Internal tsunami waves transport sediment released by underwater landslides
Internal tsunami waves transport sediment released by underwater landslides
复制标题
海啸内波输送水下山体滑坡释放的沉积物
作者：
N. Brizuela;A. Filonov;M. Alford
在重力的加速下，海底滑坡将能量转移到海洋环境，最明显的是导致灾难性的海啸。虽然人们认为海啸消耗的能量不到山体滑坡释放的总能量的15%，但人们对构成其剩余能量预算的地下过程知之甚少。在这里，我们分析了第一组描述湖泊内部对水下滑坡响应的观测结果，发现沉积物的输送是由斜压波调制的，斜压波沿着温度和沉积物浓度的垂直梯度传播。当沿着浅层温跃层传播时，这些波可以到达过去束缚浊度流的地形特征，从而扩大水下滑坡的影响范围。通过数量级计算，我们估计观测到的温跃层内波接收了大约0.7%的可用滑坡能量，并推断它们通过湍流混合对均匀化湖泊热力学性质的贡献。最后，我们发现数据集中的滑坡改变了湖泊的内在动力模式，从而对其环流产生了永久的影响。这表明对地下波传播的测量足以诊断水深变换。我们的实验构成了对内部海啸波和浊流反射的第一次直接观察。此外，本底密度分层对海底滑坡后沉积物的输运有显著影响，为模拟海底物质破坏的数值模型提供了有价值的参考。
Accelerated by gravity, submarine landslides transfer energy to the marine environment, most notably leading to catastrophic tsunamis. While tsunamis are thought to use less than 15% of the total energy released by landslides, little is known about subsurface processes comprising the rest of their energy budgets. Here, we analyze the first set of observations depicting a lake’s interior response to underwater landslides and find that sediment transport is modulated by baroclinic waves that propagate along vertical gradients in temperature and sediment concentration. When traveling along a shallow thermocline, these waves can reach past topographic features that bound turbidity currents and thus expand the influence area of underwater landslides. With order of magnitude calculations, we estimate that observed thermocline internal waves received roughly 0.7% of available landslide energy and infer their contribution to homogenize the lake’s thermodynamical properties by means of turbulent mixing. Lastly, we show that landslides in our data set modified the lake’s intrinsic dynamical modes and thus had a permanent impact on its circulation. This suggests that measurements of subsurface wave propagation are sufficient to diagnose bathymetric transformations. Our experiment constitutes the first direct observation of both internal tsunami waves and turbidity current reflection. Moreover, it demonstrates that background density stratification has a significant effect on the transport of sediment after submarine landslides and provides a valuable reference for numerical models that simulate submarine mass failures.