Slope failures along the deformation front of the Cascadia margin: linking slide morphology to subduction zone parameters

2018 ◽  
Vol 477 (1) ◽  
pp. 47-67 ◽  
Author(s):  
Michael Riedel ◽  
Michelle M. Côté ◽  
Morelia Urlaub ◽  
Jacob Geersen ◽  
Nastasja A. Scholz ◽  
...  
Keyword(s):  
Debris Flows ◽  
Slope Failure ◽  
Accretionary Prism ◽  
Tsunami Generation ◽  
Slope Failures ◽  
Deformation Front ◽  
Acoustic Data ◽  
Submarine Slope ◽  
Cascadia Margin ◽  
Zone Parameters

AbstractMarine acoustic data are used to map and characterize submarine slope failure along the accretionary prism of Cascadia. Two main styles of slope failure are identified: (1) failures with curved head scarps, which are predominantly associated with incoherent debris-flow deposits; and (2) failures with rectangular head scarps, which are predominantly associated with intact sediment blocks. Rectangular head scarps mostly occur on thrust ridges with slope angles <16° and ridge heights <650 m, whereas curved head scarps occur predominantly on steeper and higher ridges. Off Vancouver Island, failure style and head-scarp geometry also change with ridge azimuth. We propose that the curved head scarps and debris flows may be a result of higher kinetic forcing of the downsliding sediments and a higher degree of mixing. At the more gently sloped, less elevated ridges, the kinetic forcing may be smaller, which leads to intact failure masses. Extensional faults at ridges with curved scarps may result from oversteepening and collapse of the sediments that cannot withstand their own weight due to limited internal shear strength. The slide geometries and potential controls on failure style may inform subsequent studies in assessing the risks for tsunami generation from submarine slope failures along the Cascadia margin.

Investigating the controls of submarine landslides and associated hazards in Pangnirtung Fiord, Eastern Baffin Island (Nunavut)

2021 ◽  
Author(s):  
Philip Sedore ◽  
Alexandre Normandeau ◽  
Vittorio Maselli
Keyword(s):  
High Latitude ◽  
Debris Flows ◽  
Slope Failure ◽  
Recurrence Time ◽  
High Recurrence Rate ◽  
Baffin Island ◽  
Submarine Landslides ◽  
Slope Failures ◽  
Near Surface ◽  
Submarine Slope

&lt;p&gt;High-latitude fiords are susceptible to hazardous subaerial and submarine slope failures. Recent investigations have shown that past slope failures in fiords of Greenland and Alaska have generated devastating landslide induced tsunamis. Since coastal communities inhabit these high-latitude fiords, it is critical to understand the slope failure recurrence time, their distribution, potential triggers, and ability to generate tsunamis. In this study, we identified &gt; 50 near-surface submarine landslides in Pangnirtung Fiord, eastern Baffin Island, Nunavut, using multibeam bathymetric and sub-bottom profiler data, along with sediment gravity-cores collected in 2019. Morphometric and morphological analyses, along with sedimentological analyses, were carried out on submarine landslide deposits to quantify their spatial and temporal distribution throughout the fiord and to evaluate the factors that may have triggered the slope failures.&lt;/p&gt;&lt;p&gt;Combining bathymetric with topographic data from unmanned aerial vehicle imagery, we found that most of these landslide deposits are relatively small (~ 0.08 km&lt;sup&gt;2&lt;/sup&gt;) and are associated with outwash fans and steep fiord sidewalls. However, since most slope failure head scarps lie between the intertidal zone and ~30 m water depth, they could not be mapped, which makes it challenging to determine the triggers of the submarine slope failures. Radiocarbon dating reveals that most of these surficial landslide deposits are younger than 500 years old and that they were most likely triggered at different times. This finding highlights a high recurrence rate of slope failures within the fiord, suggesting that localised triggers are responsible for slope failures within the fiord, as opposed to widespread, seismically induced triggers which do not occur as frequently in the study area. In addition, the elongated morphology of the landslide deposits and the varying degrees of landslide deposit surface roughness supports localised point-source triggers. Since most landslides are associated with subaerial outwash fans and deltas, we suggest that triggers of these relatively frequent submarine landslides within Pangnirtung Fiord include rapid floodwater input, subaerial debris flows, and sea-ice loading during low tide.&lt;/p&gt;&lt;p&gt;This research shows that slope failures in a high-latitude fiord are affected by the interaction of numerous subaerial and submarine processes, leading us to speculate that a potential increase in the frequency of subaerial debris flows and river floods due to climate change may increase the recurrence of submarine landslides.&lt;strong&gt; &lt;/strong&gt;&lt;/p&gt;

