Erosion Scars Research Articles

Characterisation of erosional features associated with tsunami terrains on rocky coasts of the Maltese islands

AbstractIn recent years there has been a growing body of literature on depositional signatures associated with historic extreme waves on rocky coasts. Here, in the context of the Maltese islands, we place an innovative focus on evidence of erosional forms. The field evidence is concentrated along the NE flank of the islands at a topographically varied range of sites and up to an altitude of 13 m asl. A range of forms is broadly classified in terms of their morphologies and the forces responsible for their formation. Sockets, eroded scarps, scoured terrains, clifftop erosion scars, swept terrains and spillways are interpreted as consequences of overwashing of the landscape by an extreme wave or waves. These forms are shown to be controlled by flow intensity, topography and lithology, and especially rock bedding and jointing. They comprise the source areas for associated depositional evidence allowing transport paths to be estimated, and may significantly enhance the reconstruction of extreme wave events. It is likely that similar (and additional) erosional forms are present elsewhere in the Mediterranean domain, where comparable lithological and topographic situations are exposed to extreme waves. Copyright © 2015 John Wiley & Sons, Ltd.

Comparative study of the slurry erosion behavior of laser cladded Ni-WC coating modified by nanocrystalline WC and La2O3

The erosion performance of laser cladded Ni-60 %WC coatings subjected to a controllable abrasive water jet (AWJ) was investigated. The erosion resistance of Ni-60 %WC coatings at varied linear laser energy (from 315 to 700 J/mm) was examined under different impinging angles of a slurry jet. The chemical composition of coatings was modified by nanocrystalline WC powder and the rare earth element (La2O3). The erosion value of Ni-60 %WC was reduced to 40 % by decreasing the laser energy from 700 to 315 J/mm. Synthesized coatings with optimal weight fraction of nano-WC particles (5 %) and La2O3 (1 %) decreased the average microstructural grain size of the Ni-binder, increased the homogeneity and hardness of the coating, and consequently increased the erosion resistivity. The tribological evaluation of the erosion scars showed a log-linear relationship between coating hardness and volume loss under erosion. Adding nano-WC (5 %) and La2O3 (1 %) enhanced the bonding strength between Ni and WC and no pulled out WC particles was observed after erosion test.

Analysing the spatial patterns of erosion scars using point process theory at the coastal chalk cliff of Mesnil-Val, Normandy, northern France

Abstract. Over the last decade, many cliff erosion studies have focused on frequency-size statistics using inventories of sea cliff retreat sizes. By comparison, only a few paid attention to quantifying the spatial and temporal organisation of erosion scars over a cliff face. Yet, this spatial organisation carries essential information about the external processes and the environmental conditions that promote or initiate sea-cliff instabilities. In this article, we use summary statistics of spatial point process theory as a tool to examine the spatial and temporal pattern of a rockfall inventory recorded with repeated terrestrial laser scanning surveys at the chalk coastal cliff site of Mesnil-Val (Normandy, France). Results show that: (1) the spatial density of erosion scars is specifically conditioned alongshore by the distance to an engineered concrete groyne, with an exponential-like decreasing trend, and vertically focused both at wave breaker height and on strong lithological contrasts; (2) small erosion scars (10−3 to 10−2 m3) aggregate in clusters within a radius of 5 to 10 m, which suggests some sort of attraction or focused causative process, and disperse above this critical distance; (3) on the contrary, larger erosion scars (10−2 to 101 m3) tend to disperse above a radius of 1 to 5 m, possibly due to the spreading of successive failures across the cliff face; (4) large scars significantly occur albeit moderately, where previous large rockfalls have occurred during preceding winter; (5) this temporal trend is not apparent for small events. In conclusion, this study shows, with a worked example, how spatial point process summary statistics are a tool to test and quantify the significance of geomorphological observation organisation.

