GM6.3 | Submarine Geomorphology and offshore Geohazards

GM6.3

EDI
Submarine Geomorphology and offshore Geohazards
Co-organized by OS4/SSP1, co-sponsored by IAG
Convener: Sebastian Krastel | Co-conveners: Lara F. Pérez, Derek Sawyer, Rachel BarrettECSECS, Marta Ribo GeneECSECS, Luca FallatiECSECS, Jacob Geersen
Orals
| Wed, 26 Apr, 14:00–18:00 (CEST)
 
Room D3
Posters on site
| Attendance Wed, 26 Apr, 10:45–12:30 (CEST)
 
Hall X3
Orals |
Wed, 14:00
Wed, 10:45
The ocean floor hosts a tremendous variety of landforms that reflect the action of a range of tectonic, sedimentary, oceanographic and biological processes at multiple spatio-temporal scales. Many such processes present hazards to coastal populations and offshore installations, and their understanding constitutes a key objective of national and international research programmes and IODP expeditions. Recent advances in geophysical imaging, scientific ocean drilling, and seafloor instrumentation have increased the understanding of offshore geohazards; however, significant knowledge gaps remain in understanding the timing and interplay of geological processes at the origin of geohazards. 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, as well as to extend quantitative geomorphology offshore and to integrate it into hazard analysis. 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, as well as to promote cooperation between different parties (academic, industrial, and governmental) involved in geohazard research and management. 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 abyssal plains), as well as from lakes. Datasets of any scale, from satellite-predicted depth to ultra-high-resolution swath bathymetry, sub-surface imaging and sampling, are anticipated.

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

Orals: Wed, 26 Apr | Room D3

Chairpersons: Marta Ribo Gene, Jacob Geersen, Luca Fallati
14:00–14:05
Submarine Geomorphology I
14:05–14:15
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EGU23-10006
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GM6.3
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Virtual presentation
Rachel Nanson, Riccardo Arosio, Joana Gafeira, Mardi McNeil, Dayton Dove, Bjarnadóttir Lilja, Dolan Margaret, Guinan Janine, Alix Post, John Webb, and Scott Nichol

Maps of seabed geomorphology provide foundational information for a broad range of marine applications. To be most effective, geomorphic characterisation of the seabed requires standardised, multi-scalar and interjurisdictional approaches that can be applied locally, regionally and internationally using the best available data. An ongoing collaboration between geoscience agencies in the United Kingdom (BGS), Norway (GSN), Ireland (GSI; UCC) and Australia (GA; LU) has focused on developing a new standardised approach to meet this need. Dove et al (2016) first described a two-part approach for mapping the geomorphology of the seabed. Part 1 was subsequently published as an open access glossary that includes an illustrated list of terms and definitions that primarily draw on the International Hydrographic Organization standard (Dove et al, 2020). Morphology maps are created by applying Part 1 Morphological terms to bathymetry data. Part 2 classifies these mapped  shapes with their geomorphic interpretation; geomorphic unit terms are structured within 11 geomorphic Settings (Fluvial, Coastal, Marine, Glacial, Hard Rock) and Process (Current-induced, Biogenic, Mass movement, Fluid Flow, Karstic, Anthropogenic) categories. Consistent with Part 1, Part 2 terms are primarily sourced from established literature. The application of Part 2 requires further seabed data and/or contextual information and expert judgement, and is intended to constrain the uncertainty that is inherent to subsurface facies interpretation and prediction to this step. A draft version of Part 2 was the focus of a well-attended (>50 participants) workshop at the IAG’s International Seafloor Geomorphology Conference in Malta (July 2022: Nanson et al., 2022). Feedback from that workshop and from the broader community was integrated into a revised version of the report, which will be released early in 2023.  We will demonstrate the application of this method to several worked examples from coasts, continental shelves and the deep marine, and thereby demonstrate the utility of the two-part approach for mapping the distribution of sedimentary facies that form in these diverse marine environments.  

Dove, D., Bradwell, T., Carter, G., Cotterill, C., Gafeira Goncalves, J., Green, S., Krabbendam, M., Mellett, C., Stevenson, A., Stewart, H., 2016. Seabed geomorphology: a two-part classification system. 

Dove, D., Nanson, R., Bjarnadóttir, L.R., Guinan, J., Gafeira, J., Post, A., Dolan, M.F.J., Stewart, H., Arosio, R. and Scott, G., 2020. A two-part seabed geomorphology classification scheme:(v. 2). Part 1: morphology features glossary. https://zenodo.org/record/4071940#.Y7tURodBxPY 

Nanson, R., Arosio, R., Gafeira, J., Dove, D., Guinan, J., McNeil, M., Bjarnadóttir, L., Dolan, M., Post, A., Nichol, S., 2022. A two-part seabed geomorphology classification scheme: Part 2 Geomorphology - Version 0.9.

How to cite: Nanson, R., Arosio, R., Gafeira, J., McNeil, M., Dove, D., Lilja, B., Margaret, D., Janine, G., Post, A., Webb, J., and Nichol, S.: A two-part seabed geomorphology classification scheme: Part 2 – a geomorphic classification framework and glossary, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10006, https://doi.org/10.5194/egusphere-egu23-10006, 2023.

14:15–14:25
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EGU23-16716
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GM6.3
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ECS
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On-site presentation
Bartosz Kurjanski, Simona Caruso, Claire McGhee, Brice Rea, and Matteo Spagnolo

Sediment mobility is one of the key issues considered  during the design and construction process off offshore infrastructure ( Wind farms, cables, pipelines etc.).  Early understanding of the seabed mobility can significantly affect the project timelines, cost and, if not mitigated, can reduce the lifespan of already existing assets.  The most common approach to evaluate sediment mobility relies on repeated bathymetric surveys which aim to unravel the rate of change of the seabed over time. However, repeated surveys to be effective require to be performed over timelines allowing for confident detection of change above the uncertainty threshold and need to consider seasonal conditions within the area of interest. This time separation typically needs to be greater (several years)  the bigger the mobile bedforms across the area.  This means that it is unlikely that a result of a repeated bathymetric survey will be available early in the project life. Here, a public domain repeated bathymetric survey data from a deglaciated continental shelf area offshore N-E Scotland with moderate-to high-resolution(2-8m) data will be used to (1) identify mobile and immobile paleo bedforms, (2)quantify the rate of change of the seabed and (3) investigate the effect on different data resolution on the seabed mobility quantification.

How to cite: Kurjanski, B., Caruso, S., McGhee, C., Rea, B., and Spagnolo, M.: Effect of bathymetric data resolution on the understanding of sediment mobility: implications for offshore infrastructure projects on deglaciated continental shelves, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16716, https://doi.org/10.5194/egusphere-egu23-16716, 2023.

14:25–14:35
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EGU23-15935
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GM6.3
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On-site presentation
Daniela Accettella, Mihai Burca, Marco Cuffaro, Paolo Diviacco, Luca Gasperini, Emanuele Lodolo, Filippo Muccini, Alessandra Savini, and Andrea Giulia Varzi

Transits during oceanographic expeditions constitute a potential huge amount of acquired bathymetric data that could be systematically integrated to increase the knowledge on submarine morphology, especially for planned surveys in the equatorial Atlantic, the Arctic, the Indian and the Southern Oceans. The recent PNRA ISOBatA project aims to efficiently exploit seafloor datasets collected during transfer times within the Antarctic region and the Ross Sea. Along the route from New Zealand to the Italian Mario Zucchelli Station in the Ross Sea, the Emerald Fracture Zone and the Macquarie Triple Junction, located in the SW Pacific Ocean, represent two selected areas to test the strength of transit acquisition in remote areas, normally affected by adverse weather conditions.

 

The ISOBatA project has the main purpose to contribute to the mapping of Antarctic waters developing best practices and dedicated workflows to implement QA in multibeam data acquisition procedures during transit times, as well as in the processing, analysis and archiving of data and metadata.

The ISOBatA experience in the Southern Ocean suggests there are several critical issues associated with collection of multibeam data in remote and ice-infested waters. Operating procedures need more standardization, to avoid the acquisition of redundant data along common routes and unreliable data.

Our work aims to open a discussion to address the need for standardization in data acquisition during transit times, which should include priority in accordance with the geomorphological/geographical nature of the working areas. The integration of bathymetric data acquired during research vessel transfers to remote regions could imply a common international effort for a systematic exploration of the seafloor, sharing coverage in real time to avoid redundancy.

How to cite: Accettella, D., Burca, M., Cuffaro, M., Diviacco, P., Gasperini, L., Lodolo, E., Muccini, F., Savini, A., and Varzi, A. G.: Toward the systematic exploration of the seabed morphology during transits after the ISOBatA project experience in the Southern Ocean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15935, https://doi.org/10.5194/egusphere-egu23-15935, 2023.

14:35–14:45
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EGU23-8985
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GM6.3
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ECS
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On-site presentation
Qinqin Tang, Jens Schneider von Deimling, Jacob Geersen, and Sebastian Krastel

The Northwest (NW) African continental margin is well known for the occurrence of large-scale submarine landslides with prominent scarps exposed at the seafloor. Previous studies primarily focused on major landslides, but rarely covered small scarps. It is unclear if the distribution of landslides along the NW African continental margin is biased by the availability of processed data because data were collected mainly in designated surveys in areas of special interest. Numerous multibeam bathymetric data sets, however, are available for the area as data were also collected during transits and cruises where seafloor mapping was not a primary objective. We compiled such various datasets in the open-source MB-System software and implemented a cloud-based auto-processing and adaptive filtering workflow to handle the large bathymetric datasets (15,476 survey lines). The results show that our auto-processed bathymetric data provide a much-improved view of the seafloor (50 × 50 m), compared to EMODnet2020 and GEBCO 2022 GRID without having manually edited the data. Such a workflow allows to process large underway multibeam datasets of the given kind and therefore it resolves the unknown submarine landforms. Our results from NW Africa offer not only new insights into small-scale submarine landslides but also fulfill the missing piece from previous studies that focused on large-scale submarine landslides. Minor scarps are mainly found close to areas with major landslides, supporting the hypotheses that the NW African continental margin is characterized by large-scale but infrequent landsliding. Minor scarps are additionally identified in some other areas, such as the walls of the Agadir Canyon. Associated landsliding may contribute to the well-known Moroccan Turbidite System. The additional information on minor scarps allows us to gain a more comprehensive understanding of submarine landslides and the associated tsunami risk along the NW African continental margin.

