A Video Is Worth A Thousand Words: Ten Years Of Laboratory Experiments On Subaqueous Gravity Flows And The Insights Gained Into Their Flow And Deposition

Abstract

Abstract Submarine mass gravity flows play a significant role in the formation and alteration of the geological record along deep marine margins. Petroleum exploration requires an understanding of the processes involved in these mass transport events. The development of modern deep-marine infrastructure such as pipelines, platforms and cables must consider the risk associated with the potential occurrence of mass transport events. Both interpretations of the geologic record and risk assessment for occurrence of mass gravity flows require an understanding of the initiation, transport and depositional processes associated with subaqueous gravity flows. Unlike subaerial mass transport events, submarine events have never been observed and therefore limited understanding of the processes associated with the events is available. Controlled laboratory experiments of subaqueous mass flows is one means of studying these important events. This paper will present a summary of nearly ten years of experimental research conducted at the St. Anthony Falls Laboratory, University of Minnesota on the flow and deposition of subaqueous debris flows. In general, the experiments show that flow dynamics and deposition of mass gravity flows are linked to the amount of clay, type of clay, water content, and grain size distribution of the failed material. Specific research projects addressed five main issues:flow and deposition of sand rich debris flows,the effect of hydroplaning on subaqueous debris flow mobility,flow and deposition of laterally unconfined debris flows,the reworking of antecedent deposits by subaqueous debris flows, andrheological characterization of gravity flow mixtures. The results of these experiments provide insight into the flow and deposition of deep marine mass transport events. Many of the quantitative results can be scaled up from the laboratory to the field scale through distorted scaling methodology. The qualitative results, including observations recorded with video and photographs, provide a perspective and understanding of these events that is otherwise unavailable to the science and engineering communities. 1.0 Introduction The generation, flow and deposition of submarine mass flows are important to study for many reasons. The size of failures and the large velocity and momentum of flows may presents hazard to offshore structures such as pipelines, cables and other marine infrastructure. These scenarios represent concerns of a single event. Over longer time scales in which multiple events can occur we see submarine mass flows influencing the formation of underwater topography and regional sedimentology. For example, the formation of submarine fan bcomplexes often involves mass flows. To properly interpret the geology in a setting like this it is important to understand mass transport processes over long times scales. For example, how do mass flows influence antecedent deposits or how does existing topography influence the movement and mobility of mass flows? Numerical modeling has been the common means of studying submarine mass flows. Models allow us to exam the influence of variables such as size and type of failures, flow properties of the sediment (rheology), location of failure. One limiting factor to modeling, however, is that numerical models are constrained by our understanding and ability to describe the complex physical processes that are associated with mass flows.