GM6.3

Subaqueous spreading is a widespread type of mass movement, which involves extensional displacement along a gliding plane and the deformation of the failing layer into a sequence of ridges and troughs. Spreading has been poorly investigated, nonetheless it poses hazard to offshore infrastructures. SubSpread is a new project that will investigate the mechanics of the spreading failure and its geological controls in the subaqueous environment. The first objective of SubSpread is to identify the topographic and sedimentary signature of subaqueous environment. We have compiled a global database of subaqueous and subaerial spreads that includes information on physiography, geomorphology, sedimentology and geotechnical properties, where available. A preliminary analysis of the database reveals that spreading morphologies occur on both passive and active margins, especially in the headwall area of translational retrogressive slides. Potential causes of spreading include seismic loading (also glacially induced), sediment loading, and increased pore pressure generated by migration of fluid or gas. The latter may induce loss of shear strength and the formation of a weak layer, particularly in gentle open slopes. Information compiled in this database will also be used to develop a numerical model that can better understand the mechanics and rheological aspects of submarine spreading, focusing on the role played by pore pressure generation. The Tuaheni slide complex in the Hikurangi Margin of New Zealand is being used as a case-study in view of the wealth of geophysical and sedimentological data that are available. The final part of the SubSpread project will test whether the morphometric and sedimentological signature of spreading can provide information on past seismicity. In this case, the test site will be Lake Tekapo in the South Island of New Zealand.

How to cite: Giona Bucci, M., Micallef, A., Urlaub, M., and Mountjoy, J.: SubSpread: An integrated approach to understand the signature, mechanics and controls of subaqueous spreading, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13520, https://doi.org/10.5194/egusphere-egu21-13520, 2021.

Bathymetric data is commonly visualized as a simple shaded relief, where features oriented parallel to the light source are prone to false topographic perception or are even obscured to the viewer. On the other hand, many relief visualisation techniques developed in past decades are extensively used in visualisation and analysis of high-resolution digital elevation models, especially in geomorphological and archaeological studies. We tested and assessed the suitability of relief visualisation techniques provided by the Relief Visualisation Toolbox (RVT) software for representation of bathymetric data. We used a multibeam-sonar derived bathymetric model with a 10 x 10 m cell size from the Gulf of Trieste (northern Adriatic) characterised by a shallow low-relief seabed. Our results clearly demonstrate the effectiveness of relief visualisation techniques for exposing subtle relief variation in bathymetric data. We find that small-scale features (outcrops, wrecks, pockmarks, reefs, etc.) and negative linear features are best highlighted by “visualization for archaeological topography” (VAT) and “openness” techniques. High-relief features and topographic infection points are pronounced by “hillshade from multiple directions” and “sky-view factor” (SVF). Finally, “principal components analysis” (PCA), “prismatic openness”, “simple local relief model”, “anisotropic SVF” and “local dominance” algorithms show best results when we want to highlight both high- and low-relief features in one image. The tested techniques are far superior to a simple hillshade visualisation especially when imaging low-gradient relief (common on continental shelves and abyssal plains) where topographic details are often not adequately pronounced by hillshading. To our knowledge, this study represents the first attempt to test and compare several relief visualisation techniques for bathymetric data.  

How to cite: Novak, A., Poglajen, S., and Vrabec, M.: Enhancing subtle seafloor relief variation: relief visualisation techniques for bathymetric data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13105, https://doi.org/10.5194/egusphere-egu21-13105, 2021.

The work presents the results of applying SIMULIA Abaqus's capabilities to solve problems related to infrastructure development in the development of oil and gas fields on the continental shelf. The primary attention is paid to the stability of the load-bearing structures of infrastructure facilities. When developing oil and gas fields located in the continental shelf, several geomechanical problems not typical for onshore fields arise. First of all, there is a need to construct a detailed model of the mechanical properties of the upper layers of bottom sediments in conditions of limited data on these properties. This limitation of data is caused by the complexity and cost of engineering drilling, which in other conditions provides the necessary information regarding the properties of the upper layers of sediments. Current study describes the proposed set of methods for studying the mechanical properties of the upper layers of bottom sediments using sampling. It is shown that the process of bottom sampling itself makes it possible to estimate the mechanical properties of bottom sediments. Quantitatively, such estimations can be made based on a numerical solution of the contact problem of gravity corer indentation into visco-elastoplastic medium, the specific rheological properties of which are a priori unknown. The possibility of determining the possible values of these properties from the data obtained in the sampling process (the dependence of the acceleration of the contact point on time) is demonstrated in the study with solution of the inverse problem.

