GM6.10

GM6
Submarine geomorphology 

The ocean floor hosts a tremendous variety of forms that reflect the action of a range of tectonic, sedimentary, oceanographic and biological processes at multiple spatio-temporal scales. Many such processes are hazards to coastal populations and offshore installations, and their understanding constitutes a key objective of national and international research programmes and IODP expeditions. High quality bathymetry, especially when combined with sub-seafloor and/or seabed measurements, provides an exciting opportunity to integrate the approaches of geomorphology and geophysics, and to extend quantitative geomorphology offshore. 3D seismic reflection data has also given birth to the discipline of seismic geomorphology, which has provided a 4D perspective to continental margin evolution.

This interdisciplinary session aims to examine the causes and consequences of geomorphic processes shaping underwater landscapes, including submarine erosion and depositional processes, submarine landslides and canyons, sediment transfer and deformation, volcanic activity, fluid migration and escape, faulting and folding, and other processes acting at the seafloor. The general goal of the session is to bring together researchers who characterise the shape of past and present seafloor features, seek to understand the sub-surface and surface processes at work and their impacts, or use bathymetry and/or 3D seismic data as a model input. Contributions to this session can include work from any depth or physiographic region, e.g. oceanic plateaus, abyssal hills, mid-ocean ridges, accretionary wedges, and continental margins (from continental shelves to abyss plains). Datasets of any scale, from satellite-predicted depth to ultra high-resolution swath bathymetry, sub-surface imaging and sampling, are anticipated.

This session is organised by the IAG Submarine Geomorphology Working Group.

Co-organized by OS1/SSP3, co-sponsored by IAG
Convener: Aaron Micallef | Co-conveners: Sebastian Krastel, Alessandra Savini
Presentations
| Wed, 25 May, 08:30–10:00 (CEST)
 
Room K2

Presentations: Wed, 25 May | Room K2

Chairpersons: Sebastian Krastel, Alessandra Savini
08:30–08:35
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EGU22-5647
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ECS
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On-site presentation
Vincent Lecours

Marine applications of geomorphometry, the discipline that enables quantitative measurements of the shape of the terrain, have gained significant traction in the past decade. With these applications came the need for methodological developments to address the specific challenges associated with seabed sampling and characterization. This contribution reviews how marine geomorphometry can support submarine geomorphology efforts, with a focus on recent advances. New methods from both general (i.e., continuous measurements) and specific (i.e., discrete measurements) geomorphometry will be discussed, including multiscale approaches for seabed characterization and automated classification workflows. These recent methodological developments will be put in context with how they can contribute to the investigation of a wide variety of aspects associated with the study of submarine geomorphology, such as bedforms, geomorphic processes, and geohazards. This contribution will conclude by presenting the current challenges marine geomorphometry faces and its future opportunities for submarine geomorphology.

How to cite: Lecours, V.: Recent advances in geomorphometry: opportunities for submarine geomorphology, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5647, https://doi.org/10.5194/egusphere-egu22-5647, 2022.

08:35–08:40
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EGU22-10354
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Highlight
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On-site presentation
David Amblas and Ricardo Silva Jacinto

Downslope overflows of dense shelf-water, also known as dense shelf-water cascading (DSWC), are an important atmospheric-driven oceanographic process that occur in certain polar and temperate margins around the world. DSWC events are essential to the formation and ventilation of the deep ocean waters and provide an important link between shallow and deep waters, as they involve not just the massive transfer of water volumes but also sedimentary particles, organic carbon, pollutants and litter.

Field observations show that DSWC can rapidly reshape the seafloor, particularly in submarine canyons. It has been suggested that dense water fluxes could generate continental slope gullies in Polar Regions too. In situ near-bottom velocities up to 1.25 m·s-1 have been measured for these currents, which are similar to those attained by turbidity currents, although suspended sediment concentrations tend to be very much lower in DSWC, with values of 0.002 to 0.005 g·l-1. For this reason, these dilute flows have largely been considered as inefficient pumps for sediment transport. However, the water volumes transported by DSWC events are exceptionally large, as these flows can last for days to weeks, or even months in certain polar regions. Hence, we advocate that this fact is enough to reconsider the former assumption. We tackle this question using a process-based depth-integrated numerical model for gravity-driven density flows, which was initially developed for turbidity currents (Nixes-Tc model, developed at IFREMER). Our modelling analysis, based on Antarctica field observations, show the importance of confining morphological features (i.e. coast capes, cross-shelf troughs, canyons and gullies) to concentrate and guide dense shelf water flows and, ultimately, to renew the oceans deep water. We also study the capacity of individual DSWC events to transport sediment and provide insight into the cumulative effect of repeated DSWC events in shaping the seafloor.

Acknowledgments: This project has received funding from the Spanish Ministry of Science and Innovation and the Spanish State Research Agency (grants EIN2020-112179 and PID2020-114322RBI00), from the European Union's Horizon 2020 research and innovation programme (Marie Sklodowska-Curie grant 658358), and from a postdoctoral grant of the International Association of Sedimentologists (IAS).

How to cite: Amblas, D. and Silva Jacinto, R.: Dense shelf water cascades and particle transport. A process-based numerical model approach, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10354, https://doi.org/10.5194/egusphere-egu22-10354, 2022.

08:40–08:45
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EGU22-3650
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Highlight
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On-site presentation
Oded Katz, Leeron Ashkenazi, Sigal Abramovich, Ahuva Almogi-Labin, Yizhaq Makovsky, Omri Gadol, Mor Kanari, and Orit Hyams-Kaphzan

Nile derived siliciclastic sediments are the main source for sedimentation along the Levant continental margins. The sediments are transported along the southeastern Mediterranean coast via jet and longshore currents, mainly operating along the shelf. However, the cross shelf component of sediments transport, responsible for conveying sediments towards the upper slope, is less known. To better understand the cross-shelf vs. the longshore components of sediment transport, we studied two ~5.5 m piston cores: DOR280 and DOR350, sampled on the upper continental slope at 280 m and 350 m water depth, respectively.