How to cite: Tang, Q., Schneider von Deimling, J., Geersen, J., and Krastel, S.: Compilation and processing of bathymetric data recorded along the Northwest African continental margin over several decades, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8985, https://doi.org/10.5194/egusphere-egu23-8985, 2023.

14:45–14:55
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EGU23-13496
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GM6.3
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ECS
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Virtual presentation
Andrea Giulia Varzi, Luca Fallati, Alessandra Savini, Pietro Bazzicalupo, Valentina Alice Bracchi, and Daniela Basso

Coralligenous (C) includes calcareous build-ups of biogenic origin, characterised by the association of calcareous algae and several invertebrates. This habitat is one of the most important at the Mediterranean scale; it is a hot-spot of biodiversity thriving from shallow waters down to the limit of the mesophotic zone. The Italian project “CRESCIBLUREEF - Grown in the blue: new technologies for the knowledge and conservation of the Mediterranean reefs” aims at studying  peculiar C outcrops found along a depth gradient offshore Marzamemi village (SE Sicily). 

During the first project expedition (June 2021), we performed a Multibeam Echosounder (MBES) survey of the target area by using a R2Sonic 2022 system. A new 17 km2 high-resolution morpho-bathymetric map was realised, which interpretation led to the identification and classification of five major habitats, including different C morphotypes. C habitat in the form of banks was found mainly distributed between 30 and 35 m of water depth (w.d.). This investigation allowed us to observe and quantify the overall C distribution along a depth gradient spanning between 20 and 100 m of w.d., giving us a broad-scale perspective of its extension at the seafloor. 

A third marine survey (September 2021) was focused on collecting video and still images by using a Sony α Alpha 7ii reflex coupled with the Easydive Leo3 Wi housing and the Easydive illumination system Smart Sea - Gold Plus 7000 Lumen, through scuba diving. Data collection was performed over selected areas suitable for the application of underwater photogrammetry, taking into account the presence of C build-ups  (as confirmed by the interpretation of the MBES dataset) and the operational depth (i.e.: no more than 35 m of w.d.). Data collected by adopting this technique and processed using Structure-from-Motion (SfM) algorithms allowed us to get more information at the community level of such complex habitats, coupling the seafloor scale with the smaller scale obtained by direct observations. 

In this work, our intention is to improve the understanding of the geospatial context of Coralligenous distribution and extent from a multiscale perspective. Specifically, we want to show how eco-geomorphological indexes calculated using the high-resolution outputs of the C photogrammetry (3D meshes, DTMs, and orthomosaics) may be used to perform resolute investigations of such habitat on a broader scale, by considering their spatial distribution extrapolated from the MBES data.

How to cite: Varzi, A. G., Fallati, L., Savini, A., Bazzicalupo, P., Bracchi, V. A., and Basso, D.: Underwater Scuba Photogrammetry VS. MBES Acoustic Sounding: how to integrate multiscale data for a better understanding of Coralligenous outcrops, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13496, https://doi.org/10.5194/egusphere-egu23-13496, 2023.

14:55–15:05
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EGU23-1723
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GM6.3
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On-site presentation
Deniz Cukur, Gee-Soo Kong, David Buchs, Gwang-Soo Lee, Seong-Pil Kim, In-Kwon Um, Jong-Hwa Chun, and Senay Horozal

An uncharted field of sand waves was discovered in a low-relief submarine canyon incised in the outer shelf on the southeastern continental margin of the Korean Peninsula in water depths of 180–190 m. We characterize the nature and origin of the waves and the sand forming them using sub-bottom chirp profiles, eXpendable bathythermograph (XBT) profile, multibeam echosounder (MBES) data, and sediment samples from four piston cores. Two types of sand waves characterized by distinct height versus wavelength relationships were found in the study area. The sand waves in the upper, narrower part of the shelf-incised canyon are sinuous-crested, with amplitudes of 0.3–2.1 m (mean: ~1 m) and wavelengths of 10–45 m (mean: ~24 m). Their asymmetry indicates migration upslope in a southwesterly direction, opposite to the surface currents. In contrast, the lower part of the canyon that is wider and closer to the margin of the continental shelf hosts nine long (ca. 1 km) curvilinear-crested sand waves with symmetrical crests; these waves likely reflect transient bedforms forming under fluctuating current conditions.

The sediment of the sand waves consists of a variable mixture of siliciclastic and carbonate materials. The carbonate fraction (~22–55%; mean: ~34%) is derived mainly from the remains of bryozoans, bivalves, echinoderms, foraminifers, gastropods, and serpulids. Six bioclasts were dated by the radiocarbon method between ca. 41.3 and 11.8 ka BP. These relatively old ages and palaeontological data supports reworking from a shallow-marine environment during the last glacial transgression and limited sedimentation/sediment supply in the study area. The siliciclastic fraction (~44–79%; mean: ~37%) is composed of rounded to subrounded quartz and feldspar of moderate to good sorting and a mean grain size of ~1.3 phi (medium sand). The uppermost ~30 cm of all the sand wave cores reveals a decrease in the grain size of the siliciclastic fraction coupled with an increase in the carbonate/siliciclastic ratio, suggesting episodic sediment reworking and migration of the sand waves in response to fluctuating bottom currents. The coarser sediment that forms the core of the sand waves records bedload transport during periods of stronger currents. Finer carbonate-rich pelagic sediment (i.e., plankton) accumulated at the top of the sand waves during periods of weaker bottom currents. Significantly, our results show that the grain size and mineralogy of the sediment composing the sand waves are controlled by changes in hydrodynamic conditions. Our study provides novel geomorphological evidence for the influence of SW-flowing cold-water incursions (Korean Strait Bottom Cold Water) on the seafloor sediments.

How to cite: Cukur, D., Kong, G.-S., Buchs, D., Lee, G.-S., Kim, S.-P., Um, I.-K., Chun, J.-H., and Horozal, S.: Upslope migrating sand waves on sediment-starved shelves: An example from the southeastern continental margin of the Korean Peninsula, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1723, https://doi.org/10.5194/egusphere-egu23-1723, 2023.

15:05–15:15
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EGU23-7648
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GM6.3
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On-site presentation
Anne Bernhardt and Wolfgang Schwanghart

Submarine canyons are the main conduits that transport material such as sediment, organic carbon, and litter from the continent to the deep sea. This transport of material is more efficient when the canyon heads incise into the shelf, as opposed to canyons that are confined to the continental slope. The specific controls on the distribution of these two canyon types along the world’s continental margins remain unquantified and we still lack knowledge about these seascape shaping processes.

Spatial statistics on a global scale help to reveal these processes.  In this study, we successfully predict the global patterns of submarine canyon occurrence along major continental margins based on terrestrial and marine environmental variables using point patterns on linear networks. We show that submarine canyon density of both types increases as a function of gradient of the continental slope which is the most important predictor. Subsequently, the locations of slope-confined canyons are best predicted by age of the adjacent ocean lithosphere with old ages corresponding to high canyon densities. Shelf-incised canyons are best predicted by the shelf gradient which correlates positively with shelf-incised canyon densities and, to a lesser extent, by high water discharge from the adjacent catchments.

Our results show that marine variables – primarily the continental slope gradient - are most crucial for spatially predicting submarine canyons while terrestrial variables are of lesser importance. The influence of terrestrial conditions and shelf morphology on slope-confined canyons is minimal. However, incision of canyons into the shelf is facilitated when shelves are steep and river discharge is high, highlighting the secondary role of canyon head erosion by terrestrially derived sediment. Our results underscore that the formation of submarine canyons worldwide is mainly governed by backward erosion along steep continental slopes by mass failure and/ or erosive sediment density currents.  Erosion by sediment flows carrying sediment directly from terrestrial sources is likely less important for the formation of submarine canyons.

 

How to cite: Bernhardt, A. and Schwanghart, W.: Controls on global submarine canyon occurrence and formation processe s– Insights from Spatial Point Pattern Analysis –, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7648, https://doi.org/10.5194/egusphere-egu23-7648, 2023.

15:15–15:25
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EGU23-4582
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GM6.3
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ECS
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On-site presentation
Zaki Zulkifli, Michael Clare, and Timothy Minshull

Submarine slope failures pose a hazard to seafloor infrastructure and coastal communities. Given the high population densities, slope failures can have a particularly significant impact around river deltas, generating damaging tsunamis and breaking critical telecommunications connections. Despite the risks they pose, a lack of detailed monitoring means that the factors that lead to slope collapse remain poorly constrained. Numerical modelling is typically used to assess future slope stability. Still, sparse existing data ensure that we cannot yet determine how submerged delta slopes evolve and progress to failure at the field scale. Here, we aim to close this gap by analysing repeat seafloor surveys of the submerged Squamish prodelta, British Columbia, to determine the physical controls on slope instability. Multibeam bathymetric surveys were performed on 93 consecutive weekdays in 2011, during which time at least five large (>50,000 m3) delta slope collapses occurred, as well as numerous smaller slope failures. These surveys allow us to determine how the delta slope and geometry changes on an unusually detailed timeframe (i.e. daily) in the build-up to slope collapse and how it relates to variable sediment supply from the feeding river and tidal fluctuations. Analysis of the five large collapses reveals that a single mechanism is not responsible for every failure. So, we investigated how different parts of the delta encounter major failure at different times and locations by measuring and mapping out the delta head and associating it with sediment input and tide high. From this, we found that slope failure is likely due to a combination of enhanced slope geometry due to delta lip progradation and pore pressure fluctuations relating to sediment loading and tidal effects.

