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The battering of bedrock by bedload collisions is the primary mechanism by which bedrock rivers erode and landscapes evolve. The energy imparted via impacts acts to detach bedrock via the growth and intersection of surface fractures. We present impact experiments designed to test the influence of particle impact energy on bedrock erosion rates. We found that erosional efficiency increased with increasing impact energy. Notably, these increases in efficiency are not captured by a widely‐used mechanistic bedrock erosion model. Observed increases in erosional efficiency were linked with enhanced elastic energy dissipation captured by differences in the coefficient of restitution. We suggest that this increase in energy dissipation is indicative of enhanced crack extension for high velocity impacts. Our experiments indicate a clear energy‐dependence for bedrock detachment processes that is not yet captured by bedrock incision models but may be integrated into long‐term erosion rates and landscape evolution. Plain Language Summary: Bouncing sediment grains batter the bedrock beds of rivers during floods. As these impacts collide with the bed, they slowly chip away at the riverbed bedrock. It's perhaps intuitive that a grain with more energy when it collides with the riverbed is able to chip away more bedrock. But, how much more destructive are these high energy impacts? We designed an experiment where we hit a bedrock sample with a steel ball at a range of impact energies, over and over again, up to 30,000 times, and measured how much material was chipped away. High energy impacts eroded more material, but this increased efficiency of erosion is not fully captured by impact‐based erosion models. We hypothesize that for higher energy impacts, a larger fraction of the incoming energy is used to crack the bedrock, more easily eroding material. We liken the relative influence of these high energy impacts to a battering ram, where only a few strikes can easily break down a door, whereas lower energy impacts, similar to a simple knock, are unlikely to achieve the same result. We suggest that this effect may be important in determining the influence of extreme events on bedrock erosion over long timescales. Key Points: Impact experiments demonstrate that bedrock erosional efficiency is enhanced with increasing impact energyExperimentally‐derived coefficients of restitution and rock resistance coefficients indicate enhanced elastic energy dissipation with increasing impact energyResults suggest that more energetic impacts enhance crack extension, increasing erosional efficiency [ABSTRACT FROM AUTHOR]

Hydrogeomorphology studies river dynamics, focusing on the interactions between flow structure, sediment transport, and the morphologies that characterize rivers and their watersheds. It provides an analytical framework and tools for better integrating knowledge of river dynamics into river management in the broadest sense, and more specifically, into river restoration as well as into the assessment and prevention of risks associated with fluvial hazards. In Quebec, hydrogeomorphology is emerging as a significant contribution to risk assessment and management approaches, and is at the heart of a paradigm shift in river management whereby process restoration aims to increase the resilience of fluvial systems and societies, and improve the quality of fluvial environments. This contribution outlines the trajectory of hydrogeomorphology in Quebec, based on scientific publications by Quebec geographers, and discusses the discipline's aims in research and knowledge integration for river management. Messages clés: Les géographes du Québec ont contribué fortement au développement des connaissances et outils de l'hydrogéomorphologie.L'hydrogéomorphologie a évolué d'une science fondamentale à une science où les connaissances fondamentales sont au service de la gestion des cours d'eau.L'hydrogéomorphologie et le cortège de connaissances et d'outils qu'elle promeut font de cette discipline une partenaire clé pour une gestion holistique des cours d'eau. [ABSTRACT FROM AUTHOR]

Mount Meager is a deeply eroded quaternary volcanic complex located in southwestern British Columbia (BC) and is known for its frequent large landslides. In 2010, the south face of Mount Meager collapsed, generating a long-runout debris avalanche that was one of the largest landslides (50 × 106 m3) in Canadian history. Over the past 14 years, the landslide deposit has been reworked by stream action, delivering large amounts of sediment to Lillooet River, just downstream. In this study, we investigate 10 years of geomorphic evolution of the landslide deposit using orthophotos and digital elevation models (DEMs) generated using Structure from Motion (SfM) photogrammetry on aerial photographs acquired during unmanned aerial vehicle (UAV) and Global Navigation Satellite System (GNSS) surveys. The SfM products were used to produce a series of precise maps that highlight the geomorphological changes along the lower Meager Creek within the runout area of the landslide. Comparison of DEMs produced from 2010, 2012, 2015, and 2019 imagery allowed us to calculate deposit volume changes related to erosion, transport, and redeposition of landslide material. We estimate that about 1.1 × 106 m3 of sediment was eroded from the landslide deposit over the period 2015–2019. About 5.2 × 105 m3 of that sediment was redeposited inside the study area. About 5.8 × 105 m3 of sediment, mainly sand, silt, and clay, were exported from the study area and are being carried by Lillooet River towards Pemberton, 40 km from Mount Meager, and farther downstream. These remobilized sediments likely reduce the Lillooet River channel capacity and thus increase flood hazards to the communities of Pemberton and Mount Currie. Our study indicates a landslide persistence in the landscape, with an estimated 47-year half-life decay, suggesting that higher flood hazard conditions related to increased sediment supply may last longer than previously estimated. This study shows the value of using SfM in tandem with historic aerial photographs, UAV photos, and high-resolution satellite imagery for determining sediment budgets in fluvial systems. [ABSTRACT FROM AUTHOR]

Despite geomorphic processes being increasingly recognized as a vital component of river management projects, evidence suggests that they may not be adequately captured in common river assessment procedures. We reviewed 91 river assessment procedures from around the world to evaluate their effectiveness in capturing geomorphic processes relevant for river management goals. Our objectives were to summarize which common geomorphic indicators are measured and how in different types of river assessments categorized based on their main focus: geomorphic, physical habitat, mixed geomorphic and habitat, and hydromorphology. Our analysis identified differences in the types of geomorphic indicators included and measurement methodologies between the types of assessment procedures. Some geomorphic processes, such as sediment transport, are nearly completely absent from all assessments, despite their importance for geomorphic processes. The variability among assessment procedures suggests that a single procedure is unlikely to capture all geomorphic components required to support every river management programs. Here, we discuss how the strengths and limitations of different assessment types can be used to guide decisions around how to select assessments and geomorphic indicators to support management project goals. A companion paper expands the discussion of how to plan effective river assessment procedures to support unique management goals. [ABSTRACT FROM AUTHOR]

Natural channel design (NCD) and analytical channel design (ACD) are two competing approaches to stable channel design that share fundamental similarities in accounting for sediment transport processes with designs based on hybrid fluvial geomorphology and hydraulic engineering methods. In this paper, we highlight the linkage between ACD's capacity/supply ratio (CSR) and NCD's sediment capacity models (FLOWSED/POWERSED), illustrating how ACD and NCD have reached a point of convergent evolution within the stream restoration toolbox. We modified an existing CSR analytical spreadsheet tool which enabled us to predict relative channel stability using both conventional bed load transport equations and regional sediment regression curves. The stable channel design solutions based on measured data most closely matched the Parker (ACD) and/or Pagosa good/fair (NCD) relationships, which also showed the greatest CSR sensitivity in response to channel alterations. We found that CSR differences among the transport relationships became more extreme the further the design width deviated from the supply reach, suggesting that a stable upstream supply reach may serve as the best design analog. With this paper, we take a step toward resolving lingering controversy in the field of stream restoration, advancing the science and practice by reconciling key differences between ACD and NCD in the context of reach scale morphodynamics. [ABSTRACT FROM AUTHOR]

The interaction of sedimentary systems with oceanographic processes in deep‐water environments is not well understood yet, despite its importance for palaeoenvironmental reconstructions, and for a full understanding of source‐to‐sink sediment transport. The aim of this study is to improve the understanding of how contourite moats, elongated depressions formed by bottom currents associated with contourite drifts, develop and of the link between moat‐drift system morphology and bottom current dynamics. This study provides a systematic comparison of 185 cross‐sections of moat‐drift systems distributed at 39 different locations worldwide, and a detailed analysis of the morphology of six moats that cover a wide range of typical geological and hydrodynamic settings. Additionally, in situ measured current data were analysed to better link hydrodynamics to moat morphology. The median of all profiles across all moat‐drift systems reveals a 50 m relief, a width of 2.3 km, a relief to width ratio of 0.022, a slope angle of 6°, a drift angle of 3° and a concave‐up shaped morphology. Moats can be over 100 km long. Some moats are driven by sediment erosion while others are depositional and primarily exist due to differential sedimentation inside the moat compared to the drift alongside the moat. A new sub‐classification of moat‐drift systems based on their stratigraphy is proposed. This classification distinguishes moats depending on the degree of erosion versus deposition. No relation is found between latitude and moat‐drift morphology or stratigraphy in the analysed examples. The combined data indicate that a steeper slope focuses the current more than a gentle slope, resulting in an increase of the relief–width ratio and drift angle. Thus, this study provides new insights into the interaction of ocean currents with sedimentary morphology, which thereby affects the evolution of a poorly understood deep‐water sedimentary system. [ABSTRACT FROM AUTHOR]

