The formation and evolution of submarine headless channels

The scale of submarine channels can rival or exceed those formed on land and they form many of the largest sedimentary deposits on Earth. Turbidity currents that carve submarine channels pose a major hazard to offshore cables and pipelines, and transport globally significant amounts of organic carbon. Alongside the primary channels, many systems also exhibit a range of headless channels, which often abruptly terminate at steep headscarps. These enigmatic features are widespread in lakes and ocean floors, either as branches off the main submarine channel thalweg or as isolated secondary channels. Prior research has proposed that headless channels may be associated with early and incipient stages of channel development, but their formation and evolution remain poorly understood. Here, we investigate the morphology, origin and development of headless channels by examining repeat bathymetric surveys spanning a period from 1986 to 2018, in Bute Inlet, Canada. We show how channel switching processes, the extension of turbidity currents across distal fans, along with overbanking turbidity currents, are able to initiate headless channels in submarine settings. We discuss how the evolution of headless channels plays an important role in shaping submarine channels, promoting channel extension and modifying the overall longitudinal profile, as well as impacting the character of sedimentary records in channel-lobe transition zones.

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Character, spatial and temporal variation of turbidity currents on a source-to-sink scale.

10.5194/egusphere-egu2020-4242 ◽

2020 ◽

Author(s):

Kate Heerema ◽

Peter Talling ◽

Matthieu Cartigny ◽

Gwyn Lintern ◽

Cooper Stacey ◽

...

Keyword(s):

Full Range ◽

Turbidity Current ◽

Spatial And Temporal Variation ◽

Turbidity Currents ◽

Deep Basin ◽

Data Set ◽

Sedimentary Deposits ◽

Submarine Channel ◽

Direct Measurements ◽

Adcp Data

Seafloor avalanches of sediment called turbidity currents are one of the principle mechanisms for moving sediments across our planet. However, turbidity currents are notoriously difficult to monitor directly in action, and we still mainly depend on their sedimentary deposits as well as physical and numerical models to understand their temporal and spatial evolution. In recent years, multiple studies have successfully made direct measurements within active turbidity currents at multiple sites along their pathway. However, these direct measurements are often limited to the upper reaches of submarine systems, only cover relatively short (few months to a couple of years) time scales, or have very few measurement stations (<3). To capture the full range of turbidity current types and recurrence times we need to combine direct monitoring with longer-term archives in sedimentary deposits. Here we present an unusual data set that extends from the submarine channel on the delta, to the final deposits in the deep basin. The dataset combines short-term (< 1 year) direct measurements of flows with long-term sediment deposits (dating back to about 100 years). This combination of data types allows us to understand turbidity current frequencies, runouts, heights and characteristics along an entire submarine system. &#160;We analyse data from Bute Inlet, which is a fjord in British Colombia, Canada. The entire turbidity current system stretches out for 80 km, with an incised submarine channel extending for 45 km. 46 Cores have been collected between 2015 and 2018. Simultaneously, direct measurements of the currents have been obtained in 2016 and 2018 using Acoustic Doppler Current Profilers (ADCPs) in the submarine channel.Our objective is two-fold. First, we look at flow frequency over time and space. Visual logs of the sediment cores, as well as sediment accumulation rates for a selection of cores, are used to infer flow frequencies. We then use the ADCP data to understand more frequent and recent flows at 6 places along the channel. These ADCP measurements are used to infer frequencies which are not necessarily recorded in the deposits, and give additional insights into current-day activity. This allows us to reconstruct the change in frequency over space and time.Second, we consider the variation in turbidity current character to understand how flows evolve along the channel. Facies determination and grain size data are used to infer turbidity current character. Cores along the channel, on terraces and in the deep basin are used to understand the spatial variation. Finally, comparison of deposits and monitoring (ADCP) data shows how submarine flows are recorded by their deposits.

