scholarly journals Sediment size on talus slopes correlates with fracture spacing on bedrock cliffs: Implications for predicting initial sediment size distributions on hillslopes

2020 ◽  
Author(s):  
Joseph P. Verdian ◽  
Leonard S. Sklar ◽  
Clifford S. Riebe ◽  
Jeffrey R. Moore
Keyword(s):  
Particle Size ◽  
Size Distribution ◽  
Characteristic Size ◽  
Residence Times ◽  
Size Distributions ◽  
Initial Size ◽  
Fracture Spacing ◽  
Rock Fragments ◽  
Sediment Size ◽  
Wide Range

Abstract. The detachment of rock fragments from fractured bedrock on hillslopes creates sediment with an initial size distribution that sets the upper limits on particle size for all subsequent stages in the life of sediment in landscapes. We hypothesize that the initial size distribution should depend on the size distribution of latent sediment (i.e., blocks defined by through-going fractures) and weathering of sediment before or during detachment (e.g., disintegration along crystal grain boundaries). However, the initial size distribution is difficult to measure, because the interface across which sediment is produced is often shielded from view by overlying soil. Here we overcome this limitation by comparing fracture spacings measured from exposed bedrock on cliff faces with particle size distributions in adjacent talus deposits at 15 talus-cliff pairs spanning a wide range of climates and lithologies in California. Median fracture spacing and particle size vary by more than tenfold and correlate strongly with lithology. Fracture spacing and talus size distributions are also closely correlated in central tendency, spread, and shape, with b-axis diameters showing the closest correspondence with fracture spacing at most sites. This suggests that weathering has not modified latent sediment either before or during detachment from the cliff face. In addition, talus has not undergone much weathering after deposition and is slightly coarser than the latent sizes, suggesting that it contains some fractures inherited from bedrock. We introduce a new conceptual framework for understanding the relative importance of latent size and weathering in setting initial sediment size distributions in mountain landscapes. In this framework, hillslopes exist on a spectrum defined by the ratio of two characteristic timescales: the residence time in saprolite and weathered bedrock, and the time required to detach a particle of a characteristic size. At one end of the spectrum, where weathering residence times are negligible, the latent size distribution can be used to predict the initial size distribution. At the other end of the spectrum, where weathering residence times are long, the latent size distribution can be erased by weathering in the critical zone.

scholarly journals Sediment size on talus slopes correlates with fracture spacing on bedrock cliffs: implications for predicting initial sediment size distributions on hillslopes

2021 ◽  
Vol 9 (4) ◽  
pp. 1073-1090
Author(s):  
Joseph P. Verdian ◽  
Leonard S. Sklar ◽  
Clifford S. Riebe ◽  
Jeffrey R. Moore
Keyword(s):  
Particle Size ◽  
Size Distribution ◽  
Characteristic Size ◽  
Residence Times ◽  
Size Distributions ◽  
Initial Size ◽  
Fracture Spacing ◽  
Rock Fragments ◽  
Sediment Size ◽  
Wide Range

Abstract. The detachment of rock fragments from fractured bedrock on hillslopes creates sediment with an initial size distribution that sets the upper limits on particle size for all subsequent stages in the evolution of sediment in landscapes. We hypothesize that the initial size distribution should depend on the size distribution of latent sediment (i.e., fracture-bound blocks in unweathered bedrock) and weathering of blocks both before and during detachment (e.g., disintegration along crystal grain boundaries). However, the initial size distribution is difficult to measure because the interface across which sediment is produced is often shielded from view by overlying soil. Here we overcome this limitation by comparing fracture spacings measured from exposed bedrock on cliff faces with particle size distributions in adjacent talus deposits at 15 talus–cliff pairs spanning a wide range of climates and lithologies in California. Median fracture spacing and particle size vary by more than 10-fold and correlate strongly with lithology. Fracture spacing and talus size distributions are also closely correlated in central tendency, spread, and shape, with b-axis diameters showing the closest correspondence with fracture spacing at most sites. This suggests that weathering has not modified latent sediment either before or during detachment from the cliff face. In addition, talus at our sites has not undergone much weathering after deposition and is slightly coarser than the latent sizes because it contains unexploited fractures inherited from bedrock. We introduce a new conceptual framework for understanding the relative importance of latent size and weathering in setting initial sediment size distributions in mountain landscapes. In this framework, hillslopes exist on a spectrum defined by the ratio of two characteristic timescales: the residence time in saprolite and weathered bedrock and the time required to detach a particle of a characteristic size. At one end of the spectrum, where weathering residence times are negligible, the latent size distribution can be used to predict the initial size distribution. At the other end of the spectrum, where weathering residence times are long, the latent size distribution can be erased by weathering in the critical zone.