This study aimed to characterize the sedimentary facies and understand the morphodynamics of the study area, and their results were correlated with various analytical methods. Different analyses such as depositional environmental, statistical, shoreline change, and grain size illustrated the temporal and spatial distribution of sediments. It has previously been claimed that current research locations are locii to fluvial landforms and are affected by fluvial processes. However, there are currently no rivers in the study region. This study was done to better understand the presence of fluvial landforms and to evaluate the previous findings. The dynamic behavior of the coast was revealed through shoreline analysis, which was done using satellite images from various years. Oceanographic parameters and longshore sediment transport play a vital role in geomorphological changes in coastal zones. According to the grain size analysis results, mean values showed that the deposits predominantlyare medium grained. The outcome discussed the spatiotemporal variations in geomorphology, sedimentation, and the function of coastal and fluvial processes on the beach of an island and a sand spit. Also highlighted was the role that wave action, fluvial currents, and tidal currents had in the long-term evolution of coastal geomorphological features such as spits, beaches, open coasts, and islands. The standard deviation signifies that the sediments are very well sorted to poorly sorted. Skewness ranges from fine skewed to strongly fine skewed and the kurtosis values show that the sediments are predominately very platykurtic which implies a low-energy environment of deposition. Four sedimentary facies (Facies A, B, C, D) have been found and facies A, B, and C may be wave-influenced deposits, but facies D may be formed by fluvial processes and contain medium to sand-sized particles. The direction of the tip area is also pointing to the south and this result concluded that the tip area is continuously growing. Thus, the results of this study revealed that sediment transport and coastal geomorphology evolution may be governed by two main processes such as the present ocean hydrodynamics and paleo fluvial processes of the study regions. [ABSTRACT FROM AUTHOR]

Suspended sediment dynamics play an important role in controlling nearshore and estuarine geomorphology and the associated ecological environments. Modeling the transport of suspended sediment is a complicated and challenging research topic. The goal of this study is to improve the accuracy of modeling the suspended sediment concentrations (SSCs) with newly developed techniques. Based on a three-dimensional suspended cohesive sediment transport model, the transport of suspended sediment and SSCs are simulated by assimilating SSCs retrieved from the Geostationary Ocean Color Imager (GOCI) with the adjoint data assimilation in the Hangzhou Bay, a typical strong tidal estuary along the coast of the East China Sea. To improve the effect of the data assimilation, the penalty function method, in which the reasonable constraints of the estimated model parameters are added to the cost function as penalty terms, will be introduced for the first time into the adjoint data assimilation in the SSCs modeling. In twin experiments, the prescribed spatially varying settling velocity is estimated by assimilating the synthetic SSC observations, and the results show that the penalty function method can further improve the effect of data assimilation and parameter estimation, regardless of synthetic SSC observations being contaminated by random artificial errors. In practical experiments, the spatially varying settling velocity is firstly estimated by assimilating the actual GOCI-retrieved SSCs. The results demonstrate that the simulated results can be improved by the adjoint data assimilation, and the penalty function method can additionally reduce the mean absolute error (MAE) between the independent check observations and the corresponding simulated SSCs from 1.44 × 10−1 kg/m3 to 1.30 × 10−1 kg/m3. To pursue greater simulation accuracy, the spatially varying settling velocity, resuspension rate, critical shear stress and initial conditions are simultaneously estimated by assimilating the actual GOCI-retrieved SSCs to simulate the SSCs in the Hangzhou Bay. When the adjoint data assimilation and the penalty function method are simultaneously used, the MAE between the independent check observations and the corresponding simulated SSCs is just 9.90 × 10−2 kg/m3, which is substantially less than that when only the settling velocity is estimated. The MAE is also considerably less than that when the four model parameters are estimated to be without using the penalty function method. This study indicates that the adjoint data assimilation can effectively improve the SSC simulation accuracy, and the penalty function method can limit the variation range of the estimated model parameters to further improve the effect of data assimilation and parameter estimation. [ABSTRACT FROM AUTHOR]

An estimated 20% of the world's land surface is underlain by lithologies favorable for karst formation. Karst features (e.g., sinkholes) and soils coevolve, likely influencing local pedogenesis, soil carbon storage, and hydrologic patterns. While karst is widespread, our understanding of the influence of karst geomorphology on pedogenesis remains limited. To better estimate the impact of karst geomorphology on pedogenesis, we characterized nine pedons as a function of landscape position (i.e., toposequence) in two subsidence sinkholes located in the Inner Bluegrass physiographic region of central Kentucky; we characterized a suite of soil physical, chemical, and mineralogical properties. The Inner Bluegrass is underlain by a phosphatic limestone and is susceptible to karst formation. Expectedly, total carbon was greater in lowland positions relative to upland landscape positions. However, inverse relationships between elevation and clay content, selective iron, aluminum, and silicon extracts contradicted previous toposequence trends. Clay mineralogy differences between toeslope and summit positions suggested sediment transport from summit to toeslope positions. Karst geomorphology may limit pedogenesis and facilitate more rapid material export through karst conduits compared to other lithologies. Given the extent of karst terrains and lithologies susceptible to karst formation, future work is needed to understand the magnitude of the impact of karst on pedogenesis and other earth system processes. Core Ideas: Sinkholes are common features in karst topography and have variable morphologies.Soil physical and chemical properties are variable between karst sinkholes.Typical toposequence trends may be reversed in sinkholes due to the impact of karst features. [ABSTRACT FROM AUTHOR]

The present geomorphic study analyzes the morphometric anomalies of the lateritic badlands (West Bengal, India) to understand the erosion intensity, triggering factors and landscape evolution using the ALOS AW3D30 DEM and quantitative techniques of various hydro-geomorphic processes (viz., basin morphometry, rainfall-runoff simulation, geomorphic threshold, erosion indices, sediment yield, SPI, and STI etc.). The GIS-based analysis reflects that there is the requitement of minimum drainage area (i.e. 55.71-349.01 m²) to maintain one metre of gully channel in the basins which have the network density of 2.86-13.76 km km-2. The critical slope (i.e. geomorphic threshold) of badland terrain varies from 0.0222 to 0.0407 metre metre-1, having dominance of overland flow erosion to initiate gully heads. The basin-wise SCS-CN and USLE coupling estimates that within the daily rainfall range of 11.41-66.41 mm day-1, the potential sediment yield of gully basins varies from 2.15 to 9.10 t ha-1. The SL index (i.e. 0.81-47.32 m) diagram reflects the beats of gully energy profile due to stream erosion enhancement, slope steepness, resistance of underlying lithologies and active tectonics. Hypsometric integral values of the gully basins, ranging from 0.4 to 0.6, emphasize a low entropy-based fluvial system and development of mature-youthful landform stage. The evolutionary stages of badlands are explained here by the connectivity model and hillslope -- gully -- river coupling system, showing a quasi-equilibrium to complex stage of landscape development at present. [ABSTRACT FROM AUTHOR]

This study assessed historical morphology changes of the Msimbazi River in Dar es Salaam City, Tanzania, following heavy rainfall events using historical Google earth images. The erosion and sedimentation processes that cause morphological changes of a river are also associated with flooding within the river catchments. In this study, the bank-line movement, erosion and sedimentation areas and changes in river section width were analyzed under three-time periods: 2005-2012, 2012-2018, and 2018-2020. Data shows that, the timing for floods coincides with the historical records for heavy rains. It was found that, area in the upper reaches of the river such as Kinyerezi suffer from river bank erosion most, as indicated by the large increase in river width. This has resulted into washing away of infrastructure including houses and loss of land. The river channel width at Kinyerezi has widened a lot since 2005, with some sections having widths of more than 90 m. On the lower reaches for example around Kigogo and Jangwani areas, deposition of the soil materials prevails, resulting into raised river bed and reduced river widths. As the river section an hence carrying capacity is reduced, inundation of river banks occurs. This is among the causes of river bank flooding reported at these areas whenever there is a heavy storm event. It is therefore recommended that interventions to solve the flooding events in Dar es Salaam city should also include preventing catchment and river bank erosion on the upstream areas. [ABSTRACT FROM AUTHOR]

Sediment yield is the result of all sediment production and transport processes. Recent technological developments and increasing availability of global environmental datasets, including earth observation data, provide an opportunity to systematically examine the relationship between sediment yield and controlling catchment variables by employing geographic information system (GIS). The Sediment yield index (SYI) method is employed using soil texture, topography, rainfall erosivity, geomorphology and landuse-landcover parameters to compute the spatial distribution of sediment yield rate and plan soil conservation and prioritize watershed in the Chambal river basin. The model does not provide absolute sediment yield value and can be only used for qualitative purposes. The present study estimated the sediment yield rate between 560–2625 ton/ha/yr with an average value of 1608.89 ton/ha/yr and severe, very high, high, moderate, and low priority zones. The priority levels are determined based on average sediment yield values and conservation approaches are proposed for all the catchments. [ABSTRACT FROM AUTHOR]

Tidal flats are widely distributed on high-latitude coasts, where sea ice processes have been invoked to explain the abundance and distribution of boulders. This study documents the surface morphology and sediment dynamics of a Low-Arctic macrotidal system, the boulder-rich tidal flats of Koojesse Inlet, fronting the Nunavut capital, Iqaluit, on Baffin Island. This is a region of postglacial isostatic uplift and forced regression, with raised littoral, deltaic, and glaciomarine deposits. The spring-tidal range is 11.1 m and sea ice cover lasts roughly 9 months of the year. The extensive intertidal flats are up to 1 km wide, with a veneer of sand and gravel (including large boulders) resting on an erosional unconformity truncating the underlying glaciomarine mud, forming a terrace within the present tidal range. Over a 3-year study, no consistent pattern of erosion or deposition was evident. Over a longer time scale, the concave hypsometry, low sediment supply, slight ebb dominance of weak tidal currents, abrasion by wave-entrained sand, ebb-oriented ripples formed under subaerial drainage, and slumps on the terrace flanks are consistent with seaward hydraulic and gravitational sediment transport. These processes may be of greater importance than shoreward ice transport. This study underlines the importance of relict glaciomarine deposits, postglacial uplift, and falling relative sea level in the erosional development of these high-latitude tidal flats. Relative sea-level projections for Iqaluit are ambiguous, but a switch to rising sea level, if it occurs, combined with more open water and wave energy, could alter the foreshore dynamics of the system. [ABSTRACT FROM AUTHOR]

