Break In Slope Research Articles

Sensitivity of Arctic marine heatwaves to half-a-degree increase in global warming: 10-fold frequency increase and 15-fold extreme intensity likelihood

Abstract We utilize the 50-member MPI-ESM-LR Earth System model to investigate the projected changes in Arctic marine heatwaves' (MHWs) characteristics caused by an additional 0.5°C increase in global warming, from 1.5°C to 2°C, with respect to pre-industrial levels. Our results indicate that this 0.5°C increase in global warming triggers an intensified response in both the Arctic's mean sea surface temperature (SST) and its variability. In a 2°C warmer world, one out of every four summer months would be warmer than the current climate. We detect a nonlinear increase in MHW intensity in a 2°C world, which is characterized by a break in slope occurring around the year 2042 ± 2 (across 50 ensemble members of the SSP5-8.5 scenario). At the estimated post-break dates, the intensity rate roughly doubles, leading to MHWs in a 2°C world with average cumulative heat intensity 100°C*days higher than in a 1.5°C world. Further results reveal that an extremely rare MHW with an intensity of 3.19°C, classified as a 1-in-100-year event in a 1.5°C world, is expected to transform into a 1-in-7-year event in a 2°C world. This transition signifies an approximately 15-fold increase in the likelihood of such events occurring due to a 0.5°C increase in global warming. Likewise, an uncommon event of years with 125 MHW days in a 1.5°C world is projected to become a 1-in-10-year event in a 2°C world, resulting in a 10-fold increase in occurrence probability. The main contributor to these changes is predominantly the rise in mean SST, with enhanced SST variability playing a minor role. These findings highlight that a 2°C world could lead to a substantial escalation of the frequency and intensity of MHWs in the Arctic compared to a 1.5°C world, transforming what are currently rare extreme events into more common events, with significant implications for global climate dynamics and the well-being of Arctic ecosystems and communities.

A NEW TURBIDITE FACIES TRACT SCHEME INCLUDING SUPERCRITICAL AND TRANSITIONAL SAND–MUD FLOWS: AN OUTCROP PERSPECTIVE FROM MEDITERRANEAN-TYPE FORELAND BASINS

The studies carried out on tectonically-confined turbidite systems in Mediterranean-type foreland basins have shown that these deposits can be dominated by supercritical flows and by their transformation into subcritical and/or transit ional (mud-sand) flows. In these confined turbidite systems, flow deceleration is favoured especially by morphologies transversal to paleocurrents, e.g., slope breaks or adverse slopes that can vary in scale from regional tectonic structures to depositional features such as thick mass-transport complexes and lobes. Based on data of more than fifty years of outcrop studies in foreland and wedge top basins, a new facies tract scheme is presented that includes the occurrence of supercritical flow deposits and hybrid event beds in turbidite successions. A review of the main turbidite facies schemes available in the literature is given, and detailed field examples of the Apennine and Alpine (Peira Cava) foreland basins are given that demonstrate the effect of basin morpholo gy on the type of facies tracts. The concept of flow efficiency is revisited as sediment transport depends not only on flow behaviour but also on basin size and basin-floor morphology (e.g., large foredeeps are characterised by facies that reflect high-efficiency, whereas small piggy back basins are characterised by facies related to low-efficiency transport).

Forearc crustal faults as tsunami sources in the upper plate of the Lesser Antilles subduction zone: the case study of the Morne Piton fault system

