Subaqueous and Subaerial Debris-flow deposits: Physical experiments of debris-flow lake interactions, and controls on subaqueous flow deposits
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Subaerial debris flows occur when masses of poorly sorted and water saturated-sediments surge down slopes due to gravity force. Subaqueous debris flow arises when subaerial sliding material mixes with water and becomes a debris flow. Both flows either in subaerial or in subaqueous environment can cause major and secondary hazards. Subaqueous and subaerial debris flows are difficult to be observed in nature. Additionally, the effect of composition on subaqueous and subaerial debris flow deposit dimensions is poorly understood due to the lack of observations. Here we develop a multi-phase subaqueous and subaerial debris flow, and we focus on the effect of mass (3.5-18.0 kg), composition (e.g., water 40-60%, gravel 0-64%, and clay 0-29%), and outflow channel slope (20-400) on subaqueous and subaerial debris flow deposit dimensions and grain size sorting. The experimental setup consists of a 2.0 m outflow channel slope with a varied angle such as 20-400, a 0.90 m wide and 1.85 m long basin, and a 100 inclined outflow plain bed. The basin is either filled with water for the subaqueous runs with a water depth of 0.33 m, or empty for the subaerial runs. Debris flow deposit dimensions are highly dependent on flow momentum and velocity. Therefore, debris flow deposit runout distance, width, and thickness are controlled by the flow mass, composition, and slope variations. I found that debris flow runout distance and width are mainly determined by flow velocity and composition. Subaqueous debris flow deposit runout distance is controlled by the mass and clay variations, while subaerial flow deposits are determined by mass and gravel. Subaqueous deposit width is affected by mass, gravel, and clay variations, whereas subaerial deposit width is influenced by mass, water, and clay content variations. Deposit thickness is mainly determined by the subaqueous clay and by the subaerial gravel variations. Flow velocity and runout distance are controlled by the subaqueous mass and clay, and by the subaerial mass, water, and gravel content. Flow velocity and deposit width are controlled by the subaqueous mass, clay, and slope variations, and by the subaerial gravel. Grain size sorting varies between relatively well to poorly sorted along the subaqueous and subaerials deposits. Coarse-grained sand and gravel particles are distributed in the margins and the front, while the interior consists of fine and medium grained sand in most of subaqueous experiments like the mass, water, and slope variations. However, in clay (<21%) rich subaqueous and subaerial flows grain size sorting is absent due to high flow viscosity. Increasing gravel content causes a uniform accumulation of the coarse-grained sand, and gravel particles along the subaqueous and subaerial debris flow deposits. My results demonstrate the significance of debris flow mass, composition, and slope variations on the deposit runout distance, width, thickness, and grain size sorting.