We analyzed the particle size distribution (PSD) as well as the benthic-foraminiferal assemblages and their shells taphonomy, for documenting both the source and the transport mechanism of the upper continental-slope sediments. The radiocarbon sediment age at the DOR280 core-base is ~660 ±70 Cal Yrs. B.P., indicating an exceptionally high average sedimentation rate of ~800 cm/kyr. DOR280 consists of alternating two sedimentary facies: (1) Laminated (L) intervals with bimodal PSD and high ratio of allochthonous vs. autochthonous (allo/auto) foraminiferal species, characterized by a high percentage of benthic-foraminiferal broken and poorly preserved shells, indicating contribution of transported sediments originating from mid-shelf habitats. (2) Non-laminated (NL) intervals with unimodal PSD, low allo/auto ratio (<1) and low percentage of broken shells, indicating mostly in-situ deposition. The L intervals are interpreted as sediment laden gravity currents, possibly turbidites. Numerous centimeters-thick turbiditic events were identified, based on grain-size grading and discontinuous eroded lower stratigraphic-contacts. Sedimentation rate calculated only for the NL intervals is still exceptionally high, excluding hemipelagic sedimentation as the sole deposition. Thus, a contour bottom-current transported component is suggested for the NL sediments of DOR280 (i.e. contourites). DOR350 reveals higher sedimentation rates (age of ~350 ±80 Cal Yrs. B.P. at the core-base) and consists mostly of the L facies. Hence, the sediments of DOR350 are mostly consist of transported (by turbidities) sediments with only minor contribution of hemipelagic sedimentation or contourites.

We conclude that a hybrid contourite-turbidite system actively prevails along the Levant upper continental slope offshore Israel, apparently at water depth of less than 350 m.

How to cite: Katz, O., Ashkenazi, L., Abramovich, S., Almogi-Labin, A., Makovsky, Y., Gadol, O., Kanari, M., and Hyams-Kaphzan, O.: Hybrid turbidite-contourite sediments transport system in the Eastern Mediterranean upper continental slope, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3650, https://doi.org/10.5194/egusphere-egu22-3650, 2022.

08:45–08:50
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EGU22-8615
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ECS
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Virtual presentation
Irena Schulten and Aaron Micallef

Submarine sediment gravity flows are among the most important geological processes on earth. They drive the global sediment transport to the deep ocean and actively shape the continental slope and influence the development of sedimentary basins. These gravity driven flows also pose a hazard to offshore infrastructure and may contribute to tsunami generation. Despite their geological importance, sediment gravity flows are still not fully understood. The western Ionian Basin offshore eastern Sicily experiences high seismicity and host a considerable turbidite record. The 1908 Messina earthquake caused >60,000 casualties and generated a tsunami and an extensive turbidity current. The geohazard for this densely populated and economically important region in the central Mediterranean, however, remains poorly constrained. MARGRAF aims to improve the current understanding of submarine gravity flows on a regional and global basis using a multidisciplinary and multi-scale approach. Geophysical and sedimentological data interpretation, numerical modelling, and laser interferometry will be used to: 1) reconstruct the behaviour and evolution of the 1908 turbidity current; 2) evaluate the role of this turbidity current in the 1908 Messina tsunami; 3) test the effectiveness of using a submarine telecommunication cable to detect modern gravity flows; and 4) determine present day probability of new turbidity currents being generated along the eastern Sicilian margin. First results provide new information about the 1908 turbidity current behaviour. The main conduit for this gravity flow likely was the easternmost canyon-channel system of the western Ionian Basin, which extends from the Tyrrhenian Sea down to the accretionary wedge. High backscatter and the presence of numerous scours along its thalweg indicate recent sediment erosion and deposition. This canyon-channel system further extends to two of the three cable breaks recorded up to 18 hours after the earthquake on the Malta-Zante telecommunication cable. The presence of several sediment basins along this conduit indicates repeated sediment transport activity, while the numerous sediment failures that occur along the channel walls are interpreted as a result of flow undercutting. This canyon-channel system is connected to tributaries from both north-eastern Sicily and western Calabria, which are also characterised by high backscatter. In comparison, backscatter data from the eastern Sicilian margin south of Fiumefreddo Valley show that gravity flows are restricted to the tributary systems and do not travel long distances from the margin. The new results will be used to evaluate the role of the gravity flows for tsunamis. A potential impact of gravity flows on tsunami generation has been theorised by researchers studying submarine geohazards in the past, but needs yet to be tested. Addressing all objectives of MARGRAF has the potential to significantly improve the current understanding about submarine gravity flows.

How to cite: Schulten, I. and Micallef, A.: Modern and recent sediment gravity flows offshore eastern Sicily, western Ionian Basin – Preliminary results from the MARGRAF project , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8615, https://doi.org/10.5194/egusphere-egu22-8615, 2022.

08:50–08:55
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EGU22-7032
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ECS
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Virtual presentation
Felix Gross, Henriette Kolling, Rachel Barrett, Emma Hadré, Mirja Heinrich, Alessandro Bonforte, Salvatore Gambino, Florian Petersen, Lea Morgenweck, Peter Matzerath, Josephin Wolf, Sven Heinrich, Jannes Vollert, Marie Hundsdörfer, Christian Filbrandt, and Morelia Urlaub

Mt Etna, Europe’s largest active volcano, is located directly on the Sicilian coastline of the Ionian Sea. In addition to frequent Strombolian eruptions, Etna’s south-eastern flank is currently sliding seawards at a rate of several centimetres per year. Over the past decade, scientists from multiple countries have intensely studied the submerged sector of the volcano and its continental margin, with their results showing that the well-known onshore flank instability proceeds far into the sea and can be measured by marine geodetic networks. Nevertheless, the relationship between volcanic activity and deformation of the continental margin is still unclear, and various scenarios – from small-scale disintegration over geological time periods to abrupt catastrophic failure – have been suggested.

