Flow Direction Indicators Research Articles

A Characterisation of Benthic Currents from Seabed Bathymetry: An Object-Based Image Analysis of Cold-Water Coral Mounds

Seabed sedimentary bedforms (SSBs) are strong indicators of current flow (direction and velocity) and can be mapped in high resolution using multibeam echosounders. Many approaches have been designed to automate the classification of such SSBs imaged in multibeam echosounder data. However, these classification systems only apply a geomorphological contextualisation to the data without making direct assertions on the velocities of benthic currents that form these SSBs. Here, we apply an object-based image analysis (OBIA) workflow to derive a geomorphological classification of SSBs in the Moira Mounds area of the Belgica Mound Province, NE Atlantic through k-means clustering. Cold-water coral reefs as sessile filter-feeders benefit from strong currents are often found in close association with sediment wave fields. This OBIA provided the framework to derive SSB wavelength and wave height, these SSB attributes were used as predictor variables for a multiple linear regression to estimate current velocities. Results show a bimodal distribution of current flow directions and current speed. Furthermore, a 5 k-means classification of the SSB geomorphology exhibited an imprinting of current flow consistency which altered throughout the study site due to the interaction of regional, local, and micro scale topographic steering forces. This study is proof-of-concept for an assessment tool applied to vulnerable marine ecosystems but has wider applications for applied seabed appraisals and can inform management and monitoring practice across a variety of spatial and temporal scales. Deriving spatial patterns of hydrodynamic processes from widely available multibeam echosounder maps is pertinent to many avenues of research including scour predictions for offshore structures such as wind turbines, sediment transport modelling, benthic fisheries, e.g., scallops, cable route and pipeline risk assessment and habitat mapping.

Mineralogical control on the magnetic anisotropy of lavas and ignimbrites: a case study in the Caviahue-Copahue field (Argentina)

SUMMARY Anisotropy of magnetic susceptibility is a petrofabric tool used to estimate the alignment of minerals at the site-scale, the imbrication between the magnetic foliation and the emplacement surface being an indicator of flow direction. However, despite numerous studies examining the flow direction in pyroclastic deposits and lava flows, the effect of magnetic mineralogy and the domain state of ferromagnetic phases on the magnetic fabric remains poorly understood. This paper describes the magnetic mineralogy and its influence on the magnetic fabric of Plio-Pleistocene lava flows and ignimbrites of the Caviahue-Copahue Volcanic Complex in the Andean Southern Volcanic Zone, Argentina. Rock magnetism, anisotropy of magnetic susceptibility and anhysteretic remanent magnetization and petrographic observations were performed on 30 sites of the volcanic complex. Results revealed the extrusive and pyroclastic rocks present varied magnetic mineralogy, formed in different stages of the magmatic evolution. Magnetic mineralogy variations strongly affect the anisotropy of magnetic susceptibility data in volcanic rocks and associated ignimbrites, providing ‘scattered’ fabrics when late Ti-rich titanomagnetite phases dominate the fabric, and ‘inverse’ or ‘intermediate’ fabrics when single-domain grains are present. ‘Normal’ fabrics are typically found when early crystallized pure magnetite is present. Our results highlight the complexity in the interpretation of magnetic anisotropy data in volcanic rocks and ignimbrites.

Sedimentary and geochemical signature of the 2016 Kaikōura Tsunami at Little Pigeon Bay: A depositional benchmark for the Banks Peninsula region, New Zealand

