, allowing historical surging to be identified even if surges have not been directly observed.Through this review, we have compiled an updated database of surge-type glaciers in Svalbard and find that 36% of glaciers display surge-type behaviour, which accounts for 75% of the total glacier area on Svalbard. Only 10% of all glaciers have been directly observed to surge, yet account for 48% of the total glacier area on Svalbard. Svalbard surge-type glaciers have gentler slopes, are generally longer, and extend across a larger elevation range compared to non surge-type glaciers across the archipelago. We find that the behaviour of surge-type glaciers is variable and more closely resembles a continuum from glaciers that do not surge to those which redistribute mass in a single event of strongly enhanced ice flux. We can describe the variability in surge behaviour using the concept of enthalpy and a six-stage surge model that characterises the build-up of energy at the glacier bed driven initially by thermal change and then ice acceleration which is prompted by changes in subglacial hydrology. Observations of glacier surges have improved significantly with routine mapping from satellites such as Sentinel-1, Sentinel-2 and the Landsat satellite series. Furthermore, an increasing number of geophysical measurements is enabling an improved understanding of subglacial processes before, during and after a surge, which is crucial for improving models of surge behaviour. As our observations of surges continue to improve, we expect to uncover new elements and details of surge behaviour, reaffirming the need to rethink the binary classification of glaciers as either ‘surge-type’ or ‘not surge-type’ in Svalbard and across the world.

Approximately 21% of Svalbard’s glaciers are classified as surge-type and undergo cyclical changes in ice velocity between quiescent (slow) and active (fast) phases. Whilst it is generally understood that processes at the glacier bed drive surge initiation, the physical mechanisms translating basal sliding to ice flow variability and cyclicity remain open questions. Recent mapping of glacier velocities across Svalbard has identified an acceleration in ice flow at the Borebreen tidewater glacier which terminates on the northwestern side of Isfjorden. Before 2018, average summer velocities at Borebreen were ~0.6 m/d but more than doubled to 2.4 m/d by 2023. Borebreen last surged ~100 years ago, hence the acceleration in ice velocity suggests it is the result of the glacier transitioning to an active surge. In this contribution, we will discuss results from a summer field campaign to Borebreen in August 2023. Using a multi-sensor network of seismic arrays, Terrestrial Laser Scanners (TLS), and drones, we characterise present day surge dynamics and use the data to understand the drivers. In addition, optical imagery from the PlanetScope constellation and Synthetic Aperture Radar (SAR) data from Sentinel-1 are used to determine surface conditions (e.g. surface melt patterns, crevasses, proglacial turbid plumes) and quantify ice velocities. Here, we will report on the following: 1) basal processes (e.g. stick-slip events, icequakes) under Borebreen; 2) calving processes at the over-steepened ice cliff of the surge front; 3) ice velocity extracted from drone photogrammetry, Planetscope imagery and Sentinel-1 SAR scenes; and 4) surface conditions (e.g. crevassing, surface melt) over the course of the ablation season and its relationship with ice dynamics. We find that the surge initiated at the glacier terminus and has been propagating upglacier. The glacier speed doubles each spring in response to elevated air temperatures which leads to surface melting and the delivery of meltwater to the glacier bed. Furthermore, we identify clusters of seismicity at the glacier bed, far from the terminus, which appear to indicate sliding. Our results push forward our understanding of the processes that initiate and sustain glacier surges and glacier instabilities in general.

Thwaites Glacier, a large outlet glacier of the West Antarctic Ice Sheet, holds over a half meter of sea level rise equivalent. The large potential contribution to sea level is concerning given that the glacier may be vulnerable to self-sustaining processes of rapid retreat due to the retrograde bed slope that characterises much of the glacier’s bed. Such a reverse-sloping bed exists behind the relatively high ridge on which the western calving front (WCF) of the Thwaites Glacier terminus currently rests. Our study focuses on the factors that control the calving dynamics of the WCF and the ability of mélange to influence these dynamics. Employing the 3D Helsinki Discrete Element Model (HiDEM), we find that calving at this location currently occurs as rifts form and widen due to longitudinal tensile stresses associated with ice flow across the grounding line. Calving is restricted in HiDEM simulations that include a constricted mélange field that is confined within the bounds of the model domain. A thicker, constricted mélange field fully suppresses calving. These simulations show the development of robust force chains that transmit resistive forces to the Thwaites WCF. In the future, the ability for mélange to influence the calving dynamics at the WCF will depend on the degree to which it is constrained in the wide Amundsen Sea Embayment, either through binding in land-fast sea ice or jamming behind large, grounded icebergs. As such, sea-ice conditions and iceberg characteristics will need to be considered along with the presence of mélange in investigations of the future retreat of the prominently recognised Thwaites Glacier.

