Decrease In Erosion Rate Research Articles

Suspended sediment yield and climate change in Kamchatka, Far East of Russia

Abstract. Key factors of sediment yield formation and variability in the Kamchatsky Krai are relief characteristics and climate (especially precipitation). The last research in climate change in Kamchatka demonstrates climate warming – mean annual air temperature has increased on 1.5 ∘C during the period from 1951 to 2009 in average (the maximum increase was revealed in the west of Kamchatka and in the Kamchatka River valley, the minimum one – in the extreme south and north). Decrease of annual precipitation was observed at the same period. In addition frequency and intensity of precipitation is growing. Thereby described climate changes in Kamchatka influence on sediment yield characteristics directly (influence of precipitation on surface washout formation) and indirectly (through water runoff and hydrological regime of rivers changes). Analysis of spatio-temporal variability in suspended sediment yield demonstrated decrease since late 1970–early 1980 in the most part of rivers in the Kamchatsky Krai. Revealed fluctuations demonstrate very good coincidence with precipitation amount variability. Decrease of precipitation leads to corresponding diminution of rainfall erosive factor in the territory which is the key factor of suspended sediment yield formation and variability in rivers in the Kamchatsky Krai. The value of reduction varies from 1 % to 45 % and involves decrease of erosion rates in the territory. Thereby climate change influences on suspended sediment yield in multiple-valued way. Income of friable volcanic deposits on the catchment surface is the key factor of suspended sediment yield formation and variability in some river basins under the impact of volcanic eruptions, and in combination with raising precipitation it can lead to catastrophic increase of sediment yield.

Detecting landscape transience with in situ cosmogenic 14C and 10Be

Abstract Constraining past variations in rates of erosion remains a key challenge in geomorphology, as estimates of erosion rate on different timescales must be bridged. The Late Pleistocene to Holocene represents a key timescale for studying landscape transience, as climatic change, increasing anthropogenic activity, and/or tectonic activity changed the rate of surface processes in many landscapes. Few chronometers are suitable for studying surface processes and landscape transience on these timescales, but, although not yet widely used, in situ 14C holds much promise due to its appropriate half-life of 5.7 kyr. Furthermore, by pairing in situ 14C with a stable or longer-lived nuclide, such as 10Be, 21Ne or 26Al, it is possible to compare surface process rates on distinctly different timescales. In this paper, we explore how these paired chronometers can be used to study landscape transience in non-glacial landscapes on Late Pleistocene to Holocene timescales. Indeed, we find that paired measurements of in situ 14C and a long-lived cosmogenic nuclide (CN) in samples from eroding landscapes enable the detection of changes in erosion rate during the Late Pleistocene to Holocene, if the increase or decrease in erosion rate was larger than a factor of two, and the landscape is eroding at rates that are typical for fluvial landscapes (5–500 mm/kyr). Similarly, detecting changes in catchment-wide denudation rates using paired CN measurements in stream-sediment samples is also possible in catchments with suitable conditions, such as short sediment transport times, minimal erosion from deep-seated mass movement, etc. (von Blanckenburg, 2006).

Wetting and Erosion of ZrO2-Graphite Refractory by CaO-SiO2 and CaO-Al2O3-Based Mold Slags for Submerged Entry Nozzle

To moderate the erosion in a slag-line zone and extend the service life of a submerged entry nozzle during continuous casting of high-Mn and high-Al steel, the current study developed a low-reaction CaO-Al2O3-based slag with lower SiO2 and higher Al2O3 contents than that of conventional CaO-SiO2-based slag. The static sessile drop technique and dynamic rotating cylinder method were utilized to investigate the erosion behavior of ZrO2-graphite refractory by the above slags. The main results indicated that silicate-based slag could wet the ZrO2-graphite substrate completely, while the aluminate-based slag spread rapidly in the first 20 minutes, and then a slag drop with an unchanged profile formed on the substrate. The equilibrium contact angles with the substrate at 1623 K were 0 and 79 deg for the CaO-SiO2 and CaO-Al2O3 based slags, respectively. The comparison of the influences of the rotating speed and the temperature revealed that the decrease of erosion rate could be realized by the developed slag. An examination of ZrO2-saturation limit also indicated that the low-reaction slag could dissolve much more ZrO2 oxidation, accompanied by a less-negative effect on the viscosity of the molten slag.