During RV Meteor’s expedition M178 (Nov – Dec 2021), we revisited the continental margin offshore Mt Etna and conducted dedicated repeated shallow- and deep-water multibeam surveys. In addition, several gravity cores were recovered from the prominent amphitheatre structure, intra-slope basins, and the proposed southern boundary of Mt Etna’s moving flank. We use the baseline bathymetric data, acquired during RV Meteor’s cruise M86/2 in 2011/2012, to investigate and image changes within the geomorphological and geological setting offshore Etna by comparing them with the new multibeam data. The repeated bathymetry shows minor changes compared to the baseline study, but favours the suggestion of sediment re-deposition in the proximal to distal sectors of the continental margin. Our preliminary results from the sediment record provide evidence for syn- and post sedimentary deformation, with clear indications of compressional and extensional periods at the crest of the prominent amphitheatre structure. Furthermore, sediment cores show that the southern boundary ridge, north of the Catania Canyon, hosts several heavily reworked and disintegrated sediment patches, which indicates active deformation within the intra-slope micro-basins at the crest of the ridge.

The results of this project will increase our understanding of how landslides nucleate in extremely active settings such as offshore Mt Etna. Furthermore, the findings will be used to better assess the hazard potential of the sliding flank of the giant volcano and will feed into numerical modelling of the various scenarios that have been postulated for Mt Etna.

How to cite: Gross, F., Kolling, H., Barrett, R., Hadré, E., Heinrich, M., Bonforte, A., Gambino, S., Petersen, F., Morgenweck, L., Matzerath, P., Wolf, J., Heinrich, S., Vollert, J., Hundsdörfer, M., Filbrandt, C., and Urlaub, M.: Repeated mapping and geological sampling of Mt Etna’s submerged continental margin: First results from RV Meteor expedition M178, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7032, https://doi.org/10.5194/egusphere-egu22-7032, 2022.

08:55–09:00
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EGU22-7858
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ECS
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On-site presentation
Martin Hasenhündl, Koen Blanckaert, Peter Talling, Ed Pope, Maarten Heijnen, Sean Ruffell, Megan Baker, Ricardo Silva Jacinto, Sophie Hage, Stephen Simmons, Catherina Heerema, Claire McGhee, Michael Clare, and Matthieu Cartigny

Submarine canyons and channels include the largest sediment transport systems on our planet. They are an important transport pathway for sediment, organic carbon, nutrients and pollutants to the deep sea. However, it is challenging to study these submarine locations, especially larger systems on the deep seafloor, and they remain poorly understood. Here we use the first extensive time-lapse bathymetric surveys of the Congo Submarine Fan (offshore West Africa), one of the largest submarine fans in the world. Channel-modifying processes (such as landslides, avulsions and knickpoints) are identified by comparing new high-resolution bathymetric data from 2019 to lower-resolution bathymetric data collected between 1992 and 1998, along a 475 km section of the Congo submarine system. These channel-modifying processes leave a specific fingerprint in morphometric characteristics (e.g., bed slope, width, cross-sectional flow area, sinuosity, levee slope and height) that are automatically extracted with a Matlab script from the bathymetric data. This work has the important implication that the identification of channel-modifying processes can be based on a single bathymetric survey, and does not require repeated surveys. In the upstream part of the Congo Canyon, a re-analysis of bathymetric data collected between 1992 and 1998 reveals a previously unnoticed channel-blocking landslide, which is of similar magnitude to a more recent landslide observed from the repeated surveys with a volume of ~0.4 km³. This observation of additional landslides supports the concept that the upstream canyon is morphologically defined by flank collapses, which can locally block the channel and store material for extended periods of time. In the intermediate channel part of the Congo Fan, avulsions already identified in previous work are demonstrated to leave a specific fingerprint within the morphometric characteristics such as a change in levee slope. In the most distal and youngest part of the Congo submarine channel, upstream migrating knickpoints are dominant and are shown to also leave a specific fingerprint in morphometric characteristics. These findings can underpin efficient searches for submarine canyon and channel processes in other systems, and provide new insights into how turbidity currents flush sediment into the deep-sea.

How to cite: Hasenhündl, M., Blanckaert, K., Talling, P., Pope, E., Heijnen, M., Ruffell, S., Baker, M., Silva Jacinto, R., Hage, S., Simmons, S., Heerema, C., McGhee, C., Clare, M., and Cartigny, M.: Morphometric fingerprinting of submarine canyon and channel processes revealed by time-lapse bathymetric surveys from the Congo Fan, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7858, https://doi.org/10.5194/egusphere-egu22-7858, 2022.

09:00–09:05
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EGU22-6200
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On-site presentation
Fabiano Gamberi, Elena Scacchia, and Giacomo Dalla Valle