How to cite: Zulkifli, Z., Clare, M., and Minshull, T.: What are the controls for delta front slope failure? Insights from detailed monitoring at Squamish Delta, British Columbia., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4582, https://doi.org/10.5194/egusphere-egu23-4582, 2023.

15:25–15:35
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EGU23-5505
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GM6.3
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On-site presentation
Fynn Warnke, Ingo Pecher, Jess Hillman, Bryan Davy, and Lorna Strachan

Seafloor depressions, sometimes known as pockmarks, are commonly observed features on the ocean floor. Their shape and size can range from small, circular indentations (10s m) up to large, often irregularly shaped depressions (several kms in diameter). The origin of pockmarks is often attributed to focused fluid or gas seepage at the seafloor, but their formation mechanisms (e.g., gas/fluid composition, timing, physical processes) remain ambiguous in many cases. On the Chatham Rise, offshore New Zealand’s South Island, seafloor depressions cover an area >50,000 km², and appear to be bathymetrically controlled. For this region, it has been hypothesized that episodic release of geological CO2 resulted in the recurring formation of pockmarks at glacial terminations. Seismo-acoustic surveys allow the investigation of potential fluid-flow pathways and buried paleo-pockmarks. High-resolution imaging of shallow subsurface features can be conducted using hull-mounted, parametric subbottom profilers that are available on most larger research vessels. Higher frequencies (>1 kHz) and narrow acoustic beams provide very high vertical resolution (decimetre range) and small lateral footprints capable of resolving smaller structures than using conventional seismic. A recent voyage in 2020 acquired an extensive grid of densely spaced (~25 m) 2D subbottom profiles over a dense pockmark field on the Chatham Rise.

Here we present a novel approach to create a comprehensive pseudo-3D cube from high-resolution 2D echosounder profiles using a recently developed processing workflow. Based on this generated cube, we perform a preliminary analysis of seafloor pockmarks and paleo-pockmarks in the shallow subsurface up to 150 m below the seafloor. Our analysis includes insights into the recurrence of pockmark formation at different geological times and an assessment of morphological changes and varying spatial locations over time. Additionally, we investigate a potential polygonal fault network beneath the lowermost layer of paleo-pockmarks that might channel upward fluid migration in the area.

How to cite: Warnke, F., Pecher, I., Hillman, J., Davy, B., and Strachan, L.: Spatial-temporal development of paleo-pockmarks on the Chatham Rise from 3D imaging with subbottom profiler data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5505, https://doi.org/10.5194/egusphere-egu23-5505, 2023.

15:35–15:45
Coffee break
Chairpersons: Derek Sawyer, Rachel Barrett, Lara F. Pérez
16:15–16:20
Submarine Geomorphology II
16:20–16:30
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EGU23-15255
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GM6.3
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On-site presentation
Andrea Argnani, Claudio Pellegrini, and Marzia Rivere

Orographic reliefs are continuously created and modified in active continental tectonic settings, influencing the drainage pattern and interacting with it. It is not uncommon that stream capture occurs in these settings, causing major rearrangement of river courses. This process often produces a geomorphological feature known as wind gap, i.e. a gap through which a stream once flowed but that is now abandoned and dry as a result of the capture. Analizing a high resolution 3D seismic data set, kindly made available by ENI S.p.A., we discovered a similar feature in the Ionian offshore of the Crotone peninsula, northern Calabria. This underwater region is characterized by intense tectonic activity that is partly controlled by the occurrence of a mobile substrate, possibly overpressured shales. The relevant uplift affecting the nearby Calabria onshore can also contribute to promote gravitational instability. In this setting the "wind gap" is represented by a stretch of a downslope weakly incised channel that has soon been abandoned as a result of the growth of a tectonic structure. The course of the new submarine channel runs sub-parallel to the coast for a long strecth, before taking a downslope trajectory. The present-day submarine channel is deeply incised, showing at least two main phases: a deep valley incision containing an axial valley with a much lower relief, which likely represents the current route of turbidite flows. The main channel valley results from the major erosional episode that affected the continental slope offshore northern Calabria. The limited incision in the abandoned channel strecth suggests that drainage rearrangement occurred in the very early stage of channel incision. Therefore, the estimated age of the tectonic deformation that is responbile for originating the "wind gap" can offer a useful hint on the timing of onset of erosion in this area.

How to cite: Argnani, A., Pellegrini, C., and Rivere, M.: An underwater "wind-gap" in the Ionian offshore of northern Calabria, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15255, https://doi.org/10.5194/egusphere-egu23-15255, 2023.

16:30–16:40
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EGU23-6059
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GM6.3
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On-site presentation
Javier Lario, Tamara Martín-Pozas, Sergio Sanchez-Moral, Juan Carlos Cañaveras, Angel Fernandez-Cortes, Roberto Cano, Cecilio Lopez-Tercero, Alvaro Roldan, Esther Martin, Carlos Perez-Mejias, and Hai Cheng

The Túnel de la Atlántida (Atlantida Tunnel), located in Lanzarote Island (Canary Islands, Spain), with a length of about 2000 m and a depth of 64 m, is the largest submerged lava tunnel in the world. It corresponds to the submerged part of the lava tube complex of the La Corona volcano, with a length of about 10 km. During the development of the Sublantida Project, using diving techniques, various forms associated with the formation of the volcanic tube have been catalogued and a study of its sediments, minerals and speleothems has been carried out, including XRD, ESEM and petrological microscopy. It has been possible to propose a paleoenvironmental reconstruction from the formation of the volcanic tube, ca.21 Ka ago, to the present. The geomorphological, petrological, and sedimentary characteristics associated with the formation of the lava tube justify its importance as a World Geological Site of Interest.

Acknowledgments: This project has received funding from the Spanish Ministry of Science and Innovation and the Spanish State Research Agency (grants CGL2017-91218-EXP and PID2019-110603RB-I00-SUBSYST). It is a contribution to the IGCP Project 725.

How to cite: Lario, J., Martín-Pozas, T., Sanchez-Moral, S., Cañaveras, J. C., Fernandez-Cortes, A., Cano, R., Lopez-Tercero, C., Roldan, A., Martin, E., Perez-Mejias, C., and Cheng, H.: Geomorphological and sedimentary features of an underwater lava tube: the Túnel de la Atlántida (Lanzarote, Spain), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6059, https://doi.org/10.5194/egusphere-egu23-6059, 2023.

16:40–16:50
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EGU23-6826
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GM6.3
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ECS
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On-site presentation
Boris Secke Bekonga Gouott, Ovie Emmanuel Eruteya, Yakufu Niyazi, Mbida Yem, Joseph Quentin Yene Atangana, Adolphe Lorcin Maloh, Samuel Makoube Etame, and Elias Samankassou

Submarine fans are deposits of coarse sediments of continental origin in the deep sea, and are generally characterized by a complex depositional architecture, due to the multiple triggering mechanisms of deep-water sediment gravity flows. Consequently, this poses great challenges to deep water petroleum exploration and development. We analyzed the geomorphologic evolution and architecture of Campanian, deeply buried, submarine fans in the Kribi-Campo sub-basin, offshore Cameroon. Using a 3D seismic reflection data set and logs from two wells, we mapped seven horizons, including the fan base, fan top and five internal horizons. In cross-section, the fan is characterized by a high amplitude seismic facies exhibiting an aggradational pattern with parallel and continuous reflectors. The stacked fan-shaped morphology is up to 340 ms TWT thick, extends over an area of 600 km2 and oriented NE-SW, near the Kribi High. The analysis of lobes and channels on each horizon provided a timelapse that captures the major geomorphologic transformations of the submarine fan from its initiation, growth, and abandonment.  The submarine fan is composed of depositional lobes whose beds consist of sand, silt and mud. The detailed structure of these lobes has a finger-like morphology and is generally oriented at high angles to the channel that delivered the sediment to the lobes. The finger-like features are interpreted as thick massive sands, formed as a result of sediment-gravity flows which branched off the main flow eroding into pelagic clay substrate. Two types of channel morphology were identified (straight and sinuous). Our results show that channel and sand-body architecture evolve in a predictive manner, primarily controlled by fan aggradation. The elongated shape and morphology of the submarine fan may arise from the interaction of the fault-related folds and Kribi High, with sandstone deposition within the intervening topographic lows, sourced from the east. The 3D seismic geomorphological analysis of the submarine fan, as presented in this study, is essential to better understand their geometries, facies distribution, stacking patterns and depositional architecture to improve reservoir predictions.

How to cite: Secke Bekonga Gouott, B., Eruteya, O. E., Niyazi, Y., Yem, M., Yene Atangana, J. Q., Maloh, A. L., Makoube Etame, S., and Samankassou, E.: Submarine fans in the Kribi-Campo sub-basin, offshore Cameroon: Geomorphology and stratigraphic evolution during the Late Cretaceous, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6826, https://doi.org/10.5194/egusphere-egu23-6826, 2023.