This note analyzes for the first time the geomorphology and sedimentary features of the Simpson Submarine Canyon (SSC), located between Chiloé Island and the Taitao Peninsula. For that purpose, multibeam bathymetric data were obtained in 2018. The SSC has a unique orientation compared to most canyons on the Chilean margin. Slope escarpments, topographic irregularities, and sinuosity of the canyon could be associated with regional tectonics. Sediment transport and deposition along the axis define the transversal morphology. On the canyon walls, erosion and transport processes dominate, evidenced by gullies, channels, and mass removals, which leave debris on the axis. We report a large landslide from a canyon wall, which could be due to a highenergy event such as an earthquake; and the generation of a large sediment wave field outside the canyon mouth, indicating a great activity by sedimentary processes. All the above could indicate that the canyon is continuously evolving. [ABSTRACT FROM AUTHOR]

Well-log and three-dimensional (3D) seismic data are used to investigate the tectonic controls during the depositional periods of the Kongdian and Shahejie formations from Ek–Es4L to Es4U–Es3L–M on strata distribution, depositional systems and sediment dispersal in the Qingdong Sag, Bohai Bay Basin, East China, from a source-to-sink perspective. This tectonic transition is characterised by the Tanlu Fault switching from sinistral to dextral strike-slip as the fault system changed from a dominant NW–WNW trend during the Ek–Es4L period to a dominant WNW–EW trend during the Es4U and Es3L–M periods. These changes subsequently controlled the framework and areal extent of sediment dispersal in the inner-basin source-to-sink systems and resulted in a change in trend of inner-basin secondary structural belts, from primarily being NW-trending during the Ek–Es4L period to E–W-trending during the Es4U and Es3L–M periods. The tectonic transition also resulted in the western and southern source-to-sink systems expanding with time and controlled the flow path and sediment redistribution within each source-to-sink system with migration of the subsidence centre of the Qingdong Sag and even the region. The significant changes in the basin structure controlled the source area, flow path, sediment transport distance and direction, and have a significant impact on the interpretation of depositional environments and reservoirs in rift basins with a multi-phase evolution history. The Qingdong Sag, Bohai Bay Basin, experienced a tectonic transition during sediment deposition in the Eocene. The tectonic transition resulted in changes to the fault system and basin geomorphology. Fault movement and changes in basin geomorphology affected source-to-sink systems. [ABSTRACT FROM AUTHOR]

Dunes form where winds blow over a bed of mobile sediment grains — conditions that are common in our solar system. On Earth, dunes abound in arid continental interiors and along sandy coastlines. Dune fields have also been recognized on Venus, Mars, Saturn's moon Titan, and Pluto. In response to the different boundary conditions and other environmental forcings, dunes adopt a rich diversity of shapes, sizes, and behaviors. Thus, people around the globe and over centuries have developed a rich vocabulary to describe dunes and their complexity. As a result, existing dune nomenclature often includes redundant terms with differing definitions across scientific communities. Previous studies have endeavored to link dune shape to environmental forcing, usually by means of correlation. Although instructive, correlation-based classifications can be misleading if not based on underlying mechanics or if dune morphogenetic classes are not uniquely defined. Here, we synthesize existing dune terminology and use the last two decades of research on dune morphodynamics to propose three complementary dune classification schemes based on: (1) descriptive dune geomorphology, (2) morphodynamic processes, and (3) fluid mechanics and physics of sediment transport. The first classification relates dune types to geomorphic setting, the presence or absence of vegetation or obstacles, and dune shape (including planform shape, and cross-sectional symmetry or asymmetry). Dune classes can be further subdivided where the direction of sand transport is known independently. The second classification relates dune types and shapes to bed properties (sand-covered vs partially starved bed) and wind forcing (directional variability or the relative strengths and directions of wind modes) that together influence dune dynamics (growth, migration, elongation) and select the dominant processes by which dunes are shaped and oriented relative to the resultant transport direction. The third classification relates, for different planetary environments, the range of possible dune sizes, from minimum to maximum wavelength, to fluid flow regime (rough or smooth) and the response of sediment flux, which influence the coupling between sand bed topography, fluid flow, and sediment transport. These characteristic lengths are useful scales for comparative geomorphology. The three classification schemes provide complementary information. Together, they form a unified framework for geomorphologists, sedimentologists, geographers, physicists, and others to describe windblown sand dunes on Earth and beyond through their shape, dynamics, and size as a response to winds and boundary conditions. [ABSTRACT FROM AUTHOR]

Sandspits at river mouths are important socio-ecological but fragile coastal ecosystems. Due to their significant role, particularly in shielding areas behind them from wave impact, sandspits are crucial, albeit they also pose challenges such as increased fluvial flooding, which often necessitates substantial engineering interventions such as artificial breaching. Here, four wave-dominated sandspits are compared to determine their common behavior. The study sites at river mouths have in common a high control of waves on longshore sediment transport leading to sandspit development; the Langue de Barbarie at the Senegal River delta, the Bouche du Roi at the mouth of the Mono River in Benin, the Mataquito River mouth in Chile, and the Pomene River mouth in Mozambique, each characterized by unique hydrodynamic conditions and geomorphologic features that influence their evolution and susceptibility to natural and anthropogenic impacts. Their cycles of opening and development, typically spanning decades, are studied by collecting 37 years of shoreline and wave reanalysis data from the Landsat and Sentinel-2 missions. It is shown that part of the morphodynamics is truly intrinsic and that climatic wave evolution drives only a small part of their evolution. A simplified model is introduced to predict the cyclic behavior of spits. The proposed model for sandspit development is based on a cyclic behavior, where newly formed spits mature and eventually break, resetting the cycle. This cyclic perception is represented as a function of time, where the elongation of the spit relative to its maximum length is modeled as a function of time and a constant wave-driven longshore sediment transport component. The model is tested at several sites with similar environmental conditions and blindly at one site with reasonable results. The present work also highlights the importance of spit evolution and the associated variability they impose on coastal downdrift and updrift, especially when considering anticipating the implementation of engineering solutions. • Cyclic behavior of sand spit lengthening. • Predicting sand spit length with a conceptual model. • Updrift and downdrift coastal impact of a sand spit lengthening. [ABSTRACT FROM AUTHOR]

Chirp profiles collected on the southern Brazilian shelf were combined with sedimentological and hydrodynamic data to characterize shelf geomorphology, focusing on the development of outer shelf bedforms and their genetic links with major oceanic currents. Outer shelf sediment accumulations are interpreted as two scales of bedforms, such as dunes and sand ridges. In the São Paulo Bight, cuspate bedforms are bounded landward by a geomorphological scarp. The sector between Florianopolis and Mostardas also exhibits frequent asymmetric bedforms, whereas the inner- middle shelf is covered by semitransparent sheets. The southern Rio Grande Cone is characterized by stratified deposits covering vast outer shelf areas. Surficial sediment samples reveal a dominantly muddy composition and relatively high carbonate contents. Hydrodynamic data indicate a major influence of the Brazil Current over the São Paulo Bight. The prolific bedform outer-shelf environment is assumed to be mostly relict formed in a transgressive shallow-water setting. The sand ridges are believed to have evolved from a moribund stage characterized by morphological degradation to a relict stage, with preservation enhanced by fine-grained winnowing, coarse sediment armoring, and early cementation. Bedform migration seems to be occurring on the São Paulo Bight due to the presence of a nearly permanent meander of the Brazil Current. Over most of the inner shelf, the northward advection of sediments mainly led by the Brazilian Coastal Current has formed extensive fine-grained deposits. The occurrence of a relict shelf scarp may have conditioned the formation of the outer-shelf bedform environment. The vast spatial distribution of bedforms over most of the outer shelf seems comparable with other shelf areas, such as the south African shelf, dominated by the influence of unidirectional oceanic currents. Dune dimensions are lower on the Brazilian shelf, due to their relict character, the geomorphological configuration of the margin, and the scarcity of sand sources. • Outer shelf along the southern Brazilian margin covered by bedforms • Inner-to-middle shelf advection of fine sediments driven by Brazilian Coastal Current • Two scales bedforms (sand ridges and very large dunes) in a relict to moribund stage • Bedform preservation aided by fine-grained winnowing by the Brazil Current, armouring and cementation • Prolific bedform environment comparable with the south African shelf [ABSTRACT FROM AUTHOR]

Rocky reefs provide complex structures in the otherwise largely sand-dominated coastal North Sea. Therefore, these reefs are highly important natural habitats for the functioning of coastal ecosystems, as they provide shelter, refuge and nursery grounds for various mobile and sessile species. In the North Sea, the spatial distribution of these habitats has been intensively investigated over recent years. However, these studies generally provide static accounts of the current state of these reef systems, but limited data exist on the temporal variations in sediment dynamics at and around natural rocky reefs. In this study, we provide observations from a multiannual time series of hydroacoustic seafloor surveys conducted at an isolated rocky reef in the North Sea. We use multibeam bathymetry and side-scan sonar backscatter data in combination with video observations, sediment sampling, and sub-bottom profiler data to assess the long-term variations of the rocky reef system. The reef is located in water depths between 11 and 17 m with an areal extent of ~0.5 km2 and is surrounded by mobile sands. The topography of the rocky reef appears to create a distinct hydrodynamic system that permits mobile sands to settle or move into bathymetrical deeper parts of the reef. Our results suggest a very dynamic system surrounding the reef with large scale scouring, sediment reworking and transport, while the shallower central part of the reef remains stable over time. We demonstrate the importance of hydrodynamics and current scouring around reefs for the local variability in seafloor properties over time. These small-scale dynamics are likewise reflected in the spatial distribution of sessile species, which are less abundant in proximity to mobile sands. The hydroacoustic mapping and monitoring of seafloor dynamics at higher spatial and temporal resolutions presents an important future direction in the study of valuable coastal habitats. [ABSTRACT FROM AUTHOR]

