Sand Ripples Research Articles

Bedform variability and flow regime in a barrier-inlet system. The mesotidal Piedras mouth (Huelva, SW Spain)

Bedform fields from the Piedras River mouth (Huelva, SW Spain) have been studied using side-scan sonartechniques, combined with visual scuba-dives, and direct geometric measuring. The dominant flow regime hasbeen determined from the results in these tidal environments, where erosive processes dominate during ebb,transporting sand as a bedload towards the mouth and central sector of the tidal channel. The process is reversedduring tidal floods. During neap tides, larger bedforms maintain their geometry and position, whereas smallripples are re-oriented under different tidal conditions. Sand patches, dunes and ripples are interpreted as sedimentbypassing zones. Large forms indicate high energy flow, which can only migrate when flow velocity reachesthreshold values for the movement, with net sand transport towards open areas. Depositional features indicatelow, moderate, and high-energy conditions. Here, a depositional regime dominated by sediment accommodationis dominant, where sandy sediments are continuously remobilized, transported and re-deposited, even closer to theestuarine mouth. In inner zones finer particles, such as clay and silt, are transported by tides as suspended matterand deposited in protected inner areas. The final results are long narrow tidal flats, which alternate with sandyareas dominated by erosion.

Forging patterns and making waves from biology to geology: a commentary on Turing (1952) 'The chemical basis of morphogenesis'.

Alan Turing was neither a biologist nor a chemist, and yet the paper he published in 1952, ‘The chemical basis of morphogenesis’, on the spontaneous formation of patterns in systems undergoing reaction and diffusion of their ingredients has had a substantial impact on both fields, as well as in other areas as disparate as geomorphology and criminology. Motivated by the question of how a spherical embryo becomes a decidedly non-spherical organism such as a human being, Turing devised a mathematical model that explained how random fluctuations can drive the emergence of pattern and structure from initial uniformity. The spontaneous appearance of pattern and form in a system far away from its equilibrium state occurs in many types of natural process, and in some artificial ones too. It is often driven by very general mechanisms, of which Turing's model supplies one of the most versatile. For that reason, these patterns show striking similarities in systems that seem superficially to share nothing in common, such as the stripes of sand ripples and of pigmentation on a zebra skin. New examples of ‘Turing patterns' in biology and beyond are still being discovered today. This commentary was written to celebrate the 350th anniversary of the journal Philosophical Transactions of the Royal Society.

Experimental study of flow intensity influence on 2-D sand ripple geometry characteristics

Sand ripples are common bedforms. The formation of sand ripples is related to flow conditions; different flow conditions cause different ripple geometries. The main aim of this study was to assess the relationship between flow intensity and two-dimensional ripple geometry characteristics. The experiments were carried out in a laboratory flume with natural sand whose bulk density ρs was 2 650 kg/m3 and median diameter D50 was 0.41 mm. The Froude number (Fr), a flow intensity parameter, varied from 0.16 to 0.53, entirely within the subcritical range. Two-dimensional sand ripple geometry was measured and processed via statistical methods. The probability distributions of ripple length and height were obtained with different flow conditions. Through dimensionless analysis, the relationship between the flow intensity parameter (grain size Reynolds number Re*) and the sand ripple geometry characteristic length (Λ) and height (Δ) was analyzed, and two formulas were obtained: Λ/D50 = 191.76Re*03 and Δ/D50 = 1.97Re*13, which are consistent with previous research results.

Comparison of measured acoustic reflection fluctuations and estimates based on roughness

The extent to which the roughness of the seabed can account for the acoustic reflection fluctuations is investigated. The roughness of selected areas of the seabed off Panama City, FL, was measured with a laser profiler, as part of Target and Reverberation EXperiment of 2013 (TREX13). The site may be characterized as having small-scale roughness due to bioturbation overlying larger sand ripples due to current activity. It was largely composed of sand with shell hash crossed by ribbons of softer sediment at regular intervals. Simultaneous with the roughness measurement, the seabed reflection was measured with a wide beam echo sounder centered about 10 kHz. Both instruments were deployed on a remotely operated vehicle (ROV) at a height of approximately 2 m above the seabed. Significant fluctuations in the acoustic reflection were observed. By modeling the acoustic scattering due to the roughness, the extent to which the roughness can account for the acoustic fluctuations will be investigated. [Work supported by the Office of Naval Research, Ocean Acoustics Program.]