16:50–17:00
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EGU23-14045
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GM6.3
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ECS
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On-site presentation
Minori Kyoi, Shun Nomura, Ippei Oshima, Daisuke Nishiura, Mikito Furuichi, and Kazuo Tani

Understanding the mechanism of turbidity currents is important for siting submarine cables and pipelines. It is because the turbidity currents can transport a large amount of sediment in long distance that causes severe damages to these buried linear structures. It is not clear why turbidity currents can gain and sustain such a large amount of kinetic energy. One of possibilities to explain this process is a drag reduction which reduces the turbulent energy due to the inclusion of fine particles as previous studies reports. However, the influence of fine particles to their flow characteristics has not been fully elucidated. Thus, in this study, a series of model tests were conducted to compare the horizontal steady flows of silica suspension and NaCl solution in a flume. The test results show that the flow characteristics of silica suspension were different from that of NaCl solution. These differences are considered to be caused by silica particles, and it is suggested that drag reduction by fine particles would be taken place in turbidity currents.

How to cite: Kyoi, M., Nomura, S., Oshima, I., Nishiura, D., Furuichi, M., and Tani, K.: Experimental comparison between the turbidity and density currents, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14045, https://doi.org/10.5194/egusphere-egu23-14045, 2023.

Offshore Hazards
17:00–17:10
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EGU23-2662
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GM6.3
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On-site presentation
Roger Urgeles, Davide Gamboa, Ricardo León, Finn Lovholt, Maarten Vanneste, Antonio Cattaneo, and Carla Vila

The Euro-Mediterranean Submarine landSlide (EMSS) database is a catalogue of submarine landslides of the Mediterranean Sea and the European continental margins of the Atlantic and Arctic Oceans. The catalogue is compiled from data available in the literature as well as information collected from geophysical data and so far not published in the scientific literature. A first version has been recently made available online (https://ls3gp.icm.csic.es/?page_id=553) and OGC services are being developed to be available soon through the EPOS data portal (https://www.ics-c.epos-eu.org/) in the frame of the EU funded project Geo-INQUIRE. Within Geo-INQUIRE we are currently working on a second version of the catalogue improving both areal coverage in the Atlantic Ocean and information relative to the source areas (as opposed to the previous version where only deposits and scars was considered). The aim of the latter improvement is to better characterize the failure and post-failure stages of submarine landslides. The new catalogue stores polygon and polyline geospatial features related to landslide deposits, landslide source areas and landslide scars as well as information relative to age, volume, area, runout, thickness, typology, scar elevation, relevant slopes and depths as well as related metadata. The catalogue includes submarine landslides that span from Miocene to Present day, although a clear bias exists towards submarine landslides of younger age, particularly for the smaller events. The reason for this is that the older and smaller events are difficult to identify on lower resolution geophysical data sets in deep-water and large sub-surface depths. The catalogue aims to offer improved understanding of mass-wasting processes, the potentially resulting tsunamis and derived geohazard. Recent case studies using a data subset (Gulf of Cadiz, SW Iberian Margin) portray the application of such type of databases in (probabilistic) analysis of submarine slope instability and tsunami-genesis from submarine landslides. We believe the current EMSS is the seed for the world ocean submarine landslide database. In this regard, we encourage the offshore geohazards community to contribute to enlarge the database. Shapefile templates will be made available to ease the task. This work is supported by the European Union’s Horizon Europe Research and Innovation Program under grant agreement No 101058518 (Geo-INQUIRE).

How to cite: Urgeles, R., Gamboa, D., León, R., Lovholt, F., Vanneste, M., Cattaneo, A., and Vila, C.: The EuroMediterranean Submarine Landslide database: towards offshore geohazard quantitative assessement from submarine landslides and derived tsunamis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2662, https://doi.org/10.5194/egusphere-egu23-2662, 2023.

17:10–17:20
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EGU23-11441
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GM6.3
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ECS
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Highlight
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On-site presentation
Kristina Sass, Steffen Kutterolf, Tim Freudenthal, Sebastian Watt, Christian Berndt, Sebastian Krastel, and Katrin Huhn

Volcanic island sector collapses produce some of the volumetrically largest mass movements on Earth. They may trigger devastating tsunamis that pose hazards to coastal communities and endanger seafloor installations. However, very little is currently known about the interplay between volcanic activity and subsequent mass wasting (volume, source location, and trans­port dis­tance) as well as their specific em­place­ment pro­cesses (tim­ing, kin­emat­ics, and dy­nam­ics). Moreover, these are key information to de­vel­op­ a re­li­able tsunami haz­ard as­sess­ment for sec­tor col­lapses.

The volcanic island of Montserrat in the Lesser Antilles is an ideal target to study the timing, frequency, and kinematics of sec­tor col­lapses as well as subsequent mass wasting. In 2019, Meteor expedition M154 investigated the major landslide complex – Deposit 2, located in the southeast offshore sector of Montserrat and provided an outstanding geophysical (M154-1) and sedimentological dataset. Here, the second leg, M154-2, focused on sediment sampling. Within and in the vicinity of Deposit 2, drill cores were taken with the MeBo70 drill rig from up to 63 mbsf. Ad­di­tion­ally, 21 sup­ple­ment­ing grav­ity cores were taken in the vi­cin­ity of Me­Bo70 drill sites and along systematic transects across the slid masses. Sedimentological, geophysical, geotechnical as well as geochemical analyses of these sediment cores enable a unique opportunity to gain new insights into timing of mass wasting events and complement information on the volcanic island evolution.

Based on these sediment cores, this pro­ject aims at con­trib­ut­ing to the gen­eral com­pre­hen­sion of vol­canic is­land sec­tor col­lapses, par­tic­u­larly the in­ter­re­la­tion­ship of vol­canic pro­cesses and as­so­ci­ated mass move­ments by establishing an event chronostratigraphy for the marine sediment records off Montserrat volcanic island.

Samples from four MeBo70 drill sites at the undisturbed slope, the central and distal part of Deposit 2, and south of Montserrat were analyzed for their componentry and composition. The sediments predominantly comprise mud-rich facies interbedded with fine to coarse-grained, better-sorted sands. The sandy intervals sometimes show multiple units defined by normally-graded beds or sharp color changes with variable proportions of volcanic and biogenic clasts. In a small number, coarse volcanic sands to volcaniclastic gravels were encountered. Tuffaceous deposits are less frequent. Petrographic analyses of selected samples by polarized light microscopy enable the investigation of clast inventories to differentiate between sediment units. Geochemical fingerprinting of major elements of volcanic glasses by electron microprobe elucidates this differentiation. The geochemical analyses further show a mainly basaltic to rhyolitic volcanism in the range of Arc Tholeiitic and Calc-alkaline series. The analyzed samples represent different stages of volcanic island evolution with periods of increased volcanic activity and eruptions, flank collapses, submarine mass wasting events, and periods of relative inactivity. Moreover, trace element analyses by laser ablation inductively coupled plasma-mass spectrometry of selected potential primary volcanic layers enable the possibility to better distinguish between single eruptions and also to narrow down their source area(s) as well as that of the sedimentary material.

How to cite: Sass, K., Kutterolf, S., Freudenthal, T., Watt, S., Berndt, C., Krastel, S., and Huhn, K.: Volcanic Island Sector Collapse: Reconstruction of volcanic activity and implications for subsequent mass movements from marine records drilled with MeBo70 offshore Montserrat (Lesser Antilles), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11441, https://doi.org/10.5194/egusphere-egu23-11441, 2023.

17:20–17:30
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EGU23-8508
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GM6.3
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ECS
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On-site presentation
Bailey Fitzgerald, Derek Sawyer, Julia Reece, and Wyatt Scott

Recent work has demonstrated elevated shear strength in the uppermost 100 meters below seafloor (mbsf) on seismically active margins. This observation is consistent with the seismic strengthening hypothesis that repeated exposure to earthquake shaking progressively dewaters and densifies sediment, which leads to increased shear strength and slope stability.  However, the relative contribution of seismic strengthening versus intrinsic properties on shear strength remain largely unknown. Here, we compare sediments from seismically active and passive margins from scientific ocean drilling sites that exhibit significant shear strength differences. Active margin sites are Nankai (Site C0001), Cascadia (Site 1054), and Southern Alaska (Site U1418), and passive margin sites are Amazon Fan (Site 942), North Carolina Slope (Site 1054), and New Jersey (Site 1073). From each site, we sampled 500 g of sediment equally distributed throughout the top 100 mbsf. We combined samples to create a representative bulk sample per continental margin and reconstituted them with saltwater that matched field-measured salinity. We measured particle size (hydrometer), plasticity states (Atterberg limits), mineralogy (powder X-ray diffraction), compression behavior and permeability (1-D resedimentation experiments), and undrained shear strength (fall cone device). All samples are siliciclastic marine mud that classify as silty clay or clayey silt. Despite the apparent similarity in lithology, sand fraction varies from 0.8 wt. % (Amazon) to 10.3 wt. % (N. Carolina) and clay fraction (<2 mm) varies from 37.7 wt. % (N. Carolina) to 56.0 wt. % (Amazon). Void ratios, measured in resedimentation experiments range from 1.6 (porosity = 62%) (Nankai) to 1.0 (porosity = 50%) (S. Alaska) at a vertical effective stress of 100 kPa. Resedimentation experiments are followed by consolidation to 1 MPa (equivalent to 100 meters of burial depth) and undrained shear strength measurements, which are compared with field-measured shear strengths. We find the previously observed strengthening effect observed in the active margin field- strength is no longer present in the lab-strengths. This suggests that the exposure to seismicity in the field is potentially leading to enhanced shear strength during early burial.

