Headwall Area Research Articles

Analysis and Control of Abnormal Vibration of End Wall on High-Speed Electric Multiple Units

In view of the abnormal vibration of the body end wall during the high-speed operation of electric multiple units (referred hereafter as EMU), the vibration and noise characteristics of the body end wall area are analyzed through the line test. Combined with the end wall modal simulation results, the generation mechanism of the abnormal vibration of the body end wall is analyzed. The results show that when the train is running at a high speed, the aerodynamic excitation of the windshield cavity outside the body end wall acts on the end wall, arousing the first-order bending natural frequency of the body end wall, resulting in resonance of the body end wall, and then causing abnormal vibration and noise in the body end wall area. In order to solve this problem, installing a deflector (guiding plate) above the windshield in the vehicle body end wall area can effectively suppress the aerodynamic excitation acting on the vehicle body end wall. After optimization, the abnormal vibration and noise in the vehicle body end wall area are significantly reduced. The corresponding peak value at 40 Hz of the vehicle body end wall vibration spectrum is reduced by 85%, and the peak noise is reduced by 12%, The correctness of the mechanism analysis of abnormal vibration in the headwall area is verified, which provides a reference basis for guiding the structural optimization and operation and maintenance of rail vehicles.

Sequence of Multiple Slope Failures in the Headwall Area of the Giant Sahara Slide Complex at the NW African Continental Margin

AbstractSubmarine mega‐slides involving hundreds of cubic kilometers of slope material pose a major threat due to their potential to destroy offshore infrastructure and trigger devastating tsunamis. The Sahara Slide Complex affected about 50,000 km2 of the northwestern (NW) African continental margin. Previous studies focused either on its distal depositional zone or the uppermost headwall area, but failed in reconstructing the succession of individual slide events within the entire headwall area. New hydroacoustic data reveal a complex slide morphology including three main acoustic facies, large scale slide blocks, linear troughs, multiple glide planes and three major headwall scarps (the upper, southern and lower headwall). The evacuated slide scar hosts chaotic slide deposits that cover stratified sediments in the upper and southern headwall area, but are vertically stacked onto older slide deposits in the lower headwall area. Based on these observations, and dating of recently collected sediment samples, we reconstructed the history of slope failures that led to the formation of the structurally and morphologically complex headwall area of the Sahara Slide. Slope instability initiated when the lower headwall failed at ∼60 kyr, followed by the failure of the northeastern upper headwall at ∼14 kyr. Around 6 kyr, a major slide within the upper headwall area took place, followed by a series of smaller events within the southern and most‐proximal upper headwall area. The youngest of these slides occurred around 2 kyr. This scenario suggests a long‐lasting history of successive slope failures for the Sahara Slide Complex along the NW African continental slope.

Classification of mass-transport complexes and distribution of gashydrate-bearing sediments in the northeastern continental slope of the South China Sea

The drilling areas in Shenhu and Dongsha, South China Sea, studied from 2007 to 2015, reveal great heterogeneity in the spatial distribution of the gas hydrate reservoir. Various types of mass-transport complexes (MTCs) were developed in the study areas, which served as ideal reservoirs. To conduct exploration in these areas, it is necessary to study the different types of MTCs and the corresponding gashydrate accumulations. By integrating seismic reflection and log coring data, we classified three types of MTCs according to their stress distribution: the tension, extrusion, and shear types, and their corresponding gashydrate accumulation patterns. The results show that the accumulation of the gas-hydrate varies with the type of MTC and stress distribution depending on the MTC’s position (e.g., in the headwall, translational, or toe areas). Owing to this variance of the MTC’s position, the corresponding kinemics situation in the MTCs also varies. Accordingly, we determined the corresponding location in which the gashydrate develops for various types of MTCs. Based on the bottom simulating reflectors (BSRs) and the hydrate core and image logging data, the gashydrate reservoir shows an obvious heterogeneity in various types of MTCs. The gashydrate in the tension-type MTCs are mostly borne in the toe and the headwall parts. In extrusion-type MTCs, the translational and toe parts constitute an ideal hydrate reservoir. In shear-type MTCs, the headwall and toe parts’ coarse-grained sediments show an obviously hydrate response. After comparing the gas-hydrate saturation and MTCs morphology statics data, we were able to quantitatively prove that the main factors determining gashydrate accumulation in the different types of MTCs are the fault displacement, sedimentary rate, and flow erosion rate.

