Submarine Canyon Heads Research Articles

The role of liquefaction in the evolution of shallow submarine canyon heads from a geotechnical perspective: A case study of the Garrucha Canyon (SE Mediterranean)

This work aims to establish the role of liquefaction in a shallow submarine environment defined by a canyon head reaching the coast. The study area is the Garrucha submarine canyon head, which is located in the western Mediterranean Sea.The potential of liquefaction is approached empirically by two methods in parallel, undrained cyclic direct simple shear (UCDSS) test and piezocone penetration test (CPTu) analyses. For both approaches, considering the regional earthquake records, a cyclic load linked to Mw ≤ 6.5 earthquake events or a maximum ground surface acceleration amax of 0.25 g is considered.The sediment samples analysed are nonplastic sands with low silt/clay contents and can be defined as liquefiable. Geotechnical analysis reveals a high probability of triggering liquefaction in this kind of sediment at depths greater than 3 m below the seafloor. CPTu records are used to assess and improve the liquefaction model for the study area by defining 3 different stratigraphic configurations or liquefiable conditions: uniformly liquefiable, interbedded liquifiable and nonliquefiable.This work highlights the importance of liquefaction—a process normally underestimated in submarine environments—in the downslope transport of sediment from the upper part of a canyon and, more generally, in canyon head evolution with different potential morphosedimentary consequences.

Sedimentary record of bottom currents and internal tides in a modern highstand submarine canyon head

ABSTRACTThe evolution of submarine canyons is primarily controlled by turbidity currents, which erode and fill them over time; however, many other hydrodynamic currents operate within canyons. Bottom currents from these other hydrodynamic processes, including internal tides, can be dominant processes, but their deposits are seldom recognized in sediment cores or the rock record. This study combines autonomous underwater vehicle swath bathymetry imagery and sub‐bottom profiles, high‐resolution sediment core analyses (X‐ray imagery and thin sections), and previously collected seabed video and flow measurements within Logan Canyon head (eastern Canada) to provide a detailed, modern record of facies associated with hydrodynamic processes in a canyon head. These results suggest that bottom currents are responsible for maintaining gullies on canyon sidewalls and an axial channel on the canyon floor. Thin sections of sediment cores reveal that muddy sand in the canyon head consists of mud aggregates and silt and fine‐grained sand, both behaving similarly in terms of flow dynamics. Three facies are present at macro‐scale and micro‐scale: laminated, partially laminated and bioturbated sandy mud. Sedimentary structures include rhythmic sand and mud aggregate couplets, planar to wavy laminations, current ripple cross‐laminations and fining‐upward successions, which are attributed to bottom currents induced by internal tides. Bioturbated facies, characterized by discrete biogenic structures and cross‐cutting relationships, predominate and overprint a mottled background. A mottled bioturbation fabric also alternates with or locally disrupts layering within the partially laminated facies. Internal tide currents, capable of bedload transport and forming ripples, were measured during a monitoring period in the canyon head, followed by rapid re‐establishment of benthos and associated biogenic structures, supporting the core interpretations. Preservation of sedimentary facies associated with these internal tides occurs when the sedimentation rate outpaces the rate of bioturbation, likely during stormier conditions on the shelf. These results represent observations of sedimentary facies associated with modern bottom currents and internal tides, and can be used to interpret similar occurrences within the rock record.

Application of a multi-species bio-economic modelling approach to explore fishing traits within eligible cetacean conservation areas in the Northern Ionian Sea (Central Mediterranean Sea)

