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Surface crevasses on the Greenland Ice Sheet (GrIS) capture nearly half of the seasonal runoff, yet their role in transferring meltwater to the bed has received little attention relative to that of supraglacial lakes and moulins. Here, we present observations of crevasse ponding and investigate controls on their hydrological behavior at a fast‐moving, marine‐terminating sector of the GrIS. We map surface meltwater, crevasses, and surface‐parallel stress across a ∼2,700 km2 region using satellite data and contemporaneous uncrewed aerial vehicle (UAV) surveys. From 2017 to 2019 an average of 26% of the crevassed area exhibited ponding at locations that remained persistent between years despite rapid advection. We find that the spatial distribution of ponded crevasses does not relate to previously proposed controls on the distribution of supraglacial lakes (elevation and topography) or crevasses (von Mises stress thresholds), suggesting the operation of some other physical control(s). Ponded crevasse fields were preferentially located in regions of compressive surface‐parallel mean stress, which we interpret to result from the hydraulic isolation of these systems. This contrasts with unponded crevasse fields, which we suggest are readily able to transport meltwater into the wider supraglacial and englacial network. UAV observations show that ponded crevasses can drain episodically and rapidly, likely through hydrofracture. We therefore propose that the surface stress regime influences a spatially heterogeneous transfer of meltwater through crevasses to the bed of ice sheets, with consequences for processes, such as subglacial drainage and the heating of ice via latent heat release by refreezing meltwater. Plain Language Summary: Surface crevasses on the Greenland Ice Sheet (GrIS) transfer nearly half of all the ice sheet's meltwater to the bed, yet when, where, and how this occurs is poorly understood. We use large‐scale satellite analysis and uncrewed aerial vehicle (UAV) surveys to assess the spatial variability of meltwater ponding in crevasses across a fast‐flowing sector of the western GrIS. Between 2017 and 2019 an average of a quarter of crevasse fields ponded, in roughly the same area every year. However, the locations of such ponding cannot be explained in the same way as supraglacial lakes, which collect in surface basins. Instead, we find that ponded crevasses exist in regions of compressive surface stress. We suggest that this is because compressive regimes close pathways that elsewhere allow crevasses to drain into the wider surface hydrological system. Using UAV surveys, we show that these ponded crevasses instead drain rapidly to the bed by hydrofracture. Differing drainage processes in regions of compressive and extensional regimes may have distinct consequences for subglacial drainage and the heating of the ice sheet due to energy release during meltwater refreezing. Key Points: At a marine‐terminating sector of the Greenland Ice Sheet, 26% of all crevasses ponded between 2017 and 2019; the rest remained unfilledPonded crevasse locations persist between years but, unlike supraglacial lakes, this distribution is not topographically controlledCrevasses pond in compressive stress regimes, likely due to hydraulic isolation by creep closure, and drain predominantly via hydrofracture [ABSTRACT FROM AUTHOR]

Subglacial drainage systems are known to critically control ice flows, but their spatial configuration and temporal evolution are poorly constrained due to inaccessibility. Here we report a 12‐year‐long monitoring of the drainage underneath Bering Glacier, Alaska, by correlating ambient noise recorded at two seismic stations on the sides of the glacier. We find that the seismic surface waves traveling across Bering Glacier slowed down by 1–2% during its latest 2008–2011 surge, likely due to the switch of the subglacial drainage from a channelized system to a distributed system. In contrast to current models, the relative amplitude of velocity reductions for Rayleigh and Love waves requires the distributed drainage to be highly anisotropic and aligned perpendicular to the ice flow direction. We infer that the subglacial water flow is mainly through a network of transverse basal crevasses during surges and thus can sustain the high water pressure and ice flow speed. Plain Language Summary: Water underneath glaciers strongly controls how ice flows. However, it is difficult to map how water flows under the cover of hundreds or thousands of meters of ice. Here we propose a new approach to image and monitor water in glaciers, by using seismic waves continuously excited by the ocean and atmosphere. With sensors on both sides, we can measure the time seismic waves take to travel across a glacier. More water in glacier can slow down the seismic waves. For Bering Glacier, Alaska, we detected a substantial slowdown of seismic waves from 2008 to 2010, which coincides with a period when the ice flow accelerated by a factor of 10. We interpret the observed seismic slowdown as caused by water flowing through a network of crevasses near the base of the glacier. Key Points: Noise interferometry across Bering Glacier reveal 1‐2% seismic velocity reduction during its latest surgeThe changes require anisotropic weakening of the glacial base with elongated water pockets transverse to ice flowWe interpret the results as evidences for distributed subglacial water flow through a network of basal crevasses [ABSTRACT FROM AUTHOR]

