Variation Of Grain Size Distribution Research Articles

A novel Li3Mg4(Nb1-xVx)O8 ceramic with high Q×f value and good temperature stability with low sintering temperature

A series of low-loss Li3Mg4(Nb1-xVx)O8 (0.02 ≤ x ≤ 0.08) ceramics has been synthesized in this work, with the optimal sintering temperature lowered to 950°C due to the incorporation of V5+ ions. Moreover, the effects of substituting V5+ for Nb5+ on the sintering, composition, structure and properties of the ceramics have been systematically analyzed. It has been discovered that the permittivity (εr) and quality factor (Q×f) of Li3Mg4(Nb1-xVx)O8 ceramics exhibit a correlation with the relative density, which is influenced by the variation in grain size distribution resulting from the substitution of V5+ ions. Additionally, the total lattice energy of Li3Mg4(Nb1-xVx)O8 ceramics is also affected by the bond characteristics within the Nb-O octahedra, thus influencing the Q×f value. The resonant frequency temperature coefficient (τf) fluctuates within a small range. The Li3Mg4(Nb0.98V0.02)O8 ceramics exhibit excellent microwave dielectric properties at 950°C: εr∼14.03, Q×f∼93,425 GHz, τf∼-6.12 ppm/°C, with a relative density reaching 98.3 %. Compared to unsubstituted Li3Mg4NbO8 ceramics, the sintering temperature is reduced by 200°C without forming impurity phases. While adjusting the τf value to nearly zero, it maintains a high Q×f value, indicating promising applications in Low-Temperature Co-fired Ceramics (LTCC).

Modeling the morphological response of gravel–bed rivers subject to repeated sediment bypass tunnel operations

Introduction: Sediment bypass tunnels (SBTs) are operated during floods to re-establish sediment continuity past dams with the ultimate goal of decreasing accumulation in reservoirs. Depending on the location of the intake structure and operational conditions, SBTs may release either bed load-laden or bed load-free flows in the form of sudden floods (pulses). When evaluating the impacts of SBTs, the traditional approach has been to monitor channel changes in the years following project completion. However, by the time these impacts become evident, mitigation is challenging.Methods: This research adopts a forward-thinking methodology, emphasizing the prediction of potential impacts during the project’s early planning stages. We use a one-dimensional morphodynamic model to forecast the potential morphological response of a gravel-bed river with an idealized geometry to a series of SBT operations characteristic of projects in the Swiss Alps.Results: The morphological response of the downstream reach over the medium to long term is influenced by the alternating pattern of bed load-laden and bed load-free flow releases. This pattern is instrumental in forming a transition region near the SBT outlet hydrograph boundary layer (HBL).Discussion: Within the (HBL), fluctuations in bed elevation and slope are localized, while variations in grain-size distribution persist throughout the downstream region.

Influence of Groundwater on the Very Shallow Geothermal Potential (vSGP) in the Area of a Large-Scale Geothermal Collector System (LSC)

The water balance in the very shallow subsurface can be influenced by capillary rise due to a high groundwater table. Since moisture content is an important factor for the thermal conductivity of soils, this can also have an influence on the very shallow geothermal potential (vSGP). For this reason, the effect of spatial and seasonal variations in groundwater tables on moisture content in essential depth layers was investigated at a large-scale geothermal collector system (LSC) in Bad Nauheim, Germany. Quasi-one-dimensional simulations using the FEFLOW® finite-element simulation system were employed to determine site-dependent and seasonally varying moisture contents, from which thermal conductivities were derived. The model setup was previously validated based on recorded moisture contents. The simulations resulted in groundwater-related maximum seasonal and spatial differences in thermal conductivity of 0.14 W/(m∙K) in the LSC area. Larger differences of up to 0.21 W/(m∙K) resulted for different soil textures at the same depth due to different thermal properties. The results indicate that an efficient design of LSCs requires a sufficiently detailed subsurface exploration to account for small-scale variations in grain size distribution and groundwater level.