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New flow relaxation mechanism explains scour fields at the end of submarine channels

Nature Communications ◽

10.1038/s41467-019-12389-x ◽

2019 ◽

Vol 10 (1) ◽

Cited By ~ 15

Author(s):

F. Pohl ◽

J. T. Eggenhuisen ◽

M. Tilston ◽

M. J. B. Cartigny

Keyword(s):

Sediment Load ◽

Relaxation Mechanism ◽

Turbidity Currents ◽

Flow Mechanism ◽

Submarine Channels ◽

Sea Floor ◽

Submarine Channel ◽

Gravity Flows ◽

Rapid Flow ◽

Flow Through

Abstract Particle-laden gravity flows, called turbidity currents, flow through river-like channels across the ocean floor. These submarine channels funnel sediment, nutrients, pollutants and organic carbon into ocean basins and can extend for over 1000’s of kilometers. Upon reaching the end of these channels, flows lose their confinement, decelerate, and deposit their sediment load; this is what we read in textbooks. However, sea floor observations have shown the opposite: turbidity currents tend to erode the seafloor upon losing confinement. Here we use a state-of-the-art scaling method to produce the first experimental turbidity currents that erode upon leaving a channel. The experiments reveal a novel flow mechanism, here called flow relaxation, that explains this erosion. Flow relaxation is rapid flow deformation resulting from the loss of confinement, which enhances basal shearing of the turbidity current and leads to scouring. This flow mechanism plays a key role in the propagation of submarine channel systems.

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A field-scale laboratory to study particulate transport from river source to marine sink: Bute Inlet (Canada)

10.5194/egusphere-egu21-16596 ◽

2021 ◽

Author(s):

Sophie Hage ◽

Sanem Acikalin ◽

Lewis Bailey ◽

Matthieu Cartigny ◽

Michael Clare ◽

...

Keyword(s):

Organic Carbon ◽

Large Scale ◽

Sediment Cores ◽

Past Research ◽

Transport Processes ◽

Small Scale ◽

Turbidity Currents ◽

Upstream Migration ◽

Submarine Channel ◽

The Impact

It is often assumed that particles produced on land (e.g., sediment, pollutants and organic matter) are transported through watersheds to a terminal sediment sink at the seashore. However, terrestrial particles can continue their journey offshore via submarine channels, accumulating in abyssal plains of the oceans. Offshore sediment transport processes are key controls on the burial of organic carbon and the distribution of benthic food, yet they are challenging to study due to the difficulty of capturing usually short duration events within large-scale systems at great ocean depths. Fjords are sufficiently small scale to enable their submarine channel systems to be studied from river source to terminal sink on seafloor fans. Bute Inlet is an up to 650 m deep fjord in British Columbia, Canada. The Homathko and Southgate rivers both feed Bute Inlet with freshwater and terrestrial sediment. A large landslide occurred on 28th November 2020, which caused a Glacial-Lake Outburst Flood (GLOF) which breached a moraine-dam and transported huge volumes of material through the Southgate valley and into Bute Inlet. The impact of this recent event on the submarine system in Bute is, for now, poorly constrained but ongoing work is exploring the impact of this major event on the Inlet. Bute Inlet is one of the most studied fjords worldwide, with a range of offshore campaigns that have been conducted during the last seventy years, providing an unprecedented background dataset and thus opportunity to explore what impact a large magnitude, low frequency terrestrial event had on the submarine system. This presentation will provide an overview of the past research conducted on the Bute submarine channel system, under more usual river discharge conditions and compare this background context to the recent GLOF event.Previous studies have revealed that the floor of the Inlet is characterized by a 40 km long submarine channel formed by submarine avalanches of sediment (turbidity currents) that can be up to 30 m thick and reach velocities of up to 6.5 m/s. Based on time-lapse bathymetric mapping over 10 years, the evolution of this channel is known to be controlled by the fast (100 to 450 m/yr) upstream migration of 5 to 30 m high steps (called knickpoints) in the channel floor. Sediment cores reveal that the channel floor and proximal lobe are dominated by sand and up to 3 % of total organic carbon in the form of young woody debris. Research in Bute Inlet has thus allowed submarine flow processes, seafloor morphology and deposits to be linked in unprecedented detail. Using those past results as a baseline, new data collected after the GLOF will be crucial for testing the impact of high-magnitude catastrophic events on a marine system and the ultimate sink for the terrestrial material. Understanding what impact the GLOF had on the usual seafloor processes has direct implications for the preservation of benthic communities living in the fjord and for the global carbon cycle.

