pinecone/core-2020-05-10-deduplication huggingface dataset:
The role of peri-glacial Active Layer Development in determining soil-regolith thickness across a Triassic sandstone outcrop in the UK.

This paper examines the weathering processes that have combined to produce the distribution of soil-regolith (SR) thickness across the Triassic Sherwood Sandstone Group outcrop (750 km2) in Nottinghamshire, U.K. Archive borehole logs (n=282) taken across the outcrop showed that soil-regolith thickness had mean and median depths of ~1.8 and 1.5m respectively. Cores were taken from a forested site to depths ~3m for geochemical analysis. At this site the SR thickness was ~1.7m. Analysis of the loss of elements, compared to bedrock using mass balance calculations (τ) showed that all the calcite and gypsum cement had been removed to depths of >3m. Thus the major difference between the SR and the underlying saprolite was that the former exists as loose sand as opposed to a semi-durable rock. Scanning electron microscopy (SEM) analysis of core samples suggested that the non-durable rock or saprolite had greater cementation of clay particles. We propose that the mechanism through which the clay cement (and other interlocking grain bonds) were eased apart was through freeze-thaw processes associated with the summer ‘active layer development’ during the last glacial activity in the UK. We tested this theory by developing a Monte Carlo simulation based on a simplified version of the Stefan Equation. Current Arctic datasets of air and ground temperatures were obtained to provide reasonable starting conditions for input variables. These were combined with known data for thermal conductivity, bulk density and moisture content of the Sherwood Sandstone regolith. Model predictions (n=1000) of the distribution of SR thickness accurately reflect the observed distribution thickness from the borehole logs. This is strong evidence that freeze-thaw and ‘ALD’ processes are major factors in determining the thickness of SR across this outcrop
Limits on the validity of infinite length assumptions for modelling shallow landslides.

The infinite slope method is widely used as the geotechnical component of geomorphic and landscape evolution models. Its assumption that shallow landslides are infinitely long (in a downslope direction) is usually considered valid for natural landslides on the basis that they are generally long relative to their depth. However, this is rarely justified, because the critical length/depth (L/H) ratio below which edge effects become important is unknown. We establish this critical L/H ratio by benchmarking infinite slope stability predictions against finite element predictions for a set of synthetic two-dimensional slopes, assuming that the difference between the predictions is due to error in the infinite slope method. We test the infinite slope method for six different L/H ratios to find the critical ratio at which its predictions fall within 5% of those from the finite element method. We repeat these tests for 5000 synthetic slopes with a range of failure plane depths, pore water pressures, friction angles, soil cohesions, soil unit weights and slope angles characteristic of natural slopes. We find that: (1) infinite slope stability predictions are consistently too conservative for small L/H ratios; (2) the predictions always converge to within 5% of the finite element benchmarks by a L/H ratio of 25 (i.e. the infinite slope assumption is reasonable for landslides 25 times longer than they are deep); but (3) they can converge at much lower ratios depending on slope properties, particularly for low cohesion soils. The implication for catchment scale stability models is that the infinite length assumption is reasonable if their grid resolution is coarse (e.g. >25 m). However, it may also be valid even at much finer grid resolutions (e.g. 1 m), because spatial organization in the predicted pore water pressure field reduces the probability of short landslides and minimizes the risk that predicted landslides will have L/H ratios less than 25
Spatial variations in surface sediment structure in riffle-pool sequences : a preliminary test of the Differential Sediment Entrainment Hypothesis (DSEH).

