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  • 1
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    Malta’s Submerged Landscapes and Landforms (2019)
    Springer
    In:  In: Landscapes and Landforms of the Maltese Islands. , ed. by Gauci, R. and Schembri, J. Springer, Cham, Switzerland, pp. 117-128.
    Details
    Publication Date: 2020-01-09
    Description: The application of acoustic techniques, such as multibeam echosounders, has permitted the identification of Maltese submarine landscapes and landforms that were progressively inundated during the postglacial sea-level rise. Remarkably, geomorphological features due to fluvial, gravity-induced and karst processes that took place under former subaerial conditions can be clearly recognised on the present seafloor around the Maltese archipelago, and they were only slightly modified by sea action during the postglacial transgression phases. The analysis of the submerged landforms described in this chapter is crucial for understanding the evolution of the Maltese Islands during the last ca. 20,000 years.
    Type: Book chapter , NonPeerReviewed
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  • 2
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    Construction of an oceanic island: Insights from the El Hierro (Canary Islands) 2011-2012 submarine volcanic eruption (2013)
    GSA (Geological Society of America)
    In:  Geology, 41 (3). pp. 355-358.
    Details
    Publication Date: 2021-05-11
    Description: Eight consecutive swath bathymetry data sets were obtained to monitor the submarine eruption that occurred from 10 October 2011 to 5 March 2012 south of El Hierro Island in the Canary Islands. An increase in seismic activity since July 2011 preceded the onset of the eruption, which was marked by seismic tremor and stained waters. The first bathymetry, 15 d after the eruption started, depicts a cone topping at 205 m depth, growing on a preexisting valley. Recurrent mapping shows changes in the morphology and depth of the cone, allowing us to identify collapses and calculate eruptive volumes and rates, which peaked at 12.7 × 106 m3 d−1 of non–dense rock equivalent (NDRE) on 29–30 October. The final cone consists of at least four vents along a north-northwest–south-southeast lineation, with the shallowest summit at 89 m depth. The total accumulated volume was 329 × 106 NDRE m3, of which one-third formed the cone. Similar cones have been identified on the submerged flanks of the island, with volumes ranging from 〈50 × 106 to 〉1000 × 106 NDRE m3. As in many other volcanic islands, large-scale landslides play an important role in the evolution of El Hierro. A giant flank landslide (El Golfo, 13–134 ka, 150–180 km3) mobilized, in a single event, a volume equivalent to 450–550 eruptions of the size of the reported one, showing striking differences in the construction and destruction rates of the island. This study is relevant for future monitoring programs and geohazard assessment of new submarine eruptions.
    Type: Article , PeerReviewed
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  • 3
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    Submarine Landslides (2018)
    Springer
    In:  In: Submarine geomorphology. , ed. by Micallef, A. 〈https://orcid.org/0000-0002-9330-0648〉, Krastel, S. 〈https://orcid.org/0000-0002-5899-9748〉 and Savini, A. Springer, Cham, pp. 235-250, 16 pp.
    Details
    Publication Date: 2021-11-10
    Description: 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.
    Type: Book chapter , NonPeerReviewed
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  • 4
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    Offshore Freshened Groundwater in Continental Shelf Environments (2022)
    Springer
    Details
    Publication Date: 2022-06-02
    Description: While offshore groundwater has been utilized by coastal communities as far back as 1000 BC, only in the past 10 years has the global volume of fresh-to-brackish water hosted in offshore aquifers been truly appreciated. There are vast quantities (~300–500 × 103 km3) of offshore freshened groundwater sequestered in continental shelf sediments under water depths of less than 60 m within 110 km of the coastline. New marine geophysical methods now make it possible to map and quantify low salinity offshore groundwater bodies. To date, these offshore resources have not been developed. Offshore freshened groundwater could be produced if wells are located close to the shoreline and coastal desalination plants.
    Type: Book chapter , NonPeerReviewed
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  • 5
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    The Tsunami Inundation Hazard of the Maltese Islands (Central Mediterranean Sea): A Submarine Landslide and Earthquake Tsunami Scenario Study (2020)
    Springer
    Details
    Publication Date: 2023-02-08
    Description: The tsunami hazard for the Maltese Islands is poorly defined, and historic records are available for only two recent events. Most of the population and touristic infrastructure of the archipelago is concentrated along the eastern low-lying coastline, which is exposed to tsunamis from near-field and far-field sources. In this study we present a scenario-based tsunami inundation study to assess the impact of potential significant cases. We simulated four scenarios—two submarine landslide sources (outer Malta Plateau slide and Gela Basin slide) and two earthquake sources mimicking events comparable to the 365 A.D. western Hellenic Arc event and the 1693 south-east of Sicily event. We find that all scenarios cause inundation in densely populated low-lying bays or rias of Mellieha Bay, Xemxija, Salini, Gzira, Msida, Marsaskala, St Thomas Bay, Marsaxlokk and Birzebbuga. The largest inundation extents and flow depths (〉 10 m) are produced by the two landslide sources and the western Hellenic Arc earthquake. Of interest is the role of the Malta Escarpment and Sicily in amplifying and reflecting tsunami waves, and in generating consistent hot spots along the eastern coastline of Malta.
