Bathymetry Research Articles

Refraction Correction of the Acoustic Wave in Multibeam Systems

Dynamic surveys of the sea bottom that rely on determination of reflection points of the acoustic wave transmitted by the echosounder use the wave field theory for determination of the trajectories of the acoustic ray. Complex multibeam echosounder systems that use diagonal beams to determine the coordinates of reflecting points on the sea bed, must take into consideration the refraction phenomenon. Beam inflexion depends on the variability of sound’s velocity in water. It is increasingly more important for beams most inflected from the plumb line. It is a determinant of the angle zone of echosounder’s beam and swath width. The efficiency of bathymetric surveys relies on the swath width. It is 3-5 times the water depth for a multibeam echosounder and up to 12 times water depth for an interferometric one. High value of swath width achieved for high beams inflexion decreases the reliability of the Digital Sea Bottom Model built by data recorded during the bathymetric surveys. This article presents results of correction of the phenomenon of non-linear propagation of the acoustic wave in the multibeam echosounder calibration process in the area where the depth does not exceed 30m. A calibration test was utilised on the perpendicular profiles to determine the variance of depths. Depths measured by the diagonal beams were verified using a vertical beam during surveys on perpendicular profile. Popular models for determining the trajectory of an acoustic wave were used – one based on Snell’s law and another, a new one developed by TU Delft. The geospatial data was sourced using R2Sonic multibeam echosounder during the preliminary stage of bathymetric sounding.

Assessment of the Accuracy of Determining the Angular Position of the Unmanned Bathymetric Surveying Vehicle Based on the Sea Horizon Image.

The paper presents the results of research on assessing the accuracy of angular position measurement relative to the sea horizon using a camera mounted on an unmanned bathymetric surveying vehicle of the Unmanned Surface Vehicle (USV) or Unmanned Aerial Vehicle (UAV) type. The first part of the article presents the essence of the problem. The rules of taking the angular position of the vehicle into account in bathymetric surveys and the general concept of the two-camera tilt compensator were described. The second part presents a mathematical description of the meters characterizing a resolution and a mean error of measurements, made on the base of the horizon line image, recorded with an optical system with a Complementary Metal-Oxide Semiconductor (CMOS) matrix. The phenomenon of the horizon line curvature in the image projected onto the matrix that appears with the increase of the camera height has been characterized. The third part contains an example of a detailed analysis of selected cameras mounted on UAVs manufactured by DJI, carried out using the proposed meters. The obtained results including measurement resolutions of a single-pixel and mean errors of the horizon line slope measurement were presented in the form of many tables and charts with extensive comments. The final part presents the general conclusions from the performed research and a proposal of directions for their further development.

Retrieval of Nearshore Bathymetry around Ganquan Island from LiDAR Waveform and QuickBird Image

Optical remote sensing is an effective means of water depth measurement, but the current approach of mainstream bathymetric retrieval requires a large amount of onsite measurement data. Such data are hard to obtain from places where underwater terrains are complicated and unsteady, and from sea areas affected by issues with rights and conflicts of interest. In recent years, the emergence of airborne light detection and ranging (LiDAR) provided a new technical means for field bathymetric survey. In this study, water depth inversion was carried out around an island far from the mainland by using remote sensing images and real LiDAR waveform data. Multi-Gaussian function fitting was proposed to extract water depth data from waveform data, and bathymetric values were used as control and validation data of the active and passive combination of water depth inversion. Results show that the relative error was 5.6% for the bathymetric retrieval from LiDAR waveform data, and the accuracy meets the requirements of ocean bathymetry. The average relative error of water depth inversion based on active and passive remote sensing was less than 9%. The method used in this study can also reduce the use of LiDAR data and the cost, thus providing a new idea for future coastal engineering application and construction.