Riffle–pool sequences are maintained through the preferential entrainment of sediment grains from pools rather than riffles. This preferential entrainment has been attributed to a reversal in the magnitude of velocity and shear stress under high flows; however the Differential Sediment Entrainment Hypothesis (DSEH) postulates that differential entrainment can instead result from spatial sedimentological contrasts. Here we use a novel suite of in situ grain-scale field measurements from a riffle–pool sequence to parameterize a physically-based model of grain entrainment. Field measurements include pivoting angles, lift forces and high resolution digital elevation models (DEMs) acquired using terrestrial laser scanning, from which particle exposure, protrusion and surface roughness were derived. The entrainment model results show that grains in pools have a lower critical entrainment shear stress than grains in either pool exits or riffles. This is because pool grains have looser packing, hence greater exposure and lower pivoting angles. Conversely, riffle and pool exit grains have denser packing, lower exposure and higher pivoting angles. A cohesive matrix further stabilizes pool exit grains. The resulting predictions of critical entrainment shear stress for grains in different subunits are compared with spatial patterns of bed shear stress derived from a two-dimensional computational fluid dynamics (CFD) model of the reach. The CFD model predicts that, under bankfull conditions, pools experience lower shear stresses than riffles and pool exits. However, the difference in sediment entrainment shear stress is sufficiently large that sediment in pools is still more likely to be entrained than sediment in pool exits or riffles, resulting in differential entrainment under bankfull flows. Significantly, this differential entrainment does not require a reversal in flow velocities or shear stress, suggesting that sedimentological contrasts alone may be sufficient for the maintenance of riffle–pool sequences. This finding has implications for the prediction of sediment transport and the morphological evolution of gravel-bed rivers
An integral approach to bedrock river profile analysis

Bedrock river profiles are often interpreted with the aid of slope–area analysis, but noisy topographic data make such interpretations challenging. We present an alternative approach based on an integration of the steady-state form of the stream power equation. The main component of this approach is a transformation of the horizontal coordinate that converts a steady-state river profile into a straight line with a slope that is simply related to the ratio of the uplift rate to the erodibility. The transformed profiles, called chi plots, have other useful properties, including co-linearity of steady-state tributaries with their main stem and the ease of identifying transient erosional signals. We illustrate these applications with analyses of river profiles extracted from digital topographic datasets.National Science Foundation (U.S.) (Geomorphology and Land-use Dynamics Program Award EAR-0951672)National Science Foundation (U.S.) (Continental Dynamics Program Award EAR-0003571
Topographic structure from motion: a new development in photogrammetric measurement.

The production of topographic datasets is of increasing interest and application throughout the geomorphic sciences, and river science is no exception. Consequently, a wide range of topographic measurement methods have evolved. Despite the range of available methods, the production of high resolution, high quality digital elevation models (DEMs) requires a significant investment in personnel time, hardware and/or software. However, image-based methods such as digital photogrammetry have been decreasing in costs. Developed for the purpose of rapid, inexpensive and easy three-dimensional surveys of buildings or small objects, the ‘structure from motion’ photogrammetric approach (SfM) is an image-based method which could deliver a methodological leap if transferred to geomorphic applications, requires little training and is extremely inexpensive. Using an online SfM program, we created high-resolution digital elevation models of a river environment from ordinary photographs produced from a workflow that takes advantage of free and open source software. This process reconstructs real world scenes from SfM algorithms based on the derived positions of the photographs in three-dimensional space. The basic product of the SfM process is a point cloud of identifiable features present in the input photographs. This point cloud can be georeferenced from a small number of ground control points collected in the field or from measurements of camera positions at the time of image acquisition. The georeferenced point cloud can then be used to create a variety of digital elevation products. We examine the applicability of SfM in the Pedernales River in Texas (USA), where several hundred images taken from a hand-held helikite are used to produce DEMs of the fluvial topographic environment. This test shows that SfM and low-altitude platforms can produce point clouds with point densities comparable with airborne LiDAR, with horizontal and vertical precision in the centimeter range, and with very low capital and labor costs and low expertise levels
Why permafrost rocks become unstable: a rock-ice-mechanical model in time and space