The terminus of the ephemeral Río Colorado is located at the margins of Salar de Uyuni, Bolivia, the world's largest salt lake. The low‐gradient (<0.0006 m m‐1), non‐vegetated reaches approaching the terminus provide an excellent natural laboratory for investigating cascades of channel‐floodplain changes that occur in response to quasi‐regular flows (at least once annually) and fine‐grained sediment supply (dominantly silt and clay). High‐resolution satellite imagery (<0.65 m, various dates from 2004 onwards) and field data reveal widespread, pronounced and rapid morphodynamics on sub‐decadal timescales, including channel erosion and chute cutoff formation, and development of crevasse channels and splays, floodouts (unchannelled surfaces at channel termini), and erosion cells (floodplain scour‐transport‐fill features). In particular, following high annual precipitation (>400 mm) in 2004–2005 and two subsequent high magnitude daily precipitation events (~40 mm), all of which led to widespread flooding, numerous crevasse splays formed between 2004 and 2016, avulsions occurred at nearby floodouts, and erosion cells downstream of the splays and floodouts underwent striking morphological changes. High‐precision GPS data reveal two preferential localities for erosion cell development: partially or fully abandoned channels with crevasse splay remnants, and topographic lows between channels. In this overall low‐gradient setting, comparatively high gradients (up to ~0.0006 m m‐1) at the edge of splay deposits and topography created by crevasses and abandoned channels may initiate knickpoint retreat and thereafter erosion cell development. Abandoned channels with splays tend to give rise to narrow, deep erosion cells, while topographic lows promote relatively shallow, wide erosion cells. In both situations, erosion cells may extend upslope and downslope, and eventually connect to form straight channels. The channel‐floodplain morphodynamics near the Río Colorado terminus extend previous analyses of low‐gradient, dryland river systems, particularly because the lack of vegetation and quasi‐regular floods drive cascades of rapid changes on sub‐decadal timescales. © 2018 John Wiley & Sons, Ltd. Highlights: • Rapid cascades of channel‐floodplain changes characterise the ephemeral lower Río Colorado. • Enhanced local slope created by splays and abandoned channels promotes erosion cell development. • Erosion cells may connect up and form straighter channels. Inset: Example of erosion cell development along an abandoned channel. Letters S, T and F represent scour, transport and fill sections in the erosion cells. Pléiades imagery, with general flow direction from lower right to upper left (i.e. oblique to the abandoned channel), and north oriented to the top. Main image: Example of a relatively straight channel that may have resulted from the elongation and connection of erosion cells. The straightness of this channel contrasts with the higher sinuosity evident along older active or abandoned channels. Pléiades imagery, with general flow direction from bottom to top, and north oriented to the top. [ABSTRACT FROM AUTHOR]