Characteristics of effective marine protected areas in Hawaiʻi

Abstract Ancient Hawaiians developed sophisticated natural resource management systems that included various forms of spatial management. The state of Hawaiʻi established its first legislated marine protected area (MPA) in 1953, and today there exists a patchwork of spatial marine management strategies along a range of sizes, with varying levels of governance, enforcement, and effectiveness. Approximately 12% of waters within the 50 m depth contour and 5% of waters within state jurisdiction (≤3 nmi) have some form of marine management. No‐take areas make up <0.5% of nearshore waters, and combined with highly protected areas account for 3.4% of this habitat. Most of the existing MPAs are small, with a median area of 1.2 km2 (confidence interval 0.2–8.1). Twenty‐five datasets, representing 1,031 individual surveys conducted throughout Hawaiʻi since 2000, were used to compare fish assemblage characteristics amongst a subset of MPAs using a regulation‐based protection classification scheme. Fully and highly protected areas had significantly greater resource fish biomass than areas with intermediate or low protection did. High human population density adjacent to MPAs had a negative influence on fish trophic structure within MPAs, whereas remote MPAs harboured higher fish biomass. Complex and heterogeneous habitats were important contributors to MPA effectiveness. Long‐term monitoring of select MPAs showed mixed and complex trajectories. Resource fish biomass increased after the establishment of the Hanauma Bay Marine Life Conservation District in 1967 but plateaued after ~15 years, followed by changes in assemblage structure from fish feeding and invasive species. The Pūpūkea Marine Life Conservation District, established in 1983, was expanded sevenfold in 2003 and showed dramatic increases in resource fish biomass following increased protection. This information is critical to improving effectiveness of existing MPAs, helping inform ongoing efforts to implement a network of MPAs statewide, and aiding in the development of comprehensive statewide marine spatial planning.

Sidewall shear stress distribution effects on cohesive bank erosion in curved channels

A series of experiments were conducted to reveal the effects of the sidewall shear stress distribution (SSSD) on homogeneous cohesive bank erosion processes in a U-shaped flume. The three-dimensional flow velocities were measured in detail and the turbulent kinetic energy method was employed to estimate the SSSD. The experimental results showed that the SSSD changed with the discharge and the point of the maximum shear stress varied within a range of 0·15–0·75 of the relative water depth. The variation of underwater bank topography was found to be consistent with the SSSD and the location of the maximum erosion point was not at the bank toe. The dominant failure mechanisms were observed to be tensile and toppling failures. Furthermore, a simplified bank erosion model (SBEM) was developed with consideration of the SSSD. Compared with the bank stability and toe erosion model, the SBEM can provide a more accurate simulation of bank erosion processes. This study is expected to enrich general understanding of cohesive bank erosion processes in curved channels, which will help to formulate effective strategies for river regulation.

Abstract #4308 Genetic variation of IL-6 expression modulates age-related memory decline

An integrated approach combining swath bathymetry, high-resolution seismic reflection and seabed sediment sampling was performed to characterize a field of sand ridges on the Murcia continental shelf in the western Mediterranean Sea. The aim of this work was to improve knowledge about the formation, evolution and present-day dynamics of these bedforms on a narrow, tideless continental shelf receiving little sediment input. Sand ridges are observed on the middle shelf at water depths ranging between 58 and 78 m. The sand ridges are 1.5 to 3 m high and show a predominant E-W orientation oblique to the present-day shoreline. Smaller-scale subaqueous dunes (0.3–1.3 m high) appear superimposed on the sand ridges and beyond the ridge field. The subaqueous dunes show a NW-SE orientation and asymmetric profiles, with the lee side facing southwest. The comparison of two bathymetric surveys 10 years apart revealed that the subaqueous dunes are migrating towards the southwest at very low rates (~ 3 m yr− 1). Internally, both sand ridges and dunes display southwestward dipping oblique reflections, indicating long-term migration in that direction.The morphology, architecture and distribution of the Murcia sand ridges suggest that they were formed in a shallow-water environment during the Holocene transgression and were later detached from the coast due to the subsequent sea level rise. The shallow architecture of the sand ridges reveals the presence of small, mound-like features within the sand ridges, most probably associated with coastal deposits, which could have served as a precursor for the development of the sand ridges. The preservation of these deposits within the sand ridges evidences limited offshore ridge migration. At present, active subaqueous dunes superimposed on the sand ridges suggest that they may play a significant role in the ridge evolution. At a regional scale, the comparison of the Murcia sand ridges with those described in the western Mediterranean allows us to propose a gradation from partially evolved to fully evolved sand ridges with increasing water depth.