Surface ripple and erosion rate of stainless steel under elevated temperature erosion by angular solid particles

The actual industrial erosion caused by the impingement of particles swarming from different perspectives is often different from the single-angle impingement of solid particle in the erosion test. In order to predict the erosion problems in practical engineering more reasonably, a series of elevated temperature erosion tests were conducted to study the surface ripple and enduring erosion behavior of heat-resistance stainless steel suffering from the single-angle impingement or multiangle alternative impingement of angular particles. The test results indicated that the surface of target materials with good ductility produced large-scaled transverse ripples and small-scaled longitudinal ripples after experienced a long-time single-angle impingement of angular solid particles under a 773–873-K high-temperature environment. The longitudinal ripples could accelerate the emergence and development of large-scaled transverse ripples. Initial erosion scars caused the differentiation of material deformability and plastic flow in the different locations of concave–convex scars, which further drove the evolution of the surface morphology from disordered scars to coherent ripples under the sustained attack of high-velocity particles. The more dimples the eroded surface of target material produced, it was easier for the target materials to produce coherent ripple. However, the interactions among the erosion behaviors with different attack angles made initial concave–convex scars difficult to evolve to coherent ripples under the multiangle alternative erosion. Further statistical results of erosion tests indicated that it can basically satisfy the practical engineering need by taking the erosion rate of initial surface layer as the erosion rate of the target material within the whole life cycle.

Landslide model performance in a high resolution small-scale landscape

The frequency and severity of shallow landslides in New Zealand threatens life and property, both on- and off-site. The physically-based shallow landslide model LAPSUS-LS is tested for its performance in simulating shallow landslide locations induced by a high intensity rain event in a small-scale landscape. Furthermore, the effect of high resolution digital elevation models on the performance was tested. The performance of the model was optimised by calibrating different parameter values. A satisfactory result was achieved with a high resolution (1m) DEM. Landslides, however, were generally predicted lower on the slope than mapped erosion scars. This discrepancy could be due to i) inaccuracies in the DEM or in other model input data such as soil strength properties; ii) relevant processes for this environmental context that are not included in the model; or iii) the limited validity of the infinite length assumption in the infinite slope stability model embedded in the LAPSUS-LS. The trade-off between a correct prediction of landslides versus stable cells becomes increasingly worse with coarser resolutions; and model performance decreases mainly due to altering slope characteristics. The optimal parameter combinations differ per resolution. In this environmental context the 1m resolution topography resembles actual topography most closely and landslide locations are better distinguished from stable areas than for coarser resolutions. More gain in model performance could be achieved by adding landslide process complexities and parameter heterogeneity of the catchment.

Probabilistic coastal cliff collapse hazard from repeated terrestrial laser surveys: case study from Mesnil Val (Normandy, northern France)

ABSTRACT Dewez, T.J.B., Rohmer, J., Regard, V., and Cnudde, C., 2013, Probabilistic coastal cliff collapse hazard from repeated terrestrial laser surveys: case study from Mesnil Val (Normandy, northern France) Along cliff edges, coastal managers dealing with life-safety matters often wonder “how much time have I got left before I need to expropriate this house?” Here, we present a case study where repeated terrestrial laser scanner surveys (TLS) were performed to monitor a chalk cliff section in Normandy. The Mesnil Val cliff, cut in Upper Cretaceous chalk known as the Upper Lewes Nodular Chalk, is a ca. 750-m-long, 20–80m-high cliff section. It was surveyed 6 times between December 2005 and March 2008 at a 1 –point-per-5cm resolution. Successive Digital Surface Models (DSM) of the cliff surface were subtracted to reveal the location and shape of erosion scars. Scars detection relies on a robust indicator of observed noise distribution. The resulting scar inventory contains more than 8500 objects with vol...

Influence of erosion and deposition on carbon and nitrogen accumulation in resampled steepland soils under pasture in New Zealand

