An evaluation of regional active along-slope and down-slope

processes of the NW European continental margin

Michael Cunningham, Sophie Hodgson, Lindsay Parson and Doug Masson

In conjunction with:

BT MarineFlag TelecomGeminiGlobal Crossing / Global MarineTyco

• To develop a semi-quantitative summary of active slope

processes

• Risk assessment for submarine cables

• To reduce time and costs to UK telecommunications industry

Aims

• Compilation of all available datasets relating to slope processes and stability

• Evaluation of datasets

• Model ‘Risk Assessment’ in Geographical Information Systems (GIS)

Objectives

Datasets

• Swathe bathymetry

• Swathe Backscatter

• Side-Scan Sonar

• 3.5kHz Pinger Profiles

• Gravity / Box Cores

Data Modelling and Interpretation

GIS Layers:

3.5kHz Echo-facies (grid/image/line/point/polygon)Aspect (grid)

Backscatter (grid/polygon)Bathymetric Shaded Relief (grid)

Cables (line)Contours (line)

Morphology (grid/polygon)Relief (grid)

Sediment samples (point)Side-scan sonar (geoTiff)

Slope (grid)

Metadata (line/point/polygon/xml)

Conclusions (Goban Spur)

• Asymmetrical sediment waves infer NW sediment transport

• Continental shelf break transition dominated by glacial erosive features

• Along-, down-slope gullies/channels, and sediment slides

• S margin indented by large U-shaped canyons, with evidence of sediment slides

• Canyon floors – incised channels following topographic fault bounded escarpments

Conclusions (Celtic Margin (1))

• Sand waves on shelf break, mainly orthogonal to the canyon axes, and asymmetry infers sediment transport

into the canyon heads

• Symmetrical sand waves appear to be inactive, now being overprinted

• Active down-slope sediment transport in the form of turbidity currents dominates upper reaches of canyons

• Drainage basins on canyon heads, interpreted as retrogressive mass wasting and shelf indention

• Recent or Active NNW-SSE faulting (?)

Conclusions (Celtic Margin (2))

• Sediment deposition mid-slope

• Canyon over-bank spill – unconfined turbidite deposits

• Active down-slope sediment transport (turbidity currents) dominate upper reaches of canyons

• Major asymmetrical levees at foot of continental slope / rise

• Turbidity currents incised a major channel into the low gradient of the continental rise and the flat abyssal

plain.

• Over-spill deposits form sediment waves and the build up of wide levees