Abstract. In this study, alternatively to the megathrust, we identify upper-plate normal faults orthogonal to the trench as a possible tsunami source along the Lesser Antilles subduction zone. The Morne Piton fault system is such a trench-perpendicular upper crustal fault at the latitude of Guadeloupe. By means of seismic reflection, high-resolution bathymetry, remotely operated vehicle (ROV) imaging and dating, we reassess the slip rate of the Morne Piton fault since 7 Ma, i.e., its inception, and quantify an average rate of 0.25 mm yr−1 since ca. 1.2 Ma. This result divides by two previous estimations, increases the earthquake time recurrence and lowers the associated hazard. The ROV dive revealed a metric scarp with striae at the toe of the Morne Piton fault system, suggesting a recent fault rupture. We estimate a fault rupture area of ∼ 450–675 km2 and then a magnitude range for a maximum seismic event around Mw 6.5 ± 0.5, making this fault potentially tsunamigenic as the nearby Les Saintes fault responsible for a tsunami following the 2004 Mw 6.3 earthquake. Consequently, we simulate a multi-segment tsunami model representative of a worst-case scenario if all the identified Morne Piton fault segments ruptured together. Our model provides clues for the potential impact of local tsunamis on the surrounding coastal area as well as for local bathymetric controls on tsunami propagation. We illustrate that (i) shallow-water plateaus act as secondary sources and are responsible for a wrapping of the tsunami waves around the island of Marie-Galante; (ii) canyons indenting the shallow-water plateau slope break focus and enhance the wave height in front of the most touristic and populated town of the island; and (iii) the resonance phenomenon is observed within the Les Saintes archipelago, showing that the waves' frequency content is able to perturb the sea level for many hours after the seismic rupture.

Reconciling short- and long-term measurements of coastal cliff erosion rates

Oblique terrestrial laser scanning (TLS) enables topographic change detection at scales (10−1 –100 cm) that are appropriate for coastal cliff erosion monitoring. Despite this, published applications of TLS on cliff are limited to a small number of sites around the world. Here we report new TLS point cloud datasets from 9 years of monitoring (2014–2023) at Rothesay Bay within the Hauraki Gulf, New Zealand, which has relatively low wave energy and a meso-tidal range. The 120 m-length scan area includes cliffs of 10–30 m height, formed of horizontally bedded soft sedimentary flysch rock. The cliffs are fronted by an 140 m wide near-horizontal shore platform that terminates in an abrupt seaward edge. Previous research at this site has estimated long-term cliff erosion rates within a range of 1.4 ± 0.1 to 14.3 ± 0.1 mm/year on the basis of measured shore platform width, assuming that the shore platform has widened over time over 6000 years of stable Holocene sea level, and that the seaward edge of the shore platform has not retreated. Volumetric cliff-face erosion rates were detected through 17 scans over a 9-year window (2014–2023), including intensive monthly TLS scanning between July 2021 and July 2022. Results show that the average cliff recession rate over the past decade has been 41 ± 2 mm/year, and monthly scans show a range in erosion rates of 30 to 288 mm/year. The cliff recession rate detected with TLS is 3 to 30 times higher than erosion rates derived based on the shore platform width. If erosion had been constant at this rate over approximately 6000 years, a total cliff retreat of >245 m would be expected, whereas the contemporary shore platform is only 140 m wide. We discuss two possible hypotheses for the confounding width of the modern shore platform: 1) that modern cliff retreat rates are faster than past erosion rates; 2) that the seaward edge of the shore platform does not reliably demarcate Holocene cliff recession. We present new bathymetric survey mapping seaward of the shore platform edge that reveals multiple rocky features that are distinguished by steep slope breaks and planar surfaces. Understanding the evolution of the intertidal shore platforms during the Holocene era may necessitate new insights on how cliffs formed toward the end of the last marine transgression. This could potentially be investigated through the study of subtidal marine bathymetry.