Formation of sand ripples under a turbulent liquid flow

Sand ripples are commonly observed in both nature and industry. For example, they are found on riverbeds and in oil pipelines that transport sand. In both natural and industrial cases, ripples increase friction between the bed and fluid and are related to flooding, high pressure drops, and transients. Ripples appear when sediments are entrained as bed load (a mobile granular layer) and are usually considered to be the result of initial bedforms that eventually saturate. Given the small aspect ratio of the initial bedforms, linear analyses can be used to understand the formation of ripples. This paper presents a linear stability analysis of a granular bed under a turbulent flow of a liquid. This analysis takes into consideration all the main mechanisms and parameters involved in the turbulent liquid case, including some important parameters that have not yet been considered together such as the bed compactness and the bed-load threshold shear stress. The results of this analysis are compared with published experimental results and they show good agreement.

Bedform contributions to cross-shore sediment transport on a dissipative beach

Field measurements of hydrodynamics, suspended sediment transport rates and bedform sediment transport rates were made in the intertidal section of a dissipative sandy beach (D50=0.26mm, slope=1/80) at Perranporth (UK). Pressure transducers, acoustic Doppler velocimeters, optical backscatter sensors and an acoustic sand ripple profiler were deployed for 12 tides, measuring in a range of wave heights from 0.5 to 2.2m, water depths from 1 to 6m, and in current strengths up to 0.4m/s. Data were analysed in terms of the distance to shore (x) normalised by the surf zone width (xs), and spanned the region 0.4<x/xs<3. Bedform heights up to 30cm and wavelengths 0.5 to 2.7m were recorded. Maximum wavelengths were observed just shoreward of the breakpoint. Bedforms were classified as sub-orbital, vortex ripples. Bedform migration was mostly onshore directed, and correlated with positive (onshore) wave skewness. Migration rates increased through the shoaling zone to a maximum of 1.5cm/min just shoreward of the breakpoint (x/xs=0.8). The bedform component of sediment transport was generally onshore directed, and maximum just shoreward of the breakpoint (0.021kg/m/s). Point measurements showed that the cross-shore suspended sediment transport 25cm above the bed was dominated by the mean component, with an offshore directed maximum at x/xs=0.5. Contributions to onshore transport were only made by the incident wave (gravity band) component. The total depth integrated suspended sediment transport was offshore directed and maximum in the mid surf zone (−0.16kg/m/s). The depth integrated suspended sediment transport dominated over the bedform sediment transport in the inner to mid surf zone (x/xs<0.5) and in the outer shoaling zone (x/xs>1.5). The fractional contribution of the shoreward directed bedform transport to the total absolute transport was up to 100%, and occurred broadly in the region of the breakpoint (0.5<x/xs<1.5). However, spatial averaging in the cross-shore indicated that a more realistic bedform contribution was up to 15% of the transport, with a maximum at x/xs=0.9. Results from this dissipative beach experiment generally agree with previous findings on intermediate beaches, steep beaches, and offshore sandbars.

Wave Ripples Spaced by Flow Downstream of Ripple Peaks

The well-known ratio between sand ripple spacing and wave-driven flow oscillations may be dictated by flow dynamics downstream of ripple crests.

Dynamics of Sand Ripples and Dunes

Dynamics of Sand Ripples and Dunes

Fast Target Detection in Synthetic Aperture Sonar Imagery: A New Algorithm and Large-Scale Performance Analysis

In this paper, a new unsupervised algorithm for the detection of underwater targets in synthetic aperture sonar (SAS) imagery is proposed. The method capitalizes on the high-quality SAS imagery whose high resolution permits many pixels on target. One particularly novel component of the method also detects sand ripples and estimates their orientation. The overall algorithm is made fast by employing a cascaded architecture and by exploiting integral-image representations. As a result, the approach makes near-real-time detection of proud targets in sonar data onboard an autonomous underwater vehicle (AUV) feasible. No training data are required because the proposed method is adaptively tailored to the environmental characteristics of the sensed data that are collected in situ. To validate and assess the performance of the proposed detection algorithm, a large-scale study of SAS images containing various mine-like targets is undertaken. The data were collected with the MUSCLE AUV during six large sea experiments, conducted between 2008 and 2012, in different geographical locations with diverse environmental conditions. The analysis examines detection performance as a function of target type, aspect, range, image quality, seabed environment, and geographical site. To our knowledge, this study-based on nearly 30 000 SAS images collectively covering approximately 160 km <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> of seabed, and involving over 1100 target detection opportunities-represents the most extensive such systematic, quantitative assessment of target detection performance with SAS data to date. The analysis reveals the variables that have the largest impact on target detection performance, namely, image quality and environmental conditions on the seafloor. Ways to exploit the results for adaptive AUV surveys using through-the-sensor data are also suggested.

