| Title | 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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| Author | 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  Open Access |
| Image |  |
| Year | 2019 |
| Alt Series | Natural Resources Canada, Contribution Series 20180334 |
| Publisher | Wiley |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf (Adobe® Reader®); html |
| Province | Quebec; Eastern offshore region |
| NTS | 22G/06 |
| Area | St. Lawrence Estuary; Pointe-des-Monts |
| Lat/Long WENS | -67.5000 -67.3667 49.3667 49.2500 |
| Lat/Long WENS | -67.3667 -67.3667 49.3667 49.2500 |
| Subjects | marine geology; surficial geology/geomorphology; sedimentology; Nature and Environment; Science and Technology; turbidity currents; flow structures; bedforms; meteorology; storms; sediment stability;
continental margins; continental shelf; estuaries; bottom currents; submarine features; submarine canyons; gullies; geophysical surveys; acoustic surveys, marine; bathymetry; depositional environment; suspended sediments; sediment dispersal; sediment
volumes; monitoring; Wind; Infrastructures |
| Illustrations | location maps; geoscientific sketch maps; schematic cross-sections; bar graphs; satellite images; profiles; time series; plots; models |
| Program | Public Safety
Geoscience Marine Geohazards |
| Released | 2019 10 08 |
| Abstract | 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. |
| Summary | (Plain Language Summary, not published)
Turbidity currents were recorded on the seafloor of the St. Lawrence Estuary and were associated with the migration of bedforms. Turbidity currents were
triggered during storms in 2017 and led to significant change on the seafloor. |
| GEOSCAN ID | 313353 |
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