pinecone/core-2020-05-10-deduplication huggingface dataset:
Ice flow-unit influence on glacier structure, debris entrainment and transport

Jennings, S. J. A., Hambrey, M. J., Glasser, N. F. (2014). Ice flow-unit influence on glacier structure, debris entrainment and transport. Earth Surface Processes and Landforms, 39 (10), 1279-1292.The links between structural glaciology, glacial debris entrainment and transport have been established in a number of different glacier settings. Here we document the structural evolution of a temperate Alpine valley glacier (Vadrec del Forno, Switzerland) and demonstrate that individual flow units within the glacier have very different structural and debris characteristics. The glacier consists of a broad accumulation area with multiple basins feeding a relatively narrowtongue and is formed from six distinct flowunits. Each flow unit has its own characteristic structural assemblage. Flow units that narrow rapidly down-glacier are dominated by primary stratification that has evolved into longitudinal foliation. In contrast, wider flow units preferentially develop an axial planar foliation. Glacier structure plays a limited role in the entrainment of debris, which ismore strongly influenced by ice-marginal rockfall and avalanche inputs onto the glacier surface. However, once entrained, glacier structure controls the reorientation and redistribution of debris within the ice mass. By taking a whole-glacier approach to describing glacier structure and debris transport, we conclude that individual flow units are unique with regard to structure and debris transfer. Copyright (C) 2013 John Wiley & Sons, Ltd.authorsversionPeer reviewe
Testing techniques to quantify drumlin height and volume: Synthetic DEMs as a diagnostic tool

This article was published in the journal, Earth Surface Processes and Landforms [© John Wiley & Sons, Ltd.] and the definitive version is available at: http://dx.doi.org/10.1002/esp.3530Glacial bedform height (H) and volume (V) likely preserve important information about the behaviour of former ice sheets. However, large systematic errors exist in the measurement of H and V. Three semi-automated methods to isolate drumlins from other components of the landscape (e.g. trees, hills) as portrayed by NEXTMap have recently been devised; however, it is unclear which is most accurate. This paper undertakes the first quantitative comparison of such readily implementable methods, illustrating the use of statistically representative 'synthetic landscapes' as a diagnostic tool. From this analysis, guidelines for quantifying the 3D attributes of drumlins are proposed. Specifically, to avoid obtaining incorrect estimates caused by substantial systematic biases, interpreters should currently take three steps: declutter the digital elevation model for estimating H but not V; remove height data within the drumlin; then interpolate across the resultant hole to estimate a basal surface using Delaunay triangulation. Results are demonstrated through analysis of drumlins in an area in western central Scotland. The guidance arguably represents the best current advice for subglacial bedforms in general, highlighting the need for more studies into the quality of mapped data using synthetic landscapes
The use of live vegetation in geomorphological experiments: how to create optimal growing conditions

There has been increasing use of live vegetation in laboratory experiments, in particular in fluvial geomorphology. The results from these studies have provided useful insight into the role that vegetation plays in impacting and modifying geomorphic systems. However there has been little published on the seed preparation techniques and vegetation growing conditions required for use in these experiments. This commentary presents results from a series of experiments investigating these factors using Medicago sativa and Avena Sativa, with the aim of highlighting the optimal growing conditions found to provide a starting point for researchers interested in implementing these techniques
Channel pattern of proglacial rivers: topographic forcing due to glacier retreat

This is the peer reviewed version of the following article: Marren, P. M., & Toomath, S. C. (2014). Channel pattern of proglacial rivers: topographic forcing due to glacier retreat. Earth Surface Processes and Landforms, 39(7), 943–951. DOI: 10.1002/esp.3545, which has been published in final form at http://onlinelibrary.wiley.com/doi/10.1002/esp.3545/abstract. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-ArchivingGlacier retreat leads to changes in channel pattern during deglaciation, in response to changing water, sediment and base level controls. Recent ongoing retreat at Skaftafellsjökull, Iceland (c. 50m per year since 1998) has resulted in the formation of a sequence of river terraces, and several changes in river channel pattern. This paper compares widely used models of river channel pattern against the changes observed at Skaftafellsjökull. Doing this reveals the role of topographic forcing in determining proglacial\ud
channel pattern, whilst examining the predictive power and limitations of the various approaches to classifying river channels. Topography was found to play a large role in determining channel pattern in proglacial environments for two reasons: firstly, glacier retreat forces rivers to flow through confined moraine reaches. In these reaches, channels which theory predicts should be braided\ud
are forced to adopt a single channel. Secondly, proximal incision of proglacial rivers, accompanied by downstream aggradation, leads to changes in slope which force the river to cross channel pattern thresholds. The findings of this work indicate that in the short\ud
term, the majority of channel pattern change in proglacial rivers is due to topographic forcing, and that changes due to changing hydrology and sediment supply are initially relatively minor, although likely to increase in significance as deglaciation progresses.\ud
These findings have implications for palaeohydraulic studies, where changes in proglacial channel pattern are frequently interpretedas being due to changes in water or sediment supply. This paper shows that channel pattern can change at timescales faster than hydrological or sediment budget changes usually occur, in association with relatively minor changes in glacier mass balance
Simulation of scree-slope dynamics: investigating the distribution of debris avalanche events in an idealized two-dimensional model