Although erosion occurs under pastures in New Zealand North Island hill country, previous work shows that the soils on mid-slopes (>19°) have large and significant average gains of soil carbon (C) and nitrogen (N) over a period of about 30years. Both sheetwash erosion (from patches of bare soil) and soil deposition (from upslope) could have occurred in the intervening 30years, and this could have led to a loss or gain of soil C. The fission-derived radionuclide 137Cs is a unique tracer for studying erosion and sedimentation because it is strongly adsorbed onto soil particles, and its movement in the environment is predominantly due to physical processes. We hypothesized that accumulation and loss of 137Cs and C would be correlated if erosion and deposition processes were responsible for the observed changes in soil C. We therefore measured 137Cs in archived samples, previously used to assess changes in C and N, together with 137Cs in the re-sampled soil horizons, to an average depth of 37cm. The data show that, on average, there has been a small gain in total profile 137Cs over this time, and complex patterns within individual soil profiles over 30years. There was only a weak correlation between 137Cs and C accumulation above 15cm soil depth, but, in contrast, a much stronger relationship was found below 15cm. A possible explanation for the observed pattern is soil thickening due to deposition, but the deposition may occur with variable 137Cs contents. Generally deposition does not account for all of the increase in C, and regression analysis between Cs and C for all layers suggested that erosion/deposition accounted for 20–30% of the total change in C. In a detailed case study, the sampling of erosion scars caused by landslides showed that soil C stocks (0–20cm) can increase from 10 to 80 tonne (Mg) C ha−1 within 70years. Use of the CENTURY model indicated that input of N from legumes in the pasture enabled N and C to accumulate in the surface soil. This suggests that gains in soil C and N under hill country pasture that occur in these facets of the landscape are probably largely due to the ongoing input from C and N in the grass-legume pastures rather than erosion or deposition of soil.

Effectiveness of reforestation in erosion mitigation and implications for future sediment yields, East Coast catchments, New Zealand: A review

AbstractThis paper argues that reforestation of unstable and degraded parts of the East Coast region, predominantly with exotic pines, has successfully stabilised existing erosion forms and prevented the initiation of new ones. Effectiveness is often assessed by capturing erosion scars on aerial photography taken before and after reforestation and any change in scar size is measured in a geographic information system (GIS). Combined with forest age data, modelled reforestation scenarios indicate that sediment generation from earth flows and shallow landslides would be negligible within eight to 10 years after planting, and if all remaining gullies were to be reforested before 2020, sediment yield could halve by 2030 and remain constant thereafter. In a similar time frame, the risk to infrastructure by sedimentation and flooding would likely decrease.

Low angle scouring erosion behaviour of elastomeric materials

Abstract Elastomers are a particularly important class of material, finding increasing utilization in applications such as piping and tubular components; pumps; valves and cyclones; where considerable resistance to low angle scouring erosion is critical. Assessment of elastomers at impingement angles >10° has been readily available using various slurry jet devices, however, there is a clear need for a suitable method for evaluating these materials under conditions of high velocity, low angle ( Based on this requirement, a new specimen holder was developed for the Coriolis slurry erosion tester. This rig has previously been shown to provide a convenient and repeatable method for evaluating the scouring erosion resistance of a variety of hard materials [1]; however, until recently the capability to assess elastomeric materials was hindered by the distortion of specimens when the holding force was applied. The new holder alleviates this problem and ensures improved control of the slurry flow over the specimen surface thus producing consistent and reproducible erosion scars, which can be used for determining the expected wear of elastomers under conditions of low angle erosion. The current work examines the scouring erosion resistance and mechanisms of material removal for selected elastomers and compares data with that of various white irons, steels, cermets and overlays. The influence of erodent type on the resulting wear mechanisms has also been examined. Results have enabled correlations to be made between scouring erosion attack resistance, hardness and material type.

Geomorphic features extraction from high-resolution topography: landslide crowns and bank erosion

In recent years, new remote-sensed technologies, such as airborne and terrestrial laser scanner, have improved the detail and the quality of topographic information, providing topographical high-resolution and high-quality data over larger areas better than other technologies. A new generation of high-resolution (≤3 m) digital terrain models (DTMs) is now available for different areas and is widely used by researchers, offering new opportunities for the scientific community. These data call for the development of a new generation of methodologies for an objective extraction of geomorphic features, such as channel heads, channel networks, bank geometry, debris-flow channel, debris-flow deposits, scree slope, landslide and erosion scars, etc. A high-resolution DTM is able to detect the divergence/convergence of areas related to unchannelized/channelized processes with better detail than a coarse DTM. In this work, we tested the performance of new methodologies for an objective extraction of geomorphic features related to shallow landsliding processes (landslide crowns), and bank erosion in a complex mountainous terrain. Giving a procedure that automatically recognizes these geomorphic features can offer a strategic tool to map natural hazard and to ease the planning and the assessment of alpine regions. The methodologies proposed are based on the detection of thresholds derived by the statistical analysis of variability of landform curvature. The study was conducted on an area located in the Eastern Italian Alps, where an accurate field survey on shallow landsliding, erosive channelized processes, and a high-quality set of both terrestrial and airborne laser scanner elevation data is available. The analysis was conducted using a high-resolution DTM and different smoothing factors for landform curvature calculation in order to test the most suitable scale of curvature calculation for the recognition of the selected features. The results revealed that (1) curvature calculation is strongly scale-dependent, and an appropriate scale for derivation of the local geometry has to be selected according to the scale of the features to be detected; (2) such approach is useful to automatically detect and highlight the location of shallow slope failures and bank erosion, and it can assist the interpreter/operator to correctly recognize and delineate such phenomena. These results highlight opportunities but also challenges in fully automated methodologies for geomorphic feature extraction and recognition.

