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Offshore freshened groundwater (OFG) is groundwater with a salinity below that of seawater that is stored in sub-seafloor sediments and rocks. OFG has been proposed as an alternative solution to relieve water scarcity in coastal regions and to enhance oil recovery. Although OFG has been documented in most continental margins, we still have a poor understanding of the extent and flow characteristics of OFG systems, and their evolution through time. In view of the general absence of appropriate field data, paleohydrogeological models have been used. The majority of these models are based on 2D approaches, and they rarely consider the future evolution of OFG systems, especially in response to predicted climate change. Here we utilize recently acquired geological, geophysical and hydrogeological data from onshore and offshore the Maltese Islands, and employ 2D and 3D numerical models, to: (i) reconstruct the evolution of the onshore-offshore groundwater system during the last 188 ka, (ii) predict the evolution of the OFG system in response to climate-related changes. We show that the mechanisms emplacing OFG include a combination of active meteoric recharge at present as well as at sea-level lowstands. The Maltese onshore-offshore groundwater system is relatively dynamic, with 23% of groundwater being preserved in the last 18 ka. The control of geology is expressed by the more prevalent distribution of OFG north of the Great Fault, which is associated to the occurrence of low permeability units, and the asymmetry of the groundwater lens during the 18 ka lowstand. A 30% decrease in recharge predicted in the coming 100 years will diminish OFG extent by 38%, whereas sea-level rise will play a negligible role. At present the estimated volume of OFG is 1 km3, which could potentially provide an alternative supply of potable water to the Maltese Islands for 75 years. Exploitation of OFG with minimal salinization of onshore groundwater bodies would require locating pumping wells close to the coast.

This article presents the first evidence of bottom simulating reflectors (BSRs) on the continental margin of the western Indian Ocean, offshore Tanzania. The analysis of 2D and 3D seismic reflection data revealed two different types of BSRs. The Type 1 BSR, identified in water depths of 2250–2370 m west of the Seagap fault, shows a continuous reflection that mimics the seafloor, has a reverse polarity with respect to the seafloor and crosscuts the stratigraphy. Type 2 BSRs have been identified on the slope of the Tanzanian margin in water depths less than 1500 m. They are represented by a phase-reversed reflection that mimics the seafloor topography, revealing lateral variations in amplitude that are expressed as changes from high to moderate brightness. Modelling results show that gas hydrates of microbial origin (100% CH4) are stable in a minimum water depth of 740 m and a bottom water temperature of 9 °C, thus indicating a possible microbial origin for the type 2 BSRs. The thickest gas hydrate stability zone is observed within the Kerimbas Graben at water depths of up to 3621 m, with values ranging from 321.4–383.4 m for geothermal gradients of 5.4 °C/100 m and 6.4 °C/100 m, respectively. We suggest that the type 1 BSR may have a thermogenic gas source, as the observed BSR depths are deeper than the calculated base of the gas hydrate stability zone for 100% methane. The interpreted faults that crosscut the stratigraphy may have facilitated gas transport from deeper source rocks.

Highlights • Subaqueous spreading occurs on gently inclined surfaces (

X Congreso Geológico de España, 5-7 de julio 2021, Vitoria-Gasteiz.-- 1 page, [EN] Subaqueous landslides are of common occurrence in lacustrine, coastal and deep-marine environments. They pose a risk to coastal communities and offshore infrastructure. During the past decades geoscientists have made important contributions for improving the understanding of subaqueous landslides. Efforts in the field of geo-modelling have helped fill the gap between subaqueous landslide occurrence, dynamics and tsunami genesis. Nevertheless, other gaps like the causal mechanisms and timing of subaqueous landslides has drawn out the progress in the prediction, essential to implement appropriate mitigation measures. This complex issue can only be managed in a multidisciplinary approach. The study of subaqueous landslides spans a wide range of sub-disciplines: geologists studying the link between climate change and gas hydrate dissociation, planetary geologists using subaqueous landslides as terrestrial analogues, petroleum geologists evaluating the seal/ reservoir capacity of ancient subaqueous landslides, and engineers evaluating geotechnical risks. This project seeks to create an international and multidisciplinary platform allowing geoscientists from academia and industry to sustain a dialogue conducive to the integration of findings from different fields into a more cohesive understanding of subaqueous landslides, [ES] Subaqueous landslides are of common occurrence in lacustrine, coastal and deep-marine environments. They pose a risk to coastal communities and offshore infrastructure. During the past decades geoscientists have made important contributions for improving the understanding of subaqueous landslides. Efforts in the field of geo-modelling have helped fill the gap between subaqueous landslide occurrence, dynamics and tsunami genesis. Nevertheless, other gaps like the causal mechanisms and timing of subaqueous landslides has drawn out the progress in the prediction, essential to implement appropriate mitigation measures. This complex issue can only be managed in a multidisciplinary approach. The study of subaqueous landslides spans a wide range of sub-disciplines: geologists studying the link between climate change and gas hydrate dissociation, planetary geologists using subaqueous landslides as terrestrial analogues, petroleum geologists evaluating the seal/reservoir capacity of ancient subaqueous landslides, and engineers evaluating geotechnical risks. This project seeks to create an international and multidisciplinary platform allowing geoscientists from academia and industry to sustain a dialogue conducive to the integration of findings from different fields into a more cohesive understanding of subaqueous landslides