We present a two-dimensional model of the development of scree slopes using the discrete-element method. We concentrate on the dynamics of the accumulating debris at the cliff foot rather than on the failure modes of the cliff-face or shape of the underlying rock surface. The evolution of this unconsolidated material is intermittent and systematically changing over time, with an early high disturbance regime, dominated by a characteristic event size (where 65% of particles in the debris are in motion to some extent), replaced at later times by many shallow slides interspersed with infrequent large events that involve motion through almost the full scree depth. These large slides lead to a stratigraphy in which the layers of material are stretched almost horizontal near the base of the slope. The scree surface thus shows a gradient in age with most recent rock-fall close to the cliff and the oldest rock-fall debris outcropping at the foot. The final surface slope tends to show little curvature, and the final mean slope is well correlated with the angle of internal friction of the particles, although the change is very small over a wide range of friction angles [final slope (in degrees relative to horizontal) ~ 0.043 × internal friction angle + 17.49, with a correlation coefficient of 0.89, p-value 0.0001]. Some weak size-segregation of the debris is found, but this seems to have little to do with individual particles bounding down the slope. The shape of the rock core agrees largely with the analytic forms given by Fisher–Lehmann and Bakker–Le Heux expressions, but the original simple Fisher quadratic can give the best fit. Overall the evolution shows a remarkable insensitivity to the model parameters, suggesting that the controls on dry scree-slope evolution are primarily geometric in character.This work was performed using the Darwin Supercomputer of the University of Cambridge High Performance Computing Service (http://www.hpc.cam.ac.uk/), provided by Dell Inc. using Strategic Research Infrastructure Funding from the Higher Education Funding Council for England.This is the accepted version of the following article: Bithell M, Richards KS, Bithell EG, Earth Surface Processes and Landforms 2014, 39, 1601–1610, doi: 10.1002/esp.3548, which has been published in final form at http://dx.doi.org/10.1002/esp.354
Bedload hysteresis in a glacier-fed mountain river

Sediment transport during flood events often reveals hysteretic patterns because flow discharge can peak before (counterclockwise hysteresis) or after (clockwise hysteresis) the peak of bedload. Hysteresis in sediment transport has been used in the literature to infer the degree of sediment availability. Counterclockwise and clockwise hysteresis have been in fact interpreted as limited and unlimited sediment supply conditions, respectively. Hysteresis has been mainly explored for the case of suspended sediment transport, but it was rarely reported for bedload transport in mountain streams. This work focuses on the temporal variability of bedload transport in an alpine catchment (Saldur basin, 18.6 km2, Italian Alps) where bedload transport was monitored by means of an acoustic pipe sensor which detects the acoustic vibrations induced by particles hitting a 0.5m‐long steel pipe. Runoff dynamics are dominated by snowmelt in late spring/early summer, mostly by glacier melt in late summer/early autumn, and by a combination of the snow and glacier melt in mid‐summer. The results indicate that hysteretic patterns during daily discharge fluctuations are predominantly clockwise during the snowmelt period, likely due to the ready availability of unpacked sediments within the channel or through bank erosion in the lower part of the basin. On the contrary, counterclockwise hysteresis tend to be more frequent during late glacier melting period, possibly due to the time lag needed for sediment provided by the glacial and peri‐glacial area to be transported to the monitoring section. However, intense rainfall events occurring during the glacier melt period generated predominantly clockwise hysteresis, thus indicating the activation of different sediment sources. These results indicate that runoff generation processes play a crucial role on sediment supply and temporal availability in mountain streams
Reduced bed material stability and increased bedload transport caused by foraging fish: a flume study with juvenile Barbel (Barbus barbus)