Assessment of reservoir sedimentation of irrigation dams in northern Ghana

Adongo TA, Kyei-Baffour N, Abagale FK, Agyare WA. 2019. Assessment of reservoir sedimentation of irrigation dams in northern Ghana. Lake Reserv Manage. 36:87–105.Sedimentation in reservoirs of irrigation dams is a serious issue that threatens their functionalities. Since information on this phenomenon in irrigation dams in northern Ghana is almost nonexistent, a study was necessary. The study used bathymetric survey integrated with geographic information systems (GIS) tools to assess reservoir sedimentation of 9 irrigation dams in 3 northern regions of Ghana. The bathymetric survey was conducted during August–October 2017 using a hand-held Hondex digital depth meter. Reservoir depths at full supply level were found to range from 0.10 to 14.70 m. The volumetric storage capacity loss in the reservoirs ranged from 0.1 to 7.94 Mm3, while the percentage storage capacity loss ranged from 8.54 to 34.12%. The reservoirs were found to be losing volume by 0.26–0.91%/yr. The water surface area of the reservoirs lost due to sedimentation ranged from 5.53 to 24.10%. Estimated mean annual sediment load and sediment inflows into the reservoirs ranged from 3159 to 12,850 mg/L and from 1594 to 355,017 m3/yr, respectively. Estimated useful life of the reservoirs ranged from 22 to 160 yr. All the reservoirs except Bontanga and Tono had a well-formed delta and slightly formed tapering deposits. Major causes of the sedimentation were observed to be mainly human activities within the reservoir catchments. Enactment and enforcement of bylaws to restrict farming, burning, and sand/gravel mining activities in the buffer zones of the reservoirs are necessary to reduce the rate of sedimentation. Improved catchment management practices, construction of check dams, installation of hydrosuction sediment-removal systems, and periodic desilting are also recommended.

Application of a fish finder system to spatial distribution mapping for the razor clam Solen gordonis: Case study from coastal waters, northwestern Kyushu, Japan

Effective spatial management planning for sedentary fishery resources requires accurate spatial distribution mapping of a focal stock including both fished and associated unfished populations. This study focuses on (sub-)adult razor clams (Solen gordonis), with shell lengths ≥25 mm, in Sasebo Bay and Omura Bay, northwestern Kyushu, Japan. They are commercially harvested, but little is known about their spatial distribution pattern. The objective was to estimate the spatial distribution and configuration of clam beds existing within an area of ca. 12 km2. For this, clam and sediment sampling by scuba-equipped divers, acoustic bathymetric surveys using a recreational-grade fish finder (single-beam acoustic) system, and presence–absence modelling using generalized linear models were performed. For the collected clams, catch per unit effort (CPUE; number of clams collected/h) was calculated and used as a proxy for clam individual density. The results showed that the presence–absence variation in the spatial distribution of (sub-)adult clams was associated with the bottom sediment type. (Sub-)adult clams occurred frequently in the sediments with higher gravel (particles with diameters ≥2 mm, mainly shell fragments) and lower mud (diameters <0.063 mm) contents than the sediments of the absence sites. Acoustic signals of the fish finder system were backscattered more intensely from gravel-sand beds (i.e., typical of the presence sites) than from muddy sand beds (i.e., absence sites). Using the relationships among the presence–absence variation of (sub-)adult clams, sediment type, and backscatter strength, spatial distribution of clams was predicted with high accuracy. The presence probability of (sub-)adults (= x; continuous values from 0 to 1) predicted from the results was significantly regressed on CPUE (= y) [i.e., y = exp(−0.7984 + 4.9350x) − 0.05]. Using this relationship, a map for the relative abundance of (sub-)adult clams was obtained. This map depicted several clam beds including both exploited and unexploited ones. The latter beds virtually conform to no-take zones in the razor clam fishery.

Simultaneous Mapping of Coastal Topography and Bathymetry From a Lightweight Multicamera UAS

A low-cost multicamera Unmanned Aircraft System (UAS) is used to simultaneously estimate open-coast topography and bathymetry from a single longitudinal coastal flight. The UAS combines nadir and oblique imagery to create a wide field of view (FOV), which enables collection of mobile, long dwell timeseries of the littoral zone suitable for structure-from-motion (SfM), and wave speed inversion algorithms. Resultant digital surface models (DSMs) compare well with terrestrial topographic lidar and bathymetric survey data at Duck, NC, USA, with roor-mean-square error (RMSE)/bias of 0.26/–0.05 and 0.34/–0.05 m, respectively. Bathymetric data from another flight at Virginia Beach, VA, USA, demonstrates successful comparison (RMSE/bias of 0.17/0.06 m) in a secondary environment. UAS-derived engineering data products, total volume profiles and shoreline position, were congruent with those calculated from traditional topo-bathymetric surveys at Duck. Capturing both topography and bathymetry within a single flight, the presented multicamera system is more efficient than data acquisition with a single camera UAS; this advantage grows for longer stretches of coastline (10 km). Efficiency increases further with an on-board Global Navigation Satellite System–Inertial Navigation System (GNSS-INS) to eliminate ground control point (GCP) placement. The Appendix reprocesses the Virginia Beach flight with the GNSS–INS input and no GCPs. The resultant DSM products are comparable [root-mean-squared difference (RMSD)/bias of 0.62/−0.09 m, and processing time is significantly reduced.

