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TitreStorm-induced turbidity currents on a sediment-starved shelf: insight from direct monitoring and repeat seabed mapping of upslope migrating bedforms
AuteurNormandeau, A; Bourgault, D; Neumeier, U; Lajeunesse, P; St-Onge, G; Gostiaux, L; Chavanne, C
SourceSedimentology 2019 p. 1-24, https://doi.org/10.1111/sed.12673
Année2019
Séries alt.Ressources naturelles Canada, Contribution externe 20180334
ÉditeurWiley
Documentpublication en série
Lang.anglais
DOIhttps://doi.org/10.1111/sed.12673
Mediapapier; en ligne; numérique
Formatspdf (Adobe® Reader®); html
ProvinceQuébec; Région extracotière de l'est
SNRC22G/06
Lat/Long OENS -67.5000 -67.3667 49.3667 49.2500
Lat/Long OENS -67.3667 -67.3667 49.3667 49.2500
Sujetscourants de turbidite; structures flui dales; configurations lit; météorologie; tempêtes; stabilité du sédiment; marges continentales; plate-forme continentale; estuaires; courants de fond; caractéristiques sous-marines; canyons sous-marins; rigoles; levés géophysiques; levés acoustiques marins; bathymétrie; milieu sédimentaire; sediments en suspension; dispersion des sédiments; volumes de sediment; surveillance; vent; infrastructure; géologie marine; géologie des dépôts meubles/géomorphologie; sédimentologie; Nature et environnement; Sciences et technologie
Illustrationslocation maps; geoscientific sketch maps; schematic cross-sections; bar graphs; satellite images; profiles; time series; plots; models
ProgrammeGéo-risques marins, Géoscience pour la sécurité publique
Diffusé2019 10 08
Résumé(disponible en anglais seulement)
The monitoring of turbidity currents enables accurate internal structure and timing of these flows to be understood. Without monitoring, triggers of turbidity currents often remain hypothetical and are inferred from sedimentary structures of deposits and their age. In this study, the bottom currents within 20 m of the seabed in one of the Pointe-des-Monts (Gulf of St. Lawrence, eastern Canada) submarine canyons were monitored for two consecutive years using Acoustic Doppler Current Profilers. In addition, multibeam bathymetric surveys were carried out during deployment of the Acoustic Doppler Current Profilers and recovery operations. These new surveys, along with previous multibeam surveys carried out over the last decade, revealed that crescentic bedforms have migrated upslope by about 20 to 40 m since 2007, despite the limited supply of sediment on the shelf or river inflow in the region. During the winter of 2017, two turbidity currents with velocities reaching 0.5 m/sec and 2.0 m/sec, respectively, were recorded and were responsible for the rapid (<1 min) upstream migration of crescentic bedforms measured between the autumn surveys of 2016 and 2017. The 200 kg (in water) mooring was also displaced 10 m down-canyon, up the stoss side of a bedform, suggesting that a dense basal layer could be driving the flow during the first minute of the event. Two other weaker turbidity currents with speeds <0.5 m/sec occurred, but did not lead to any significant change on the seabed. These four turbidity currents coincided with strong and sustained wind speed >60 km/h and higher than normal wave heights. Repeat seabed mapping suggests that the turbidity currents cannot be attributed to a canyon-wall slope failure. Rather, sustained windstorms triggered turbidity currents either by remobilizing limited volumes of sediment on the shelf or by resuspending sediment in the canyon head. Turbidity currents can thus be triggered when the sediment volume available is limited, likely by eroding and incorporating canyon thalweg sediment in the flow, thereby igniting the flow. This process appears to be particularly important for the generation of turbidity currents capable of eroding the lee side of upslope migrating bedforms in sediment-starved environments and might have wider implications for the activity of submarine canyons worldwide. In addition, this study suggests that a large external trigger (in this case storms) is required to initiate turbidity currents in sediment-starved environments, which contrasts with supply-dominated environments where turbidity currents are sometimes recorded without a clear triggering mechanism.
Résumé(Résumé en langage clair et simple, non publié)
Des courants de turbidité ont été enregistrés dans les fonds marins de l'estuaire du Saint-Laurent, et ceux-ci ont été associés à la migration des figures sédimentaires. Les courants de turbidité ont été déclenchés lors des tempêtes de 2017 et ont entraîné une modification importante du fond marin.
GEOSCAN ID313353