scholarly journals The influence of clay content on submarine slope failure: insights from laboratory experiments and numerical models

2020 ◽  
Vol 500 (1) ◽  
pp. 301-309 ◽  
Author(s):  
M. M. W. Silver ◽  
B. Dugan
Keyword(s):  
Pore Pressure ◽  
Slope Failure ◽  
Failure Modes ◽  
Initial Conditions ◽  
Numerical Models ◽  
Clay Content ◽  
Passive Margin ◽  
Slope Failures ◽  
Submarine Slope ◽  
Failure Evolution

AbstractSubmarine slope failures pose risks to coastlines because they can damage infrastructure and generate tsunamis. Passive margin slope failures represent the largest mass failures on Earth, yet we know little about their dynamics. While numerous studies characterize the lithology, structure, seismic attributes and geometry of failure deposits, we lack direct observations of failure evolution. Thus, we lack insight into the relationships between initial conditions, slope failure initiation and evolution, and final deposits. To investigate submarine slope failure dynamics in relation to initial conditions and to observe failure processes we performed physical experiments in a benchtop flume and produced numerical models. Submarine slope failures were induced under controlled pore pressure within sand–clay mixtures (0–5 wt% clay). Increased clay content corresponded to increased cohesion and pore pressure required for failure. Subsurface fractures and tensile cracks were only generated in experiments containing clay. Falling head tests showed a log-linear relation between hydraulic conductivity and clay content, which we used in our numerical models. Models of our experiments effectively simulate overpressure (pressure in excess of hydrostatic) and failure potential for (non)cohesive sediment mixtures. Overall our work shows the importance of clay in reducing permeability and increasing cohesion to create different failure modes due to overpressure.

Influence of Salt Tectonics On Fault Displacements and Submarine Slope Failures from Algeria To Sardinia

2019 ◽  
Vol 25 (4) ◽  
pp. 318-330 ◽  
Author(s):  
Julia A. Yeakley ◽  
Abdul Shakoor ◽  
William Johnson
Keyword(s):  
Debris Flows ◽  
Average Rate ◽  
Plate Boundary ◽  
Western Mediterranean ◽  
Turbidity Currents ◽  
Salt Tectonics ◽  
Slope Failures ◽  
Submarine Slope ◽  
Lateral Extent ◽  
Pipeline Route

ABSTRACT We used previously obtained marine geophysical and geotechnical data for the proposed Galsi pipeline route from Algeria to Sardinia to analyze the buried salt distribution, rates of fault displacements, and frequency and lateral extent of submarine slope failures. Crossing the convergent African/Nubian–European plate boundary, the southern section of the pipeline route traverses continental shelves and slopes of Algeria and Sardinia as well as the Algerian abyssal plain of the western Mediterranean. Deeply buried Messinian-aged salt is present throughout this area. Being less dense and more buoyant than the overburden sediment, the salt tends to flow upward to form diapiric structures that, in turn, result in the formation of faults and landslides in the overlying sediment. Measured offsets from seismic profiles of different resolutions were compared with predicted sediment age at depth of each offset, yielding an average rate of fault displacement of 1.5 cm/kiloyear (ky). The highest rates of displacement are along the Cagliari slope near Sardinia (2.5-2.7 cm/ky) and near the convergent plate boundary (2.3 cm/ky). Utilizing the same geophysical data, the frequency and lateral extent of submarine slope failures in the study area can also be linked to the distribution of salt and the influence of salt tectonics. Turbidity currents and hyperpycnal flows are present within the Algerian basin, whereas local debris flows, landslide runouts, and channelized debris flows are present along the Sardinian slope. The low sedimentation rates, determined in this study, suggest that the most recent slope failures related to salt tectonics occurred more than 12,000 years ago.