Understanding the hydrocarbon prospect of Buzdar block, Southern Indus basin, Pakistan, by using 2-D seismic data: A case study

Abstract The sub-surface structural analysis to understand the geology and tectonics of an area is always useful to locate the hydrocarbon resources. Oil and gas based energy supplies have become a vital source for Pakistan, which is passing through an era of severe energy crisis. The study area, Buzdar block, in the southern Indus Basin is tectonically an extensional regime and is expected to have a huge hydrocarbon potential. In this study, we did the interpretation of the migrated seismic lines of the 872-SGR-527, 872-SGR-529, 872-SGR-531, 872-SGR-532 of Buzdar block, District TandoAllahyar, Sindh. The lines 872-SGR-529, 872-SGR-531, 872-SGR-532 were oriented W–E whereas the line 872-SGR-527 was oriented NW–SE. The obtained data was analysed and three reflectors were marked named top Khadro Formation, top lower Goru formation and top Chiltan limestone (probable). Through this study faults have been also marked on seismic lines which are normal faults by nature; collectively form horsts and grabens which is the evidence of effect of extensional tectonics in the area. Time contour maps were also generated. After that, time was converted into depth with the help of well velocity from VSP data for lower Goru formation and average velocity for Chiltan limestone (probable) from regression analysis. Finally, depth contour maps were generated which helped to know the basic mechanism of tectonic movement in the area. On the basis of present analysis we propose that a well may be drilled at Lower Goru formation near fault F1 on western side at a depth of 1370 meters and at 1290 meters near fault F4 on eastern side.

Marine Observing Applications Using AIS: Automatic Identification System

The Automatic Identification System (AIS) is a real-time network of transmitters and receivers that allow vessel movements to be broadcast, tracked and recorded. Though traditionally used for real-time maritime applications related to keeping track of vessel traffic for collision avoidance, there is increasing interest in using AIS data and the AIS platform for maritime safety planning, resource management and weather forecasting. AIS data are being made tractable for alternative non-real-time applications like determining trends and patterns in vessel traffic and helping to prioritize where modern bathymetric surveys are needed to ensure safe maritime transit. The AIS is also being used for widespread transmission of critical environmental conditions information, such as sea state and weather, to mariners, forecasters and emergency response providers. Several pilot projects are underway that demonstrate the capacity and promise of AIS data and the AIS platform to serve multiple purposes, providing overall maritime domain awareness while maintaining its most important objective of tracking vessels.

Modeling of a dispersive tsunami caused by a submarine landslide based on detailed bathymetry of the continental slope in the Nankai trough, southwest Japan

Tsunamis caused by submarine landslides are not accompanied by seismic waves and thus may appear at the coast without warning. In this study, detailed bathymetric surveys with a multi-narrow beam echo sounder were used to map submarine landslides on the continental shelf near Cape Muroto, in the Nankai trough off southwestern Japan. One of the surveyed submarine landslides was selected to supply dimensions for the simulation of a submarine mass movement by a two-layer flow model in which the upper and lower layers correspond to seawater and turbidity currents, respectively. The time series of seafloor deformation during this simulated landslide was used as the boundary condition to drive a tsunami simulation. The results showed strong directivity effects during tsunami generation in which pushing-dominant (positive) tsunami waves propagated seaward, in the direction of the submarine landslide, and pulling-dominant (negative) tsunami waves propagated landward. Both types of waves were strongly modified by frequency dispersion. For pulling-dominant waves, a tsunami simulation that included dispersion (Boussinesq) terms predicted greater maximum tsunami heights than a non-dispersive tsunami simulation. To avoid underestimation of tsunami heights, we recommend including dispersion terms when modeling tsunamis caused by submarine landslides for disaster planning purposes.