The 14 November 2016 Kaikōura Tsunami inundated Little Pigeon Bay in Banks Peninsula, New Zealand, and left a distinct sedimentary deposit, on the ground and within the cottage near the shore. Sedimentary (grain size) and geochemical (electrical conductivity and X-Ray Fluorescence) analyses on samples collected over successive field campaigns are used to characterize the deposits. Sediment distribution observed in the cottage in combination with flow direction indicators suggests that sediment and debris laid down within the building were predominantly the result of a single wave that had been channeled up the stream bed rather than from offshore. Salinity data indicated that the maximum tsunami-wetted and/or seawater-sprayed area extended 12.5 m farther inland than the maximum inundation distance inferred from the debris line observed a few days after the event. In addition, the salinity signature was short-lived. An overall inland waning of tsunami energy was indicated by the mean grain size and portable X-Ray Fluorescence elemental results. ITRAX data collected from three cores along an inland transect indicated a distinct elevated elemental signature at the surfaces of the cores, with an associated increase in magnetic susceptibility. Comparable signatures were also identified within subsurface stratigraphic sequences, and likely represent older tsunamis known to have inundated this bay as well as adjacent bays in Banks Peninsula. The sedimentary and geochemical signatures of the 2016 Kaikōura Tsunami at Little Pigeon Bay provide a modern benchmark that can be used to identify older tsunami deposits in the Banks Peninsula region.

Determining glacier flow direction from till fabrics

Field and experimental data indicate that fabrics of sheared basal tills, based on particle orientations and on anisotropy of magnetic susceptibility, are inclined relative to the macroscopic plane of shear. As a result, if this plane is tilted with a transverse component, one of the longest-standing axioms of glacial geology—that particles in basal till are preferentially oriented parallel to the direction of shear—is not strictly true. The resultant correction to the shearing direction increases with the transverse and longitudinal components of shear-plane inclination and with the magnitude of the fabric inclination relative to the shear plane. Azimuthal corrections calculated herein range from being negligible to a few tens of degrees for reasonable ranges of shear-plane tilt. The past success of fabric azimuths as indicators of flow direction, despite the absence of this correction, likely reflects the clustering of shear planes about the horizontal in basal tills. However, on the flanks of accreting subglacial bedforms, shear-plane attitudes may well conform to the local bedform slope. As illustrated with hypothetical fabrics of drumlins and flutes, azimuthal corrections can in that case be sufficiently large and systematic to seriously affect interpretations of bedform genesis.

Simple Nonparametric Estimators for the Bid-Ask Spread in the Roll Model

We propose new methods for estimating the bid-ask spread from observed transaction prices alone. Our methods are based on the empirical characteristic function instead of the sample autocovariance function like the method of Roll (1984). As in Roll (1984), we have a closed form expression for the spread, but this is only based on a limited amount of the model-implied identification restrictions. We also provide methods that take account of more identification information. We compare our methods theoretically and numerically with the Roll method as well as with its best known competitor, the Hasbrouck (2004) method, which uses a Bayesian Gibbs methodology under a Gaussian assumption. Our estimators are competitive with Roll’s and Hasbrouck’s when the latent true fundamental return distribution is Gaussian, and perform much better when this distribution is far from Gaussian. Our methods are applied to the E-mini futures contract on the S&P 500 during the Flash Crash of May 6, 2010. Extensions to models allowing for unbalanced order flow or Hidden Markov trade direction indicators or trade direction indicators having general asymmetric support or adverse selection are also presented, without requiring additional data.

Directions of ice flow during the last glaciation in counties Meath, Westmeath and Cavan

Ice flow direction indicators in north-west County Meath and adjacent parts of Westmeath and Cavan are described. Drumlins. striae, roche moulonnees. and oilier streamlined features, as well as till fabrics, suggest a general How during glacial maximum of north-west to south-east when combined with erratic carriage data. Analysis of the configuration of ice marginal moraines and subglacially deposited esker ridges deposited during glacial retreat, as well as till fabric analysis of deglacial sediments, suggest a more complicated retreat of ice, with margins oriented south-wesI to north-east prevailing in the south and cast of the study area. Further to the west and south-west there seems to be an element of retreat towards the west, with a north-south trending ice margin. This is suggested as providing evidence for a decoupling of the ice into separate lobes in that area.