5th International Network for Submarine Canyon Investigation and Scientific Exchange International Symposium (INCISE), 14-18 June 2021, Bottom trawling is one of the most widespread fishing practices in the world’s oceans. It involves towing of nets to harvest benthic and demersal living resources. The dragging of trawling gears along the seafloor results in scraping and ploughing the seabed, which leads to the formation of turbid plumes of resuspended sediments, changes in the sediment erosion/accumulation rates and modifications of their fluxes and budgets, which results in measurable alterations of the submarine geomorphology. As submarine canyons are increasingly targeted by trawlers, there is a growing need to quantify, monitor and mitigate the impacts of bottom trawling in these environments. The TrawledSeas Project aims to quantitatively characterise the contribution of bottom trawling on the geomorphic evolution of submarine canyons, over a range of spatial scales, from fine (m–dam) to mesoscale (5–100 km). To address this objective, a new automated marine landscape mapping technique is being developed to quantify the morphological signature of bottom trawling, based on the analysis of high-resolution multibeam data implemented in a Geographic Information System (GIS). The proposed methodology integrates standard general (e.g. curvature, rugosity, roughness or fractal dimension) and specific (e.g. object-based image methods) geomorphic techniques with new ones developed in this project in a multiscale approach. It combines GIS open source tools with bathymetric dataset at different resolutions, from hull-mounted multibeam data to compare the large-scale morphology of trawled and untrawled areas, to Remotely Operated Vehicles (ROV) and autonomous underwater vehicle (AUV) bathymetric data to identify and quantify trawl marks at small spatial scale. Additionally, data from repeated surveys will be used to assess potential temporal changes in the seafloor morphology of new fishing grounds. The implementation of these geomorphological tools in different study sites incised by submarine canyons (e.g. Catalan, Malta-Sicilian, Norwegian, Canterbury, Patagonian and W Canadian continental margins), will allow to characterise the differential impact of bottom trawling on the canyons’ seafloor, in terms of extent, rates and volume change in different geologic and climatic settings

The sheared-passive margin offshore Durban (South Africa) is characterised by a narrow continental shelf and steep slope hosting numerous submarine canyons. Supply of sediment to the margin is predominantly terrigenous, dominated by discharge from several short but fast-flowing rivers. IODP Expedition 361 provides a unique opportunity to investigate the role of sea level fluctuations on the sedimentation patterns and slope instability along the South African margin. We analysed >300 sediment samples and downcore variations in P-wave, magnetic susceptibility, bioturbation intensity, and bulk density from site U1474, as well as regional seismic reflection profiles to: (i) document an increase in sand input since the mid-Pliocene; (ii) associate this change to a drop in sea level and extension of subaerial drainage systems towards the shelf-edge; (iii) demonstrate that slope instability has played a key role in the evolution of the South Africa margin facing the Natal Valley. Furthermore, we highlight how the widespread occurrence of failure events reflects the tectonic control on the morphology of the shelf and slope, as well as bottom current scour and instability of fan complexes. This information in important to improve hazard assessment in a populated coastal region with growing offshore hydrocarbon activities.