How to cite: Fitzgerald, B., Sawyer, D., Reece, J., and Scott, W.: Shear Strength Development During Early Burial on Seismically Active Margins: A Geotechnical Investigation into Seismic Strengthening, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8508, https://doi.org/10.5194/egusphere-egu23-8508, 2023.

17:30–17:40
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EGU23-14647
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GM6.3
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ECS
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On-site presentation
Ricarda Gatter, Madhusudhan BN Murthy, and Katrin Huhn

Submarine landslides are common on all sediment bearing submarine slopes worldwide. They have the potential to damage expensive subsea infrastructure such as pipelines or telecommunication cables, and generate hazardous tsunamis. Numerous studies have shown that weak layers embedded within the slope stratigraphy play a crucial role in controlling the formation of submarine landslides; however, very little is known about their internal structure and composition. Although weak layers seem to be an essential pre-conditioning factor for slope failure, many questions remain unanswered, such as where with respect to weak layers do failure planes form: within the weak layer, above or below it? Previous studies usually relied on sedimentological and geotechnical sediment core and in-situ analyses to investigate weak layers. These analyses, however, do not provide insights into the internal structure of the sediments on a micro-scale level and hence, lack information needed to qualitatively and quantitatively investigate weak layers.

Here, we present a new approach towards weak layer investigation that is based on high-resolution micro-Computed Tomography (µCT) imaging. µCT is used to visualise, and qualitatively and quantitatively investigate selected sediment samples taken from within weak layers and the background sediment of submarine landslides. Our results show clear compositional and structural differences between individual sub-units of the investigated weak layers, as well as the background sediment. These differences can be attributed partly to different sediment types, i.e. coarse- versus fine-grained sediments, but also reveal a dependency on the sedimentation regime. We find that pore space distribution is highly spatially variable and works on a sub-millimetre scale. Such high variability may be masked by standard bulk porosity measurements, which require larger (several centimetre) sediment samples and only provide information averaged over the entire sample. The identification of small-scale changes, however, appears to be crucial for the formation of weak layers. Our results therefore demonstrate the huge potential of µCT to investigate the internal structure of weak layers, obtaining information that is not resolved and lost in other analytical methods.

How to cite: Gatter, R., BN Murthy, M., and Huhn, K.: Micro-structural characterisation of weak layers of submarine landslides, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14647, https://doi.org/10.5194/egusphere-egu23-14647, 2023.

17:40–17:50
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EGU23-7464
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GM6.3
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ECS
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On-site presentation
Jonathan Ford, Angelo Camerlenghi, Francesca Zolezzi, and Marilena Calarco

Mass-transport deposits often show a low-amplitude, “acoustically transparent” seismic response compared to unfailed sediments. This amplitude signature is often interpreted as a lack of coherent internal reflectivity caused by a loss of internal structure during transport and emplacement, and is widely used to delineate mass-transport deposits in sub-bottom profiler data. An apparent contradiction is that cores penetrating such “acoustically transparent” deposits can sometimes retrieve well-stratified sediments that show little evidence of deformation.

In this study we examine the variation in the single-channel seismic amplitude response with changing heterogeneity using synthetic seismic modelling. We model the internal structure of mass-transport deposits as a two-component binarised random medium, where the lateral correlation length is used to artificially control the degree of internal deformation/scale of internal structure, while maintaining the magnitude of the internal reflectivity constant. We construct two synthetic models: i) a simplified single-source marine example and ii) a multi-source example based on a real world “acoustically transparent” mass-transport deposit imaged by a dense network of AUV sub-bottom profiles in the Black Sea. We use 2-D elastic finite-difference modelling to model the seismic response (at sub-bottom profiler bandwidths) of an ensemble of both synthetic models with varying geostatistical parameters and random seeds for the mass-transport deposit zones. For the single-source synthetic model a reduction in observed amplitude with reduced lateral scale length is consistently observed across a range of vertical correlation lengths. For the real world Black Sea example, with realistic elastic and geostatistical parameters based on cone-penetration tests and physical property measurements from sediment cores, we find that when the lateral scale length of the random medium is around 1 m, recorded seismic amplitudes are, on average, reduced by ∼15% relative to unfailed sediments.

We conclude that relatively small amounts of deformation at scales larger than the dominant seismic wavelength are, in general, able to a generate significant decrease in seismic amplitude, without requiring a reduction in the average reflectivity. Our synthetic modelling results should discourage interpretation of the internal structure of mass-transport deposits based on seismic amplitudes alone as “acoustically transparent” mass-transport deposits may still preserve coherent, metre-scale internal structure. In addition, the minimum scale of heterogeneity required to produce a reduction in seismic amplitudes is likely much larger than the diameter of sediment cores, meaning that such mass-transport deposits may still appear well-stratified and undeformed when cored.

How to cite: Ford, J., Camerlenghi, A., Zolezzi, F., and Calarco, M.: Modelling the seismic amplitude response to internal heterogeneity of mass-transport deposits, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7464, https://doi.org/10.5194/egusphere-egu23-7464, 2023.

17:50–18:00

Posters on site: Wed, 26 Apr, 10:45–12:30 | Hall X3

Chairpersons: Sebastian Krastel, Derek Sawyer, Jacob Geersen
X3.23
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EGU23-4521
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GM6.3
Marta Ribo, Sally Watson, Helen Mcdonald, and Lorna Strachan

On inner continental shelves, a variety of coarse grained bedforms, such as gravel dunes, are shaped by hydrodynamic and morphodynamic processes. Repeat, high-resolution, multibeam surveys are crucial to identify geomorphological changes on the seafloor, especially in the extremely dynamic shallow waters (< 200 m water depth). Timeseries bathymetric datasets allow us to measure and monitor spatial- and temporal changes in submarine bedforms and determine their evolution patterns. This is important for a better understanding of the sediment transport processes and the related hydrodynamics, but also to determine the settings for benthic ecosystems and identify changes in seafloor geomorphology to prevent potential damage of offshore infrastructure and maritime pathways.
We present three multibeam data sets acquired in 2017, 2020 and 2021 over a field of gravel-sand bedforms located in the high-energy Cook Strait / Te Moana-o-Raukawa. In this study we combine timeseries bathymetric data, ground-truth data (video footage and sediment samples) and oceanographic modelling to understand the sediment dynamics in the area. Results show that coarse sand and gravel field of dunes with superimposed megaripples have undergone intricate morphological changes. The ~100-m length and ~15-m height submarine dune crests bifurcate, becoming more complex between 2017-2020, followed by the reforming of dune crests between 2020-2021. Hydrodynamic modelling suggests there is an interaction between the tidal near-bottom currents and the sediment transport, creating a morphological positive feedback, which might be leading the complex bedform morphological changes observed in the repeated mapping surveys.
This study reveals the dynamic nature of the seabed over short time-scales (years) in highly dynamic areas, such as the tidally vigorous Cook Strait region. Our findings demonstrate the importance of repeat multibeam mapping in understanding of the rate and scale of changes on the seafloor.

How to cite: Ribo, M., Watson, S., Mcdonald, H., and Strachan, L.: Complex morphological changes in marine coarse sediment bedforms, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4521, https://doi.org/10.5194/egusphere-egu23-4521, 2023.

X3.24
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EGU23-13850
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GM6.3
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ECS
Luca Fallati, Alessandra Savini, Andrea Giulia Varzi, Claudio Argentino, Stephan Bunz, and Giuliana Panieri

Multibeam echosounders (MBES) mounted on remotely operated vehicles (ROVs) can acquire sub-metric resolution bathymetry in deep water environments. However, a general lack of complexity measurements of peculiar seafloor morphologies (sub-metric and centimetric resolution) represents a knowledge gap that can be mitigated through an innovative image analysis technique: Structure from Motion (SfM). 3D photogrammetry is becoming more relevant in land and marine imaging research, opening new opportunities for the extraction of fine-scale terrain variables and high-resolution habitat mapping that may contribute to understanding the functioning of extreme deep-sea environments, such as cold seeps habitats.

Cold seeps are seafloor areas where reduced compounds from subsurface hydrocarbon reserves either enrich sediment fluids or emanate freely as gas from the seabed. Numerous underwater landscapes and various chemosynthetic communities are associated with these biodiversity hotspots, which were uncovered during the last decades of seafloor exploration. 

In this work, we integrated ROV-based MBES bathymetric datasets with multi-dimensional, high-resolution seafloor models obtained from ROV photogrammetry to improve (i) the understanding of the geospatial context of Cold Seeps distribution and (ii) their spatial extent from a multiscale perspective.

An arctic cold seep on Svyatogor Ridge, offshore Svalbard, was explored using Ægir6000, a work-class ROV equipped with a Kongsberg EM 2040 MBES and 8 HD and composite video camera inputs, which provide a fully operational vision with a zoom and focus capability able to film the ocean floor at different angles. The lighting capacity includes ten dimmable lights and has a maximum total load of 2300 W.

ROV-based multibeam micro-bathymetry was performed on a selected area at 45 m of altitude from the seafloor at a speed of 0,5 knot to map the near bottom environments in detail. Sub-portions of the same areas were then mapped using a photogrammetric workflow. The ROV moved at a constant speed of 0,2 knot, following predefined routes to guarantee optimal lateral overlap between adjacent transects. A photogram every two seconds was automatically extracted from the nadiral camera's videos. The images were later processed in Agisoft Metashape®, following a well-established photogrammetry workflow. As final outputs, we obtained 3D meshes, orthomosaics and DTMs at ultra-high-resolution (mm), which allowed us to get detailed morphometric maps.