The development of colluvial wedges at the base of fault scarps following normal-faulting earthquakes serves as a sedimentary record of paleoearthquakes and is thus crucial in assessing seismic hazard. Although there is a large body of observations of colluvial wedge development, connecting this knowledge to the physics of sediment transport can open new frontiers in our understanding. To explore theoretical colluvial wedge evolution, we develop a cellular automata model driven by the production and disturbance (e.g., bioturbative reworking) of mobile regolith and fault-scarp collapse. We consider both 90 and 60 ∘ dipping faults and allow the colluvial wedges to develop over 2000 model years. By tracking sediment transport time, velocity, and provenance, we classify cells into analogs for the debris and wash sedimentary facies commonly described in paleoseismic studies. High values of mobile regolith production and disturbance rates produce relatively larger and more wash-facies-dominated wedges, whereas lower values produced relatively smaller, debris-facies-dominated wedges. Higher lateral collapse rates lead to more debris facies relative to wash facies. Many of the modeled colluvial wedges fully developed within 2000 model years after the earthquake, with many being much faster when process rates are high. Finally, for scenarios with the same amount of vertical displacement, differently sized colluvial wedges developed depending on the rates of geomorphic processes and fault dip. A change in these variables, say by environmental change such as precipitation rates, could theoretically result in different colluvial wedge facies assemblages for the same characteristic earthquake rupture scenario. Finally, the stochastic nature of collapse events, when coupled with high disturbance, illustrates that multiple phases of colluvial deposition are theoretically possible for a single earthquake event. [ABSTRACT FROM AUTHOR]

Stream ecosystem metabolism contributes to global carbon cycling, yet predicting metabolism across ecosystems remains elusive. Even within stream segments, spatial variation in metabolic rates and their controls can be substantial, exhibiting sudden rather than continuous changes. We measured metabolism at 6 sites along a 75-km mainstem segment of Marsh Creek, Idaho. This agricultural stream lacks major geomorphic transitions such as tributaries or changes in valley width, but possesses patchy patterns of turbidity. We asked: (1) How variable is metabolism along this segment, and (2) How do the controls on metabolism vary along this segment? Metabolism varied several-fold along this stream segment. Average rates of gross primary production (GPP), ecosystem respiration (ER), and net ecosystem production (NEP) among sites did not correlate with water quality or aquatic macrophyte cover. Rather, reaches along this segment appear to represent different process domains that were characterized by turbidity: More turbid reaches saw negative effects of turbidity on GPP and NEP and positive effects on ER. Turbidity was associated with increased respiration and decoupled ER from GPP at turbid sites. Less turbid sites had stronger coupling between GPP and ER, and GPP was predicted by light and temperature. Heterogeneous sediment supply and transport capacity along Marsh Creek create patchy patterns of turbidity, which affects the controls on metabolism. Geomorphic controls on ecosystem processes are complex but not random. Understanding how metabolism and its controls vary across process domains is needed to scale up process rates and understand how process rates might respond to future changes. [ABSTRACT FROM AUTHOR]

Proglacial areas in the European Alps and other high-elevation mountains are currently undergoing rapid change due to global warming. Because of rising temperatures, glaciers and glacier forefields are subjected to increased melting and associated sediment export. This observation is increasingly important with respect to high-elevation geomorphological and ecological dynamics, emerging natural hazards and mitigation efforts, and hydropower plant management. It is therefore crucial to analyze the factors and feedback mechanisms governing sediment production, transport, and deposition in these rapidly changing areas. In this study, we investigated the sediment dynamics of a proglacial area located in the Eastern Italian Alps over the period 1969–2021 with the aims of: i) identifying the areas of sediment production; ii) quantifying volumes and rates of bedload sediment transport; and iii) determining the relative contribution of glacial export and fluvial erosion to the total sediment budget. We found that i) apart from glaciers, moraines and fluvial channels have been the most important sediment sources, albeit with substantial differences in terms of connectivity and thus supply rates; ii) the volumes and rates of sediment erosion varied by one order of magnitude (between tens and hundreds of mm per year), and were generally higher along the channel network; and iii) for a relatively shorter time interval between 2005 and 2021, the relative contribution of glacial bedload input with respect to the total sediment budget ranged between 34 % and 37 %, whereas 45 % to 59 % was derived from lateral fluvial erosion. Only a relatively small sediment volume was generated by net channel bed incision. These results imply that most of the sediment released from the proglacial area of the Sulden glacier is progressively transferred to the downstream sector of the channel network, with volumes that range between 931 and 1017 tons yr−1 km−2. These values are in the typical range of sediment export volumes from glaciated basins and highlight the high dynamicity of this region of the Alps. In general, our results confirm the complexity – in terms of spatial and temporal variability – of Alpine proglacial systems and highlight the need to systematically study these areas on a wide spatial and temporal scale, since the information provided by single locations or individual sectors of the sediment cascade, may not be adequate for understanding the dynamics acting in the entire proglacial regions. [Display omitted] • Proglacial areas change rapidly and supply sediment to the downstream valleys. • Moraines and channels are the most important sediment sources. • Glacial and fluvial erosion contribute between 35 % and 50 % to the sediment budget. • The proglacial area of the Sulden glacier is dominated by sediment transport. • In the Sulden region, sediment export may increase in the near future. [ABSTRACT FROM AUTHOR]

Direct measurements of erosional response to past climate change are scarce, but mid‐latitude landscapes can record how shifts between cold and warm periods altered erosion outside glacial margins. To study hillslope responses to periglaciation, we measured bulk geochemistry and cosmogenic 10Be and 26Al concentrations in colluvium and weathered bedrock in an 18 m regolith core from Bear Meadows, Pennsylvania, ∼100 km south of maximum glacial extent. Using core lithology, cosmogenic nuclide concentrations, and regional 10Be‐derived erosion rates, we show the onset of 100‐Kyr glacial cycles at the Mid‐Pleistocene Transition (1.2–0.7 Ma) instigated multiple periglacial episodes in central Appalachia, increasing erosion rates compared to the relatively warmer Neogene. Our results show the higher efficiency of periglacial versus temperate erosion processes and highlight a pervasive Pleistocene periglacial erosion signal preserved in the 10Be inventory of surface sediments in central Appalachia, where erosion rates are slow enough to integrate previous cold‐climate processes. Plain Language Summary: During ice ages in the past 2.6 million years, mid‐latitude landscapes like central Pennsylvania were shaped by extreme cold and thawing permafrost, conditions that promote fast breakdown and transport of soil. However, the effect of these cold climates and subsequent warming on erosion rates is unclear since we often lack records of hillslope erosion of warm and cold periods. We drilled 18 m through hillslope material emplaced during permafrost thaw and into the underlying weathered bedrock, and measured the concentrations of 10Be and 26Al, two isotopes that serve as tracers of burial timing and erosion rate. The ratio of 26Al/10Be in the oldest permafrost thaw unit indicates the material was deposited about one million years ago, corresponding to a switch to colder glacial periods followed by more abrupt and extreme warming. The concentrations of 10Be in bedrock below the deposits also imply slower erosion rates prior to the onset of glacial‐interglacial cycles. Our results indicate that cold climate processes are more efficient at eroding rock and transporting sediment than temperate processes and help explain patterns in erosion rates across the mid‐Atlantic region measured over different time scales. Key Points: In situ 10Be and 26Al measured in 18 m regolith core from central Pennsylvania, 100 km south of Pleistocene maximum glacial extentPeriglacial activity began at onset of 100‐Kyr glacial cycles, marked by permafrost thaw during abrupt warming following sustained coldPleistocene periglacial conditions led to an increase in erosion rates compared to the more temperate Neogene climate [ABSTRACT FROM AUTHOR]

Assessing rivers' and hillslopes' sensitivity to external forcing is paramount to understand landscape evolution, in particular as a response to Quaternary climate changes. River networks are usually considered to be the main conveyors of environmental signals, such as changes in precipitation, temperature, or baselevel. Yet because hillslopes provide the source of sediment for river networks, their response to environmental change also modulates landscape dynamics. In order to characterize such behavior, we analyze the response times of a transport‐limited hillslope. We use simple numerical models of denudation to study hillslope responses to oscillatory forcing and understand their filtering effects on environmental signals. Modifications in the frequency of climate oscillation, such as the change that occurred at the Mid‐Pleistocene Transition, can significantly modulate hillslope sediment‐flux response. We infer a wide range of hillslope responses, ranging from negligible change over the full range of climate‐forcing frequencies, to a significant filtering of long‐period signals. Plain Language Summary: Landscapes are constituted of hillslopes and rivers where different types of erosion and sediment transport processes take place. Due to their large extent, river networks are an important driver of global landscape response to climatic or tectonic changes. Hillslopes have smaller dimensions but are also where most sediment production occurs and for that reason it is important to have a good understanding of how they respond to perturbations. We use simple numerical models of hillslope evolution to study the influence of oscillating changes of either the efficiency of sediment transport across the hillslope or the rate of channel downcutting at its base. Our results indicates that the period of oscillations for these perturbations controls the amplitude of the sediment flux response out of the hillslope, and provide a framework to understand how this landscape component reacts to climatic cycles such as the glacial/inter‐glacial oscillations of the Quaternary. For example, a major change occurred 800 ka ago with a shift in climate oscillation from 40 to 100 ka period. Our models suggest that in some landscapes this change in period alone could have induced a significant decrease in the amplitude of hillslope sediment flux response. Key Points: A complex hillslope dynamics is associated with the linear to nonlinear sediment flux transitionHillslopes filtering potential of external signals is highly contrasted depending on the type of forcingChanges in the climatic signal frequency at the Mid‐Pleistocene Transition could induce a significant shift in hillslope erosional response [ABSTRACT FROM AUTHOR]