A Cross-Shore Beach Profile Evolution Model

Developing an accurate and reliable time-averaged beach profile evolution model under storm and nonstorm conditions is a challenging task. Over the last few decades, a number of beach deformation models have been developed under limited experimental conditions and uncertainties, and sometimes they required a long computation time. It is quite evident that a large amount of wave, current, sediment and beach profile data is available today. The present study leads to the development of a simple two-dimensional beach profile evolution model with on-offshore sand bar formation under nonstorm and storm conditions based on the time-averaged suspended sediment concentration models of Jayaratne and Shibayama [Jayaratne, M. P. R. and Shibayama, T. [2007] “Suspended sediment concentration on beaches under three different mechanisms,” Coastal Eng. J., JSCE 49(4), 357–392.] and Jayaratne et al. [Jayaratne, M. P. R., Sritharan, S. and Shibayama, T. [2011] “Examination of the suspended sediment concentration formulae using full-scale rippled bed and sheet flow data,” Coastal Eng. J., JSCE 53(4), 451–489.]. These models were formulated for computing sediment concentration in and outside the surf zone under three different mechanisms: (1) suspension due to turbulent motion over sand ripples, (2) suspension from sheet flow layer and (3) suspension due to turbulent motion under breaking waves. The suspended load is calculated by the product of time-averaged sediment concentration and undertow velocity from edge of the wave boundary layer to wave trough and mass transport velocity from wave trough to crest (bore-like wave region). Sediment transport in wave boundary layer is computed from the modified Watanabe [Watanabe, A. [1982] “Numerical model of nearshore currents and beach deformation model,” Coastal Eng. Jpn., JSCE 25, 147–161.] model. Rattanapitikon and Shibayama [Rattanapitikon, W. and Shibayama, T. [1998] “Energy dissipation model for regular and irregular breaking waves,” Coastal Eng. J., JSCE 40(4), 327–346.] wave model is used to calculate the average rate of energy dissipation due to wave breaking. The beach deformation is calculated from the conservation of sediment mass while the avalanching concept of Larson and Kraus [Larson, M. and Kraus, N. C. [1989] SBEACH: Numerical model for simulating storm induced beach change, Report 1, Technical Report CERC-89-9, US Army Eng. Water. Exp. Station.] is used to re-distribute the sediment mass in neighboring grids for a steady solution. Published field-scale experimental and natural beach profiles from five high-quality data sources from 1983–2009 [Kajima et al., 1983; Kraus and Larson, 1988; Port and Airport Research Institute, Japan, 2005, 2009; Hasan and Takewaka, 2007, 2009; Ruessink et al., 2007] are used to verify the performance of the proposed numerical model. The key feature in this process-based model is that it takes about a couple of minutes to simulate beach profiles of a 2–3 days storm qualitatively at a fairly satisfactory level using a standard personal computer. It is found that the present numerical predictions are not better than the null hypothesis as the model is in a stage of ongoing development. Therefore, it is believed that the final model is often of more value to a practical coastal engineer than a very detailed study of hydrodynamics and sediment transport study, however an incorporation of swash dynamics, more precise evaluation of offshore sand bar formation and continuation to a longer time scale with precise beach deformation are recommended as the next stage of the model.

Analysis of wind-blown sand movement over transverse dunes.

