Sedimentation from gravity currents generated by turbulent plumes
Sedimentation from gravity currents generated by turbulent plumes
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DOI：
10.1111/j.1365-3091.1991.tb01875.x
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发表时间：
1991-10
期刊：
影响因子：
3.5
通讯作者：
R. Sparks;S. Carey;H. Sigurdsson
中科院分区：
文献类型：
--
作者：
R. Sparks;S. Carey;H. Sigurdsson
沉积从径向扩散的重力流产生的顶部上升的沉积物载羽流是由一个模型，该模型假设沉积物是均匀分散的湍流在重力流，导致在指数下降的浓度随时间的沉积物的颗粒解决了目前的下边界。对于径向扩散，该模型预测了远离源的沉积物积累的高斯分布，具有指数常数B，其取决于流速Q和颗粒沉降速度v（B= v/Q）。在所描述的实验中，沉积发生在盐水罐中的浮力，充满颗粒的淡水羽流上升产生的重力流中。沉积物积累与理论模型非常吻合，高斯衰减常数B可由单位距离沉积物积累质量的最大值和直线In（S/S 0）= -Br 2的斜率确定，其中r为径向距离，S为单位面积沉积物质量通量，S 0为r=0时S的值。火山喷出物从一个大的（c。亚速尔群岛中（约24 km高）的普利尼期喷发柱也显示出与该理论很好的一致性，证实了该理论的普遍性，且与规模和流体性质无关。实验数据还表明，在远离源（对应于羽流拐角）的地方，沉积行为发生变化，羽流转向横向重力流，垂直速度突然下降。粗粒度的沉积，源和角落之间，发生从倾斜的羽边缘，并不表现为理论模型预测。
Sedimentation from radially spreading gravity currents generated at the top of ascending sediment-laden plumes is described by a model which assumes that sediment is dispersed homogeneously by turbulence in the gravity current, resulting in an exponential decrease in the concentration of sediment with time as particles settle out of the lower boundary of the current. For radial spreading this model predicts a Gaussian distribution of sediment accumulation away from the source with an exponential constant, B, which depends on flow rate, Q, and particle settling velocity, v (B=nv/Q). In the experiments described, sedimentation occurs from gravity currents generated by ascent of buoyant, particle-laden plumes of fresh water in a tank of salty water. The sediment accumulation shows close agreement with the theoretical model, and the Gaussian decay constant, B, can be determined from a maximum in the accumulated mass of sediment per unit distance and from the slope of the line In(S/S0) = -Br2, where r is the radial distance, S is the sediment mass flux per unit area and S0 is the value of S at r=0. Data from the dispersal of volcanic ejecta from a large (c. 24 km high) plinian eruption column in the Azores also show good agreement with the theory, confirming that it is general and independent of scale and the nature of the fluid. The experimental data also show a change in sedimentation behaviour at distances from the source corresponding to the corner of the plume where it diverts into a lateral gravity current and there is an abrupt decrease in vertical velocity. Sedimentation of coarse grain sizes, between the source and the corner, occurs from the inclined plume margins and does not behave as predicted by the theoretical model.