Characterising the discharge of hillslope karstic aquifers from hydrodynamic and physicochemical data (Sierra Seca, SE Spain)

Groundwater flow has been investigated in the Sierra Seca, Spain. Maximum recharge to the central core of the mountain occurs at high elevations, which provides recharge to two overlapping karst aquifers constituting a groundwater storage zone at a lower elevation break in slope. Both karst aquifers are associated with three springs arising from the upper part of the permeable formations. The climate is characterized by long and intense periods of drought and short periods of rainfall, which trigger discharges from the springs. Spring flow recession curve analysis, cross-correlation and monitoring of groundwater temperature and electrical conductivity have demonstrated contrasts observed in the hydrodynamic and physicochemical response of the three springs during flood events. One spring records floods with narrow and short peaks of high discharge accompanied by sharp drops in temperature and electrical conductivity. Another spring records floods with somewhat wider peaks and sharp increases in temperature and electrical conductivity (piston effect), whereas the third spring shows great consistency in all monitored characteristics. It is concluded that the absence of a piston effect in the spring with the highest flow rates is due to the contribution of rapidly circulating water that is expelled by semi-active karst networks (overflow) before reaching the saturated zone, which does not occur in the other springs due to the absence of overflow hydrological pathways. The most regular spring owes its functioning to the contribution of infiltrated water in the bed of an upstream riverbed, which explains this regularity.

A simple method to automatically remove artificial terrain from airborne LiDAR DTMs in plain areas

Alluvial plains are highly vulnerable to floods and ground disasters. Recent rapid urbanization and climate change have heightened disaster risks in urban areas. Geomorphological maps, crucial for estimating disaster risks, delineate landform boundaries based on patterns of concave breaks of slope and micro-landforms. However, enhancing the accuracy of such maps requires data extraction methods capable of capturing these features with greater precision. Traditional topographic measurements derived from adjacent elevation points in airborne light detection and ranging (LiDAR) digital terrain models (DTMs) fail to accurately represent slope variations on low ground surfaces due to the inclusion of numerous noise-like artificial terrain features. Consequently, analyzing natural terrain becomes challenging. To address this issue, our study devised a method to automatically identify and eliminate noise-like artificial terrain from LiDAR DTMs. We achieved this by removing major artificial terrain features from land-use vector data, creating an edge-preserving smooth DTM, and selectively removing and interpolating only those areas where were large differences between the smooth DTM and the LiDAR DTM. This method minimizes the interpolation of artificial terrain and quotes the LiDAR DTM for other areas, thereby minimizing the data quality loss. It is possible to identify and demarcate topographic boundaries in plains with a longitudinal gradient of approximately 1% or less at a high resolution, which can be used to investigate the relationship between flood and ground characteristics and landform volume in the plains. This method can be easily processed using only QGIS and free open data. This approach enhances the precision of disaster risk estimation and facilitates more effective urban planning in vulnerable areas.

Seismic stratigraphy of the Cretaceous post-rift sedimentary interval in the Punta del Este Basin (offshore Uruguay) and its implications for deep-water reservoirs

The formation of the Punta del Este Basin is associated with the fragmentation of West Gondwana and consequently the opening of the South Atlantic Ocean during the Early Cretaceous. The basin comprises the Cretaceous depocentre of the Uruguayan continental margin (UCM). This study provides a seismic stratigraphic analysis of the Cretaceous post-rift sedimentary interval in the basin by defining its seismic facies, depositional sequences, shelf-edge trajectories and palaeophysiographical settings. All depositional sequences of the Cretaceous post-rift sedimentary interval represent intense basinward progradation marked by two depositional trends. The Lower Cretaceous sedimentary interval exhibits a dominant flat-to-descending shelf-edge trajectory with a migration of up to 37 km. Deposition occurred over an irregular physiography with proximal NW–SE and distal WSW–ENE trends controlled by the characteristics of the volcanic margin. The basin geometry has strong implications for understanding the deposition of a deep-water turbidite system in the UCM, with a strong analogy to the recent discovery of the Venus well in the Orange Basin, offshore Namibia. Towards the Late Cretaceous, the NW–SE depositional trend was controlled by a NE–SW slope break, indicating deposition over the south and north highs. A low-angle ascending shelf-edge trajectory was observed, with a migration of up to 16 km.

