Internal Versus External Forcing of Aggradational Submarine Channel Avulsion
William
. D. McCaffrey1, Benjamin and C. Kneller2
1 University of Leeds, Leeds, United Kingdom
2 University of Aberdeen, Aberdeen, United Kingdom
Both internal and external forcing may influence the development of aggradational submarine channels, and in particular, their likelihood of avulsion. Given fixed input conditions, it can be shown that submarine channel levee systems cannot grow with a fixed geometry, necessitating changes in one or more of: 1) sediment fractionation (in terms of the ratios of material deposited inside to outside of the channel); 2) the outer-levee slope and 3) the channel cross sectional area. Any of these changes will increase the likelihood of avulsions. In addition, externally-forced changes in the type of flow entering a channel-levee system may progressively change the in-channel morphology increasing the likelihood of avulsions when the channel cross sectional area is reduced. Internal and external forcing must commonly co-occur. Internal forcing may be the predominant cause of avulsions in high sedimentation rate systems, whereas external forcing may predominate in lower sedimentation rate systems. In intermediate systems the controls may switch in influence as the sediment input rate varies.
AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005