Author Correction: Rapidly-migrating and internally-generated knickpoints can control submarine channel evolution (Nature Communications, (2020), 11, 1, (3129), 10.1038/s41467-020-16861-x)

© 2020, The Author(s). The original version of this Article contained an error in the labelling of the cross-section in Fig. 2g and the vertical axis in Fig. 2b. This has been corrected in both the PDF and HTML versions of the Article

Lessons learned from monitoring of turbidity currents and guidance for future platform designs

Turbidity currents transport globally significant volumes of sediment and organic carbon into the deep-sea and pose a hazard to critical infrastructure. Despite advances in technology, their powerful nature often damages expensive instruments placed in their path. These challenges mean that turbidity currents have only been measured in a few locations worldwide, in relatively shallow water depths (≪2 km). Here, we share lessons from recent field deployments about how to design the platforms on which instruments are deployed. First, we show how monitoring platforms have been affected by turbidity currents including instability, displacement, tumbling and damage. Second, we relate these issues to specifics of the platform design, such as exposure of large surface area instruments within a flow and inadequate anchoring or seafloor support. Third, we provide recommended improvements to improve design by simplifying mooring configurations, minimising surface area, and enhancing seafloor stability. Finally we highlight novel multi-point moorings that avoid interaction between the instruments and the flow, and flow-resilient seafloor platforms with innovative engineering design features, such as ejectable feet and ballast. Our experience will provide guidance for future deployments, so that more detailed insights can be provided into turbidity current behaviour, and in a wider range of settings

Global monitoring data shows grain size controls turbidity current structure

The first detailed measurements from active turbidity currents have been made in the last few years, at multiple sites worldwide. These data allow us to investigate the factors that control the structure of these flows. By analyzing the temporal evolution of the maximum velocity of turbidity currents at different sites, we aim to understand whether there are distinct types of flow, or if a continuum exists between end-members; and to investigate the physical controls on the different types of observed flow. Our results show that the evolution of the maximum velocity of turbidity currents falls between two end-members. Either the events show a rapid peak in velocity followed by an exponential decay or, flows continue at a plateau-like, near constant velocity. Our analysis suggests that rather than triggers or system input type, flow structure is primarily governed by the grain size of the sediment available for incorporation into the flow

Fluvial Response to Climate Change in the Pacific Northwest: Skeena River Discharge and Sediment Yield

Changes in climate affect the hydrological regime of rivers worldwide and differ with geographic location and basin characteristics. Such changes within a basin are captured in the flux of water and sediment at river mouths, which can impact coastal productivity and development. Here, we model discharge and sediment yield of the Skeena River, a significant river in British Columbia, Canada. We use HydroTrend 3.0, two global climate models (GCMs), and two representative concentration pathways (RCPs) to model changes in fluvial fluxes related to climate change until the end of the century. Contributions of sediment to the river from glaciers decreases throughout the century, while basin-wide overland and instream contributions driven by precipitation increase. Bedload, though increased compared to the period (1981–2010), is on a decreasing trajectory by the end of the century. For overall yield, the model simulations suggest conflicting results, with those GCMs that predict higher increases in precipitation and temperature predicting an increase in total (suspended and bedload) sediment yield by up to 10% in some scenarios, and those predicting more moderate increases predicting a decrease in yield by as much as 20%. The model results highlight the complexity of sediment conveyance in rivers within British Columbia and present the first comprehensive investigation into the sediment fluxes of this understudied river system

Sedimentary Processes and Sediment Dispersal in the southern Strait of Georgia, BC, Canada

International audienc

How turbidity current frequency and character varies down a fjord-delta system: Combining direct monitoring, deposits and seismic data