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Effects of extreme events on the morphology of submarine channels: the case of the Elliot hazard cascade

10.5194/egusphere-egu21-16595 ◽

2021 ◽

Author(s):

Michael Tilston ◽

Dan H. Shugar ◽

Michael Clare ◽

Maarten Heijnen ◽

Sanem Acikalin ◽

...

Keyword(s):

Extreme Event ◽

Dynamic Equilibrium ◽

River Mouth ◽

Channel Morphology ◽

Sediment Supply ◽

Turbidity Currents ◽

Lateral Migration ◽

Submarine Channels ◽

Submarine Channel ◽

Early Results

Submarine systems where the canyon head is directly connected to the river mouth arguably provide the best setting for in situ studies of turbidity currents since the sediment supply propelling them arrive in periodic pulses linked to fluvial freshet events. Consequently, the frequency of, and similarity between, the turbidity currents flowing through these systems make it easier for their channel morphology to evolve towards a state of dynamic equilibrium. Therefore, if an extreme event occurs that dramatically alters the system&#8217;s sediment supply, it is reasonable to assume that submarine channels will undergo a period of rapid adjustment. This is the present scenario occurring in Bute Inlet following the recent Elliot Creek hazard cascade. Bute Inlet is one of the most actively monitored sites for turbidity currents in the world, and the extensive historical dataset that has been amassed at this site along with the rare Elliot Creek event provides the unique opportunity to study the impacts of extreme allogenic forcing mechanisms on the morphodynamics of submarine channels.Preliminary measurements indicate that the turbidity in Elliot Creek has increased by ~40x compared to pre-slide measurements, and oceanographic measurements within a few days of the event show very high turbidity in ocean bottom water to a distance of almost 70 km from the delta. While the bathymetric survey since the landslide is so far constrained to the proximal region of the inlet, early results show that channel morphology was rapidly altered. Specifically, the submarine channel fed by Southgate River, which supplied water and sediment from the landslide and glacial outburst flood, was lowered by about 3m across the width of the channel bed. Conversely, the morphology of the channel fed by Homathko River has remained static between the 2020 and 2021 surveys. Below the confluence of these two submarine channels, the cyclic steps that once dominated the bed morphology appear to have been largely infilled by a 1-2m thick drape of sediment along the inner half of the channel bend, whereas the outer banks have laterally eroded by upwards of 50m at some points. This trend of channel widening and lateral migration appear to be propagating down the system. Importantly, the nature of the slide suggests that sediment delivery will remain elevated with respect to background conditions for decades into the future, suggesting that the submarine channel may be in the process of adapting to an entirely new flow regime rather than reacting to a singular extreme flow event.

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Key controls on submarine channel development in structurally active settings

Marine and Petroleum Geology ◽

10.1016/j.marpetgeo.2011.02.001 ◽

2011 ◽

Vol 28 (7) ◽

pp. 1333-1349 ◽

Cited By ~ 18

Author(s):

Ian R. Clark ◽

Joseph A. Cartwright

Keyword(s):

Submarine Channel ◽

Channel Development

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Linking submarine channel-levee facies and architecture to flow structure of turbidity currents: insights from flume tank experiments

Sedimentology ◽

10.1111/sed.12411 ◽

2017 ◽

Vol 65 (3) ◽

pp. 931-951 ◽

Cited By ~ 13

Author(s):

Jan de Leeuw ◽

Joris T. Eggenhuisen ◽

Matthieu J. B. Cartigny

Keyword(s):

Flow Structure ◽

Turbidity Currents ◽

Submarine Channel

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Environment of Deposition and Paleogeography of the Late Cretaceous Glenburn Formation, Eastern North Island, New Zealand