How to cite: Dubinya, N., Nachev, V., and Sergey, T.: Numerical Modeling of Sampling Seafloor Sediments to Study Their Rheological Properties, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15812, https://doi.org/10.5194/egusphere-egu21-15812, 2021.

Seamounts are spectacular bathymetric features common within volcanic and tectonically active continental margins. During their lifecycles, they evolve through stages of construction and destruction. Seamount chains on the Southwest Iberian Margin are prone to instability and collapse due to regionally complex tectonism with moderate to high seismicity. In this work we investigate collapse episodes during the lifecycle of the tectonic Gorringe Bank (GB), the largest submarine seamount offshore European margins, based on recurrence patterns of MTDs on the active thrust flank. Eight MTDs with relevant expression on the seismic data were analysed, four of estimated Miocene age and four on a Pliocene-Quarternary interval. Miocene MTDs are overall larger and correlate with the main uplift stages of the GB structure. Their distribution and relative timing suggest that failure-triggering earthquakes were common along the whole length of the GB. Pliocene to Quarternary MTDs tend to cluster along the northern half of the GB flank and are generally smaller. Based on our observations, we propose that the lifecycle of tectonic seamounts is marked by morphological rejuvenation episodes driven by tectonic activity between major collapse events or cycles. Tectonic-driven rejuvenation is thus key to hinder or obliterate evidence of past high-magnitude destructive events on tectonic seamount morphology.

How to cite: Gamboa, D., Omira, R., Piedade, A., Terrinha, P., Roque, C., and Zitellini, N.: Morphological rejuvenation on tectonic seamounts: insights from the Gorringe Bank, SW Iberian Margin, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12712, https://doi.org/10.5194/egusphere-egu21-12712, 2021.

Submarine landslides are major geohazards occurring on distinct seabed domains ranging from shallow coastal areas to the deeper points of the ocean. The nature and relief of the seabed are key factors influencing the location and size of submarine landslides. Mass-failures on the continental slopes are frequent, but collapses on and along chains of oceanic seamounts and ridges can account also for a high frequency of events. Regardless of their area of occurrence, submarine landslides are a major hazard that needs to be recognised and categorised. For this purpose, numerous efforts have been made to compile databases of submarine landslides with the aim to better understand their distribution and characteristics on marine settings around the world.

This work presents the initial efforts of the MAGICLAND (Marine Geo-hazards Induced by underwater Landslides in the SW Iberian Margin) database which, based on bathymetric DEMs available through EmodNET, compiled geomorphological properties of 1552 morphological scars and submarine landslides offshore West and Southwest Portugal. These are distributed through seven morphological domains: 1) canyons incising the continental slope (232 landslide episodes); 2) continental slope (233 landslide episodes); 3) large seamounts (437 landslide episodes); 4) submarine ridges and small seamounts (263 landslide episodes); 5) Gulf of Cadiz (226 landslide episodes); 6) Gulf of Cadiz banks and channels (123 landslide episodes); and 7) Estremadura Spur (38 landslide episodes). A wealth of 43 parameters were measured or calculated, which include a subset of morphological quantifications for the evacuation and deposit sections for 347 occurrences where the latter was observed. We present the morphological data and any derived computations as measured on the 3D surface in order to increase their accuracy and mitigate the effect of slope gradient on map-based 2D analysis. The larger events were recorded on the large seamounts and the ridges domains, which also correspond to the larger recorded landslide heights (measured as the difference between minimum and maximum depths). Good correlations (coefficient of determination R²>0.8) where obtained for Area-Volume, Width-Area, and Length-Area relationships. Where evacuation and deposit sections were discernible, their area relationships present a better correlation compared to their lengths.

Further stages of the database development will involve the addition of still unmapped scars, as well as further statistical analysis and integration with available geophysical and geotechnical datasets for the areas of study. This dataset will be made available for the free use and benefit of the international marine community. Further contributions or analysis based on, and complementing the MAGICLAND database will be welcome.