The assessment of the spatial overlap between eligible cetacean conservation areas (CCAs) and fishing grounds could be a strategic element in the implementation of effective conservation measures in the pelagic offshore areas. A multi-species bio-economic modelling approach has been applied to estimate the fishing traits in eligible CCAs in the Northern Ionian Sea (NIS, Central Mediterranean Sea) between 10-800 m of depth, adopting the Spatial MAnagement of demersal Resources for Trawl fisheries model (SMART). Four possible CCAs were defined according to the distribution of cetacean species, their bio-ecological needs, as well as socio-economic needs of human activities, identifying a Blue, Red, Orange and Green CCAs in the NIS. SMART spatial domain was a grid with 500 square cells (15×15 NM). The analysis was conducted for the period 2016-2019, considering the Otter Trawl Bottom (OTB) fleet activities in the study areas through the Vessel Monitoring System. The spatial extension of fishing activities, hourly fishing effort (h), landings (tons) and economic value (euros) for each CCA and the NIS were estimated as yearly median values. Fishing activities were absent in the Blue CCA, where the presence of the submarine canyon head does not offer accessible fishing grounds. The hourly fishing effort in the Green area accounted for about 22% (3443 h) of the total hourly effort of the NIS, while the Orange and Red areas were about 8% (1226 h) and 2% (295 h), respectively. The Green CCA corresponded to about 14% (36 tons) of the total landings in the NIS, whereas the Orange and Red areas represented about 9% (22 tons) and 6% (16 tons), respectively. The Green CCA accounted for about 13% (156 thousand euros) of the total economic value of the NIS, while the Orange and Red areas represented about 6% (69 thousand euros) and 4% (44thousand euros), respectively. Results showed no or negligible negative effects on trawl activities by potential spatial restrictions due to the establishment of CCAs highlighting the importance to consider spatially integrated information during the establishment process of conservation areas for cetacean biodiversity according to the principles of Ecosystem Based Management.

Controls of Submarine Canyons Connected to Shore during the LGM Sea-Level Rise: Examples from Taiwan

During the Last Glacial Maximum (LGM) (~20,000 years ago), the sea level was lower than that during the present day by 120 m and the heads of most submarine canyons were close or connected to the coastline or shore, with enhanced terrestrial sediment input due to direct connections with river mouths. This was followed by a relative sea-level rise of 120 m and the migration of coastlines landward. As a result, the heads of some paleo-submarine canyons were no longer near river mouths or connected to the shore. Such canyons became inactive due to the lack of terrestrial sediment input. Only 4% of the world’s submarine canyons reach the coastline and remain active today. Among 13 submarine canyons off the shore of Taiwan, we identified seven (n = 7, 54%) that remain connected to the shore and are active during the present-day highstand. The purpose of this study is to determine the key controls of canyon heads that remain connected to the shore with terrestrial sediment input during the Holocene sea-level rise. As a result of high uplift rates, narrow coastal range, steep gradients, frequent earthquakes, and typhoon development in the Taiwan mountain belt, Taiwan has the highest-yield river and sediment supply. This has led to the transportation of large volumes of sediment to the surrounding deep seas. Narrow steep shelves and large sediment volumes associated with small mountain rivers are the main controls involved in the development of shore-connected canyons on the active Taiwan margin. Shore-connected canyons are present in greater numbers in the major earthquake zone on the eastern Taiwan margin. Frequent earthquake events are another significant factor in the occurrence of shore-connected canyons in the Taiwan region.

Different Ground Subsidence Contributions Revealed by Integrated Discussion of Sentinel-1 Datasets, Well Discharge, Stratigraphical and Geomorphological Data: The Case of the Gioia Tauro Coastal Plain (Southern Italy)

Groundwater is the main water supply for agricultural and industrial needs in many coastal plains worldwide. Groundwater depletion often triggers land subsidence, which threatens manmade infrastructure and activities and aggravates other geohazards. We applied a multi-temporal interferometric synthetic aperture radar technique to Sentinel-1 datasets to detect ground motion in the Gioia Tauro plain (Calabria, Southern Italy) from 2018 to 2021. The InSAR data were analysed through the integrated use of groundwater head, stratigraphical and geomorphological data, and land use information to distinguish the potential subsidence divers. The results show that subsiding areas, with a mean rate of about 10 mm/yr, are in the middle of the plain, and their location is influenced by the spatial distribution of compressible sediments included in the shallow aquifer. Furthermore, the subsidence arrangement is spatially accordant with the main groundwater depression area, which can be ascribed to the ongoing and increasing water pumping for predominantly agricultural usage. We also observed that subsidence (up to 10 mm/yr) affects the western dock of the Gioia Tauro harbour, in front of which, in very shallow water, are two submarine canyon heads already affected by slides in the past.