These data permit us to reconstruct accurate georeferenced 3D models representing a variety of small-scale seabed features. Such ultra-high-resolution models can provide essential information for a better understanding of the spatial pattern associated with seafloor biogeochemical and physical processes. Furthermore, the opportunity to accurately locate push core sampling sites on ROV photomosaic allows us to investigate closer spatial relationships between measured methane fluxes and associated seafloor habitats. 

This work was supported by the Research Council of Norway, for AKMA - Advancing Knowledge on Methane in the Arctic, project number 287869.

 

How to cite: Fallati, L., Savini, A., Varzi, A. G., Argentino, C., Bunz, S., and Panieri, G.: Integration of ROV-based acoustic and optical high-resolution remote sensing survey for a multiscale geomorphological seafloor mapping approach: an Arctic Cold seep case study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13850, https://doi.org/10.5194/egusphere-egu23-13850, 2023.

X3.25
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EGU23-8954
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GM6.3
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Highlight
Jacob Geersen, Felix Gross, Sebastian Krastel, Christoph Böttner, Olga Sánchez-Guillamón, Juan-Tomás Vázquez, Ricardo Leon, Luisa Rollwage, Henriette Sudhaus, Christian Sippl, and Morelia Urlaub

The land and seascape of the Canary Islands witnesses a long history of volcanic growth and volcano-tectonic deformation. This interplay has generated a spectacular morphology that stretches over almost 8 km (vertically) from the foot of the western volcanic islands at 4.000 m water depth to the top of the Pico del Teide at 3.718 m above sea level. On 19th September 2021, Cumbre Vieja volcano on the island of La Palma, experienced its longest eruption in historic times, lasting for three months. The eruption was accompanied by widespread deformation, expressed among others by tens of thousands of earthquakes, meter-scale vertical elevation changes, fractures and eruptive fissures that opened along the onshore flank, and the build-up and collapse of volcanic cones. It is now a major task for researchers to identify and untangle the different deformation patterns in order to learn about volcano-tectonic and related sedimentary processes before, during, and after the eruption. Because the largest volume of the volcano locates underwater, a comprehensive analysis of volcano-tectonic deformation requires marine data. Here we present a synthesis of legacy hydroacoustic data from the last century together with new data collected in recent years and especially after the 2021 eruption. The new data include multibeam bathymetry from VULCANA_1015, VULCANA_0318 and VULCANA_III_LP_0921/1021-0222 cruises which were supported by the Spanish Institute of Oceanography (IEO-CSIC) funds through the VULCANA project. These data cover the submerged flank down to a water depths of 1940 m with a 10x10 m grid spacing. We further collected multibeam and sediment echosounder data from the lower part of the island slope and adjacent abyssal seafloor between the islands of La Palma and El Hierro during RV MARIA S. MERIAN Cruise 113 in January 2023. Together the different data cover the western side of La Palma, which has collapsed repeatedly in a likely catastrophic manner over geologic times, with the Cumbre Nueva debris avalanche at 125–536 ka representing the youngest event. We use the data to map sedimentary and tectonic structures including fault outcrops, submarine canyons and channels, mass-transport deposits, landslide scars and blocks as well as folded and faulted strata between the coast and about 4500 m water depth. The results add to a land-to-sea analysis of volcano-tectonic deformation at Cumbre Vieja volcano including the spatial extent and outline of the mobile western flank, which seems to be moving into the Atlantic Ocean.

How to cite: Geersen, J., Gross, F., Krastel, S., Böttner, C., Sánchez-Guillamón, O., Vázquez, J.-T., Leon, R., Rollwage, L., Sudhaus, H., Sippl, C., and Urlaub, M.: Volcano-tectonic deformation of the submarine flank of Cumbre Vieja volcano, La Palma, Canary Islands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8954, https://doi.org/10.5194/egusphere-egu23-8954, 2023.

X3.26
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EGU23-17288
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GM6.3
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ECS
Sally Watson, Marta Ribo, Sarah Seabrook, Lorna Strachan, Rachel Hale, and Geoffroy Lamarche

With the SARS-CoV-2 coronavirus came what media has deemed the “port congestion pandemic”. Since it began, thousands of ships have been reported waiting outside heavily congested ports relying on anchoring gear to hold fast. While the shipping industry is known to contribute to air, water and noise pollution, the physical impact of shipping practices, such as anchor use on the seafloor, has received much less attention. With a regional survey using high-resolution (1 m) bathymetry data of a comparatively low congestion port in New Zealand-Aotearoa, we demonstrate that high-tonnage ship anchors excavate the seabed by up to 80 cm and the associated impacts are preserved for at least 4 years. This is the first characterisation of the intensity and extent of damage to the seafloor and benthic environment caused by high-tonnage ship anchoring. We demonstrate that the observed seabed damage is attributed to high-tonnage passenger and cargo vessels. Anchor use in port regions has significantly changed the structure of the seafloor, with downstream impacts on benthic habitats and ecosystem functions. Extrapolating these findings to a global scale, we estimate that between 6,000 and 20,000 km2 of coastal seafloor is adversely affected. With the predicted increase in global marine traffic, a less destructive method of managing high-tonnage vessels awaiting port calls is necessary to mitigate the impact of maritime activities on chemically and biologically important shallow marine environments.

How to cite: Watson, S., Ribo, M., Seabrook, S., Strachan, L., Hale, R., and Lamarche, G.: The footprint of ship anchoring on the seafloor, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17288, https://doi.org/10.5194/egusphere-egu23-17288, 2023.

X3.27
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EGU23-17221
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GM6.3
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ECS
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Highlight
Marta Ribo, Shane Cronin, Sönke Stern, Sung-Hyun Park, James Garvin, and Taaniela Kula

Submarine eruptions dominate volcanism on Earth, but the recent eruption of Hunga Tonga–Hunga Haʻapai volcano in January 2022 was one of the most explosive eruptions ever recorded. Many large calderas collapse during eruptions and the resulting morphology provides unvaluable information for understanding the processes during highly unpredictable eruptions.

Here we present a detailed analyses of the post-eruption morphology of the caldera of the Hunga Tonga–Hunga Haʻapai submarine volcano. We use the first multibeam bathymetry of the caldera, acquired only 5 months after the eruption on the MV Pacific Horizon, in May 2022.

The multibeam data shows landslides with 0.5-1 km wide scars, mainly on the southern rim, with the deposits extending to the central part of the caldera. However, the flat inner caldera suggests that most of the material was deposited simultaneously to the caldera drop following the eruption, on the order of 800 m. Sediment cores collected inside the caldera show repeated turbidity current sedimentation pointing to ongoing mass wasting, which could have potentially led to eventual breaching of the rim on the north and east side. Submarine ridges were preserved on these sites, separating the inner caldera and two erosional channels on the outer part, which point to the main debris transport paths during the eruption. More than 50 active gas plumes are observed on the eastern side, located following a straight W-E transect, and on the northern side, where the vents are covering the collapse walls close to the eastern Hunga Tonga–Hunga Haʻapai island. The presence of these vents and their distribution related to the morphology of the caldera, indicate the most energetic parts of the volcano, which can potentially still be hazardous. Our morphological analyses provide new insights of transport and depositional processes following highly energetic submarine eruptions.

How to cite: Ribo, M., Cronin, S., Stern, S., Park, S.-H., Garvin, J., and Kula, T.: Morphological evolution of the Hunga Tonga–Hunga Haʻapai submarine volcano after the explosive eruption, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17221, https://doi.org/10.5194/egusphere-egu23-17221, 2023.

X3.28
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EGU23-14238
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GM6.3
Derek Sawyer, Roger Urgeles, and Claudio Lo Iacono

Megabeds, or ¨megaturbidites¨, are exceptionally large submarine deposits interpreted to originate from significant geohazard events. Megabeds result from rapid discharges of large volumes of sediments from continental margins to the deep ocean. Using high resolution 3.5 kHz subbottom profiler data, we discover four megabeds constituting ~75% of the deposits in the upper 60 meters (~ last 60 ky) of the western Marsili Basin, Tyrrhenian Sea. The megabeds are widespread and imaged as distinct acoustically transparent units with ponded geometries, 10 to 25 m thick, separated by parallel-bedded strata. Each megabed is thinner and volumetrically smaller than the proceeding one. Minimum volume estimates of 1.3, 9.4, 11.8, and 13.3 km3, respectively.  A synthetic seismogram and well tie at Site 650 of Ocean Drilling Program Leg 107 demonstrates that megabeds correspond to a thick unit of mud lying on top of a high amplitude facies of normally graded volcaniclastic silt or sand. Mud deposits are structureless, consistent with a turbidite origin, except for the transparent facies of Megabed 3, which corresponds to a highly deformed muddy debris flow. The detailed well-tie together with previous chronological constraints from volcaniclastics glass chemistry, suggest that Megabeds 3, and possibly 4 may be associated with the 39.8 ka Campanian Ignimbrite super-eruption of the Campi Flegrei caldera, Italy, described among the largest eruptions on Earth. Most likely source areas for the most recent megabeds are the volcanic provinces to the north or south, and the Stromboli canyon-channel system to the east. Surprisingly, the deposit geometries suggest the megabeds are not sourced locally from the Marsili seamount, which is the largest active volcano in Europe. Regardless of source locality, the megabeds entered the Marsili Basin rapidly as evidenced by significant basal erosion and fluid escape structures, some of which remain active. The newly discovered megabeds of the Marsili basin may indicate significant geohazard events for the circum-Tyrrhenian Sea coastlines. 

How to cite: Sawyer, D., Urgeles, R., and Lo Iacono, C.: 60,000 years of recurrent volcaniclastic megabed deposition in the Marsili Basin, Tyrrhenian Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14238, https://doi.org/10.5194/egusphere-egu23-14238, 2023.