Abstract: Accommodation space in the unconfined distal part of low‐gradient fluvial fans facilitates abundant floodplain deposition. Here, the development of crevasse splays plays a key role in the aggradation of alluvial ridges and subsequent river avulsion. This study presents an analysis of different stages in the evolution of crevasse splays based on observations made in the modern‐day Río Colorado dryland fluvial fan fringing the endorheic Altiplano Basin in Bolivia. A generic life cycle is proposed in which crevasse‐splay channels adjust towards a graded equilibrium profile with their lower‐lying distal termini acting as a local base level. Initial development is dominantly controlled by the outflow of floodwater, promoting erosion near the crevasse apex and deposition towards the splay fringes. When proximal incision advances to below the maximum level of floodplain inundation, return flow occurs during the waning stage of flooding. This floodwater reflux leads to a temporary repositioning of the local base level to the deeper trunk‐channel thalweg at the apex of the crevasse‐splay channels. The resultant decrease in the floodplainward gradient of these channels ultimately leads to backfilling and abandonment of the crevasse splay, leaving a subtle local elevation of the floodplain. Consecutive splays form an alluvial ridge through lateral amalgamation and subsequent vertical stacking, which is mirrored by the aggradation of their parent channel floor. As this alluvial ridge becomes increasingly perched above the surrounding floodplain, splay equilibration may cause incision of the levee crevasse down to or below its trunk channel thalweg, leading to an avulsion. The mechanisms proposed in this study are relevant to fluvial settings promoting progradational avulsions. The relatively rapid accumulation rate and high preservation potential of crevasse splays in this setting makes them an important constituent of the resultant fluvial stratigraphy, amongst which are hydrocarbon‐bearing successions. Copyright © 2018 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Abstract: Twelve years of continuous monitoring of diverse ground properties reveals the dynamics of three ice wedges and adjacent ground in a low‐centered polygon area in Svalbard. The monitoring documented ground displacements, the timing of crack generation, ground thermal and moisture conditions from the surface to the top permafrost, and snow conditions. The focus is on seasonal ground deformation in and around ice‐wedge troughs, interannual variability of ice‐wedge activity and thermal thresholds for ice‐wedge cracking. Seasonal ice‐wedge activity is mainly associated with frost heave and thaw settlement, as well as thermal expansion and contraction. In mid‐ to late winter, temporary expansion and cracking of troughs by thermal contraction occurs during rapid cooling periods. Following intensive ground microcracking events, troughs show rapid expansion and in some cases major cracking in the frozen active layer. A common threshold for cracking is identified by a combination of ground surface cooling below −20°C and a thermal gradient steeper than −10°C m−1 in the upper meter of ground, indicating that cracking requires both a brittle frozen layer and rapid ground cooling. Our results highlight that in marginal thermal conditions for ice‐wedge activity, the primary control on ice‐wedge cracking is rapid winter cooling enhanced by minimum snow cover. [ABSTRACT FROM AUTHOR]

To investigate the mechanism of frost wedging in fractured low-porosity bedrock, we monitored the opening of an artificial 4 mm wide and 80 mm deep crack, cut 20 mm from the end of a rectangular granite block. Two freezing protocols were employed - top-down and bottom-up, the former consisting of short- and long-term variants, lasting 1 and 53 days, respectively. Our results demonstrate that (i) in 1-day experiments, maximum crack widening during top-down freezing is around 0.11 mm, while bottom-up freezing produces only 0.02 mm of deformation; (ii) neither ice nor water pressure causes measurable irreversible crack widening during 1-day tests; (iii) irreversible crack widening is only observed following the 53-day experiment under top-down freezing. Based on these results, we suggest (i) freezing direction plays a key role in determining the magnitude of crack widening; and (ii) freezing duration could be essential for crack propagation. The fracturing is both time-dependent and subcritical; thus, persistent freezing in winter could actually be the active period of crack propagation. This allows us to propose a simplified method to calculate ice pressure according to crack widening. Here we show how freezing direction and duration in ice-filled cracks control the path-dependent efficacy of frost-wedging. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Weathering microforms associated with exfoliation were investigated on 40 granitic spheroidal boulders identified on Pricopan Ridge (Măcin Mountains) in order to establish a spatial distribution pattern. Continuous thermal monitoring allowed the frequency and intensity distribution assessment of short-term temperature changes triggered by summer storms, of intense day-night amplitudes and frost cycles across a uniform rounded boulder. Rock strength estimated by Schmidt hammer tests differentiates a significantly weaker resistance on the southern face of the boulders (rebound values of 27 to 33) in comparison with the northern face (43-50). The lowest resistance of the north-south cross-boulder profile corresponds to the southern gentle slopes (0°-45°) thus defining the most susceptible area to exfoliation and other weathering processes. It is argued that this low-resistant sector fits well with the maximum frequency and intensity of thermal processes recorded on the low and mid slopes (0°-45°) of the boulders south side, with small differences from one process to another, whilst the sector of 20° to 30° south corresponds to the peak activity of all. In accordance, the overlay map of exfoliated surfaces places the high frequency area on a spherical cap developed similarly (between 5° north and 45° south). The smallest exfoliated surfaces normally appear around 30° south and are inferred to extend in time both to the boulder top and downslope. The correlations between the frequency/intensity maps of thermal processes and the frequency map of exfoliated surfaces point to a complementary action in the exfoliated surfaces development of the short-term temperature changes and diurnal cooling and heating due to the directional insolation effect, as similarly inferred in the development of meridional cracks. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The drumlin field at Múlaj€okull, Iceland, is considered to be an active field in that partly and fully ice-covered drumlins are being shaped by the current glacier regime. We test the hypothesis that the drumlins form by a combination of erosion and deposition during successive surge cycles. We mapped and measured 143 drumlins and studied their stratigraphy in four exposures. All exposures reveal several till units where the youngest till commonly truncates older tills on the drumlin flanks and proximal slope. Drumlins inside a 1992 moraine are relatively long and narrow whereas drumlins outside the moraine are wider and shorter. A conceptual model suggests that radial crevasses create spatial heterogeneity in normal stress on the bed so that deposition is favoured beneath crevasses and erosion in adjacent areas. Consequently, the crevasse pattern of the glacier controls the location of proto-drumlins. A feedback mechanism leads to continued crevassing and increased sedimentation at the location of the proto-drumlins. The drumlin relief and elongation ratio increases as the glacier erodes the sides and drapes a new till over the landform through successive surges. Our observations of this only known active drumlin field may have implications for the formation and morphological evolution of Pleistocene drumlin fields with similar composition, and our model may be tested on modern drumlins that may become exposed upon future ice retreat. [ABSTRACT FROM AUTHOR]