The moment ratios of particle size distributions in some simple growth models

1980 ◽  
Vol 17 (4) ◽  
pp. 956-967 ◽  
Author(s):  
H. L. MacGillivray
Keyword(s):  
Particle Size ◽  
Size Distribution ◽  
Growth Model ◽  
Hazard Rate ◽  
Growth Models ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Initial Size ◽  
The Moment ◽  
Simple Growth

Important parameters of particle size distributions in dispersed systems in engineering and related fields are ratios of moments and inverse powers of these ratios, known as mean sizes. The variation in these parameters is examined for the simplest growth model in which the size distribution is translated, and the results for this process considered in relation to the problems of models of other growth processes. For initial size distributions with monotone hazard rate, the results are particularly significant, and the properties of the normalised moments of other distributions are also considered.

The moment ratios of particle size distributions in some simple growth models

1980 ◽  
Vol 17 (04) ◽  
pp. 956-967 ◽  
Author(s):  
H. L. MacGillivray
Keyword(s):  
Particle Size ◽  
Size Distribution ◽  
Growth Model ◽  
Hazard Rate ◽  
Growth Models ◽  
Size Distributions ◽  
Particle Size Distributions ◽  
Initial Size ◽  
The Moment ◽  
Simple Growth

Important parameters of particle size distributions in dispersed systems in engineering and related fields are ratios of moments and inverse powers of these ratios, known as mean sizes. The variation in these parameters is examined for the simplest growth model in which the size distribution is translated, and the results for this process considered in relation to the problems of models of other growth processes. For initial size distributions with monotone hazard rate, the results are particularly significant, and the properties of the normalised moments of other distributions are also considered.

Factors Influencing the Particle Size Distribution in an Abrasive Waterjet

1991 ◽  
Vol 113 (4) ◽  
pp. 402-411 ◽  
Author(s):  
T. J. Labus ◽  
K. F. Neusen ◽  
D. G. Alberts ◽  
T. J. Gores
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Cutting Speed ◽  
Target Material ◽  
Abrasive Waterjet ◽  
Sieve Analysis ◽  
Size Distributions ◽  
Mixing Process ◽  
Jet Mixing

A basic investigation of the factors which influence the abrasive jet mixing process was conducted. Particle size analysis was performed on abrasive samples for the “as-received” condition, at the exit of the mixing tube, and after cutting a target material. Grit size distributions were obtained through sieve analysis for both water and air collectors. Two different mixing chamber geometries were evaluated, as well as the effects of pressure, abrasive feed rate, cutting speed, and target material properties on particle size distributions. An analysis of the particle size distribution shows that the main particle breakdown is from 180 microns directly to 63 microns or less, for a nominal 80 grit garnet. This selective breakdown occurs during the cutting process, but not during the mixing process.

Effects of Multiple Impacts and Size Distribution of Particles on Erosion Predictions Using CFD

2007 ◽  
Author(s):  
Yongli Zhang ◽  
Brenton S. McLaury ◽  
Siamack A. Shirzai
Keyword(s):  
Experimental Data ◽  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Target Material ◽  
Average Particle ◽  
Multiple Impacts ◽  
Cfd Simulations ◽  
Erosion Damage ◽  
Wide Range