scholarly journals On the potential of gassy marine soils triggering submarine slope instabilities

2020 ◽  
Vol 205 ◽  
pp. 12006
Author(s):  
Pauline Kaminski ◽  
Jürgen Grabe
Keyword(s):  
Slope Failure ◽  
Turbidity Currents ◽  
Continental Margins ◽  
Extensive Literature ◽  
Slope Failures ◽  
Free Gas ◽  
Submarine Slope ◽  
Failure Event ◽  
Liquefaction Failure ◽  
Excess Pore Pressures

The development of debris flows and turbidity currents in the course of a submarine slope failure event can cause major damage in offshore infrastructure. Additionally, the tsunamogenic potential of large slope failures at continental margins poses a direct threat to coastal communities. Therefore, the trigger mechanisms of submarine slope failures have been thoroughly investigated in the past. However, the influence of free gas in the sediment, which has been observed close to several slide events, remains unexplained. In order to evaluate the potential of gassy marine soils to precondition or trigger slope failure the mechanical behaviour of gassy soils is assessed based on an extensive literature review. It is found that gas-induced excess pore pressures can lead to liquefaction failure in sands, while cohesive, gassy soils show a less conclusive response. Hence, fine-grained soils and approaches to implement the gas impact into relevant existing constitutive soil models are assessed in greater detail. Concludingly, based on the predominant boundary conditions in failure prone regions at the continental margins, free gas occurrence can be defined as a preconditioning factor rather than as a definite trigger mechanism.

Seafloor geomorphology and submarine landslide hazards along the continental slope in the Carnarvon Basin, Exmouth Plateau, North West Shelf, Australia

2012 ◽  
Vol 52 (1) ◽  
pp. 493 ◽  
Author(s):  
James Hengesh ◽  
James K. Dirstein ◽  
Alistair J. Stanley
Keyword(s):  
Continental Slope ◽  
Seismic Data ◽  
Slope Failure ◽  
Sediment Accumulation ◽  
Infrastructure Development ◽  
Slope Failures ◽  
North West ◽  
Exmouth Plateau ◽  
Submarine Slope ◽  
Carnarvon Basin

3D exploration seismic data were interpreted to investigate the locations and characteristics of submarine slope failures along the continental slope in the offshore Carnarvon Basin on Australia’s North West Shelf. Seisnetics™, a patented genetic algorithm was used to process the 3D seismic data to extract virtually all trough and peak surfaces in an unbiased and automated manner. The extracted surfaces were combined in the 3D visual database to develop a seafloor digital terrain model that extends from the continental slope to the Exmouth Plateau. The 3D data were used to map the subsurface extent and geometry of landslide failure planes, as well as to estimate the thickness and volumes of slide deposits. This paper describes the geomorphic characteristics of five of the survey areas. Geomorphic mapping shows the presence of slope failures ranging from small (20 km across) mass transport complexes (MTC). The features are associated with debris flow chutes, turbidity flow channels, and debris fields. Analysis of failure planes show prominent grooves or striations related to the mobilisation of slide material down both the continental slope and Exmouth Plateau and into the Kangaroo Syncline. Submarine slope failures can occur at the continental shelf break in about 200–300 m of water and run out to the Exmouth Plateau surface in about 1,100–1,400 m water depths. The largest individual slides in the survey areas have widths of 30 km and minimum run-out lengths of 75 km, though associated turbidity flow deposits likely extend much further. The subsurface expression of the large MTCs illustrates a history of sediment accumulation along the mid-slope followed by repeated slope failure and debris run-out. Sediment accumulation and slope failure processes are actively occurring along the continental slope and submarine landslides thus are a major driver of hazard to subsea infrastructure development. Smaller more frequent slides may pose a greater hazard than large infrequent MTCs.

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