Estimation of eruption source parameters for the 2021 La Soufrière eruption (St Vincent): implications for quantification of eruption magnitude on volcanic islands

Abstract Eruption source parameters (ESPs) used to characterize explosive eruptions are estimated from tephra deposit data using different models (statistical or numerical) and inversion approaches. The ESPs thus derived are subject to substantial uncertainties when the bulk of the tephra deposit, including information about its full spatial extent and spatial variation in grain-size distribution is missing due to geographical and environmental conditions. We use an advection–diffusion model coupled with a Bayesian inversion and uncertainty quantification algorithm to investigate how ESPs can be robustly estimated given such conditions. The 2021 eruption of La Soufrière volcano (St Vincent and the Grenadines) is our case study. An inversion is conducted for the first two explosive phases of this eruption (U1 and U2). We estimate: an erupted mass of 3.3 × 10 10 ± 1 × 10 10 kg for U1 and 3.1 × 10 10 ± 1.9 × 10 9 kg for U2, with an average particles release height of c. 13.5 km a.s.l. ±0.5 km for both phases. Given the efficiency of the proposed approach and the plausibility of the stochastic inversion results, we recommend this procedure for estimating ESPs for explosive eruptions for which the bulk of the deposit is missing or is inaccessible.

Effect of bed shear stress on the mobile armor layer at the riverbed

Armoring is forming an armor layer of the riverbed which is preceded by the transportation of bed sediment. Mobile armor occurs when the riverbed reaches equilibrium, then eroded, and the surface of the riverbed recovers. Therefore, protection is formed by moving riverbed material. This research used a simulation model generated through HEC RAS software version 6.1. The model input location was Krasak River, Sleman, Yogyakarta. The data for model input were the topography of the Krasak River from upstream to the point of view, flood discharge hydrograph, and grain size gradations. The simulation combination consisted of three locations with the riverbed material of each location sampled tested for grain size distribution. The running simulations combined the flood discharge at return periods of 2, 5, 10, 25, 50, and 100 years. There were three variations of grain size distribution used as input data. Meanwhile, variations of sediment transport methods used the Meyer-Peter Muller and Wilcock-Crowe methods. Overall, the simulation results show that the shear stress and the proportion of sand-to-grain material affect the armoring process and riverbed changes.

Fe-SiC-Sn-Mn reinforced surface composite via FSP: A comprehensive analysis

This investigation reports a maiden work on the fabrication of surface composite through hybrid reinforcement powders by adding Fe, Mn, and Sn metallic powders to ceramics (SiC) in aluminum AA5083 alloy matrix via friction stir processing. Stitched micrographs were employed to demonstrate the variation in grain size distribution from the stir zone (10 µm) to the base metal (52.68 µm) during the processing. With the aid of scanning electron microscopy, energy dispersive spectroscopy, area mapping and X-ray diffraction analysis, it has been determined how reinforcement was distributed and what phases evolved in the stir zone. Tensile test was performed to evaluate the strength of the fabricated composite and micro-hardness maps indicated a 54.4 % increase in hardness after processing.The observed enhancement is attributed to the Hall-Petch and pinning effect. A potentiodynamic polarization test was carried out to study the corrosion behavior and it was ascertained that corrosion resistance of the processed sample got enhanced because of grain refinement, formation of galvanic couple and breakdown of second phase particles owing to intense stirring.

The influence of burial rate on variability in tephra thickness and grain size distribution in Iceland

We explore whether the rate at which a tephra deposit is buried influences the variability (thickness and grain size distribution) within the tephra layer subsequently preserved within the stratigraphic record. This has important implications for understanding how processes of soil formation interact with the creation of a volcanic record. To assess the relationship between soil formation and the preservation of tephra layers, the thickness and grain size distribution of the Katla 1918 tephra in Iceland and the rate at which it was buried (inferred from the thickness of the overlying soil) was measured 1620 times at six locations. Tephra layer thickness does not correlate with rate of burial, but the proportion of original deposit retained does, and variations in grain size distribution are correlated with burial rate. Our results indicate that whilst medium term (i.e. years-decades) burial processes may contribute less to tephra layer variability than environmental processes operating immediately after deposition, rapid burial facilitates better preservation of the original fallout characteristics with important implications for the accurate reconstruction of past volcanic eruptions based on tephra layer characteristics. There are two key implications: firstly, sites need to be chosen where surface characteristics minimise the initial alterations of tephra deposits, and secondly sites with rapid burial will produce the best quality data, although workable data can be gathered elsewhere if areas of uncertainty are acknowledged.

