M. Mike Tilston chercheur associé postdoctoral à l'Université d'Utrecht au Pays-Bas (bio ci-dessous), présentera une conférence le 22 février 2019 à 10h30, à la salle 2422 du Centre Eau Terre Environnement de l'INRS.
Sa conférence s'intitule Density matters : Autogenic controls on the morphologic evolution of the planet’s seascapes (résumé ci-dessous).
Bienvenue à tous!
Résumé : Submarine, particle-laden density flows transport a disproportionately large volume of sediment and serve as the primary conduits connecting the Earth’s fluvial and coastal systems to the deep ocean. Due to the hostile environment where these currents are active, monitoring these systems was thought to be untenable. Yet due to ambitious research efforts over the past decade, we are now getting the first glimpses on the velocity structure of these powerful flows. As such, it seems timely to begin considering the effects of the principal factor propelling these powerful flows: their sediment load. While at times the geometry and assemblage of depositional structures seen in submarine channels appear cosmetically similar to their fluvial counterparts, more often than not there are notable differences between these two systems. The likely reason for the variations in their morphodynamics is related to their sources of excess density that propel the flow. In fluvial systems, the source of excess density is principally the fluid, and the influence of their suspended load can largely be neglected when describing their flow structure and linking it to bed development. In striking contrast, the source of excess density in turbidity currents is their suspended load, which then entrains the surrounding ambient fluid. Consequently, the fluid and solid phases cannot be interpreted in isolation and relating their flow dynamics to a morphologic response is more complicated when compared to fluvial systems. The chief hindrance to advancing our understanding of turbidity currents are the numerous technical challenges to accurately characterize their density structure. My work relies on the use of novel instrumentation (computed tomography (CT) scanning) and analytical approaches (acoustic back-scatter) to quantify the density structure of experimental turbidity currents. The aim of my research is to address the role of density in defining (1) the flow structure of turbidity currents; (2) the sedimentary structures observed in their bed-scale deposits; and (3) how sediment is preferentially routed on the ocean floor to explain the avulsion cycle of submarine lobes. I will outline short-term research objectives related to the integration of my experimental work with ongoing international monitoring programs of natural turbidity currents, as well as projects with other experimental research groups to develop analytical models of these systems. I will further outline the uncertainty surrounding the triggering mechanisms for these systems, stressing the need for further research on the remobilization of coastal sediments to understand how particles and nutrients are conveyed between the planet’s subaerial and submarine landscapes.
Biographie : My research interests focus on coupling hydrodynamic and morphodynamic processes that dictate the evolution of the planet’s past and present sedimentary systems. The focus of my early research and professional career was on the dynamics of fluvial environments and the effects of anthropogenic overprints on their evolution. Subsequently, the aim of my doctoral and post-doctoral work has focused on studying the sediment transport dynamics of turbidity currents and linking them to the morphologic expression of their deposits from bed-scale features to the overall architecture of the system. Thus, the natural trajectory of my research is to focus on costal environments to develop a comprehensive ‘source-to-sink’ overview of the planet’s sedimentary systems.