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  • 1
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    Seismic evidence for shallow gas-escape features associated with a retreating gas hydrate zone offshore west Svalbard (2012)
    AGU (American Geophysical Union)
    In:  Journal of Geophysical Research: Solid Earth, 117 (B9). B09102.
    Details
    Publication Date: 2018-04-27
    Description: Active gas venting occurs on the uppermost continental slope off west Svalbard, close to and upslope from the present-day intersection of the base of methane hydrate stability (BMHS) with the seabed in about 400 m water depth in the inter-fan region between the Kongsfjorden and Isfjorden cross-shelf troughs. From an integrated analysis of high-resolution, two-dimensional, pre-stack migrated seismic reflection profiles and multibeam bathymetric data, we map out a bottom simulating reflector (BSR) in the inter-fan region and analyze the subsurface gas migration and accumulation. Gas seeps mostly occur in the zone from which the BMHS at the seabed has retreated over the recent past (1975–2008) as a consequence of a bottom water temperature rise of 1°C. The overall margin-parallel alignment of the gas seeps is not related to fault-controlled gas migration, as seismic evidence of faults is absent. There is no evidence for a BSR close to the gas flare region in the upper slope but numerous gas pockets exist directly below the predicted BMHS. While the contour following trend of the gas seeps could be a consequence of retreat of the landward limit of the BMHS and gas hydrate dissociation, the scattered distribution of seeps within the probable hydrate dissociation corridor and the occurrence of a cluster of seeps outside the predicted BMHS limit and near the shelf break indicate the role of lithological heterogeneity in focusing gas migration.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2011JB009126
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    The Sahara Slide: initiation and processes from headwall to deposit of a giant submarine slide (2010)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 11 (7). Q07014.
    Details
    Publication Date: 2017-11-07
    Description: The Sahara Slide is a giant submarine landslide on the northwest African continental margin. The landslide is located on the open continental slope offshore arid Western Sahara, with a headwall at a water depth of ∼2000 m. High primary productivity in surface waters drives accumulation of thick fine-grained pelagic/hemipelagic sediment sequences in the slide source area. Rare but large-scale slope failures, such as the Sahara Slide that remobilized approximately 600 km3 of sediment, are characteristic of this sedimentological setting. Seismic profiles collected from the slide scar reveal a stepped profile with two 100 m high headwalls, suggesting that the slide occurred retrogressively as a slab-type failure. Sediment cores recovered from the slide deposit provide new insights into the process by which the slide eroded and entrained a volcaniclastic sand layer. When this layer was entrained at the base of the slide it became fluidized and resulted in low apparent friction, facilitating the exceptionally long runout of ∼900 km. The slide location appears to be controlled by the buried headwall of an older slope failure, and we suggest that the cause of the slide relates to differential sedimentation rates and compaction across these scarps, leading to local increases of pore pressure. Sediment cores yield a date of 50–60 ka for the main slide event, a period of global sea level rise which may have contributed to pore pressure buildup. The link with sea level rising is consistent with other submarine landslides on this margin, drawing attention to this potential hazard during global warming.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2010GC003066
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Multifrequency geoacoustic imaging of fluid escape structures offshore Costa Rica: Implications for the quantification of seep processes (2008)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 9 (4). Q04010.
    Details
    Publication Date: 2018-03-07
    Description: Quantification of fluid fluxes from cold seeps depends on accurate estimates of the spatial validity of flux measurements. These estimates are strongly influenced by the choice of geoacoustic mapping tools. Multibeam bathymetry, side-scan sonar, and Chirp subbottom profiler data of several mound-shaped cold seeps offshore central Costa Rica show great variety in morphology and structure although the features are only a few kilometers apart. Mound 11 (a 35 m high and 1000 m in diameter structure), situated in the SE of the study area, has an irregular morphology but a smooth surface on side-scan sonar data, while mound 12 (30 m high, 600 m across) is a cone of more regular outline but with a rough surface, and mound Grillo (5 m high, 500 m across) shows the same rough surface as mound 12 but without relief. Video observations and sediment cores indicate that the structures are formed by the precipitation of authigenic carbonates and indications for extensive mud extrusion are absent, except for one possible mudflow at mound 11. Different sonar frequencies result in variable estimates of the extent of these mounds with low frequencies suggesting much wider cold seeps, consequently overestimating fluid fluxes. The absence of mud volcanism compared to accretionary prisms where mud volcanism occurs is related to different tectonic styles: strong sediment overpressure and thrust faulting in typical accretionary prisms can generate mud volcanism, while subduction erosion and normal faulting (extension) of the overriding plate at the Costa Rican margin result in fluid venting driven by only slight fluid overpressures.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2007GC001708
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    What causes large submarine landslides on low gradient (〈2°) continental slopes with slow (∼0.15 m/kyr) sediment accumulation? (2015)
    AGU (American Geophysical Union) | Wiley
    In:  Journal of Geophysical Research: Solid Earth, 120 (10). pp. 6722-6739.
    Details
    Publication Date: 2017-05-02
    Description: Submarine landslides can cause damaging tsunamis, the height of which scales up with the volume of the displaced mass. The largest underwater landslides are far bigger than any landslides on land, and these submarine megaslides tend to occur on open continental slopes with remarkably low gradients of less than 2°. For geohazard assessments it is essential to understand what preconditions and triggers slope failure on such low gradients. Previous work has suggested that generation of high excess pore pressure due to rapid sediment deposition plays a key role in such failures. However, submarine slope failure also occurs where sedimentation rates are low (〈0.15 m/kyr), such as off northwest Africa. We use a fully coupled stress and fluid flow finite element model to test whether such low sedimentation rates can generate sufficient excess pore pressures to cause failure of a 2° slope. The sensitivity of overpressure generation and slope stability is assessed with respect to different sedimentation rates and patterns, sediment consolidation properties, and stratigraphic layer configurations. The simulations show that, in general, it is difficult to generate significant excess pore pressure if sediment accumulation is slow and the only pressure source. However, we identify a sediment compression behavior that can lead to submarine landslides in locations worldwide. Our results imply that compressibility is an important factor for the stability of low gradient continental slopes.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
    DOI: 10.1002/2015JB012347
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Multiscale high-resolution mapping of the Pacific convergent margin off Costa Rica - first results of the cruise SO-163 (2002)
    In:  [Talk] In: AGU Fall Meeting 2002, 06.- 10.12.2002, San Francisco, USA .