This is the peer reviewed version of the following article: PLEDGER, A.G., RICE, S.P. and MILLETT, J., 2014. Reduced bed material stability and increased bedload transport caused by foraging fish: a flume study with juvenile Barbel (Barbus barbus). Earth Surface Processes and Landforms, 39 (11), pp. 1500 - 1513, which has been published in final form at http://dx.doi.org/10.1002/esp.3592 This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.The plants and animals that inhabit river channels may act as zoogeomorphic agents affecting the nature and rates of sediment recruitment, transport and deposition. The impact of benthic-feeding fish, which disturb bed material sediments during their search for food, has received very little attention, even though benthic feeding species are widespread in rivers and may collectively expend significant amounts of energy foraging across the bed. An ex situ experiment was conducted to investigate the impact of a benthic feeding fish (Barbel Barbus barbus) on particle displacements, bed sediment structures, gravel entrainment and transport fluxes. In a laboratory flume changes in bed surface topography were measured and grain displacements examined when an imbricated, water-worked bed of 5.6 to 16 mm gravels was exposed to feeding juvenile Barbel (on average, 0.195 m in length). Grain entrainment rates and bedload fluxes were measured under a moderate transport regime for substrates that had been exposed to feeding fish and control substrates which had not. On average, approximately 37% of the substrate, by area, was modified by foraging fish during a four-hour treatment period, resulting in increased microtopographic roughness and reduced particle imbrication. Structural changes by fish corresponded with an average increase in bedload flux of 60% under entrainment flows, whilst on average the total number of grains transported during the entrainment phase was 82% higher from substrates that had been disturbed by Barbel. Together, these results indicate that by increasing surface microtopography and undoing the naturally stable structures produced by water working, foraging can increase the mobility of gravel-bed materials. An interesting implication of this result is that by increasing the quantity of available, transportable sediment and lowering entrainment thresholds, benthic feeding might affect bedload fluxes in gravel-bed rivers. The evidence presented here is sufficient to suggest that further investigation of this possibility is warrante
Quantifying submerged fluvial topography using hyperspatial resolution UAS imagery and structure from motion photogrammetry.

Quantifying the topography of rivers and their associated bedforms has been a fundamental concern of fluvial geomorphology for decades. Such data, acquired at high temporal and spatial resolutions, are increasingly in demand for process-oriented investigations of flow hydraulics, sediment dynamics and in-stream habitat. In these riverine environments, the most challenging region for topographic measurement is the wetted, submerged channel. Generally, dry bed topography and submerged bathymetry are measured using different methods and technology. This adds to the costs, logistical challenges and data processing requirements of comprehensive river surveys. However, some technologies are capable of measuring the submerged topography. Through-water photogrammetry and bathymetric LiDAR are capable of reasonably accurate measurements of channel beds in clear water. While the cost of bathymetric LiDAR remains high and its resolution relatively coarse, the recent developments in photogrammetry using Structure from Motion (SfM) algorithms promise a fundamental shift in the accessibility of topographic data for a wide range of settings. Here we present results demonstrating the potential of so called SfM-photogrammetry for quantifying both exposed and submerged fluvial topography at the mesohabitat scale. We show that imagery acquired from a rotary-winged Unmanned Aerial System (UAS) can be processed in order to produce digital elevation models (DEMs) with hyperspatial resolutions (c. 0.02 m) for two different river systems over channel lengths of 50–100 m. Errors in submerged areas range from 0.016 m to 0.089 m, which can be reduced to between 0.008 m and 0.053 m with the application of a simple refraction correction. This work therefore demonstrates the potential of UAS platforms and SfM-photogrammetry as a single technique for surveying fluvial topography at the mesoscale (defined as lengths of channel from c.10 m to a few hundred metres)
Innovative analysis and use of high-resolution DTMs for quantitative interrogation of Earth-surface processes

This is the peer reviewed version of the following article: PASSALACQUA, P., HILLIER, J.K. and TAROLLI, P., 2014. Innovative analysis and use of high-resolution DTMs for quantitative interrogation of Earth-surface processes. Earth Surface Processes and Landforms, 39 (10), pp. 1400 - 1403., which has been published in final form at http://dx.doi.org/10.1002/esp.3616. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.This is the era of digital landscapes; the widespread availability of powerful sensing technologies has revolutionized\ud
the way it is possible to interrogate landscapes in order to understand the processes sculpting them. Vastly greater areas have now\ud
been acquired at ‘high resolution’: currently tens of metres globally to millimetric precision and accuracy locally. This permits\ud
geomorphic features to be visualized and analysed across the scales at which Earth-surface processes operate. Especially exciting\ud
is the capturing of process dynamics in repeated surveying, which will only become more important with low-cost accessible data\ud
generation through techniques such as Structure from Motion (SfM). But the key challenge remains; to interpret high resolution\ud
Digital Terrain Models (DTMs), particularly by extracting geomorphic features in robust and objective ways and then linking the\ud
observed features to the underlying physical processes. In response to the new data and challenges, recent years have seen improved\ud
processing of raw data into DTMs, development of data fusion techniques, novel quantitative analysis of topographic data, and\ud
innovative geomorphological mapping. The twelve papers collected in this volume sample this progress in interrogating Earthsurface\ud
processes through the analysis of DTMs. They cover a wide range of disciplines and spatio-temporal scales, from landslide\ud
prone landscapes, to agriculturally modified regions, to mountainous landscapes, and coastal zones. They all, however, showcase\ud
the quantitative exploitation of information contained in high-resolution topographic data that we believe will underpin the improvement\ud
of our understanding of many elements of Earth-surface processes. Most of the papers introduced here were first presented in a\ud
conference session at the European Geosciences Union General Assembly in 2011
Sediment connectivity : a framework for understanding sediment transfer at multiple scales.