Recent Eruptions Between 2012 and 2018 Discovered at West Mata Submarine Volcano (NE Lau Basin, SW Pacific) and Characterized by New Ship, AUV, and ROV Data

West Mata is a submarine volcano located in the SW Pacific Ocean between Fiji and Samoa in the NE Lau Basin. West Mata was discovered to be actively erupting at its summit in September 2008 and May 2009. Water-column chemistry and hydrophone data suggest it was probably continuously active until early 2011. Subsequent repeated bathymetric surveys of West Mata have shown that it changed to a style of frequent but intermittent eruptions away from the summit since then. We present new data from ship-based bathymetric surveys, high-resolution bathymetry from an autonomous underwater vehicle, and observations from remotely operated vehicle dives that document four additional eruptions between 2012-2018. Three of those eruptions occurred between September 2012 and March 2016; one near the summit on the upper ENE rift, a second on the NE flank away from any rift zone, and a third at the NE base of the volcano. The latter intruded a sill into a basin with thick sediments, uplifted them, and then extruded lava onto the seafloor around them. The most recent of the four eruptions occurred between March 2016 and November 2017 along the middle ENE rift zone and produced pillow lava flows with a shingled morphology and tephra as well as clastic debris that mantled the SE slope. ROV dive observations show that the shallower recent eruptions at West Mata include a substantial pyroclastic component, based on thick (>1m) tephra deposits near eruptive vents. The deepest eruption sites lack these near-vent tephra deposits, suggesting that pyroclastic activity is minimal below ~2500 mbsl. The multibeam sonar re-surveys constrain the timing, thickness, area, morphology, and volume of the new eruptions. The cumulative erupted volume since 1996 suggests that eruptions at West Mata are volume-predictable with an average eruption rate of 7.8 x 106 m3/yr. This relatively low magma supply rate and the high frequency of eruptions (every 1-2 years) suggests that the magma reservoir at West Mata is relatively small. With its frequent activity, West Mata continues to be an ideal natural laboratory for the study of submarine volcanic eruptions.

Dynamic Wedge Failure and Along‐Arc Variations of Tsunamigenesis in the Japan Trench Margin

AbstractElastic dislocation models require large near‐trench slip to explain large tsunamigenesis, which is probably best exemplified in the 2011 M9 Tohoku earthquake. However, it is puzzling that the largest Tohoku tsunami heights occurred about 100 km north of the largest slip zone, where bathymetric surveys indicate no large slip at the trench or submarine landslides. Here we show that coseismic yielding of plentiful sediments in the northern Japan Trench margin can induce large inelastic uplift landward from the trench and diminish slip near the trench. The scarcity of sediments in the south leads to nearly elastic response with large slip at the trench and mostly horizontal seafloor displacement. Thus, the variations of sediments along the Japan Trench and sediment yielding can explain the puzzling variations of tsunamigenesis and near‐trench slip in this earthquake. Inelastic wedge deformation can be an important mechanism of tsunamigenesis in accretionary and other sediment‐filled plate margins.

Field investigation of siltation at a tidal harbor: North Port of Incheon, Korea

To understand siltation processes within the North Port of Incheon, Korea, this study estimated the sedimentation rate and then determined the dominant mechanisms for the siltation. The sedimentation rate was estimated by comparing bathymetric surveys adjusted with the dredged volume, and verified by the penetration depth of 11 gravity cores to the previous dredging surface. The average sedimentation rate was 64 cm/year but varied from 10 cm/year in the interior to about 100 cm/year at the entrance. To determine the dominant mechanisms for siltation, two ADCPs were deployed at the entrance and the interior end of the harbor over a month to estimate sediment flux. Detailed sediment transport processes were examined by two 13-h CTD profiling surveys near the entrance and interior end of the harbor. High siltation at the entrance is attributable to the influx of high turbidity water, the decrease of current velocity, and the formation of an eddy. Low sedimentation inside the harbor was attained by the slow settling of microflocs of about 20–30 mg/l concentration that are maintained regardless of time and space.