Seismic Imaging of Seafloor Deformation Induced by Impact from Large Submarine Landslide Blocks, Offshore Oregon

A series of large blocks from the 44-North Slide, offshore Oregon, impacted the seafloor with sufficient force to induce a broad zone of deformation. In 2017, we acquired a seismic profile from the headwall area to the outer toe of this slide. Previous work identified this slide, but it has not been imaged at high resolution before this survey. A striking surficial feature is a collection of blocks that lie downslope from an amphitheater-shaped headwall. The blocks traveled up to 20-km horizontally and about 1200-m vertically down a 13° slope and now cover an area of ~100 km2. The blocks have rough and angular edges that extend up to 400-m above the surrounding seafloor. Seaward of the blocks, a 10-km zone of sediment is deformed, horizontally shortened by 8%. We interpret the strain field to be a result of the dynamic impact forces of the slide. This suggests a high-mobility failure with tsunamigenic potential. It is unclear what preconditioned and triggered this event, however, earthquake-induced failure is one possibility. Gas hydrate dissociation may have also played a role due to the presence of a bottom-simulating reflector beneath the source area. This study underscores the need to understand the dynamic processes of submarine landslides to more accurately estimate their societal impacts.

Thaw slump activity measured using stationary cameras in time-lapse and Structure-from-Motion photogrammetry

Thaw slumps are one of the most dynamic features in permafrost terrain. Improved temporal and spatial resolution monitoring of slump activity is required to better characterize their dynamics over the thaw season. We assess how a ground-based stationary camera array in a time-lapse configuration can be integrated with unmanned aerial vehicle (UAV)-based surveys and Structure-from-Motion processing to monitor the activity of thaw slumps at high temporal and spatial resolutions. We successfully constructed point-clouds and digital surface models of the headwall area of a thaw slump at 6- to 13-day intervals over the summer, significantly improving the decadal to annual temporal resolution of previous studies. The successfully modeled headwall portion of the slump revealed that headwall retreat rates were significantly correlated with mean daily air temperature, thawing degree-days, and average net short-wave radiation and suggest a two-phased slump activity. The main challenges were related to strong JPEG image compression, drifting camera clocks, and highly dynamic nature of the feature. Combined with annual UAV-based surveys, the proposed methodology can address temporal gaps in our understanding of factors driving thaw slump activity. Such insight could help predict how slumps could modify their behavior under changing climate.

The Agadir Slide offshore NW Africa: Morphology, emplacement dynamics, and potential contribution to the Moroccan Turbidite System

A newly identified large-scale submarine landslide on the NW African margin (Agadir Slide) is investigated in terms of its morphology, internal architecture, timing, and emplacement processes using high-resolution multibeam bathymetry data, 2D seismic profiles, and gravity cores. The Agadir Slide is located south of the Agadir Canyon at a water depth ranging from 500 m to 3,500 m, showing an estimated affected area of approximately 5,500 km2. The analysis of the Agadir Slide's complex morphology reveals the presence of two headwall areas and two slide fairways (the Western and Central slide fairways). Volume calculations indicate that ∼340 km3 of sediment were accumulated downslope along the slide fairways (∼270 km3) and inside the Agadir Canyon (∼70 km3). Stratigraphic correlations based on five gravity cores indicate an emplacement age of 142±1 ka for the Agadir Slide. However, its emplacement dynamics suggest that the slide was developed in two distinct, successive stages. The presence of two weak layers (glide planes) is a major preconditioning factor for the occurrence of slope instability in the study area, and local seismicity related to fault activity and halokinesis likely triggered the Agadir Slide. Importantly, the Agadir Slide neither disintegrated into sediment blocks nor was transformed into turbidity currents. The emplacement timing of the Agadir Slide does not correlate with any turbidites cored downslope across the Moroccan Turbidite System.

