Abstract New high-resolution surveying techniques allow subaqueous geomorphology to be investigated in great detail. Such analyses are important as the morphologies are often indicative of past processes, including mass movements. For peri-alpine Lake Zurich, many mass-wasting events have occurred in the past millennia. While the ages of these events are known from past studies on the respective deposits in the lake basin, the surface expressions and distribution of the respective features on the slopes have not been extensively described. Here we quantitatively characterize the morphologic features on the entire lake floor. A total of 50 subaqueous landslides are morphologically identified in a high-resolution digital bathymetric model (DBM), mapped and characterized using a geographic information system (GIS). Many slides show relatively small erosion areas (<0.05 km 2 ) and are located in shallow water (<10 m water depth). The roughness of the individual landslide-translation areas is quantified using the standard deviation of a measure called bathymetric position index (BPI) and related to the slides ages. The DBM allows the detection of traces of mass-movements dating back to c. 5000 cal years BP. Our results demonstrate that morphometric analyses on a high-resolution DBM can contribute to a better understanding of sublacustrine mass movements.

Abstract Martian gullies were initially hypothesized to be carved by liquid water, due to their resemblance to gullies on Earth. Recent observations have highlighted significant sediment transport events occurring in Martian gullies at times and places where CO 2 ice should be actively sublimating. Here we explore the role of CO 2 sublimation in mobilizing sediment through laboratory simulation. In our previous experimental work, we reported the first observations of sediment slope movement triggered by the sublimation of CO 2 frost. We used a Mars regolith simulant near the angle of repose. The current study extends our previous work by including two additional substrates, fine and coarse sand, and by testing slope angles down to 10°. We find that the Mars regolith simulant is active down to 17°, the fine sand is active only near the angle of repose and the coarse sand shows negligible movement. Using an analytical model, we show that under Martian gravity motion should be possible at even lower slope angles. We conclude that these mass-wasting processes could be involved in shaping Martian gullies at the present day and intriguingly the newly reported CO 2 -creep process could provide an alternative explanation for putative solifluction lobes on Mars. Supplementary material: Video clips depicting sediment transport types are available at https://doi.org/10.6084/m9.figshare.5208847

Abstract Gullies are widespread morphological features on Mars for which current changes have been observed. Liquid water has been one of the potential mechanisms to explain their formation and activity. However, under present-day Martian conditions, liquid water is unstable and should only be transiently present in small amounts at the surface. Yet little attention has been paid to the mechanisms by which unstable water transports sediment under low atmospheric pressure. Here we present the results of laboratory experiments studying the interaction between liquid water flowing over a sand bed under Mars-like atmospheric pressure ( c. 9 mbar). The experiments were performed in a Mars Simulation Chamber (at the Open University, UK), in which we placed a test bed of fine sand at a 25° slope. We chose to investigate the influence of two parameters: the temperature of the water and the temperature of the sand. We performed 27 experiments with nine different combinations of water and sand temperatures ranging from 278 to 297 K. Under all experimental conditions, the water was boiling. We investigated and compared the types and timing of sediment transport events, and the shapes, characteristics and volumes of the resulting morphologies. In agreement with previous laboratory studies we found that more intense boiling increased the volume of sediment transported for a given volume of water. We found four main types of sediment transport: entrainment by overland flow; grain ejection; grain avalanches; and levitation of saturated sand pellets. Our results showed that increasing sand temperature was the main driving parameter in increasing the sand transport and in modifying the dominant sediment transport mechanism. The temperature of the water played a negligible or minor role, apart from the duration of sand ejection and avalanches, which lasted longer at low water temperature. At low sand temperature the majority of the sand was transported by overland flow of the liquid water. At higher sand temperatures the transport was dominated by processes triggered by the boiling behaviour of the water. At the highest temperatures, sediment transport was dominated by the formation of levitating pellets, dry avalanches and ejection of the sand grains. This resulted in a transport volume about nine times greater at a sand temperature of 297 K compared with 278 K. Our heat transfer scaling shows that the boiling behaviour will be enhanced under Martian low gravity, resulting in more efficient transport of sediment by levitating sand pellets even at temperatures close to the triple point. Our results showed that the boiling intensity played an important role in the physics of sediment transport by liquid water. This implied that the amount of water required to produce morphological changes at the surface of Mars could be lower than previously estimated by assuming stable liquid water. Boiling is a critical process to be considered when assessing gully formation and modification mechanisms mobilized by liquid water. Our work could have similar implications for any water-formed landform on Mars, which could include recurring slope lineae, dark dune flows and slope streaks. Supplementary material: Videos of the experiments are available at https://doi.org/10.6084/m9.figshare.c.3990330