Closed vessel burning rate measurements of composite propellants using microwave interferometry

AbstractBurning rate as a function of pressure is one of the primary evaluation metrics of solid propellants. Most solid propellant burning rate measurements are made at a nearly constant pressure using a variety of measurement approaches. This type of burning rate data is highly discretized and requires many tests to accurately determine the burning rate response to pressure. It would be more efficient to measure burning rate dynamically as pressures are varied. Techniques used to make transient burning rate measurements are reviewed briefly and initial results using a microwave interferometry (MI) technique are presented. The MI method used in tandem with a closed bomb enables nearly continuous measurement of burning rates for self‐pressurizing burns, capturing burning rate data over a wide range of pressures. This approach is especially useful for characterization of propellants with complex burning behaviors (e. g., slope breaks or mesa burning). The burning rates of three research propellants were characterized over a pressure range of 0.101–24.14 MPa (14–3500 psi). One research propellant exhibited a slope break at a pressure of 6.63 MPa (960 psi). Using MI in a closed pressure vessel, 14 propellant strand burns resulted in a nearly continuous burning rate curve over a pressure range of 0.41–24.13 MPa (60–3500 psi) that reasonably matched conventional burning rate measurements. The development of this technique provides an opportunity to quickly characterize the burning rate curve of solid propellants with greater fidelity and efficiency than traditional quasi‐static pressure testing techniques.

Kaiwi shoreline basalts fed by the west rift zone of East Molokaʻi

Bathymetry and acoustic imagery swath mapping, along with observations and samples from four manned submersible and four ROV dives, confirm that a seafloor slope break on the northern approaches to Kaiwi Channel, between the islands of Oʻahu and Molokaʻi, Hawaiʻi is a former shoreline, now submerged ∼800 m below present sea level. Subaerially emplaced, low-relief basaltic lavas above the slope break transition to submarine morphologies below. The entire region has been tilted about 1° to the SSE (150°), and is cut by an 8–15 m-high, north-facing scarp, 100–400 m south of the slope break. The distribution of platy, table-top, and rarer mounded branching corals indicates the former presence of fringing reefs around low-relief paleo-islands. We infer that the regional tilt resulted from loading by younger Hawaiian volcanoes, compounded by flexural uplift and back tilting away from the unloaded footwall of a flank landslide to the north.Basalt samples collected from both above and below the slope break have petrography, chemical composition, and age (1.64–1.80 Ma) indicating correlation with the (late-shield) Lower Member of the East Molokaʻi Volcanics, rather than with the more proximal volcano of West Molokaʻi. The most likely source of the Kaiwi basalts is a submarine ridge (rift zone) that extends northwest away from ʻĪlio Point on West Molokaʻi. Although the submarine ridge was previously assumed to be an extension of West Molokaʻi's northwest rift, we conclude that regional bathymetry and gravity are consistent with this feature being an extension of the west rift of East Molokaʻi. A corallary of this interpretation is that the shoreline slope break (SSB 7 of Taylor, 2019) in this area is distinct from and younger than the southern SSB 7 formed on West Molokaʻi volcano (∼1.65 Ma vs. ∼1.8 Ma).

Predicting suitable habitats for foraging and migration in Eastern Indian Ocean pygmy blue whales from satellite tracking data