10.26686/wgtn.17071979 ◽

2021 ◽

Author(s):

◽

James McClintock

Keyword(s):

New Zealand ◽

Late Cretaceous ◽

Large Scale ◽

East Coast ◽

Three Dimensional ◽

Depositional Environments ◽

Tectonic Deformation ◽

Turbidity Currents ◽

Submarine Fan ◽

Submarine Channels

The Glenburn Formation of the East Coast of New Zealand is a Late Cretaceous sedimentary formation consisting of alternating layers of sandstone, mudstone and conglomerate. The Glenburn Formation spans a depositional timeframe of over 10 Ma, is over 1000 m thick, is regionally extensive and is possibly present over large areas offshore. For these reasons, it is important to constrain the paleoenvironment of this unit. Late Cretaceous paleogeographic reconstructions of the East Coast Basin are, however, hampered by a number of factors, including the pervasive Neogene to modern tectonic deformation of the region, the poorly understood nature of the plate tectonic regime during the Cretaceous, and a lack of detailed sedimentological studies of most of the region’s Cretaceous units. Through detailed mapping of the Glenburn Formation, this study aims to improve inferences of regional Cretaceous depositional environments and paleogeography. Detailed facies based analysis was undertaken on several measured sections in eastern Wairarapa and southern Hawke’s Bay. Information such as bed thickness, grain size and sedimentary structures were recorded in order to identify distinct facies. Although outcrop is locally extensive, separate outcrop localities generally lie in different thrust blocks, which complicates comparisons of individual field areas and prevents construction of the large-scale, three-dimensional geometry of the Glenburn Formation. Glenburn Formation consists of facies deposited by sediment gravity flows that were primarily turbidity currents and debris flows. Facies observed are consistent with deposition on a prograding submarine fan system. There is significant variation in facies both within and between sections. Several distinct submarine fan architectural components are recognised, such as fan fringes, fan lobes, submarine channels and overbank deposits. Provenance and paleocurrent indicators are consistent with deposition having occurred on several separate submarine fans, and an integrated regional paleogeographic reconstruction suggests that deposition most likely occurred in a fossil trench following the mid-Cretaceous cessation of subduction along the Pacific-facing margin of Gondwana.

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Effects of tributary inflow and sediment input on reservoir turbidity current formation and evolution

10.5194/egusphere-egu21-4656 ◽

2021 ◽

Author(s):

Yining Sun ◽

Ji Li ◽

Zhixian Cao ◽

Alistair G.L. Borthwick

Keyword(s):

Yellow River ◽

Sediment Concentration ◽

Turbidity Current ◽

Turbidity Currents ◽

Front Speed ◽

Sediment Input ◽

Formation And Evolution ◽

Maximum Utilization

For reservoirs built on a hyper-concentrated river, tributary inflow and sediment input may affect the formation and evolution of reservoir turbidity current, and accordingly bed morphology. However, the understanding of tributary effects on reservoir turbidity currents has remained poor. Here a series of laboratory-scale reservoir turbidity currents are investigated using a coupled 2D double layer-averaged shallow water hydro-sediment-morphodynamic model. It is shown that the tributary location may lead to distinctive effects on reservoir turbidity current. Clear-water flow from the tributary may cause the stable plunge point to migrate upstream, and reduce its front speed. Sediment-laden inflow from the tributary may increase the discharge, sediment concentration, and front speed of the turbidity current, and also cause the plunge point to migrate downstream when the tributary is located upstream of the plunge point. In contrast, if the tributary is located downstream of the plunge point, sediment-laden flow from the tributary causes the stable plunge point to migrate upstream, and while the tributary effects on discharge, sediment concentration, and front speed of the turbidity current are minor. A case study is presented as of the Guxian Reservoir (under planning) on the middle Yellow River, China. The present finding highlights the significance of tributary inflow and sediment input in the formation and propagation of reservoir turbidity current and also riverbed deformation. Appropriate account of tributary effects is warranted for long-term maintenance of reservoir capacity and maximum utilization of the reservoir.

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