Riverine measurements of sediment and solute transport give empirical basin-scale estimates of bed-load, suspended-sediment, and silicate-solute fluxes for 100,000 km2 of northwestern California and western Oregon. This spatially explicit sediment budget shows the multifaceted control of geology and physiography on the rates and processes of fluvial denudation. Bed-load transport is greatest for steep basins, particularly in areas underlain by the accreted Klamath terrane. Bed-load flux commonly decreases downstream as clasts convert to suspended load by breakage and attrition, particularly for softer rock types. Suspended load correlates strongly with lithology, basin slope, precipitation, and wildfire disturbance. It is highest in steep regions of soft rocks, and our estimates suggest that much of the suspended load is derived from bed-load comminution. Dissolution, measured by basin-scale silicate-solute yield, constitutes a third of regional landscape denudation. Solute yield correlates with precipitation and is proportionally greatest in low-gradient and wet basins and for high parts of the Cascade Range, where undissected Quaternary volcanic rocks soak in 2-3 m of annual precipitation. Combined, these estimates provide basin-scale erosion rates ranging from ~50 t · km-2 · yr-1 (approximately equivalent to 0.02 mm · yr-1) for low-gradient basins such as the Willamette River to ~500 t · km-2 · yr-1 (~0.2 mm · yr-1) for steep coastal drainages. The denudation rates determined here from modern measurements are less than those estimated by longer-term geologic assessments, suggesting episodic disturbances such as fire, flood, seismic shaking, and climate change significantly add to long-term landscape denudation. [ABSTRACT FROM AUTHOR]

Invertebrates are important sediment engineers, making up for their small body size with abundance and behavioral diversity. However, despite the recognized importance of invertebrates as sediment engineers in terrestrial and marine environments, zoogeomorphology in rivers has primarily considered larger taxa, such as fish and beaver. This article reviews the zoogeomorphic effects of invertebrates in freshwater habitats, with a focus on rivers. To better synthesize current zoogeomorphic research and to help guide future studies we build a conceptual model considering biotic (behavior, abundance, body size, life history, and species invasions) and abiotic (geophysical energy and sediment grain size) controls on the direction and magnitude of zoogeomorphology. We also incorporate invertebrate engineers into conceptual sediment entrainment models, to understand their geomorphic role in the context of hydraulic power and sediment size. We structure our review around invertebrate behavior as a key control on whether invertebrates have a sediment destabilizing or stabilizing impact. Invertebrate zoogeomorphic behavior are diverse; the majority of research concerns bioturbation, a result of locomotion, foraging, and burrowing behaviors by many taxa. Similarly, burrowing into bedrock by a caddisfly and non‐biting midge larvae promotes bioerosion. Attachment to the substrate, (e.g., silk nets by caddisfly larvae or byssal threads by some mussels) can stabilize sediment, providing bioprotection. Bioconstructions (e.g., caddisfly cases and mussel shells) may have either stabilizing or destabilizing effects depending on their density and abiotic context. Interactions between lotic invertebrates and fluvial processes are complex and understudied, requiring further research across a greater range of taxa, behaviors, and spatiotemporal scales. This article is categorized under:Water and Life > Nature of Freshwater EcosystemsWater and Life > Conservation, Management, and Awareness [ABSTRACT FROM AUTHOR]

This study presents the first geochemical and petrophysical data on the composition of the bedload sediments transported by the Algal and Bohemian Stream, and the latter's prominent tributary: the Dirty Stream. The catchments of these rivers are partially glacierised, with only 2% and 6% ice cover in the Algal and Bohemian stream catchments, respectively. Therefore, the primary sources of liquid water to these rivers are snowmelt and active layer thawing. This study shows that the Cretaceous marine sedimentary rocks deposited in the back-arc James Ross Basin, which underlies the studied rivers, represent the main constituent of fluvial bedload. This is in contrast to suspended sediment loads, whose composition is a mixture of volcanic rocks from the surrounding James Ross Island Volcanic Group. This also suggests that bedload is only transported for a distance of few hundreds of metres, while suspended sediment load is transported throughout the Algal and Bohemian streams to the sea. It is anticipated that this work will serve as the source of data for further studies from fluvial geomorphology to river ecology. [ABSTRACT FROM AUTHOR]

Wind‐blown sand dunes are both a consequence and a driver of climate dynamics; they arise under persistently dry and windy conditions, and are sometimes a source for airborne dust. Dune fields experience extreme daily changes in temperature, yet the role of atmospheric stability in driving sand transport and dust emission has not been established. Here, we report on an unprecedented multiscale field experiment at the White Sands Dune Field (New Mexico, USA), where by measuring wind, humidity and temperature profiles in the atmosphere concurrently with sediment transport, we demonstrate that a daily rhythm of sand and dust transport arises from nonequilibrium atmospheric boundary layer convection. A global analysis of 45 dune fields confirms the connection found in situ between surface wind speed and diurnal temperature cycles, revealing an unrecognized climate feedback that may contribute to the growth of deserts on Earth and dune activity on Mars. Plain Language Summary: As the bottom of the atmosphere heats and cools throughout the day, the winds near the land surface pick up and slow down, respectively, all else equal. This happens because it is easier to "mix" the fast winds high up in the atmosphere down to the surface when the surface air is convecting. We find that this wind effect is pronounced over dune fields, expansive patches of sand that are extreme in their daily heat cycles, and that the knock‐on effect is for those fast daytime winds to move sand and dust (the process that must occur for dune fields to grow). This is interesting because often the effect of heat on the near‐surface winds is ignored when considering sediment movement, and also because over geologic timescales this process might contribute to the growth of dune fields. Key Points: Winds that move sand and dust at White Sands Dune Field are strongly tied to boundary layer convectionThe typical equilibrium assumption for atmospheric boundary layer theory fails in White Sands' extreme daily cycleThe above key points likely scale with dune field size and contribute to dune field growth [ABSTRACT FROM AUTHOR]

• Overlapping crater populations constrain the total era of martian valley formation. • Martian valleys may have formed intermittently over hundreds of millions of years. • Long-term erosion rates would have been similar to the modern Atacama Desert. A number of studies have constrained the cessation of martian valley network activity to around the Noachian-Hesperian boundary, but the total time period over which these features formed remains poorly constrained. Most attempts to ascertain valley network formative timescales rely on an intermittency factor that varies widely for terrestrial rivers and is unknown for Mars. In this contribution, superposition relationships are used to identify crater populations that pre- and postdate valley network incision, resulting in maximum cumulative valley formation times of ∼108 years. These timescales correspond with long-term erosion rates of ∼0.25 m/Myr, similar to those calculated for the Middle to Late Noachian as well as the central Atacama Desert since the Late Miocene. Assuming sediment transport rates previously calculated for other martian valley networks, this implies a minimum fluvial intermittency of ∼10−5, several orders of magnitude lower than modern day Earth rivers but similar to values independently calculated for some martian fluvial deposits. This low intermittency suggests that martian valley incision may have been significantly hindered by erosion into existing bedrock or by boulder armoring of the valley floor. Alternatively, unlike river valleys on Earth, runoff events driving martian valley network activity may have been non-seasonal, Milankovitch-like cycles, with long eras of quiescence between periods of intensified fluvial activity. [ABSTRACT FROM AUTHOR]

Uranium (U) isotopes can be used to estimate the comminution age of sediments , i.e. the time elapsed from sediment production on continents, via weathering and physical erosion, to deposition in the sedimentary record. The calculation of this comminution age is based on measured (234U/238U) activity ratios in river sediments, and inferred time-dependent recoil effect, which leads to the preferential release of 234U from mineral lattices during erosion processes. In this study, we report on a large-scale (234U/238U) investigation of modern river sediments worldwide, with the aim to determine the extent to which parameters such as grain size, lithology, weathering, climate and geomorphology may influence the distribution of U isotopes in fine-grained sediments. Our extensive dataset (N = 64) includes U isotopic measurements for many of the world's largest rivers, but also rivers draining particular climatic and geological settings. Our results indicate that sediments collected from river basins draining mostly igneous, metamorphic or volcanic rocks often display (234U/238U) ratios > 1, with clay-size fractions (<4 µm) being less depleted in 234U (higher 234U/238U) than corresponding silt-size fractions (4–63 µm). In contrast, sediments derived from multi-lithological basins or draining sedimentary rocks are typically characterized by (234U/238U) ratios <1, with clays generally exhibiting more depleted 234U signatures than silts. Taken together, these observations suggest that the formation of secondary clay minerals in soils from basins draining mostly igneous, metamorphic is accompanied by partial incorporation by recoil injection of 234U initially released during weathering processes, possibly from U-rich minerals, such as sphene or apatite. Instead, in multi-lithological catchments draining sedimentary rocks, we propose that the erosion of recycled sediments having experienced several cycles of weathering, possibly over glacial-interglacial timescales, could explain the much lower (234U/238U) ratios observed in clay-size fractions. While no direct relationships can be identified between sediment (234U/238U) ratios and lithology, weathering intensity, climatic or geomorphic parameters in corresponding river basins, we show that the catchment size probably plays an important role in controlling the distribution of (234U/238U) in river sediments, through its direct influence on the sediment residence time. Finally, a multiple regression analysis of our data, combining various environmental parameters for the lithology, climate and geomorphology of studied river basins, indicates predicted (234U/238U) values that are very similar to measured values (with R2 ∼ 0.8). This finding provides further support for the usefulness of (234U/238U) ratios in the sedimentary record for reconstructing past landscape changes and their effect on sediment transport and residence time in river basins. [ABSTRACT FROM AUTHOR]