Abstract In contrast with the archetypal definition of an alluvial fan, this study shows that fans interacting with axial rivers in Yukon and Alaska commonly exhibit asymmetrical morphology in planform. Hypothesis tests relating to the geomorphological characteristics of these alluvial fans were conducted on a dataset of 63 fluvial-dominated fans. A significant relationship existed between fan asymmetry and the direction of axial river flow, which was attributed to two factors supported by examples: (1) axial rivers have a propensity to trim the toes on the up-valley sides of fans; and (2) axial river channels are deflected across the broad valley floors, which allows the profiles on the down-valley sides of fans to be longer than on the up-valley sides. However, an asymmetrical planform morphology does not lead to a significant bias in the spatial distribution of surface streams towards the up-valley sides of fans, which typically have shorter profiles from apex to boundary. If the asymmetry in fan morphology is preserved in the sedimentary record, then the interpretation of fan deposits that developed in broad valleys and that interacted with axial rivers would be improved by understanding this modern analogue.

Abstract We applied a computational method to aid in clustering 41 alluvial fans along the southern coast of the Gulf of Corinth, Greece. The morphology of the fans and their catchments was quantitatively expressed through 12 morphometric parameters estimated using geographical information system techniques and the relationships among the geomorphometric features of the fans and their catchments were examined. Self-organizing maps were used to investigate the clustering tendency of fans based on morphometric variables describing both the fans and their corresponding catchments. The results of unsupervised classification through the self-organizing maps method revealed correlations among the morphometric parameters and five groups of alluvial fans were identified. These groups had a clear physical explanation, showed a preferred geographical distribution and reflected the processes related to the development of the fans. The geographical distribution of the fan catchment groups was partially controlled by variations in the relative tectonic uplift rate, which was the main control on the accommodation space for the development and accretion of the fans. The smaller fans were located in the central part of the study area, where the uplift rates were higher, whereas larger fluvial-dominated fan deltas formed to the east and west of the central group, where the uplift rates were lower.

Abstract As hydrocarbon-prone basins mature through time, stratigraphic traps become increasingly important as hosts for yet-to-find reserves. Explorationists strive to reduce the uncertainty in reservoir distribution and quality, but considerable complications exist in the evaluation of stratigraphic traps owing to the inextricable links between stratigraphy, trap definition and their subsequent risking. This study quantifies the relationships that exist between reservoir geometries and the rates of reservoir property degradation in a turbidite sandstone pinch-out zone. The investigation focuses on the Paleocene Forties Sandstone Member of the Everest and Arran fields of the East Central Graben of the UK North Sea. We utilized standard seismic interpretation techniques and integrated stratigraphic and petrophysical analysis of wireline log data to map deep-water turbidite sandstone terminations and develop a predictive model for reservoir property changes close to the feather edge. The Forties Sandstone Member thins systematically up on to a palaeoramp on the eastern basin margin of the Central Graben. Results reveal that the net reservoir sandstones pinch out after the turbidite flows had traversed 5 km across the palaeoramp. The gross interval is predicted to completely terminate 6.4 km up the palaeoramp. The reservoir properties decrease in concert with the thinning trend in the wedge zone as a function of the interaction of palaeotopography and the hydraulics of the decelerating flows. The inclination of the counter-regional slope is considered to be a key controlling factor that determines the rate of thinning and thus the termination position of the sandstones and their concomitant reservoir property decline. The results of this study demonstrate that characterization of pinch-outs into distinct zones based on a palaeotopographic template can be of utility in stratigraphic and combination trap definition. This work also has wider implications for prospect risking, volumetric analysis, the population of properties and geological modelling of stratigraphic traps.