Bathymetric Survey and Topography Changes Investigation of Part of Badagry Creek and Yewa River, Lagos State, Southwest Nigeria

Bathymetry survey of Part of Badagry Creek and Yewa River was conducted with the aim of investigating the topography changes in depth between two epoch dataset by calculating the volume of sediment and dredged material between the two periods. Depth sounding at 100m interval, data grid of 100 m interval, constant vessel speed of 2.2 m/secs (8Km/hr) for data capture, data storage at interval of 30 Secs was ensured at both the creek and the river. Seabed topography changes of Part of Badagry Creek and Yewa River was investigated. The two dataset investigated was the data acquired in September 2008 and November 2015. Data acquisition was done using digital echo sounder SDE28, Handheld Real time Kinematic (RTK) Global Positioning System (GPS) in acquiring the spatial coordinates (x, y) and water depth (z). Six (6) wrecks (Shipping Boat) were determined along both the creek and the river. The initial processing was carried out with the use of HYPACK 2008 software for data sorting. ArcGIS 10.2.1 was used for data analysis as well as graphics design. The processed depths were presented in form of tables, map/plan and charts. The result showed that In 2008, the depth observed ranges from (-0.5 to 10.4) m while in 2015, the depth observed ranges from (-0.32 to 10.85) m which implies that some area have been cut. Also, the results of the volume of deposited sediments and dredged material are computed as 10.55 x 106 m3 and 7.24 x 106 m3. It showed from the result that volume of accreted sediment is greater than volume of the material dredged. Increase in volume of sediment deposited could be as a result of the adjoining river Yewa flowing into the larger river (tributaries) of the Badagry Creek. Therefore, further studies need to carry out in order to know the source of accreted mass through integrated coastal management plan.

Continental slope-confined canyons in the Pearl River Mouth Basin in the South China Sea dominated by erosion, 2004–2018

Repeat multibeam bathymetric surveys conducted in 2004, 2005 and 2018 show that seven slope-confined canyons on the continental slope of the Pearl River Mouth Basin, South China Sea, were dominated by large volume, widespread erosion. Erosion volumes were up to 3.4 times greater than deposition volumes. Erosion-dominated areas of the canyons are up to 2.3 times greater than areas dominated by deposition. Average rates of erosion (ranging from 0.7 to 0.8 m/yr) were greater than average rates of deposition (ranging from 0.5 to 0.8 m/yr). In plan view, the erosion-dominated zones exhibit two characteristic shapes: (1) linear, found mainly in upper canyon reaches, distributed predominantly along canyon axes and at the base of eastern canyon walls, and; (2) blocky, found mainly in lower canyon reaches, widely distributed along the steep canyon walls and on lower-canyon interfluves. The deposition-dominated zones are scattered along canyon floors and walls. Seismic reflection data show lateral shifts of canyon fill deposits through time, indicative of longer-term eastward canyon migration. The linear erosion-dominated zones may be attributed to erosive turbidity currents triggered by energetic internal solitary waves shoaling on the shelf. The eastward canyon shifts were likely induced by rapid near-bed eastward currents generated mainly by westward propagating powerful internal solitary waves of depression. The widespread erosion in the deeper canyon areas and interfluves is likely a consequence of slope instabilities associated with the presence of gas hydrates. This study indicates that active sedimentary processes can occur in slope-confined canyons even during sea level highstands. Local, site-specific oceanographic and geological features (e.g., internal solitary waves, gas hydrates) can significantly increase sedimentary activity in and around submarine canyons.

First Results of a Bathymetric Survey of Palu Bay, Central Sulawesi, Indonesia following the Tsunamigenic Earthquake of 28 September 2018

On 28 September 2018, a 7.7 Mw strike-slip earthquake struck Central Sulawesi at 0.18°S, 119.85°E, ~ 10 km northwest of Palu, the capital of Central Sulawesi Province, affecting more than 230,000 people. The rapid arrival of the wave suggests a tsunami source within Palu Bay. A bathymetric campaign was conducted in Palu Bay and the region south of Cape Manimbaya from 9 to 18 October 2018. One of the goals was to identify a potential source for the tsunami. The bathymetry data show a prominent submarine channel within Palu Bay with sinuosity controlled by the Palu-Koro Fault. The submarine channel continues into deeper water south and west of Cape Manimbaya with a sinuosity index of up to 1.770. Several submarine slumps were identified within the bay, due to the arcuate head scarp, the abrupt change in slope and debris on the seafloor, or the undulating shape of the slope. One possible source location near the mouth of Palu Bay is identified from the estimated volume of displaced sediment. The bathymetry data also show traces of the Palu-Koro Fault and suggestions of uplift of Cape Manimbaya related to activity of the Palu-Koro Fault.