Landslides are common in aquatic settings worldwide, from lakes and coastal environments to the deep sea. Fast-moving, large-volume landslides can potentially trigger destructive tsunamis. Landslides damage and disrupt global communication links and other critical marine infrastructure. Landslide deposits act as foci for localized, but important, deep-seafloor biological communities. Under burial, landslide deposits play an important role in a successful petroleum system. While the broad importance of understanding subaqueous landslide processes is evident, a number of important scientific questions have yet to receive the needed attention. Collecting quantitative data is a critical step to addressing questions surrounding subaqueous landslides. Quantitative metrics of subaqueous landslides are routinely recorded, but which ones, and how they are defined, depends on the end-user focus. Differences in focus can inhibit communication of knowledge between communities, and complicate comparative analysis. This study outlines an approach specifically for consistent measurement of subaqueous landslide morphometrics to be used in the design of a broader, global open-source, peer-curated database. Examples from different settings illustrate how the approach can be applied, as well as the difficulties encountered when analysing different landslides and data types. Standardizing data collection for subaqueous landslides should result in more accurate geohazard predictions and resource estimation.

EGU General Assembly 2019 in Viena, Austria , 7-12 april, 2019, During the Messinian salinity crisis (MSC), between 5.97 and 5.33 Ma, the Mediterranean Sea became disconnectedfromtheworld’soceansandafastandcontinuousevaporationgenerateditspartialdesiccation,resultingin the deposition of more than one million cubic kilometres of salt. The extent of the evaporative drawdown phases associated to the MSC remain poorly constrained, particularly in the central Mediterranean. In this study we investigate the geomorphology of the Malta Escarpment to provide answers to these questions. We use multibeam echosounder, seismic reflection data, and gravity cores to identify more than two hundred linear to arcuate scars and more than two hundred canyons. The largest of the canyons – Noto, Cumecs, and Heron Canyons – are up to 100 km long and 39 km wide. We also identify concave breaks of slopes and terraces, the most extensive of which are located in the northern Malta Escarpment, and which are 70 km long and 2478 m deep, and 25 km long and 2545 m deep. Along most of the base of the northern Malta Escarpment, the western Ionian Basin seafloor is characterised by a series of ridges that are up to 8 km long, have an average height of 30 m and are spaced 2-3 km apart. Seismic reflection profiles from the western Ionian Basin show the occurrence of lenses of intermediate amplitude and sub-parallel reflectors, which are up to 0.2 s (TWTT) thick and 8 km wide, downslope of the large canyonmouthsandbeneaththeevaporitesequence.Gravitycoresfromthelargesubmarinecanyonsfeaturesandy turbidites and debrites. We propose that during the MSC, base level fall, fluvial erosion formed a dense network of canyons across the Malta Escarpment whilst coastal erosion developed extensive palaeoshorelines and shore platforms. We carry out an isostatic restoration of the palaeoshorelines and shore platforms on the northern Malta Escarpment to infer an evaporative drawdown of 1800 – 2000 m in the eastern Mediterranean Sea during the MSC. We interpret the occurrence of pre-evaporite sedimentary lobes in the western Ionian Basin as suggesting that either evaporative drawdown and canyon formation occurred predominantly before salt deposition, or that only the latest salt deposition at the basin margin occurred after the formation of the sedimentary lobes. After the MSC, the drivers of geomorphic evolution of the Malta Escarpment included: (i) canyon erosion by submarine gravity flows, with the most recent activity taking place

The original version of the book was inadvertently published with the following errors, which have been now corrected: In Chapter “Oceanic Trenches”, the overlapped Fig. 5 has been corrected. In Chapter “Cold-Water Carbonate Bioconstructions” the reference “Guinan et al. (2000)” has been changed to read as “Guinan et al. (2009)” in the reference list and citation, which is a belated correction. In Chapter “National Programmes: Geomorphological Mapping at Multiple Scales for Multiple Purposes”, Figs. 1, 3 and 4 have been replaced correctly. The erratum book has been updated with the changes., peer-reviewed

Offshore freshwater aquifers represent significant pathways for material transport across the coastal zone and have been proposed as an important agent in the geomorphic evolution of continental margins. However, the methods used to map the extent, volume, controls, and connectivity of offshore/onshore freshwater aquifers are still in the experimental phase. In this study, we present results from a series of marine controlled-source electromagnetic (CSEM) surveys performed in the Canterbury Basin, offshore the South Island of New Zealand. Nearly 300 km of marine CSEM data was collected using a newly developed seafloor-towed CSEM system that measures contrasts in the bulk electrical conductivity structure beneath the seafloor. Four surveys were collected across and/or in close proximity to IODP Expedition 317 Site U1353 in an area that contains a known shallow ( 50 m) freshwater anomaly., peer-reviewed