The Si K Edge Gas and Dust Optical Depths Toward the Galactic Bulge

Knowledge of the dust content in interstellar matter is important to our understanding of the composition and evolution of the interstellar medium. The Chandra High Energy Transmission Grating (HETG) Spectrometer provides a unique opportunity to measure X-ray absorption of interstellar dust and its compositions through the X-ray edge absorption structure. We measure gas and dust optical depths at Si K toward nine bright low-mass x-ray binaries in the Galactic Bulge with very high-precision and pileup-free spectra. We include a likely instrumental feature affecting the Si K edge structure in our analysis. While gas optical depths grow consistently with broadband hydrogen-equivalent columns, the dust optical depths do not. Calculations including dust self-shielding show that the observed dust optical depths can be explained by variations in dust grain columns between various lines of sight. At least three grain column regimes can be identified toward the Galactic Bulge. While grain sizes define the self-shielding effect, variations in grain size distributions do not seem relevant. This shows that the gas-to-dust optical depth ratio toward sources in the Galactic Bulge is not homogeneous. The dust optical depths also roughly correlate with molecular hydrogen columns. Lowly ionized Si K contributions toward the Galactic Bulge were detected but are very small. We also find Si xiii absorption with velocity widths of 800–1100 km s−1, which we attribute to the circumbinary medium.

Grain size analysis of the latest Quaternary Kordofan Sand of Central Sudan: Depositional environment and mode of transportation

Grain size analysis is a powerful tool for determining the depositional environment. Grain size analysis for 48 samples from four sections along a 280 km long, nearly north–south-trending transect, has been conducted in the mainly Holocene Kordofan Sand in the Kordofan Region of Central Sudan. In these sections, this part of the Kordofan Sand comprises three pedosedimentary sequences. The lower sequence (∼13–10 kyr) has been pedogenized during the African Humid Period and ends up farther West with lacustrine or palustrine carbonates. The middle sequence (∼6–3 kyr) is represented by sand with low degree of pedogenesis and corresponds to the African Humid Period. The upper sequence was deposited after a hiatus lasting from ∼3.3 to 1.1 ka BP, and constitutes the present-day surficial deposits, showing little or no pedogenesis. Spatial grain size distribution and mode of transport show a southward fining trend, indicating that the sandy sediments were transported from north to south. This interpretation is supported by the results of mean grain size – sorting, and sorting – skewness interrelations, which provided a linear relationship. Vertical variation in grain size distribution in the studied sections shows variable energy over time in the north and constant, low energy in the south. The dominance of saltation as a transport mode confirms that the studied sediments were deposited in aeolian environment. The low sorting degree, the presence of coarse grains, and the still active transverse dunes and barchans in the North, indicate that the Late Pleistocene part of the Kordofan Sandstone is submitted to reworking until now. Consequently, the mainly Holocene sand sequences were fed both by distal, fine-grained Saharan material and by proximal, coarser-grained sand proceeding from the Late Pleistocene aeolian dunes.

Sedimentological and Grain Size Characteristics of Two Lake Cores from Himachal Pradesh, India

Two lake cores from Khajjiar (length 746 cm) and Rewalsar lakes (length 647 cm) in Himachal Pradesh (India) were retrieved to understand the sedimentological characteristics and variation in grain size distribution. Both the lake cores are Upper Holocene in age. The Rewalsar lake sediments are composed predominantly of silt with small amounts of clay, whereas the Khajjiar sediments contain sand, silt and clay and both cores have high carbonaceous matter. The standard deviation ranges from 0.88 ϕ to 2.56 ϕ for Khajjiar lake and from 0.957 ϕ to 2.264 ϕ for Rewalsar lake, indicating poorly to very poorly sorted core sediments. The values of the Kurtosis vary between 0.678 ϕ and 1.205 ϕ for Khajjiar lake and from 0.8 ϕ to 1.2.4 ϕ for Rewalsar lake, viewing platykurtic to leptokurtic nature. Further, the skewness value ranges from -0.097 ϕ to 0.240 ϕ for Khajjiar lake and 0.079 ϕ to 0.25 ϕ for Rewalsar lake revealing fine to symmetrical skewness model. The bivariate plots by using the grain-size parameters were also interpreted. The Total Organic Carbon (TOC) is higher in the Khajjiar lake sediments (0.9 to 31.2%; av. 10.6%), compared to that in the Rewalsar lake sediments (1.0 to 9.0; av. 2.6%). The sedimentological characteristics indicate that the energy conditions were linked to the climatic conditions prevailing in the area. In general, the Khajjiar lake core is composed of relatively coarser sediments and more affected by arid conditions while the fine fraction of the Rewalsar shows the consequence of lower energy conditions. The Khajjiar lake shows the transition from fluctuating conditions (zone 1) to humid (zone 2) to arid (zone 3), while the Rewalsar shows the change from fluctuating (zone 1) to humid conditions (zones 2 and 3). The similarity between zone 1 and 2 of both the lake profiles shows that both lakes have experienced similar climatic conditions during the deposition, revealing domination of fluctuating and arid conditions.

