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Subglacial hydrologic systems regulate ice sheet flow, causing acceleration or deceleration, depending on hydraulic efficiency and the rate at which surface meltwater is delivered to the bed. Because these systems are rarely observed, ice sheet basal drainage represents a poorly integrated and uncertain component of models used to predict sea level changes. Here, we report radarderived basal melt rates and unexpectedly warm subglacial conditions beneath a large Greenlandic outlet glacier. The basal melt rates averaged 14 mm · d−1 over 4 months, peaking at 57 mm · d−1 when basal water temperature reached +0.88 ◦C in a nearby borehole. We attribute both observations to the conversion of potential energy of surface water to heat in the basal drainage system, which peaked during a period of rainfall and intense surface melting. Our findings reveal limitations in the theory of channel formation, and we show that viscous dissipation far surpasses other basal heat sources, even in a distributed, highpressure system. [ABSTRACT FROM AUTHOR]

Supraglacial lake drainage events influence Greenland Ice Sheet dynamics on hourly to interannual timescales. However, direct observations are rare, and, to date, no in situ studies exist from fast-flowing sectors of the ice sheet. Here, we present observations of a rapid lake drainage event at Store Glacier, west Greenland, in 2018. The drainage event transported 4.8 x 106 m³ of meltwater to the glacier bed in ~5 h, reducing the lake to a third of its original volume. During drainage, the local ice surface rose by 0.55 m, and surface velocity increased from 2.0 m⋅d-1 to 5.3 m⋅d-1. Dynamic responses were greatest ~4 km downstream from the lake, which we interpret as an area of transient water storage constrained by basal topography. Drainage initiated, without any precursory trigger, when the lake expanded and reactivated a preexisting fracture that had been responsible for a drainage event 1 y earlier. Since formation, this fracture had advected ~500 m from the lake's deepest point, meaning the lake did not fully drain. Partial drainage events have previously been assumed to occur slowly via lake overtopping, with a comparatively small dynamic influence. In contrast, our findings show that partial drainage events can be caused by hydrofracture, producing new hydrological connections that continue to concentrate the supply of surface meltwater to the bed of the ice sheet throughout the melt season. Our findings therefore indicate that the quantity and resultant dynamic influence of rapid lake drainages are likely being underestimated. [ABSTRACT FROM AUTHOR]

The phase-sensitive radio-echo sounder (pRES) is a powerful new instrument that can measure the depth of internal layers and the glacier bed to millimetre accuracy. We use a stationary 16-antenna pRES array on Store Glacier in West Greenland to measure the three-dimensional orientation of dipping internal reflectors, extending the capabilities of pRES beyond conventional depth sounding. This novel technique portrays the effectiveness of pRES in deriving the orientation of dipping internal layers that may complement profiles obtained through other geophysical surveying methods. Deriving ice vertical strain rates from changes in layer depth as measured by a sequence of pRES observations assumes that the internal reflections come from vertically beneath the antenna. By revealing the orientation of internal reflectors and the potential deviation from nadir of their associated reflections, the use of an antenna array can correct this assumption. While the array configuration was able to resolve the geometry of englacial layers, the same configuration could not be used to accurately image the glacier bed. Here, we use simulations of the performance of different array geometries to identify configurations that can be tailored to study different types of basal geometry for future deployments. [ABSTRACT FROM AUTHOR]

Structural glaciological maps can be used to study the structural evolution and past dynamics of glaciers. The map described here documents the glacier-wide structural characteristics of Austre Brøggerbreen, ac. 12 km2predominantly cold-based valley glacier in northwest Svalbard. The structural map reveals that the glacier is dominated by deep-penetrating fractures that are now relict (crevasse traces). These structures indicate that, despite being relatively inactive at present, the glacier was once much more dynamic, presumably during its last advance in the Neoglacial (c. 1900 AD). Contemporary glacier structures (i.e. those that are actively forming) include primary stratification, longitudinal foliation and rare surface fracturing (crevasses and water-healed crevasses). Relict fracture sets become increasingly re-orientated and folded down-glacier as a result of ductile flow. Individual flow units show large differences in the evolution of structures, indicating that the flow units have been subject to different flow histories and dynamics. The map will also be useful for future change-detection studies on this rapidly receding glacier. [ABSTRACT FROM PUBLISHER]

This paper presents and describes a glaciological and geomorphological map of Glacier Noir and Glacier Blanc, French Alps. Glacier Noir is a debris-covered glacier and is adjacent to Glacier Blanc, a clean-ice (debris-free) glacier. The glaciological and geomorphological evolution of Glacier Blanc is well known, but the evolution of Glacier Noir is poorly understood, as is the case for many debris-covered glaciers globally, despite their importance in a number of mountain ranges around the world (e.g. European and Southern Alps, the Himalayas and the Rockies). The accompanying map was created by manually digitising aerial ortho-images and historical georeferenced photographs from 1952 to 2013. The main glacial and geomorphological features of both glaciers were mapped, including debris cover, crevasses, moraines, hummocky terrain and scree areas. Hydrological features (supra- and pro-glacial streams and meltwater ponds) were also mapped. The map illustrates the key differences between Glacier Noir and Glacier Blanc, and is important for understanding future glaciological and geomorphological changes. [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]