Using magnetic fabric to reconstruct the dynamics of tsunami deposition on the Sendai Plain, Japan — The 2011 Tohoku-oki tsunami

Abstract The magnetic fabric and grain size of sand deposits emplaced during the 2011 Tohoku-oki tsunami were studied in five trenches along a 1800 m long shore normal transect on the Sendai plain as well as in a near shore sedimentary infill of a scour depression. The magnetic susceptibility in all deposits is due to ferromagnetic minerals (mainly magnetite) making the anisotropy of magnetic susceptibility (magnetic fabric) suitable for fabric analyses. The dominant magnetic fabric is planar in all trenches and stronger in finer-grained inland deposits than in the coarser sediments. This planar fabric is related to tractive shearing of the bedload basal portion of the tsunami flow that led to the deposition of traction carpet layers. Among the various fabric parameters used for this study, the vertical evolution of the shape factor ( q ) of the magnetic ellipsoid in each trench follows the evolution of the magnetic lineation ( L ) and foliation ( F ). These parameters provide information on the hydrodynamic energy (flow speed) fluctuations during the emplacement of the tsunami deposit. For the most proximal deposits, characterized by well-sorted reworked beach sand with minor fluctuations in grain-size distribution, the magnetic fabric is sensitive to hydrodynamic energy variations during sedimentation. Reconstruction of tsunami flow orientation in the sediments, based on the orientation of the mean K max calculated for each trench, appears to be unambiguous only for the sandy infills of small topographic depressions. The variations in flow direction indicators elsewhere could be related to local variation of the flow and to micro-topographic effects. These findings are encouraging for the use of the magnetic fabric proxy in the study of paleotsunami deposits.

The Use of Topography as an Indicator of Ground Water Flow Direction and Its Implications for Due Diligence

Abstract Topography often is used as a quick and preliminary method to identify local and regional ground water flow patterns within the upper-most saturated interval. This approach usually is applied in designing shallow monitoring networks at properties or in areas where little to no site specific hydrogeologic data are available. Perhaps the most problematic application of this method is in due diligence. Critical business decisions regularly are made based on potential environmental impacts from surrounding parcels using topographic presumptions about upgradient or downgradient ground water flow directions. However, what most practitioners fail to realize is that topography is a reliable predictor of ground water flow only under a fairly narrow range of physiographic conditions. To assist in determining when topography should be used to evaluate ground water flow direction within the upper-most saturated interval, we have developed an evaluation matrix that allows the investigator, who may have only modest hydrogeologic training, to rapidly identify when topography can be appropriately and reliably used to determine shallow ground water flow directions. Limitations on the use of the matrix are provided as well as suggestions for obtaining site specific data that allow for a more definitive understanding of shallow ground water flow without the need for intrusive field work.

The topography of drumlins; assessing their long profile shape

AbstractThe literature on drumlins is pervaded by the notion that their longitudinal profile is usually highly asymmetric with a stoss steeper end and a lee gentler end, and that this can be used to infer the palaeo ice flow direction. The idea is built up in many papers covering more than a century of research. However, most of the early published papers were qualitative in nature and more recent quantitative papers appear to challenge the ubiquity of the classical stoss–lee shape. Here the shape of the drumlin longitudinal profile of 29,238 drumlins in the British Isles has been analysed. Drumlins were grouped into flowsets for which a palaeo ice flow direction was inferred independently of the drumlin shape. Given such ice flow directions it was then possible to identify the upflow and downflow ends of each drumlin and to trace and extract its longitudinal profile. Results indicate that the highest point of the drumlin is usually found around half way along the profile. The mean slope angles at the stoss and lee ends were found to be very similar. Finally, the average profile built from all mapped drumlins appears almost symmetric. In conclusion, drumlin longitudinal profile is far from being the classically asymmetric shape widely reported in text‐book descriptions. Drumlins are mostly symmetrical in shape with a very slight tendency towards the classical shape. Highly asymmetric drumlins do exist but are rare and with an almost equal numbers of drumlins that are the reverse of this. These findings are verified both at the entire population level and the flowset level. This demonstrates that the idealized stoss–lee shape of classically‐asymmetric drumlins is not representative of the population and should be replaced with that of mostly symmetric bumps. Drumlin shape is not a good indicator of the palaeo ice flow direction. Copyright © 2010 John Wiley & Sons, Ltd.