Contemporary Trend in Erosion of Arable Ordinary Chernozems (Haplic Chernozems (Pachic)) within the Volga Upland (Saratov Oblast, Russia)

The current trend in erosion rate of ordinary chernozems in Saratov oblast has been assessed. Detailed studies have been performed in a small catchment area of the Bolshoi Kolyshley River (Medveditsa River basin) using the radiocesium and soil-morphological methods. Data of long-term hydrometeorological observations in the region, reported results of observations of water runoff and soil loss on the runoff plots of the South-Eastern Research Institute of Agriculture (Saratov oblast), results of analysis of the grain size and mineral composition of stratozems developed on the catchment valley bottom were also used for analysis. The quantification of sedimentation rate in the valley bottom during two time windows (1963–1986 and 1986–2017) based on the sediment dating using 137Cs as a chronomarker indicates their decrease at least in 4–6 times after 1986, which points to a proportional reduction in erosion rate on the plowed slopes of the catchment area. The analysis of the temporal variability of suspended yields in the regional rivers (Medveditsa and Khopyor) during the period from 1940 to the present time allows us to draw an analogous conclusion for the Volga Upland within Saratov oblast. The decrease in the erosion rate of ordinary chernozems could be mainly caused by the reduction in water runoff from slopes during the spring snowmelt because of reduction in soil freezing depth against the background of rising air temperature in winter and spring. This decrease in erosion rate during the snowmelt period was not balanced by the regional increase in rainfall erosion related to some increase in the rate of runoff-forming rainfalls. In the part of Saratov oblast, located within the Volga Upland, where the studied catchment is situated, on the contrary, even a reduction in the frequency of rains with a rainfall depth of more than 30 mm occurred over the last decades. The reduction in the cultivated land area since the late 1980s because of the abandonment of plowlands on the steepest slopes also contributed to the decrease in total soil loss by erosion at the river basin scale. Within the studied small catchment, the share of perennial grasses in crop rotations increased after 1986, which also led to reduction of the rate of erosion of ordinary chernozems.

Contribution of climate and land cover changes to reduction in soil erosion rates within small cultivated catchments in the eastern part of the Russian Plain during the last 60 years

The eastern part of the Russian Plain is an important agricultural region of European Russia with high proportion of cultivated lands in the steppe, forest-steppe and forest (southern part) landscape zones. Soil erosion is the main process of land degradation and surface water contamination there. Climate and land cover changes have been observed in this region during the last 30 years. However, field quantitative assessments of soil erosion rates are not available for the eastern part of European Russia due to the lack of monitoring data as well as the evaluation of erosion/deposition processes in cultivated catchments using other field methods. Three representative small cultivated catchments with high (> 80%) proportion of cultivated lands were selected in the forest (southern part), forest-steppe and steppe zones of the study region to evaluate sedimentation rates in dry valley bottoms of the catchments for two-time intervals (1963–1986 and 1987–2016) based on the application of the bomb-derived and Chernobyl-derived 137Cs isotope for sediment dating. The 3–4 depth 137Cs profiles were used to assess the sedimentation rates within the each investigated catchment. It was established that the sedimentation rates have considerably decreased (at least 2–3 times) over the last 30 years compared to 1963–1986 in all the investigated catchments. This is in agreement with results of erosion rate calculations using erosion models for the forest zone, however not consistent with erosion rates assessments for the forest-steppe and steppe zones. According to the model calculations, erosion rates show a slight decrease in the forest-steppe zone and increase in the steppe zone. The reduction in surface runoff during snowmelt period is one of the reasons for decrease in erosion rates within cultivated slopes for all the investigated catchments. The increase in proportion of perennial grasses in the regional crop rotation is another important reason for the decrease in erosion rates for the catchment located in the south of the forest zone. The importance of land cover changes in a major decrease of soil losses from the cultivated fields of the investigated catchments located in the forest-steppe and steppe zones cannot be identified due to the lack detailed information about crop rotation for those particular sites. However, available regional information about crop rotation changes for the two-time intervals (1960–1980 and 1996–2012) do not explain very high reduction in sedimentation rates in the dry valley bottoms after 1986.