Abstract: We present a stand-alone software platform, Borehole and Ice Feature Annotation Tool (BIFAT), for the examination, annotation and analysis of glacier borehole images. This tool aids in the lengthy and often subjective process of annotating layers and other features in optical and acoustic glacier borehole televiewer logs. Since these view 360° around the full circumference of an exploratory borehole, intersecting planes are reconstructed on the televiewer image as sinusoids, the amplitude and phase of which can be used to calculate, respectively, the dip and direction of dip of each of these planes. The program aids in the annotation and examination of such planes, as well as a number of other features, including clusters and inclusions. BIFAT also provides an automatic layer detection option to aid and speed up the often lengthy process of identifying planar features in glacier borehole images. The software also shows promising results in rock borehole images and in the detection of planar layers in line-scan ice core images. We describe the capability and operation of BIFAT, and illustrate its application with reference to the automatic identification and annotation of sections from an optical televiewer (OPTV) borehole log from Roi Baudouin, Dronning Maud Land, Antarctica. The software is freely available for download from http://users.aber.ac.uk/byh/iceoptv. [Copyright &y& Elsevier]

Roberson, S., Hubbard, B., Coulson, H. and Boomer, I. Physical properties and formation of flutes at a polythermal valley glacier: Midre Lovénbreen, Svalbard. Geografika Annaler: Series A, Physical Geography, 93, 71–88. DOI: 10.1111/j.1468‐0459.2011.00420.x Flutes are widespread across the forefield of a polythermal valley glacier Midre Lovénbreen, Svalbard, where they consistently form on the downglacier face of cobble to boulder‐sized subglacially‐transported clasts ploughed into proglacial till. The width of flutes at Midre Lovénbreen is constant along their long‐axes and proportional to the size of their associated subglacially‐transported boulders. Frozen flutes are observed subglacially where they protrude into the debris‐rich basal ice layer of the glacier. Particle‐size analysis shows that flutes are depleted in gravel‐sized particles relative to adjacent subglacial till. Ice sampled from flutes is enriched in δ18O relative to overlying glacier ice and debris‐rich basal ice. These properties are interpreted to reflect the formation of flutes by the squeezing of till into basal cavities associated with boulders beneath warm‐based ice in the interior of the glacier. It is hypothesized that localized freeze‐on of flute sediments, within a broader zone of warm‐based ice, occurs within cavities due to either (i) a 'heat‐pump' effect operating across these boulders leading to the development of a cold patch within the cavity, and/or (ii) fluctuations in cavity length caused by slip‐stick glacial motion. Once incorporated into the basal ice layer, the frozen flute sediment would then be transported away from the boulder by ice flow, allowing the cavity to remain continuously open and the flute to propagate downflow. [ABSTRACT FROM AUTHOR]

The diversity of highly active bacterial communities in cryoconite holes on three Arctic glaciers in Svalbard was investigated using terminal restriction fragment length polymorphism (T-RFLP) of the 16S rRNA locus. Construction and sequencing of clone libraries allowed several members of these communities to be identified, with Proteobacteria being the dominant one, followed by Cyanobacteria and Bacteroidetes. T-RFLP data revealed significantly different communities in holes on the (cold) valley glacier Austre Brøggerbreen relative to two adjacent (polythermal) valley glaciers, Midtre Lovénbreen and Vestre Brøggerbreen. These population compositions correlate with differences in organic matter content, temperature and the metabolic activity of microbial communities concerned. No within-glacier spatial patterns were observed in the communities identified over the 2-year period and with the 1 km-spaced sampling. We infer that surface hydrology is an important factor in the development of cryoconite bacterial communities. [ABSTRACT FROM AUTHOR]

The article reports on the study conducted by Douglas Mair and colleagues on the diurnal fluctuations in glacier ice deformation in Haut Glacier d'Arolla, Switzerland. Researchers measured surface velocity, ice deformation and proglacial stream discharge to determine diurnal patterns of variation. They analysed these data to understand better the relationship between hydraulically induced basal motion and glacier ice deformation over short timescales. Result reveals that the hydraulically induced localized basal slippery spots are created over diurnal cycles, thus causing enhanced basal motion and variable glacier speed-up.

Two carbonate deposits are identified on the exposed bedrock surfacein the forefield of Glacier de Tsanfleuron, Switzerland: macrocrystalline sparite and microcrystalline micrite. Comparison of the distributions of these forms with lee-side slope facets identified by high-pass filtering of a flow-parallel bedrock profile at a range of frequencies reveals two significant results. First, while the distribution of sparite is consistent with formation in the lee side of subglacialbedrock hummocks, that of micrite is not. This contrasts with previous investigations in which both sparite and micrite have been considered to form by mineral concentration and precipitation during the refreezing of regelation-related basal meltwaters in the lee side of bedrock hummocks. Alternative mechanisms of micrite formation involving carbonate deposition and/or precipitation within subglacial bedrock hollows are proposed. Second, the distribution of sparite is most strongly correlated with the distribution of lee-side slope facets identified by filtering at a frequency equivalent to a hummock wavelength of c. 071 m. This correspondence indicates empirically that pressure-related melting and refreezing (regelation) operates most effectively around bedrock hummocks that are shorter than c. 071 m. [ABSTRACT FROM AUTHOR]