BackgroundAccurate predictions of animal occurrence in time and space are crucial for informing and implementing science-based management strategies for threatened species.MethodsWe compiled known, available satellite tracking data for pygmy blue whales in the Eastern Indian Ocean (n = 38), applied movement models to define low (foraging and reproduction) and high (migratory) move persistence underlying location estimates and matched these with environmental data. We then used machine learning models to identify the relationship between whale occurrence and environment, and predict foraging and migration habitat suitability in Australia and Southeast Asia.ResultsOur model predictions were validated by producing spatially varying accuracy metrics. We identified the shelf off the Bonney Coast, Great Australian Bight, and southern Western Australia as well as the slope off the Western Australian coast as suitable habitat for migration, with predicted foraging/reproduction suitable habitat in Southeast Asia region occurring on slope and in deep ocean waters. Suitable foraging habitat occurred primarily on slope and shelf break throughout most of Australia, with use of the continental shelf also occurring, predominanly in South West and Southern Australia. Depth of the water column (bathymetry) was consistently a top predictor of suitable habitat for most regions, however, dynamic environmental variables (sea surface temperature, surface height anomaly) influenced the probability of whale occurrence.ConclusionsOur results indicate suitable habitat is related to dynamic, localised oceanic processes that may occur at fine temporal scales or seasonally. An increase in the sample size of tagged whales is required to move towards developing more dynamic distribution models at seasonal and monthly temporal scales. Our validation metrics also indicated areas where further data collection is needed to improve model accuracy. This is of particular importance for pygmy blue whale management, since threats (e.g., shipping, underwater noise and artificial structures) from the offshore energy and shipping industries will persist or may increase with the onset of an offshore renewable energy sector in Australia.

Optimising the reintroduction of a specialist peatland butterfly Coenonympha tullia onto peatland restoration sites

The two main goals of peatland restoration are habitat improvement and climate change mitigation by reducing greenhouse gas emissions from damaged peatlands and providing a net carbon sink. The biodiversity of specialist peatland species is threatened because of habitat destruction and the large heath butterfly Coenonympha tullia has become a flagship species for peatland ecosystem restoration, with a species reintroduction programme currently underway on a peatland restoration site within Chat Moss, Greater Manchester, UK. The aim of this study was to improve our quantitative understanding of C. tullia habitat resource requirements to optimise habitat restoration for further reintroduction attempts. We monitored butterfly micro-distribution and dispersal during the first three flight seasons (2020, 2021 and 2022) of the reintroduction using high-accuracy GPS, combined with a distance-bearing protocol. Analysis of butterfly flight points and rest points in relation to plant species distribution and abundance, identified the most important habitat resources. Using logistic regression, treatment-response curves were constructed, enabling us to identify critical thresholds for the abundance of these important habitat resources. The break of slope near the top of the logistic curve was identified using segmented regression, giving an estimate of the near-optimal abundance; fourteen Eriophorum vaginatum tussocks per 2 m quadrat and 13.4% Erica tetralix cover.Implications for insect conservationDuring ecosystem restorations, prior to the reintroduction of species with specialist habitat requirements, it is necessary to have a clear understanding of the abundance of the important habitat resources that need to be provided. The quantitative approach we describe defines the most significant environmental factors and habitat resources, then uses segmented regression to estimate the near-optimal habitat resource requirements; increasing the likelihood of reintroduced populations thriving and reintroduction programmes achieving long-term success.

Geochemical Pathways Defined by Predictive Regolith-Landform Models Using TanDEM-X Data in the Tanami Region, Australia

The Granites-Tanami Orogen (GTO) is a significant auriferous province located in the poorly exposed southwestern part of the North Australian Craton. This paper looks at the data sources that are suited to studying regolith-landform in areas such as the Tanami Region. One of the most useful datasets for regional regolith-landform mapping is a digital elevation model (DEM). The DEM data that were reviewed demonstrated the utility of TanDEM over other sources, and quantitative results focused on these data for identifying regolith-landform patterns that would aid in geochemical sampling and other land use studies. This paper will demonstrate that neither the classical approach of mapping boundaries based on visual estimates of breaks in slope, nor the alternative approach of producing maps and models derived from algorithms, can be used in isolation. Visual estimates of many boundaries are complex, unreliable and time consuming, and algorithmic mapping is driven by parameters than can produce an infinite set of models. This paper shows that simple landform visualisation is often the most powerful tool for map and model creation, supported by geomorphometric analysis and remotely sensed spectral imagery. The use of TanDEM data is shown to produce the best regolith-landform maps and models of the Tanami Region, which can then improve mineral exploration success.

