For a better assessment of hazards related to tsunamis triggered by pyroclastic flows entering water, it is crucial to know and quantify the contribution of the physical parameters involved in the generation of waves. For this purpose, we investigate experimentally the effect of pyroclastic flow density on tsunami generation by considering variably fluidized granular flows denser or less dense than water, referred to as heavy and light granular flows, respectively, by varying the particle density. Qualitative observations show that differences in bulk flow density mainly affect the propagation of granular flows underwater. In contrast, the bulk flow density has little effect on the amplitude of the leading and largest wave. In fact, the wave amplitude is initially similar to the local water depth along the inclined plane, and then reaches a maximum value that depends mainly on the other flow parameters (i.e., velocity, thickness, volume of flows). Far from the shoreline, we provide evidence of the bulk flow density effect on the wave amplitude, while other characteristics of the leading wave remain broadly unaffected in the range of parameters considered. Finally, a main difference on the tsunami generation between light and heavy granular flows is related to the energy distribution between the leading largest wave and the wave train, which is attributed to different modes of interaction of the two flow types with the water. For tsunami hazard assessment, our study suggests that the contribution of the bulk flow density on tsunami generation has a second-order effect compared to other flow parameters.

为了更好地评估与火山碎屑流进入水中引发的海啸相关的危害，了解和量化波浪产生所涉及的物理参数的贡献至关重要。为此，我们通过实验研究火山碎屑流密度对海啸产生的影响，通过改变颗粒密度，考虑比水密度更大或更小的可变流化颗粒流（分别称为重颗粒流和轻颗粒流）。定性观察表明，体积流密度的差异主要影响水下颗粒流的传播。相比之下，体积流密度对主波和最大波的振幅影响很小。事实上，波幅最初与沿斜面的局部水深相似，然后达到最大值，该最大值主要取决于其他流动参数（即速度、厚度、流量）。在远离海岸线的地方，我们提供了体积流密度对波幅影响的证据，而在考虑的参数范围内，主波的其他特征基本上不受影响。最后，轻颗粒流和重颗粒流之间的海啸产生的主要区别与主导最大波和波列之间的能量分布有关，这归因于两种流类型与水相互作用的不同模式。对于海啸灾害评估，我们的研究表明，与其他流动参数相比，总体流动密度对海啸产生的贡献具有二阶效应。