This work is supported by the FCT funded project MAGICLAND - MArine Geo-hazards InduCed by underwater LANDslides in the SW Iberian Margin (Ref: PTDC/CTA-GEO/30381/2017).

How to cite: Omira, R., Gamboa, D., and Terrinha, P.: The MAGICLAND (Marine Geohazards InduCed by LANDslides) database: Early results on submarine landslide distribution and morphometrics offshore Portugal, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12602, https://doi.org/10.5194/egusphere-egu21-12602, 2021.

The north-western Mediterranean continental margin is one of the few regions in the world where bottom trawling has been continuously practised since several decades. Among the existing trawling techniques, the one practised on this region is the "otter trawling", which has a strong impact on the seafloor morphology via scraping and ploughing, especially on muddy substrates. High-resolution multibeam bathymetry and backscatter data, side scan sonar images, sediment cores and satellite based Vessel Monitoring System (VMS) data have been integrated to investigate the impact of bottom trawling on the seafloor morphology of the northern Catalan continental shelf (NW Mediterranean). Satellite-based navigation tracks from bottom trawlers operating in the study area during 6 years (2006-2011) reveal the spatial distribution of fishing grounds and the occurrence of an intense trawling effort around the 50-60 m isobaths, since trawling is banned at shallow depths. Backscatter imagery shows a narrow (120-250 m wide) and discontinuous high backscatter facies along this depth range, extending parallel to the coastline for more than 40 km from Portbou to l’Estartit. In the bathymetric data, this high backscatter region also coincides with an abrupt change in the mean seafloor gradient (from 0.8° in the inner shelf to 0.4° in the middle shelf), or locally with a narrow (50-150 m wide) slightly depressed (0.2-0.6 m deep) channeled morphology. Side-scan sonar images display high density of trawl marks generated by fishing gears in this area. Further offshore, scattered narrower trawl hauls are also observed on the middle shelf (60-90 m deep), where they can be traced across several thousands of meters. Sediment cores retrieved from the area of high backscatter and largest trawling intensity display sediment coarsening in the upper layers (0-4 cm) caused by winnowing of finer fractions. These findings demonstrate that chronic stirring, mixing and erosion of surface sediments induced by recurrent trawling persisting over the same fishing grounds can cause long-term morphological and sedimentary changes on the continental shelf seafloor.

This study has received funding from the ABIDES (Assessment of Bottom-trawling Impacts in the Deep-sea Sediments) Spanish Research Project (CTM2015-65142-R) and the European Union's Horizon 2020 research and innovation programme under Marie Sklodowska-Curie grant agreement No. 867471. Additional funds were provided by the Generalitat de Catalunya Generalitat de Catalunya (2017 SGR-663 and -1588) and by the Spanish Research Project ABRIC (RTI2018-096434-B-I00). This work is contributing to the ICM’s ‘Center of Excellence’ Severo Ochoa (CEX2019-000928-S). The authors wish to thank the Secretaría General de Pesca and Tragsa for the 2004 Espace Project dataset.

How to cite: Durán, R., Puig, P., Muñoz, A., Lo Iacono, C., Guillén, J., Micallef, A., and Palanques, A.: Long-term seafloor morphological changes generated by bottom trawling on the northern Catalan continental shelf (NW Mediterranean), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9713, https://doi.org/10.5194/egusphere-egu21-9713, 2021.

Given the potentially devastating consequences of shallow submarine landslides on infrastructure and human lives, it is imperative that we understand potential slope stability issues within marine coastal regions. In Scottish waters, our lack of knowledge regarding the nature of the seabed within the fjords and coastal inlets is concerning given that these sea lochs have similar morphological features and settings to global examples (e.g. Norway) where recent slope failures have had such highly devastating results. Global examples from similar physiographic settings also demonstrate the temporal aspect of these events, highlighting that they are caused by active modern processes and therefore represent contemporary geohazards. In addition, previous studies have highlighted that there tends to be a scale bias towards the mapping and reporting of large-scale events, and there is a requirement for studies that focus on small-scale (≤1 km³) mass movements which can still have damaging consequences on seafloor and coastal (both nearshore and onshore) infrastructure.