A major challenge for geomorphologists is to scale up small-magnitude processes to produce landscape form, yet existing approaches have been found to be severely limited. New ways to scale erosion and transfer of sediment are thus needed. This paper evaluates the concept of sediment connectivity as a framework for understanding processes involved in sediment transfer across multiple scales. We propose that the concept of sediment connectivity can be used to explain the connected transfer of sediment from a source to a sink in a catchment, and movement of sediment between different zones within a catchment: over hillslopes, between hillslopes and channels, and within channels. Using fluvial systems as an example we explore four scenarios of sediment connectivity which represent end-members of behaviour from fully linked to fully unlinked hydrological and sediment connectivity. Sediment-travel distance – when combined with an entrainment parameter reflecting the frequency–magnitude response of the system – maps onto these end-members, providing a coherent conceptual model for the upscaling of erosion predictions. This conceptual model could be readily expanded to other process domains to provide a more comprehensive underpinning of landscape-evolution models. Thus, further research on the controls and dynamics of travel distances under different modes of transport is fundamental
Considering river structure and stability in the light of evolution: feedbacks between riparian vegetation and hydrogeomorphology

River ecological functioning can be conceptualized according to a four-dimensional framework, based on the responses of aquatic and riparian communities to hydrogeomorphic constraints along the longitudinal, transverse, vertical and temporal dimensions of rivers. Contemporary riparian vegetation responds to river dynamics at ecological timescales, but riparian vegetation, in one form or another, has existed on Earth since at least the Middle Ordovician (c. 450 Ma) and has been a significant controlling factor on river geomorphology since the late Silurian (c. 420 Ma). On such evolutionary timescales, plant adaptations to the fluvial environment and the subsequent effects of these adaptations on aspects of fluvial sediment and landform dynamics resulted in the emergence, from the Silurian to the Carboniferous, of a variety of contrasted fluvial biogeomorphic types where water flow, morphodynamics and vegetation interacted to different degrees. Here we identify several of these types and describe the consequences for biogeomorphic structure and stability (i.e. resistance and resilience), along the four river dimensions, of feedbacks between riparian plants and hydrogeomorphic processes on contrasting ecological and evolutionary timescales.This is the author's accepted manuscript and will be under embargo until the 18th of September 2015. The final version is available from Wiley at onlinelibrary.wiley.com/doi/10.1002/esp.3643/abstrac
Topographic stress and rock fracture: a two-dimensional numerical model for arbitrary topography and preliminary comparison with borehole observations

Theoretical calculations indicate that elastic stresses induced by surface topography may be large enough in some landscapes to fracture rocks, which in turn could influence slope stability, erosion rates, and bedrock hydrologic properties. These calculations typically have involved idealized topographic profiles, with few direct comparisons of predicted topographic stresses and observed fractures at specific field sites. We use a numerical model to calculate the stresses induced by measured topographic profiles and compare the calculated stress field with fractures observed in shallow boreholes. The model uses a boundary element method to calculate the stress distribution beneath an arbitrary topographic profile in the presence of ambient tectonic stress. When applied to a topographic profile across the Susquehanna Shale Hills Critical Zone Observatory in central Pennsylvania, the model predicts where shear fractures would occur based on a Mohr–Coulomb criterion, with considerable differences in profiles of stresses with depth beneath ridgetops and valley floors. We calculate the minimum cohesion required to prevent shear failure, C[subscript min], as a proxy for the potential for fracturing or reactivation of existing fractures. We compare depth profiles of C[subscript min] with structural analyses of image logs from four boreholes located on the valley floor, and find that fracture abundance declines sharply with depth in the uppermost 15 m of the bedrock, consistent with the modeled profile of C[subscript min]. In contrast, C[subscript min] increases with depth at comparable depths below ridgetops, suggesting that ridgetop fracture abundance patterns may differ if topographic stresses are indeed important. Thus, the present results are consistent with the hypothesis that topography can influence subsurface rock fracture patterns and provide a basis for further observational tests.United States. Army Research Office (Award W911NF-14-1-0037)United States. Dept. of Energy (Award DE-FG01-97ER14760