Exponentially decreasing erosion rates protect the high-elevation crests of the Himalaya

Glacierised mountains erode rapidly due to efficient glacial erosion around the long-term equilibrium line altitude (ELA), as well as by intense frost-cracking action. This ‘glacial buzzsaw’ is hypothesised to limit mountain heights globally to within about 1.5 km of the local ELA. However, we show that the high Himalaya contrasts this picture with a precipitous decline in the erosion rate at its high-elevation crests. We obtain headwall-erosion rates at eight Himalayan debris-covered glaciers from estimates of the corresponding supraglacial debris flux. The data reveal large variation of erosion rates in the range of 0.04–1.0 mm/yr. We establish that this variability is controlled by an exponential decrease in erosion rate with decreasing mean annual temperature of the headwall due to a decline in frost-cracking intensity at low temperatures. The implied order of magnitude decline of erosion rate at the high altitude of the Himalaya, apart from the pattern and magnitude of uplift, may be crucial for generating relief, and for protecting the spectacularly high crests from the action of ‘glacial buzzsaw’.

Modelling the Hydro‐Sedimentary Dynamics of a Mediterranean Semiarid Ungauged Watershed Beyond the Instrumental Period

AbstractThe development of reliable tools to quantify long‐term sediment budgets is critical to establish adequate environmental and management policies in semiarid Mediterranean regions. In this study, we apply a multidisciplinary methodology to estimate water and sediment yields in ungauged Mediterranean watersheds over a period of scarce instrumental data (i.e. second half of 19th and first half of 20th centuries). Runoff and precipitation reconstructions have been obtained using an integrative approach involving synoptic reanalysis models, regional climatic datasets, historical archives and palaeoflood proxies from natural archives. The resulting hydrological reconstruction has been implemented on a hydro‐sedimentary distributed model (i.e. TETIS) to understand the hydro‐sedimentary dynamics in the studied watershed. We highlight that, in our study area, regional‐data (instrumental, historical and sedimentary) based models show higher accuracy in the sediment yield and runoff reconstruction than synoptic reanalysis climate models. The modelled sedimentary dynamics for the studied period respond to a complex interplay between human activities and climate variability. During the 19th century deforestation and grazing activities combined with higher frequency on extreme runoff events resulted in higher runoff and sediment yield in the period 1863–1900. Over the 20th century, reduced precipitation and land abandonment led to a decrease in erosion rates and sediment yield although increased in 1945–1960 coinciding with a period of higher frequency of heavy rainfalls. This hydrological response to climate and human activities in the study watershed improves our understanding of plausible future trends of environmental degradation in small Mediterranean watersheds under different land use and climate change scenarios.This article includes supporting information which features an explanation of GILMCLIM downscaling model, The precipitation series resulting from the reanalysis data (Figure S1), an analysis of the different precipitation series used (Table S1) and an extensive explanation of how the relation between Puentes and Valdeinfierno reservoirs was considered. Copyright © 2016 John Wiley & Sons, Ltd.

High temperature erosion behavior of spark plasma sintered ZrB 2 -SiC composites

Abstract Damage of structural components of hypersonic vehicles by atmospheric particles demands thorough understanding on their wear behavior. In the present work, dense ZrB2-SiC (10, 20, and 30 vol%) composites are prepared by spark plasma sintering at 55 MPa in two stages: 1400 °C for 6 min followed by 1600 °C for 2 min. With increase in SiC content, microstructures of sintered composites reveal strongly bonded ZrB2 grains with SiC particles. A combination of maximum hardness of 23 GPa, elastic modulus of 398 GPa and fracture toughness of 5.4 MPa m1/2 are obtained for the composite containing 30 vol% SiC particles. It is found that cracks are bridged or deflected by SiC particles in the composites. When the composites are subjected to SiC particle erosion at 800 °C, a 14% decrease in erosion rate is obtained with increase in SiC content from 10 to 30 vol%. The formation of large extent of boro-silicate rich viscous surface on eroded surfaces is attributed to reduced fracture or removal of ZrB2 grains of the composites with increased SiC content.