In this study, a review of multibeam echo sounder (MBES) survey datasets from five locations around the United Kingdom northwest coast has led to the identification of a total of 14 separate submarine mass movement scars and deposits within the fjords (sea lochs) and coastal inlets of mainland Scotland, and the channels between the islands of the Inner Hebrides. In these areas, Quaternary sediment deposition was dominated by glacial and glaciomarine processes. Analysis of the morphometric parameters of each submarine mass movement has revealed that they fall into four distinct groups of subaqueous landslides; Singular Slumps, Singular Translational, Multiple Single-Type, and Complex (translational & rotational) failures. The Singular Slump Group includes discrete, individual subaqueous slumps that exhibit no evidence of modification through the merging of several scars. The Singular Translational Group comprise a single slide that displays characteristics associated with a single translational (planar) failure with no merging of multiple events. The Multiple Single-Type Group incorporates scars and deposits that displayed morphometric features consistent with the amalgamation of several failure events of the same type (e.g. debris flows or slumps). Finally, the Complex (translational & rotational) Group comprises landslides that exhibited complex styles of failures, including both translational and rotational mechanisms controlling the same slide. The submarine mass movements that comprise this dataset are then discussed in relation to global fjordic and glaciomarine nearshore settings, and slope failure trigger mechanisms associated with these environments are described with tentative links to individual submarine landslides from the database, where appropriate. It is acknowledged that additional MBES data are needed not only to expand this database but also to create a more statistically robust study. However, this initial study provides the basis for a much wider investigation of submarine mass movements and correlations between their morphometric parameters.

How to cite: Carter, G., Cooper, R., Gafeira, J., Howe, J., and Long, D.: Morphology of small-scale submarine mass movement events across the northwest United Kingdom, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15380, https://doi.org/10.5194/egusphere-egu21-15380, 2021.

High-latitude fiords are susceptible to hazardous subaerial and submarine slope failures. Recent investigations have shown that past slope failures in fiords of Greenland and Alaska have generated devastating landslide induced tsunamis. Since coastal communities inhabit these high-latitude fiords, it is critical to understand the slope failure recurrence time, their distribution, potential triggers, and ability to generate tsunamis. In this study, we identified > 50 near-surface submarine landslides in Pangnirtung Fiord, eastern Baffin Island, Nunavut, using multibeam bathymetric and sub-bottom profiler data, along with sediment gravity-cores collected in 2019. Morphometric and morphological analyses, along with sedimentological analyses, were carried out on submarine landslide deposits to quantify their spatial and temporal distribution throughout the fiord and to evaluate the factors that may have triggered the slope failures.

Combining bathymetric with topographic data from unmanned aerial vehicle imagery, we found that most of these landslide deposits are relatively small (~ 0.08 km²) and are associated with outwash fans and steep fiord sidewalls. However, since most slope failure head scarps lie between the intertidal zone and ~30 m water depth, they could not be mapped, which makes it challenging to determine the triggers of the submarine slope failures. Radiocarbon dating reveals that most of these surficial landslide deposits are younger than 500 years old and that they were most likely triggered at different times. This finding highlights a high recurrence rate of slope failures within the fiord, suggesting that localised triggers are responsible for slope failures within the fiord, as opposed to widespread, seismically induced triggers which do not occur as frequently in the study area. In addition, the elongated morphology of the landslide deposits and the varying degrees of landslide deposit surface roughness supports localised point-source triggers. Since most landslides are associated with subaerial outwash fans and deltas, we suggest that triggers of these relatively frequent submarine landslides within Pangnirtung Fiord include rapid floodwater input, subaerial debris flows, and sea-ice loading during low tide.

This research shows that slope failures in a high-latitude fiord are affected by the interaction of numerous subaerial and submarine processes, leading us to speculate that a potential increase in the frequency of subaerial debris flows and river floods due to climate change may increase the recurrence of submarine landslides.

How to cite: Sedore, P., Normandeau, A., and Maselli, V.: Investigating the controls of submarine landslides and associated hazards in Pangnirtung Fiord, Eastern Baffin Island (Nunavut), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13364, https://doi.org/10.5194/egusphere-egu21-13364, 2021.