X3.29
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EGU23-15073
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GM6.3
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ECS
Rachel Barrett, Philipp Held, Aaron Micallef, Felix Gross, Christian Berndt, and Sebastian Krastel

Morphometric features within subaqueous landslide deposits provide critical information about the process of failure – a factor that is directly linked to the hazard potential of a landslide. However, some morphometric features, such as compressional and extensional (spreading) ridges, have similar geomorphology even though they form through very different processes. Identification and classification of these ridges in subaqueous landslide deposits is typically carried out manually and, as such, is heavily dependent on interpreter experience and bias. In this study, we make use of bedform analysis techniques typically used to identify seafloor features, such as ripples and dunes, to quantitatively characterize and distinguish between spreading and compressional ridges in subaqueous landslide deposits in a variety of settings, both lacustrine and submarine. Our approach involves identifying local maxima and minima, grouping them using neighbourhood analysis, and then calibrating these ridges using a series of closely-spaced perpendicular profiles following existing methods for bedform analysis. We then compare the metrics (including wavelength, height, slope, symmetry, and sinuosity) of the two kinds of ridges, and use these to distinguish between them. The application of quantitative, semi-automatic methodology such as this is critical to enable a move towards a less subjective interpretation of subaqueous landslide deposits, and to ensure accurate identification of features formed through different morphological processes.

How to cite: Barrett, R., Held, P., Micallef, A., Gross, F., Berndt, C., and Krastel, S.: Applying quantitative methods to identify and distinguish between extensional and compressional ridges in subaqueous landslide deposits, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15073, https://doi.org/10.5194/egusphere-egu23-15073, 2023.

X3.30
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EGU23-15248
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GM6.3
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ECS
|
Nora Markezic, Marianne Coste, Massimo Zecchin, Emanuele Forte, and Silvia Ceramicola

The Ionian Calabrian and Apulian margins are severely incised by a dense network of submarine canyon systems, that have formed in response to ongoing km-scale uplift of Calabria over the last ca. 1Ma. Despite their young age (Pleistocene) they incise the continental shelf and slope over lengths of tens of kilometres, with thalwegs up to 2 km wide, walls higher than 200m and headwalls, that can extend over more than 50 km.

Some of the canyon headwalls are very close to the coastline and in some cases, retrogressive features are observed from morphology and sub-bottom observations, representing a potential hazard for population and coastal infrastructures. Some of the canyons are isolated, others form hierarchic systems with five or more canyons merging into dendritic (cauliflower) systems that may or may not be connected to onshore drainage networks. They exhibit different characteristics in terms of headwall geometry, profile concavity and sinuosity.

We present new information on their geomorphic attributes to gain new understanding about the dynamic and evolution of the different canyon systems in the last 1Ma. In addition, we aim at extracting information regarding the grain size and sediment type from vintage backscatter geophysical data and subbottom data, to analyse canyon headwall enlargement and their erosive activity. The overall purpose of my study is to bring new insights about the inception and evolution of the different canyon systems in relation to tectonic and sea level changes and thus be able to assess the potential geohazards that retrogressive canyon headwalls may represent today for coastal areas and infrastructures.

How to cite: Markezic, N., Coste, M., Zecchin, M., Forte, E., and Ceramicola, S.: Geohazard assessment of submarine canyon headwalls activity along the Ionian Calabrian and Apulian margin (Ionian Sea), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15248, https://doi.org/10.5194/egusphere-egu23-15248, 2023.

X3.31
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EGU23-860
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GM6.3
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ECS
|
Marco Bianchini, Nora Markezic, Daniele Casalbore, Daniele Spatola, Silvia Ceramicola, and Francesco Latino Chiocci

Submarine landslides are very large events occurring across both active and passive continental margin. They are sediment transport processes caused by submarine slope’s instability and the result of both internal structure changes and external dynamic conditions. The genesis and evolution of slope failure is controlled by different geological factors which may be considered as predisposing factors (e.g., seafloor morphology, lithology, type of sediment, presence of fluid or weak layers) and triggering factors (e.g., earthquakes).

The Italian continental margins provide an excellent playfield to study submarine landslides because they have been identified and mapped in different morpho-tectonic and sedimentary contexts (e.g., accretionary prism, volcanic edifices, foredeep continental slope, upper slope in front of large deltas…). Between the 2007 and 2013, in the framework of MaGIC project funded by the Italian Civil Protection (DPC) a detailed mapping program of seafloor morphologies and features including landslides was carried out. The morphological features identified during the Magic Project will be used as a base to create a geodatabase of the Italian submarine landslides. This will include a careful reclassification of the different features, extraction of morphometric parameters and identification of triggering and preconditioning factors for the different case studies.  This work has been funded by  PNRR GEOSCIENCES IR project, and aim at use statistical methods to better classify the landslides that are relate than to different geological settings, and constrain the relation between different parameters and the triggers. When a relation will be established, we may build a step towards a better geohazard assessment, and may be define the likelihood of submarine landslide occurrences across the Italian Continental Margins, even in the areas when the landslides did not occurred yet. In fact, landslide hazard assessment requires the estimation of where, when (or how frequently) and how large a given landslide event may be. In marine realm this is very difficult because the cost of direct analysis is higher than in the subaerial counterpart. Therefore, a geostatistical approach on very large number of features could probably be the most realistic approach to the problem.

How to cite: Bianchini, M., Markezic, N., Casalbore, D., Spatola, D., Ceramicola, S., and Chiocci, F. L.: Geostatistical study of Italian submarine landslides, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-860, https://doi.org/10.5194/egusphere-egu23-860, 2023.

X3.32
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EGU23-105
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GM6.3
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ECS
Radha Krishna Pillutla, Andrew Tien-Shun Lin, Chih-Chieh Su, Shu-Kun Hsu, Nathalie Babonneau, Gueorgui Ratzov, and Serge Lallemand

The tectonic features of offshore SW Taiwan are dominantly controlled by the subduction and collision processes between the Eurasian and the Philippine Sea plates. Marine sediments may serve as archives of extreme events, including earthquakes, typhoons, submarine landslides, etc. The most common event bed is turbidite, while homogenites are relatively less well known. The distinction between various deposits like muddy turbidites, homogenites and hemipelagites has long been a matter of intricate controversy. Homogenites are one of the many event beds and are likely to develop in enclosed basins where suspended sediment clouds are trapped and deposited. They are very fine-grained sediments, initiated from re-suspended fine-grained sediments or from sediment gravity flows, and are transported and deposited from suspension fall-out. Two giant piston cores, MD18-3547 (35.27 m) and MD18-3548 (20.07 m), were collected in the perched/isolated basins of the Taiwan accretionary wedge, at a water depth of 1806m and 1752m respectively. A total of 29 event beds (homogenites and turbidites) are identified from the piston cores. Detailed grain-size analysis (1 cm resolution), 14C AMS dating and CT-scan of the above-mentioned cores were performed. CT scans reveal homogenites as thick structureless mud totally devoid of bioturbation while hemipelagites show bioturbation. The average thickness of homogenites and turbidites are ~250 cm and 5 cm, respectively, while the thickest homogenite layer is ~420 cm and the thickest turbidite layer is ~15 cm. All homogenite layers are floored by a thin (usually less than 10 cm thick) and fining-upward sandy unit. Grain size parameters like mean, mode, and median are highly constant for homogenites, excluding the basal sandy unit, between 6 and 8 µm. Both hemipelagite and homogenite are poorly sorted with homogenites displaying a uniform sorting throughout the unit. A total of 17 14C AMS dating of foraminifera were carried out from the two marine cores. The youngest homogenite is of ~2,375 BP cal yrs and the oldest one is ~ 17,926 BP cal yrs, while the youngest turbidite corresponds to ~2,375 BP cal yrs and the oldest one is ~18,871 BP cal yrs.

Keywords: perched basins; homogenites; turbidites; ct-scan; 14C dating; grain size

How to cite: Pillutla, R. K., Lin, A. T.-S., Su, C.-C., Hsu, S.-K., Babonneau, N., Ratzov, G., and Lallemand, S.: Seismogenic event beds in perched basins during the last 20 kyr: Examples from offshore SW Taiwan, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-105, https://doi.org/10.5194/egusphere-egu23-105, 2023.

X3.33
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EGU23-15125
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GM6.3
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ECS
Frances Cooke, Andreia Plaza-Faverola, Stefan Buenz, Khalid Amrouch, Rosalind King, and Jean-Baptiste Koehl

Processes such as oblique mid ocean ridge spreading, glacial isostatic adjustment and slope instability provide a highly complex spatial and temporal record of stress in the Fram Strait. The Vestnesa Ridge is a contourite drift bounded by two slow spreading mid ocean ridges located beside a formerly glaciated margin. The total state of stress is difficult to separate into individual components therefore our focus is to ascertain whether there is a stress transfer from the deep crust into the shallow overlying (~200m) sedimentary cover. We use high-resolution P-cable 3D seismic volumes together with 2D seismic, to map deeper faults connecting with near surface deformation. We perform high resolution mapping of the ridge by examining the dip and strike of each distinct fault system. We use a pre trained 3D model to predict faults within each 3D volume and automatically extract faults at multiple intervals to capture temporal stress changes. To minimize noise, the model identifies faults based on edge preserved smoothing for a selection of peak frequencies. In our results we observe fault linkage between parallel faults that may become favourable locations for transtensional and transpressional stress expected in the strike slip regime predicted in the west of the ridge. Our results show that the east of the ridge has a dominant NW-SE fault strike and a present day tensile stress regime while towards the west, the NW-SE assemblage becomes less prominent and multiple fault systems dominate increasing the complexity of the system. We present a high detail comprehensive structural analysis of 3 study sites across the shallow ridge sediments and use our results to investigate differences in the strike and dip between sites to explore the influence of sedimentary faults and ridge geomorphology on the spatial evolution of seafloor seepage at a deep Arctic oceanic basin.