Mass wasting along the NW African continental margin

Abstract The NW African continental margin is well known for the occurrence of large-scale but infrequent submarine landslides. The aim of this paper is to synthesize the current knowledge on submarine mass wasting off NW Africa with a special focus on the distribution and timing of large landslides. The described area reaches from southern Senegal to the Agadir Canyon. The largest landslides from south to north are the Dakar Slide, the Mauritania Slide, the Cap Blanc Slide, the Sahara Slide and the Agadir Slide. Volumes of individual slides reach several hundreds of cubic kilometres; run-outs are up to 900 km. In addition, giant volcanic debris avalanches are widespread on the flanks of the Canary Islands. All headwall areas are complex with clear indications of multiple failures. The most prominent similarity between all investigated landsides is the existence of widespread glide planes that follow the stratigraphy, which points to weak layers as most important preconditioning factor for the failures. Landslides with volumes larger than 100 m 3 are close to being evenly distributed over time, contradicting previous suggestions that landslides off NW Africa occur at periods of low or rising sea level. The risk associated with the landslides off NW Africa, however, is relatively low due to their long recurrence rates.

Entrainment and abrasion of megaclasts during submarine landsliding and their impact on flow behaviour

Abstract Many mass transport complexes (MTCs) contain up to kilometre-scale (mega)clasts encased in a debritic matrix. Although many megaclasts are sourced from the headwall areas, the irregular basal shear surfaces of many MTCs indicate that megaclast entrainment during the passage of flows into the deeper basin is also common. However, the mechanisms responsible for the entrainment of large blocks of substrate, and their influence on the longitudinal behaviour of the associated flows, have not been widely considered. We present examples of megaclasts from exhumed MTCs (the Neuquén Basin, Argentina and the Karoo Basin, South Africa) and MTCs imaged in three-dimensional seismic reflection data (Magdalena Fan, offshore Colombia and Santos Basin, offshore Brazil) to investigate these process–product interactions. We show that highly sheared basal surfaces are well developed in distal locations, sometimes extending beyond their associated deposit. This points to deformation and weakening of the substrate ahead of the flow, suggesting that preconditioning of the substrate by distributed shear ahead of, and to the side of, a mass flow could result in the entrainment of large fragments. An improved understanding of the interactions between flow evolution, seabed topography, and the entrainment and abrasion of megaclasts will help to refine estimates of run-out distances, and therefore the geohazard potential of submarine landslides.

Giant mass-transport deposits in the southern Scotia Sea (Antarctica)

Abstract On the basis of 2D multichannel and very-high-resolution seismic data and swath bathymetry, we report a sequence of giant mass-transport deposits (MTDs) in the Scan Basin (southern Scotia Sea, Antarctica). MTDs with a maximum thickness of c. 300 m extend up to 50 km from the Discovery and Bruce banks towards the Scan Basin. The headwall area consists of multiple U-shaped scars intercalated between volcanic edifices, up to 250 m high and 7 km wide, extending c. 14 km downslope from 1750 to 2900 m water depth. Seismic sections show that these giant MTDs are triggered by the intersection between diagenetic fronts related to silica transformation and vertical fluid-flow pipes linked to magmatic sills emplaced within the sedimentary sequence of the Scan Basin. This work supports that the diagenetic alteration of siliceous sediments is a possible cause of slope instability along world continental margins where bottom-simulating reflectors related to silica diagenesis are present at a regional scale.

Morphology, age and sediment dynamics of the upper headwall of the Sahara Slide Complex, Northwest Africa: Evidence for a large Late Holocene failure

The Sahara Slide Complex in Northwest Africa is a giant submarine landslide with an estimated run-out length of ~900km. We present newly acquired high-resolution multibeam bathymetry, sidescan sonar, and sub-bottom profiler data to investigate seafloor morphology, sediment dynamics and the timing of formation of the upper headwall area of the Sahara Slide Complex. The data reveal a ~35-km wide upper headwall,opening towards the northwest, with multiple slide scarps, glide planes, plateaus, lobes, slide blocks and slide debris. The slide scarps were generated by retrogressive failure events associated with two types of mass movements: translational sliding and gravitational spreading. As a result of this evolution, three different glide planes (GP I, II, and III) can be distinguished approximately 100m, 50m and 20m below the seafloor. These glide planes are widespread and suggest failure along pronounced, continuous weak layers. Our data suggest an age of only about 2ka for the failure of the upper headwall area, a date much younger than that derived for landslide deposits on the lower reaches of the Sahara Slide Complex, which are dated at 50–60ka. The young age of the failure contradicts the postulate of a stable slope offshore Northwest Africa during sea-level highstands. Such an observation suggests that submarine-landslide risk along the continental margin of Northwest Africa should be reassessed based on a robust dating of proximal and distal slope failures.

