[S-CG65] [EE] 混濁流:発生源から堆積物・地形形成まで

[SCG65-12] Framework for tying the fluid mechanics of turbidity currents to the excavation of submarine canyons

*Gary Parker¹ (1.University of Illinois at Urbana Champaign USA)

キーワード：bedrock, morphodynamics, submarine canyons, turbidity currents

The field of erodible-bed morphodynamics, in which the flow interacts with the bed to create morphologic structure and change, has its origins in the study of alluvial rivers. Such morphodynamic analysis has served to characterize the formation of such features as dunes, antidunes, alternate bars, meander point bars, upward-concave long profiles and patterns of sediment sorting. In the case of alluvial rivers, the sediment is assumed to be non-cohesive and loose, with no limitation on mobility imposed by cohesion or lithification. It is only in the present century that the morphodynamic formulation necessary to handle bedrock rivers has been developed. In the case of mixed bedrock-alluvial rivers, the bed is assumed to be lithified bedrock with an intermittent and discontinuous cover of alluvium. If this alluvium is gravel, then the bed can be abraded due to collisions between rolling or saltating grains and the bed. One such morphodynamic formulation is the MRSAA (Macro-Roughness based Saltation-Abrasion-Alluvium) Model. This formulation and related formulations have been used to study the evolution of incisional long profiles in uplifting basins, below-capacity alternate bars moving over bedrock (and incising it), bedrock grooves, alluvial-bedrock bend migration and canyon formation. Yet the largest canyons in the world were excavated not by rivers, but by submarine turbidity currents. The research body on the morphodynamics of submarine canyons is relatively small. Early attempts have involved the assumption that the sediment of the canyon bed is loose, non-cohesive material. The substrate being eroded, however, is likely to have lithified to some degree, or may consist of continental shelf-slope mud that has developed considerable strength. Here we define a framework for treating the morphodynamics of incision in submarine canyons.