In the submarine environment, plunge or impact pools are depressions, which form through perturbations in the behaviour of submarine gravity-flows, at places of abrupt gradient reductions. In this paper, we examine a large number of plunge pools in the Tyrrhenian Sea, a back-arc basin characterized by large, complex slope sectors often with alternating higher- and lower-gradient areas.  In the present analysis, we target the morphologic parameters, the physiographic setting and the upslope and downslope surroundings of the slope breaks and the associated plunge pools. Canyon-mouth plunge pools are located where turbidity currents, originally confined within steep canyons, experience an abrupt slope reduction and a loss of confinement. This setting, occurring at the base of both the continental slope and intra-slope steps, results in enhanced erosion and in relatively large and deep plunge pools with long-axis perpendicular to the slope. Lateral bulges, which fade gradually away, laterally and downslope, flank some of the plunge pools. They resemble levees and are thus an indication of depositional processes associated with the spill-over of the highest portion of flows. These constructional features are not present in the frontal part of the plunge pools, which rather connects downslope to channels. In other cases, canyon-mouth plunge pools connect downslope to relatively large radial bulges suggesting deposition in fan bodies from rapid flow deceleration; concentric bedforms show that flow instabilities formed in the plunge pool area propagate in large part of the fan bodies. In some cases, the central deeper part of the plunge pools connects laterally to erosional moats parallel to the inbound slope, showing that flows spreading laterally away from the canyon-mouth have increased erosional power along the tectonic structure. Gully-mouth and slope-embayment plunge pools are mainly sub-circular and often surrounded by a rampart, evidence of rapid deposition at the border of the structure. Open-slope-plunge pool form at the base of featureless slope sectors and are likely due to mostly unconfined currents flowing down the slope of seamounts. Fault-controlled plunge pools occur in grabens, where unconfined flows cross an escarpment formed by a transverse fault. They form at the base of the structure as continuous depressions parallel to the structure or as an array of isolated, laterally discontinuous, circular structures. Landslide-plunge pool are located downslope from slope sectors characterized by extensive landslide scars; we interpret them as resulting from turbidity currents formed by the transformation of repeated landslides. Our analysis details the wide range of seafloor topography and turbidity current character that are conducive to plunge pool formation. It shows that plunge pools display large morphologic variability and a multiplicity of genesis, thus widening our process understanding of slope-break settings. Furthermore, our analysis show that plunge pools and their impact on sedimentary processes further downslope are important elements to be considered in environmental and facies models of topographically complex slopes. As such, it can contribute to submarine geo-hazard evaluations and to hydrocarbon reservoir assessment in areas characterized by slope breaks.

How to cite: Gamberi, F., Scacchia, E., and Dalla Valle, G.: Slope breaks and turbidity currents interaction: process understanding from plunge pool analysis in the Tyrrhenian Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6200, https://doi.org/10.5194/egusphere-egu22-6200, 2022.

09:05–09:10
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EGU22-4343
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ECS
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On-site presentation
Thore Sager, Morelia Urlaub, Jacob Geersen, and Christian Berndt

Submarine landslides can cause devastating tsunamis and inundate surrounding coastal areas or directly compromise offshore infrastructure. A landslides’ ability to generate a tsunami is expressed as the tsunamigenic potential controlled, amongst other parameters, by the amount of landslide material mobilized during failure. The Ana Slide, located in the Eivissa Channel on the Balearic Promontory, western Mediterranean Sea, developed as a frontally confined landslide. This means that the mobilized mass is frontally buttressed against unaffected strata. Unique to the Ana Slide is that it is completely covered by high-resolution 2D, 3D reflection seismic and bathymetric data. Steady hemipelagic sedimentation prevailed in the study area way before the occurrence of the Ana Slide. Strata outside the perimeter of the Ana Slide shows predictable thicknesses that can be interpolated from outside to inside the landslide.

Within this study, we reconstruct the pre-failure seafloor morphology of the Ana Slide. We use a published GIS-tool for the source area and facilitate predictive sedimentary thicknesses as an interpretational basis for the sink area. These methods allow the actual volume of mobilized landslide material from the evacuational source into the accumulational sink area to be determined. In addition, we can calculate the ratio between actually mobilized landslide and affected material that was not directly involved in the landslide motion. Results of the volume balance calculation expose that the Ana Slide represents a “closed system” landslide because all evacuated landslide material from the source area has completely accumulated within the sink area with an uncertainty of < 5%.

Based on a detailed kinematic analysis previously performed for the Ana Slide, we show that the volume of actually mobilized landslide material is significantly smaller than that of the affected material that was not directly involved in the landslide motion. We show that mobilized landslide material can affect strata to significant depths beneath the deposit, while being relatively thin itself. This could potentially lead to erroneous or excessive landslide volume estimations. Our findings may therefore be critical for tsunamigenic potential assessment and geological hazard predictions.

How to cite: Sager, T., Urlaub, M., Geersen, J., and Berndt, C.: Volume balance of frontally confined submarine landslides - a case study of the Ana Slide, Eivissa Channel, western Mediterranean Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4343, https://doi.org/10.5194/egusphere-egu22-4343, 2022.

09:10–09:15
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EGU22-5341
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Virtual presentation
Elia d'Acremont, Sara Lafuerza, Alain Rabaute, Manfred Lafosse, Martin Jollivet Castelot, Christian Gorini, Belen Alonso, Gemma Ercilla, Juan Tomas Vazquez, Thomas Vandorpe, Carmen Juan, Sébastien Migeon, Silvia Ceramicola, Nieves Lopez-Gonzalez, Mathieu Rodriguez, Bouchta El Moumni, Oumnia Benmarha, and Abdellah Ammar

In the South Alboran Sea, the moderate seismicity (Mw=6.4) of the strike-slip Al Idrissi Fault Zone does not appear to control directly the landslides distribution. To provide a preliminary geohazard assessment, we characterized the spatial distribution, the volume and the ages of the submarine landslides from multibeam and seismic reflection data in the southern part of the Alboran Sea. Since the Quaternary numerous submarine landslide processes affect the marine sedimentary cover with volumes of the mass transport deposits (MTD) estimated between 0.01 to 15 km3.

West of the Al Idrissi Fault Zone, along the South Alboran Ridge’s northern flank, the distribution of the MTD follows the SW-NE bank and ridge trend that correlates with blind thrusts and folds covered by a plastered contourite drift. A pockmark field, related to fluid escape, is visible near landslide scars where the contourite drift is relatively thicker. In this area, landslide scars occur on variable slopes (2-24°) and their associated MTD have variable decompacted volumes (0.01-10km3). East of the Al Idrissi Fault Zone, between the Alboran Ridge and the Pytheas Bank, the mapped MTDs have uneven volumes. The smaller ones (<1 km3) have their slide scars on steep slopes (>10°), whereas those of the largest ones (3-15 km3) occur on gentler slopes (<5°).