Geomorphology of the huge Hinlopen–Yermak landslide on the northern Svalbard margin

Submarine landslide scars, including the huge Hinlopen–Yermak slide-scar north of Svalbard (Fig. 1) (Vanneste et al. 2006; Winkelmann et al. 2006), are relatively common geomorphological features on glaciated continental margins. However, landslide characteristics, for example scar area, run-out and displaced volume, vary significantly (Hogan et al. 2013). A key pre-condition for failure is rapid deposition of mainly diamictic glacier-derived sediment on the slope during full-glacials, alternating with fine-grained interglacial deposition. This layered architecture, and the varying geotechnical properties of the debris, facilitate downslope mass-movements with a variety of possible triggers. Fig. 1. Marine geophysical data over Hinlopen–Yermak landslide scar, northern Svalbard. ( a ) Multibeam image showing slide scar. PR, arcuate pressure ridges. DR, detached sediment ridges. Acquisition systems Kongsberg EM300. Frequency 30 kHz (RV Jan Mayen ). Hydrosweep DS2. Frequency 15.5 kHz (RV Polarstern ). Kongsberg EM120. Frequency 12 kHz (RSS James Clark Ross ). Grid-cell size 100 m. ( b ) Seismic-reflection profile of slide headwall and post-slide sediment fill. Acquisition system two 40 cubic inch airguns. VE×6. ( c ) Bathymetric image of the complex eastern headwall area showing detached sediment ridges (DR and inset; VE×7) and blocky debris (BD) on slip planes. ( d ) Bathymetric image of rafted mega-blocks within slide debris. Ridges of material pushed up …

Origin, structural geometry, and development of a giant coherent slide: The South Makassar Strait mass transport complex

The South Makassar Strait mass transport complex (MTC) covers an area of at least 9000 km 2 and has a total volume of 2438 km 3 . It is composed of a shale-dominated sedimentary unit with high water content. Seismic reflection data across the South Makassar Strait MTC show that it displays relatively coherent internal sedimentary stratigraphy that in the toe region is deformed into well-defined thrust-related structures (imbricates, ramps and flats, fault bend folds). It is one of the largest known coherent MTCs. The bowl-shaped central core region is as much as 1.7 km thick, and is confined to the west and east by 355° and 325° trending (respectively) lateral ramps in the upper slope area that pass via oblique ramps into a northeast-southwest–trending frontal ramp area. The core area passes via the lateral, oblique, and frontal ramps into an extensive, thin (tens of meters thick) region of the MTC (the lateral and frontal apron areas) that are internally deformed by thrusts, normal faults, and thrust faults reactivated as normal faults. The MTC anatomy can be divided into extension headwall, translational, toe, flank, lateral apron, and frontal apron domains. The headwall region is located in the upper slope area of the Paternoster platform; the main body of the slide is in the deep-water region of the Makassar Strait. The complex is interpreted to be triggered by uplift of the platform area (accompanied by inversion), and/or basin subsidence, which caused seaward rotation of ∼2° of the Paternoster platform in the Pliocene. Variable uplift promoted sliding dominantly from the eastern and western margins of the headwall. The internal fault patterns of the MTC show that extension in the upper slope to lower slope in the core area changes downslope to compressional structures in the toe domain and apron. Later extensional collapse of parts of the compressional toe area occurred with negative inversion on some faults. The coherent internal stratigraphy, and evidence for multiphase extension in the eastern headwall area, suggests that the ∼6–7 km of shortening in the toe region of the MTC occurred at a slow strain rate. Therefore, this type of MTC does not have the potential to generate tsunamis.

New insights into slide processes and seafloor geology revealed by side-scan imagery of the massive Hinlopen Slide, Arctic Ocean margin