Fractal and re-breakage behavior of the saturated rock granular material under compaction

A compaction experiment of the saturated rock granular material is conducted to investigate its fractal and re-breakage behavior under compaction. The samples after compaction have obvious fraction characteristics, the variation of grain size distribution (GSD) and the fractal characteristics of samples with different Talbot power exponent (TPE) are analyzed. It presents that samples after compaction still obey to the modified Talbot continuous gradation equation, and its coefficient increases with the compaction degree going on; however, the samples with larger TPE are much easier to far away from the modified equation than samples with smaller TPEs. Sample with different TPEs reach their most obvious re-breakage at the different compaction levels. It can be inferred that 10 mm is an appropriate compression for the sample with the TPE of 0.5, and 30 mm for 0.6. The suitable compaction for the samples with TPEs of 0.7, 0.8, and 0.9 could be found as the curves are converged. During the compaction process, the fractal dimension (FD) and re-breakage degree of samples with the different TPEs increase with the compression going on, which result in the new GSD. These results could be used to guide engineering practice to obtain the optimal compaction for samples with different TPE.

The variation of grain size distribution in rock granular material in seepage process considering the mechanical-hydrological-chemical coupling effect: an experimental research.

As a common solid waste in geotechnical engineering, rock granular material should be properly treated and recycled. Rock granular material often coexists with water when it is used as the filling material in geotechnical engineering. Water flowing in rock granular materials is a complex progress with the mechanical–hydrological–chemical (MHC) coupling effect, i.e. the water scours in the gaps and spaces in the rock granular material structure, produces chemical reactions with rock grains, rock grains squeeze each other under the water pressure and compression leading to re-breakage and producing secondary rock grains, and the fine rock grains are migrated with water and rushed out. In this process, rock grain size distribution (GSD) changes, it affects the physical and mechanical characteristics of the rock granular materials, and even influences the seepage stability of the rock granular materials. To study the variation of GSD in the rock granular material considering the MHC coupling effect after the seepage process, seepage experiments of rock grain samples are carried out and analysed in this paper. The result is expected to have a positive impact on further studies of the properties of the rock granular material.

Surface sediment characteristics related to provenance and ocean circulation in the Drake Passage sector of the Southern Ocean

Understanding present-day sediment provenance and transport processes is crucial for studies about the dynamics of ocean circulation, as well as for paleoclimate reconstructions in the Drake Passage (DP), a key area for Earth's global oceanic circulation and climate during past and future. Based on a comprehensive set of surface sediment samples, we used spatial variations in grain-size distribution, bulk sediment mineralogy, silt and clay mineralogy across the entire DP region to elucidate the terrigenous sources and transport mechanisms. The statistical evaluation of these data identifies southern Patagonia (carbonate, illite, chlorite, feldspar and quartz) and the Antarctic Peninsula (chlorite, smectite, and amphibole) as the main sources for terrigenous sediments in the DP region. Different current systems are transporting the sediment material. Here, we provide a new, robust flow speed calibration for silt grain-sizes to enable the reconstruction of Antarctic Circumpolar Current (ACC) dynamics in the DP sector of the Southern Ocean. We correlated the sortable silt mean grain-size records of surface sediments with adjacent long-term current meter data. A clear bottom current speed pattern shows the variability of the ACC in the DP responding to the dynamics of ocean fronts, in agreement with modern observation.

Effects of experimental frost–thaw cycles on sandstones with different weathering degrees: a case from the Bingling Temple Grottoes, China