These observations and a slope stability analysis suggest that the combination of seismic shaking, blind thrusts activity, relatively high sedimentation of contourite deposits, and fluid escape dynamics are likely the main controlling mechanisms rather than seismic shaking only. These causal factors would explain the concentration of landslide head scarps at the edge of the thickest parts of the contourite drifts (i.e. crests) may have been controlled locally by fluid overpressures in line with blind thrusts. Additionally, low to moderate seismicity potentially triggered by nearby faults might regionally have played a role in destabilising the seafloor sediments since 1.12 Ma, which coincides with the propagation of the Al Idrissi Fault Zone in the southern Alboran Sea. 

How to cite: d'Acremont, E., Lafuerza, S., Rabaute, A., Lafosse, M., Jollivet Castelot, M., Gorini, C., Alonso, B., Ercilla, G., Vazquez, J. T., Vandorpe, T., Juan, C., Migeon, S., Ceramicola, S., Lopez-Gonzalez, N., Rodriguez, M., El Moumni, B., Benmarha, O., and Ammar, A.: Distribution and origin of submarine landslides in the active margin of the southern Alboran Sea (Western Mediterranean Sea), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5341, https://doi.org/10.5194/egusphere-egu22-5341, 2022.

09:15–09:20
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EGU22-6547
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Virtual presentation
Sara Lafuerza, Elia d'Acremont, Alain Rabaute, Christian Gorini, Sylvie Leroy, Belen Alonso, Pascal Le Roy, Jaime Frigola, Marcelo Ketzer, Daniel Praeg, and Nieves Lopez-Gonzalez and the ALBACORE Scientific Party

The Alboran Sea (Western Mediterranean) is a relatively small ocean basin connected with the Atlantic that provides a rich archive of tectonic and sedimentary processes at distinct temporal and spatial scales during the Quaternary. Since the collisional boundary of the Eurasia-Nubia plates crosses the Alboran Sea, this basin is also the locus of active geohazards: the constant seismic activity, concentrated mostly along the Al Idrissi strike-slip fault system and submarine landslides, that can cause tsunami hazards affecting the entire Alboran coasts and damages to submarine cables and infrastructures. Previous understanding of the Alboran Sea has been based on seafloor and subsurface geophysical data of differing resolution and scale, combined with very short sediment coring and IODP and industrial boreholes. In order to obtain new constrains on the geology of the Alboran Sea, the ALBACORE cruise was held in October and November 2021 onboard the R/V Pourquoi Pas? In addition to sites in the northern Alboran Sea targeting contourites, several sites in the southern Alboran Sea were selected as key study areas: the Al-Idrissi active fault zone, the Al-Hoceima shelf, the Xauen/Tofiño and the Francesc Pages banks.

The scientific work of the ALBACORE campaign included the acquisition of Calypso cores (up to 28m long), sampling of consolidated strata with Cnexoville, in situ geotechnical measurements (Penfeld) with a seabed cone penetration test device (up to 50m long), heat flow measurements (up to 6m long), swath bathymetric imaging of the seafloor and water column, and sub-bottom profiling. The total length of sediments recovered reached 734m. Results from the ALBACORE cruise address the following scientific objectives:

  • To understand better the causal relationships between the present-day morpho-structural pattern and date Quaternary tectonic pulse and associated sedimentary systems
  • To determine the Late Pleistocene-Holocene stratigraphic pattern and the paleo-oceanographic implications of contourites.
  • To explore the chronological evolution of cold-water coral mounds and their paleoceanographic and palaeoclimatic signature since the Middle Pleistocene.
  • To investigate the causal factors of slope instability processes and evaluate the geological hazard associated with tectonic pulses and fluid seepage.
  • To determine the recent high-resolution sequence stratigraphy of the Al-Hoceima shelf in order to decode the late Pleistocene and Holocene sea-level changes at millennial scale.

How to cite: Lafuerza, S., d'Acremont, E., Rabaute, A., Gorini, C., Leroy, S., Alonso, B., Le Roy, P., Frigola, J., Ketzer, M., Praeg, D., and Lopez-Gonzalez, N. and the ALBACORE Scientific Party: The ALBACORE oceanographic cruise: tectonic and sedimentary processes at distinct temporal and spatial scales in the Alboran Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6547, https://doi.org/10.5194/egusphere-egu22-6547, 2022.

09:20–09:25
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EGU22-4797
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ECS
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Highlight
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On-site presentation
Guillaume Michel, Mark Coughlan, Andy Emery, Riccardo Arosio, and Andrew Wheeler

To understand the advance and retreat of the British and Irish Ice Sheet (BIIS), geomorphic features have been extensively characterised onshore. The extent of these features in the Irish Sea has been poorly constrained, even though the Irish Sea Ice Stream (ISIS) was the largest drainage system of the BIIS and had a strong impact in shaping the present-day seafloor. Previous studies have highlighted the occurrence of till surfaces, glacio-marine and transitional stratigraphic units to marine environments. Constraining the extension of these units and characterising the associated geomorphic features is important to any attempt to reconstruct the history of the BIIS evolution since the Last Glacial Maximum.

This study presents new information produced by interrogating large geophysical datasets of sub-bottom profiler, single-channel Sparker, and multibeam echosounder bathymetry in the North-Western Irish Sea, from Dundalk Bay to Lambay Deep. These data spatially map the complex sub-surface stratigraphy, comprising different glacial and post-glacial units and the geomorphic features they form, including grounding-zone wedges, channels, and iceberg scouring. Initial interpretation of these features has been performed with regard to established stratigraphic frameworks and regional glacial and postglacial geodynamic models. This presentation will focus on the results of the geomorphic feature interpretation, with the aim of constraining the ISIS advance and retreat in the North-western Irish Sea, filling a critical gap in our understanding of the demise of the BIIS.