The submarine Hinlopen Slide, located along the Arctic Ocean margin, is one of the largest known mass movements on Earth. The slide scar has several unusual morphometric characteristics, including headwalls up to 1,500 m high and spectacularly large, steep-sided rafted megablocks. The slide processes and continental margin properties that produced these features are not well known. A new high-resolution TOBI (towed ocean bottom instrument) side-scan sonar dataset reveals information about the detailed seafloor morphology and, therefore, slide dynamics during the final stages of sliding. First, the headwall area was efficiently and almost completely evacuated of slide debris, which is unusual for large submarine slides. Second, features relating to the propagation of extension to the shelf behind the headwall are absent, suggesting “strong” cohesive shelf material here or that a very stable shelf configuration was reached, possibly defined by NE-SW-trending faults. Third, there is little evidence for the translation of shelf material, again uncommon for submarine slides. Taken together with the occurrence of massive megablocks in the slide debris, Hinlopen Slide is distinct because of the juxtaposition of apparently “stronger” shelf material that has remained intact (headwalls, megablocks), and “weaker” shelf material that disaggregated fully during slope failure. Nevertheless, there is sonograph evidence of variable post-slide disintegration of the megablocks. Contrary to previous interpretations, this suggests that the blocks comprise sedimentary lithologies that are prone to failure, a key aspect awaiting confirmation.

Geomorphometry of a submarine mass-transport complex and relationships with active faults in a rapidly uplifting margin (Gioia Basin, NE Sicily margin)

Abstract Along the NE Sicily margin, between Capo Milazzo and Capo Peloro, in the offshore Gioia Basin area facing the Castanea Ridge, a mass-transport complex (MTC) was first imaged by multibeam data acquired by the end of the 1990s. It was interpreted as resulting from the stacking of different mass-transport deposits due to repeated failures of the shelf edge and upper slope area and of the nearby Villafranca slope channel-levee wedge. New high resolution swath bathymetry and seismic data, acquired in 2009–2011, allowed the complete coverage of the headwall area of the 48 km3 Villafranca frontally-confined slide, which represents the bulk of the MTC, and that was previously not mapped. Seven smaller individual zones of instability that represent the source areas of distinct mass-transport deposits emplaced in the upper and lower slope, having surface areas between 10 km2 and 60 km2, were also mapped. The new data show that, although the Villafranca slide and the subsequent more recent failures were not sourced from the same headwall area, they are similarly associated to the activity of the faults that characterize the NE Sicily rapidly uplifting margin. The Villafranca slide has its headwall along a normal fault parallel to the coast, which is visible in the shelf at 80–85 m water depth offsetting the seafloor for 30 m. The slab slide and the debris flow lobes have their headwalls along a NNE–SSW oriented normal fault, which offsets the seafloor for 30 m and is the offshore prolongation of a regional structure on land. The largest debris flow lobe in the area was actually generated through flow transformation mechanisms from an initial slump mass. The main headwall scarps are rectilinear and exploit regional normal faults along which the principal and larger slope failures (slide and slumps) root, possibly during episodes of accelerated uplift, recognized by several authors in the area, both in Late Pleistocene and during the Holocene. Successive morphological modifications and flow transformations, resulting from smaller scale failures (debris flows), generate more complex headwalls. In addition, the MTC is bounded to the NE by a recent reverse fault which prolongs in a structural ridge (Acquarone Ridge) where evidence of seafloor fluid escapes (pockmarks) is present, implying that compressive and transpressive structures can be active in the area and play an underestimated role in the instability of the NE Sicily margin.

Morphological indicators of Late Quaternary co-seismic vertical displacements and catastrophic wave impact in Lesvos Island (NE Aegean Sea)

Along the NE Sicily margin, between Capo Milazzo and Capo Peloro, in the offshore Gioia Basin area facing the Castanea Ridge, a mass-transport complex (MTC) was first imaged by multibeam data acquired by the end of the 1990s. It was interpreted as resulting from the stacking of different mass-transport deposits due to repeated failures of the shelf edge and upper slope area and of the nearby Villafranca slope channel-levee wedge. New high resolution swath bathymetry and seismic data, acquired in 2009–2011, allowed the complete coverage of the headwall area of the 48 km3 Villafranca frontally-confined slide, which represents the bulk of the MTC, and that was previously not mapped. Seven smaller individual zones of instability that represent the source areas of distinct mass-transport deposits emplaced in the upper and lower slope, having surface areas between 10 km2 and 60 km2, were also mapped.The new data show that, although the Villafranca slide and the subsequent more recent failures were not sourced from the same headwall area, they are similarly associated to the activity of the faults that characterize the NE Sicily rapidly uplifting margin. The Villafranca slide has its headwall along a normal fault parallel to the coast, which is visible in the shelf at 80–85 m water depth offsetting the seafloor for 30 m. The slab slide and the debris flow lobes have their headwalls along a NNE–SSW oriented normal fault, which offsets the seafloor for 30 m and is the offshore prolongation of a regional structure on land. The largest debris flow lobe in the area was actually generated through flow transformation mechanisms from an initial slump mass.The main headwall scarps are rectilinear and exploit regional normal faults along which the principal and larger slope failures (slide and slumps) root, possibly during episodes of accelerated uplift, recognized by several authors in the area, both in Late Pleistocene and during the Holocene. Successive morphological modifications and flow transformations, resulting from smaller scale failures (debris flows), generate more complex headwalls.In addition, the MTC is bounded to the NE by a recent reverse fault which prolongs in a structural ridge (Acquarone Ridge) where evidence of seafloor fluid escapes (pockmarks) is present, implying that compressive and transpressive structures can be active in the area and play an underestimated role in the instability of the NE Sicily margin.