Abstract Defining the size and shape of hydrocarbon traps is a critical component in estimating the economic value of potential and existing oil and gas fields and is, therefore, a key business risk. Structural traps, defined by fault and fold geometries, form the most common type of hydrocarbon trap, the size estimates of which are based on interpretation of subsurface data, most notably seismic imagery. Interpretation of seismic image data is uncertain, as the subsurface images have limited resolution and quality; in 2D datasets the imagery is spatially limited and the interpretation requires interpolation between images. Here we present data from top reservoir maps created by eight interpretation teams, each of which interpreted a grid of 2D seismic sections at a regular spacing of 1 km, over a 220 km 2 area. The resultant maps are compared for interpretation variability. Fault statistics have been generated for each map and compared with analogue datasets to aid in the identification of anomalous interpretations, and to create a likelihood rank for each map. The structural traps identified by each team are compared, and the two largest traps are assessed for their potential trapped hydrocarbon volume. An initial volume and a corrected volume, accounting for potential fault seal breach by reservoir–reservoir juxtaposition across the trap-defining faults, are calculated. The integrated analysis of the multiple interpretations: (a) captures the interpretational uncertainty, (b) determines the likeliness (or risk) of each interpretation being valid, when compared with analogue datasets and (c) assesses the impact of each interpretation on the economic viability of potential prospects (defined by structural traps).

Abstract For safety and environmental reasons, removal of aging dams is an increasingly common practice, but it also can lead to channel incision, bank erosion, and increased sediment loads downstream. The morphological and sedimentological effects of dam removal are not well understood, and few studies have tracked a reservoir for more than a year or two after dam breaching. Breaching and removal of obsolete milldams over the last century have caused widespread channel entrenchment and stream bank erosion in the Mid-Atlantic region, even along un-urbanized, forested stream reaches. We document here that rates of stream bank erosion in breached millponds remain relatively high for at least several decades after dam breaching. Cohesive, fine-grained banks remain near vertical and retreat laterally across the coarse-grained pre- reservoir substrate, leading to an increased channel width-to-depth ratio for high-stage flow in the stream corridor with time. Bank erosion rates in breached reservoirs decelerate with time, similar to recent observations of sediment flushing after the Marmot Dam removal in Oregon. Whereas mass movement plays an important role in bank failure, particularly immediately after dam breaching, we find that freeze-thaw processes play a major role in bank retreat during winter months for decades after dam removal. The implication of these findings is that this newly recognized source of sediment stored behind breached historic dams is sufficient to account for much of the high loads of fine-grained sediment carried in suspension in Mid-Atlantic Piedmont streams and contributed to the Chesapeake Bay.

Abstract This volume provides an authoritative and comprehensive state-of-the-art review of hot desert terrains in all parts of the world, their geomaterials and influence on civil engineering site investigation, design and construction. It primarily covers conditions and materials in modern hot deserts, but there is also coverage of unmodified ancient desert soils that exhibit engineering behaviour similar to modern desert materials. Thorough and up-to-date guidance on modern field evaluation and ground investigation techniques in hot arid areas is provided, including reference to a new approach to the desert model and detailed specialized assessments of the latest methods for materials characterization and testing. The volume is based on world-wide experience in hot desert terrain and draws upon the knowledge and expertise of the members of a Geological Society Engineering Group Working Party comprising practising geologists, geomorphologists and civil engineers with a wealth of varied, but complementary experience of working in hot deserts. This is an essential reference book for professionals, as well as a valuable textbook for students. It is written in a style that is accessible to the non-specialist. A comprehensive glossary is also included.