How to cite: Michel, G., Coughlan, M., Emery, A., Arosio, R., and Wheeler, A.: Buried geomorphic features in the North-western Irish Sea: markers of the last glaciation and deglaciation episodes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4797, https://doi.org/10.5194/egusphere-egu22-4797, 2022.

09:25–09:30
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EGU22-6947
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Highlight
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Virtual presentation
Jacob Geersen, Elena Pesenti, Michael Riedel, Jens Schneider von Deimling, Luisa Rollwage, Noemi Schulze, and Martin Scherwath

Pockmarks are crater-like depressions of erosive nature in marine or lacustrine sediments. They are often interpreted as the surface manifestation of hydrocarbon venting but may also result from freshwater flow in coastal regions, compaction induced sediment dewatering, or bottom scouring around natural or anthropogenic objects. Hence, they can be of relevance for the global carbon cycle, offshore infrastructure, benthic life, and slope stability. New bathymetric data from offshore Vancouver Island, Canada, indicate the presence of a huge pockmark field that had escaped attention in previous studies. The pockmarks are located between 100 and 200 mt depth around the head of Barkley Canyon. Owing to the presence of a large cabled underwater observatory related to the canyon, a wealth of multi-resolution and multi-disciplinary seafloor data is available from the pockmark field. Available data include multibeam surveys, seafloor video footage, seismic and EK60 echo-sounder profiles, and multibeam water-column information. First results from seafloor mapping indicate that the pockmark field consists of several thousands of pockmarks. By applying workflows that automatically map the pockmarks in digital elevation models, we are able to quantitatively investigate their morphology and spatial distribution. The pockmarks range in size between 100 - 500 m², with some exceptions as large as 900 m². Their mean depth varies between 0.5 - 2 m. Seepage of gas from the seafloor is well known from the area but could not yet been directly associated with the pockmark depressions. Instead, limited video footage from the seafloor indicate that at least some depressions host meter-sized boulders within their craters. We will next investigate possible temporal changes in pockmark morphology and seep activity by individual analysis of datasets that have been repeatedly collected between 2010-2020. By resolving pockmark morphologies and seep activities on an annual time-scale over a decade, the results will hopefully add a level of detail to our understanding of pockmark formation and seep activity within one of North Americas largest pockmark fields.

How to cite: Geersen, J., Pesenti, E., Riedel, M., Schneider von Deimling, J., Rollwage, L., Schulze, N., and Scherwath, M.: Seafloor pockmarks offshore Vancouver Island, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6947, https://doi.org/10.5194/egusphere-egu22-6947, 2022.

09:30–09:35
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EGU22-4003
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ECS
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On-site presentation
Quang Nguyen, Michal Malinowski, Regina Kramarska, Dorota Kaulbarsz, and Christian Huebscher

Presence of methane in the shallow sediments of the southern Baltic Sea area is a well-known phenomenon. In the Polish Exclusive Economic Zone (Polish EEZ), the observations were mostly based on hydroacoustic data, as well as sediment and water sampling. However, majority of the occurrences were reported in the eastern part of the EEZ (e.g., Gulf of Gdansk). Here we focus on the western part of the Polish EEZ (Pomeranian Bight) and combination of both hydroacoustic and seismic data to provide evidences of free gas in the shallow sediments.

Our study area is located in the inverted part of the Permo-Mesozoic Polish Basin, so called Mid-Polish Swell, with the main inversion-related fault zones: Adler-Kamień and Trzebiatów faults, rooted in the pre-Permian basement (Devonian, Carboniferous?).  Both the Permian and Paleozoic rocks are a proven hydrocarbon exploration play, with an ongoing exploration at the structural trend extending further onshore towards SE. We use seismic data acquired during the RV Maria S. Merian cruise in 2016 (cruise MSM52) with the co-located sub-bottom sediment profiler (Parasound) data.

Various signatures of shallow gas were identified across the seismic section including gas chimneys, shallow bright spots, seafloor polarity reversal and acoustic blanking. Seismic attributes were used to highlight and support interpretation of shallow gas anomalies. Anomalous zones in seismic data were observed in both the Cretaceous, Jurassic and Triassic section in the vicinity of the Adler-Kamień and Trzebiatów fault zones. Parasound data illustrated corresponding free gas accumulation in Pleistocene to Quaternary successions. Amplitude versus offset (AVO) analysis was carried out at two locations of the assumed gas chimney. The gradient analysis from angle gathers shows clearly amplitude variations with increasing offset due to existence of gas in the formation, in addition, free gas amplitude anomalies were highlight in the intercept vs gradient crossplot.

Our data indicate existence of potential fluid migration pathways from the Permian-Paleozoic reservoirs to shallow sediments below the seabed and helps in explanation of how this free gas escapes to the sea bottom.

This study was funded by the Polish National Science Centre grant no UMO-2017/27/B/ST10/02316. Cruise MSM52 has been funded by German Science Foundation DFG and Federal Ministry of Education and Research (BMBF). We thank Federal Institute for Geosciences and Natural Resources (BGR) for their support during seismic data acquisition and sharing the data.

How to cite: Nguyen, Q., Malinowski, M., Kramarska, R., Kaulbarsz, D., and Huebscher, C.: Linking shallow gas occurrences and deeper structure offshore western Poland (Pomeranian Bight), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4003, https://doi.org/10.5194/egusphere-egu22-4003, 2022.