    Type: Article , PeerReviewed
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  • 6
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    First Evidence of Bottom Simulation Reflectors in the Western Indian Ocean Offshore Tanzania (2022)
    Springer
    Details
    Publication Date: 2023-10-06
    Description: 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.
    Type: Book chapter , NonPeerReviewed
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  • 7
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    Modelling the Influence of Erosive Fluidization on the Morphology of Fluid Flow and Escape Structures (2023)
    Springer
    Details
    Publication Date: 2024-02-07
    Description: Focused fluid flow through sub-seafloor pipes and chimneys, and their seafloor manifestations as pockmarks, are ubiquitous. However, the dynamics of flow localization and evolution of fluid escape structures remain poorly understood. Models based on geomechanical mechanisms like hydro-fracturing and porosity wave propagation offer some useful insights into fluid flow and escape dynamics, but face limitations in capturing features like mobilized granular matter, especially in the upper sediment layers where the link between fracture and pockmark is not always clear. Here, we propose a mathematical model based on the multiphase theory of porous media, where changes in subsurface and seafloor morphology are resolved through seepage-induced erosion, fluidization, transport, and re-deposition of granular material. Through simulation of an idealized scenario of gas escape from overpressured shallow gas reservoir, we demonstrate that our model can capture flow localization and formation of pipes, chimneys, and pockmarks. Our simulations show (1) formation of conical focused-flow conduits with a brecciated core and annular gas channels; (2) pockmarks of W and ring shapes; and (3) pulsed release of gas. Sediment erodibility and flow anisotropy control the morphology of focused fluid flow and escape structures, while permeability shows negligible impact. While the geological setting for this study is theoretical, we show that our results have real-world analogs.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 8
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    Groundwater seepage is a key driver of theater-headed valley formation in limestone (2022)
    GSA (Geological Society of America)
    Details
    Publication Date: 2024-02-07
    Description: Groundwater seepage leads to the formation of theater-headed valleys (THVs) in unconsolidated sediments. In bedrock, the role of groundwater in THV development remains disputed. Here, we integrate field and remote-sensing observations from Gnejna Valley (Maltese Islands) with numerical modeling to demonstrate that groundwater seepage can be the main driver of THV formation in jointed limestone overlying clays. The inferred erosion mechanisms entail (1) widening of joints and fractures by fluid pressure and dissolution and (2) creeping of an underlying clay layer, which lead to slope failure at the valley head and its upslope retreat. The latter is slower than the removal of the talus by creep and sliding on the valley bed. The location and width of THVs are controlled by the location of the master fault and the extent of the damage zone, respectively. The variability of seepage across the fault zone determines the shape of the valley head, with an exponential decrease in seepage away from the fault giving rise to a theater-shaped head that best matches that of Gnejna Valley. Our model may explain the formation of THVs by groundwater in jointed, strong-over-weak chemical sedimentary lithologies, particularly in arid terrestrial settings.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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  • 9
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    Active faulting controls bedform development on a deep-water fan (2021)
    GSA (Geological Society of America)
    Details
    Publication Date: 2024-02-07
    Description: Tectonically controlled topography influences deep-water sedimentary systems. Using 3-D seismic reflection data from the Levant Basin, eastern Mediterranean Sea, we investigate the spatial and temporal evolution of bedforms on a deep-water fan cut by an active normal fault. In the footwall, the fan comprises cyclic steps and antidunes along its axial and external portions, respectively, which we interpret to result from the spatial variation in flow velocity due to the loss of confinement at the canyon mouth. Conversely, in the hanging wall, the seafloor is nearly featureless at seismic scale. Numerical modeling of turbidity currents shows that the fault triggers a hydraulic jump that suppresses the flow velocity downstream, which thus explains the lack of visible bedforms basinward. This study shows that the topography generated by active normal faulting controls the downslope evolution of turbidity currents and the associated bedforms and that seafloor geomorphology can be used to evince syn-tectonic deposition.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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