Morphology of small-scale submarine mass movement events across the northwest United Kingdom
0
Citation
0
Reference
10
Related Paper
Abstract:
<p>Given the potentially devastating consequences of shallow submarine landslides on infrastructure and human lives, it is imperative that we understand potential slope stability issues within marine coastal regions. In Scottish waters, our lack of knowledge regarding the nature of the seabed within the fjords and coastal inlets is concerning given that these sea lochs have similar morphological features and settings to global examples (e.g. Norway) where recent slope failures have had such highly devastating results. Global examples from similar physiographic settings also demonstrate the temporal aspect of these events, highlighting that they are caused by active modern processes and therefore represent contemporary geohazards. In addition, previous studies have highlighted that there tends to be a scale bias towards the mapping and reporting of large-scale events, and there is a requirement for studies that focus on small-scale (&#8804;1 km<sup>3</sup>) mass movements which can still have damaging consequences on seafloor and coastal (both nearshore and onshore) infrastructure.</p><p>In this study, a review of multibeam echo sounder (MBES) survey datasets from five locations around the United Kingdom northwest coast has led to the identification of a total of 14 separate submarine mass movement scars and deposits within the fjords (sea lochs) and coastal inlets of mainland Scotland, and the channels between the islands of the Inner Hebrides. In these areas, Quaternary sediment deposition was dominated by glacial and glaciomarine processes. Analysis of the morphometric parameters of each submarine mass movement has revealed that they fall into four distinct groups of subaqueous landslides; Singular Slumps, Singular Translational, Multiple Single-Type, and Complex (translational & rotational) failures. The Singular Slump Group includes discrete, individual subaqueous slumps that exhibit no evidence of modification through the merging of several scars. The Singular Translational Group comprise a single slide that displays characteristics associated with a single translational (planar) failure with no merging of multiple events. The Multiple Single-Type Group incorporates scars and deposits that displayed morphometric features consistent with the amalgamation of several failure events of the same type (e.g. debris flows or slumps). Finally, the Complex (translational & rotational) Group comprises landslides that exhibited complex styles of failures, including both translational and rotational mechanisms controlling the same slide. The submarine mass movements that comprise this dataset are then discussed in relation to global fjordic and glaciomarine nearshore settings, and slope failure trigger mechanisms associated with these environments are described with tentative links to individual submarine landslides from the database, where appropriate. It is acknowledged that additional MBES data are needed not only to expand this database but also to create a more statistically robust study. However, this initial study provides the basis for a much wider investigation of submarine mass movements and correlations between their morphometric parameters.</p>Keywords:
Fjord
Channelized
Submarine landslide
Seafloor Spreading
Seabed
“Fjord are best developed on the coasts of British Columbia, southern Alaska, southern Chile, eastern Canada, Greenland, Norway, Iceland and Spitsbergen, the south-west of South Island (New Zealand); and finally Antarctica-Embleton & King (1968): Glacial and Periglacial Geomorphology p. 234”“fjord, or FIORD, long narrow arm of the sea, commonly extending far inland, that results from marine inundation of a glaciated valley. Many fjords are astonishingly deep-The New Encyclopaedia Britannica, 1968”There are 56 fjords in Denmark. The fjords in east-Jylland are the result of marine submergence of the deepest parts of the tunnel valleys, good examples are given by Vejle Fjord, Mariager Fjord. Sidinge fjord and Lamme fjord in Sjælland are central depressions under sea level. Maximum extent of the Stone Age Sea, and Ringkø bing Fjord, Nissum Fjord in west-Jylland are lagoons.
Fjord
Cite
Citations (0)
Fjord
Submarine landslide
Debris flow
Cite
Citations (23)
Abstract The Meiwa tsunami of AD 1771 is regarded as an extremely strong tsunami event causing devastating damage in Japan in historical times. Earlier studies explored the possibility that a submarine landslide enhanced the Meiwa tsunami waves. We collected detailed seafloor bathymetry data, sub-bottom structure data and surface sediments in a putative Meiwa tsunami source region to ascertain any signature related to a submarine landslide in the forearc region, which is located south of Ishigaki-jima. The forearc-region seafloor is characterized by its surface submarine landslide morphology. However, the investigated magnetic fabric of surface sediment revealed that there was no landslide mass deposit during historical times. The described landslide morphology in the basin is unrelated to the generation or enhancement of the AD 1771 Meiwa tsunami, although the disturbed relief in the topography of the study area indicates that the forearc region is susceptible to slope failure because of its tectonic setting.
Forearc
Submarine landslide
Seafloor Spreading
Cite
Citations (3)
Seafloor Spreading
Submarine landslide
Flank
Cite
Citations (93)
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.
Seafloor Spreading
Submarine landslide
Geohazard
Seabed
Cite
Citations (16)
Evaluation of wave impacts on submarine landslides is an essential element in geohazard studies. The slight desaturation of sediments (due to dissociation of gas hydrates) has been found to adversely impact the slide of the sloping seabed in the Fraser River Delta in Canada. In this study, to investigate the role of wave action on the slide of partially saturated seabed slopes, an integrated FEM model is developed. Despite most earlier studies that used a simplified decoupled undrained analysis, in this article, a more realistic model for coupled flow-and-deformation processes (within the sediments) and fluid-seabed interaction is utilized. Linear wave theory and Biot's poroelasticity for the fluid and seabed domains are considered, respectively, and continuity of flux and traction is enforced along the interface of the media. The instability of the sloping seabed is investigated using strength reduction finite element method (SRFEM) with Mohr-Coulomb failure criterion. The limitation of limit equilibrium methods in the evaluation of submarine landslides is shown through comparison with SRFEM analyses where partly-dynamic and quasi-static idealizations of seabed response are considered. Finally, the adverse impacts of slight desaturation on seabed instability are assessed, and the reduction of the stability number with seabed steepness is presented.
Seabed
Submarine landslide
Geohazard
Biot number
Wave loading
Cite
Citations (6)