Understanding the ecological function of developed large rivers remains elusive because these systems have long been altered for multiple uses. In particular, floodplains of large rivers, such as the Mississippi River, have been contained behind extensive levees. A historic flood occurred in the lower Mississippi River system during spring of 2011, prompting the US Army Corps of Engineers to activate the Bird's Point-New Madrid floodway, a 55 000-ha, agriculturally dominated, leveed area. Water entered the floodway at flows >1 m s−1 through two crevasses created in the upper portion of the levee and exited through a crevasse at the lower end. During the month, the floodway was inundated; we quantified discharge, water chemistry, primary production and fish production in the floodway and the adjacent river. Water entering the floodway was retained <1.3 d, and nutrient concentrations were not elevated in the floodway beyond those in the river, despite expected contributions from a legacy of fertilization. Primary production equaled respiration in the floodway, while the adjacent river was heterotrophic. Gizzard shad and freshwater drum were more abundant in the floodway than the river, while channel catfish were more abundant in the river. Growth rates of young native fishes, normalized for temperature, were the same in the floodway and the river, with the exception of gizzard shad, which grew faster in the floodway. Fish community structure, especially in the lower floodway, was temporally and spatially dynamic. Even though it has been heavily modified for agriculture, the floodway provided benefits, albeit limited, to the Mississippi River. With multifunctional management and strategic planning, systems such as these may provide substantial services such as flood abatement, nutrient transformation and fish production in the Mississippi River basin and potentially reduce nutrient loading downstream in areas such as the Gulf of Mexico. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Crevasse splays are common geomorphological features in alluvial and deltaic floodplains. Although crevasse splays can develop into full avulsions, thereby transforming large areas of floodbasins, little is known about their sedimentary and geomorphological development at the decadal scale and their avulsion potential. We used aerial photography and lithological cross-sections to reconstruct crevasse-splay formation in the largely unmanaged floodplain of the Saskatchewan River in the Cumberland Marshes (Saskatchewan, Canada). Based on surface geomorphology and subsurface deposits, various stages of crevasse-splay development were described which were linked to both external forcing and internal morphodynamics. Initial splay deposition, following a levee breach during a large flood, occurred as a broad but relatively thin sandy sheet in a down-basin direction in the receiving backswamp area. In a next phase, these primary crevasse-splay deposits blocked local down-basin flow, thereby forcing the crevasse-splay channel in a direction perpendicular to the parent channel and original floodbasin gradient. This created an asymmetrical splay sequence composition, which differs in appearance from more commonly observed dendritic crevasse splays. It is concluded that sedimentation patterns in the splay have been influenced by inherited effects of previously formed deposits. Feedbacks of the original floodbasin gradient and earlier stages of splay formation are suggested as prominent mechanisms in creating the current morphology, orientation, and architecture of its deposits. Copyright © 2015 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We reconstruct englacial and subglacial drainage at Skálafellsjökull, Iceland, using ground penetrating radar (GPR) common offset surveys, borehole studies and Glacsweb probe data. We find that englacial water is not stored within the glacier (water content ~0-0.3%). Instead, the glacier is mostly impermeable and meltwater is able to pass quickly through the main body of the glacier via crevasses and moulins. Once at the glacier bed, water is stored within a thin (1 m) layer of debris-rich basal ice (2% water content) and the till. The hydraulic potential mapped across the survey area indicates that when water pressures are high (most of the year), water flows parallel to the margin, and emerges 3 km down glacier at an outlet tongue. GPR data indicates that these flow pathways may have formed a series of braided channels. We show that this glacier has a very low water-storage capacity, but an efficient englacial drainage network for transferring water to the glacier bed and, therefore, it has the potential to respond rapidly to changes in melt-water inputs. [ABSTRACT FROM AUTHOR]