Marsh edge erosion and associated carbon dynamics in coastal Louisiana: A proxy for future wetland-dominated coastlines world-wide

Coastal wetland loss through marsh edge erosion is a serious problem in Louisiana. The majority of studies on coastal land loss use aerial and satellite photographic analysis while field and site-specific measurements are limited. The aim of this study was to spatially and temporally measure coastal marsh edge erosion and investigate factors responsible for differences in erosion including shoreline orientation, soil physio-chemical properties, and wind speed and duration. A total of 33 transects across six island sites in northern Barataria Basin, Louisiana were established. Transects on shorelines facing different compass directions were measured for erosion for up to 2 years. Soils were analyzed for physiochemical properties including bulk density, organic matter, total carbon, nitrogen, and phosphorus. Bathymetric surveys were conducted to determine the extent of the erosive bay bottom profile. In addition, 14C dating of the basal organic matter (1.5–1.6 m) was conducted. Erosion rates ranged from 49.27 to 324.85 cm y-1 with a mean value of 141.69 ± 22.45 cm y−1. As expected, erosion rates were significantly different (p < 0.001) between protected and unprotected sites. The erosion rate was not correlated with wind speed (r = -0.07), weakly correlated with compass direction of shoreline (r = 0.25) and water level (r = 0.25) but strongly correlated with duration of wind (r = 0.60). Erosion rate was negatively correlated (r = -0.45) with bulk density and positively correlated with organic matter content (r = 0.42) of the top 40 cm of the soil. Over time, the marsh is eroded down to a depth of 1.5 m, which correlates to annual loss of 1.82 ± 0.29 m3 volume of marsh per meter shoreline length including a loss of organic matter (141.5 ± 22.55 kg m−1) and carbon (63.32 ± 10.09 kg m−1) previously preserved for up to 850 years. As a consequence, annual CO2 emissions for Barataria Basin were estimated to be 1.56 ± 0.26 million tCO2e y−1. Results can inform coastal managers as to the most vulnerable marshes to target restoration efforts. Due to high relative sea level rise in coastal Louisiana, these results can also be used to inform the world's stable coastlines on the relative vulnerability of their coastal marshes in the near future, due to projected eustatic sea level. Consequently, the eroding coastlines across the globe may be a significant source of CO2 emissions in near future, as millennial age stored soil carbon is released in a relatively short time, potentially overwhelming human efforts to slow rising atmospheric CO2 levels.

A Multi-Disciplinary Approach to the Study of Large Rock Avalanches Combining Remote Sensing, GIS and Field Surveys: The Case of the Scanno Landslide, Italy

This research aims to highlight the importance of adopting a multi-disciplinary approach to understanding the factors controlling large rock avalanches using the Scanno landslide, Italy, as a case study. The study area is the Mount Genzana, Abruzzi Central Apennines, characterized by the regional Difesa-Mount Genzana-Vallone delle Masserie fault zone. The Scanno landslide is famous for its role in the formation of the Scanno Lake. The landslide is characterized by a wide exposed scar, which was interpreted in previous studies as the intersection of high-angle joints and an outcropping bedding plane on which the landslide failed sometime between the Upper Pleistocene and the Holocene. In this study, the Scanno landslide was investigated through the integration of geological, geomechanical and geomorphological surveys. Remote sensing techniques were used to enrich the conventionally gathered datasets, while Geographic Information Systems (GIS) were used to integrate, manage and investigate the data. The results of the authors investigation show that the outcropping landslide scar can be interpreted as a low-angle fault, associated with the Difesa-Mount Genzana-Vallone delle Masserie fault zone, which differs from previous investigations and interpretations of the area. The low-angle fault provides the basal failure surface of the landslide, with two systematic high-angle joint sets acting as lateral release and back scarp surfaces, respectively. In light of these new findings, pre- and post-failure models of the area have been created. The models were generated in GIS by combining LiDAR (Light Detection and Ranging) and geophysics data acquired on the landslide body and through bathymetric survey data of the Scanno Lake. Using the pre- and post-failure models it was possible to estimate the approximate volume of the landslide. Finally, back-analyses using static and dynamic limit equilibrium methods is also used to show the possible influence of medium-to-high magnitude seismic events in triggering the Scanno landslide.