Wind-blown sand movement often occurs in a very complicated desert environment where sand dunes and ripples are the basic forms. However, most current studies on the theoretic and numerical models of wind-blown sand movement only consider ideal conditions such as steady wind velocity, flat sand surface, etc. In fact, the windward slope gradient plays a great role in the lift-off and sand particle saltation. In this paper, we propose a numerical model for the coupling effect between wind flow and saltating sand particles to simulate wind-blown sand movement over the slope surface and use the SIMPLE algorithm to calculate wind flow and simulate sands transport by tracking sand particle trajectories. We furthermore compare the result of numerical simulation with wind tunnel experiments. These results prove that sand particles have obvious effect on wind flow, especially that over the leeward slope. This study is a preliminary study on windblown sand movement in a complex terrain, and is of significance in the control of dust storms and land desertification.

EULER-LAGRANGE SIMULATIONS OF SEDIMENT TRANSPORT IN OSCILLATORY BOUNDARY LAYERS WITH BEDFORMS

Accurate prediction of sediment transport in the presence of bedforms such as sand ripples requires an advanced understanding of how dynamic sediment beds interact with turbulent oscillatory flows. In this paper we propose a new approach for simulating these interactions, based on a fixed grid multiphase Euler-Lagrange simulation, that fully couples dynamic bed evolution to the motion of a sub-grid scale Lagrangian sediment phase. The sediment phase is evolved by computing hydrodynamic and inter-particle forces and torques acting on individual particles, and is coupled to the fluid phase through the volume-filtered Navier-Stokes equations. We validate the approach for sediment transport applications using hindered settling velocity tests, and show very good agreement with the experimental data of Baldock et al. (2004). We then apply the approach to simulate sediment transport and ripple bed morphology in oscillatory flow conditions corresponding to the experimental studies of Van der Werf et al. (2007). During the simulation, particles near ripple surface are isolated from immobile ones below allowing the computation to devote resources only to particles that may be become mobilized. Although preliminary in nature, the simulation results demonstrate that that the model can correctly capture the near bed velocities, suspended sediment concentrations, and pick-up of sediment by key vortical structures.

Roughness measurement by laser profiler and acoustic scattering strength of a sandy bottom

The roughness of a sandy seabed off Panama City, FL, was measured with a laser profiler. This was the site of the target and reverberation experiment of 2013 (TREX13) in which propagation loss and reverberation strength were measured. The area may be characterized as having small scale roughness due to bioturbation overlaying larger sand ripples due to current activity. The area was largely composed of sand with shell hash crossed by ribbons of softer sediment at regular intervals. The roughness measurements were concentrated in the areas where the ribbons intersected the designated sound propagation track. Laser lines projected on the sand were imaged by a high-definition video recorder. The video images were processed to yield bottom profiles in three dimensions. Finally, the roughness data are used to estimate acoustic bottom scattering strength. [Work supported by the Office of Naval Research, Ocean Acoustics Program.]

Numerical modeling of wind-blown sand on Mars.

Recent observation results show that sand ripples and dunes are movable like those on Earth under current Martian climate. And the aeolian process on Mars therefore is re-attracting the eyes of scientific researchers in different fields. In this paper, the spatial and temporal evolution of wind-blown sand on Mars is simulated by the large-eddy simulation method. The simulations are conducted under the conditions of both friction wind speed higher and lower than the "fluid threshold", respectively. The fluid entrainment of the sand particles, the processes among saltation sand particles and sand bed, and the negative feedback of sand movement to flow field are considered. Our results show that the "overshoot" phenomenon also exists in the evolution of wind-blown sand on Mars both temporally and spatially; impact entrainment affects the sand transport rate on Mars when the wind speed is smaller or larger than the fluid threshold; and both the average saltation length and height are one order of magnitudes larger than those on Earth. Eventually, the formulas describing the sand transport rate, average saltation length and height on Mars are given, respectively.

Chemistry and texture of the rocks at Rocknest, Gale Crater: Evidence for sedimentary origin and diagenetic alteration

AbstractA suite of eight rocks analyzed by the Curiosity Rover while it was stopped at the Rocknest sand ripple shows the greatest chemical divergence of any potentially sedimentary rocks analyzed in the early part of the mission. Relative to average Martian soil and to the stratigraphically lower units encountered as part of the Yellowknife Bay formation, these rocks are significantly depleted in MgO, with a mean of 1.3 wt %, and high in Fe, averaging over 20 wt % FeOT, with values between 15 and 26 wt % FeOT. The variable iron and low magnesium and rock texture make it unlikely that these are igneous rocks. Rock surface textures range from rough to smooth, can be pitted or grooved, and show various degrees of wind erosion. Some rocks display poorly defined layering while others seem to show possible fractures. Narrow vertical voids are present in Rocknest 3, one of the rocks showing the strongest layering. Rocks in the vicinity of Rocknest may have undergone some diagenesis similar to other rocks in the Yellowknife Bay Formation as indicated by the presence of soluble calcium phases. The most reasonable scenario is that fine‐grained sediments, potentially a mixture of feldspar‐rich rocks from Bradbury Rise and normal Martian soil, were lithified together by an iron‐rich cement.

