| Titre | Storm-induced turbidity currents on a sediment-starved shelf: insight from direct monitoring and repeat seabed mapping of upslope migrating bedforms |
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| Auteur | Normandeau, A ;
Bourgault, D; Neumeier, U; Lajeunesse, P; St-Onge, G; Gostiaux, L; Chavanne, C |
| Source | Sedimentology 2019 p. 1-24, https://doi.org/10.1111/sed.12673 |
| Image |  |
| Année | 2019 |
| Séries alt. | Ressources naturelles Canada, Contribution externe 20180334 |
| Éditeur | Wiley |
| Document | publication en série |
| Lang. | anglais |
| DOI | https://doi.org/10.1111/sed.12673 |
| Media | papier; en ligne; numérique |
| Formats | pdf (Adobe® Reader®); html |
| Province | Québec; Région extracotière de l'est |
| SNRC | 22G/06 |
| Région | St. Lawrence Estuary; Pointe-des-Monts |
| Lat/Long OENS | -67.5000 -67.3667 49.3667 49.2500 |
| Lat/Long OENS | -67.3667 -67.3667 49.3667 49.2500 |
| Sujets | courants 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 |
| Illustrations | cartes de localisation; cartes géolscientiques généralisées; coupes schématiques transversales; graphique à barres; images satellitaires; profils; séries chronologiques; graphiques;
modèles |
| Programme | Géoscience pour la sécurité publique Géo-risques marins |
| Diffusé | 2019 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. |
| Sommaire | (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 ID | 313353 |
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