Where and Why Do Submarine Canyons Remain Connected to the Shore During Sea‐Level Rise? Insights From Global Topographic Analysis and Bayesian Regression

AbstractThe efficiency of sediment routing from land to the ocean depends on the position of submarine canyon heads with regard to terrestrial sediment sources. We aim to identify the main controls on whether a submarine canyon head remains connected to terrestrial sediment input during Holocene sea‐level rise. Globally, we identified 798 canyon heads that are currently located at the 120m‐depth contour (the Last Glacial Maximum shoreline) and 183 canyon heads that are connected to the shore (within a distance of 6 km) during the present‐day highstand. Regional hotspots of shore‐connected canyons are the Mediterranean active margin and the Pacific coast of Central and South America. We used 34 terrestrial and marine predictor variables to predict shore‐connected canyon occurrence using Bayesian regression. Our analysis shows that steep and narrow shelves facilitate canyon‐head connectivity to the shore. Moreover, shore‐connected canyons occur preferentially along active margins characterized by resistant bedrock and high river‐water discharge.

Controls on sediment distribution in the coastal zone of the central California transform continental margin, USA

We use >10,000 km of high-resolution seismic-reflection data together with multibeam bathymetry to document complex and highly variable post-Last Glacial Maximum (LGM) sediment distribution and thickness in the coastal zone (~10 m isobath to 5.6 km offshore) along a ~800 km section of central California's transform continental margin. Sediment thickness ranges from 0 (seafloor bedrock) to 64 m with a mean of 8.7 m. We delineate 25 coastal zone “sediment domains,” and group them based on common geomorphology and sediment occurrence. Thickest sediment occurs in “mountain front” and “large river” domains, which comprise 14.5% and 7.9% of the coastal zone and contain 30.1% and 18.2% of coastal zone sediment, respectively. In contrast, “small river” domains and “sediment-poor shelf” domains comprise 50.7% and 15.7% of the coastal zone and contain 18.4% and 12.7% of its sediment.The distribution and thickness of post-LGM sediment in the coastal zone is controlled by a combination of tectonics, sediment supply, and eustasy. Sediment is derived from a tectonically controlled coastal landscape of rapidly uplifting mountain fronts, more slowly uplifting marine terraces, and fault-bounded headlands and alluvial-estuarine troughs. Sediment supply is maximized along steep, landslide-prone, mountain fronts and at the mouths of large watersheds, and minimized along lower-relief, terraced coastal landscape drained by smaller rivers and creeks. In the offshore coastal zone, tectonics generates local uplifts and basins, and influences shelf width and gradient as well as the locations of some shelf-incised submarine canyons. Sea-level rise raises base level, drowns estuaries, creates accommodation space on the shelf (amount based on gradient), and isolates the heads of many submarine canyons at or near the shelfbreak. Comparison of shelf sediment volumes with estimates of “unaltered” watershed sediment supply reveals that a relatively small proportion of post-LGM sediment supply is preserved on the shelf offshore of some of the largest rivers. Sediments deposited in shoreline and shelf environments have limited preservation potential, and the most complete long-term geologic record of the post-LGM transgression and highstand is likely represented in slope and submarine fan deposits.

Seeking the Shore: Evidence for Active Submarine Canyon Head Incision Due to Coarse Sediment Supply and Focusing of Wave Energy

AbstractSubmarine flows carve canyons into continental shelves, yet the conditions and events responsible for canyon incision are incompletely understood. Coarse sediment flux has been shown to promote terrestrial bedrock incision via abrasion in rivers, but similar processes in submarine canyons have yet to be systematically documented. We use repeat bathymetry, provenance analysis, wave modeling, and channel network analysis to show that longshore sheltering and wave focusing by the Delgada submarine canyon induce sediment accumulation and elevated wave shear stresses in its headwall region that frequently mobilize coarse bed material. These mobilizations scour bedrock in the headwall and generate abrasive turbidity currents that work to carve the canyon's active channel into bedrock. These findings highlight an important positive feedback between submarine canyons, waves, and sediment supply and suggest that submarine canyons adjacent to wave‐dominated, coarse sediment‐rich coastlines seek the shoreline through headward incision.