Facies analysis of Sunakothi Formation, Kathmandu basin, Nepal and its significance

This study decipher facies characteristic of Sunakothi Formation at southern part of Kathmandu Basin. Thick sandy and muddy sequence is found on an open lacustrine facies of the Kalimati Formation. Five facies associations have been recognized within the sandy and muddy facies. These are: (a) muddy rhythmites and silt and laminated to ripple sand bed of the prodeltaic origin (pd), (b) association of cross-stratification, rippledrift and parallel lamination in the lacustrine delta front origin (df), (c) muddy flood-plain and alteration of the fine and coarse sediments of delta-plain origin (dp), (d) sandy to silty rhythmites of the marginal shallow lacustrine origin above the delta-plain (ml), and (e) association of fluvial origin (fl ). Former three associations are interbeded by the thick gravel deposits, which is gravelly braided river origin. Transition from lacustrine to alluvial system is characterized by fluvial and deltaic system in the south. Sedimentology of the Sunakothi Formation indicates deposition during rapid lake level rise and also the thick channelized fluvial gravel beds within the sandy and muddy sequence indicate lake level fall. The cause could be climatic as well as activity of the basin margin tectonics. Sunakothi Formation is the southern counterpart of the Thimi-Gokarna Formations distributed in the northern part of the basin.

Three-dimensional vegetation structure of Tillandsia latifolia on a coppice dune

Coppice dunes covered by epiarenic Tillandsia fog vegetation occur in the Peruvian coastal desert. To analyse the three-dimensional vegetation structure on such a coppice dune, a photogrammetric structure-from-motion approach is applied. A photogrammetric plant height map was derived from a digital surface model and a digital terrain model created by this approach. This plant height map is analysed in conjunction with stand-scale vegetation patterns, regional wind direction derived from migrating dunes, near-surface wind direction derived from the orientation of sand ripples and ground observations. Tillandsia vegetation patterns are non-random. Banded and reticulate patterns occur at stand scale. At metre to sub-metre scale, groups of tall plants occur in clusters as well as in rows aligned with air movement. While self-organisation processes related to maximising fog moisture capture by the plants and to coppice dune growth appear to control the development of the banded to reticulate pattern, retaining an upright growing position (and hence continued exposure to fog moisture on decadal time scales) by minimising aeolian erosion at the base of these rootless plants appears to control the development of rows and clusters at metre to sub-metre scale.

Megaripple dynamics on a dissipative sandy beach

Miles, J., Thorpe, A., Russell, P., Masselink, G., 2014. Megaripple dynamics on a dissipative sandy beach. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 187–192, ISSN 0749-0208.Conventional force models of bedform dimensions link bedform wavelength and height to wave orbital excursion and wave orbital velocity. Self-organization models, however, suggest that bedform wavelengths either: grow, remain stable, or are wiped flat, but are unable to reduce in length. This paper presents measurements of megaripple evolution on a macrotidal sandy dissipative beach at Perranporth, England, using measurements from a Sand Ripple Profiler. Measurements were made as the tide flooded and ebbed over the instruments, producing a cross-section of the moving surf zone for 12 separate tides. Water depths varied from 1 to 6 m, and wave heights were up to 2.2 m. The data allowed megaripple dimensions to be observed with heights up to 30 cm and wavelengths up to 1.8 m. Megaripples were observed to grow and decay in both length and height. Megaripple spacing did not increase consistently with age of ripple. Megaripple lengths changed at rates of up to 5 cm/minute, and height changed at rates of up to 0.5 cm/minute. Maximum changes took place in large orbital velocity conditions. At orbital velocities > 0.5 m/s, ripples attempted to stabilize at a wavelength related to the orbital excursion, suggesting a forced mode. The most stable ripples had the greatest height and steepness. At orbital velocities < 0.5 m/s the spacing was greater than the orbital excursion, suggesting self-organized growth may be a more appropriate model for small orbital velocities.