09:35–09:40
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EGU22-8576
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ECS
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On-site presentation
Shauna Creane, Mark Coughlan, Michael O'Shea, and Jimmy Murphy

With the recent push for a transition towards a climate resilient economy, the demand on marine resources is accelerating. For many economic exploits, a comprehensive understanding of environmental parameters underpinning seabed morphodynamics in tidally-dominated shelf seas, and the relationship between local and regional scale sediment transport regimes as an entire system, is imperative. In this paper, high-resolution, time-lapse bathymetry datasets, hydrodynamic numerical modelling outputs and various theoretical parameters are used to describe the morphological characteristics of sediment waves and their spatio-temporal evolution in a hydrodynamic and morphodynamic complex region of the Irish Sea. Analysis reveals sediment waves in a range of sizes (height = 0.1 to 25.7 m, and wavelength  = 17 to 983 m), occurring in water depths of 8.2 to 83 mLAT, and migrating at a rate of 1.1 to 79 m/yr. Combined with numerical modelling outputs, a strong divergence of sediment transport pathways from the previously understood predominantly southward flow in the south Irish Sea is revealed, both at offshore sand banks and independent sediment wave assemblages. This evidence supports the presence of a semi-closed circulatory hydrodynamic and sediment transport system at Arklow Bank (an open-shelf linear sand bank). Contrastingly, the Lucifer-Blackwater bank complex and associated sediment waves are heavily influenced by the interaction between a dominant southward flow and a residual headland eddy, of which also exerts a strong influence on the adjacent banner bank. Furthermore, a new source and sink mechanism are defined for offshore independent sediment wave assemblages, whereby each sediment wave field is supported by circulatory residual current cells originating from offshore sand banks. This new data and results improve knowledge of seabed morphodynamics in tidally-dominated shelf seas which has direct implications for offshore renewable developments and long-term marine spatial planning.

How to cite: Creane, S., Coughlan, M., O'Shea, M., and Murphy, J.: Development and dynamics of sediment waves in a complex morphological and tidal dominant system: southern Irish Sea, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8576, https://doi.org/10.5194/egusphere-egu22-8576, 2022.

09:40–09:45
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EGU22-9864
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Presentation form not yet defined
Paraskevi Nomikou, Dimitris Evangelidis, Dimitrios Papanikolaou, Danai Lampridou, Dimitris Litsas, Yannis Tsaparas, Ilias Koliopanos, and Maria Petroulia

Morphotectonic analysis of the offshore margins of the Aegean Islands in combination with onshore structures offers a rather complete image of the ongoing deformation within the Aegean micro-plate and especially along its eastern border zone with the Anatolian micro-plate. The swath data, off Lesvos and Samos islands, have been acquired by the hull-mounted RESON SeaBat 7160 on the oceanographic vessel NAFTILOS of the Hellenic Navy Hydrographic Service and gridded at 15m spatial resolution. Active tectonics affect both areas, as recorded by the intense seismic activity along with pronounced erosional and mass wasting processes.

The southern margin of Lesvos Island is divided into three sub-basins. The main feature is the central elongated sub-basin extending nearly parallel to the coast, reaching 700m water depth. Its northern margin is bounded by an abrupt WNW-ESE normal fault with morphological slopes up to 41o, whereas its southern one is smoother with 5o of slope and the overall structure corresponds to a half-graben. At its eastern edge, the basin is interrupted by a narrow steep channel, trending NW-SE, and progressively becomes shallower. At the western part of the Lesvos margin, a shallow basin forms an assymetric tectonic graben. Along the northwestern margin, three E-W basins lying approximately at 300-400 m water depth, constitute pull-apart basins within the complex ENE-WSW shear zone of the southern strand of the North Anatolian Fault, bounded by the sub-parallel Skyros and Adramytion Faults. Seismic activity in 2017 comprised a 6.3 magnitude earthquake on the WSW-ESE normal fault of the Lesvos Basin and two major aftershocks of magnitude 5.2 and 5.0 at the NW-SE strike-slip faults of the channel. During 2020 and 2021 normal WNW-ESE faulting with magnitude 5.1 and ENE-WSW dextral strike-slip faulting with magnitudes 4.8, and 5.0 occurred at the western and northwestern basins. However, a magnitude 7.0 earthquake had occurred onshore at the NE-SW  Kalloni-Aghia Paraskevi strike-slip fault in 1867.

The northern margin of Samos Island is bounded by a normal north dipping E-W fault that generated the strong earthquake of magnitude 7.0 on 30October 2020.The Samos Basin forms a half-graben of 690m water depth with morphological slopes of 31o along the fault zone. Several canyons trending N-S, carve the northern margin ending up between 100m and 600m water depth, and several mass wasting events can be identified alongside the Samos coastline. Westwards, the Ikaria Basin is significantly deeper, reaching 1100m water depth and is delineated by an abrupt zone of nearly 51⁰ slope values, corresponding to the NE-SW Samos active western margin, probably related to strike-slip faulting. Additionally, an impressive retrogressive erosional structure occupies the area between Samos and Ikaria islands, with two prominent meandering narrow canyons debouching at the Ikaria Basin.

The combination of E-W to WNW-ESE normal faulting and NE-SW to ENE-WSW dextral strike-slip faulting with minor NW-SE sinistral strike-slip faulting is observed all over the North Aegean Sea, acommodating the southwestward motion of the Aegean micro-plate, relative to the Eurasian plate in the north and the Anatolian micro-plate in the East.

 

How to cite: Nomikou, P., Evangelidis, D., Papanikolaou, D., Lampridou, D., Litsas, D., Tsaparas, Y., Koliopanos, I., and Petroulia, M.: Co-existence of active E-W normal faulting and NE-SW strike-slip faulting in the Eastern Aegean Islands; evidence from offshore studies in Lesvos and Samos, Greece., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9864, https://doi.org/10.5194/egusphere-egu22-9864, 2022.

