1,722,469 research outputs found
Failure processes in submarine landslides: a geomorphological approach
No full textThis thesis presents a novel technique for the quantitative characterisation of bathymetricdata sets. The technique integrates three main geomorphometric methods: morphometricattributes and their statistical analyses, feature-based quantitative representation, andautomated topographic classification. These methods allow useful morphologicalinformation to be extracted from bathymetric data and can significantly enhance submarinegeomorphological investigations. The methods are applied to bathymetric data from theStoregga Slide, one of the largest known submarine landslides, to investigate three aspectsof submarine mass movements: spreading, fractal statistics and morphology and slidedevelopment.The morphological signature of spreading, in the form of a repetitive pattern of ridges andtroughs, covers at least 25% of the Storegga Slide scar. Two modes of failure can beidentified for submarine spreading. The first involves retrogressive slide development viathe unloading of the headwall. The second entails the extension of a thin coherent slab ofsemi-consolidated material downslope by gravity. Both modes of failure involve the breakup of surface sediment units into coherent blocks and their displacement along planar slipsurfaces. The block movement pattern entails an exponential increase of displacement, andthinning of the failing sediment, with distance downslope. Loss of support and seismicloading are the main potential triggering mechanisms of submarine spreading.Analysis of headwall morphologies within the Storegga Slide reveals the occurrence ofspatial scale invariance. One explanation for this scale invariance is that the Storegga Slideis a geomorphological system that may exhibit self-organised criticality. Spatial scaleinvariance may also be linked to the retrogressive nature of the Storegga Slide. The shapeand fractal dimension of headwalls, on the other hand, can be used as a proxy for the typeand number of the formative mass movements.A detailed reconstruction of the development of the north-eastern Storegga Slide showsthat after the initial evacuation of the surface sediment as turbidity currents, the area failedas an extensive spread. The spreading blocks subsequently underwent higher displacementand remoulding, and were partly removed by debris flows and turbidity currents. Therenewed instability within the spreading areas may have been related to gas hydratedissociation and pore pressure increases due in response to the changing overburden, andthe distribution of contourite drift deposits within underlying palaeoslide scars
Submarine Landslides
No full textRobust 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
Evidence of active fluid seepage (AFS) in the southern region of the central Mediterranean Sea
No full textActive fluid seepage (AFS) at the seafloor is a global phenomenon associated with seafloor morphologies in different geodynamic contexts. Advanced geophysical techniques have allowed geoscientists to characterise pockmarks, mounds and flares associated with AFS. We present a range of new marine geological data acquired in the southern region of the central Mediterranean Sea (northern Sicily continental margin, northwestern Sicily Channel and offshore of the Maltese Islands), which allow us to identify AFSs. AFSs are spatially distributed as clusters, aligned or isolated at different depths, ranging from few decametres offshore of the Maltese Islands; up to 400 m offshore of northern Sicily and in the northwestern Sicily Channel. Mounds have heights ranging from 2 to 15 m and form hummocky surfaces. Seafloor samples were collected at the top of the mounds and were analysed using a SEM with an EDX. Geochemical features reveal that seafloor samples are slightly enriched in O, S and Ba and seem to indicate the existence of an external source of fluids and the occurrence of sediment-fluids interaction processes. 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 as well as the upper slope
Gathering different marine geology data (seismics, acoustics, sedimentological) to investigate active fluid seepage (AFS) in the southern region of the central Mediterranean Sea
No full textActive 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
Novel nitroxides and pronitroxides : synthesis and properties of new spin traps and spin probes with potential for biological application
No full textScale invariant characteristics of the Storegga Slide and implications for large-scale submarine mass movements
No full textThis study documents the fractal characteristics of submarine mass movement statistics and morphology within the Storegga Slide. Geomorphometric mapping is used to identify one hundred and fifteen mass movements from within the Storegga Slide scar and to extract morphological information about their headwalls. Analyses of this morphological information reveal the occurrence of spatial scale invariance within the Storegga Slide. Non-cumulative frequency-area distribution of mass movements within the Storegga Slide satisfies an inverse power law with an exponent of 1.52. The headwalls exhibit geometric similarity at a wide range of scales and the lengths of headwalls scale with mass movement areas. Composite headwalls are self-similar.One of the explanations of the observed spatial scale invariance is that the Storegga Slide is a geomorphological system that may exhibit self-organized criticality. In such a system, the input of sediment is in the form of hemipelagic sedimentation and glacial sediment deposition, and the output is represented by mass movements that are spatially scale invariant. In comparison to subaerial mass movements, the aggregate behavior of the Storegga Slide mass movements is more comparable to that of the theoretical ‘sandpile’ model. The origin of spatial scale invariance may also be linked to the retrogressive nature of the Storegga Slide. The geometric similarity in headwall morphology implies that the slope failure processes are active on a range of scales, and that modeling of slope failures and geohazard assessment can extrapolate the properties of small landslides to those of larger landslides, within the limits of power law behavior. The results also have implications for the morphological classification of submarine mass movements, because headwall shape can be used as a proxy for the type of mass movement, which can otherwise only be detected with very high resolution acoustic data that are not commonly available
Morphology and mechanics of submarine spreading: a case study from the Storegga Slide
Full text linkSpreading 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: etrogressive 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
Synthesis and EPR spin trapping properties of a new isoindole-based nitrone: 1,1,3-trimethylisoindole N-oxide (TMINO)
No full textHere we describe the synthesis and characterisation of a new isoindole-based nitrone spin trap, 1,1,3-trimethylisoindole N-oxide (TMINO). This nitrone and its radical adducts (isoindoline nitroxides) exhibit enhanced stability with respect to other commonly used spin traps and their adducts. We also report EPR trapping studies of this new nitrone with some carbon- and oxygen-centred radicals including alkyl, aryl, hydroxyl and benzoyloxyl systems. The narrow EPR line-widths and stability of the resulting nitroxide spin adducts allowed the detection of the expected radicals as well as secondary and minor radical components in the reaction mixtures
SEG-Y Multichannel seismic data collected during RV METEOR expedition M199 and used for publication by Micallef et al., in prep.
No full text<p><span>The dataset comprises 3 multichannel seismic profiles, which have been collected during RV METEOR expedition M199 in February 2024 by the University of Hamburg. Data format is SEG-Y. Trace headers follow SEG-Y Revision 1 standard.</span></p>
<p><span>The profiles are:</span></p>
<p><span>M199_MCS_HH24-03</span></p>
<p><span>M199_MCS_HH24-05</span></p>
<p><span>M199_MCS_HH24-29</span></p>
The submerged paleolandscape of the Maltese Islands: Morphology, evolution and relation to Quaternary environmental change
No full textAfter 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
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