Bedform Dynamics in a Rip Current

ABSTRACT Thorpe, A., Miles, J., Masselink, G., Russell, P., 2014. Bedform Dynamics in a Rip Current, Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 700–705, ISSN 0749-0208. A Sand Ripple Profiler (SRP) was deployed in a rip channel on a dissipative sandy beach to measure bedform height (Δ), length (λ) and migration rate (Mr) throughout a macro-tidal cycle. Data were collected in significant wave heights ranging from 0.5 m to 2.1 m and water depths of between 0.9 m and 7.4 m. Periods when the rip current was active were identified by comparing measured cross-shore velocity (U) with predicted cross-shore velocity from a bed return flow model. Rip flow was found to commence when offshore velocities reached approximately 0.1 m/s, maximum rip velocity as a 5 minute mean was 0.74 m/s. At lower tidal elevations (h < 2.5 m), in the strong offshore flow of the rip current megaripples were found to migrate offshore (Mr = 0–4 cm/min). W...

경기만 서부 덕적도 사퇴의 탄성파층서 및 퇴적환경 연구

서해 경기만의 덕적도 서부에 발달하고 있는 사퇴해역에서 획득된 고해상 탄성파탐사자료, 해저면측사탐사자료, 표층퇴적물 및 주상코어시료에 대한 정밀분석과 연구가 실시되었다. 탄성파탐사 자료에 의하면 사퇴의 층서는 3개의 퇴적단위(sequence I, II, III)로 구분되어진다. 최상부 퇴적단위 I은 <TEX>$^{14}C$</TEX> 연대측정 자료에 의하면 5,000~6,000 yr BP경 본 해역이 해침을 받은 후 강한 왕복성 조류에 의하여 형성된 것으로 사료된다. 퇴적단위 II는 주상코어 자료에 의하면 니질이 주로 분포하는 고 조간대 니질퇴적층으로 추정된다. 퇴적단위 III은 중생대에 관입한 화강암으로 분포된 음향기반암 상부에 플라이스토세 말기로 추정되는 육성퇴적층인 자갈 내지는 조립질 퇴적물이 부정합으로 퇴적된 것으로 판단된다. 해저면측사탐사 자료에 의하면 사퇴 정상의 해저면은 모래파가 발달되어 있으며, 이는 대체로 조류의 방향과 일치하는 <TEX>$N20^{\circ}W$</TEX> 방향이다. 사퇴 정상부에서 멀어지면 모래물결자국이 발달하고, 경사면에서는 균질한 사질로 분포한다. 표층퇴적물과 주상퇴적물(시료 VC-1, 2, 3)은 특정 내부 구조를 갖지 않는 비교적 균질한 중립토 내지 세립토(Mz, 1-<TEX>$2{\phi}$</TEX>)로 분포하는 특징을 보인다. We examined high-resolution seismic data, side scan sonar data, surface sediments, and vibrocore samples from a sand ridge off the western part of Dukjuk-Do in Gyeonggi Bay, with the aim of interpretation of seismic stratigraphy and sedimentary environment. Based on the seismic data, the deposited sands are divided into three sedimentary units. 14C age data indicate that the top sequence (sequence I) formed at 5000-6000 yr BP, when a transgression resulted in strong shifting tides. Analyses of the vibrocore samples indicate that sequence II is a paleo-mudflat layer of intertidal sediments dominated by mud. Sequence III consists of terrestrial sediments that are presumed to have been deposited at the end of the Pleistocene, unconformably overlying the acoustic bedrock and Mesozoic granite. The side scan sonar data indicate that sand waves were formed on the seabed on top of the sand ridge. Generally, this is the direction of <TEX>$N20^{\circ}E$</TEX>, which coincides with the direction of tidal flow. Sand ripples occur away from the top of the sand ridge and are distributed homogeneously across a sandy slope. Vibrocore analyses indicate that the surface sediments and core sediments (samples VC-1, -2, and -3) are homogeneous, without any internal structures, and are characterized by a mixture of medium and fine sand (1-<TEX>$2{\phi}$</TEX>), respectively.