On‐demand microwave growth of porosity within a granular composite energetic material: Void formation via a dielectric loss phase change binder additive for propellant burning rate control

AbstractThis study demonstrates, for the first time ever, the ability to grow, in an on‐command fashion, porosity within a granular composite energetic material to effect a change in energy output rate. Specifically, the study investigates the change in burning rates of ammonium perchlorate composite propellants as a result of porosity created in situ via microwave field‐driven volatilization of the low boiling point binder additive, ethylene glycol. Theoretical mass densities were measured before and after microwave irradiation finding that the maximum observed %TMD change for tested propellants is 6 %. Propellants were burned at 1.72 MPa to 6.89 MPa pressures, finding that for all propellants, microwave irradiation produced a change in ballistic characteristics. Most propellant formulations demonstrate acceptable burning rate parameters for use within rocket motors; some exhibited a large change in their pressure exponent as well as slope breaks attributed to the onset of convective burning, while microwave irradiation produced no change in burning rate or density in reference propellants without the additive. Microwave heating simulation results are presented to gain insight into the thermal environment of the propellant during microwave irradiation. These results provide valuable insight into propellant formulations that can have their burning rates (and thus the thrust profile for motor grains) altered after casting via microwave irradiation.

Sedimentary evolutionary processes, architecture, and sedimentary model of a lobate shallow-water delta: insights from flume simulation experiments

By using equipment such as time-lapse cameras and 3D laser scanners, this study conducted flume simulation experiments to obtain topographic elevation, the amount of sediment increment, sedimentary cross sections, and other related data and diagrams. Quantitative software was then utilized for sedimentological analysis to clarify the depositional evolution, architecture, and depositional model of lobate shallow-water deltas. The research results show that under the influence of hydraulic conditions and main distributary channels, lobate shallow-water deltas primarily undergo three evolution stages: initial channel formation, distributary channel system formation, and continuous stable evolution stage. The architecture elements of lobate shallow-water deltas can be divided into distributary channels dominated by channel deposition, proximal river mouth bars, transitional bars, and distal bars. The lateral composition and downstream deposition of the river-bar combination are the main structural units of the shallow water delta. The proximal profile distributary channels exist in the form of thick channel sand bodies with multiple repetitive intercalation cycles, and thick proximal bar deposits form on both sides of the distributary channels. The bifurcation of distributary channels in the middle profile leads to a reduction in channel scale, while large-scale proximal bars still develop on both sides of the channel. In the distal profile, a substantial river mouth bar complex is formed at the break of the delta front slope, and with the gradual progradation of the delta, the river mouth bar deposition zone becomes flattened. Based on the insights of the flume simulation experiments, a sedimentary model for lobate shallow-water delta was established.

A JWST Project on 47 Tucanae. Overview, Photometry, and Early Spectroscopic Results of M Dwarfs and Observations of Brown Dwarfs* *The main data set presented in this article was obtained from the Mikulski Archive for Space Telescopes (MAST) at the Space Telescope Science Institute. The specific observations analyzed can be accessed via doi:10.17909/6t82-4360.

James Webb Space Telescope (JWST) observations have been demonstrated to be efficient in detecting multiple stellar populations in globular clusters (GCs) in the low-mass regime of M dwarfs. We present an overview, and first results, of different projects that can be explored by using the JWST observations gathered under program GO2560 for 47 Tucanae, the first program entirely devoted to the investigation of multiple populations in very-low-mass stars, which includes spectroscopic data for the faintest GC stars for which spectra are available. Our color–magnitude diagram (CMD) shows some substructures for ultracool stars, including gaps and breaks in slope. In particular, we observe both a gap and a minimum in the F322W2 luminosity function less than 1 mag apart, and discuss which it could be associated with the H-burning limit. We detect stars fainter than this minimum, very likely brown dwarfs. We corroborate the ubiquity of the multiple populations across different masses, from ∼0.1 M ⊙ up to red giants (∼0.8 M ⊙). The oxygen range inferred for the M dwarfs, both from the CMD and from the spectra of two M dwarfs associated with different populations, is similar to that observed for giants. We have not detected any difference between the fractions of stars in distinct populations across stellar masses ≳ 0.1 M ⊙. This work demonstrates the JWST's capability in uncovering multiple populations within M dwarfs and illustrates the possibility to analyze very-low-mass stars in GCs approaching the H-burning limit and the brown-dwarf sequence.