Emplacement of multiple magma sheets and wall rock deformation: Trachyte Mesa intrusion, Henry Mountains, Utah

A detailed structural and rock magnetic study of the Trachyte Mesa intrusion and deformed sedimentary wall rocks, Henry Mountains, Utah, indicates that the intrusion grew vertically and horizontally by the accumulation of multiple horizontal magma sheets. 2–3 cm thick shear zones recognized by intensely cataclasized plagioclase phenocrysts define the contact between sheets. Sheets have bulbous and / or steep frontal terminations and are flat on top. The foliation within the interior of the sheets, near the frontal termination, is subvertical. This steep foliation rotates into the subhorizontal shear zones near the top and bottom contacts and provides a magma flow direction indicator. Away from the frontal termination, the interior foliation rotates to become subhorizontal, similar to the fabric in recent analog experimental studies. Sheets are interpreted as being emplaced as plug flows. Both the field fabric and the rock magnetic data collected from 103 locations on the top of the intrusion and from 73 locations along a vertical cross section exposed in a stream gorge support a multi-stage model of intrusion growth. Emplacement begins as narrow magma channels and magma spreads radially outward from the channels to form sheets. Sheets are stacked upon one another and stop at the same lateral termination. The deformation of the sandstones at the margin of the intrusion, which are rotated upward from the margin to become the roof, is partitioned into layer parallel extension, shearing and layer-parallel shortening components. Bulk strain within the thickest sandstone layer indicates ∼20% thinning and microstructures indicate that the thinning was accommodated by grain-scale fracture-induced porosity collapse. Extension occurred as the layer was stretched over the margin of the rising intrusion. Shearing and layer-parallel shortening are a result of coupling with the underlying sheets as they advanced and accommodated through numerous faults parallel to bedding and at low angles to bedding. The deformation of thinner sedimentary layers is consistent with the sedimentary layering immediately in front of an advancing sheet being translated upward and over the top of the sheet as the hinge zone migrates with the front edge of the advancing sheet.

Erosion and Sedimentation from the 17 July, 1998 Papua New Guinea Tsunami

— This paper describes erosion and sedimentation associated with the 17 July 1998 Papua New Guinea tsunami. Observed within two months of the tsunami, distinct deposits of a layer averaging 8-cm thick of gray sand rested on a brown muddy soil. In most cases the sand is normally graded, with more coarse sand near the base and fine sand at the top. In some cases the deposit contains rip-up clasts of muddy soil and in some locations it has a mud cap. Detailed measurements of coastal topography, tsunami flow height and direction indicators, and deposit thickness were made in the field, and samples of the deposit were collected for grain-size analysis in the laboratory. Four shore-normal transects were examined in detail to assess the shore-normal and along shore distribution of the tsunami deposit. Near the shoreline, the tsunami eroded approximately 10–25 cm of sand from the beach and berm. The sandy layer deposited by the tsunami began 50–150 m inland from the shoreline and extended across the coastal plain to within about 40 m of the limit of inundation; a total distance of up to 750 m from the beach. As much as 2/3 of the sand in the deposit originated from offshore. Across most of the coastal plain the deposit thickness and mean grain size varied little. In the along-shore direction the deposit thickness varied with the tsunami wave height; both largest near the entrance to Sissano Lagoon.

Automatic flow angle correction by ultrasonic vector

An ultrasound system produces an image including a blood vessel. A blood flow direction indicator is displayed over the blood vessel to indicate the direction of blood flow within the vessel. The direction of blood flow is used to correct the Doppler estimate for angle of insonation. The orientation of the blood flow direction indicator is set automatically by a vector processor. The automatically calculated angle is used to display the correct flow velocity without user intervention.

Flow mechanism of the Des Moines lobe of the Laurentide ice sheet

AbstractRapid flow of the Des Moines lobe of the Laurentide ice sheet may have been related to its unlithified substrate. New reconstructions of the lobe, based on moraine elevations, sediment subsidence during moraine deposition, and flow-direction indicators, indicate that the lobe may have been ∼3 times thicker than in previous reconstructions. Nevertheless, implied basal shear stresses are <15 kPa, so internal ice deformation was not significant. Instead, the lobe likely moved by a combination of sliding, plowing of particles through the bed surface, and bed shear. Consolidation tests on basal till yield preconsolidation stresses of 125–300 kPa, so effective normal stresses on the bed were small. A model of sliding and plowing indicates that at such stresses most particles gripped by the ice may have plowed easily through the till bed, resulting in too small a shear traction on the bed to shear it at depth. Consistent with this prediction, measurements of orientations of clasts in basal till yield a weak fabric, implying pervasive bed shear strain less than ∼2, although some stronger fabrics have been reported by others. We infer, tentatively, that movement was principally at the bed surface by plowing.