09:45–09:50
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EGU22-12531
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ECS
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On-site presentation
Andrea Giulia Varzi, Luca Fallati, Alessandra Savini, Valentina Bracchi, Pietro Bazzicalupo, Antonietta Rosso, Rossana Sanfilippo, and Daniela Basso

Coralligenous Bioconstructions (CB) include calcareous build-ups of biogenic origin that typify selected regions of the Mediterranean continental shelves, where they formed since the Holocene transgression. They can be from few to tens of meters large, displaying variable lateral continuity and thickness. Offshore Marzamemi (south-eastern Sicily, Ionian Sea) the occurrence of peculiar columnar-shaped CB have been documented in 2002, but their actual extension and distribution across the shelf was not known until recent time. The project “CresciBluReef: New technologies for knowledge and conservation of Mediterranean reefs” produced a new 17 km2 high-resolution bathymetric map using a R2Sonic2022 MBES, ground-truthed by ROV observations, that generated a good knowledge of the extension of CB in the region. The bioconstructions are preferentially distributed along selected depth ranges (from 30 to 40 m, and from 85 and 95 m of w.d.), with a good lateral continuity. The coupling of documented uplift rate (ca. 0.2 mm/yr since the Tyrrhenian time) and evidences reported in literature for Holocene relative sea-level curves, shows a good correlation between the distribution of CB and local and short stasis associated to the rapid Flandrian transgression. However, as revealed by the geomorphological map obtained by our study, a more in-depth investigation is needed to understand (1) the role of the inherited continental shelf landscape, shaped by previous low-stand periods, in creating favourable substrate for the settlement and growth of CB during the Holocene, and (2) the extent to which CB can in turn affect the evolution of present-day continental shelf landforms and landscapes.

How to cite: Varzi, A. G., Fallati, L., Savini, A., Bracchi, V., Bazzicalupo, P., Rosso, A., Sanfilippo, R., and Basso, D.: GEOMORPHOLOGICAL MAPPING OF CORALLIGENOUS BIOCONSTRUCTIONS OFFSHORE SOUTH-EASTERN SICILY (Italy, Mediterranean Sea), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12531, https://doi.org/10.5194/egusphere-egu22-12531, 2022.

09:50–09:55
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EGU22-7461
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ECS
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On-site presentation
Audrey Recouvreur, Andrew Wheeler, Ruaihri Strachan, Patrick Meere, Richard Unitt, and Aaron Lim

The Irish continental margin hosts many complex sedimentary basins, and diverse geomorphological domains displaying bedrock outcrops that can host a large variety of habitats from shallow to cryptic fauna. More recent surveying in the Irish offshore territory has indicated extensive areas of bedrock exposure. The BeTar_Drill2 (Bedrock Target analysis for ROV RockDrill sampling) project applies novel bedrock suitability mapping to the full Irish continental margin (ICM); to determine potential habitat areas from shallow to deep domains for the entire ICM; to ground truth this mapping with petrographic analysis of physical samples correlated to existing seismic data. The project’s overall aim is to improve the appraisal of the regional geology and habitat mapping of the Irish margin. 

This study has improved the Bedrock Suitability Index (BSI) previously developed for the Porcupine Bank Canyon by fine tuning the variables to the wider margin. The improved BSI model has been constructed across the southern Irish continental margin, covering more than 140,000 km2, producing a high resolution (25m2) model of predictive bedrock outcrop locations. Validation by video observations and correlations of predicted bedrock exposures has established an appropriate level of confidence with BSI accuracy. The BSI mapping reveals a strong structural control on bedrock outcrop occurrence, with BSI correlating with deep structural fabrics of the margin as expressed by fault lines. 

How to cite: Recouvreur, A., Wheeler, A., Strachan, R., Meere, P., Unitt, R., and Lim, A.: Probability mapping for bedrock occurrence on the Irish Continental Margin: Applications for regional bedrock outcrop and habitat mapping , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7461, https://doi.org/10.5194/egusphere-egu22-7461, 2022.

09:55–10:00
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EGU22-11828
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ECS
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On-site presentation
Michele Montuschi, Matteo Alberi, Daniele Attala, Enrico Chiarelli, Andrea Maino, Kassandra Cristina Giulia Raptis, Stefano Sandroni, Enrico Sassi, Filippo Semenza, Virginia Strati, and Fabio Mantovani

The accurate knowledge of seabed properties is in increasing demand for telecommunication companies, national governments, military forces, academic institutions and oil and gas corporations. Recently the quality of bathymetry and seafloor mapping extraordinarily improved thanks to the employment of Autonomous Underwater Vehicles, which mount on board multiparametric instruments such as high resolution multibeam echo sounders, synthetic aperture sonars, sub bottom profilers, magnetometers, camera laser profilers and environmental sensors.

The fruition of this huge amount of high-resolution information is often limited to advanced experts on GIS software which requires a long and steep learning curve in addition to a properly equipped workstation. With the increasing interest in bathymetry and oceanography from the larger community, the challenge is definitively to improve the visualization and the online handling for users with little familiarity on sophisticated applications.

For this purpose, we developed a Plotly Dash (an open-source Python library) web-based GIS application for real time rendering of 3D high-resolution bathymetric data. An easy-to-interpret and easy-to-manage visualization is obtained through the creation of an interactive 2D map with Mapbox (a provider of custom online maps) for positioning in the world and for selecting bathymetric data. The user can also easily set different visualization parameters such as depth color scales and the stage lighting and shadowing to enhance the seabed details.

For an optimized usability on mobile devices, the web application loads the 3D model obtained from a raster flexible interpolation. The rendering speed is further boosted by automatically varying the 3D mesh resolution in accordance with the extension of the selected region.

Starting from an ASCII file containing depth and coordinates data together with their map projection system, our innovative tool automatically organizes the data into a raster file with the WGS84 spatial reference system. Data collected from different surveys can therefore be effortlessly processed, managed, and visualized.

How to cite: Montuschi, M., Alberi, M., Attala, D., Chiarelli, E., Maino, A., Raptis, K. C. G., Sandroni, S., Sassi, E., Semenza, F., Strati, V., and Mantovani, F.: A Web GIS tool for 3D visualization of bathymetric data, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11828, https://doi.org/10.5194/egusphere-egu22-11828, 2022.