The sedimentary processes taking place beneath contemporary surging glaciers are difficult to observe directly, yet they are crucial for building a holistic understanding of glacier surge processes and mechanisms. Settings where the sediment-landform assemblages characterising the ice-bed interface are preserved without significant modification are therefore an important archive of the subglacial processes that are active during a surge. At tidewater surging glaciers, landforms are often excellently preserved in a submarine setting, but analysis of these beyond mapping from high-resolution bathymetry data (where available) can be limited. However, in most cases, there are also subaerially exposed sediments and landforms at the terrestrial fjord margins, providing an accessible and rich source of data of the subglacial environment of a surging glacier. Borebreen is a tidewater glacier on the northwestern side of Isfjorden in Svalbard. Previously published detailed bathymetric data has identified a suit of submarine glacial landforms formed during the last surge of Borebreen ~100 years ago. The subsequent quiescent phase has exposed a wide spread of crevasse-squeeze ridges (CSRs) both in the fjord and on the terrestrial margins. These are important landforms that are unique to surging glaciers and can therefore provide information concerning surge dynamics and subglacial processes. We present initial geomorphological and geotechnical data from the CSRs through mapping and direct measurements using a hand-held shear vane test, pocket penetrometer and particle size analysis. High-resolution orthmosaics and Digital Elevation Models (DEMs) from drone surveys of the proglacial foreland were collected in order to assess the spatial pattern of CSRs and a Python-based ArcGIS toolbox was used to automatically extract 3D morphometric data from the DEMs. These data provide an opportunity to investigate the links between the sediment geotechnical properties, CSR geometries and surge processes and mechanisms; such as the identification of spatial patterns in the state of sediment consolidation within CSRs and CSR morphometrics.

Recent advances in the Elmer/Ice modelling suite have allowed 3D simulation of unrestricted calving geometries at tidewater glaciers such as Jakobshavn Isbrae. We present the first use of this model in an Antarctic setting. The more stochastic nature of calving at Antarctic ice sheets when compared to a Greenlandic setting has discouraged the development of calving laws and models. For shorter term calving simulations, it is sufficient to determine the local attractor or pinning point where the terminus stabilises following a transient period of retreat or advance. Importantly, this can only be achieved through a position-based law, as a positional attractor is independent of velocity. Using a deterministic position-based crevasse depth calving law it is possible to simulate the observed calving behaviour at the western ice front of Thwaites Glacier. The calving law identifies the attractor point beyond which ice will calve following a variable but short delay. The geometric attractor is defined by local topography along with grounding zone dynamics. Beyond this point there are a lack of lateral or basal pinning points, so any downstream ice is effectively lost from the system. More generally, across the floating extensions of Thwaites Glacier, the model reliably predicts regions of crevasse formation. Accurately simulating crevasse formation on ice shelves along with determining the attractor within the glacier retreat and advance cycle is the first step towards a reliable Antarctic calving law.

The holistic assessment of glacial sediment-landform associations facilitates the reconstruction of glacier and ice-sheet dynamics (palaeoglaciology) and this relies on comparisons with modern analogues where process can be linked to form. Typical glacial depositional environments are presented here based upon sediment-landform associations that are characteristic of the process-form regimes operating in particular topographic and environmental settings or landsystems. These include the subglacial environment, the margins of active temperate, polythermal and polar-continental ice masses, surging glaciers, the subaquatic settings of fjords, continental shelves and large proglacial lakes, and mountain glaciers.