Baby Giants are found at the heads of submarine canyons.

Baby Giants are found at the heads of submarine canyons.

Distribution and Recruitment of Young-of-the-Year Giant Sea Bass,Stereolepis gigas, off Southern California

This study identified nursery habitat, recruitment patterns, the planktonic larval duration (PLD), size and age at settlement, and growth rate of the young-of-the-year (YOY) Giant Sea Bass (GSB), Stereolepis gigas, off Southern California. A total of 160 YOY GSB were sighted on 150 transects over a three-year period. Young-of-the-year GSB were relatively rare (maximum density of 40/ha) and recruitment was limited to a few areas. In 2014–2015, densities of YOY GSB were significantly higher at six locations off sandy beaches nearest the heads of submarine canyons off Redondo Beach, Newport Beach, and La Jolla, California. The vast majority of occurrences of YOY (73%) were within 500 m of the heads of submarine canyons. Three color phases of YOY were discovered ranging (smallest to largest individuals) from black to brown to orange. Recruitment occurred from July through February with peak abundances occurring in the late summer months from August through October. YOY occurred at depths from 2 m to nearly 10...

Neotectonics of the Big Sur Bend, San Gregorio‐Hosgri Fault System, Central California

AbstractThe right‐lateral San Gregorio‐Hosgri fault system (SGHF) extends mainly offshore for about 400 km along the central California coast and is a major structure in the distributed transform margin of western North America. We mapped a poorly known 64‐km‐long section of the SGHF offshore Big Sur between Piedras Blancas and Point Sur using high‐resolution bathymetry, seismic reflection, and marine magnetic data. In this region, the SGHF is characterized by multiple strands, step overs, scarps and lineaments, shutter ridges, deflected drainages, and other geomorphic features consistent with strike‐slip faulting. Analysis of offset shelfbreak gullies suggest a lateral slip rate of about 3.35 mm/year. Vertical slip rates range as high as 0.8 to 1.2 mm/year. Lateral slip combined with high vertical slip rates result in a northwest decrease in shelf width, a northward increase in shelf and upper slope gradient, and progressive incision of submarine canyon heads. The SGHF between Point Sur and Piedras Blancas trends ~321° and forms a 105‐km‐long transpressive bend (the Big Sur Bend) between more north trending transtensional fault sections to the south (120 km long, ~336° trend) and north (180 km long, ~337° trend). This transpressional bend and SGHF splay faults have had a significant role in shaping the modern geomorphology of the central California coast, controlling or influencing the locations of mountainous uplifts, large coastal headlands, embayments, and rivers.

Controls on submarine canyon head evolution: Monterey Canyon, offshore central California

The Monterey submarine canyon, incised across the continental shelf in Monterey Bay, California, provides a record of the link between onshore tectonism, fluvial transport, and deep-marine deposition. High-resolution seismic-reflection imaging in Monterey Bay reveals an extensive paleocanyon unit buried below the seafloor of the continental shelf around Monterey and Soquel canyon heads. Paleocanyons shifted position through numerous phases of cut-and-fill in response to Salinas, Pajaro, and San Lorenzo river extensions and avulsions across the continental shelf during high-frequency Pleistocene sea-level and climatic variations. Five seismic facies within the Monterey paleocanyon unit and below the modern canyon are defined to interpret canyon evolution during the Pleistocene. Repeated sea-level oscillations appear to have switched the main fairway(s) of sediment transport. Large-scale erosion and fill occurred in marine environments. Paleocanyon fill is characterized by paleo-axial channel deposits and mass transport deposits, followed by canyon head abandonment and marine sedimentation. The upper portion of the paleocanyon unit contains relatively small channels that were likely incised by erosion in the paleo-Salinas and Pajaro rivers and filled with a mix of nonmarine and marine deposits. Shifting position of submarine canyons over time is characteristic of Monterey Bay, east of the Monterey Bay Fault Zone, and is likely unidentified in other submarine canyon head regions that lack dense high-resolution seismic-reflection subbottom images. We show that canyon heads can be areas of sediment accumulation linked to sea-level oscillations, providing new insights into submarine canyon evolution and sequence stratigraphy.