Submarine turbidity currents are one of the most important processes for moving sediment across our planet; they are hazardous to offshore infrastructure, deposit petroleum reservoirs worldwide, and may record tsunamigenic landslides. However, there are few studies that have monitored these submarine flows in action, and even fewer studies that have combined direct monitoring with longer‐term records from core and seismic data of deposits. This article provides one of the most complete studies yet of a turbidity current system. The aim here is to understand what controls changes in flow frequency and character along the turbidite system. The study area is a 12 km long delta‐fed fjord (Howe Sound) in British Columbia, Canada. Over 100 often powerful (up to 2 to 3 m sec−1) events occur each year in the highly‐active proximal channels, which extend for 1 to 2 km from the delta lip. About half of these events reach the lobes at the channel mouths. However, flow frequency decreases rapidly once these initially sand‐rich flows become unconfined, and only one to five flows run out across the mid‐slope each year. Many of these sand‐rich, channelized, delta‐sourced flows therefore dissipated over a few hundred metres, once unconfined, rather than eroding and igniting. Upflow migrating bedforms indicate that supercritical flow dominated in the proximal channels and lobes, and also across the unconfined mid‐slope. These supercritical flows deposited thick sand beds in proximal channels and lobes, but thinner and finer beds on the unconfined mid‐slope. The distal flat basin records far larger volume and more hazardous events that have a recurrence interval of ca 100 years. This study shows how sand‐rich delta‐fed flows dissipate rapidly once they become unconfined, that supercritical flows dominate in both confined and unconfined settings, and how a second type of more hazardous, and much less frequent event is linked to a different scale of margin failure

Seismic and Acoustic Monitoring of Submarine Landslides: Ongoing Challenges, Recent Successes and Future Opportunities

Submarine landslides pose a hazard to coastal communities due to the tsunamis they can generate, and can damage critical seafloor infrastructure, such as the network of cables that underpin global data transfer and communications. These mass movements can be orders of magnitude larger than their onshore equivalents and are found on all of the world’s continental margins; from coastal zones to hadal trenches. Despite their prevalence, and importance to society, offshore monitoring studies have been limited by the largely unpredictable occurrence of submarine landslide and the need to cover large regions of extensive continental margins. Recent subsea monitoring has provided new insights into the preconditioning and run-out of submarine landslides using active geophysical techniques, but these tools only measure a very small spatial footprint, and are power and memory intensive, thus limiting long duration monitoring campaigns. Most landslide events therefore remain entirely unrecorded. Here we first show how passive acoustic and seismologic techniques can record acoustic emissions and ground motions created by terrestrial landslides. We then show how this terrestrial-focused research has catalysed advances in the detection and characterisation of submarine landslides, using both onshore and offshore networks of broadband seismometers, hydrophones and geophones. We then discuss some of the new insights into submarine landslide preconditioning, timing, location, velocity and their down-slope evolution that is arising from these advances. We finally outline some of the outstanding challenges, in particular emphasising the need for calibration of seismic and acoustic signals generated by submarine landslides and their run-out. Once confidence can be enhanced in submarine landslide signal detection and interpretation, passive seismic and acoustic sensing has strong potential to enable more complete hazard catalogues to be built, and opens the door to emerging techniques (such as fibre-optic sensing), to fill key, but outstanding, knowledge gaps concerning these important underwater phenomena

Predicting turbidity current activity offshore from meltwater-fed river deltas

Quantification of the controls on turbidity current recurrence is required to better constrain land to sea fluxes of sediment, carbon and pollutants, and design resilient infrastructure that is vulnerable to such flows. This is particularly important offshore from river deltas, where sediment supply is high. Numerous mechanisms can trigger turbidity currents, even at a single river mouth. However quantitative analysis of recurrence and triggers has been limited to an individual trigger for each turbidity current due to the low number of precisely timed (via direct monitoring) flows. We are therefore yet to quantify if and how coincident processes combine to generate turbidity currents, and their relative importance. Here, we analyse the timing and causes of 113 turbidity currents directly-monitored from the source of turbidity current initiation to depositional sink in a single submarine channel. This submarine channel is located offshore from glacial-fed river-deltas at Bute Inlet, a fjord in British Columbia, Canada. Using a multivariate statistical approach, we demonstrate the statistical significance of combined river discharge and tidal controls on turbidity current occurrence during 2018, from which we derive a statistical model that calculates turbidity current probability for any given input of river discharge and water level. This new model predicts turbidity current activity with >84% success offshore other river deltas where flow timing is precisely constrained by directly monitoring, including the Squamish and Fraser River-deltas in British Columbia. We suggest that this model will be applicable for turbidity current prediction at glacial meltwater-fed fjords in many other regions worldwide

