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A new calving algorithm is developed in the glacier model Elmer/Ice that allows unrestricted calving and terminus advance in 3D. The algorithm uses the meshing software Mmg to implement anisotropic remeshing and allow mesh adaptation at each time step. The development of the algorithm, along with the implementation of the crevasse depth law, produces a new full-Stokes calving model capable of simulating calving and terminus advance across an array of complex geometries. Using a synthetic tidewater glacier geometry, the model is tested to highlight the numerical model parameters that can alter calving when using the crevasse depth law. For a system with no clear attractor at a pinning point, the model time step and mesh resolution are shown to alter the simulated calving. In particular, the vertical mesh resolution has a large impact, increasing calving, as the frontal bending stresses are better resolved. However, when the system has a strong attractor, provided by basal pinning points, numerical model parameters have a limited effect on the terminus evolution. Conversely, transient systems with no clear attractors are highly influenced by the choice of numerical model parameters. The new algorithm is capable of implementing unlimited terminus advance and retreat, as well as unrestricted calving geometries, applying any vertically varying melt distribution to the front for use in conjunction with any calving law or potentially advecting variables downstream. In overcoming previous technical hurdles, the algorithm opens up the opportunity to improve both our understanding of the physical processes and our ability to predict calving. [ABSTRACT FROM AUTHOR]

Ice sheet models are the main tool to generate forecasts of ice sheet mass loss, a significant contributor to sea level rise; thus, knowing the likelihood of such projections is of critical societal importance. However, to capture the complete range of possible projections of mass loss, ice sheet models need efficient methods to quantify the forecast uncertainty. Uncertainties originate from the model structure, from the climate and ocean forcing used to run the model, and from model calibration. Here we quantify the latter, applying an error propagation framework to a realistic setting in West Antarctica. As in many other ice sheet modelling studies we use a control method to calibrate grid-scale flow parameters (parameters describing the basal drag and ice stiffness) with remotely sensed observations. Yet our framework augments the control method with a Hessian-based Bayesian approach that estimates the posterior covariance of the inverted parameters. This enables us to quantify the impact of the calibration uncertainty on forecasts of sea level rise contribution or volume above flotation (VAF) due to the choice of different regularization strengths (prior strengths), sliding laws, and velocity inputs. We find that by choosing different satellite ice velocity products our model leads to different estimates of VAF after 40 years. We use this difference in model output to quantify the variance that projections of VAF are expected to have after 40 years and identify prior strengths that can reproduce that variability. We demonstrate that if we use prior strengths suggested by L -curve analysis, as is typically done in ice sheet calibration studies, our uncertainty quantification is not able to reproduce that same variability. The regularization suggested by the L curves is too strong, and thus propagating the observational error through to VAF uncertainties under this choice of prior leads to errors that are smaller than those suggested by our two-member "sample" of observed velocity fields. [ABSTRACT FROM AUTHOR]

Social connectedness among neighbours impacts health and well-being, especially during stressful life events like a pandemic. An activity such as neighbourhood walking enables urban inhabitants to engage in incidental sociability and acts of "neighbouring"--that is, authentic social interactions with neighbours--to potentially bolster the social fabric of neighbourhoods and strengthen relationships. With the potential of neighbourhood walking in mind, this article investigates how everyday encounters while engaged in routine neighbourhood walks strengthen and/or weaken social ties among neighbours. To this end, the article draws on three sources of qualitative data from neighbourhood walkers in Southwestern Ontario, Canada: (a) "walking diaries" in which participants took note of their walking routes, the people they observed on their walks, and other details of their walking experiences; (b) maps of their neighbourhoods that outlined the boundaries of their self-identified neighbourhoods, their routine walking routes, and the people they recognized during their neighbourhood walks; and (c) one-on-one interviews during which participants provided crucial context and meaning to the maps and their walking experiences. The findings provide evidence of how interactions among inhabitants, while engaged in neighbourhood walking, help generate greater social connectedness. [ABSTRACT FROM AUTHOR]

We present the first fully coupled 3D full-Stokes model of a tidewater glacier, incorporating ice flow, subglacial hydrology, plume-induced frontal melting and calving. We apply the model to Store Glacier (Sermeq Kujalleq) in west Greenland to simulate a year of high melt (2012) and one of low melt (2017). In terms of modelled hydrology, we find perennial channels extending 5 km inland from the terminus and up to 41 and 29 km inland in summer 2012 and 2017, respectively. We also report a hydrodynamic feedback that suppresses channel growth under thicker ice inland and allows water to be stored in the distributed system. At the terminus, we find hydrodynamic feedbacks exert a major control on calving through their impact on velocity. We show that 2012 marked a year in which Store Glacier developed a fully channelised drainage system, unlike 2017, where it remained only partially developed. This contrast in modelled behaviour indicates that tidewater glaciers can experience a strong hydrological, as well as oceanic, control, which is consistent with observations showing glaciers switching between types of behaviour. The fully coupled nature of the model allows us to demonstrate the likely lack of any hydrological or ice-dynamic memory at Store Glacier. [ABSTRACT FROM AUTHOR]