Failure mechanisms of Ana Slide from geotechnical evidence, Eivissa Channel, Western Mediterranean Sea

This work deals with the failure mechanisms of Ana Slide in the Eivissa Channel, in between the Iberian Peninsula and the Balearic Islands, under the effects of gas charging and seismic loading. In situ geotechnical tests and sediment cores obtained at the eastern Balearic slope of the Eivissa Channel suggest that the basal failure surface (BFS) developed as a result of subtle contrasting hydro-mechanical properties at the boundary between a fine-grained unit (U6) overlying a methane-charged relatively coarser unit (U7). Past methane seepage is inferred from seismic reflection profiles and high magnetic susceptibility values in sediments from the slide headwall area. Past methane charging is also supported by further seismic reflection data and isotopic analyses of benthic foraminifera published separately. The possibility of failure for different critical failure surfaces has been investigated by using the SAMU-3D slope stability model software taking into account the role of free methane in the development of the landslide. Failure would occur after SAMU-3D if the undrained shear strength of units U6 and U7 is strongly degraded (i.e. 95%). Wheeler's theory suggests that a 9% free gas saturation would be required to reduce the undrained shear strength by 95%. However, the theory of the undrained equilibrium behaviour of gassy sediments for this methane concentration shows that the excess fluid pressure generated by gas exsolution, estimated at 12% of the effective stress, is not high enough to bring the slope to fail. This led us to consider seismic loading as an additional potential failure mechanism despite the lack of historical data (including instrumental records) on seismicity in the Balearic Islands, therefore assuming that the historical period is not necessarily representative of seismic activity further back in time (i.e. when Ana Slide occurred ~61.5ka ago). Considering current slope conditions, the most critical failure surface obtained by SAMU-3D relates to peak ground accelerations (PGA) of 0.24g, which relates to magnitude moment Mw=5 at epicentral distances of 1km, and 7≥Mw≥5 at epicentral distances ≤15km to Ana Slide. However, no active faults have been identified at so short distance from Ana Slide. Only when shear strength is degraded due to the presence of free methane in units U6 and U7 is considered, the most critical failure surface obtained by SAMU-3D fits with lower magnitude and larger epicentral distances. Consequently, the most plausible hypothesis to explain the occurrence of Ana Slide is the combination of free gas and seismic loading.

Mass-transport complex evolution in a tectonically active margin (Gioia Basin, Southeastern Tyrrhenian Sea)

Along the southeastern Tyrrhenian Sea margin, the Gioia Basin formed as a result of extensional tectonics at the rear of the Maghrebian thrust belt. In the central part of the basin, mass-transport deposits represent up to 80% of its recent infill. The basin-wide Nicotera slump is the deepest mass-transport deposit present in the basin and was followed by sheet turbidite deposition. Above the turbidite package, a mass-transport complex (MTC) formed through the stacking of different mass-transport deposits due to repeated failures of the continental slope and of a base of slope channel levee wedge, which is still preserved in the western side of the basin. The Villafranca frontally-confined slide, a body mainly consisting of coherent blocks, represents the bulk of the MTC. The failure of the Villafranca slide was due to asymmetric loading of a permeable condensed horizon in the thinnest, distal lateral part of the channel levee wedge. The relatively large thickness of the Villafranca slide caused it to remain confined at its toe region. Smaller scale mass-transport deposits, a debris-flow sheet and a debris-flow lobe, followed the Villafranca slide and were sourced from the same headwall area. Their different run out and internal character are possibly a function of the lithology of the material involved in the collapse. A slab slide, characterized by little internal deformation and frontal contractional ridges, originated when seafloor instability propagated towards the north, causing clockwise rotation of a sediment wedge. Along the linear headwall of the slab slide, a localized upslope failure propagation is shown by a small scale re-entrant. The Sicilian margin, along which the Gioia Basin develops, is characterized by strong differential vertical movements due to ongoing extensional tectonics. The effects of both local and regional strong earthquakes are frequently felt in the area. Thus, slope oversteepening and earthquakes are suggested as the more likely causes for the observed repeated events of seafloor failure. In addition, an evolution of the MTC through larger slides controlled by the migration of uplift of the basin bounding submarine ridge, followed by smaller scale failures due to the consequent slope profile modification, is here advanced.