Marine-terminating glaciers and ice shelves are notoriously complex, with a wide range of ice-dynamic and calving processes occuring in response to oceanographic, atmospheric and glaciological influences. Within this complexity, however, we can recognise order on at least two scales. First, marine ice fronts typically form vertical cliffs, reflecting competition between oversteepening (ice flow and melt-undercutting) and failure. Calving magnitude-frequency distributions have power-law form with an exponent of -1.2, characteristic of self-organising criticality (SOC). Such systems have a critical point as an attractor, such that the system converges on the failure threshold. The second scale is that of the whole ice tongue. Tidewater glaciers and ice shelves typically oscillate around stable positions for multiple years, punctuated by transitions to new quasi-stable positions. Stability is encouraged by pinning points which function as attractors at thresholds between stable and metastable states. Ice tongues may exist in metastable states for variable amounts of time, from days to decades. Factors encouraging rapid relaxation to the threshold include large stress gradients and rapid basal melt, and factors encouraging long relaxation times include low stress gradients, low melt rates, and buttressing from mélange or sea ice. Calving magnitude-frequency distributions have exponential form, reflecting the stochastic nature of calving in the metastable zone. Both scales of self-organisation emerge spontaneously from physically-based calving models such as the Helsinki Discrete Element Model (HiDEM) and the crevasse-depth (CD) calving law implemented in Elmer/Ice. Purely deterministic models, however, are not optimal for long-term simulations, especially in Antarctic contexts. We present results of preliminary simulations using a stochastic CD calving law, which opens up the possibility of a universal calving model applicable to both the Greenland and Antarctic ice sheets.

The complexity of the processes and the difficulty of collecting observations mean that the treatment of the ice-ocean boundary remains one of the most challenging aspects of running models of the Greenland ice sheet. With geometry, climate forcing, ice properties and feedbacks between these factors all playing a role, tidewater glaciers display a range of calving styles that are hard to capture within the simple parameterisations that are necessary for large-scale ice sheet modeling. Here we attempt to place some dominant calving styles within a single framework. We study submarine melt undercut-driven calving using linear elastic fracture mechanics within 2D elastic simulations, together with analytical approaches to calving driven by the intersection of basal and surface crevasses and to ice cliff failure. Taken together, these approaches give a prediction of calving style as a function of the calving front ice thickness, ocean depth and submarine melt undercut length, or equivalently as a function of the frontal tension, bending moment and shear. We discuss possible implementations in ice sheet models.

The crevasse depth (CD) calving law predicts the position of glacier termini from the penetration of surface and basal crevasses computed from stresses in the ice. When applied to Greenland tidewater glaciers, it has high skill when implemented in a full-Stokes 3D model, although its performance in 2D and 1D models is still subject to debate, especially its ability to induce ice shelf calving without the addition of unrealistic amounts of water in surface crevasses. This study re-evaluates the CD law within a 1D flowline model of an ice shelf. We show that the model predicts deep crevasse penetration at locations where drag at the shelf boundaries diminishes,such as the grounding line or embayment mouths. Crevasse depth depends on the rate at which these resistance sources decrease along-flow, influencing the longitudinal stress gradient. While full-depth penetration may occur in thinned shelves (due to extensive basal melt), full-depth calving is generally not predicted for unconfined ice shelves. Observations of Antarctic ice shelves and floating ice tongues well beyond embayments or basal pinning points suggest that additional triggers, like slow rift growth, basal melting, or oceanographic stresses, are essential for calving. The addition of water to surface crevasses can greatly facilitate calving. In some cases, reflecting real-world conditions, such as the hydrofracturing-induced collapse of vulnerable ice shelves. However, the need for water-depth tuning in other situations has raised concerns about the physical fidelity of the model. We propose a modified stochastic CD calving criterion in which the probability of calving ramps from zero for a threshold crevasse depth to one for full-depth penetration. This non-deterministic approach captures the statistical structure of calving events, and allows a range of observed behaviours to emerge, such as long Antarctic ice shelf calving cycles (ice-tongue advance punctuated by rare calving events), and short-term fluctuations of tidewater glaciers (frequent calving retreat back to pinning points). We argue that a probabilistic approach represents an important step towards a universal calving law.

We present the first simulations of Jakobshavn Isbrae (Sermeq Kujalleq), west Greenland, using a 3D Stokes calving model that permits unrestricted advance and retreat. Using the position-based crevasse-depth calving law, the model is applied to simulate the calving dynamics of 2016-2017 season when Jakobshavn Isbrae is assumed to be stable because of the presence of a strong proglacial ice m & eacute;lange. The calving law needs to be adjusted to avoid an underestimation of calving, but once adjusted the calving model simulates seasonal calving dynamics that reflect observed calving-driven retreat very well. We find that a crevasse penetration threshold of 94.5% best matches observations from satellite imagery. Additional, 2-year transient simulations show that although ice m & eacute;lange is essential to the glacier's winter readvance, when removed, the glacier only retreats a couple of kilometres before reaching a stable position. While the backstress provided by the ice m & eacute;lange allows the glacier to advance beyond this point, the retreated terminus position is determined by a combination of bed geometry and glacier dynamics. Ultimately, while the ice m & eacute;lange allows winter readvance, cessation of the well-documented rapid retreat of Jakobshavn Isbrae will be influenced by the bed geometry.