Numerous ancient sandstone grottoes remain in northwest and central China, and weathering issues have significantly influenced their preservation conditions. The dramatic naturally cyclic changes in water content and temperature in the environment have been considered to be the main drivers of the physical weathering that commonly occurs at these archaeological sites. Therefore, comparing and understanding the behaviors of sandstone with different weathering degrees under variable environmental conditions would be helpful for further study on predicting the type, location and extent of deterioration of sandstone relics in a small region (such as the surrounding rock of grottoes). This study examines Cretaceous sandstones with two weathering degrees from Bingling Temple Grottoes, China. Standard thin section photomicrographs provide petrographic and mineralogical data and show that the sandstones have identical lithologies. Three types of specifically designed frost weathering tests are then conducted on the samples. After every six weathering cycles, the weathering processes are suspended, and the corresponding parameters, such as dry weight loss, dry density, effective porosity, porosity, P wave velocity, surface hardness and drilling resistance, are measured. At the end of the weathering cycles, the sample variations in grain size distributions are compared, and statistical tests are performed to show the statistical significance of the results. The results indicate that similar deterioration patterns occur on the samples with two weathering degrees under the same weathering tests. The increase in effective porosity surpasses that of the porosity only when the weathering effect is large enough. Furthermore, sandstone with a high degree of weathering might be more susceptible to changes in the internal pores due to its greater initial interconnectivity. In an open system, physical weathering (frost–thaw and dry–wet cycles) would cause the superficial grain size distributions of different rocks to become relatively uniform. Finally, when exposed to the same weathering process, the decreases in the overall mechanical strength in the two sandstones do not differ significantly, but the loss of superficial strength may be different.

An aeolian sediment reconstruction of regional wind intensity and links to larger scale climate variability since the last deglaciation from the east coast of southern Africa

Few long-term environmental records are available for southern Africa where shifts in atmospheric circulation and changes in sea surface temperatures interact to influence regional climate dynamics. We present downcore grain size and inorganic geochemistry data covering the last ~23,000years from a peatland on the east coast of South Africa and examine links between shifts in regional wind activity and palaeoclimatic variability. Our record documents substantial variations in aeolian flux associated with changes in regional climate and wind patterns that reflect larger scale atmospheric circulation patterns. Substantially higher fluxes observed during the Last Glacial Maximum (LGM) are linked to widespread aridification and an expansion in local source areas brought about by a clear shift to dry and cool conditions. Variations in grain size distribution reveal that the aeolian record from Mfabeni comprises two dominant end-members; locally-derived coarse-grained material and a more fine-grained dust component. Marked changes in composition and modal grain size suggest that hydrological shifts in the region during the LGM were accompanied by an increase in storm frequency and wind strength that we link to a northward displacement in the westerly wind belt and a strengthening in wind intensity. Coupling between a rapid increase in sea surface temperature (SST) and an approximate three-fold decrease in aeolian activity after 15kcalyrBP suggests that changes in SST and its effect on the position and intensity of the westerlies in the Southern Ocean was the dominant climatic driver in the region during deglaciation. Substantially lower aeolian activities through the early Holocene indicate a warming in regional climate and the establishment of more humid conditions under the influence of enhanced tropical easterly flow. Our record also documents more subtle changes in climate over the mid to late Holocene and provides support for an arid phase in southern African climate 6–4kcalyrBP, as well as an increase in climate variability associated with a strengthening in El Niño–Southern Oscillation (ENSO) activity ~2kcalyrBP. The study contributes to current knowledge of atmospheric circulation patterns in the Southern Hemisphere and provides new insight into links between aeolian activity, regional wind patterns and climatic variability over glacial-interglacial timescales for a region where existing palaeoclimate records are scarce.

Investigation of the Quasi-Brittle Failure of Alashan Granite Viewed from Laboratory Experiments and Grain-Based Discrete Element Modeling.

Granite is a typical crystalline material, often used as a building material, but also a candidate host rock for the repository of high-level radioactive waste. The petrographic texture—including mineral constituents, grain shape, size, and distribution—controls the fracture initiation, propagation, and coalescence within granitic rocks. In this paper, experimental laboratory tests and numerical simulations of a grain-based approach in two-dimensional Particle Flow Code (PFC2D) were conducted on the mechanical strength and failure behavior of Alashan granite, in which the grain-like structure of granitic rock was considered. The microparameters for simulating Alashan granite were calibrated based on real laboratory strength values and strain-stress curves. The unconfined uniaxial compressive test and Brazilian indirect tensile test were performed using a grain-based approach to examine and discuss the influence of mineral grain size and distribution on the strength and patterns of microcracks in granitic rocks. The results show it is possible to reproduce the uniaxial compressive strength (UCS) and uniaxial tensile strength (UTS) of Alashan granite using the grain-based approach in PFC2D, and the average mineral size has a positive relationship with the UCS and UTS. During the modeling, most of the generated microcracks were tensile cracks. Moreover, the ratio of the different types of generated microcracks is related to the average grain size. When the average grain size in numerical models is increased, the ratio of the number of intragrain tensile cracks to the number of intergrain tensile cracks increases, and the UCS of rock samples also increases with this ratio. However, the variation in grain size distribution does not have a significant influence on the likelihood of generated microcracks.