For the last several years, the Institute of Limnology RAS has been conducting geological and geomorphological studies of the bottom of Lake Ladoga, the largest lake in Europe. Beginning in 2018, these studies began to use underwater photo and video camera, created at INOZ RAS. The use of this new research tool led to the discovery of a number of new facts of the structure of the bottom of Lake Ladoga. In particular, during the 2020 field season, the authors discovered in several areas of Lake Ladoga the existence of underwater subvertical scarps, composed of bedrocks. At the same time, the submarine towing boat stood in one place, and the camera vertically upward from depths of about 100 - 120 meters to depths of 20 - 30 meters. During this entire rise, the camera recorded the bedrock ledge with vertical and even negative angles. No traces of glacier processing were found, which indicates the Holocene age of the found scarps. In 2020, such ledges were found in 3 regions of Lake Ladoga: in a depression near the  Pitkyaranta in the northeastern part of the lake, in the Suuri-Viroluoto trench in the northern part of the lake and on the western underwater slope of Valaam Island. A mention of the possibility of the existence of such ledges (up to the first tens of meters in height) in the northern part of Lake Ladoga is found in the works of V.A. Rumyantsev and V.N. Rybakina (2012), A.V. Amantov (2014), Bolshiyanov (2018). M.A.Naumenko, who studied the underwater slope of Valaam Island, considered the maximum angle of this slope to be 60 degrees (2019). We found sub-vertical ledges up to 100 meters high. In addition, these scarps are in spatial relationship with the existing tectonic faults, confirming their significant fault component. The presence of young vertical high ledges at the bottom of Lake Ladoga indicates powerful young tectonic movements in this region.

How to cite: Anokhin, V., Dudakova, D., and Dudakov, M.: Tectonic ledges at the bottom of Lake Ladoga, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1789, https://doi.org/10.5194/egusphere-egu21-1789, 2021.

Submarine canyons are morphological features found along continental margins that play a key role channeling and connecting sediment from continental shelves to the abyssal plains. The current morphological characterization of the Blanes and Cap de Creus canyon heads, located on the Catalan continental margin (NW Mediterranean Sea), has been recently conducted during the CRIMA cruise in September 2020 using high-resolution (4 m grid size) multibeam bathymetry data. These data have been compared with a previous dataset collected in 2004 during the ESPACE project to evaluate the morphological changes during this 16-year interval. Since these canyon heads are located at shallow water depths and at short distances from the shoreline, their short-term evolution is related to the sediment dynamics on the continental shelf.

A large-scale change in the seafloor morphology was observed in the Blanes canyon head, indicating the prevalence of erosion in the western canyon rim and non-deposition in the eastern rim. In the Cap de Creus canyon head, the excavation of pre-existing erosive structures was also evidenced in the southwestern canyon rim. These changes mainly happen in the area where the shelf is narrower, which coincide with the main zone of dense water advection along the shelf and toward the canyon interior. The different small-scale morphological evolution between both canyon heads seems to be related to the local geological characteristic of the subsurface deposits of the continental shelf. The Blanes canyon head incises a succession of relict (Holocene) sediment bodies that can act as a source of erodible sediments to the canyon, mainly during strong storms. The continental shelf in the vicinity of the Cap de Creus canyon head, however, is characterized by a rocky substratum (Paleozoic) with a limited sediment coverage and numerous erosive features that evidence relative sand starvation. This creates a greater erosive resistance, although the erosive character of strong storms and major dense-shelf water cascading events occurring during the studied time interval is evident. Additionally, small changes in the shelf bedforms indicate that such high-energetic oceanographic processes also modify the fine-scale seafloor morphology.

These results reveal that both submarine canyon heads are dynamic and sensitive to oceanographic processes that enhance the erosion and transport of sediment from the shelf into the canyon, particularly during energetic storms and dense shelf water cascading events. Nevertheless, their small-scale evolution seems to be closely related to the type of geological substrate of the shelf on which they are developing.

This study has received funding from the ABRIC (RTI2018-096434-B-I00) and CRIMA (RTI2018-095770-B-I00) Spanish Research Projects, the European Union's Horizon 2020 research and innovation programme under Marie Sklodowska-Curie grant agreement No. 867471 and the Generalitat de Catalunya (2017 SGR-663 and -1588). This work is contributing to the ICM’s ‘Center of Excellence’ Severo Ochoa (CEX2019-000928-S). The authors thank the Secretaría General de Pesca and Tragsa for the 2004 ESPACE Project dataset.