European Geosciences Union (EGU) General Assembly 2018, 8-13 April 2018, Vienna, Austria.-- 1 page., One of the main competing scenarios proposed for the termination of the Messinian salinity crisis consists of a geologically-rapid refill of the Mediterranean after a km-scale drawdown of the Mediterranean Sea level. The main evidence supporting this Zanclean Flood scenario is a nearly 400 km long and several hundred meters deep erosion channel across the Strait of Gibraltar. This erosion channel extends from the Gulf of Cadiz to the Algerian Basin and implies the excavation of ca. 1000 km3 of Miocene sediment and older bedrock. However, additional evidence supporting this catastrophic flood hypothesis is missing, other than the fast transition from MSC deposits to open-marine facies. Here we test two consequences that an outburst flood of the Mediterranean should imply: First, an excavated channel similar to the one across the Gibraltar Strait should be present in the old sill separating the east and west Mediterranean domains (none has been yet reported). A second smoking gun would be finding the present emplacement of the materials eroded during the Zanclean flood (but quantitative predictions of where to look for them are still missing). In a first attempt to predict the distribution of those flood deposits, we show results from a 2D numerical model of water flow to simulate the transport of material eroded from the Strait of Gibraltar. We estimate the areas of sediment deposition in the Mediterranean Sea depending on the grain size. Suspended load is deposited in areas sheltered from the jet of incoming water by the local topography and areas where water currents abruptly decrease due to a sudden increase in water depth. Bed-load sediment, in contrast, follows water streamlines and deposits are much more localized than in the case of suspended-load. We compare the results with seismic profiles that may exhibit flood-related deposits in the eastern Alboran Sea. Furthermore, we make use of a preliminary interpretation of multichannel data in the western Ionian Basin to identifying a chaotic body of up to 760 m in thickness and 2400 km3 in volume. The location of these deposits next to the Cassibile theatre-shaped canyon (SE Sicily margin) suggest that this may have been excavated by a large flow event in the geological past, a hypothesis that we discuss by comparing to other well-known, subaerial megaflooding scenarios.

The Messinian salinity crisis (MSC) was an outstanding palaeo-oceanographic event that affected the Mediterranean region from 5.97 to 5.33 Ma. This event resulted in the deposition of kilometre-thick sequences of salt and is widely associated with the partial desiccation of the Mediterranean Basin. What is unclear is how normal marine conditions were restored at the end of the MSC. In this study we present topographic and stratigraphic evidence for a Mediterranean-wide catastrophic flood at the end of the MSC. We utilise academic and industry geological and geophysical data from the western Ionian Basin to identify a thick and extensive sedimentary body overlying Messinian evaporites. In view of its volume, wedge-shaped geometry and chaotic seismic character, we interpret this body as a deposit of material eroded and transported from the western to the eastern Mediterranean during the Zanclean flood. Based on the extent of this sedimentary body, the reconstructed Messinian topography and the occurrence of a unique, relict erosional canyon on the Malta Escarpment, we infer that the gateway for the flood was likely located in SE Sicily. Our findings suggest that the identified sedimentary body is one of the largest known megaflood deposits on Earth.

Landslides are common in aquatic settings worldwide, from lakes and coastal environments to the deep-sea. Fast-moving, large volume landslides can potentially trigger destructive tsunamis. Landslides damage and disrupt global communication links and other critical marine infrastructure. Landslide deposits act as foci for localised, but important deep-seafloor biological communities. Under burial, landslide deposits play an important role in a successful petroleum system. While the broad importance of understanding subaqueous landslide processes is evident, a number of important scientific questions have yet to receive the needed attention. Collecting quantitative data is a critical step to addressing questions surrounding subaqueous landslides. Quantitative metrics of subaqueous landslides are routinely recorded, but which ones, and how they are defined, depends on the end-user focus. Differences in focus can inhibit communication of knowledge between communities, and complicate comparative analysis. This study outlines an approach specifically for consistent measurement of subaqueous landslide morphometrics to be used in design of a broader, global open-source, peer-curated database. Examples from different settings illustrate how the approach can be applied, as well as the difficulties encountered when analysing different landslides and data types. Standardising data collection for subaqueous landslides should result in more accurate geohazard predictions and resource estimation.

