## 3 Case Studies
### Acheron Rock Vvalanche  
The Acheron rock avalanche occurred in Canterbury, New Zealand, approximately 1100 years BP [39; 40] based on radiocarbon dating analysis. An earthquake may have triggered the landslide, as it is located close to fault zones. In Figure 4, an overview of the Acheron rock avalanche is shown. The numerical analysis was performed using a 10 m \(\times\) 10 m digital terrain model. It is estimated that about 6.4 million m\({}^{3}\) of rock mass with the maximum release height of 78.5 m ran down the hillside and traveled 3.5 km with a travel angle of 18\({}^{\circ}\) to the south-east. Figure 4: **(a)** A general view of the source area, (b) the area impacted by the avalanche, and (c) its location (Google Maps). Validation of sets of code relies on the availability of reliable information, including the impact area or deposition area of the event; and estimated deposition thickness, velocities, and final run-out. The Acheron Rock Avalanche has been back-analyzed by [PERSON] et al. (2017) [11] using the ravaflow code. The same back-calculated parameters were used here for both sets of code to simulate the rock avalanche. Flow parameters and coefficients required for both sets of code are given in Table 1.  
The densities of solid and fluid particles were taken as \(\rho_{s}=2700\) kg/m\({}^{3}\) and \(\rho_{w}=1000\) kg/m\({}^{3}\), respectively. In the GeoFlow-SPH code, the initial porosity is computed based on densities. On the other hand, the r.avaflow code uses the defined heights of fluid and solid phases to obtain porosities. For both sets of code, an initial porosity of 0.2, for which \(\rho=2350\) kg/m\({}^{3}\), was considered. In the previous numerical analysis [11], the best results were obtained with the dynamic basal friction angle of 17\({}^{\circ}\). In the ravaflow code, the simulation was based on Mohr-Coulomb-type plastic flow and was performed with an internal angle of friction of 35\({}^{\circ}\) and a bed friction angle 17\({}^{\circ}\). On the other hand, the GeoFlow-SPH code uses the voellmy rheological model to analysis case studies. Concerning its rheological parameters, the basal friction angle of 17\({}^{\circ}\) and no turbulence coefficient were considered for this particular case. In both sets of code, the fluid phase is modeled based on the Manning formula. However, the fluid friction coefficient was neglected in this study. The output of r.avaflow is discretized on the basis of geographic information system (GIS) coordinates and consists of raster maps. One of the advantages of the ravaflow code is performing the simulation model in a GIS in order to manage geo-referenced data and facilitate the use of the results. In the GeoFlow-SPH code, post-processing tools are used to deal with the visualization of output. The main result is the evolution of solid and fluid flow heights, and the outputs are the values of velocity and depositional height computed at each time step. Optionally, total flow pressures and kinetic energies are generated in the ravaflow code; relative pore-water pressure and total pore-water pressure are generated in the GeoFlow-SPH code. Figure 5 illustrates the comparison between the numerical results using the r.avaflow and GeoFlow-SPH sets of code, with the parameter values given in Table 1, at different time steps. As shown in the figure, with the same geotechnical parameter values, the two