“…The formulation that we adopt to describe the dynamics of this two-phase flow under the above assumptions follows especially the work of Harlow and Amsden [17], Sainsaulieu [40,42,41], and Saito [43]. In particular, the physical and numerical model in [17] has been widely used in the field of geophysics to study the particle-laden flows ejected during volcanic eruptions, e.g., [46,44,10,32,36,9].…”