In this paper, we develop a mechanical model that relates the destabilisation of thawing permafrost rock slopes to temperature-related effects on both, rock- and ice mechanics;and laboratory testing of key assumptions is performed. Degrading permafrost is considered to be an important factor for rock-slope failures in alpine and arctic environments, but the mechanics are poorly understood. The destabilisation is commonly attributed to changes in ice-mechanical properties while bedrock friction and fracture propagation have not been considered yet. However, fracture toughness, compressive and tensile strength decrease by up to 50 % and more when intact water-saturated rock thaws. Based on literature and experiments, we develop a modified Mohr-Coulomb failure criterion for ice-filled rock fractures thatincorporates fracturing of rock bridges, friction of rough fracture surfaces, ductile creep of ice and detachment mechanisms along rock-ice interfaces. Novel laboratory setups were developed to assess the temperature dependency of the friction of ice-free rock-rock interfaces and the shear detachment of rock-ice interfaces. Indegrading permafrost, rock-mechanical properties may control early stages of destabilisation and become more important for higher normal stress, i.e. higher magnitudes of rock slope failure. Ice-mechanical properties outbalance the importance of rock-mechanical components after the deformation accelerates and are more relevant for smaller magnitudes. The model explains why all magnitudes of rock slope failures can be prepared and triggered by permafrost degradation and is capable of conditioning long paraglacial response times. Here, we present a synoptic rock- and ice-mechanical model that explains the mechanical destabilisation processes operating in warming permafrost rocks
Sensitivity of interfacial hydraulics to the microtopographic roughness of water-lain gravels

This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.\ud
This article was published in the journal, Earth Surface Processes and Landforms [© 2014 The Authors. Earth Surface Processes and Landforms Published by John Wiley & Sons Ltd.] and is also available at: http://dx.doi.org/10.1002/esp.3438Flow within the interfacial layer of gravel-bed rivers is poorly understood, but this zone is important because the hydraulics here transport sediment, generate flow structures and interact with benthic organisms. We hypothesized that different gravel-bed microtopographies generate measurable differences in hydraulic characteristics within the interfacial layer. This was tested using a high density of spatially and vertically distributed, velocity time series measured in the interfacial layers above three surfaces of contrasting microtopography. These surfaces had natural water-worked textures, captured in the field using a casting procedure. Analysis was repeated for three discharges, with Reynolds numbers between 165000 and 287000, to evaluate whether discharge affected the impact of microtopography on interfacial flows. Relative submergence varied over a small range (3.5 to 8.1) characteristic of upland gravel-bed rivers. Between-surface differences in the median and variance of several time-averaged and turbulent flow parameters were tested using non-parametric statistics. Across all discharges, microtopographic differences did not affect spatially averaged (median) values of streamwise velocity, but were associated with significant differences in its spatial variance, and did affect spatially averaged (median) turbulent kinetic energy. Sweep and ejection events dominated the interfacial region above all surfaces at all flows, but there was a microtopographic effect, with Q2 and Q4 events less dominant and structures less persistent above the surface with the widest relief distribution, especially at the highest Reynolds number flow. Results are broadly consistent with earlier work, although this analysis is unique because of the focus on interfacial hydraulics, spatially averaged 'patch scale' metrics and a statistical approach to data analysis. An important implication is that observable differences in microtopography do not necessarily produce differences in interfacial hydraulics. An important observation is that appropriate roughness parameterizations for gravel-bed rivers remain elusive, partly because the relative contributions to flow resistance of different aspects of bed microtopography are poorly constrained
Using air photos to parameterize landscape predictors of channel wetted width