Quantification of erosion distributions in complex geometries

Development and validation of improved erosion models demands accurate, high resolution measurement techniques to quantify the distribution of erosion over large-scale and/or complex geometries. However, current sophisticated geometric scanning equipment is mostly used to examine small-scale erosion scars, and such techniques are not applicable when researching the erosion of complex or large-scale samples. To address this limitation, we consider alternative metrology technologies for erosion quantification, including 3D laser scanners and coordinate measuring machines (CMM). Erosion experiments were performed on both a pipe elbow and a cylindrical intrusion in a pipe, and the erosion distributions were quantified with a CMM. The results for the pipe elbow and cylindrical intrusion agree well with paint modelling tests and computation fluid dynamics erosion predictions, respectively, suggesting that these metrology techniques represent a useful tool for erosion research and industrial appraisal.

Forecasting the outbreak of moorland wildfires in the English Peak District

Warmer, drier summers brought by climate change increase the potential risk of wildfires on the moorland of the Peak District of northern England. Fires are costly to fight, damage the ecosystem, harm water catchments, cause erosion scars and disrupt transport. Fires release carbon dioxide to the atmosphere. Accurate forecasts of the timing of fires help deployment of fire fighting resources. A probit model is used to assess the chance of fires at different times of the year, days of the week and under various weather conditions. Current and past rainfall damp fire risk. The likelihood of fire increases with maximum temperature. Dry spells or recent fire activity also signal extra fire hazard. Certain days are fire prone due to visitors and some months of the year are more risky reflecting the changing flammability of moorland vegetation. The model back-predicts earlier fires during a hot dry summer. The impact of climate change on fire incidence is not straightforward. Risks may be reduced if wetter winters and earlier onset of spring add to plant moisture content. Yet a warm spring increases biomass and potential fuel load in summer. Climate change may cause the timing of moorland wildfires to shift from a damper and more verdant spring to drought-stressed summer.

Assessment of sandstone deterioration at Ta Keo temple (Angkor): first results and future prospects

A first application of geomorphological methods to the assessment of sandstone deterioration at Angkor is presented. Damage diagnosis was carried out on the first eastern tier of the central pyramid of the 1,000 year-old Ta Keo temple. Methods combine field observations and measurements at 230 sampling points, high-resolution lasergrammetry and stereophotogrammetry on a 2-m2 test zone, and SEM observations. The first results indicate that decay operates through a synergistic combination of weathering phenomena dominated by scaling and solution, and exhibits a high spatial variability. Percentages of deteriorated surfaces vary from 17.6 to 93.8%, and average stone recession values from 0.00 to 2.71 cm (minimum) and 0.34 to 5.49 cm (maximum). On the test-zone, stereophotogrammetry and 3D-mapping of the present and reconstructed initial states using lasergrammetry indicate that erosion scars up to 6 cm deep have formed since 1963. On the whole, the amount of deteriorated surfaces more than tripled between 1963 and 2008. The degree of implication of salts in stone decay remains unclear for most efflorescences are composed of calcite (CaCO3), with secondary importance of barite (BaSO4) and gypsum (CaSO4 2H2O). Future prospects aim to evaluate the impact on stone decay of the clearing out of the temple from the forest in the 1920s.