Erosion equations are usually obtained from experiments by impacting solid particles entrained in a gas or liquid on a target material. The erosion equations are utilized in CFD (Computational Fluid Dynamics) models to predict erosion damage caused by solid particle impingements. Many erosion equations are provided in terms of an erosion ratio. By definition, the erosion ratio is the mass loss of target material divided by the mass of impacting particles. The mass of impacting particles is the summation of (particle mass × number of impacts) of each particle. In erosion experiments conducted to determine erosion equations, some particles may impact the target wall many times and some other particles may not impact the target at all. Therefore, the experimental data may not reflect the actual erosion ratio because the mass of the sand that is used to run the experiments is assumed to be the mass of the impacting particles. CFD and particle trajectory simulations are applied in the present work to study effects of multiple impacts on developing erosion ratio equations. The erosion equation as well as the CFD-based erosion modeling procedure is validated against a variety of experimental data. The results show that the effect of multiple impacts is negligible in air cases. In water cases, however, this effect needs to be accounted for especially for small particles. This makes it impractical to develop erosion ratio equations from experimental data obtained for tests with sand in water or dense gases. Many factors affecting erosion damage are accounted for in various erosion equations. In addition to some well-studied parameters such as particle impacting speed and impacting angle, particle size also plays a significant role in the erosion process. An average particle size is usually used in analyzing experimental data or estimating erosion damage cases of practical interest. In petroleum production applications, however, the size of sand particles that are entrained in produced fluids can vary over a fairly broad range. CFD simulations are also performed to study the effect of particle size distribution. In CFD simulations, particle sizes are normally distributed with the mean equaling the average size of interest and the standard deviation varying over a wide range. Based on CFD simulations, an equation is developed and can be applied to account for the effect of the particle size distribution on erosion prediction for gases and liquids.

Determination of atmospheric aerosol particle size distribution and visibility using a mobile laboratory

1982 ◽  
Vol 60 (8) ◽  
pp. 1101-1107
Author(s):  
C. V. Mathai ◽  
A. W. Harrison
Keyword(s):  
Particle Size ◽  
Particle Size Distribution ◽  
Size Distribution ◽  
Atmospheric Aerosols ◽  
Suspended Particle ◽  
Aerosol Size Distribution ◽  
Size Distributions ◽  
Mobile Laboratory ◽  
Mean Values ◽  
The City

As part of an ongoing general research program on the effects of atmospheric aerosols on visibility and its dependence on aerosol size distributions in Calgary, this paper presents the results of a comparative study of particle size distribution and visibility in residential (NW) and industrial (SE) sections of the city using a mobile laboratory. The study was conducted in the period October–December, 1979. An active scattering aerosol spectrometer measured the size distributions and the corresponding visibilities were deduced from scattering coefficients measured with an integrating nephelometer.The results of this transit study show significantly higher suspended particle concentrations and reduced visibilities in the SE than in the NW. The mean values of the visibilities are 44 and 97 km for the SE and the NW respectively. The exponent of R (particle radius) in the power law aerosol size distribution has a mean value of −3.36 ± 0.24 in the SE compared with the corresponding value of −3.89 ± 0.39 for the NW. These results arc in good agreement with the observations of Alberta Environment; however, they are in contradiction with a recent report published by the City of Calgary.

scholarly journals Automated System for Kinetic Analysis of Particle Size Distributions for Pharmaceutically Relevant Systems

2014 ◽  
Vol 2014 ◽  
pp. 1-8
Author(s):  
John-Bruce D. Green ◽  
Phillip W. Carter ◽  
Yingqing Zhang ◽  
Dipa Patel ◽  
Priyanka Kotha ◽  
...  
Keyword(s):  
Particle Size ◽  
Clinical Importance ◽  
Automated System ◽  
Size Distributions ◽  
Mixing Conditions ◽  
Particle Size Distributions ◽  
Complex Formulation ◽  
Wide Range ◽  
Key Variables ◽  
Kinetics Of

Detailing the kinetics of particle formation for pharmaceutically relevant solutions is challenging, especially when considering the combination of formulations, containers, and timescales of clinical importance. This paper describes a method for using commercial software Automate with a stream-selector valve capable of sampling container solutions from within an environmental chamber. The tool was built to monitor changes in particle size distributions via instrumental particle counters but can be adapted to other solution-based sensors. The tool and methodology were demonstrated to be highly effective for measuring dynamic changes in emulsion globule distributions as a function of storage and mixing conditions important for parenteral nutrition. Higher levels of agitation induced the fastest growth of large globules (≥5 μm) while the gentler conditions actually showed a decrease in the number of these large globules. The same methodology recorded calcium phosphate precipitation kinetics as a function of [Ca2+] and pH. This automated system is readily adaptable to a wide range of pharmaceutically relevant systems where the particle size is expected to vary with time. This instrumentation can dramatically reduce the time and resources needed to probe complex formulation issues while providing new insights for monitoring the kinetics as a function of key variables.