Spreading is a type of mass movement where a sediment unit is extended and broken up into coherent blocks that are displaced and tilted along a planar slip. High-resolution seafloor data demonstrate that spreading is a common style of submarine mass movement. Submarine spreading is clearly exemplified in the Storegga Slide, Norwegian margin (Fig. 1a, b). The slide occurred 8100 + 250 cal a BP as a retrogressive slope failure (Haflidason et al. 2005). It is one of the largest known submarine slides and the site of repeated sliding activity. Failures on the Norwegian margin are linked strongly to the growth and retreat of the Fennoscandian ice sheets, in particular to the alternating deposition of glacigenic debrites and basal and deformation tills during glacial maxima (e.g. O1–O2 30–15 ka and O4–O7 200–130 ka sub-units of the Naust Formation), and of fine-grained glacimarine, hemipelagic and contouritic sediments during interglacials (e.g. O3 130–30 ka sub-unit of the Naust Formation). The Naust sub-units are described in full in Berg et al. (2005). Differences in the geotechnical properties of these sediments, coupled with seismicity, rapid sediment deposition, associated high pore pressures and the regional topography and structural setting, are responsible for .20 slope failures across the region during the Quaternary (Solheim et al. 2005).

Integration of multibeam and seismic data shows that at least four different mass transport complexes (MTCs) developed since the Pliocene. Three large scale MTCs, are buried at a depth of up to 500 m below the seafloor. They are characterized by chaotic to discontinuous seismic facies and pinch out against the foreland ramp. The forth and most recent MTC is exposed at the sea floor and has been imaged with multibeam bathymetry and high resolution Chirp profiles. This MTC has a variety of seafloor textures, morphologies and internal deformational geometries. They represent the different elements of landslide movement:exposed failure plane, extensional blocks, debris flows, and blocky debris flow lobes.In the toe region of the landslide exists a confined compression zone indicated by the presence of pressure ridges.

European Geosciences Union General Assembly 2013, 7-12 April, Vienna, Austria.-- 1 page, 40% of submarine canyons worldwide are located in passive margins, where they constitute preferential conduits of sediment and biodiversity hotspots. Recent studies have presented evidence that submarine canyons incising passive, progradational margins can co-evolve with the adjacent continental slope during long-term margin construction. The stages of submarine canyon initiation and their development into a mature canyon-channel system are still poorly constrained, however, which is problematic when attempting to reconstruct the development of passive continental margins. In this study we analyse multibeam echosounder and seismic reflection data from the southern Ebro margin (western Mediterranean Sea) to document the stages through which a first-order gully develops into a mature, shelf-breaching canyon and, finally, into a canyon-channel system. This morphological evolution allows the application of a space-for-time substitution approach. Initial gully growth on the continental slope takes place via incision and downslope elongation, with limited upslope head retreat. Gravity flows are the main driver of canyon evolution, whereas slope failures are the main agent of erosion; they control the extent of valley widening, promote tributary development, and their influence becomes more significant with time. Breaching of the continental shelf by a canyon results in higher water/sediment loads that enhance canyon development, particularly in the upper reaches. Connection of the canyon head with a paleo-river changes evolution dynamics significantly, promoting development of a channel and formation of depositional landforms. Morphometric analyses demonstrate that canyons develop into geometrically self-similar systems that approach steady-state and higher drainage efficiency. Canyon activity in the southern Ebro margin is pulsating and enhanced during sea level lowstands. Rapid sedimentation by extension of the palaeo-Millars River into the outermost shelf and upper slope is inferred as the source of gravity flows driving canyon evolution. Canyon morphology is shown to be maintained over the course of more than one fall and rise in sea-level. Our model of canyon evolution is applicable to other passive margins (e.g. Argentine continental margin)

After the end of the Last Glacial Maximum, 450 km2 of former terrestrial and coastal landscape of the Maltese Islands was drowned by the ensuing sea level rise. In this study we use high resolution seafloor data (multibeam echosounder data, seismic reflection profiles, and Remotely Operated Vehicle imagery) and bottom samples to reconstruct ~ 300 km2 of this submerged Maltese paleolandscape. The observed paleolandscape is exceptionally well preserved and comprises former coastal landforms – (i) fault-related escarpments, (ii) paleoshore platforms and associated shorelines, (iii) paleoshoreline deposits, and (iv) mass movement deposits – and former terrestrial landforms – (v) river valleys, (vi) alluvial plains, (vii) karstified limestone plateaus, and (viii) sinkholes. These elements indicate that the paleolandscape has been primarily shaped by tectonic activity combined with fluvial, coastal, slope instability and karstic processes; these are the same processes the shaped the current terrestrial and coastal landscape. By correlating the identified landforms with the timing of known changes in sea level during the last glacial cycle, we infer that the alluvial plains and the shallowest limestone plateaus had up to 100 kyr to develop, whereas the paleoshoreline deposits are likely to have formed between 28 kyr and 14 kyr. The most prominent paleoshore platforms, shorelines and river valleys were generated between 60 kyr and 20 kyr. Fluvial erosion is likely to have been prevalent during periods of low sea level (Last Glacial Maximum and stadial conditions during MIS 3), whereas karst processes should have been more effective during warm and humid interstadial periods. Our results have implications for improving the characterization of past environments and climates, as well as providing a much needed background for prehistoric and geoarcheological research in the central Mediterranean region.

