Search

The origin of supraglacial debris covers is often conceptualised as the formation of a surface lag by melt‐out of englacial debris from slow‐moving ice, where complexity arises from feedback between debris thickness and sub‐debris ice melt. Here, we examine the origin of a debris cover from the perspective of debris provenance and changing tributary supply in a high‐elevation compound valley glacier. Geochemical analysis of 11 major elements in 21 debris samples from six tributaries of Khumbu Glacier (Nepal) shows unambiguous statistical differentiation of debris sources reflecting lithological differences between tributary catchments. Twenty‐four samples from transects across the ablation area are partitioned according to their source areas using the FR2000 sediment unmixing model. We estimate the age of ice at each transect using a higher order ice flow model. The results show greater proportions of debris from lateral tributaries in downglacier locations that have experienced longer flowline histories. More recently, ice from the Main Himalayan Divide (Western Cwm) has become relatively more important. This suggests a change in the state of the lower glacier's structure depending on the relative ice discharges of lateral and divide sources. Ice flux from lower elevation tributaries was more important probably prior to a weakening of the Indian Summer Monsoon at around 1420 CE. The lower elevation tributaries lie within the range of late Holocene equilibrium line altitude variation and therefore respond most sensitively to climatic drivers of the glacier's flow structure. Negative glacier mass balance since around 1900 CE caused tributary glaciers to detach and high‐elevation catchments to re‐establish as the dominant ice source to Khumbu Glacier. [ABSTRACT FROM AUTHOR]

The density structure of firn has implications for hydrological and climate modelling, and ice-shelf stability. The structure of firn can be evaluated from depth models of seismic velocity, widely obtained with Herglotz–Wiechert inversion (HWI), an approach that considers the slowness of refracted seismic arrivals. However, HWI is strictly appropriate only for steady-state firn profiles and the inversion accuracy can be compromised where firn contains ice layers. In these cases, full waveform inversion (FWI) may yield more success than HWI. FWI extends HWI capabilities by considering the full seismic waveform and incorporates reflected arrivals. Using synthetic firn density profiles, assuming both steady- and non-steady-state accumulation, we show that FWI outperforms HWI for detecting ice slab boundaries (5–80 m thick, 5–80 m deep) and velocity anomalies within firn. FWI can detect slabs thicker than one wavelength (here, 20 m, assuming a maximum frequency of 60 Hz) but requires the starting velocity model to be accurate to ±2.5%. We recommend for field practice that the shallowest layers of velocity models are constrained with ground-truth data. Nonetheless, FWI shows advantages over established methods, and should be considered when the characterisation of firn ice slabs is the goal of the seismic survey. [ABSTRACT FROM AUTHOR]

Subglacial hydrological systems require innovative technological solutions to access and observe. Wireless sensor platforms can be used to collect and return data, but their performance in deep and fast-moving ice requires quantification. We report experimental results from Cryoegg: a spherical probe that can be deployed into a borehole or moulin and transit through the subglacial hydrological system. The probe measures temperature, pressure and electrical conductivity in situ and returns all data wirelessly via a radio link. We demonstrate Cryoegg's utility in studying englacial channels and moulins, including in situ salt dilution gauging. Cryoegg uses VHF radio to transmit data to a surface receiving array. We demonstrate transmission through up to 1.3 km of cold ice – a significant improvement on the previous design. The wireless transmission uses Wireless M-Bus on 169 MHz; we present a simple radio link budget model for its performance in cold ice and experimentally confirm its validity. Cryoegg has also been tested successfully in temperate ice. The battery capacity should allow measurements to be made every 2 h for more than a year. Future iterations of the radio system will enable Cryoegg to transmit data through up to 2.5 km of ice. [ABSTRACT FROM AUTHOR]

Direct measurements of spatially distributed vertical strain within ice masses are scientifically valuable but challenging to acquire. We use manual marker tracking and automatic cross correlation between two repeat optical televiewer (OPTV) images of an ~100 m-long borehole at Derwael Ice Rise (DIR), Antarctica, to reconstruct discretised, vertical strain rate and velocity at millimetre resolution. The resulting profiles decay with depth, from −0.07 a−1 at the surface to ~−0.002 a−1 towards the base in strain and from −1.3 m a−1 at the surface to ~−0.5 m a−1 towards the base in velocity. Both profiles also show substantial local variability. Three coffee-can markers installed at different depths into adjacent boreholes record consistent strain rates and velocities, although averaged over longer depth ranges and subject to greater uncertainty. Measured strain-rate profiles generally compare closely with output from a 2-D ice-flow model, while the former additionally reveal substantial high-resolution variability. We conclude that repeat OPTV borehole logging represents an effective means of measuring distributed vertical strain at millimetre scale, revealing high-resolution variability along the uppermost ~100 m of DIR, Antarctica. [ABSTRACT FROM AUTHOR]

