## 6 Conclusions  
Numerical experiments were carried out using the computational fluid dynamics method to investigate the processes of transformation from debris flows into turbidity currents during the transportation of submarine landslides. The two-phase mixture module was adopted to mimic the interactions between the slurry and the ambient water, which we validated through a dam-break case. In the numerical models, slurries with different clay contents were considered, and their rheological behaviors were characterized using the Herschel-Bulkley model. To examine the effects of the initial slurry thickness, shear strength, slope angle and flow depth on the fluid conversion, sensitivity analyses were also conducted.  
Based on the multiphase flow theory and numerical simulations, it was found that the shearing effect on the transformation of debris flows into turbidity currents and the process of mixture between them can be effectively captured by the two-phase mixture module. The shear stress on the upper surface of the debris flow can be estimated by Equation (12) with the drag coefficient varied between 0.0015 and 0.007. The shearing mechanism of the transformation from debris flows into turbidity currents was validated by comparing the shear stress on the upper surface of the debris flow calculated from the numerical and theoretical methods.  
A formula for the transformation rates was best fitted through a case series of debris flows. In particular, the activation stress was derived from the cases as a coefficient times the  
Figure 14: Change in the transformation ratio T throughout the whole process.  
Figure 13: Changes in the velocity and run-out distance of the real-scale case as a function of time.  
threshold shear strength of the debris, where the coefficient was estimated as 6.55 \(\times\) 10\({}^{-5}\). Similarly, the other two coefficients in the formula, i.e., the coefficient \(M\) and the power index \(n\), were determined as 1.61 and 0.26, respectively. Finally, in a real-scale debris flow case study, we found that the slurry was fully transformed before it was deposited.  
Based on the above analysis, the shearing theory behind the transformation from the debris flow to the turbidity current is unveiled. The expected outcome, the mechanical theory, the activation stress and the transformation rate would be applied to assess the influence area of the realistic turbidity currents and their harm to the subsea environment.  
There are six mechanisms for the transformation from debris flow to turbidity currents as described in [PERSON] and [PERSON] [21]. In future studies, quantitative analysis is expected to be conducted for each transformation mechanism to investigate the transformation efficiency under different underwater environments. The hazards caused by the submarine landslides could be better understood, based on which more reasonable mitigation measures could be proposed.  
Conceptualization, Y.L. and Y.D.; Methodology, Y.L., Y.D. and G.C.; Software, Y.L. and Y.D.; Validation, Y.L. and Y.D.; Investigation, Y.L. and Y.D.; Resources, Y.L., Y.D. and G.C.; Writing--original draft, Y.L. and Y.D.; Writing--review & editing, Y.L. and Y.D.; Supervision, Y.D. and G.C.; Funding acquisition, Y.L., Y.D. and G.C. All authors have read and agreed to the published version of the manuscript.  
This research was supported by the National Natural Science Foundation of China (grant No. 51909248) and the \"CUG Scholar\" Scientific Research Funds of China University of Geosciences (Wuhan) (project No. 2022182).  
The data that support the findings of this study are available from the corresponding author upon reasonable request.  
The authors declare