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We investigated which landscape and climate-related data (including information on hydrological source of flow) were statistically significant predictors of channel wetted width (WW) across a sizeable (2200 km2) region of the UK. This was conducted specifically when flow was less than mean daily flow (MDF) and where channels are in a near natural state. Orthorectified air photos at 25 cm spatial resolution were used to measure WW, with the magnitude of the errors in these measurements quantified. We used flow information from local gauging stations to ensure that channels were below MDF for the days on which the air photos were captured. The root mean squared difference between the field and air photo measurements of WW (n = 28 sites) was small (0.14 m) in comparison to median WW (3.07 m).\ud
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We created points along sections of channels visible in air photos and used a terrain model to create drainage catchments for these points and computed their catchment area (CA). We selected a subset of points (n = 472) and measured their WW from air photos, and computed landscape-related data for each of their catchments (mean slope, mean annual rainfall, land cover type, elevation) and also mean BFIHOST, a quantitative index relating to hydrological source of flow. We used a linear mixed model to predict WW by including the landscape data (including CA 0.5) as fixed effects, plus a spatial covariance function estimated by residual maximum likelihood to determine unbiased estimates of the predictors. There was no evidence for retaining the spatial covariance function. With the exception of land cover, all the predictors were statistically significant and accounted for 76% of the variance of WW. When CA 0.5 alone was used as a predictor it captured 54% of the variance. The vast majority of this difference was due to inclusion of an interaction between CA and hydrological source of flow (BFIHOST). As catchment area increases, those channels with larger mean catchment BFIHOST values (greater proportion of baseflow contribution) have narrower WW in comparison with those having smaller mean BFIHOST for the same CA. Improved predictions of channel WW (based on our findings) could be used in channel restoration\u
Enhanced rock-slope failure following ice-sheet deglaciation : timing and causes

This research was supported by NERC Cosmogenic Isotope Analysis Facility [Grant Number: 9046.0308]The temporal pattern of rock-slope failures (RSFs) following Late Pleistocene deglaciation on tectonically stable terrains is controversial: previous studies variously suggest (1) a rapid response due to removal of supporting ice (‘debuttressing’), (2) a progressive decline in RSF frequency, and (3) a millennial-scale delay before peak RSF activity. We test these competing models through beryllium-10 (10Be) exposure dating of five closely-spaced quartzite RSFs on the Isle of Jura, Scotland, to establish the relationship between timing of failure and those of deglaciation, episodes of rapid warming and periods of rapid glacio-isostatic uplift. All five dated RSFs occurred at least 720–2240 years after deglaciation, with the probability of failure peaking ~2 ka after deglaciation, consistent with millennial-scale delay model (3). This excludes debuttressing as an immediate cause of failure, though it is likely that time-dependent stress release due to deglacial unloading resulted in progressive development of failure planes within the rock. Thaw of permafrost ice in joints is unlikely to have been a prime trigger of failure as some RSFs occurred several centuries after the onset of interstadial warming. Conversely, the timespan of the RSFs coincides with the period of maximum glacio-isostatic crustal uplift, suggesting that failure was triggered by uplift-driven seismic events acting on fractured rock masses. Implications of this and related research are: (1) that retreat of the last Pleistocene ice sheets across tectonically-stable mountainous terrains was succeeded by a period of enhanced rock-slope failure due to deglacial unloading and probably uplift-driven seismicity; (2) that the great majority of RSFs in the British Isles outside the limits of Loch Lomond Stadial (= Younger Dryas) glaciation are of Lateglacial (pre-Holocene) age; and (3) numerous RSFs must also have occurred inside Loch Lomond Stadial (LLS) glacial limits, but that runout debris was removed by LLS glaciers.PostprintPeer reviewe
The influence of bedrock orientation on the landscape evolution, surface morphology and denudation (10Be) at the Niesen, Switzerland