The western region of the wide Thwaites Glacier terminus is characterized by a near-vertical calving front. The grounding line at this western calving front (WCF) rests on a relatively high ridge, behind which exists a reverse-sloping bed; retreat of the grounding line into this over-deepening basin could therefore expose deep calving faces that may be subject to ice-cliff failure. Here, we use the 3D Helsinki Discrete Element Model to identify the factors that control the calving dynamics in this location. We then focus on the ability of m & eacute;lange to influence these dynamics given the wide embayment in which Thwaites Glacier terminates. We find that calving along the WCF is currently influenced by ice flow across the grounding line and consequent longitudinal tensile stress and rift formation. Calving is slowed in simulations that are initiated with a highly constricted m & eacute;lange, with a thicker m & eacute;lange suppressing calving entirely. We liken the constrained simulations to a scenario in which m & eacute;lange piles behind a large grounded iceberg. In a future which may see calving become a more dominant control on the retreat of Thwaites Glacier, this type of blockage will be necessary for robust force chains to develop and transmit resistive forces to the terminus. The ability of the m & eacute;lange to hinder calving at this location will be determined by the presence and rigidity of binding land-fast sea ice and iceberg keel depths. Therefore, it is necessary to represent calving, m & eacute;lange and sea ice in a single framework to predict the fate of Thwaites Glacier. Thwaites Glacier, a major outlet glacier of the West Antarctic Ice Sheet, may be vulnerable to rapid retreat. The terminus of Thwaites Glacier is over 100 km wide; in this paper, we focus on the western terminus region, which meets the Amundsen Sea at a near-vertical ice face. We use a 3D glacier model that simulates ice fracture to identify the factors controlling iceberg calving. We also run simulations to explore the potential for m & eacute;lange, a conglomerate of variably sized ice pieces in front of a glacier, to impact calving dynamics at this location. Our simulations show that iceberg calving currently occurs through the growth of short ice-shelf extensions and the loss of resisting forces as the ice begins to float. Our simulations also demonstrate that calving is slowed when a thick immobile m & eacute;lange is present. The ability of the m & eacute;lange to apply a backforce to glaciers has been previously identified as an important brake on such calving-driven retreat. In a future that may see calving become a more dominant control on the retreat of Thwaites Glacier, this type of blockage will be necessary for the transmission of resistive forces to the terminus. Calving at Thwaites Glacier's western terminus is controlled by longitudinal tensile stresses and fracturing as basal traction is lost 3D modeling demonstrates that m & eacute;lange, if constrained, can inhibit calving at this location Future sea-ice conditions and iceberg morphology will determine if m & eacute;lange can compact and transmit substantial resistive forces

The collapse of ice shelves could expose tall ice cliffs at ice sheet margins. The marine ice cliff instability (MICI) is a hypothesis that predicts that, if these cliffs are tall enough, ice may fail structurally leading to self-sustained retreat. To date, projections that include MICI have been performed with a single model based on a simple parameterization. Here, we implement a physically motivated parameterization in three ice sheet models and simulate the response of the Amundsen Sea Embayment after a hypothetical collapse of floating ice. All models show that Thwaites Glacier would not retreat further in the 21st century. In another set of simulations, we force the grounding line to retreat into Thwaites’ deeper basin to expose a taller cliff. In these simulations, rapid thinning and velocity increase reduce the calving rate, stabilizing the cliff. These experiments show that Thwaites may be less vulnerable to MICI than previously thought, and model projections that include this process should be re-evaluated.