Remote Sensing-based Morphometry on the Petroliferous Cambay Rift Basin (Gujarat, Western India)

Abstract The Cambay Rift Basin (CRB) is a product of rifting in western India that formed during India’s drift following the breakup of Gondwanaland during the Early Jurassic and Tertiary Periods. Being petroliferous, the basin has attained paramount attention. Seismicity in CRB proves its present-day tectonic sensitivity. Several NNW-SSE, NW-SE and NE-SW trending faults regulate the channel morphology within a portion of the basin. Drainage network systems are proxies of active faulting. Geomorphic indices e.g., long profile analysis, basin-scale parameters, stream length gradient index and sinuosity index along the main channels in the five watersheds have been evaluated in this work. The Index of Active Tectonics (IAT) is derived from the basin-scale parameters and is clubbed into three classes: class 1 (IAT = 1.4 - 1.9), class 2 (IAT = 1.91 - 2.4) and class 3 (IAT = 2.41 - 2.9). IAT Class 1 indicates a higher present-day tectonic activity than the other watersheds such as 1, 2 and 5. Watersheds in the northern and eastern Cambay region (watersheds 3 and 4, and portions of 1 and 5) exhibit higher tectonic activity. Slope breaks and low sinuosity index near the crossing-points in these northern and eastern portions indicate active / weak zones. Along these zones, channels incise vertically and more efficiently than laterally in watersheds 3 and 4. These weak zones may indicate older structures such as lineaments and faults. The Ahmedabad-Mehsana block in watershed 3 and partly in watershed 1 within the CRB with several oil fields are tectonically highly active. Therefore, well-bore stability studies need to be carried out in this block.

Assessment of Sediments’ Transport Triggering Processes through the Identification of Deposition Shapes in Large Reservoirs

Sediment deposition at the bottom of artificial reservoirs has become a worldwide problem. This comprises a dual issue that is, in the first place, associated with the reduction in storage capacity and lifetime of large reservoirs. The second aspect comprises the threat that the sediment represents for the dam structure. This research is mainly aimed at identifying and inferring the main sediments’ triggering processes through a rigorous analysis of deposition shapes in a large reservoir. For identifying the main deposition shapes, a sequential methodology was designed and developed comprising the following stages. First, an analysis of XYZ cartography from bathymetric development was conducted. Then, a shapes categorization was developed that comprises the identification of six types of shapes based on four parameters: slope continuity, slope break, absolute and relative slope, and arc configuration. The third stage comprised a visualization and spatial calculation of shapes through GIS-based cartography. The fourth stage comprised an interpretation of deposition shapes processes: for that, a dual analysis was developed. First, an analysis based on fluvial sediments transport processes was realized. The second stage implied an analysis of the dam influence on fluvial hydrodynamics and sediments transport. Results comprised a quantitative assessment of each shape as well as physical processes identification and interpretation, generating a robust equivalence between shapes and triggering processes. This research proved successful for the identification and characterization of the main deposition and transport processes that may help to prevent, palliate, and/or correct phenomenon of silting in large reservoirs. This detailed knowledge of deposition forms opens new strategies to release sediments from storage water more effectively.