Recently acquired high-resolution bathymetric and seismic data illustrate numerous current-generated bedforms on the continental shelf of Roses, mostly in the vicinity of the submarine canyons of Cap de Creus and La Fonera, which are deeply incised in the continental shelf. The set of bedforms includes oval and irregularly shaped depressions, lineations, obstacle marks and sediment waves. Bedform characteristics reveal that most of them are presently active under episodically strong (>60 cm s-1) near-bottom currents as part of a complex flow pattern on the shelf, influenced by the presence of submarine canyon heads. The strongest bottom currents flow from the north and are directed towards Cap de Creus canyon head. South of this canyon head, shelf bedforms are indicative of a diverging south-eastwards sediment transport pattern towards the shelf edge and southwards along the middle shelf. Farther south, bottom features are indicative of bottom current re-intensification close to La Fonera canyon head. The current regime deduced from bedforms is further confirmed by in situ current meter measurements in the Cap de Creus canyon and the adjacent continental shelf, and by previous numerical simulations. Current and sediment transport peaks result from high-energy episodic events, such as dense shelf water flows and major Eastern storms. Our findings show that shelf floor morphology provides valuable information about present-day sediment dynamics, the shelf bottom current regime and the physical processes governing erosion, transport and deposition of sediments in such temperate shelf environments., N/A

Spreading is a common type of ground failure in subaerial environments. However, this type of mass movement has hardly been documented in submarine settings. In this paper we show that spreading covers at least 25% of the Storegga Slide scar area, a giant submarine slide located offshore mid-Norway. The morphological signature of spreading is a repetitive pattern of ridges and troughs oriented perpendicular to the direction of movement. Two modes of failure can be identified: retrogressive failure of the headwall and slab failure and extension, both involving the breakup of a sediment unit into coherent blocks. These blocks are displaced downslope along planar slip surfaces. Limit equilibrium modeling indicates that loss of support and seismic loading are the main potential triggering mechanisms. The extent of displacement of the spreading sediment is controlled by gravitationally induced stress, angle of internal friction of the sediment, pore pressure escape, and friction. The resulting block movement pattern entails an exponential increase of displacement and thinning of the failing sediment with distance downslope. Sediment properties explain the remaining spatial variation of ridge and trough morphologies associated with spreading.

Seismic reflection and refraction methods are routinely used to illuminate sub-seafloor geological relationships, thereby providing a means to investigate a wide range of Earth processes that influence submarine geomorphology. Since the birth of seismic methods for exploration of ore bodies and petroleum in the early part of the 20th century, progressive technological advancements have ensured that the seismic method remains a fundamental geophysical tool in both the oil and gas industry and scientific research. For both marine seismic reflection and refraction methods, the primary principles are based around the notion of sending artificially-generated sound waves downward into the Earth and recording the energy that returns to recording instruments (receivers). In the case of seismic reflection, the down-going wavefield reflects off geological boundaries characterized by density and velocity contrasts before being recorded by an array of receivers. In seismic refraction experiments, the notion is to record energy that has been refracted at multiple geological boundaries before, ultimately, being refracted at a critical angle and then returning to receivers on the seafloor. Survey designs for both methods are many and varied, ranging from relatively simple two-dimensional surveys, to multi-azimuth three-dimensional surveys that illuminate the subsurface from different directions. Although the state of the art in seismic methods is continually evolving, this chapter gives some examples of modern and developing trends that are relevant to investigations into submarine geomorphology. Examples include high-resolution 3D seismic imaging, high-frequency sub-bottom profiling, waveform inversion and deep-towed seismic acquisition. The strength of the seismic reflection method lies in its ability to gain insight into structural and stratigraphic relationships beneath the seafloor, as well as in investigating fluid flow processes. The refraction method, on the other hand, is often used as the tool of choice for crustal-scale investigations into deeply-rooted geological processes that shape the seafloor, such as plate tectonics and volcanism. As with all scientific methods, seismic methods are most powerful when combined with complementary geophysical, geological or geochemical methods to address a common Earth science question.