Predicting turbidity current activity offshore from meltwater-fed river deltas

Quantification of the controls on turbidity current recurrence is required to better constrain land to sea fluxes of sediment, carbon and pollutants, and design resilient infrastructure that is vulnerable to such flows. This is particularly important offshore from river deltas, where sediment supply is high. Numerous mechanisms can trigger turbidity currents, even at a single river mouth. However quantitative analysis of recurrence and triggers has been limited to an individual trigger for each turbidity current due to the low number of precisely timed (via direct monitoring) flows. We are therefore yet to quantify if and how coincident processes combine to generate turbidity currents, and their relative importance. Here, we analyse the timing and causes of 113 turbidity currents directly-monitored from the source of turbidity current initiation to depositional sink in a single submarine channel. This submarine channel is located offshore from glacial-fed river-deltas at Bute Inlet, a fjord in British Columbia, Canada. Using a multivariate statistical approach, we demonstrate the statistical significance of combined river discharge and tidal controls on turbidity current occurrence during 2018, from which we derive a statistical model that calculates turbidity current probability for any given input of river discharge and water level. This new model predicts turbidity current activity with >84% success offshore other river deltas where flow timing is precisely constrained by directly monitoring, including the Squamish and Fraser River-deltas in British Columbia. We suggest that this model will be applicable for turbidity current prediction at glacial meltwater-fed fjords in many other regions worldwide

Quantifying the three‐dimensional stratigraphic expression of cyclic steps by integrating seafloor and deep‐water outcrop observations

Deep‐water deposits are important archives of Earth’s history including the occurrence of powerful flow events and the transfer of large volumes of terrestrial detritus into the world’s oceans. However the interpretation of depositional processes and palaeoflow conditions from the deep‐water sedimentary record has been limited due to a lack of direct observations from modern depositional systems. Recent seafloor studies have resulted in novel findings, including the presence of upslope‐migrating bedforms such as cyclic steps formed by supercritical turbidity currents that produce distinct depositional signatures. This study builds on process to product relationships for cyclic steps using modern and ancient datasets by providing sedimentological and quantitative, three‐dimensional architectural analyses of their deposits, which are required for recognition and palaeoflow interpretations of sedimentary structures in the rock record. Repeat‐bathymetric surveys from two modern environments (Squamish prodelta, Canada, and Monterey Canyon, USA) were used to examine the stratigraphic evolution connected with relatively small‐scale (average 40 to 55 m wavelengths and 1.5 to 3.0 m wave heights) upslope‐migrating bedforms interpreted to be cyclic steps within submarine channels and lobes. These results are integrated to interpret a succession of Late Cretaceous Nanaimo Group deep‐water slope deposits exposed on Gabriola Island, Canada. Similar deposit dimensions, facies and architecture are observed in all datasets, which span different turbidite‐dominated settings (prodelta, upper submarine canyon and deep‐water slope) and timescales (days, years or thousands of years). Bedform deposits are typically tens of metres long/wide, <1 m thick and make up successions of low‐angle, backstepping trough‐shaped lenses composed of massive sands/sandstones. These results support process‐based relationships for these deposits, associated with similar cyclic step bedforms formed by turbidity currents with dense basal layers under low‐aggradation conditions. Modern to ancient comparisons reveal the stratigraphic expression of globally prevalent, small‐scale, sandy upslope‐migrating bedforms on the seafloor, which can be applied to enhance palaeoenvironmental interpretations and understand long‐term preservation from ancient deep‐water deposits