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Ongoing evolution of submarine canyon rockwalls; examples from the Whittard Canyon, Celtic Margin (NE Atlantic)

Ongoing evolution of submarine canyon rockwalls; examples from the Whittard Canyon, Celtic Margin (NE Atlantic)
Ongoing evolution of submarine canyon rockwalls; examples from the Whittard Canyon, Celtic Margin (NE Atlantic)

During the CODEMAP 2015 research expedition to the Whittard Canyon, Celtic Margin (NE Atlantic), a Remotely Operated Vehicle (ROV) gathered High Definition video footage of the canyon rockwalls at depths of approximately 412–4184 m below sea level. This dataset was supplemented by predominantly carbonate rock samples collected during the dives, which were subsequently tested for key physical property characteristics in a geotechnical laboratory. The high-resolution video footage revealed small-scale rockwall slope processes that would not have been visible if shipboard geophysical equipment was solely relied upon during the survey. Of particular interest was the apparent spalling failure of mudstone and chalk rockwalls, with fresh superficial “flaking” scars and an absence of sessile fauna possibly suggesting relatively recent mass-wasting activity. Extensive talus slopes, often consisting of coarse gravel, cobble and occasionally boulder-sized clasts, were observed at the foot of slopes impacted by spalling failures; this debris was rarely colonised by biological communities, which could be an indicator of frequent rockfall events. Bio-erosion was also noted on many of the walls prone to this form of rock slope failure (RSF). As in subaerial equivalents, internal fracture networks appear to control the prevalence of RSF and the geometries of blocks, often resulting in cubic and tabular blocks (0.2–1.0 m scale) of bedrock toppling or sliding out of the cliff face. Tensile strength parameters of carbonate rock samples were determined and these may affect the mass wasting processes observed within the canyon. It was found that carbonate samples which appeared to have a higher mud content, and reduced porosity, produced significantly higher tensile strength values. It is proposed that these stronger, “muddy” carbonate units form the overhanging ledges that often provide an ideal setting for sessile species, such as Acesta excavata clams, to colonise whereas the weaker “pure” carbonate units are more easily eroded and therefore form the undercutting, receding sections of the rockwall. By combining the ROV observations, basic discontinuity assessments (estimation of fracture orientations) and laboratory testing results, an understanding of the geomechanical properties of the bedrock can be obtained and linked with past and ongoing rock slope processes within the Whittard Canyon. These conclusions will have a wider implication for ongoing geomechanical processes within submarine canyons on a global scale.

Bedrock erosion, Bioerosion, Canyon rockwalls, Celtic Margin, NE Atlantic, Remotely Operated Vehicle, Submarine canyons, Whittard Canyon
0079-6611
79-88
Carter, Gareth D.O.
ae9248e5-ab8e-4d88-afc4-608d8ce6b27e
Huvenne, Veerle A.I.
f22be3e2-708c-491b-b985-a438470fa053
Gales, Jennifer A.
89a90ab1-01a8-4b0d-87f8-b381678f50cd
Lo Iacono, Claudio
2ec2b5f4-a134-462b-b8ba-f7bd757040f5
Marsh, Leigh
b9d089aa-91e4-4a2e-b716-a7352616c6a2
Ougier-Simonin, Audrey
750ecb0f-0b90-4a82-82ab-0ac21ddfe9c5
Robert, Katleen
49e4bfa2-0999-41ec-b50d-65c0f8896583
Wynn, Russell B.
72ccd765-9240-45f8-9951-4552b497475a
Carter, Gareth D.O.
ae9248e5-ab8e-4d88-afc4-608d8ce6b27e
Huvenne, Veerle A.I.
f22be3e2-708c-491b-b985-a438470fa053
Gales, Jennifer A.
89a90ab1-01a8-4b0d-87f8-b381678f50cd
Lo Iacono, Claudio
2ec2b5f4-a134-462b-b8ba-f7bd757040f5
Marsh, Leigh
b9d089aa-91e4-4a2e-b716-a7352616c6a2
Ougier-Simonin, Audrey
750ecb0f-0b90-4a82-82ab-0ac21ddfe9c5
Robert, Katleen
49e4bfa2-0999-41ec-b50d-65c0f8896583
Wynn, Russell B.
72ccd765-9240-45f8-9951-4552b497475a

