The physical processes of seabed disturbance during iceberg grounding and scouring

Woodworth-Lynas, C.; Josenhans, H; Barrie, J. Vaughn; Lewis, C F M; Parrott, D R

doi:10.1016/0278-4343(91)90086-l

Cited by 135 publications

(60 citation statements)

References 8 publications

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“…Since the sampled diamicton in this investigation is unaffected entirely by subglacial processes, and the wide, flat bed of the outer fjord is likely to preclude processes related to large-scale mass-wasting (Dowdeswell et al, 1994a,b;Ó Cofaigh et al, 2001), grain turbates in this investigation are likely to have developed in response to iceberg scouring. Sediment rotation responsible for grain turbates may occur through i) direct downward stress from a scouring iceberg keel (similar to subglacial environments if, for example, confined conditions were created below a large tabular iceberg) (Linch et al, 2012), and/or ii) in relation to the initial impact of a scouring keel (when stress is very high before equilibrium between the keel and the sediment is reached) (Woodworth-Lynas et al, 1991) (Fig. 10).…”

Section: Rotation Compression and Slumpmentioning

confidence: 99%

“…'Half' a turbate is identified also in iceberg scoured pebbly sandy mud (Linch and van der Meer, 2014). If small-scale localised sediment rotation is responsible for development of grain turbates, it will be likely to occur in response to smallscale localised debris flows produced during iceberg scour by i) impact during calving and by the ploughing process itself (Lien et al, 1989) (lateral and distal to the keel); ii) generation of strong local currents responsible for debris slides (Lien et al, 1989) (lateral and distal to the keel); iii) turbulence around the keel in the same way turbulence is produced by flow-deflecting boulders (Phillips, 2006;Kilfeather et al, 2010); iv) gravityinduced collapse of the surcharge of bull-dozed material at the front of the keel (Woodworth-Lynas et al, 1991); v) redistribution of non-cohesive sediment down the inner scour slopes back into the trough or down the outer scour slopes after the keel has passed (Lien et al, 1989;Woodworth-Lynas et al, 1991); and vi) collapse of sediment in the space left by melt-out of blocks of ice broken from the keel and driven into the sediment (Woodworth-Lynas et al, 1991) (Fig. 10).…”

Section: Rotation Compression and Slumpmentioning

confidence: 99%

“…Such blocks form the iceberg scour berm (e.g. Woodworth-Lynas et al, 1991;Woodworth-Lynas and Dowdeswell, 1994), but are also likely to roll away immediately in front (surcharge) and to the sides of a scouring keel, as well as back down into the scour trough after the keel has passed (Linch et al, 2012) (Fig. 10).…”

Section: Rotation Compression and Slumpmentioning

confidence: 99%

“…Failure planes occur during horizontal and vertical displacement of sediment by compression and/or extension as the keel moves through it (Woodworth-Lynas and Landva, 1988;Woodworth-Lynas and Guigné, 1990;Woodworth-Lynas et al, 1991;Linch et al, 2012). Compression may occur i) vertically, below the keel (Poorooshasb et al, 1989); ii) ahead of the scouring keel (Woodworth-Lynas and Landva, 1988); and iii) between slabs of sediment displaced away from the advancing keel (Woodworth-Lynas and Guigné, 1990) (Fig.…”

Section: Planar Shearmentioning

confidence: 99%

“…10). Extension may occur i) during shear and drag between the keel and the sediment at the sides of the keel (Woodworth-Lynas et al, 1991); ii) as a result of stress release during sediment expulsion from beneath the keel (Woodworth-Lynas et al, 1991); and iii) during gravity-induced shear on resultant scour slopes (Woodworth-Lynas and Guigné, 1990) (Fig. 10).…”

Section: Planar Shearmentioning

confidence: 99%

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Micromorphology of diamicton affected by iceberg-keel scouring, Scoresby Sund, East Greenland

Linch

Dowdeswell

2016

Quaternary Science Reviews

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Icebergs are important as agents of deposition and seafloor reworking on glacier-influenced continental margins. When the keel of an iceberg exceeds water depth it ploughs through soft sediments producing scours/ploughmarks that can be kilometres long, hundreds of metres wide and sometimes tens of metres deep. Because the influence of iceberg keels on sediment is a critical factor when offshore structures (e.g. pipelines, power cables) are installed, the surface morphology of iceberg scours on the seafloor is relatively welldocumented. Less however, is known about sub-scour deformation below the seafloor. This is particularly true of iceberg scoured diamicton (poorly sorted sediment comprising a variety of particle sizes), which is present in many high-latitude fjords and continental shelves. The aim of this research is to examine directly (macroscopically and microscopically, with thin sections) the style and intensity of deformation caused by the scouring action of iceberg keels in diamicton offshore of East Greenland. Results show that a distinctive suite of deformation structures (individual structures and overprinted structural patterns) dominated by planar shear, sediment mixing and high porewater, and dropstones characterises iceberg scoured diamicton. In addition, diamicton from areas of high-intensity iceberg scouring tends to show a wider variety, higher frequency and distribution, more abundant and better-developed deformation structures than diamicton from areas of intermediate-and low-intensity iceberg scouring. Characterising the effects of iceberg scour in diamicton is important more widely to inform: i) reconstruction of the geometry and dynamics of former ice sheets; and ii) installation and protection of offshore engineering structures in diamicton where iceberg scouring presents a geohazard. The value of micromorphology is significant especially in the absence of macroscopic sediment exposures/outcrops where the study of cores is necessary instead.