Local topography and erosion rate control regolith thickness along a ridgeline in the Sierra Nevada, California

AbstractThe ridgelines of mountain ranges are a source of geomorphic information unadulterated by the arrival of sediment from upslope. Studies along ridgecrests, therefore, can help identify and isolate the controls on important regolith properties such as thickness and texture. A 1.5 km section of ridgeline in the Sierra Nevada (CA) with a tenfold decrease in erosion rate (inferred from ridgetop convexity) provided an opportunity to conduct a high‐resolution survey of regolith properties and investigate their controls. We found that regolith along the most quickly eroding section of the ridge was the rockiest and had the lowest clay concentrations. Furthermore, a general increase in regolith thickness with a slowing of erosion rate was accompanied by an increase in biomass, changes in vegetation community, broader ridgeline profiles, and an apparent increase in total available moisture. The greatest source of variation in regolith thickness at the 10–100 m scale, however, was the local topography along the ridgeline, with the deepest regolith in the saddles and the thinnest on the knobs. Because regolith in the saddles had higher surface soil moisture than the knobs, we conclude that the hydrological conditions primarily driven by local topography (i.e. rapid vs. slow drainage and water‐storage potential) provide the fundamental controls on regolith thickness through feedbacks incorporating physical weathering by the biota and chemical weathering. Moreover, because the ridgeline saddles are the uppermost extensions of first‐order valleys, we propose that the fluvial network affects regolith properties in the furthest reaches of the watershed. Copyright © 2015 John Wiley & Sons, Ltd.

Constraints on the tectonic and landscape evolution of the Bhutan Himalaya from thermochronometry

The observed geomorphology and calculated thermal histories of the Bhutan Himalaya provide an excellent platform to test ideas regarding the influence of tectonics and climate on the evolution of a convergentmountain range. However, little consensus has been reached regarding the late Cenozoic history of the Bhutan Himalaya. Some researchers have argued that observed geologic relationships show slowing deformation rates, such that the range is decaying from a geomorphic perspective, while others see the range as growing and steepening. We suggest that a better understanding is possible through the integrated interpretation of geomorphic and thermochronometric data from the comparison of predictions from models of landscape evolution and thermal-kinematic models of orogenic systems. New thermochronometric data throughout Bhutan aremost consistent with a significant decrease in erosion rates, from2 to 3 km/Ma down to 0.1–0.3 km/Ma, around 6–4Ma. We interpret this pattern as a decrease in rock uplift rates due to the activation of contractional structures of the Shillong Plateau, an uplifted region approximately 100 km south of Bhutan. However, low-relief, fluvial landscapes throughout the Bhutanese hinterland record a late pulse of surface uplift likely due to a recent increase in rock uplift rates. Constraints from our youngest thermochronometers suggest that this increase in rock uplift and surface uplift occurred within the last 1.75Ma. These results imply that the dynamics of the Bhutan Himalaya and Shillong Plateau have been linked during the late Cenozoic, with structural elements of both regions active in variable ways and times over that interval.

The effect of fluid viscosity on the erosion wear behavior of Ti(C,N)-based cermets

The effect of fluid viscosity on the erosion wear behavior of Ti(C,N)-based cermets was investigated in this study. Five viscous fluids containing 5wt% Al2O3 were used as the experimental medium. Besides, the effect of pure fluid without erodents was also investigated. The results indicate that fluid viscosity has a significant effect on the erosion process in the slurry flow. With the increase of fluid viscosity, the erosion wear rate decreases remarkably. Fluid viscosity leads to peeling off of broken debris and debonding on the surface, and the tearing effect is much more obvious with the increase of fluid viscosity. Fluid viscosity restricts the movement of solid erodents, and reduces the impingement energy, finally results in the decrease of erosion rate. Additionally, the single factor of fluid viscosity doesn’t have obvious effect on the erosion behavior of cermets, and the main effect of fluid viscosity is to work by influencing the movement of erodents in the fluid, and then indirectly affects the process of material failure.