For streams draining urban catchments, sediment transport capacity is the key driver of physical impacts including bed sediment removal and channel incision. The main unanswered question is the relative role of flow alteration compared to sediment supply in influencing sediment transport capacity. With this objective, we computed sand and gravel bed sediment transport capacity using the Wilcock and Kenworthy two-fraction bedload transport relation for nine streams in catchments covering a gradient of urbanisation. Computations were done for typical natural bed surface material, based on conditions in the least urban study streams. We compared transport capacity distributions and cumulative transport capacity over one-year between the streams. Transport capacity was up to three orders of magnitude higher in urban streams than in forested-catchment streams. This was driven overwhelmingly by the urbanisation-induced alterations to the flow regime, with only minor feedback from channel form changes. Transport capacity was two to three orders of magnitude greater than measured bedload transport in all but the least urban streams. This excess bedload transport capacity mobilises and removes bed sediment, produces channel incision and enlargement and reduces channel complexity. Rebalancing transport capacity with sediment supply therefore requires significant flow mitigation towards pre-urban conditions. Other responses, which may theoretically help to regain this balance – channel widening, grade control, increasing roughness, sediment augmentation – are either inappropriate or only feasible following flow mitigation measures. [ABSTRACT FROM AUTHOR]

Aeolian dune fields are self‐organized patterns formed by wind‐blown sand. Dunes are topographic roughness elements that impose drag on the atmospheric boundary layer (ABL), creating a natural coupling between form and flow. While the steady‐state influence of drag on the ABL is well studied, nonequilibrium effects due to roughness transitions are less understood. Here we examine the large‐scale coupling between the ABL and an entire dune field. Field observations at White Sands, New Mexico, reveal a concomitant decline in wind speed and sand flux downwind of the transition from smooth playa to rough dunes at the upwind dune‐field margin, that affects the entire ∼10‐km ‐long dune field. Using a theory for the system that accounts for the observations, we generalize to other roughness scenarios. We find that, via transitional ABL dynamics, aeolian sediment aggradation can be influenced by roughness both inside and outside dune fields. Plain Language Summary: Just as how cyclists opt to have smooth skin to gain a speed advantage, near‐surface winds in the atmosphere are faster over smooth topography. Dunes slow winds down because they are rough, but these features are also shaped by the winds. When wind passes over a boundary between smooth and rough surfaces, it cannot instantaneously slow down; instead, there is a transition zone where it decelerates. This area of transition can exist at the edge of a dune field if the land upwind of it is relatively smooth. We observe this at White Sands Dune Field, and generalize the results with theory. Aside from helping to explain the striking patterns we see on planetary surfaces, this result is useful because dunes are often used to interpret wind conditions. Key Points: Wind and sediment flux decrease downwind from the leading edge of White Sands Dune FieldA Lagrangian 1‐D model explains how nonequilibrium flow induced by surface roughness transitions produces observed dynamicsResults are generalized using the 1‐D model for other roughness scenarios [ABSTRACT FROM AUTHOR]

The way in which sediment is transported (creep, saltation, suspension), is traditionally interpreted from grain size distribution characteristics. However, the grain size range associated with transitions from one transport mode to the other is highly variable because it depends on the amount of transport energy available. In this study we present a novel methodology for determination of the sediment transport mode based on grain size and shape data from dynamic image analysis. The data are integrated into grain size–shape distributions, and primary components are determined using endmember modelling. In real-world datasets, primary components can be interpreted in terms of different transport mechanisms and/or sediment sources. Accuracy of the method is assessed using artificial datasets with known primary components that are mixed in known proportions. The results show that the proposed technique accurately identifies primary components, with the exception of those primary components that only form minor contributions to the samples (highly mixed components). The new method is tested on sediment samples from an active aeolian system in the Dutch coastal dunes. Aeolian transport processes and geomorphology of these type of systems are well known and can therefore be linked to the spatial distribution of endmembers to assess the physical significance of the method's output. The grain size–shape distributions of the aeolian dune dataset are unmixed into three primary components. The spatial distribution of these components is constrained by geomorphology and reflects the three dominant aeolian transport processes known to occur along a beach–dune transect: bedload on the beach and in notches that were dug by man through the shore-parallel foredune ridge, modified saltation on the windward and leeward slope of the intact foredune, and suspension in the vegetated hinterland. The three transport modes are characterised by distinctly different trends in grain shape with grain size: with increasing size, bedload shows a constant grain regularity, modified saltation a minor decrease in grain regularity, and suspension a strong decrease in grain regularity. These trends, or in other words, the shape of the grain size–shape distributions, can be used to determine the transport mode responsible for an aeolian sediment deposit. Results of the method are therefore less ambiguous than those of traditional grain size distribution endmember modelling, especially if multiple transport modes occur or if primary components overlap in terms of grain size but differ in grain shape. [ABSTRACT FROM AUTHOR]

We present major new findings on the stability of Norse landing places on the island of Unst, Shetland, using a combination of geomorphology, OSL dating, fetch analysis, and sediment transport modeling. Islanders needed reliable access to the sea, and exploited sandy beaches as safe landing places. The persistence of beaches was important for long-term continuity of settlement and could be threatened by stormy conditions. Sediment modeling undertaken on two embayments on Unst, Lunda Wick, and Sandwick, reveals major differences in the ability of sandy beaches to reform in these embayments after the onset of persistent stormy conditions; sandy beaches can endure under these conditions at Sandwick, but not at Lunda Wick. OSL dating of blown sands at Lunda Wick reveals a history of sand blow events pointing to large-scale depletion of beach material throughout the Little Ice Age (beginning circa 1250 CE). This correlates with known sand blows at Sandwick, but here the beach could be replenished from the nearshore environment, something that was more problematic at Lunda Wick. These findings agree with the emerging picture of increased environment pressure from blown sands on communities throughout the North Atlantic, and identifies different models of related beach persistence and change. [ABSTRACT FROM AUTHOR]

Glaciated and recently (post-Little Ice Age) deglaciated areas are very dynamic environments, undergoing continuous changes, in particular as a consequence of climatic fluctuations and cryosphere changes. The intense geomorphic activity that takes place here conditions natural hazard, sediment transport and tourist fruition. A geo-morphological mapping with applicative purposes has to take into account the peculiarities and the dynamism of these specific areas. We here propose a methodological approach based on the interpretation of a multitemporal set of aerial photos (from 1983 to 2012), in a GIS environment, with application to the sectors modeled by Little Ice Age glaciers in the upper Orco Valley (NW Italy). The result is a geo-morphological map focused on the elements that are most relevant for application purposes, complemented by a map of the spatio-temporal distribution of the natural instability processes identified in the study area for the reference period, aimed to highlight the recent dynamism of the geomorphological elements in the map. [ABSTRACT FROM AUTHOR]

The upper third member of Eocene Dongying Formation (Ed 3 u) is considered to be one of the most important hydrocarbon-rich intervals in Nanpu Sag, Bohai Bay Basin, China. Through integrated analysis of the drilling cores, wire-line logs, and high-quality three-dimensional (3-D) seismic data, the sedimentary characteristics of Ed 3 u were analyzed by utilizing the seismic geomorphology approach in the double slope systems of Laoyemiao transverse anticline, Nanpu Sag. The Ed 3 u, a third-order sequence, can be subdivided into three fourth-order sequences (from base to top as SS1, SS2, and SS3). The fan delta front and sublacustrine fan have been identified from well-based analysis of the sedimentary facies and core examinations reveal that the sublacustrine fan deposits were dominated by six types of resedimented lithofacies, namely, slides, slumps, sandy debris flows, muddy debris flows, turbidity currents, and hyperpycnal flows. Stratal slices were obtained from 3-D single-frequency seismic volumes to map the sediment dispersal characteristics and document the evolution of the depositional systems constrained by the double slope break zones of Laoyemiao transverse anticline. The unique structures of the double slope break zones and the variation in the lake level associated with the system tracts of the third-order sequence jointly control the dispersal patterns of the sand bodies and the spatial-temporal evolution of the depositional systems. Based on the above analysis, the depositional evolution model of Ed 3 u was established. The proposed facies-controlled model and sediment transport model can be used to accurately predict the favorable reservoir sandstones. • Analysis lithofacies and origin of sublacustrine fan. • Investigate the controls of double slope break zones over the distribution of sedimentary systems and sand bodies. • Exhibit the spatial-temporal evolution of fan delta front and sublacustrine fan in the systems tract. • Establish the depositional model from source to sink under the control of the transfer zones and slope systems. [ABSTRACT FROM AUTHOR]