Retreat of calving glaciers worldwide has contributed substantially to sea-level rise in recent decades. Mass loss by calving contributes significantly to the uncertainty of sea-level rise projections. At Bowdoin Glacier, Northwest Greenland, most calving occurs by a few large events resulting from kilometre-scale fractures forming parallel to the calving front. High-resolution terrestrial radar interferometry data of such an event reveal that crevasse opening is fastest at low tide and accelerates during the final 36 h before calving. Using the ice flow model Elmer/Ice, we identify the crevasse water level as a key driver of modelled opening rates. Sea water-level variations in the range of local tidal amplitude (1 m) can reproduce observed opening rate fluctuations, provided crevasse water level is at least 4 m above the low-tide sea level. The accelerated opening rates within the final 36 h before calving can be modelled by additional meltwater input into the crevasse, enhanced ice cliff undercutting by submarine melt, ice damage increase due to tidal cyclic fatigue, crevasse deepening or a combination of these processes. Our results highlight the influence of surface meltwater and tides on crevasse opening leading to major calving events at grounded tidewater glaciers such as Bowdoin. [ABSTRACT FROM AUTHOR]

Three-dimensional ice flow modelling requires a lot of computing resources and observation data, such that 2D simulations are often preferable, at least when the stream lines are parallel; otherwise the lateral divergence of the flow should be accounted for (2.5D models). Assuming that the stream lines follow the steepest slope of the surface, the width variations of a flow tube are computed thanks to the surface curvature. The ability of the 2.5D models to account properly for a 3D state of strain and stress has not clearly been established, especially their sensitivity on how the ice surface curvature is determined (scanning window on a DEM), and on the geometry of the ice surface. In particular, these models might fail for divergent flows, and need to be more clearly defined. A twin experiment is here carried out, comparing 3D and 2.5D computed velocities, on three dome geometries, for several scanning windows and thermal conditions. The chosen scanning window used to evaluate the ice surface curvature should be comparable to the typical size of the measured ice relief. For isothermal ice, the error made by the 2.5D model is in the range 0-10% but for highly diverging flows the errors are 2 or 3 times higher and could lead to a non-physical reversed surface convexity at the dome. For non-isothermal ice, assuming a realistic temperature profile, the presence of a sharp ridge leads to a partly reversed velocity profile. The warmer bottom ice is more deformed than the upper ice, and this results in the non-verticality of the walls of the flow tube, violating the 2.5D assumptions. [ABSTRACT FROM AUTHOR]

The ongoing retreat of many tidewater glaciers has been attributed to the increased submarine melting of calving fronts in response to warming oceans and increased meltwater runoff. The mechanisms through which submarine melting affects the stability of tidewater glaciers remain poorly understood however. In particular, the existence of a 'calving amplifier effect', in which submarine melting leads to a further increase in ice loss through calving, remains uncertain. Numerical modelling experiments have shown that this effect may occur when a glacier calving front is undercut due to vertical variation in the rate of submarine melting. There has however been relatively little investigation of the impact on calving, and thus total mass loss, of lateral variation in melting across the calving front.Here, we use a three-dimensional, full-Stokes glacier calving model implemented in Elmer/Ice to examine the response of an idealised tidewater glacier to spatially variable submarine melting. The model uses a crevasse-depth calving criterion that triggers calving when surface and basal crevasses penetrate the full thickness of the glacier. We subject the model glacier to spatially discrete areas of submarine melting representing the zones of intense localised melting that occur at tidewater glaciers where the input of subglacial runoff drives vigorous plumes adjacent to the calving front. We find that submarine melting may have both a positive and a negative impact on the calving rate, depending on a range of variables including the intensity of the melting, the extent of the calving front subject to melting, and location of these zones of intense melting along the calving front. In particular, we find that the greatest positive impact on calving occurs when submarine melting is applied close to the ice margins rather than in the centre of the glacier. This occurs because as the melting incises notches into the calving front, it disrupts the natural compressive stress-arch that provides support to the centre of the glacier, isolating it from the stabilising influence of the fjord walls and thus triggering calving until a new stable geometry is formed. It is thus possible that through this calving amplifier effect, small areas of intense plume-driven melting could trigger enhanced calving and retreat even at large and fast-flowing glaciers at which the average submarine melt rate remains below the glacier velocity. [ABSTRACT FROM AUTHOR]

The dynamic response of calving glaciers to warming climate is one of the greatest uncertainties in predictions of future sea level rise. A growing body of observational evidence suggests that the calving glaciers which drain the Greenland and Antarctic ice sheets are highly sensitive to environmental forcing, but the current generation of glacier models is unable to adequately resolve this critical interaction between ice sheets and climate. We present results from a new approach combining the continuum model Elmer/Ice and the discrete element/particle model HiDEM, applied to Store Glacier, a large calving glacier in West Greenland. We use Elmer/Ice to investigate the dynamic/stress response to both submarine melting and ice mélange buttressing of the calving front, and use HiDEM to investigate fracture propagation and calving for specific geometries. We implement a new approach to investigating ice mélange; by allowing the glacier to calve repeatedly into the fjord, we effectively 'build' a mélange from previously calved icebergs.Our results indicate that lateral support from valley walls plays a critical role in the stability of the calving front; a persistent compressive stress arch exists just behind the current terminus position, transmitting resistive stress from sidewalls to centreline. Furthermore, we find that minimal mélange buttressing applied near the lateral margins is sufficient to advance this compressive arch, allowing the terminus to advance in winter. With respect to submarine melting, we find that a modest melt undercut (60m) can promote calving at an otherwise stable terminus position. Our HiDEM simulations for Store Glacier closely match the calving style observed in satellite imagery; the ability to accurately resolve calving at the event scale is a major step forward in our understanding of calving processes. By comparing stress patterns in Elmer/Ice with fracture patterns in HiDEM, we seek to formulate improved calving laws which can be implemented in ice-sheet scale continuum models. [ABSTRACT FROM AUTHOR]