Rock uplift and erosion rate history of the Bergell intrusion from the inversion of low temperature thermochronometric data

The Bergell intrusion (European Alps) was one of the first locations where thermochronometry was used to resolve changes in erosion rate, yet, relating these changes to variations in climate or in local tectonics remains challenging. One approach that enables changes in erosion rate to be related to changes in climate or rock uplift rate is to utilize landscape evolution models, as topographic response to these forcing parameters is unique. Furthermore, low temperature thermochronometric systems have the potential to resolve topography through time and thus topographic response. We present new (U-Th)/He data for samples collected across 2 km of relief from the Bergell. The ages range from ∼2 to ∼16 Ma and define an age elevation with an apparent exhumation rate of 0.1 km/Myr. In order to infer erosion rates, we use a thermokinematic model to solve the heat equation in the crust, track material points through time and predict thermochronometric data. Paleo-topography and erosion rate are parameterized using the stream power model. We find that rock uplift rates were 0.4 km/Myr from ∼25 to ∼20 Ma and subsequently decreased to 0.05 km/Myr. This results in a gradual decrease in erosion rate from rates of 0.4 to 0.1 km/Myr. A recent increase in rock uplift rate at ∼4 Ma to ∼0.6 km/Myr is required to explain the youngest ages and high topographic relief.

Temperature effects of sputtering of Langmuir–Blodgett multilayers

Time-of-flight secondary ion mass spectrometry (TOF-SIMS) and atomic force microscopy (AFM) are employed to characterize a wedge-shaped crater eroded by a 40 keV C(60) (+) cluster ion beam on an organic thin film of 402 nm of barium arachidate (AA) multilayers prepared by the Langmuir-Blodgett (LB) technique. Sample cooling to 90 K was used to help reduce chemical damage, improve depth resolution and maintain constant erosion rate during depth profiling. The film was characterized at 90 K, 135 K, 165 K, 205 K, 265 K and 300 K. It is shown that sample cooling to 205 K or lower helps to inhibit erosion rate decay, whereas at 300 K and 265 K the erosion rate continues to drop after 250 nm of erosion, reaching about half of the initial value after removal of the entire film. Depth profiles are acquired from the SIMS images of the eroded wedge crater. The results suggest that sample cooling only slightly improves the altered layer thickness, but eliminates the decrease in erosion rate observed above 265 K.

10Be‐derived assessment of accelerated erosion in a glacially conditioned inner gorge, Entlebuch, Central Alps of Switzerland

ABSTRACTInner gorges often result from the propagation of erosional waves related to glacial/interglacial climate shifts. However, only few studies have quantified the modern erosional response to this glacial conditioning. Here, we report in situ 10Be data from the 64 km2 Entlen catchment (Swiss Alps). This basin hosts a 7 km long central inner gorge with two tributaries that are >100 m‐deeply incised into thick glacial till and bedrock. The 10Be concentrations measured at the downstream end of the gorge yield a catchment‐wide erosion rate of 0.42 ± 0.04 mm yr‐1, while erosion rates are consistently lower upstream of the inner gorge, ranging from 0.14 ± 0.01 mm yr‐1 to 0.23 ± 0.02 mm yr‐1. However, 10Be‐based sediment budget calculations yield rates of ~1.3 mm yr‐1 for the inner gorge of the trunk stream. Likewise, in the two incised tributary reaches, erosion rates are ~2.0 mm yr‐1 and ~1.9 mm yr‐1. Moreover, at the erosional front of the gorge, we measured bedrock incision rates ranging from ~2.5 mm yr‐1 to ~3.8 mm yr‐1. These rates, however, are too low to infer a post‐glacial age (15–20 ka) for the gorge initiation. This would require erosion rates that are between 2 and 6 times higher than present‐day estimates. However, the downcutting into unconsolidated glacial till favored high erosion rates through knickzone propagation immediately after the retreat of the LGM glaciers, and subsequent hillslope relaxation led to a progressive decrease in erosion rates. This hypothesis of a two‐ to sixfold decrease in erosion rates does not conflict with the 10Be‐based erosion rate budgets, because the modern erosional time scale recorded by 10Be cover the past 2–3 ka only. These results point to the acceleration of Holocene erosion in response to the glacial overprint of the landscape. Copyright © 2012 John Wiley & Sons, Ltd.