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Section: Rotation Compression and Slumpmentioning

confidence: 99%

Section: Rotation Compression and Slumpmentioning

confidence: 99%

Section: Rotation Compression and Slumpmentioning

confidence: 99%

Section: Planar Shearmentioning

confidence: 99%

Section: Planar Shearmentioning

confidence: 99%

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Micromorphology of diamicton affected by iceberg-keel scouring, Scoresby Sund, East Greenland

Linch

Dowdeswell

2016

Quaternary Science Reviews

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The periodic topography of ice stream beds: Insights from the Fourier spectra of mega‐scale glacial lineations

et al. 2017

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Ice stream bed topography contains key evidence for the ways ice streams interact with, and are potentially controlled by, their beds. Here we present the first application of two‐dimensional Fourier analysis to 22 marine and terrestrial topographies from 5 regions in Antarctica and Canada, with and without mega‐scale glacial lineations (MSGLs). We find that the topography of MSGL‐rich ice stream sedimentary beds is characterized by multiple, periodic wavelengths between 300 and 1200 m and amplitudes from decimeters to a few meters. This periodic topography is consistent with the idea that instability is a key element to the formation of MSGL bedforms. Dominant wavelengths vary among locations and, on one paleo ice stream bed, increase along the direction of ice flow by 1.7 ± 0.52% km−1. We suggest that these changes are likely to reflect pattern evolution via downstream wavelength coarsening, even under potentially steady ice stream geometry and flow conditions. The amplitude of MSGLs is smaller than that of other fluvial and glacial topographies but within the same order of magnitude. However, MSGLs are a striking component of ice stream beds because the topographic amplitude of features not aligned with ice flow is reduced by an order of magnitude relative to those oriented with the flow direction. This study represents the first attempt to automatically derive the spectral signatures of MSGLs. It highlights the plausibility of identifying these landform assemblages using automated techniques and provides a benchmark for numerical models of ice stream flow and subglacial landscape evolution.

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Glacial geomorphology of the Central Arctic Ocean: the Chukchi Borderland and the Lomonosov Ridge

Polyak

Klemån

Coakley

2008

Earth Surf Processes Landf

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The last decade of geophysical seafloor mapping in the Arctic Ocean from nuclear submarines and icebreakers reveals a wide variety of glaciogenic geomorphic features at water depths reaching 1000 m. These findings provide new and intriguing insights into the Quaternary glacial history of the Northern Hemisphere. Here we integrate multi-and single beam bathymetric data, chirp sonar profiles and sidescan images from the Chukchi Borderland and Lomonosov Ridge to perform a comparative morphological seafloor study. This investigation aims to elucidate the nature and provenance of ice masses that impacted the Arctic Ocean sea floor during the Quaternary. Mapped glaciogenic bedforms include iceberg keel scours, most abundant at water depths shallower than ~350-400 m, flutes and megascale glacial lineations extending as deep as ~1000 m below the present sea level, small drumlinlike features and morainic ridges and grounding-zone wedges. The combination of these features indicates that very large glacial ice masses extended into the central Arctic Ocean from surrounding North American and Eurasian ice sheets several times during the Quaternary. Ice shelves occupied large parts of the Arctic Ocean during glacial maxima and ice rises were formed over the Chukchi Borderland and portions of the Lomonosov Ridge. More geophysical and sediment core data combined with modeling experiments are needed to reconstruct the timing and patterns of these events. CruiseArctic Ocean 96 SCICEX 98/99 HLY0302 HLY0501/0503 *The bathymetric and sidescan sonar data acquisition was only partly working during the 1998 cruise. VesselSwedish icebreaker Oden US Navy nuclear submarines USS Pargo and Hawkbill USCGC Healy USCGC Healy Geophysical mapping/geological sampling chirp sonar profiling/sediment coring chirp sonar profiling/swath bathymetry and sidescan with interferometric sonar* chirp sonar profiling/multibeam bathymetry chirp sonar profiling/multibeam bathymetry/sediment coring References (e.g.)Backman et al. (1997) Edwards and Coakley (2003) Jakobsson et al. (2005) Darby et al. (2005) 528 M. Jakobsson et al.Figure 2. (a) Bathymetric map of the Chukchi Borderland and Mendeleev Ridge (see the methods section for an explanation of the bathymetric compilation). Major glaciogenic features and mapped limits of erosion are indicated. The directional features refer to drumlins (Northwind Ridge) and ice-dragged sediment blocks or boulders (Chukchi Plateau). Locations of sub-bottom profiles in Figures 4(a) and 8 are indicated with bold yellow lines; also shown are locations of Figures 6 and 7. The 1000 m isobath is shown with a white line and the 600 m with a black line. (b) Bathymetric profile along the Northwind Ridge. Mapped depths of erosion are shown by dashed lines. Also shown is the location of chirp sonar fragments and locations of figures with multibeam and sidescan images.contain widespread, diverse glaciogenic morphology such as sets of parallel lineations (flutes), transverse ridges and drumlins . The combination of these features depict...

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The physical processes of seabed disturbance during iceberg grounding and scouring

Cited by 135 publications

References 8 publications

Micromorphology of diamicton affected by iceberg-keel scouring, Scoresby Sund, East Greenland

Micromorphology of diamicton affected by iceberg-keel scouring, Scoresby Sund, East Greenland

The periodic topography of ice stream beds: Insights from the Fourier spectra of mega‐scale glacial lineations

Glacial geomorphology of the Central Arctic Ocean: the Chukchi Borderland and the Lomonosov Ridge

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