High pressure testing sand erosion in 3D flow channels and correlation with CFD

An experimental approach to accelerated laboratory testing sand erosion in high pressure flow channels of complicated 3D configurations was developed. The channels were designed for erosion-resistant valves in natural gas and oil severe service applications. An analysis of equations of the particle motion in turbulent flow defined a method for scaling the channel dimensions, the erodent size and fluid parameters in order to simulate erosion in the field by using an environmentally-friendly fluid at the laboratory conditions. A testing facility that operated at 40 bar of nitrogen pressure with silica sand as an erodent was built and calibrated. The flow channels were manufactured from organic glass (PMMA) in separate plates that facilitated weight loss measurements in different parts of the channels as well as erosion visualization. The particular grade of glass was selected after testing erosion in a range of materials in order to find close resemblance to stainless steel in terms of both the erosion rate angle function and the velocity exponent. The test results were used for validation of a CFD model of the particles motion and for understanding the reliability of the CFD predictions for the valve lifetime assessment. The CFD model was found to reproduce the complicated erosion patterns and actual weight losses on early stages of erosion very well. CFD predictions were reasonably accurate even as erosion progressed if integral values of the computed erosion rate over the erosion scars were used.

The Bioeroding Sponge Aka paratypica, a Modern Tracemaking Analogue for the Paleozoic Ichnogenus Entobia devonica

Many attempts have been made by ichnologists to match bioerosion traces to their respective tracemakers. This task has been considered difficult, especially for fossil samples. The present study demonstrates that the Australian bioeroding sponge Aka paratypica can generate a cavity similar to the ichnospecies Entobia devonica. The modern sponge and its cavity are redescribed and compared to the fossil boring. A. paratypica has white fistules and soft, mucoid endosomal tissue. Spicules are stout oxeas with often telescoped or mucronate tips. Observed borings of A. paratypica are rounded and cavernous, with canals and apertures radiating from the chambers in all directions. It was noted that the internal openings of such canals are covered with porous nodules, which may act as sieves against larger particles or intruding endofauna. No obvious microsculpturing was observed in the erosion scars. A. paratypica borings are analogous to ancient E. devonica borings, which to date were only known from the fossil record.

The influence of grazing on vegetation, soil properties and stream discharge in a small Dartmoor catchment, southwest England, UK

AbstractIntensive grazing has been responsible for environmental degradation of moorland landscapes over the last 50 years. Anecdotal evidence on Dartmoor, UK, for example, has suggested that it is particularly associated with a greater frequency of large floods, lower baseflow and a greater occurrence of erosion. A study was therefore conducted at Holne Moor, a small catchment on east Dartmoor, to investigate the impacts of grazing animals on hillslope hydrology and stream discharge. The vegetation in the study area ranged from heather (Calluna vulgaris), in areas with low grazing intensity, to short grass with occasional erosion scars visible associated with larger sheep numbers. The physical characteristics of the topsoil beneath heather species were very different compared with short grass. This was not due so much to the direct physical impact of grazing animals, but indirectly to the chemical and biological differences brought about by changes in vegetation response and soil structure. The experiment at Holne Moor indicated that soil water content on the hillslope was linked directly to the stream's rainfall–runoff response via the soil water pathways. In relatively dry conditions, the soil water content is mainly determined by local factors such as vegetation. In wet periods, non‐local influences such as slope and contributing area are more important. A soil water content threshold of around field capacity separated the two conditions. A comparison between soil physical properties and soil moisture under different vegetation types indicated that this ‘runoff’ threshold between dry and wet states is lower in heavily grazed areas. It is argued that more intense grazing causes conditions suited to the increased delivery of soil water to rapid flowpaths such as sheep tracks and other rapid routes which connect the source of this hillslope water to the contributing areas during large floods. Any alteration of vegetation and soil properties due to management causes a substantial increase in ‘active’ source areas and therefore discharge during large storm events even before any erosion occurs. Copyright © 2006 John Wiley & Sons, Ltd.