Tidal flats connect terrestrial and oceanic environments, and play an important role in the evolution of coastal ecosystems and geomorphology. Taking tidal flat on Zhairuoshan Island (ZRS) as an example, we studied the dynamic characteristics of suspended sediment concentration (SSC), sediment resuspension, and transportation in tidal flats. The field data of the waves, currents, and sediments were obtained from the tidal flat on the east of ZRS Island. The results show that current-induced bed shear stress is dominant. Under the combined action of waves, tides, and currents, SSC has two main periods (12.2 h, 6.2 h, 60−80%) and three minor periods (23.5 h, 8.2 h, and 5.1 h, 20−40%). Advection transport is dominant, at approximately 2–3 times the sediment resuspension, and the net sediment flux is onshore. Turbulent intermittent events play an important role in sediment resuspension, and their probability is affected by velocity. The vertical instantaneous transport of sediment depends on wave height. The vertical profile of SSC shows that, at high current velocity, the sedimentation formula that considers flocculation better fits the vertical profile of suspended sediment using the Rouse formula. The settling velocity of a single particle fits better at low current velocities, indicating that the flocculation of sediment is weak at low velocities. This study improves our understanding on near-bottom sediment characteristics and controlling mechanism in tidal flat in muddy coasts. • Suspended sediment concentration (SSC) in the tidal flat of Zhairuoshan Island is dominated by advection, followed by resuspension. • Intermittent turbulence is important for sediment resuspension, affected by wave and velocity. • Settling velocity with considering flocculation better fits the near-bottom sediment vertical profile at high velocity. • Harmonic analysis of SSC reveals the contribution of tides, waves, and turbulence events. [ABSTRACT FROM AUTHOR]

Patterns of sediment yield have been widely investigated across a variety of scales, but few of these studies have been carried out in urban watersheds. The design of this study represented a unique opportunity to use high-frequency sensor data to compare sediment yields across spatial and temporal scales in an urbanized watershed. Near real-time turbidity and discharge data were collected continuously for four years at five stream gages over three nested spatial scales in the highly impervious 14.2-km2 Dead Run watershed, located in Baltimore County, Maryland, USA. Monthly suspended sediment yields varied by over two orders of magnitude across all stations. Two mid-watershed stations on tributaries to the mainstem of Dead Run are located only about 500 m apart and about 500 m upstream of their confluence, yet displayed observable differences in the timing of their highest sediment yields. Average annual suspended sediment yield was higher at the headwater station with older development (78.2 t/km2/yr) than at the headwater station with more recent development (47.0 t/km2/yr). Average annual yields increased with watershed size from the headwater stations to the mid-watershed stations (87.0 t/km2/yr and 60.4 t/km2/yr). Additionally, yields at the station farthest downstream (81.7 t/km2/yr) were slightly larger than the yield calculated from the sum of both mid-watershed stations (74.6 t/km2/yr), which together represented about 80% of the upstream drainage area. Several additional patterns highlighting spatial heterogeneity of the system were observed. The ratio of sediment yields between the headwater stations increased steadily over time while the runoff ratio remained almost constant. Yields at one mid-watershed station were consistently higher than yields at the other mid-watershed station, despite similarity in runoff totals. Upstream watersheds show year-to-year variation in sediment yield. In contrast, yields at the farthest downstream station show minimal variation. This observation is consistent with the possibility that internal storage and remobilization tend to modulate downstream yields even with spatial and temporal variation in upstream sources. Observable inconsistencies in sediment yields between subwatersheds at monthly time scales suggest that there is a substantial degree of heterogeneity in terms of sediment response to large storm events. Despite significant internal variability, the overall range of sediment yield values at each site was consistent with values reported for multiple urban mid-Atlantic Piedmont watersheds. Comparison with global values indicates that sediment yields from Dead Run are in the same general range as the 25% quartile of urban sediment yields. • Urban sediment data collected from 5 gages at 3 nested scales for 4 years • Temporal patterns of sediment yield differ from temporal patterns of runoff. • Dominant sources of sediment vary spatially in a 14 km2 highly impervious catchment. • Downstream site exhibits lower variation in annual sediment yield than tributaries. • Storage has a substantial role in the sediment dynamics of a small, urban watershed. [ABSTRACT FROM AUTHOR]

The MARSSIM landform evolution model has been used successfully over the past three decades to simulate sediment transport on the surface of Mars. The model relies on an advection–diffusion relation that has been used to describe the difference in scale efficiency and profile concavity in landscapes. Beyond this, MARSSIM has also been used to simulate groundwater flow, eolian transport, and impact cratering. We first describe the history of the model in the published literature, followed by an in-depth analysis of the physical theory on which it is based. We review the successes and limitations of the current model and how these have been addressed. Other parts of the model included in the source code have been rarely used, so we also investigate new applications in these areas. Finally, we propose a modification to the model that would allow for an integrated system of precipitation, infiltration, and groundwater flow, and provide a practical example on a simulated cratered terrain similar to those found in past MARSSIM studies. We find that the introduction of an integrated model has noticeable effects on erosion patterns within the simulation domain compared to cases of either complete infiltration or complete runoff. • MARSSIM is a powerful computational tool for understanding early Mars hydrology. • Model parameterizes an advection–diffusion relation to simulate sediment transport. • Modification of current model allows groundwater infiltration from runoff. • Addition of infiltration represents distinct landform evolution scenario for Mars. [ABSTRACT FROM AUTHOR]

Several decades of studies on shelf-margin evolution have led to recognition that both accommodation-dominated and supply-dominated sediment-delivery systems are capable of transporting sediments from the shelf down into deep-water basins. The former case relies on falling sea level and lowstands to move deltas to the shelf edge, whereas the latter depends on well-supplied deltas reaching the shelf edge regardless of sea-level rise. However, it remains unclear how to distinguish between the two sediment-dispersal alternatives, and which of these is more efficient in delivering sediments to deep water. We explore sediment-volume partitioning into deep-water areas by analyzing >1600 runs of a geometric delta model with varying eustatic, shelf-morphologic, and sediment-supply conditions. Previous studies suggest that greenhouse eustatic (low amplitude and frequency) conditions generate lower shelf accommodation, and permit the shoreline to arrive at the shelf edge quickly. Further investigation reveals that (1) this argument works only for the supply-dominated system, and (2) the proportion of total sediment that reaches deep water is not correlated to the frequency of sea-level change, but depends strongly on the shelf width and the amplitude of sea-level change. We suggest a ratio between (1) the product of shelf width and the amplitude of sea-level change and (2) total sediment supply to quantitatively characterize the sediment dispersal system. A ratio of 0.4 forms a good boundary between accommodation- and supply-dominated systems in the modeling results, and in three well-studied ancient systems (the Maastrichtian Washakie Basin, Wyoming, USA; the Pliocene paleo--Orinoco margin, Trinidad and Tobago; and the Miocene New Jersey margin, northeastern USA). This work also suggests that the sediment mass balance becomes more important for continental margin building regardless of sea-level scenarios over the longer term. [ABSTRACT FROM AUTHOR]

Abstract Megaclast-dominated fluvial systems have been largely ignored by researchers. Yet megaclasts exert an important control on channel geomorphology, flow behaviour and sediment transport, and such systems are probably far more common than this neglect would suggest. Despite the explicit identification of megaclasts as the products of cataclysmic flow, observation of modern fluvial systems confirms that megaclasts can be entrained by flows that lie within the normal flow regime. The pattern of fining along the megaclast-dominated Sabeto River of western Viti Levu, Fiji reveals a strong negative exponential relationship between particle size and distance downstream, and a rate of downstream fining comparable with that of other gravel-bed rivers. The downstream fining pattern is straightforward and step-like discontinuities in the fining gradient are absent. This is suggestive of a sedimentary system only minimally disrupted by the supply of sediment from tributaries or the reworking of material from sources such as hillslopes and alluvial terraces. There is evidence, however, of anomalously coarse sub-populations at two sites. These coarser components must pre-date the other deposits at the sites. We speculate that they represent the products of earlier and higher-magnitude events. The bed sediments may thus be composite features, made up of individual components each transported by a specific event of particular magnitude. Our work confirms the relationship between the rate of downstream fining and particle size. This may arise because the distance over which individual particles are transported is likely to be size dependent. It is also possible that abrasion may be more effective in the case of larger particles than smaller ones, with the result that the coarser fraction of the river's bed sediment fines downstream more rapidly than the finer fraction. There is a long-standing debate about the relative roles of abrasion and sorting in downstream fining. Our data reveal little evidence for a downstream increase in the roundness of the river's gravels, implying that abrasion is likely to play a minor role in the fining process in this system. Highlights • Megaclast-dominated rivers occur widely, but have been largely ignored by researchers. • Megaclasts may be entrained by normal flows and not solely by catastrophic events. • Megaclast downstream-fining rates are comparable with those of other gravel-bed rivers. • There is a close relationship between bed-sediment size and rate of downstream fining. • Bed-sediment assemblages consist of discrete components, each transported by individual events. [ABSTRACT FROM AUTHOR]