ABSTRACT Active and semi-active anastomosing Holocene channels upstream of the delta in the lower valley of the meandering Neches River in southeast Texas represent several morphologically distinct and hydrologically independent channel systems. These appear to have a common origin as multi-thread crevasse channels strongly influenced by antecedent morphology. Levee breaching leads to steeper cross-valley flows toward floodplain basins associated with Pleistocene meander scars, creating multi-thread channels that persist due to additional tributary contributions and ground water inputs. Results are consistent with the notion of plural systems where main channels, tributaries, and sub-channels may have different morphologies and hydrogeomorphic functions. The adjacent Trinity and Sabine Rivers have similar environmental controls, yet the Trinity lacks evidence of extensive anastomosing channels on its floodplain, and those of the Sabine appear to be of different origin. The paper highlights the effects of geographical and historical contingency and hydrological idiosyncrasy. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The siliciclastic sediments of the uppermost section of 185 mcd (meters composite depth) from ODP Site 1146 on the northern continental slope of the South China Sea (SCS) were partitioned according to their sources using end-member modeling on grain-size data. The goal was to evaluate the evolution of the East Asian monsoon over the past 2 million years. The siliciclastic sediments were described as hybrids of four end-members, EM1, EM2, EM3, and EM4, with modal grain sizes of 8-22 μm, 2-8 μm, 31-125 μm, and 4-11 μm, respectively. EM1 and EM3 are interpreted as eolian dust and EM2 and EM4 as fluvial mud. The ratio of eolian dust to fluvial mud ((EM1+EM3)/(EM2+EM4)) is regarded as an indicator of the East Asian monsoon. The variation in this ratio not only shows periodical oscillations consistent with oxygen isotope stages, but also exhibits a phased increasing trend corresponding with the phased uplifts of the Tibetan Plateau, indicating that the evolution of the East Asian Monsoon was controlled not only by glacial-interglacial cycles, but also by the phased uplifts of the Tibetan Plateau during the Quaternary. [ABSTRACT FROM AUTHOR]

ABSTRACT Induced polarization (IP) is a geophysical method that is potentially sensitive to the presence of cracks in porous rocks and therefore to damage. We performed time-domain and frequency domain IP measurements at the Tournemire Underground Research Laboratory (URL, Aveyron, France) in areas where different types of cracks are observed. These cracks correspond to both tectonic fractures and new cracks associated with stress release and desiccation resulting from the excavation of a gallery. These measurements were performed both in eastern and northern galleries of the test site. The eastern gallery was excavated in 1996 while the northern gallery was excavated recently in 2008. This gives us the opportunity to study the electrical characteristics of the excavation damaged zone surrounding the galleries with respect to the age of the excavation. Longitudinal profiles were performed along the floor of the galleries with 48 Cu/CuSO4 electrodes separated by a distance of 20 cm. Chargeability and resistivity were inverted using a Gauss-Newton iterative approach assuming an isotropic heterogeneous clay-rock material. The resulting IP tomograms show a correlation between high values of chargeability and the presence of calcite-filled tectonic fractures. X-ray analysis indicates that the presence of pyrite in these fractures is a potential source of the observed IP signals. The cracks associated with the mechanical damage of the formation exhibit low values of chargeability, on the same order of magnitude than the chargeability of the clay-rock matrix and are therefore hardly observable. A smaller IP response associated with the presence of these cracks is observed in the older gallery and this observation is qualitatively related to the desaturation process associated with these cracks. In a specific area of one of the galleries, the presence of calcareous nodules is observed to be an important source of anomalous chargeability. This signature seems to be associated with the presence of pyrite. [ABSTRACT FROM AUTHOR]