Connections Between Fluvial To Shallow Marine Environments and Submarine Canyons: Implications For Sediment Transfer To Deep Water

Abstract The heads of submarine canyons represent a critical link in the transfer of sediment from terrestrial sources to deep basin sinks. Here we report data on grain size, bathymetry, and geochronology from twenty-five modern submarine canyons that suggest this link to be very sensitive to the distance between the canyon head and the shoreline, and, to a lesser extent, wave energy. These data show the width of this zone filters the caliber of sediment delivered into deep water, which has significant implications for understanding sediment budgets and the distribution of reservoir and seal facies. Data from modern systems show that the river mouths or longshore drift cells must come within about 500 m of the head of the canyon to deliver gravel-size material and within 1 to 5 km to deliver sand-size material to be transported down the canyon into deep water. Clay- and silt-size particles are transported greater distances across the shelf, up to a few tens of km, whereas beyond about 40 km, little sediment makes the connection to the heads of canyons and deposits are dominated by condensed, carbonate-rich sediments. Our data from modern systems are consistent with existing sequence stratigraphic models for sediment delivery to deep water. The significance of our work is to show in more detail how and when connections can occur between fluvial to shallow-water systems and submarine canyons and how these connections regulate the quantity and caliber of sediment that can be transported into deep water. Once the process-based conditions for connection are met, then the geology and climate of the source area control the quantity and caliber of sediment that can be moved to deep water. We hypothesize that connection times, and the resultant fractionation of sediment mass and grain size between shelf and deep-water depocenters, may have varied in a predictable way through geologic history. For example, during greenhouse times when sea level was relatively high, but with inherently low high-frequency variability, longer-lived connections between fluvial to nearshore environments and deep water may have been more likely. This scenario would favor the preferential transfer of sediment, especially sand, into deep water, and the development of thick, laterally extensive sand-rich basin-floor deposits. By contrast, during icehouse periods, high-amplitude sea-level fluctuations and inherently wider continental shelves may have resulted in repeated landward and seaward transits of river mouths and shorelines, shorter connection times between source and sink, especially for sand-size sediment, and preferential sequestration of sediment in shelf to shelf-margin parts of the system. These conditions would have resulted in deep-water deposits that are a mixture of locally thick sands, abundant turbidity-current-derived mud, and thin but basin-wide condensed sections that represent periods of sediment starvation in deep water.

Cold-Water Corals and Anthropogenic Impacts in La Fonera Submarine Canyon Head, Northwestern Mediterranean Sea.

We assess the occurrence and extent of cold-water coral (CWC) species Madrepora oculata and Dendrophyllia cornigera, as well as gorgonian red coral Corallium rubrum, in La Fonera canyon head (Northwestern Mediterranean Sea), as well as human impacts taking place in their habitats. Occurrence is assessed based on Remotely Operated Vehicle (ROV) video imaging. Terrain classification techniques are applied to high-resolution swath bathymetric data to obtain semi-automatic interpretative maps to identify the relationship between coral distribution patterns and canyon environments. A total of 21 ROV immersions were carried out in different canyon environments at depths ranging between 79 and 401 m. Large, healthy colonies of M. oculata occur on abrupt, protected, often overhanging, rocky sections of the canyon walls, especially in Illa Negra branch. D. cornigera is sparser and evenly distributed at depth, on relatively low sloping areas, in rocky but also partially sedimented areas. C. rubrum is most frequent between 100 and 160 m on highly sloping rocky areas. The probable extent of CWC habitats is quantified by applying a maximum entropy model to predict habitat suitability: 0.36 km2 yield M. oculata occurrence probabilities over 70%. Similar predictive models have been produced for D. cornigera and C. rubrum. All ROV transects document either the presence of litter on the seafloor or pervasive trawling marks. Nets and longlines are imaged entangled on coral colonies. Coral rubble is observed at the foot of impacted colonies. Some colonies are partially covered by sediment that could be the result of the resuspension generated by bottom trawling on neighbouring fishing grounds, which has been demonstrated to be responsible of daily increases in sediment fluxes within the canyon. The characteristics of the CWC community in La Fonera canyon are indicative that it withstands high environmental stress of both natural and human origin.