Statistical Analysis in Fluvial Sediments of Selangor Rivers: Downstream variation in grain size distribution

Statistical Analysis in Fluvial Sediments of Selangor Rivers: Downstream variation in grain size distribution

Influence of grain size heterogeneity on strength and microcracking behavior of crystalline rocks

AbstractThis study numerically investigates the influence of material heterogeneity on the strength and deformation behavior and the associated microcracking process of a felsic crystalline rock using a grain‐based modeling approach in two‐dimensional Particle Flow Code. By using a heterogeneity index defined in this study, the heterogeneity induced by variation of grain size distribution can be explicitly incorporated into the numerical specimen models quantitatively. Under compressive loading, the peak strength and the elastic modulus are found to increase as the numerical model gradually changes from heterogeneous to homogeneous, i.e., a decrease of heterogeneity index. Meanwhile, the number of grain boundary tensile cracks gradually decreases and the number of intragrain cracks increases at the moment of failure. However, the total number of generated microcracks seems not to be significantly influenced by heterogeneity. The orientation of grain boundary microcracks is mainly controlled by the geometry of assembled grain structure of the numerical specimen model, while the orientation of intragrain microcracks is to a large degree influenced by the confinement. In addition, the development of intragrain cracks (both tensile and shear) is much more favored in quartz than in other minerals. Under direct tensile loading, heterogeneity is found to have no significant influence on the simulated stress‐strain responses and rock strength. Only grain boundary tensile cracks are generated when the numerical models are loaded in direct tension, and the position of generated macroscopic fracture developed upon failure of the specimen is largely affected by heterogeneity.

Processing of a metastable titanium alloy (Ti-5553) by selective laser melting

The metastable beta titanium alloy Ti-5Al-5V-5Mo-3Cr is characterised by multifaceted mechanical properties (high - strength, hardened, ductile) depending on applied heat treatment. Compared to α-β titanium alloy Ti-6Al-4V, a higher tensile strength up to 1400 MPa as well as a yield strength of 1250 MPa can be achieved. As a result, Ti-5553 is used for special aerospace applications e.g. landing gear components or helicopter rotors. Aim of this paper is to study the processibility of Ti-5553 by using selective laser melting. First, a suitable and stable process parameter set for a reference grain fraction (10–63 μm) have been developed. Second, variations of grain size distribution will be taken into account, so that a high material density as well as high surface quality can be achieved. Furthermore, an identical process window was applied on fine and coarse grain fractions to show effects regarding material porosity. Material densities above 99.93% were achieved by optimisation of energy input during selective laser melting process. However, the use of reference fraction (10–63 μm) allowed the highest material density. Regarding to surface quality, an impact of coarse grain (53–63 μm) was identified and an optimised grain size distribution derived. An optimum averaged surface roughness could be calculated, using a grain size between 25–32 μm.

Long-term coastal openness variation and its impact on sediment grain-size distribution: a case study from the Baltic Sea

Abstract. We analysed the long-term variations in grain-size distribution in sediments from Gåsfjärden, a fjord-like inlet in the southwestern Baltic Sea, and explored potential drivers of the recorded changes in the sediment grain-size data. Over the last 5.4 thousand years (ky) in the study region, the relative sea level decreased 17 m, which was caused by isostatic land uplift. As a consequence, Gåsfjärden was transformed from an open coastal setting to a semi-closed inlet surrounded by numerous small islands on the seaward side. To quantitatively estimate the morphological changes in Gåsfjärden over the investigated time period and to further link the changes to the grain-size distribution data, a digital elevation model (DEM)-based openness index was calculated. The largest values of the openness indices were found between 5.4 and 4.4 cal ka BP, which indicates relatively high bottom water energy. During the same period, the highest sand content (∼ 0.4 %) and silt / clay ratio ( ∼ 0.3) in the sediment sequence were also recorded. After 4.4 cal ka BP, the average sand content was halved to ∼ 0.2 % and the silt / clay ratio showed a significant decreasing trend over the last 4 ky. These changes were found to be associated with the gradual embayment of Gåsfjärden, as represented by the openness indices. The silt / clay ratios exhibited a delayed and relatively slower change compared with the sand content, which indicates different grain-size sediment responses to the changes in hydrodynamic energy. Our DEM-based coastal openness indices have proved to be a useful tool for interpreting the temporal dynamics of sedimentary grain size.