The largest uncertainty in future sea-level rise is loss of ice from the Greenland and Antarctic Ice Sheets. Ice shelves, freely floating platforms of ice that fringe the ice sheets, play a crucial role in restraining discharge of grounded ice into the ocean through buttressing. However, since the 1990s, several ice shelves have thinned, retreated, and collapsed. If this pattern continues, it could expose thick cliffs that become structurally unstable and collapse in a process called marine ice cliff instability (MICI). However, the feedbacks between calving, retreat, and other forcings are not well understood. Here we review observed modes of calving from ice shelves and marine-terminating glaciers, and their relation to environmental forces. We show that the primary driver of calving is long-term internal glaciological stress, but as ice shelves thin they may become more vulnerable to environmental forcing. This vulnerability—and the potential for MICI—comes from a combination of the distribution of preexisting flaws within the ice and regions where the stress is large enough to initiate fracture. Although significant progress has been made modeling these processes, theories must now be tested against a wide range of environmental and glaciological conditions in both modern and paleo conditions. ▪Ice shelves, floating platforms of ice fed by ice sheets, shed mass in a near-instantaneous fashion through iceberg calving.▪Most ice shelves exhibit a stable cycle of calving front advance and retreat that is insensitive to small changes in environmental conditions.▪Some ice shelves have retreated or collapsed completely, and in the future this could expose thick cliffs that could become structurally unstable called ice cliff instability.▪The potential for ice shelf and ice cliff instability is controlled by the presence and evolution of flaws or fractures within the ice.

The crevasse depth (CD) calving law predicts the position of glacier termini from the penetration of surface and basal crevasses computed from stresses in the ice. When applied to Greenland tidewater glaciers, it has high skill when implemented in a full-Stokes 3D model, although its performance in 2D and 1D models is still subject to debate, especially its ability to induce ice shelf calving without the addition of unrealistic amounts of  water in surface crevasses.  This study re-evaluates the CD law within a 1D flowline model of an ice shelf.  We show that the model predicts deep crevasse penetration at locations where drag at the shelf boundaries diminishes,such as the grounding line or embayment mouths. Crevasse depth depends on the rate at which these resistance sources decrease along-flow, influencing the longitudinal stress gradient. While full-depth penetration may occur in thinned shelves (due to extensive basal melt), full-depth calving is generally not predicted for unconfined ice shelves. Observations of Antarctic ice shelves and floating ice tongues well beyond embayments or basal pinning points suggest that additional triggers, like slow rift growth, basal melting, or oceanographic stresses, are essential for calving.  The addition of water to surface crevasses can greatly facilitate calving. In some cases, reflecting real-world conditions, such as the hydrofracturing-induced collapse of vulnerable ice shelves. However, the need for water-depth tuning in other situations has raised concerns about the physical fidelity of the model. We propose a modified stochastic CD calving criterion in which the probability of calving ramps from zero for a threshold crevasse depth to one for full-depth penetration. This non-deterministic approach captures the statistical structure of calving events, and allows a range of observed behaviours to emerge, such as long Antarctic ice shelf calving cycles (ice-tongue advance punctuated by rare calving events), and short-term fluctuations of tidewater glaciers (frequent calving retreat back to pinning points). We argue that a probabilistic approach represents an important step towards a universal calving law.

The widespread retreat of Svalbard glaciers has been frequently interrupted by short-lived surge advances. In the case of marine-terminating glaciers this is often expressed in the remodelling of coastal zones. Here, we analyzed the coastal zone changes in front of the recently surging Recherchebreen. The glacier advanced ca 1200 m since 2018 and suddenly stopped in June 2020 followed by the rapid formation of a delta system in front of its subglacial meltwater outlet. The delta advanced by ca 450 m with probably the fastest progradation rate ever detected in the Arctic region (ca 7 m/day). The synchroneity of the final slow-down of the glacier with the delta building indicates that this event records the release of stored water and sediments from beneath the glacier and thus provides direct evidence of drainage reorganisation at the termination of a surge. Such behaviour is likely common among Svalbard surging glaciers, but it only rarely leaves any direct geomorphic evidence. The Recherchebreen glacier in Svalbard, which had been advancing at 1200 m since 2018, abruptly stopped in June 2020, forming a rapid delta system with a daily progradation rate of 7 meters, suggesting drainage reorganization at the end of the surge, according to analysis of the changes in the coastal zone of the Recherchebreen glacier.

We investigate the physical basis of the crevasse-depth (CD) calving law by analysing relationships between glaciological stresses and calving behaviour at Sermeq Kujalleq (Store Glacier), Greenland. Our observations and model simulations show that the glacier has a stable position defined by a compressive arch between lateral pinning points. Ice advance beyond the arch results in calving back to the stable position; conversely, if melt-undercutting forces the ice front behind the stable position, it readvances because ice velocities exceed subaqueous melt rates. This behaviour is typical of self-organising criticality, in which the stable ice-front position acts as an attractor between unstable super-critical and sub-critical regimes. This perspective provides strong support for a ‘position-law’ approach to modelling calving at Sermeq Kujalleq, because any calving ‘rate’ is simply a by-product of how quickly ice is delivered to the critical point. The CD calving law predicts ice-front position from the penetration of surface and basal crevasse fields, and accurately simulates super-critical calving back to the compressive arch and melt-driven calving into the sub-critical zone. The CD calving law reflects the glaciological controls on calving at Sermeq Kujalleq and exhibits considerable skill in simulating its mean position and seasonal fluctuations.