Erosion of tungsten-doped amorphous carbon films exposed to deuterium plasmas

Tungsten-doped amorphous carbon films with 0–9.5at.% W concentration were produced by magnetron sputtering and exposed to deuterium plasmas applying different ion energies and fluences. The partial C and W erosion rates were determined from the C and W areal density changes, respectively, measured by Rutherford backscattering spectrometry. For W-doped films the erosion rate decreases with increasing W concentration and incident fluence. During deuterium plasma exposure carbon is preferentially eroded while tungsten atoms accumulate at the surface leading to the formation of a W-rich layer, which decreases the removal efficiency and leads to a continuous decrease of the erosion rate. At 30eV/D incident energy a relatively compact W-rich layer is formed on films with higher (⩾5%) W concentration which protects the carbon underneath from further erosion. For films with lower (⩽2.5%) W concentration the erosion rate decreases, but the erosion process does not stop because the W-rich layer has a high porosity. Reactive neutral species can penetrate through this porous layer and react with carbon atoms below it. At 100eV/D incident energy the erosion rate is significantly higher compared with 30eV/D. In addition, slight tungsten sputtering is observed due to the presence of a small fraction of D+ plasma ions which impinge with 300eV/D.

Early Mars hydrology: 2. Hydrological evolution in the Noachian and Hesperian epochs

[1] Mars was warmer and wetter during the early to middle Noachian, before a hydrologic and climatic transition in the late Noachian led to a decrease in erosion rates, a change in valley network morphology, and a geochemical shift from phyllosilicate to sulfate formation that culminated in the formation of widespread sulfate-rich sedimentary deposits in Meridiani Planum and the surrounding Arabia Terra region. This secular evolution was overprinted by episodic and periodic variability, as recorded in the fluvial record, sedimentary layering, and erosional discontinuities. We investigate the temporal evolution of Martian groundwater hydrology during the Noachian and early Hesperian epochs using global-scale hydrological models. The results suggest that the more active hydrological cycle in the Noachian was a result of a greater total water inventory, causing a saturated near-surface and high precipitation rates. The late Noachian hydrologic, climatic, and geochemical transition can be explained by a fundamental shift in the hydrological regime driven by a net loss of water due to impact and solar wind erosion of the atmosphere. Following this transition, the water table retreated deep beneath the surface, except in isolated regions of focused groundwater upwelling and evaporation, producing the playa evaporites in Meridiani Planum and Arabia Terra. This long-term evolution was modulated by shorter-term climate forcing in the form of periodic and chaotic variations in the orbital parameters of Mars, resulting in changes in the volume of water sequestered in the polar caps and cryosphere. This shorter-term forcing can explain the observed periodic and bundled sedimentary layering, erosional unconformities, and evidence for a fluctuating water table at Meridiani Planum.

Comonomer Compositional Distribution, Physical Properties, and Enzymatic Degradability of Bacterial Poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate) Copolyesters

Poly(3-hydroxybutyrate-co-3-hydroxy-4-methylvalerate) (P(3HB-co-3H4MV)) was synthesized by using Ralstonia eutropha strain PHB(-)4 (PHA-negative mutant) harboring with the N149S/D171G double mutation of PHA synthase gene from Aeromonas caviae (PhaC(Ac) NSDG mutant) with 4-methylvaleric acid and fructose as the carbon sources. Because the microbially synthesized P(3HB-co-3H4MV) samples were found to have broad comonomer compositional distribution, P(3HB-co-3H4MV) samples with 3H4MV content of 7, 11, and 35 mol % were fractionated into several fractions with different comonomer composition ranging from 2 to 47 mol % by using a chloroform/n-hexane mixture. It was confirmed that a series of well-fractionated P(3HB-co-3H4MV) samples had a statistically random distribution. Physical properties and structure of the fractionated P(3HB-co-3H4MV) random copolymers were investigated. Both the melting temperature and glass-transition temperature of P(3HB-co-3H4MV) copolymers decreased with an increase in the 3H4MV composition. The degree of X-ray crystallinity of fractionated P(3HB-co-3H4MV) films decreased from 60 to 13% as the 3H4MV fraction increased from 0 to 39 mol %. Enzymatic degradation test for fractionated P(3HB-co-3H4MV) films was carried out at 37 degrees C in the presence of PHB depolymerase from Ralstonia pickettii T1. The rates of enzymatic erosion markedly increased with an increase in the 3H4MV composition to reach the highest one at 7 mol % of 3H4MV, followed by a decrease in erosion rate.