Downflow amplitude decrease of ground penetrating radar reflections in base surge deposits

Ground penetrating radar (GPR) data were collected parallel to a flow direction in the base surge deposits of the Ubehebe hydrovolcanic field (Death Valley, California). These data showed a downflow amplitude decrease of the reflections that was displayed by computing Fourier transforms and the average square of the sample points of the traces. This trend probably reflects some aspects of the lateral facies variation of base surge deposits, and could be explained by the concomitant downflow increase in sorting and decrease in grain size with a consequent reduction of the differences between the beds, which, in turn, causes a reduction of the reflected energy. These results suggest that, although the GPR profiles are traditionally used merely as 2-D images of the subsurface stratigraphy, they could be useful in obtaining information about the heterogeneous distribution of subsurface physical properties. The downflow decrease of the amplitude of the signal could be used as a flow direction indicator when the position of the vent is unknown, although other geologic information and field constraints are probably necessary.

New advances in mitigating environmental impact of pipe-type cables

Through a comprehensive and aggressive research program, the Consolidated Edison Company of New York, Inc. (Con Edison) has designed, developed and installed several new products to address the environmental impact of leaked dielectric fluid from pipe-type cable systems. These include online leak detection, leak location, retractable flow direction indicator, full stop joints and transition joints. This paper describes the application of the aforementioned products on the Con Edison underground transmission system.

Reconstruction of ice flow across the Bunger Hills, East Antarctica

In the Bunger Hills, mapping of glacial drift sheets and examination of striae patterns and other palaeo-ice flow direction indicators show that the largely ice-free region records the imprint of ice sheet expansion(s) during the late Cenozoic. In particular, ice moulded features and striae in southern Bunger Hills suggest formation during at least two episodes of ice sheet expansion, although whether they were formed during separate events or merely different phases of the same expansion of the ice sheet is not able to be discerned at present. The older event relates to thin ice with flow constrained by the topography, whilst the younger event relates to regional expansion of thick ice across the area. Discrimination of the order of emplacement of the cross-cutting striae patterns is possible at a number of sites. Palaeo-ice flow indicators confirm that ice sheet expansion over southern Bunger Hills was purely from the southern and eastern margins, although minor advances of the north-east flowing Edisto Glacier onto coastal areas occurred following retreat of the last extensive ice sheet phase.

The reliability of anisotropy of magnetic susceptibility (AMS) data as flow direction indicators in friable base surge and ignimbrite deposits: Italian examples

The base surge deposits in Linosa and Procida islands (Italy) show minimum axes ( K 3) of the anisotropy of magnetic susceptibility (AMS) that are mostly parallel to the flow directions inferred from field evidence, but sometimes perpendicular to them. Samples from different heights above the base of an ignimbrite bed (Vulsini area, Italy), showing a coarse tail reverse grading and a fine-grained basal layer, have different magnetic fabrics: at 10 and 40 cm from the base the declinations of maximum axes ( K 1) of the AMS are approximately 90 ° from the theoretical flow direction, whereas at 60 and 75 cm from the base the K 1 axes are approximately parallel to the flow direction. This bed also shows a decrease upward of the magnetic foliation, lineation and degree of anisotropy, suggesting that the AMS data could be used to obtain information about flow mechanisms. The AIRM data in the case of the ignimbrite bed show that the long shape axes of the ferromagnetic grains are probably aligned with the maximum axes of the AMS. For this reason the change in the magnetic fabric at different distances from the base is probably due to differences in the flow behaviour rather than the domain state of magnetite grains. This study shows that the AMS lineations can indicate the flow direction in base surge and ignimbrite deposits but other geological and magnetic information is necessary to assess if these lineations are flow perpendicular or flow parallel.

