Search

Ground-penetrating radar data acquired in the 2016/17 austral summer on Sørsdal Glacier, East Antarctica, provide evidence for meltwater lenses within porous surface ice that are conceptually similar to firn aquifers observed on the Greenland Ice Sheet and the Arctic and Alpine glaciers. These englacial water bodies are associated with a dry relict surface basin and consistent with perennial drainage into an interconnected englacial drainage system, which may explain a large englacial outburst flood observed in satellite imagery in the early 2016/17 melt season. Our observations indicate the rarely-documented presence of an englacial hydrological system in Antarctica, with implications for the storage and routing of surface meltwater. Future work should ascertain the spatial prevalence of such systems around the Antarctic coastline, and identify the degree of surface runoff redistribution and storage in the near surface, to quantify their impact on surface mass balance. [ABSTRACT FROM AUTHOR]

Free-surface thin-film flows can principally be described by two types of models. Lubrication models assume that shear stresses are dominant in the force balance of the flow and are appropriate where there is little or no slip at the base of the flow. Conversely, membrane or ‘free-film’ models are appropriate in situations where there is rapid slip and normal (or extensional) stresses play a significant role in force balance. In some physical applications, notably in glaciology, both rapid and slow slip can occur within the same fluid film. In order to capture the dynamics of rapid and slow slip in a single model that describes the entire fluid film, a hybrid of membrane and lubrication models is therefore required. Several of these hybrid models have been constructed on an ad hoc basis in glaciology, where they are usually termed ‘higher order models’. Here, we present a self-consistent asymptotic analysis of the most common of these models due originally to Blatter. We show that Blatter's model reproduces the solution to the underlying Stokes equations to second order in the film's aspect ratio, regardless of the amount of slip at the base of the fluid. In doing so, we also construct asymptotic expansions for the Stokes equations to this order for shear-thinning power-law fluids, paying particular attention to a high-viscosity boundary layer that develops at the free surface when there is little or no slip at the base. Lastly, we demonstrate that a depth-integrated hybrid model of comparable accuracy to Blatter's model—which cannot be depth integrated—can also be constructed, which we suggest as a viable tool for numerical simulations of thin films that contain both slowly and rapidly sliding parts. [ABSTRACT FROM PUBLISHER]

We consider a widely used higher-order glacier flow model with a variety of parametrizations of wall slip, including Coulomb friction, regularized Coulomb friction laws and a power law. Mathematically, the Coulomb friction problem is found to be analogous to a classical friction problem in elasticity theory. We specifically analyze the case in which slip is possible everywhere at the boundary, in which case the weak formulation becomes a semi-coercive convex minimization problem which has a solution only if a solvability condition representing force and torque balance is satisfied. Going beyond previous work, we study the uniqueness of solutions in depth, finding that non-unique solutions are possible under very specialized circumstances. Further, in an extension of work by Campos, Oden and Kikuchi, we show that solutions to the regularized Coulomb friction and power law problems converge to the Coulomb friction problem in appropriate parametric limits, provided the latter is unique, and briefly discuss the implications of possible non-unique solutions for a priori error estimation in numerical approximations. [ABSTRACT FROM AUTHOR]

In a time of retreating glaciers, outburst floods from ice-marginal lakes are poised to becomemore prevalent as glaciers thin and tributaries detach. A detailed field-based investigation ofthe filling and drainage of one such lake, dammed by the 70-km-long Kaskawulsh Glacier inYukon, Canada, was conducted to characterize the role of the little-studied englacialhydrological system during these events. We deployed a variety of geophysical andhydrometeorological instruments in and around the ∼1 km2 lake to monitor thehydrology and dynamics of the lake—glacier system. By integrating the resultsfrom all instruments and surveys, we develop a conceptual model that describes theevolution of various storage reservoirs leading up to, during and following lakedrainage. From the beginning of the instrument record in June 2017, the subaerial lake filled at anaverage rate of 0.5 m d−1 before reaching a maximum volume of 9.9x106m3 on 17 August.GPS and timelapse imagery reveal vertical glacier displacements exceeding 25 m near the icefront and 3 m at a kilometer distance, as water is injected beneath a partially floating ice shelf.These data are used to estimate the evolution of the subglacial hydraulic potential, fromwhich a hydraulic seal and likely flood flowpaths are delineated. Abrupt changes in ice-shelfuplift rates, associated with the formation of fractures and faulting, are linked to aredistribution of englacial water. Near the surface, water pressures in multiple boreholesexhibit sudden changes of up to 15 m of head, while at depth, ice-penetrating radarreflection-power measurements indicate fast and slow adjustments in englacialwater storage. The onset of drainage begins within six days of a reversal in thesubglacial hydraulic gradient near the lake, whereby flow across 55% of the lakecatchment area is redirected away from the lake and toward the Kaskawulsh Glacier.Lake outflow discharge appears to increase exponentially over the course of ∼19days, before reaching an estimated maximum of 75-110 m3s−1 on 4 September.Radar data collected after the drainage event suggest that the englacial reservoir didnot empty entirely, hinting at a possible buffering role for the englacial drainagesystem. According to water-balance calculations, the subglacial and englacial reservoirs storeapproximately 55% and 22%, respectively, of the water in the catchment at peak lake level,compared to 23% in the subaerially exposed lake. In our conceptual model, the subaerial,subglacial and deep/shallow englacial reservoirs connect abruptly in a series ofhydromechanical events detected across multiple sensor types. The dynamic coupling ofthese reservoirs and the abrupt nature of connections between them represent anadvance in our conceptual understanding of outburst floods from ice-marginal lakes. [ABSTRACT FROM AUTHOR]