Landscape evolution and surface morphology in mountainous settings are a function of the relative importance between sediment transport processes acting on hillslopes and in channels, modulated by climate variables. The Niesen nappe in the Swiss Penninic Prealps presents a unique setting in which opposite facing flanks host basins underlain by identical lithologies, but contrasting litho-tectonic architectures where lithologies either dip parallel to the topographic slope or in the opposite direction (i.e. dip slope and non-dip slope). The north-western facing Diemtigen flank represents such a dip slope situation and is characterized by a gentle topography, low hillslope gradients, poorly dissected channels, and it hosts large landslides. In contrast, the south-eastern facing Frutigen side can be described as non-dip slope flank with deeply incised bedrock channels, high mean hillslope gradients and high relief topography. Results from morphometric analysis reveal that noticeable differences in morphometric parameters can be related to the contrasts in the relative importance of the internal hillslope-channel system between both valley flanks. While the contrasting dip-orientations of the underlying flysch bedrock has promoted hillslope and channelized processes to contrasting extents and particularly the occurrence of large landslides on the dip slope flank, the flank averaged beryllium-10 (10Be)-derived denudation rates are very similar and range between 0.20 and 0.26 mm yr−1. In addition, our denudation rates offer no direct relationship to basin's slope, area, steepness or concavity index, but reveal a positive correlation to mean basin elevation that we interpret as having been controlled by climatically driven factors such as frost-induced processes and orographic precipitation. Our findings illustrate that while the landscape properties in this part of the northern Alpine border can mainly be related to the tectonic architecture of the underlying bedrock, the denudation rates have a strong orographic control through elevation dependent mean annual temperature and precipitation
The biogeomorphological life cycle of poplars during the fluvial biogeomorphological succession: a special focus on Populus nigra L.

Riverine ecosystems are recurrently rejuvenated during destructive flood events and vegetation succession starts again. Poplars (i.e. species from Populus genera) respond to hydrogeomorphological  constraints, but, in turn, also influence these processes. Thus, poplar development on bare mineral substrates is not exclusively a one-way vegetative process. Reciprocal interactions and adjustments between poplar species and sediment dynamics during their life cycle lead to the emergence of biogeomorphological entities within the fluvial corridor, such as vegetated islands, benches and floodplains. Based on a review of geomorphological, biological and ecological literature, we have identified and described the co-constructing processes between riparian poplars and their fluvial environment. We have explored the possibility that the modification of the hydrogeomorphological environment exerted, in particular, by the European black poplar (Populus nigra L.), increases its\ud
fitness and thus results in positive niche construction. We focus on the fundamental phases of dispersal, recruitment and establishment until sexual maturity of P. nigra by describing the hierarchy of interactions and the pattern of feedbacks between biotic and abiotic components. We explicitly relate the biological life cycle of P. nigra to the fluvial biogeomorphic succession model by referring to the ‘biogeomorphological life cycle’ of P. nigra. Finally, we propose new research perspectives based on this theoretical framework
Quantifying the rate and depth dependence of bioturbation based on optically-stimulated luminescence (OSL) dates and meteoric (10)Be

Article first published online: 16 JAN 2014Both the rate and the vertical distribution of soil disturbance modify soil properties such as porosity, particle size, chemical composition and age structure; all of which play an important role in a soil's biogeochemical functioning. Whereas rates of mixing have been previously quantified, the nature of bioturbation's depth dependence remains poorly constrained. Here we constrain, for the first time, the relationship between mixing rate and depth in a bioturbated soil in northeast Queensland, Australia using a novel method combining OSL (optically-stimulated luminescence) ages and meteoric beryllium-10 (10Be) inventories. We find that the best fit mixing rate decreases non-linearly with increasing soil depth in this soil and the characteristic length scale of 0.28 m over which the mixing coefficient decays is comparable to reported rooting depth coefficients. In addition we show that estimates of surface mixing rates from OSL data are highly dependent on erosion rate and that erosion rate must be constrained if accurate mixing rates are to be quantified. We calculate surface diffusion-like mixing coefficients of 1.8 × 10−4 and 2.1 × 10−4 m2 yr−1 for the studied soil for two different estimates of soil erosion.Michelle O. Johnson, Simon M. Mudd, Brad Pillans, Nigel A. Spooner, L. Keith Fifield, Mike J. Kirkby and Manuel Gloo