Abstract The adjustment of a gravel bed during cycles of sediment storage was analyzed for a flume experiment, designed to study the effects of episodic sediment supply regimes. As the bed aggraded and degraded due to changes in sediment feed, it developed a complex topography with bedforms at different scales (e.g., pebble-clusters, bars). Sediment inputs increased bedload rates and promoted large changes in bed morphology. Without an external supply, the bed armored, which increased bed stability, counteracted bed degradation, and decreased bedload rates. Fully-mobile gravel (2–8 mm) was the only fraction that exhibited a deficit over the experiment. Preferential storage of coarse grains caused the development of a sediment wedge upstream and downstream fining on the bed surface. The storage of sand was also significant (60 % of feed) probably because of infiltration (e.g., in the upstream wedge) and hiding effects promoted by bed armor and structures. Size-selective transport caused a cumulative increase in bed slope, which was likely to affect sediment transport capacity. The large variability in bedload rates for same levels of bed storage indicated that sediment availability and bed state were the main controls on sediment transport regime. We provide empirical evidence that cycles of aggradation and degradation, caused by changes in sediment feed upstream, condition bed composition and topography, and the rate and texture of sediment output. Highlights • Aggradation-degradation cycles condition sediment transport rates. • Partial mobility promotes coarse sediment storage upstream and downstream fining. • Sand storage is significant within lag coarse deposits. • Differences in sediment availability cause hysteresis in bedload rates. [ABSTRACT FROM AUTHOR]

Abstract During the transition from the last glacial into the Holocene interglacial, the atmospheric circulation in the North Atlantic area changed from a glacial mode, influenced by the presence of large ice sheets, into a system more similar to that of the present day. This change had implications for wind, temperature and precipitation patterns that can be traced in geological archives. Here, we focus on reconstructing past wind directions over southern Scandinavia, as inferred from the net sediment transport direction of inland dunes in south-central Sweden. We analysed single dunes and dune fields along a 540-km-long S-N transect with LiDAR (Light detection and ranging) derived DEMs (digital elevation models) to determine their geomorphological type and the directional mode of the wind that led to their formation. Luminescence ages of sand drift and dune formation were compiled from previous studies, allowing us to build a chronology of sand drift after the deglaciation of south-central Sweden. The majority of the dunes appear to have been formed by westerly or northwesterly winds and stabilised ∼10.5–9.0 ka. Although this is rather close in time to the local deglaciation for the northern sites, it is long after the disappearance of ice from the more southern sites. The coeval dune stabilisation over such a large geographical area suggests that regional environmental conditions played an important role. It is likely that an unstable climate in conjunction with low groundwater tables during the early Holocene locally delayed vegetation from stabilising the dunes. Highlights • Palaeowind directions are inferred from stabilised inland dunes, Sweden. • W and NW winds are the most abundant palaeowind directions. • Dune stabilisation primarily occurred 10,500 to 9000 years ago. • Prolonged dune activity is thought to have been caused by unstable climate. [ABSTRACT FROM AUTHOR]

The nature of geomorphic connectivity in headwater mountainous catchments influences the delivery of sediment to the downstream channel network. A reduced sediment supply from mountainous regions results in channel instability and loss of physical habitats. The aim of this study is to show how the small, mid‐mountainous Černá Opava catchment in the Czech Republic is organised in terms of sediment sources, sinks and (dis)connectivity of sediment transport. A field‐based approach combining GIS analysis and geomorphological mapping was adopted to unravel the nature of present‐day sediment delivery to the channel network. When the lithology and land use of an area are relatively uniform, the sediment delivery to the channel network varies spatially, according to slope–channel connectivity and the distribution of in‐channel sources (cut banks and incising reaches). Despite sediment supply being limited by forested slopes and a number of natural and anthropogenic in‐channel barriers, stream channels display no signs of "hungry water" conditions. [ABSTRACT FROM AUTHOR]

Abstract During the second half of the twentieth century, in the central part of the Călimani Mountains, the mining activities for sulfur-rich ore extraction and processing produced significant landscape changes. Sediment transfers across the affected catchments started during the mining period and are still ongoing today, more than two decades after the cessation of the mining activities in 1997. Subsequently, neither rehabilitation works nor erosion control measures were undertaken to stabilize the spoil heap deposits and natural reforestation. Also, material consolidation was impeded by the highly unstable talus slopes. Moreover, little is known about the frequency of the hydrogeomorphic processes responsible for sediment transfers and their consequences. Dendrogeomorphic investigations, grain-size analyses, and topographic surveys were carried out to document the history of hydrogeomorphic activity, the volume of material stored behind the retention dams, and the rate of sediment accumulation. Tree-ring analysis allowed us to reconstruct ten debris flow events in the natural environment, as well as in mining disturbed environment for the period 1931–2017 and 1970–2017, respectively. Triggering of debris flows appears related to spring and summer precipitation originating from short duration convective systems or long-lasting rainfalls. In these remote mining areas, the -reconstructed frequency of debris flows (return intervals of 8.1 and 4.7 years) might be explained by the rainwater accumulation on the spoil heap platform and the availability of sediments, which flow down the talus and then follow the stream channels to reach one of the sediment retention reservoirs (7.4–8.4 cm y−1). Highlights • Debris flows in undisturbed vs. anthropogenically disturbed sites were assessed • Past events with return intervals of 8.1 respectively 4.7 years were reconstructed • Sediment accumulation rates within the reservoirs varied from 7.4 to 8.4 cm yr−1 • Debris flows threaten tailing ponds, infrastructure and human activities [ABSTRACT FROM AUTHOR]

Changes in 137Cs export over time following clearcutting were investigated in a Japanese forested catchment affected by the Fukushima nuclear accident. A total of 13% of the catchment area was clear-cut 2 years after the accident. Annual suspended solids (SS) export at the catchment outlet increased 1.4 to 2.0 times after clearcutting; however, 137Cs export increased slightly (up to 1.1 times), corresponding to 0.21% to 0.30% of the 137Cs inventory in the catchment. The smaller change in 137Cs export than in SS export was due to a rapid decrease in the activity concentration following clearcutting. This decrease was likely caused by both natural attenuation and SS derived from sources with a low activity concentration in the clear-cut area. Monitoring of the sediment transport from hillslopes in small-scale experimental plots showed that the 137Cs yield in the skid trail was 3.6 to 21 times greater than those in clear-cut and unlogged forest floors. This significant 137Cs transport was due to greater soil erosion (by up to two orders of magnitude) along the skid trail, despite the lower activity concentration than those in the other plots. This indicates that while skid trails were involved in the rapid decrease of the activity concentration of SS, they were a potential source of the increased export of 137Cs and SS. Net 137Cs export increased by clearcutting (the export excluding the decrease accompanied by natural attenuation) was estimated to account for only 0.092% of the inventory in the catchment for 2.5 years. These results imply that the impact of clearcutting on 137Cs export was temporary in this catchment. [ABSTRACT FROM AUTHOR]

Abstract Nearshore bars are important morphologic features associated with intermediate and dissipative natural beaches. Bars impact the direction, magnitude, and patterns of sediment transport in the nearshore. They serve as a buffer against extreme and meso-scale events. In this review article, we investigate remotely-based observations, specifically near-Earth and satellite imagery, which have been used to investigate nearshore bars. Several recent advances in technology and techniques allow the remote measurement of bar width and height, beach slope, shoreline orientation, and bar count. Video monitoring imagery is presently the most popular method to derive these data. However, spatial prediction models using satellite imagery can also provide reliable bar morphodynamic information. Highlights • Synthesis of remote sensing techniques used to identify bar characteristics. • Remote sensing allows for longer temporal and larger spatial scale studies. • Video monitoring is the most popular method used to study bar characteristics. • Reliable bar morphodynamic data can be obtained from satellite imagery. [ABSTRACT FROM AUTHOR]

Controversy over the alpine route taken by the Hannibalic Army from the Rhône Basin into Italia in 218 bc (2168 cal bp) has raged amongst classicists for over two millennia. Because Hannibal crossed the Alps, the significance for identifying the route taken by the Punic Army lies more in its potential for identifying sites of historical archaeological significance than a resolution of one of history's most enduring questions. While compelling stratigraphic, geochemical and microbiological evidence has been recovered from an alluvial floodplain mire in the upper Guil Valley, located below the Col de la Traversette (about 3000 masl) on the French–Italian border, it potentially identifies the invasion route as the one originally proposed by Sir Gavin de Beer in 1974. The dated layers in several sections, termed the MAD (mass animal deposition) beds based on disrupted/churned bedding and key/specialized biological components strongly supports de Beer's thesis that Hannibal chose the highest transit col into Italia. In addition to other physical evidence, we present here new physical, geomorphological and stratigraphic evidence, all calibrated by radiocarbon dating, that suggests Hannibal's imprint on the landscape exists in coalescing alluvial fans in the upper Po catchment of northern Italy. [ABSTRACT FROM AUTHOR]

Abstract The impact of wind waves and salt marsh erosion on sediment transport dynamics of macro-tidal estuarine systems has been examined using a numerical model. Morphological changes associated with salt marsh erosion facilitate the propagation of waves to the marsh edges, and increase the resuspension and export of sediments from the estuary. Results also highlight the impact of tidally-modulated changes in wave action upon sediment transport dynamics throughout a tidal cycle and from neap to spring tide. In particular, wave action at the landward margin of the estuary is limited by the shallow water depth, and tidally induced increments in water depth only cause a modest increase in wave shear stresses. At the seaward side of the domain, the impact of waves is limited by the deeper water, and tidally induced water level variations have a more significant control on wave shear stresses. The outcomes contribute new insights that are important for the sediment budget of macro-tidal estuaries facing climate change and have implications for the long-term morphological evolution of estuarine wetlands. Highlights • Enhanced sediment export from estuaries caused by wind waves • Enhanced salt marsh erosion caused by wind waves • Salt marsh erosion due to morphological changes of estuaries • Wave impact changes with varying water depth [ABSTRACT FROM AUTHOR]