Author(s): D. C. J. D. Hoyal; B. A. Sheets
Linked Author(s):
Keywords: No Keywords
Abstract: An experimental investigation of growth patterns on mildly supercritical, noncohesive submarine fans demonstrates a counter-intuitive relationship between sediment transport and slope. Over a range of experimental conditions, longer channels that suggest relatively efficient sediment transport form on lower slopes, whereas sediment transport becomes progressively more inefficient as slope increases. We infer the mechanism controlling this behavior to be the formation of a hydraulic jump in the channel. As proposed by Grant (1997) for mobile bed subaerial streams, growth patterns on supercritical submarine fans may reflect self-organization to a Froude critical state (densimetric Froude number ～ 1), involving both hydrodynamic and morphodynamic flow modulation. We suggest that the observed inverse power-law relation between channel extension length and slope (length v slope-0.5) can be explained by acceleration to jump conditions over shorter distances on steeper slopes, although scaling analysis suggests that ambient fluid entrainment may lead to a similar functional form. Hydraulic jumps have often been interpreted at channel mouths on fans before (e.g., Normark, 1970, Komar, 1971), but their significance in setting distributive channel length has largely been overlooked. The experimental results suggest a new autogenic mechanism for the ramp-like progradational style commonly observed at deep water basin margins and for ‘perched' stratal patterns in minibasins. At smaller scales these results may be important for understanding the unique surface dynamics and stratigraphy of avulsion cycles in supercritical fans.
Year: 2009