The impacts of profile concavity on turbidite deposits: Insights from the submarine canyons on global continental margins

Submarine canyons are primary conduits for turbidity currents transporting terrestrial sediments, nutrients, pollutants and organic carbon to the deep sea. The concavity in the longitudinal profile of these canyons (i.e. the downstream flattening rate along the profiles) influences the transport processes and results in variations in turbidite thickness, impacting the transfer and burial of particles. To better understand the controlling mechanisms of canyon concavity on the distribution of turbidite deposits, here we investigate the variation in sediment accumulation as a function of canyon concavity of 20 different modern submarine canyons, distributed on global continental margins. In order to effectively assess the isolated impact of the concavity of 20 different canyons, a series of two-dimensional, depth-resolved numerical simulations are conducted. Simulation results show that the highly concave profile (e.g. Surveyor and Horizon) tends to concentrate the turbidite deposits mainly at the slope break, while nearly straight profiles (e.g. Amazon and Congo) result in deposition focused at the canyon head. Moderately concave profiles with a smoother canyon floor (e.g. Norfolk-Washington and Mukluk) effectively facilitate the downstream transport of suspended sediments in turbidity currents. Furthermore, smooth and steep upper reaches of canyons commonly contribute to sediment bypass (i.e. Mukluk and Chirikof), while low slope angles lead to deposition at upper reaches (i.e. Bounty and Valencia). At lower reaches, the distribution of turbidite deposits is consistent with the occurrence of hydraulic jumps. Under the influence of different canyon concavities, three types of deposition patterns are inferred in this study, and verified by comparison with observed turbidite deposits on the modern or paleo-canyon floor. This study demonstrates a potential difference in sediment transport efficiency of submarine canyons with different concavities, which has potential consequences for sediment and organic carbon transport through submarine canyons.

Scattering of mode-1 M2 internal tide in the South China Sea

When the internal tides encounter topography during propagation, the scattering effect will induce the baroclinic energy to transfer from the low mode to the higher mode, which may cause the internal tide to become unstable or even enhance dissipation. The characteristics of scattering of mode-1 M2 internal tide in the northern South China Sea (SCS) and its impact on baroclinic energy dissipation are explored in this study based on numerical simulations. The results show that the energy flux of the mode-1 M2 internal tide gradually weakens during propagation into the South China Sea. In the northern SCS, which has more complex topography, such as the continental slope, scattering will occur, resulting in a vertical mode increase and shear enhancement, and finally, the baroclinic energy is dissipated. Next, the effect of different topographies on mode-1 M2 internal tide scattering is analyzed by ideal experiments. The mode-1 M2 internal tide is scattered by topography, and the propagation as well as dissipation are also modified. The results show that the strong energy flux is mainly distributed on the surface of the continental slope and the area near the slope break. With the increase in criticality, the energy flux around the seamount and on the shelf gradually weakens, and the dissipation rate increases continuously. In addition, the slope topography is more likely to induce internal tide scattering than the seamount topography.

Characteristics and geological significance of early carboniferous soft-sediment deformation structures in the Kushanhe section, southwest Tarim Basin, Northwest China

The early Carboniferous Kushanhe Formation and Hantiereke Formation in the Kushanhe section in the piedmont of the southwestern margin of Tarim Basin are in a medium-deep water sedimentary environment with a stratigraphic thickness of more than 500 m, and the sedimentary facies is slope-shelf facies. Among these deposits, soft-sediment deformation structures (SSDS) are common, dominated by various types of slumps. The appearance of SSDS is related to the geotectonic environment of early Carboniferous in southwest Tarim Basin. In the Early Carboniferous, the Paleo-Tethys ocean dived under the Tarim plate, forming a back-arc structure, and a structural slope break belt easily appeared along the basin edge, which provided topographic conditions for the development of marginal platform marginal belt and slope facies. Under this background, the ultra-thick volcanic rocks of Wulate Formation accumulate along the subduction zone, and earthquakes with M≥ 5.0 are prone to occur. Landslides related to earthquakes and corresponding SSDS are easily triggered at the outer edge of the slope break zone. The large earthquake induced by tectonic environment is an important trigger factor of early Carboniferous SSDS. Therefore, the appearance of early carboniferous SSDS in Kushanhe section is an important sedimentary response to the early carboniferous piedmont tectonic activities in southwestern Tarim.