Validation of a region-wide model of landslide susceptibility in the Manawatu–Wanganui region of New Zealand

Since European settlement 160 years ago, much of the indigenous forest in New Zealand hill country has been cleared for pastoral agriculture, resulting in increased erosion and sedimentation. To prioritise soil conservation work in the Manawatu–Wanganui region, we developed a model of landslide susceptibility. It assigns high susceptibility to steep land not protected by woody vegetation and low susceptibility everywhere else, following the commonly used approach for identifying inappropriate land use. A major storm on 15–16 February 2004 that produced many landslides was used to validate the model. The model predicted hills at risk to landsliding with moderate accuracy: 58% of erosion scars in the February storm occurred on hillsides considered to be susceptible. The model concept of slope thresholds, above which the probability of landsliding is high and below which the probability is low, is not adequate because below 30° the probability of landsliding is approximately linearly related to slope. Thus, reforestation of steep slopes will need to be combined with improved vegetation management for soil conservation on moderate slopes to significantly reduce future landsliding.

Shore platform morphology on a rapidly uplifting coast, Wellington, New Zealand

AbstractThe coast of Wellington, New Zealand, is tectonically active and contains a series of uplifted and contemporary shore platforms that are developed in Triassic Greywacke. The platform profiles are rugged with relief of metre scale common. The surveyed platforms were formed at, and at two distinct levels 1–1·5 and 2–2·5 m above, mean sea level. They range in width up to 70 m and are highly fractured with fracture densities in excess of 20[sol ]m2 common. The rate of development of these platforms is rapid, with lateral erosion rates of up to 0·15 m[sol ]yr calculated, allowing platform development to occur over centennial scales. Even given this rapid development, continued instantaneous uplift of the coast has meant they are unable to reach an equilibrium state, whereby the effectiveness of wave processes in removing material is reduced by platform extension. The co‐seismic uplift means that the rear of the platforms is raised beyond the limits of marine process and has become an area of deposition. Although no direct process measurements were made the highly fractured nature of the bedrock appears to play a major role in platform evolution, with wave processes being easily able to pluck blocks as evidenced by fresh erosion scars and active gravel beaches at the rear of many platforms. This coast therefore represents an extremely dynamic youthful shore platform environment, where the processes of marine abrasion can be observed over historical timescales. Copyright © 2005 John Wiley & Sons, Ltd.

Study by Confocal Laser Scanning Microscopy of the Influence of Hydrogels on the Wound Healing Rate after Mechanical Corneal Injury

Laser assisted refractive surgery is a common procedure for the correction of visual defects. However, this technique is sometimes associated with complications such as recurrent erosion scars or late-onset corneal haze formation due to irregular wound healing. In order to improve the risk/benefit ratio of this surgery, a better understanding of the wound healing process is absolutely necessary. The aim of the present study was to investigate in an animal model the influence of biopolymeric hydrogels in the modulation of the wound healing. Mechanical wounds were generated in rabbit cornea with the aid of an Algerbrush burr. The closure of the wound was monitored after staining with fluorescein by means of a confocal microscope. A hydrogel based on 1% xanthan gum stimulated significantly corneal wound healing whereas other viscosified solutions or hydrogels based on lower concentrations of xanthan gum or on hyaluronic acid did not promote wound healing.

The slurry erosion behaviour of high velocity oxy-fuel (HVOF) sprayed aluminium bronze coatings

This paper investigates the erosion aspects of a novel high velocity oxy-fuel (HVOF) sprayed aluminium bronze coating under sand particle impingement conditions, using a free-jet impingement erosion rig. Erodents at various kinetic energies (0.1–0.8 μJ) and impingement angles (30, 60 and 90°) were used to simulate actual service conditions. Gravimetric measurements, surface profilometry and microscopy techniques were utilised to determine both the erosion rate and the mechanisms of coating failure. The erosion rate of the coating was found to be comparable to bulk 90/10 cupro-nickel (C70600) and about twice that of Marinel and AISI 316L stainless steel. These results suggest that HVOF aluminium bronze coatings are suitable candidates for marine applications. Analysis of the erosion scars suggest that coating erosion occurred by a combination of cutting wear, plastic deformation, and crack propagation at splat boundaries (brittle oxides) leading to the detachment of coating splats, cutting wear was found to be the most dominant. The cutting process was dominated by smaller particle impacts. The number of these particles which cause damage appears to be a function of kinetic energy.