scholarly journals Aged boreal biomass burning aerosol size distributions from BORTAS 2011

2014 ◽  
Vol 14 (17) ◽  
pp. 24349-24385 ◽  
Author(s):  
K. M. Sakamoto ◽  
J. D. Allan ◽  
H. Coe ◽  
J. W. Taylor ◽  
T. J. Duck ◽  
...  
Keyword(s):  
Size Distribution ◽  
Biomass Burning ◽  
Radiative Forcing ◽  
Climate Model ◽  
Sampling Period ◽  
Characteristic Size ◽  
Entrainment Rate ◽  
Size Distributions ◽  
Eastern Canada ◽  
Median Diameter

Abstract. Biomass-burning aerosols contribute to aerosol radiative forcing on the climate system. The magnitude of this effect is partially determined by aerosol size distributions, which are functions of source fire characteristics (e.g. fuel type, MCE) and in-plume microphysical processing. The uncertainties in biomass-burning emission number size-distributions in climate model inventories lead to uncertainties in the CCN concentrations and forcing estimates derived from these models. The BORTAS-B measurement campaign was designed to sample boreal biomass-burning outflow over Eastern Canada in the summer of 2011. Using these BORTAS-B data, we implement plume criteria to isolate the characteristic size-distribution of aged biomass-burning emissions (aged ∼1–2 days) from boreal wildfires in Northwestern Ontario. The composite median size-distribution yields a single dominant accumulation mode with Dpm = 230 nm (number-median diameter), σ = 1.7, which are comparable to literature values of other aged plumes of a similar type. The organic aerosol enhancement ratios (ΔOA / ΔCO) along the path of Flight b622 show values of 0.05–0.18 μg m−3 ppbv−1 with no significant trend with distance from the source. This lack of enhancement ratio increase/decrease with distance suggests no detectable net OA production/evaporation within the aged plume over the sampling period. A Lagrangian microphysical model was used to determine an estimate of the freshly emitted size distribution corresponding to the BORTAS-B aged size-distributions. The model was restricted to coagulation and dilution processes based on the insignificant net OA production/evaporation derived from the ΔOA / ΔCO enhancement ratios. We estimate that the fresh-plume median diameter was in the range of 59–94 nm with modal widths in the range of 1.7–2.8 (the ranges are due to uncertainty in the entrainment rate). Thus, the size of the freshly emitted particles is relatively unconstrained due to the uncertainties in the plume dilution rates.

Effects of vegetation cover on sediment particle size distribution and transport processes in natural rainfall conditions on post-fire hillslope plots in South Korea

Soil Research ◽  
2016 ◽  
Vol 54 (8) ◽  
pp. 937 ◽  
Author(s):  
Ewane Basil Ewane ◽  
Heon-Ho Lee
Keyword(s):  
Particle Size ◽  
Size Distribution ◽  
Vegetation Cover ◽  
Rainfall Intensity ◽  
Transport Processes ◽  
Vegetation Recovery ◽  
Particle Sizes ◽  
Sediment Size ◽  
Aggregate Breakdown ◽  
Soil Burn Severity