Seafloor morphology plays a key role in submarine mineral exploration as precious minerals are associated with specific geomorphological settings. Mn-nodules occur in abyssal plains, seafloor massive sulphides are strongly connected to volcanic areas and sand, gravel and other marine minable aggregates are deposited in coastal environments. For resource assessments and exploitation, a detailed knowledge of the seafloor morphology is essential to evaluate areas of terrain that cannot be mined due to technical limitations, and to estimate abundance, extent and thickness of the deposits. The most important method used is multibeam mapping, from which bathymetric and backscatter data are derived. These are often linked to side scan sonar surveys and sub-bottom profiling. Optical video and photo data provide additional information about substrate type and ecology, and help improve and adapt exploration and exploitation plans and technology. For the three most important marine mineral types—sand and gravel, Mn-nodules and seafloor massive sulphides—exploration and exploitation methods are described and the environmental impacts associated with mining these resources are discussed.

The most significant breakthroughs in science are often made as a result of technological developments and innovation. A new capacity to gather more data, measure more precisely or make entirely new observations generally leads to new insights and fundamental understanding. The future of ocean research and exploration therefore lies in robotics: marine robotic systems can be deployed at depths and in environments that are out of direct reach for humans, they can work around the clock, and they can be autonomous, freeing up time and money for other activities. To advance the field of submarine geomorphology, the two types of robots that currently make the biggest difference are Remotely Operated Vehicles (ROVs) and Autonomous Underwater Vehicles (AUVs). Other autonomous or robotic systems are available for marine research (e.g. gliders, autonomous surface vehicles, benthic crawlers etc.), but their application for geomorphological studies is less extensive. This chapter gives an overview of the main characteristics of ROVs and AUVs, their advantages and disadvantages, and their main applications for geomorphological research. In comparison to the other geomorphological methods discussed in this book, however, it has to be made clear that ROVs and AUVs are not so much methods per se, instead they are platforms from which existing and new approaches can be applied.

Robust interpretation of geomorphology is a primary method of understanding failure modes, emplacement mechanisms and post-failure modification of submarine landslides. Since high-resolution hull-mounted multibeam systems became widely available in the last 20 years, our understanding of submarine landslides has improved dramatically. Techniques such as 3D seismic and cm-resolution seafloor mapping has revealed both surface and sub-surface geomorphology in unprecedented detail, and we are making rapid advancements towards refining our understanding of the processes that lead to specific geomorphological signatures associated with slope failure. One of the greatest challenges in the geomorphological analysis of submarine landslides is in accounting for post-failure modification processes. As erosional processes, such as gullying, erode the easily recognisable landslide geomorphology, or sediment drape smothers landslide features, it becomes increasingly more challenging to identify where landslides have occurred. In some depositional environments (e.g. a slope basin) the landslide debris may be preserved in the stratigraphy and analysed using 3D data. However, in erosional environments, such as submarine canyons, there is often little or no remaining deposit and interpretation of landslide processes must be based solely on the landslide scar, which is often heavily modified due to the dynamic nature of the canyon environment. Accurate interpretation and quantification of landslide parameters becomes important for determining magnitude frequency for landslide populations, which is a key piece of information for hazard studies.

Active Fluid Seepage (AFS) at the seafloor is a global phenomenon associated with seafloor morphologies in different geodynamic contexts. Advances geophysical techniques have allowed geoscientists to characterise pockmarks, mounds and flares associated with AFS. We present a range of marine geological data acquired in the central Mediterranean Sea (northern Sicily continental margin, northwestern Sicily Channel and offshore the Maltese Islands), which allow us to identify AFSs. The AFSs are spatially distributed as clusters, aligned or isolated at different depths, ranging from few decametres offshore the Maltese Islands, up to 400 m offshore north Sicily and in the northwestern Sicily channel. Mounds have heights ranging from 2 to 15 m and form hummocky surfaces. Pockmarks with sub-circular planform shapes and U/V-shaped cross-sections are found in sizes ranging from 5 to 530 m. Gas flares occur on both the continental shelf and upper slope.