The nucleation and propagation of polygonal cracks in hydrous sulphate dunes at White Sands National Monument, New Mexico, are affected by water availability, transport through the sand and exchange with the atmosphere. These gypsum sands are cohesive enough to crack due to capillary forces and gypsum cements formed during evaporation. Surface cracks form five-sided polygons with a variety of triple-junction angles. Cracks extend down to variable depths and polygons increase in size with depth, showing a maturation similar to experimentally produced polygonal columns in drying corn starch. Results from two years of monitoring crack geometries, temperature and humidity demonstrate that cracks form when water is lost to the atmosphere through the transport of water vapour. Subsurface relative humidity below 5 to 10 cm is almost always maintained at 100% by the evaporation and condensation of water in thin films on grains. The amplitude of daily temperature and thus absolute humidity changes decreases with depth, consistent with lower evaporation and condensation rates with increasing depth. Changes in absolute humidity and the contrast between humidity in pore spaces versus the overlying atmosphere result in significant water loss from the dunes except during times of precipitation and frost/dew condensation. This water loss allows cracks to nucleate and propagate into the dunes. This study hypothesizes that crack tips propagate into sand to the depth at which thin films of water on grains are drying, and that this depth varies from the surface of the dune during precipitation events to depths greater than 45 cm when dunes are drier. [ABSTRACT FROM AUTHOR]

Net accumulation measurements from two glaciers located on opposite sides of the New Zealand Southern Alps were used to explore processes controlling spatial variability. The degree of variability, as measured by the spatial variogram, differed in each of the three successive years, but the lowest variance occurred on both glaciers in March 2008, after a hot and dry summer. Strong relationships between net accumulation and elevation within the accumulation area were only found on Franz Josef Glacier (FJG), despite this being the primary control used in glacier mass balance modelling. Interaction between wind and topography was found to be important to the distribution of net accumulation on both glaciers. The crevasse stratigraphy method is an ideal way to gain good spatial coverage of net accumulation, and particularly suited to glaciers with high annual precipitation. Copyright © 2010 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Fabrication of oxide fiber composites is accompanied by the development of drying cracks in the matrix following slurry infiltration. The cracks are a result of the inherent shrinkage in particle compacts during drying coupled with the mechanical constraints imposed on the matrix by the fibers. The effects are most pronounced in systems with three-dimensional fiber architectures. A mitigation strategy based on the addition of coarse matrix particles to the fine particulates has been devised and demonstrated. Among the various implementation strategies explored, the most effective involves combining the two particle types (coarse and fine) into a single slurry and coinfiltrating the slurry through sequential vibration- and vacuum-assisted processes. Regardless of the infiltration route, the SiC particles have no apparent detrimental effect on the fiber bundle properties. Additionally, they increase the through-thickness thermal diffusivity by 50%–100%. [ABSTRACT FROM AUTHOR]

In the present paper, an analytical solution for the stress intensity factor in the case of cracks produced by Vickers indenters has been extended to the cases of triangular indenters, i.e., Berkovich and cube-corner. According to the adopted approach, median/radial cracks produced by indentations are modeled as loaded by either a point-force or a symmetric disk-shaped wedge. The wedge diameter is assumed to be equal to the plastic zone size whereas the wedge thickness is evaluated by comparing the wedge volume with the hardness-impression volume. The point-force and the disk-shaped wedge analyses produce an upper and a lower bound, respectively, of the geometry-dependent parameter appearing in the expression for the fracture toughness. The predictions of the present analysis are in good agreement with similar experimental and numerical results. [ABSTRACT FROM AUTHOR]

A push moraine deposited by the surging tidewater glacier Paulabreen (Svalbard) was investigated using 2D resistivity profiling. Six longitudinal and transverse profiles were obtained on the moraine and the resistivities were compared with data from three boreholes. Four profiles indicate that the inner part of the moraine is ice-cored and that the buried glacier ice is more than 30 m thick. A transverse profile shows evidence of basal crevasses near the former glacier margin. Three profiles cross the former glacier margin and onto a proglacial plain which dips slightly away from the former glacier margin. Low resistivities were encountered where borehole and field observations indicate that the plain consists of marine muds with a high salt content. This landform has previously been interpreted as a slab of seabed pushed up in front of the surging glacier, possibly facilitated by permafrost in the seabed. We suggest, alternatively, that the landform originated from sediments extruded from below (or pushed in front of) the glacier at the surge terminus and deposited as a debrisflow. Ground penetrating radar can reveal small-scale structures, but larger structures and overall composition are better imaged by resistivity measurements. [ABSTRACT FROM AUTHOR]