How to cite: Cabrera, C., Durán, R., Puig, P., Guillén, J., Muñoz, A., Demestre, M., and Palanques, A.: Short-term evolution of submarine canyon head morphologies in the NW Mediterranean: Blanes and Cap de Creus canyons, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12286, https://doi.org/10.5194/egusphere-egu21-12286, 2021.

In October 2020, during the marine expedition FocusX1 onboard the research vessel PourquoiPas? microbathymetric mapping was performed using the ROV Victor6000. The main goal was to map the seafloor expression of the North Alfeo fault and select the best path for deployment of a 6-km long fiber optic strain cable designed to monitor movement along the fault and the deployment sites for 8 geodetic stations.

Bathymetric data were collected through a Reson Seabat 7125 multibeam echosounder (400 kHz). ROV navigation data were processed using DelphINS, resulting in an optimal merging of navigation sensors (GPS, USBL, DVL, pressure). The MBES data processing (GLOBE software) mainly consisted in estimating and correcting static angular offsets, applying actual in-situ sound speed profile, and finally performing an automatical and manual soundings filtering.

The resulting bathymetric grid spans a region of roughly 3 km x 1.5 km, with a 1m cell size, and allows  us to identify a variety of morphological features:

1 - a set of narrow, linear, E-W oriented gulleys, all parallel (not merging/branching) on a regional E dipping 5-15° slope

2 - a striking, continuous curvi-linear feature, which is interpreted as the primary surface expression of the fault.The fault morphology changes from a smooth less than 10 m depression in the NW to a up to 10-20m high scarp with slopes of 20-30°, and locally sub-vertical cliff faces.

3 - a local bathymetric plateau (mesa like feature) with a gently E-dipping summit region, showing signs of eastward sliding / rafting tectonics, indicated by N-S oriented gashes/depressions.

The 3-km long segment of the fault covered by our survey includes the mesa-like bathymetric high (at the NW extremity) interpreted as a transpressional pop-up feature and an elongated, fault bounded trough (at the SE extremity) interpreted as a transtensional pull-apart basin. Video-camera images recorded by ROV Victor6000 from the seafloor provide visual documentation of the fault scarp and seafloor morphology. Future surveys with a sub-bottom profiler and/or HR- seismics can help confirm these interpretations. The ongoing monitoring with the fiber-optic strain cable is being calibrated by a 3-4 year deployment of seafloor geodetic instruments (Canopus acoustic beacons manufactured by iXblue) which started in Oct. 2020, and will allow us to quantify relative displacement across the fault.

How to cite: Gaillot, A., Gutscher, M.-A., Murphy, S., and Klingelhoefer, F.: Micro-bathymetric mapping of the North Alfeo strike-slip fault (offshore Catania Sicily): preliminary results from the FocusX1 expedition, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2731, https://doi.org/10.5194/egusphere-egu21-2731, 2021.

Bathymetric models representing the topography of the seafloor are an important parameter in almost all maritime related research. Traditional bathymetric shipborne or airborne surveys are cost and/or time consuming, and access to the measured data is mostly limited or expensive. Alternative bathymetric data sources for marine researchers are publicly available bathymetric models whose quality is often unknown and/or uneven. This research presents the study on the bathymetric prediction for the Adriatic Sea from altimetry-derived gravity anomalies and in-situ soundings using the gravity - geologic method (GGM). Bathymetric soundings used to determine the density contrast between seawater and bedrock were derived from nautical charts, EMODnet (European Marine Observation and Data Network) bathymetric grid, and GEBCO (General Bathymetric Chart of the Oceans) One Minute grid. More than 3000 chart soundings distributed across the Adriatic Sea were used to estimate the quality of the predicted bathymetric model as well as the quality of the latest versions of publicly available bathymetric models: DTU10Bat (Technical University of Denmark), GEBCO 2020, EMODnet 2018, ETOPO1, Smith and Sandwell v.19.1, and SRTM (Shuttle Radar Topography Mission) 15+ V.2.1. The results show that the computed model represents an update to bathymetric data in the Adriatic Sea, especially along its eastern coast.

