Quantitative analysis of the geometry of submarine external levées

Takeshi Nakajima, Benjamin C. Kneller

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

The shape of submarine external channel levées has been assessed in a variety of systems, over a range of slope gradients, measuring both their thickness decay away from the parent channel and also the maximum gradient on the back-slope of the levée. The mathematical description of the shapes of the levées has been based on normalized data, using as characteristic length scales the distance from channel axis to the levée crest and the thickness of the entire levée (or levée package) at the levée crest. The variation in levée thickness perpendicular to the channel shows a clear pattern of power-law decay on steeper slopes (generally > 0·6°) and either exponential or logarithmic decay on gentler slopes. The levée shape is sensitive to local variations in slope and may change over only a few hundreds of metres in the flow direction. The threshold gradient between these two styles shows some variation and may be dependent on grain size. The maximum gradient on the back-slope of the levée shows a weak correlation with slope gradient, which varies from one system to another; this may also be a function of grain size. The variations in behaviour can be explained, in part, by differing rates of entrainment of ambient sea water into the currents as they flow over the levées, these rates being dependent upon the slope. Negligible entrainment on low gradients helps to explain the tendency to wider levées on low-gradient basin floors, as well as the persistence of channelized flows on low gradients, with little dissipation over extreme distances.
Original languageEnglish
Pages (from-to)877-910
Number of pages34
JournalSedimentology
Volume60
Issue number4
Early online date22 Oct 2012
DOIs
Publication statusPublished - Jun 2013

Fingerprint

quantitative analysis
geometry
entrainment
grain size
dissipation
power law
persistence
seawater
basin

Keywords

  • grain size
  • levée
  • slope
  • submarine channel
  • turbidity currents

Cite this

Quantitative analysis of the geometry of submarine external levées. / Nakajima, Takeshi; Kneller, Benjamin C.

In: Sedimentology, Vol. 60, No. 4, 06.2013, p. 877-910.

Research output: Contribution to journalArticle

Nakajima, Takeshi ; Kneller, Benjamin C. / Quantitative analysis of the geometry of submarine external levées. In: Sedimentology. 2013 ; Vol. 60, No. 4. pp. 877-910.
@article{3d42339cbf4048e6980ab26da361d68f,
title = "Quantitative analysis of the geometry of submarine external lev{\'e}es",
abstract = "The shape of submarine external channel lev{\'e}es has been assessed in a variety of systems, over a range of slope gradients, measuring both their thickness decay away from the parent channel and also the maximum gradient on the back-slope of the lev{\'e}e. The mathematical description of the shapes of the lev{\'e}es has been based on normalized data, using as characteristic length scales the distance from channel axis to the lev{\'e}e crest and the thickness of the entire lev{\'e}e (or lev{\'e}e package) at the lev{\'e}e crest. The variation in lev{\'e}e thickness perpendicular to the channel shows a clear pattern of power-law decay on steeper slopes (generally > 0·6°) and either exponential or logarithmic decay on gentler slopes. The lev{\'e}e shape is sensitive to local variations in slope and may change over only a few hundreds of metres in the flow direction. The threshold gradient between these two styles shows some variation and may be dependent on grain size. The maximum gradient on the back-slope of the lev{\'e}e shows a weak correlation with slope gradient, which varies from one system to another; this may also be a function of grain size. The variations in behaviour can be explained, in part, by differing rates of entrainment of ambient sea water into the currents as they flow over the lev{\'e}es, these rates being dependent upon the slope. Negligible entrainment on low gradients helps to explain the tendency to wider lev{\'e}es on low-gradient basin floors, as well as the persistence of channelized flows on low gradients, with little dissipation over extreme distances.",
keywords = "grain size, lev{\'e}e, slope, submarine channel, turbidity currents",
author = "Takeshi Nakajima and Kneller, {Benjamin C.}",
year = "2013",
month = "6",
doi = "10.1111/j.1365-3091.2012.01366.x",
language = "English",
volume = "60",
pages = "877--910",
journal = "Sedimentology",
issn = "0037-0746",
publisher = "Wiley-Blackwell",
number = "4",

}

TY - JOUR

T1 - Quantitative analysis of the geometry of submarine external levées

AU - Nakajima, Takeshi

AU - Kneller, Benjamin C.

PY - 2013/6

Y1 - 2013/6

N2 - The shape of submarine external channel levées has been assessed in a variety of systems, over a range of slope gradients, measuring both their thickness decay away from the parent channel and also the maximum gradient on the back-slope of the levée. The mathematical description of the shapes of the levées has been based on normalized data, using as characteristic length scales the distance from channel axis to the levée crest and the thickness of the entire levée (or levée package) at the levée crest. The variation in levée thickness perpendicular to the channel shows a clear pattern of power-law decay on steeper slopes (generally > 0·6°) and either exponential or logarithmic decay on gentler slopes. The levée shape is sensitive to local variations in slope and may change over only a few hundreds of metres in the flow direction. The threshold gradient between these two styles shows some variation and may be dependent on grain size. The maximum gradient on the back-slope of the levée shows a weak correlation with slope gradient, which varies from one system to another; this may also be a function of grain size. The variations in behaviour can be explained, in part, by differing rates of entrainment of ambient sea water into the currents as they flow over the levées, these rates being dependent upon the slope. Negligible entrainment on low gradients helps to explain the tendency to wider levées on low-gradient basin floors, as well as the persistence of channelized flows on low gradients, with little dissipation over extreme distances.

AB - The shape of submarine external channel levées has been assessed in a variety of systems, over a range of slope gradients, measuring both their thickness decay away from the parent channel and also the maximum gradient on the back-slope of the levée. The mathematical description of the shapes of the levées has been based on normalized data, using as characteristic length scales the distance from channel axis to the levée crest and the thickness of the entire levée (or levée package) at the levée crest. The variation in levée thickness perpendicular to the channel shows a clear pattern of power-law decay on steeper slopes (generally > 0·6°) and either exponential or logarithmic decay on gentler slopes. The levée shape is sensitive to local variations in slope and may change over only a few hundreds of metres in the flow direction. The threshold gradient between these two styles shows some variation and may be dependent on grain size. The maximum gradient on the back-slope of the levée shows a weak correlation with slope gradient, which varies from one system to another; this may also be a function of grain size. The variations in behaviour can be explained, in part, by differing rates of entrainment of ambient sea water into the currents as they flow over the levées, these rates being dependent upon the slope. Negligible entrainment on low gradients helps to explain the tendency to wider levées on low-gradient basin floors, as well as the persistence of channelized flows on low gradients, with little dissipation over extreme distances.

KW - grain size

KW - levée

KW - slope

KW - submarine channel

KW - turbidity currents

UR - http://www.scopus.com/inward/record.url?scp=84867643208&partnerID=8YFLogxK

U2 - 10.1111/j.1365-3091.2012.01366.x

DO - 10.1111/j.1365-3091.2012.01366.x

M3 - Article

VL - 60

SP - 877

EP - 910

JO - Sedimentology

JF - Sedimentology

SN - 0037-0746

IS - 4

ER -