Sediments were collected from four slow vegetation recovery plots, six fast vegetation recovery plots and five unburned plots at a post-fire site on a rainfall event basis and sorted for size distribution. The aim was to evaluate the effects of vegetation cover, soil aggregate stability, slope and rainfall intensity on sediment size distribution, transport selectivity and erosion processes between the burned and unburned treatment plots. Sediment detachment and transport mechanisms and the particle size transport selectivity of the eroded sediment were assessed based on enrichment ratios (ER) and mean weighted diameter (MWD) methods. The most eroded particle size class in all treatment plots was the 125–250μm class and, generally, the percentage of eroded particle sizes did not increase with slope and rainfall intensity. Higher MWD of the eroded sediment was related to a higher percentage of bare soil exposed and gravel content associated with high soil burn severity and soil disaggregation in the slow vegetation recovery plots. The enrichment of finer clay silt particle sizes increased with varying maximum 30-min rainfall intensity (I30) in the slow vegetation recovery plots, and reflected increased aggregate breakdown and transport selectivity, whereas no good relationship was found in the fast vegetation recovery and unburned plots with varying I30. A minimum I30 of <3.56mmh–1 and a maximum of 10.9mmh–1 were found to be the threshold rainfall intensity values necessary for aggregate breakdown and transport of finer particles by both rainsplash and rainflow in the slow vegetation recovery plots, whereas the response was weak in the fast vegetation recovery and unburned plots following varying I30 dominated only by rainsplash transport closer to the plot sediment collector. The results show that higher vegetation cover in the fast vegetation recovery and unburned plots reduces erosive rainfall energy by 5.6- and 17.7-fold respectively, and runoff energy by 6.3- and 21.3-fold respectively, limiting aggregate breakdown and transport selectivity of finer particles compared with the slow vegetation recovery plots.

scholarly journals Arctic marine secondary organic aerosol contributes significantly to summertime particle size distributions in the Canadian Arctic Archipelago

2019 ◽  
Vol 19 (5) ◽  
pp. 2787-2812 ◽  
Author(s):  
Betty Croft ◽  
Randall V. Martin ◽  
W. Richard Leaitch ◽  
Julia Burkart ◽  
Rachel Y.-W. Chang ◽  
...  
Keyword(s):  
Particle Size ◽  
Size Distribution ◽  
Secondary Organic Aerosol ◽  
Canadian Arctic ◽  
Particle Growth ◽  
Organic Aerosol ◽  
The Arctic ◽  
Canadian Arctic Archipelago ◽  
Size Distributions ◽  
Fractional Error

Abstract. Summertime Arctic aerosol size distributions are strongly controlled by natural regional emissions. Within this context, we use a chemical transport model with size-resolved aerosol microphysics (GEOS-Chem-TOMAS) to interpret measurements of aerosol size distributions from the Canadian Arctic Archipelago during the summer of 2016, as part of the “NETwork on Climate and Aerosols: Addressing key uncertainties in Remote Canadian Environments” (NETCARE) project. Our simulations suggest that condensation of secondary organic aerosol (SOA) from precursor vapors emitted in the Arctic and near Arctic marine (ice-free seawater) regions plays a key role in particle growth events that shape the aerosol size distributions observed at Alert (82.5∘ N, 62.3∘ W), Eureka (80.1∘ N, 86.4∘ W), and along a NETCARE ship track within the Archipelago. We refer to this SOA as Arctic marine SOA (AMSOA) to reflect the Arctic marine-based and likely biogenic sources for the precursors of the condensing organic vapors. AMSOA from a simulated flux (500 µgm-2day-1, north of 50∘ N) of precursor vapors (with an assumed yield of unity) reduces the summertime particle size distribution model–observation mean fractional error 2- to 4-fold, relative to a simulation without this AMSOA. Particle growth due to the condensable organic vapor flux contributes strongly (30 %–50 %) to the simulated summertime-mean number of particles with diameters larger than 20 nm in the study region. This growth couples with ternary particle nucleation (sulfuric acid, ammonia, and water vapor) and biogenic sulfate condensation to account for more than 90 % of this simulated particle number, which represents a strong biogenic influence. The simulated fit to summertime size-distribution observations is further improved at Eureka and for the ship track by scaling up the nucleation rate by a factor of 100 to account for other particle precursors such as gas-phase iodine and/or amines and/or fragmenting primary particles that could be missing from our simulations. Additionally, the fits to the observed size distributions and total aerosol number concentrations for particles larger than 4 nm improve with the assumption that the AMSOA contains semi-volatile species: the model–observation mean fractional error is reduced 2- to 3-fold for the Alert and ship track size distributions. AMSOA accounts for about half of the simulated particle surface area and volume distributions in the summertime Canadian Arctic Archipelago, with climate-relevant simulated summertime pan-Arctic-mean top-of-the-atmosphere aerosol direct (−0.04 W m−2) and cloud-albedo indirect (−0.4 W m−2) radiative effects, which due to uncertainties are viewed as an order of magnitude estimate. Future work should focus on further understanding summertime Arctic sources of AMSOA.

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