How to cite: Vrdoljak, L., Grgić, M., and Bašić, T.: Bathymetry estimation from altimeter - derived gravity data in the Adriatic Sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-660, https://doi.org/10.5194/egusphere-egu21-660, 2021.

Submerged paleolandscapes constitute records of long-term paleoenvironmental change, climate, and sea level. To date, there is a very limited knowledge concerning the submerged karst paleolandscapes of the eastern Adriatic coast and the Late Quaternary sedimentary sequences along the eastern part of the Mid Adriatic Deep (MAD). We aim to improve this through the project “Sediments between source and sink during a Late Quaternary eustatic cycle: The Krka and the Mid Adriatic Deep System” (QMAD). The QMAD project supports multidisciplinary research by application of the high-resolution geophysical surveys (multibeam, side-scan sonar and sub-bottom profiler), in combination with sedimentological, petrophysical, geochemical (trace elements and isotopes), micropaleontological (ostracod and foraminifera), mineralogical and aDNA techniques. This suite of analyses will enable tracking of the paleoenvironmental evolution from fluvial/lake to deeper marine environments, on a short transect less than 100 km in length (Lake Prokljan in the Krka River estuary to the eastern part of MAD). The submerged Late Pleistocene and Holocene environments that occur include isolation basins, lagoons, deltas, estuaries, submarine channels and shelf. The continuous marine sedimentation during the Late Quaternary is investigated in the MAD. In the case of the central part of the eastern side of the Adriatic Sea (Krka catchment - MAD) these different environments compose an integrated system; thus, they can’t be analysed separately. The main goals of this project fill the existing gaps in understanding of the climatic and environmental changes, including sea-level related landscape changes and their interplay during the Late Quaternary eustatic cycle. More data on the Pleistocene environments, especially from the region of Krka estuary that was land during the Last Glacial Maximum (LGM), will complete the picture of the evolution and environmental adaptation of Paleolithic humans and their relationship with vegetation changes. Attention is also paid to potential anthropogenic environments, recent sedimentation rates, landscape features and artefacts. All results of the multi-proxy approach applied in this project will eventually be merged into a comprehensive Late Quaternary paleoenvironmental and paleoclimatic reconstruction of the eastern Adriatic landscapes that contribute to the understanding of these changes in the Mediterranean region.

How to cite: Miko, S. and the QMAD Project Team: Submerged landscapes of the eastern Adriatic – from the river across the lake all the way to the sea, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12177, https://doi.org/10.5194/egusphere-egu21-12177, 2021.

The ongoing tectonism in the Western Anatolia creates N-S extension and counter-clockwise rotational motion along the right-lateral North Anatolian fault (NAF) and left-lateral East Anatolian Fault (EAF). This continental extension creates predominantly E-W extending onshore grabens rarely NE to SW and NW to SE trending onshore/offshore grabens characterised by the intense seismic activity, high heat flow associated with volcanism, crustal thinning and geothermal systems. Our study area, the gulf of İzmir, has an “L” shape composing of an E-W oriented inner bay from İzmir to Urla and incompatibly NNW-SSE oriented outer bay between offshore Foça and Karaburun. It is located at the intersection of the E-W oriented onshore Gediz Graben and NE-SW oriented onshore Bakırçay graben. Geophysical evidence for fluid discharge and subsurface gas-associated structures such as gas chimneys, pockmarks, mud diapirs and acoustic turbidity zones have been detected in the inner and outer parts of the Gulf of İzmir by the previous studies. For this reason, the Gulf of İzmir and the adjacent onshore grabens are areas of great interest for further study of the region.