The article presents a study which observes the implications for late quaternary ice cover and timing of speleogenesis in the uranium series dates from the windy pits of the North York Moors, England. It presents nine thermal ionization mass spectrometry (TIMS) U-Th on speleothem from the windy pits. It utilizes speleothem sampling in three areas including Antofts, Noodle End Windy Pits in Ryedale, and in the cave-like fissure in Spaunton Quarry. It discovers that the pattern of speleothem growth is indicative of two controls including palaeoclimatic conditions and the presence of drippling water. The speleothem dates reveal that growth was confined to interglacial periods or Holocene. It concludes that the windy pits of the North York Moors have existed for at least 208,000 years.

In this paper, the finite element method is used to analyze the behaviour of repaired cracks in 2024-T3 aluminum with bonded patches made of unidirectional composite plates. The problem is considered in Mode I condition. First the KI stress intensity factor (SIF) is calculated by the finite element method using displacement correlation technique. Different plate and patch thicknesses and crack lengths are considered in the analyses. Then an equation is determined by using genetic algorithms for the calculation of stress intensity factor without any further finite element analysis. The equation gives reasonably accurate results. [ABSTRACT FROM AUTHOR]

Compression and crevasses are common cutting artefacts in cryo-ultramicrotomy of vitreous sections. They can be reduced or suppressed under optimal cutting conditions. In the present study, compression and thickness were measured for different cutting speeds and knife angles. It was found that compression decreased with feed and that crevasses appeared only above a certain thickness. The optimal feed for vitreous sections was between 50 and 80 nm. The thickness, calculated by two independent methods, was quantitatively related to feed and compression. [ABSTRACT FROM AUTHOR]

Much previous research at surge-type glaciers has sought to identify features diagnostic of surge-type behaviour. However, in comparatively little work have subglacial landform–sediment characteristics been used to reconstruct changing basal processes and conditions during surge events. Subglacial bedforms described in this article are associated with the 1991 surge of Skeiðarárjökull, Iceland, and include a series of drumlins with superimposed flutes and basal crevasse-fill ridges. The drumlins were formed by the subglacial erosion of ice-contact fans. Sedimentary evidence indicates a shift from rigid-bed to soft-bed conditions during the surge. The presence of eroded but undeformed fan sediments suggests that they acted as a rigid bed when initially overridden. Subsequent deposition of a layer of deformation till resulted in a change to soft-bed conditions and the generation of flutes and subglacial crevasse-fill ridges. The lack of mixing between this till and the underlying stratified sediments indicates that subglacial sediment deformation was restricted to a thin layer and that its deposition resulted in a cessation of subglacial erosion. The drumlin is therefore a composite of both rigid-bed and soft-bed processes that illustrates changes in basal conditions and processes during the course of the event. The limited time frame in which the drumlin formed and the presence of kettleholes across its surface are distinctive features that may warrant further investigation in the search for features diagnostic of past surge events. [ABSTRACT FROM AUTHOR]

The article offers a look on the recent changes that occur in the Debeli Namet glacier in Dutmitor massif, Montenegro. Researchers reported that the sediment ridges found in front of the glacier are regarded as moraines which originated from glacier activity in the 130 years. Such information was acquired through the use of lichenometry, an instrument which determine the approximate ages of different moraines with Aspicilia calcarea agg. A certain set of moraines dates from about 1878 A.D. while another inner moraines dates from about 1904 A.D. Moreover, the most recent moraines appear to have formed within the last 11 years in front of an active glacier margin.

The article reports the measure of changes in the amount of ice in the earth's polar region, based on the findings by National Aeronautics and Space Administration (NASA) Ice Satellite. According to glaciologists, Jay Zwally, head of NASA's Ice Satellite project, increase surface melting and acceleration of outlet glaciers are observed in Greenland. The net loss of melting reaches upto 50 cubic kilometers of ice volume per year.