How to cite: Cooke, F., Plaza-Faverola, A., Buenz, S., Amrouch, K., King, R., and Koehl, J.-B.: High resolution fault analysis of the Vestnesa Ridge: a highly complex deep water fluid flow system in the east Fram Strait, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15125, https://doi.org/10.5194/egusphere-egu23-15125, 2023.

X3.34
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EGU23-1036
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GM6.3
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ECS
Piyaphong Chenrai and Chawisa Phujareanchaiwon

The Late Cretaceous Rakopi Formation in the Deepwater Taranaki Basin is one of the most important source rocks and potential reservoirs in the Taranaki Basin. This study aims to interpret the depositional environments of the Rakopi Formation in the Deepwater Taranaki Basin by using seismic and well log interpretations. Based on seismic interpretation, the Rakopi Formation was interpreted to deposit in a delta setting which developed from the prograding delta into the distributary channels and swamps deposits on the delta plain. Sandstone distributions can be demonstrated from seismic attribute map in the prograding delta. Well log data provided significant source rock intervals consisting mainly of coal measures and were developed in the delta plain setting. The results from this study also shown that the coal intervals are generally corresponding to high negative amplitude reflections. Thus, integration of seismic and well log data can be used to reveal reservoir and source rock distributions in the petroleum exploration areas.

How to cite: Chenrai, P. and Phujareanchaiwon, C.: Depositional Environment of the Late Cretaceous Rakopi Formation in the Deepwater Taranaki Basin, New Zealand, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1036, https://doi.org/10.5194/egusphere-egu23-1036, 2023.

X3.35
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EGU23-2529
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GM6.3
Young-Jun Kim, Jong-Hwa Chun, Gee-Soo Kong, Mario E. Veloso Alarcon, Deniz Cukur, Youngho Yoon, Jung-Ki Kim, and Joung-Gyu Choi

Since most of the shallow gas is composed of methane, studies on its availability as a resource and global warming are being conducted. A gas flare is called a phenomenon in which shallow gas escapes from the sub-bottom into the seawater. Gas flares cause seafloor deformation and can trigger large-scale geohazards such as landslides and tsunamis. We discovered the gas flares in 2021 and 2022 by conducting seismic and acoustic surveys using R/V TamaheⅡ seismic vessel at the southeastern continental shelf of the East Sea in Korea. The gas flares were detected on the water column data obtained by an EK60 of 38 kHz frequency and a multi-beam echo sounder of 20 – 40 kHz frequency bands (Kongsberg EM2040). We observed the deformation of the seafloor and sub-bottom using a Chirp sub-bottom profiler (SBP) of 2 – 7 kHz frequency bands (FalMouth HMS-622 CHIRPceiver). The water depth of the survey area ranges from 130 to 140 m. Four gas flares are distributed within approximately 3.5 km in a northwest-southeast direction. The height of the gas flare is about a maximum of 100 m from the seafloor. The seafloor where the gas escaped was observed to deform into dome shapes and pockmark. Additionally, we performed the seismic survey using a 60 in3 mini GI gun and a 48-channel streamer cable with a 12.5 m group interval to detect the source layer of shallow gas and the migration pathways. We tried using VBALab software to quantify the gas flow rate on the acoustic data of EK60.

How to cite: Kim, Y.-J., Chun, J.-H., Kong, G.-S., Alarcon, M. E. V., Cukur, D., Yoon, Y., Kim, J.-K., and Choi, J.-G.: Case study on the detection and quantification of the gas flares on the southeastern continental shelf of the East Sea, Korea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2529, https://doi.org/10.5194/egusphere-egu23-2529, 2023.

X3.36
|
EGU23-3829
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GM6.3
Chia-Ming Lo, Yu-Sen Lai, and Kai-Chin Ma

At present, the construction technology of offshore wind power of Taiwan is mostly based on foreign case experience and related design standards. However, the long-term scour effect of the Taiwan current will take away the soil around the pile foundation with the current, thus reducing the embedding depth of the foundation and reducing the stability of the foundation. In addition to being affected by loads such as wind and waves, the offshore wind power foundation is also the key to the overall design of the interaction between the seabed soil and the offshore wind power foundation. Therefore, this study adopts the method of discrete element method coupled with fluid mechanics to deeply explore the pore water pressure and stress changes inside the seabed soil during the seabed scour process around the offshore wind power foundation, and also explores the seabed under different scour mechanism scenarios for offshore wind power foundations. The results of this study show that the sand density of the seabed has a significant impact on the development of the scouring pit. The greater the sand density, the smaller the scouring depth, and the horizontal and vertical development of the scouring pit will also be reduced. the higher the sand density of the seabed, the smaller the lateral displacement of the single pile foundation affected by the erosion effect, which means the higher the lateral bearing capacity that the seabed sand can provide to the monopile foundation.

Key words: scour effect, the offshore wind power foundation, discrete element method, scour process; monopile.

How to cite: Lo, C.-M., Lai, Y.-S., and Ma, K.-C.: Study on the influence of seabed scour on monopile stability of offshore wind power by discrete element method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3829, https://doi.org/10.5194/egusphere-egu23-3829, 2023.

X3.37
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EGU23-7610
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GM6.3
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ECS
|
Yi-Chin Lin and Jing-Yi Lin

After the Ml 5.8 Hualien earthquake occurred the 4 February 2018, the power of the submarine cable seismic and tsunami observation system of Taiwan's Central Weather Bureau (CWB) has been shut down for several days, and the attitude of one of the OBS, EOS4, shown 37° rotation and an increase of pressure by an equivalent of 4 meters in depth after the power restoration. To find the actual position of this station, we applied the method of Trabattoni et al. (2020), which calculated the cepstrum based on the time difference between the direct and first reverberation wave of ship noise. However, the flat seabed assumption in this approach may not be suitable for EOS4 which is characterized by a dramatic topography variation. In our study, we developed a Fortran program to calculate the travel time curve by incorporating bathymetry variation and compared it with the result obtained by using active sources to assess the applicability of the program. The result shows the bathymetry variation does affect the OBS relocation. Apart from the position difference, the time difference between the observed and theoretical cepstrum curves could be induced by bathymetry variation. In addition, signal strength indicates the roughness and material of the area around the reflection point. To investigate the drift of EOS4, we select the AIS data of cargo ships within a radius of 30km from the EOS4 for two different time periods, which are 2/1-2/4 15:00 and 2/6-2/15, before and after the 2018 ML 5.8 earthquake. We select 27 and 76 ship traces has significant signals for two time periods, respectively. The minor change in the lateral direction of the cepstrum shows that the site location after the earthquake could not drift for a long distance, but the 0.2s time difference in the vertical direction of the cepstrum could indicate that the site has been buried, which is in the agreement of the pressure change of the station. The energy ratio of the hydrophone and the vertical channel of seismometer decreases at relatively lower frequencies and increases at higher frequencies. This phenomenon also supports our estimation. In addition, based on the cepstrum obtained from the ship tracks for a different direction, we obtained the time difference distribution in two dimensions, which may provide a new approach for bathymetry variation monitoring.

How to cite: Lin, Y.-C. and Lin, J.-Y.: Submarine cable drifting and landslide investigation based on ship noise recorded by seismometer, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7610, https://doi.org/10.5194/egusphere-egu23-7610, 2023.

X3.38
|
EGU23-16236
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GM6.3
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ECS
|
Highlight
Samaneh Baranbooei and Christopher J. Bean

Traditionally, there are different approaches to monitoring the ocean wave field consisting of 1) measurements using insitu buoys, 2) numerical ocean wave modeling using wind forecast, and 3) satellite altimetry. Each of these ocean wave monitoring techniques has their own advantages and disadvantages associated with their spatial and temporal resolution. For example, buoys are physical point measurements with excellent temporal resolution (e.g., sub-hourly), but their spatial resolution is very poor (e.g., a single point in space). Buoys are also expensive to maintain; ‘Real-time’ wave height estimations from numerical wave modeling is based on forecast wind, hence the model accuracy is dependent on wind prediction accuracy.  Compare to buoys, the temporal resolution of available outputs from large-scale numerical models is usually low (e.g., every 3 hours), but the spatial resolution is much better (various resolutions depending on the grid size); Satellite altimetry looks over a large region so the spatial coverage is very good but the temporal resolution is very poor (e.g., once every four days). In this work, we consider terrestrial seismic (microseism) data as a proxy for wave heights. Under certain conditions, it has the potential for combined good spatial and temporal resolution, in quasi-real time. 

This technique is based on the relationship between secondary microseism amplitudes recorded on land and the ocean wave-wave interactions which excite the sea floor, generating these secondary microseisms.  Here we take a data-driven approach, implementing an Artificial Neural Network (ANN) to quantify the complex underlying relationship between ocean wave height and microseism amplitude. Thus far we trained the ANN using the available seismic and numerical simulated data and then used the trained ANN to estimate significant Ocean Wave Height (SWH) at a particular location(s) in the Northeast Atlantic using amplitudes from seismic stations distributed across Ireland.

Our preliminary results look very promising and show relatively small residuals for measured wave height using the ANN compare to the real buoy data for both small and moderate wave heights.  However, currently larger residuals are seen for the largest ocean wave heights. We expect this to improve as ever more data becomes available.  

How to cite: Baranbooei, S. and Bean, C. J.: Estimations of the Ocean Wave Heights using terrestrial seismic data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16236, https://doi.org/10.5194/egusphere-egu23-16236, 2023.