The Hinlopen Slide: A giant, submarine slope failure on the northern Svalbard margin, Arctic Ocean

New swath bathymetry data unveil a giant, submarine landslide located at the mouth of the Hinlopen transverse trough on the northern Svalbard margin, Arctic Ocean. Despite the relatively small drainage and slide scar areas, the Hinlopen Slide is exceptional in volume, headwall height and dimensions of the rafted blocks. From the c. 2200 km 2 large headwall area, approximately 1350 km 3 of Plio-Pleistocene sediments have been evacuated from the continental margin to the Nansen Basin. The escarpment heights are unprecedented, exceeding 1400 m, whereas the rafted blocks observed in the intermediate part of the slide area are up to 450 m high and more than 5 km wide. These characteristics make the Hinlopen Slide one of the largest landslides worldwide, and the first mapped mega-slide in the Arctic Ocean. Within the amphitheatre-shaped slide scar area, a composite set of escarpments and multiple, roughly planar slip surfaces occur, as well as detached sediment ridges adjacent to the outer escarpment, arcuate pressure ridges in debris lobes and isolated slump debris or blocks. From this complex slide scar geomorphology, we infer that the Hinlopen Slide was a translational, multi-phase slope failure that developed retrogressively. The slide has not been dated yet; however, the geophysical data suggest a relatively young age, though probably pre-Holocene, inferred from the pattern of sediment infill within the slide scar area derived from the Hinlopen cross-shelf trough. A submarine landslide with these dimensions could have created a devastating tsunami, although its potential depends on sea ice conditions as well as the time lags of the multi-phase, retrogressive movement. Climate changes and the response of ice sheets, ocean-current systems, sediment delivery and seismicity related to glacio-isostatic deformation appear as critical factors controlling stability on glaciated margins.

Fluid flow impact on slope failure from 3D seismic data: a case study in the Storegga Slide

AbstractAnalysis of three‐dimensional (3D) seismic data from the headwall area of the Storegga Slide on the mid‐Norwegian margin provides new insights into buried mass movements and their failure mechanisms. These mass movements are located above the Ormen Lange dome, a Tertiary dome structure, which hosts a large gas reservoir. Slope instabilities occurred as early as the start of the Plio‐Pleistocene glacial–interglacial cycles. The 3D seismic data provide geophysical evidence for gas that leaks from the reservoir and migrates upward into the shallow geosphere. Sediments with increased gas content might have liquefied during mobilization of the sliding and show different flow mechanisms than sediments containing less gas. In areas where there is no evidence for gas, the sediments remained intact. This stability is inherited by overlying strata. The distribution of gas in the shallow subsurface (<600 m) may explain the shape of the lower Storegga headwall in the Ormen Lange area.

Ship Mountains Megabreccia: Implications for Miocene Extensional Tectonics, Eastern Mojave Desert, California

The megabreccia of the Ship Mountains is part of a sedimentary sequence displaying characteristics of a catastrophic landslide deposit: (1) fractured clasts; (2) a graded, fine-grained upper mantling layer; (3) sandstone dikes injected from below; (4) fine-grained, massive matrix; and (5) local, monolithologic character. Its presence downslope from the headwall of a large Miocene normal fault, and correlation of breccia clasts with basement lithologies in the headwall area, further support the landslide hypothesis. This interpretation has important implications for the structural evolution of the area, suggesting two major phases of fault block rotation associated with extensional stresses along the western flank of the Old Woman Mountains structural horst.