    Details
    Publication Date: 2020-05-08
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 6
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    Mehrskalige Kartierung des konvergenten Kontinentalrandes vor Costa Rica - erste Ergebnisse der Fahrt SO163 mit FS SONNE (2003)
    In:  [Talk] In: 63. Jahrestagung DGG, 23.- 28.02.2003, Jena, Germany .
    Details
    Publication Date: 2019-09-23
    Type: Conference or Workshop Item , NonPeerReviewed
    Format: text
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    OceanRep: Talk
  • 7
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    Surface structures related to fluid venting in the subduction zone off Costa Rica: results from multiscale high-resolution mapping (2003)
    In:  [Talk] In: DMG-GV-DGG-Tagung GEO2003, 22.- 25.09.2003, Bochum, Deutschland .
    Details
    Publication Date: 2020-05-20
    Type: Conference or Workshop Item , NonPeerReviewed
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    OceanRep: Talk
  • 8
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    Styles and productivity of mud diapirism along the Middle American Margin, Part I: Margin evolution, segmentation, dewatering and mud diapirism (2005)
    Springer
    In:  In: Mud volcanoes, geodynamics and seismicity. , ed. by Martinelli, G. and Panahi, B. NATO science series : Series 4, Earth and environmental sciences, 51 . Springer, Dordrecht, pp. 35-48. ISBN 1-402-03203-X
    Details
    Publication Date: 2019-09-23
    Type: Book chapter , PeerReviewed
    DOI: 10.1007/1-4020-3204-8_4
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    OceanRep: Book chapter
  • 9
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    Sedimentary processes of the lower Monterey Fan channel and channel-mouth lobe (2004)
    Elsevier
    In:  Marine Geology, 206 (1-4). pp. 181-198.
    Details
    Publication Date: 2017-07-28
    Description: The distribution of deposits, sediment transport pathways and processes on the lower Monterey Fan channel and channel-mouth lobe (CML) are studied through the integration of GLORIA and TOBI sidescan sonar data with 7-kHz subbottom profiler records and sediment cores for ground-truthing. The lower Monterey channel is characterised by an up to 30-m-deep channel with poorly developed levees and alternating muddy and silty muddy overbank deposits. The channel is discontinuous, disappearing where gradients are less than about 1:350. Ground-truthing of the large CML shows that the entire CML is characterised by widespread deposits of generally fine sand, with coarser sand at the base of turbidites. Sand is particularly concentrated in finger-like areas of low-backscatter intensity and is interpreted as the result of non-turbulent sediment-gravity flows depositing metres thick massive, fine sand. TOBI sidescan sonar data reveal recent erosional features in the form of scours, secondary channels, large flow slides, and trains of blocks at the distal end of the CML. Erosion is probably related to increasing gradient as the CML approaches Murray Fracture zone and to differential loading of sandy submarine fan deposits onto pelagic clays. Reworking of older flow slides by sediment transport processes on the lobe produces trains of blocks that are several metres in diameter and aligned parallel to the flow direction.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1016/j.margeo.2004.02.006
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    Fluid seepage at the continental margin offshore Costa Rica and southern Nicaragua (2008)
    AGU (American Geophysical Union)
    In:  Geochemistry, Geophysics, Geosystems, 9 (5). Q05S05.
    Details
    Publication Date: 2019-09-23
    Description: [1] A systematic search for methane-rich fluid seeps at the seafloor was conducted at the Pacific continental margin offshore southern Nicaragua and northern central Costa Rica, a convergent margin characterized by subduction erosion. More than 100 fluid seeps were discovered using a combination of multibeam bathymetry, side-scan sonar imagery, TV-sled observations, and sampling. This corresponds, on average, to a seep site every 4 km along the continental slope. In the northwestern part of the study area, subduction of oceanic crust formed at the East Pacific Rise is characterized by pervasive bending-induced faulting of the oceanic plate and a relatively uniform morphology of the overriding continental margin. Seepage at this part of the margin typically occurs at approximately cone-shaped mounds 50 - 100 m high and up to 1 km wide at the base. Over 60 such mounds were identified on the 240 km long margin segment. Some normal faults also host localized seepage. In contrast, in the southeast, the 220 km long margin segment overriding the oceanic crust formed at the Cocos-Nazca Spreading Centre has a comparatively more irregular morphology caused mainly by the subduction of ridges and seamounts sitting on the oceanic plate. Over 40 seeps were located on this part of the margin. This margin segment with irregular morphology exhibits diverse seep structures. Seeps are related to landslide scars, seamount-subduction related fractures, mounds, and faults. Several backscatter anomalies in side-scan images are without apparent relief and are probably related to carbonate precipitation. Detected fluid seeps are not evenly distributed across the margin but occur in a roughly margin parallel band centered 28 ± 7 km landward of the trench. This distribution suggests that seeps are possibly fed to fluids rising from the plate boundary along deep-penetrating faults through the upper plate.
    Type: Article , PeerReviewed
    Format: text
    DOI: 10.1029/2008GC001978
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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