Origin and chronology of the Augias deposit in the Ionian Sea (Central Mediterranean Sea), based on new regional sedimentological data

In the Ionian Sea (Central Mediterranean Sea), several thick acoustically transparent layers are present including the Augias deposit. The Augias deposit is the most recent, thick layer covering the entire floor of the Ionian Abyssal Plain with an average thickness of 10–12m and a maximum thickness of up to 24m in the Sirte Abyssal Plain. This deposit has also been observed in several adjacent smaller basins in waters deeper than 3000m. Its estimated volume is>65km3. There are multiple plausible hypotheses regarding its age and triggering event, which include the 1600 BC Santorini volcanic caldera collapse, the 365 AD Crete M 8.5 earthquake and other smaller earthquakes such as the 374 AD Calabria M 6.3 earthquake and the 361 AD Sicily M 6.6 earthquake. Understanding the cause of this mass-transport deposit is crucial for improving the natural hazard assessment of a vast area between southern Italy and western Greece. In this study, we propose a new interpretation of the Augias deposit in terms of sedimentary processes and origin, based on sediment cores collected in the NW Ionian Sea during the CIRCEE cruise onboard R/V Le Suroit in October 2013.The sedimentological analysis of seven piston cores reveals three sedimentary facies corresponding to the Augias deposit: 1) “homogenite”, 2) “megaturbidite” and 3) “thick sandy turbidite”. These sedimentary facies are distributed within specific morpho-tectonic regions as defined by newly acquired bathymetric data, indicating a strong control by transport and depositional processes. Sixteen radiocarbon dates obtained above and below the Augias deposit indicate a possible time window of about 500years. This means that we cannot definitively prove a link to the 365 AD Crete earthquake, but we regard it as the most likely trigger. Other depositional models may be plausible, but here we propose a sequence of events as follows: (1) earthquake shock and possible triggering of submarine mass flow in the eastern part of the Ionian Sea (western Hellenic subduction zone); (2) tsunami waves amplified by the confined morphology of the Sicily and Calabria continental shelves inducing an intense re-suspension of fine-grained sediment and massive destabilization at the heads of submarine canyons triggering turbidity currents; (3) gravity driven downslope transport of suspended sediment toward the deep basin and decantation; and (4) a final stage of decantation from seiche waves forming the majority of the homogenite facies in the Ionian Abyssal Plain.

Lonely populations in the deep: genetic structure of red gorgonians at the heads of submarine canyons in the north-western Mediterranean Sea

The red gorgonian Paramuricea clavata plays a central role in coralligenous ecosystems of the Mediterranean Sea, being relatively abundant in shallow habitats (5–35 m depth). Recently, deeper populations have been discovered at the heads of submarine canyons in the north-western Mediterranean Sea, between 50 and 70 m deep. Colonies from some of these deeper populations were exceptionally large (>1 m high), contrasting with the general prevalence of smaller size classes in shallower populations. Importantly, the high pressure of trawling activities on the nearby continental shelf could threaten these populations of large and old colonies. Although the genetic diversity and structure of populations in shallow habitats is relatively well known, very little is known about deeper populations. We aimed to assess the genetic structure, connectivity and potential demographic decline of six deep populations of P. clavata located at the heads of La Fonera, Blanes and Arenys de Mar submarine canyons, as well as potential gene flow between those and the two nearest shallow populations. A total of 188 individuals were genotyped using nine microsatellite loci. Results showed strong genetic differentiation among populations in different submarine canyons, among populations within one of the canyons and between shallow and deep populations. Gene flow among populations was very limited, estimates of effective population size in some populations were small, and evidence of recent population reductions (bottlenecks) was detected in several populations. The large genetic differentiation in populations of P. clavata among canyons is related to limited effective dispersal.