Carter, Gareth D.O., Huvenne, Veerle A.I., Gales, Jennifer A., Lo Iacono, Claudio, Marsh, Leigh, Ougier-Simonin, Audrey, Robert, Katleen and Wynn, Russell B. (2018) Ongoing evolution of submarine canyon rockwalls; examples from the Whittard Canyon, Celtic Margin (NE Atlantic). Progress in Oceanography, 169, 79-88. (doi:10.1016/j.pocean.2018.02.001).

Record type: Article

Abstract

During the CODEMAP 2015 research expedition to the Whittard Canyon, Celtic Margin (NE Atlantic), a Remotely Operated Vehicle (ROV) gathered High Definition video footage of the canyon rockwalls at depths of approximately 412–4184 m below sea level. This dataset was supplemented by predominantly carbonate rock samples collected during the dives, which were subsequently tested for key physical property characteristics in a geotechnical laboratory. The high-resolution video footage revealed small-scale rockwall slope processes that would not have been visible if shipboard geophysical equipment was solely relied upon during the survey. Of particular interest was the apparent spalling failure of mudstone and chalk rockwalls, with fresh superficial “flaking” scars and an absence of sessile fauna possibly suggesting relatively recent mass-wasting activity. Extensive talus slopes, often consisting of coarse gravel, cobble and occasionally boulder-sized clasts, were observed at the foot of slopes impacted by spalling failures; this debris was rarely colonised by biological communities, which could be an indicator of frequent rockfall events. Bio-erosion was also noted on many of the walls prone to this form of rock slope failure (RSF). As in subaerial equivalents, internal fracture networks appear to control the prevalence of RSF and the geometries of blocks, often resulting in cubic and tabular blocks (0.2–1.0 m scale) of bedrock toppling or sliding out of the cliff face. Tensile strength parameters of carbonate rock samples were determined and these may affect the mass wasting processes observed within the canyon. It was found that carbonate samples which appeared to have a higher mud content, and reduced porosity, produced significantly higher tensile strength values. It is proposed that these stronger, “muddy” carbonate units form the overhanging ledges that often provide an ideal setting for sessile species, such as Acesta excavata clams, to colonise whereas the weaker “pure” carbonate units are more easily eroded and therefore form the undercutting, receding sections of the rockwall. By combining the ROV observations, basic discontinuity assessments (estimation of fracture orientations) and laboratory testing results, an understanding of the geomechanical properties of the bedrock can be obtained and linked with past and ongoing rock slope processes within the Whittard Canyon. These conclusions will have a wider implication for ongoing geomechanical processes within submarine canyons on a global scale.

Full text not available from this repository.

More information

Accepted/In Press date: 2018
e-pub ahead of print date: 2 February 2018
Published date: December 2018
Keywords: Bedrock erosion, Bioerosion, Canyon rockwalls, Celtic Margin, NE Atlantic, Remotely Operated Vehicle, Submarine canyons, Whittard Canyon
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Identifiers

Local EPrints ID: 427499
URI: http://eprints.soton.ac.uk/id/eprint/427499
DOI: doi:10.1016/j.pocean.2018.02.001
ISSN: 0079-6611
PURE UUID: 0176a819-78c5-47ab-91c3-36adae7c4d6a
ORCID for Veerle A.I. Huvenne: ORCID iD orcid.org/0000-0001-7135-6360

Catalogue record

Date deposited: 21 Jan 2019 17:31
Last modified: 07 Oct 2020 01:49

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Contributors

Author: Gareth D.O. Carter
Author: Veerle A.I. Huvenne ORCID iD
Author: Jennifer A. Gales
Author: Claudio Lo Iacono
Author: Leigh Marsh
Author: Audrey Ougier-Simonin
Author: Katleen Robert
Author: Russell B. Wynn

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