The Kizilkaya ignimbrite — an unusual low-aspect-ratio ignimbrite from Cappadocia, central Turkey

The 4.3-m.y.-old medium-volume low-aspect-ratio Kizilkaya ignimbrite (50–100 km 3 DRE) is one of the most widespread in the Cappadocian Volcanic Province covering about 8500–10,600 km 2. The ignimbrite rests on a relatively fine-grained fan of Plinian pumice-fall deposit ( Md of 1.0–1.80 mm in proximal locations). The eruptive center was located in the Misli plain northeast of Nigde, as deduced from thickness and grain-size variations of the fall deposit, flow direction indicators, welding patterns of the ignimbrite and the distribution of certain types ofxenoliths. The massive ignimbrite, generally about 15 m thick, covers a paleoplain throughout at least two thirds of its areal extent. It comprizes two flow units, identified by local pumice enrichment in the upper part of the lower unit. The ignimbrite is completely welded in many places. In other places, the lower flow unit is non-welded, particularly where the initial pumice-fall deposit was eroded, a fine-grained ground layer was deposited, and undulating or cross-laminations with antidunes were developed. The ground layer was derived from the ignimbrite ground-mass by loss of fines < 250–500 μm. Depositional characteristics indicate that the ignimbrite was emplaced as high-concentration flows with relatively low velocity and low heat loss during runout. Local development of a ground layer and internal bedding structures indicate local increased turbulence only within individual flow portions due to agitated fluidization from engulfed air. The degree of welding of the lower flow unit was controlled by this turbulence and is not related to thickness variations.

Magmatic flow-direction indicators in a giant diabase feeder dike, Connecticut

Recent studies have suggested that many large diabase dikes have been emplaced laterally rather than vertically. These studies report only unidirectional flow, which is usually based on measurements of anisotropy of magnetic susceptibility. However, in the 250-km-long Higganum dike of southern New England (United States), seven independent flow-direction indicators record a complex history of forward- and backward-moving magma. We would expect other similar-size dikes to have had equally complex histories. Measurements within one en echelon segment of the Higganum dike show that as the magma rose, it spread laterally toward the ends of the segment and that backflow was in the reverse direction of the forward flow. The Higganum dike is interpreted to have formed from a linear array of intrusive fingers, each finger spreading laterally to form an en echelon dike segment as it rose through the lithosphere.

Late Quaternary turbidity current pathways to the Madeira Abyssal Plain and some constraints on turbidity current mechanisms

AbstractTurbidites deposited in the Madeira Abyssal Plain during the last 200 000 yr originated mainly from the flanks of the Canary Islands and from the Northwest African continental margin north of the Canaries. Derivation of these turbidites from sources to the east of the abyssal plain apparently contradicts flow direction indicators derived from the sediments on the plain, which indicate derivation from the north‐east. However, two systems of shallow channels, mapped using side‐scan sonar and 3.5‐kHz data, link the easterly sediment sources to the north‐eastern edge of the abyssal plain, reconciling the apparently contradictory flow direction data. A northern system originates in the area between Madeira and the Canary Islands and follows a westerly and then north‐westerly path, in part cutting obliquely across regional bathymetric trends. It carries sediment from the African continental margin north of the Canary Islands, and from the eastern Canaries, to the north‐eastern abyssal plain. The southern channel system carries material from the western Canary Islands more directly westward to the central part of the plain. The pathways of individual turbidites can be reconstructed in some detail, by combining channel mapping with published information on turbidite provenance and flow directions on the Madeira Abyssal Plain. Interaction between turbidity currents and channel morphology controls turbidite depositional patterns. Small turbidites are completely contained within channels 20 m deep and 2 km wide. It is proposed that these are relatively high‐density flows which have evolved in crossing the almost flat floor of a basin south‐east of Madeira before entering the channel system. Larger turbidites show evidence of flow stripping where they interact with channels, with the result that their coarse and fine fractions follow different paths to and across the abyssal plain.