Changes in Submarine Channel Morphology and Slope Sedimentation Patterns from Repeat Multibeam Surveys in the Fraser River Delta, Western Canada

  1. Michael Z. Li2,
  2. Christopher R. Sherwood3 and
  3. Philip R. Hill4
  1. Philip R. Hill

Published Online: 3 JAN 2013

DOI: 10.1002/9781118311172.ch3

Sediments, Morphology and Sedimentary Processes on Continental Shelves: Advances in Technologies, Research, and Applications

Sediments, Morphology and Sedimentary Processes on Continental Shelves: Advances in Technologies, Research, and Applications

How to Cite

Hill, P. R. (2012) Changes in Submarine Channel Morphology and Slope Sedimentation Patterns from Repeat Multibeam Surveys in the Fraser River Delta, Western Canada, in Sediments, Morphology and Sedimentary Processes on Continental Shelves: Advances in Technologies, Research, and Applications (eds M. Z. Li, C. R. Sherwood and P. R. Hill), John Wiley & Sons, Ltd, Chichester, West Sussex, UK. doi: 10.1002/9781118311172.ch3

Editor Information

  1. 2

    Geological Survey of Canada (Atlantic), Natural Resources Canada, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, B2Y 4A2 Canada

  2. 3

    U. S. Geological Survey, Woods Hole, MA 02543-1598 USA

  3. 4

    Natural Resources Canada, Sidney, BC, Canada V8L 4B2

Author Information

  1. Natural Resources Canada, Geological Survey of Canada, P.O. Box 6000, Sidney, BC, V8L 4B2, Canada

Publication History

  1. Published Online: 3 JAN 2013
  2. Published Print: 26 JAN 2012

ISBN Information

Print ISBN: 9781444350821

Online ISBN: 9781118311172

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Keywords:

  • fraser river delta;
  • multibeam bathymetry;
  • backscatter intensity;
  • submarine channel;
  • fan;
  • turbidity current;
  • hyperpycnal flow

Summary

The Strait of Georgia is a forearc basin located between the subducting Juan de Fuca plate and the volcanic arc of the Coast Mountains. The predominant source of sediment to the basin is the Fraser River, which has formed a large Holocene delta. Multibeam surveys of the main distributary channel mouth and delta slope confirm the presence of a submarine channel-fan system consisting of two main tributary networks with steep headwalls on the upper slope, a single main channel reach, partially constricted by a bedrock or till ridge, channel levees and a base-of-slope fan. At the base of slope, the main submarine channel dies out and erosional flute forms are observed. The fan consists of a broad area of high backscatter intensity and smaller ephemeral channels. Repeat multibeam surveys show that the upper slope is characterized by high rates of sediment accumulation and small-scale slope failure on an inter-annual time scale. Erosional features include headwall flow failures and retrogressive intra-channel erosion. Repeat surveys also indicate that sediment accumulates within the upper reaches of the tributary slope channels in the form of retrogradationally-stacked depositional wedges. These are interpreted to be formed by short-lived turbidity currents originating from density underflows created when dredge waste impacts the seafloor. The retrogradational stacking is thought to be a response to a feedback process whereby each wedge, deposited at the critical gradient for ignition, reduces the gradient for the next flow. The non-channelled portion of the delta slope adjacent to the distributary channel is characterized by sediment waves which repeat surveys show to be migrating up-slope. It is suggested that this is evidence for unconfined turbidity currents.