Influence of rock mass strength on the erosion rate of alpine cliffs

AbstractCollapse of cliff faces by rockfall is a primary mode of bedrock erosion in alpine environments and exerts a first‐order control on the morphologic development of these landscapes. In this work we investigate the influence of rock mass strength on the retreat rate of alpine cliffs. To quantify rockwall competence we employed the Slope Mass Rating (SMR) geomechanical strength index, a metric that combines numerous factors contributing to the strength of a rock mass. The magnitude of cliff retreat was calculated by estimating the volume of talus at the toe of each rockwall and projecting that material back on to the cliff face, while accounting for the loss of production area as talus buries the base of the wall. Selecting sites within basins swept clean by advancing Last Glacial Maximum (LGM) glaciers allowed us to estimate the time period over which talus accumulation occurred (i.e. the production time). Dividing the magnitude of normal cliff retreat by the production time, we calculated recession rates for each site. Our study area included a portion of the Sierra Nevada between Yosemite National Park and Lake Tahoe. Rockwall recession rates determined for 40 alpine cliffs in this region range from 0·02 to 1·22 mm/year, with an average value of 0·28 mm/year. We found good correlation between rockwall recession rate and SMR which is best characterized by an exponential decrease in erosion rate with increasing rock mass strength. Analysis of the individual components of the SMR reveals that joint orientation (with respect to the cliff face) is the most important parameter affecting the rockwall erosion rate. The complete SMR score, however, best synthesizes the lithologic variables that contribute to the strength and erodibility of these rock slopes. Our data reveal no strong independent correlations between rockwall retreat rate and topographic attributes such as elevation, aspect, or slope angle. Copyright © 2009 John Wiley & Sons, Ltd.

Influence of microstructure on slurry erosive wear characteristics of laser surface alloyed 13Cr–4Ni steel

The significance and effect of microstructure and hardness on the slurry erosion rates of laser surface modified 13Cr–4Ni steel are discussed in this paper. Commercial Stellite 6 and Colmonoy 88 powders were deposited on 13Cr–4Ni steel using two stage processes of laser surface alloying (LSA). Series of slurry erosive wear tests have been conducted on 13Cr–4Ni steel and LSA deposits by varying angles of impingement for a constant slurry velocity and also at different slurry velocities for two different angles of impingements. Characterization of deposits have revealed that the presence of hard complex secondary phases, which in turn have lead to 1.5–2-fold enhancement of surface hardness of LSA deposits. The erosive wear rates of LSA deposits are found to be increased linearly with angle of impingement and also showed power law character with slurry velocity. Colmonoy 88 deposits showed at least two-fold decrease in erosion rates when compared to 13Cr–4Ni steel for all test conditions. It is found that micro cutting and deep crater formation are the two main material removal mechanisms for substrate and Stellite 6 deposits, whereas progressive fracturing of secondary phases along with deep crater formation are instrumental in Colmonoy 88 deposits.

鉄鋼材料の長時間のキャビテーション壊食

Cavitation erosion often occurs in fluid machinery and piping systems of industrial plants. The erosion damage causes a reduction of performance, noise and a leak accident of fluid machine. In this study, cavitation erosion tests were carried out for cast iron FC250 and stainless steel SUS304 under the condition of the stationary specimen test method using the vibratory apparatus specified by ASTM G32-03. Test results are compared to our previous paper of S15C and discussed in terms of the maximum depth of erosion, the erosion rate and the eroded shape of test specimen after long exposure. It was found that the erosion rate decreases and the maximum depth increases with erosion time with a power of about 0.5 after long exposure regardless of the kind iron and steel.