The mid-latitudes of Mars host numerous ice-related landforms that bear many similarities to terrestrial ice masses. This collection of landforms, termed viscous flow features (VFFs), is composed primarily of H2O ice and shows evidence of viscous deformation. Recent work has hypothesised that VFFs are the diminishing remains of once larger ice masses, formed during one or more previous ice ages, and the landscape therefore records evidence of polyphase glaciation. However, debate persists concerning the former extent and volume of ice, and style of former glaciations. The accompanying map (1:100,000 scale) presents a geomorphic and structural assessment of a glacial landscape in eastern Hellas Planitia, Mars. Here, we present a description of the features identified, comprising four geomorphic units (plains, lobate debris apron, degraded glacial material, and glacier-like form) and 16 structures (craters, moraine-like ridges, flow unit boundaries, arcuate transvers structures, longitudinal surface structures, ring-mold craters, terraces, medial moraine-like ridges, raised textured areas, flow-parallel and flow-transverse lineations, crevasses and crevasse traces, and ridge clusters). [ABSTRACT FROM PUBLISHER]

Highlights: [•] We map in detail the glacial geomorphology of ice flows, Protonilus Mensae, Mars. [•] We propose an alternative interpretation of ice flow direction in one key location. [•] Our interpretation influences former ice level reconstructions in the region. [ABSTRACT FROM AUTHOR]

Near-surface water ice, either pure or mixed with regolith, forms a widespread suite of distinctive landforms in Mars’ mid-latitudes. These landforms are in many cases sufficiently similar to cryospheric features on Earth to allow analogue-based comparisons to be made. However, our understanding of glacial processes in Mars’ subpolar latitudes remains far from complete, and crucial fundamental issues remain unresolved. These include basic glaciological information such as the internal physical and thermal structure of martian ice masses, whether (and how) those ice masses move, and the nature of any mass-balance regime they are subject to. Addressing these issues is complicated by the fact that any current knowledge, being based overwhelmingly on the visual interpretation of remotely sensed images, is insufficient to determine the extent to which these landforms are currently active or relict. Addressing these issues would contribute not only to our understanding of Mars’ current landscape but also to our knowledge of Mars’ long-term climatic variability and to our awareness of where and in what form H2O exists on Mars – information that would be of value to future space missions. The aim of this review is to bring the state of knowledge regarding mid-latitude glaciation on Mars to the attention of the wider research community. As background, we provide an overview of the geological and planetary framework within which Mars’ mid-latitude ice was deposited. We then define and describe the various ice-related landforms that have been identified within Mars’ mid-latitudes, and we review the processes that have been proposed to explain the origin and physical characteristics of those landforms. Finally, we present what we consider to be key avenues for further research. [ABSTRACT FROM AUTHOR]

Abstract: Martian glacier-like forms (GLFs) indicate that water ice has undergone deformation on the planet within its recent geological past, but the driving mechanisms behind the origin, evolution and dynamics of these landforms remain poorly understood. Here, we present the results of a comprehensive inventory of GLFs, derived from a database of 8058 Context Camera (CTX) images, to describe the physical controls on GLF concentration and morphometry. The inventory identifies 1309 GLFs (727 GLFs in the northern hemisphere and 582 in the southern hemisphere) clustered in the mid-latitudes (centred on a mean latitude of 39.3° in the north and −40.7° in the south) and in areas of rough topography. Morphometric data show inter-hemispheric similarity in GLF length (mean=4.66km) and width (mean=1.27km), suggesting a common evolutionary history, and a poleward orientation of GLFs in both hemispheres, indicating a sensitivity to climate and insolation. On a local scale, elevation is shown to be the most important control on GLF location, with most GLFs occurring above an altitude threshold of −3000m (AOD), and in areas of moderate, but not high, relief. We propose, therefore, that martian GLFs may not exhibit accumulation or ablation areas as is the norm for terrestrial glacial systems, but reflect ice motion in response to local relief within a widely distributed reservoir of ice deposited within prescribed latitudinal and elevational ranges. [Copyright &y& Elsevier]

We outline a method of assessing the roughness of the bed beneath ice-masses, applicable to data collected in a wide variety of (glaciated) environments. Roughness at scales >102m in particular is poorly constrained and understood in glaciated systems, and regional geophysical surveys collected over the past 30 years are ideally suited to addressing this issue. We demonstrate the technique using a radio-echo sounding data set collected during the 1970s, showing that regional characterization of roughness over a wide range of wavelengths (1 to >40km) is possible using Fast Fourier Transforms, even with quite coarse horizontal sampling. Coarse sampling captures all of the variation of higher resolution analyses and the technique appears robust up to the limit imposed by the Nyquist frequency. [Copyright &y& Elsevier]