<p>The oft-quoted statistic that 1% of the world’s glaciers are surge-type may suggest that surging is a rare, anomalous phenomenon. Among some populations of glaciers, however, surge-type glaciers are in the majority. For example, for glaciers over 16 km in length in Svalbard and Iceland over half have recorded surges. Surge-type glaciers are widespread in a broad arc stretching from Alaska to Novaya Zemlya (the Arctic Ring) and in many parts of High Mountain Asia. This distribution is defined by ranges of temperature and precipitation within which many glaciers cannot achieve stable steady states, as predicted by Enthalpy Balance Theory. </p> <p>Climatic controls on surging behaviour imply that the distribution of surge-type glaciers will shift in response to changes in temperature and/or precipitation. For example, the Arctic Ring may have been located south of its current position during some colder periods of the Quaternary. This was likely the case for Younger Dryas glaciers in Scotland. Reconstructions of palaeotemperature and palaeoprecipitation indicate that the Highlands and Islands of Scotland fell within the optimal climatic envelope for surging during the Younger Dryas. Examination of the landform record supports the conjecture that surge-type glaciers were widespread, including many outlet glaciers of the West Highland Icefield and smaller icecaps on the islands. </p> <p>Recognition of palaeosurges is important, because glacier reconstructions are commonly used as climatic proxies based on the assumption that glacier geometries represent stable steady states. Landsystem models are useful in this regard, provided they are applied flexibly with due consideration for local conditions and preservation biases. Systematic use of landsystem models and other tools may reveal other former clusters of surge-type glaciers in mid-latitude mountain regions.</p>

The impact of submarine melting on calving is thought to be central in the response of marine-terminating glaciers to climate, yet we currently have no settled parameterisation that can represent this process in ice sheet models. The crevasse-depth calving law has been widely applied with arguable success, but in its present form accounts only for depth-mean stresses. As such, it does not account for the bending stresses induced by undercutting that may be key to the impact of submarine melting on calving.Here, we combine elastic beam theory with linear elastic fracture mechanics to study the propagation of surface and basal crevasses near the front of tidewater glaciers in response to melt undercutting. We check our results against a numerical approach involving 2D elastic simulations and the displacement correlation method for estimating fracture depth. Our results suggest that bending stresses can play a significant role in modifying crevasse depth, with undercutting promoting the opening of surface crevasses and protruding ‘ice feet’ promoting the opening of basal crevasses. Lastly, we seek a revised crevasse-depth calving law that accounts for these effects.

<p>Below ice shelves, complex interactions between the ice and the ocean are at stake that have large implications for future sea level rise. Basal melting from the ocean is recognised to have large impacts on the stability. Many studies focus on theses interactions in coupled models at different spatio-temporal scales. However, most of them consider the basal topography of the shelf as smooth ignoring its irregular state due to basal crevassing or channel-like features. We propose to investigate the impact of these features on basal melt and ice shelf stability by using a discrete particule model and an ocean model applied at the ice shelf of Thwaites glacier.</p>

It is commonly asserted that there are two distinct classes of glacier surges: slow, long-duration 'Svalbard-type' surges, triggered by a transition from cold- to warm-based conditions (thermal switching), and fast, shorter-duration 'Alaska-type' surges triggered by a reorganisation of the basal drainage system (hydraulic switching). This classification, however, reflects neither the diversity of surges in Svalbard and Alaska (and other regions), nor the fundamental dynamic processes underlying all surges. We argue that enthalpy balance theory offers a framework for understanding the spectrum of glacier surging behaviours while emphasising their essential dynamic unity. In this paper, we summarise enthalpy balance theory, illustrate its potential to explain so-called 'Svalbard-type' and 'Alaska-type' surges using a single set of principles, and show examples of a much wider range of glacier surge behaviour than previously observed. We then identify some future directions for research, including strategies for testing predictions of the theory against field and remote sensing data, and priorities for numerical model development.