In this study, the 3-D stratigraphic architecture (up to 1.5 km) and the Upper Miocene-Pliocene depositional settings of the Gulf of İzmir reconstructed by reflection tomography for the first time. Three seismic stratigraphic units, labelled SSU1, SSU2 and SSU3 from bottom to top, were identified by their bounding unconformity surfaces (H1-H5). We have subdivided unit SSU1 into three subunits named SSU1c-SSU1a. The acoustic basement associated with SSU3 is likely tied to the Lower-Middle Miocene Yuntdağ Volcanics consisting of tuffs, sandstones, limestones and volcanics. The upper surface of SSU3 (horizon H5) is marked as a major regional unconformity representing a basin-ridge morphology. The first rocks deposited on top of acoustic basement (SSU2) correspond to the sandstones, limestones, volcanics and shales of the Bozköy Formation and the limestones of the Ularca Formation, dating from the Late Miocene to the Pliocene. The top of SSU2 (horizon H4) is interpreted as another unconformity and is correlated with the Pliocene unconformity. Above that, part of the Bayramiç Formation (SSU1c) is dated as Quaternary, consisting of conglomerates at the base overlain by sandstones and shales above. On top of the SSU1c are two further sub-units of the Bayramiç Formation separated by horizons H3 and H2. SSU1b consists of a similar sequence of conglomerates, sandstones and shales; SSU1a consists of Quaternary sandstones. Following the tomographic analysis, the isopach map of the Plio-Quaternary sediment fills was derived from the depth of interpreted horizons calculated using tomographic interval velocities. According to the isopach map of the sedimentary fills, thickness abruptly decreasing from NW to SE. The maximum thickness of total sedimentary succession is ~1400 m in the NW, whereas the thickness decreases through the west, east (up to ~450 m) and the southeastern flank of the basin, reaching ~150 m forming a ridge. A few local lateral velocity variations were identified within the Plio-Quaternary sedimentary succession associated with faults, fluid escape and shallow gas occurrences or a combination of these. 

How to cite: Altan, Z., Ocakoğlu, N., and Böhm, G.: 3-D Architecture and the Upper Miocene-Pliocene Depositional Pattern of the Gulf of İzmir by Reflection Tomography, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16246, https://doi.org/10.5194/egusphere-egu21-16246, 2021.

ABSTRACT

With the fast and highly growing demand for all possible ways of remote work as a result of COVID19 pandemic, new technologies using Satellite data were highly encouraged for multidisciplinary applications in different fields such as; agriculture, climate change, environment, coastal management, maritime, security and Blue Economy.

This work supports applying Satellite Derived Bathymetry (SDB) with the available low-cost multispectral satellite imagery applications, instruments and readily accessible data for different areas with only their benthic parameters, water characteristics and atmospheric conditions.  The main goal of this work is to derive bathymetric data needed for different hydrographic applications, such as: nautical charting, coastal engineering, water quality monitoring, sediment movement monitoring and supporting both green carbon and marine data science.  Also, this work proposes and assesses a SDB procedure that makes use of publicly-available multispectral satellite images (Sentinel2 MSI) and applies algorithms available in the SNAP software package for extracting bathymetry and supporting bathymetric layers against highly expensive traditional in-situ hydrographic surveys. The procedure was applied at SAFAGA harbor area, located south of Hurghada at (26°44′N, 33°56′E), on the Egyptian Red Sea coast.  SAFAGA controls important maritime traffic line in Red Sea such as (Safaga – Deba, Saudi Arabia) maritime cruises.  SAFAGA depths change between 6 m to 22m surrounded by many shoal batches and confined waters that largely affect maritime safety of navigation.  Therefore, there is always a high demand for updated nautical charts which this work supports.  The outcome of this work provides and fulfils those demands with bathymetric layers data for the approach channel and harbour usage bands electronic nautical chart of SAFAGA with reasonable accuracies.  The coefficient of determination (R²) differs between 0.42 to 0.71 after applying water column correction by Lyzenga algorithm and deriving bathymetric data depending on reflectance /radiance of optical imagery collected by sentinel2 missions with in-situ depth data values relationship by Stumpf equation.  The adopted approach proved to give  highly reasonable results that could be used in nautical charts compilation. Similar methodologies could be applied to inland water bodies.  This study is part of the MSc Thesis of the first author and is in the framework of a bilateral project between ASRT of Egypt and CNR of Italy which is still running.

Keywords: Algorithm, Bathymetry, Sentinel 2, nautical charting, Safaga port, satellite imagery, water depth, Egypt.

How to cite: Saeed, R., Abdelrahman, S., Scozari, A., and Negm, A.: Sentinel-2 mission Contribution for Supporting Bathymetric layers of SAFAGA coastal zone, Egypt, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14327, https://doi.org/10.5194/egusphere-egu21-14327, 2021.