High-resolution morphobathymetric analysis and evolution of Capbreton submarine canyon head (Southeast Bay of Biscay—French Atlantic Coast) over the last decade using descriptive and numerical modeling

Abstract In this study, the Capbreton canyon head, just off the coast, is investigated using high-resolution multibeam bathymetry datasets, sediment samples and numerical modeling. The HR bathymetry analysis reveals a morphological connection between the longshore trough and the head of the canyon. The analysis of recent sediment samples shows a clear correlation between the sediment of the canyon head and that of the nearshore. Hydrodynamic modeling (a coupled wave-flow model) shows that for high-energy waves, the rotational nature of surf-zone circulation reverses and wave-induced currents have the potential to transport large quantities of nearshore sands toward the canyon head. All these arguments support the assumption that the canyon head captures a part of the sand transported by longshore drift. Over the 15 years of observation (1998–2013), time-lapse bathymetry shows that the floor of the canyon head and one lateral gully network experienced significant morphological reworking. In terms of hazards, despite this strong activity, the position of the canyon head and the profile of its longitudinal slope remained stable and appear as a comforting factor. However, the activity of unusual lateral erosions needs to be monitored.

High-resolution morphobathymetric analysis and evolution of Capbreton submarine canyon head (Southeast Bay of Biscay French Atlantic Coast) over the last decade using descriptive and numerical modeling

High-resolution morphobathymetric analysis and evolution of Capbreton submarine canyon head (Southeast Bay of Biscay French Atlantic Coast) over the last decade using descriptive and numerical modeling

Direct sediment transfer from land to deep-sea: Insights into shallow multibeam bathymetry at La Réunion Island

Abstract Submarine canyon heads are key areas for understanding the triggering factors of gravity currents responsible for the transfer of detrital sediment to the deep basins. This contribution offers a detailed picture of canyon heads off La Reunion Island, with high-resolution multibeam bathymetry in the water depth range of 4–220 m. The present feeding of the Cilaos turbidite system, one of the largest modern volcaniclastic systems in the world, is deduced from morphological and sedimentological interpretations of newly acquired data. The study highlights small-scale sedimentary features indicating hydrodynamic and sedimentary processes. A direct connexion between the Saint-Etienne river mouth and submarine canyons is evidenced by the complete incision of the shelf and the presence of canyon heads connected to the modern deltaic bar. This direct connection, supplied by river torrential floods (cyclonic floods every two or three years), suggests the continuity of high-density fluvial flows to submarine gravity flows, forming hyperpycnal flows in the canyon. The initiation of secondary submarine gravity flows by storm waves (large austral waves and cyclonic waves) is also proposed for submarine canyons with large canyon heads developed in the surf zone from a sandy coastal bar. Bedforms in active canyon axis are considered as an indicator of the frequent activity of high-density turbidity currents. Moreover, a morphological record of last glacial and deglacial sea level variations is preserved, and particularly the Last Glacial Maximum sea level with the presence of small vertical cliffs, observed in this bathymetric data, which likely corresponds to a paleo-shoreline or paleo-reefs.

Understanding the coastal variability at Norte beach, Portugal

ABSTRACT Silva, A.N., Taborda, R., Antunes, C., Catalao, J. and Duarte, J. 2013. Understanding the coastal variability at Norte beach, Portugal Norte beach stands in a coastal stretch fully exposed to the high energetic North Atlantic wave regime. The beach is located updrift of the Nazare submarine canyon head, a sedimentary sink that captures the southward directed longshore drift. Systematic monitoring of Norte beach has been conducted by a coastal video monitoring system since 2008. A total of 31 monthly coastlines were extracted and analyzed in the period between December 2008 and May 2012. Results show a rare high seasonal coastline variability which exceeds 160 m in the southward sector (adjacent to the headland) and 70 m at the central and north sectors. These coastline variations are related with modifications in the planform beach configuration: beach oscillates between a straight (generally from June to August) and an arcuate configuration (during the remaining months of the year). Results sugg...