## 4 Results and Discussions
### Effect of Falling Angle under Different Submergence Conditions
#### 4.2.4 Effect of Falling Angles  
Six different falling angles were calculated for each initial submergence condition, for a total of 18 cases. The change of maximum wave height with falling height is shown in Figure 14. The maximum wave heights measured at \(\mathrm{G_{1}}\) are marked as the solid lines in Figure 14 and that at \(\mathrm{G_{2}}\) are marked as dotted lines. The triangle, square and circle, respectively, represent the subaerial landslide, partial subaerial landslide and submarine landslide in Figure 14. It can be seen that as the falling angle increases, the maximum wave height of the tsunami caused by the subaerial landslide first decreases and then increases, and the maximum wave height difference between \(\mathrm{G_{1}}\) and \(\mathrm{G_{2}}\) first increases and then decreases, among which the turning point is about \(45^{\circ}\). This indicates that, for the subaerial landslide-induced tsunami, the horizontal movement of the slider is the dominant factor that causes the tsunami when the falling angle is small (below \(45^{\circ}\)) by squeezing and pushing the water horizontally. As the falling angle of the slider increases from \(20^{\circ}\) to \(45^{\circ}\), although the horizontal acceleration component of gravity of the slider increases, that of the flow resistance increases more intensely due to the increase in the area of horizontal incoming flow (\(Bx\)), which causes the total horizontal acceleration of the slider to decrease. This decrease in the total horizontal acceleration component and the decrease in horizontal movement distance result in the attenuation of the horizontal influence of the slider on the water and the decrease in the maximum wave height. When the falling angle exceeds \(45^{\circ}\), the vertical acceleration component becomes the main component of the slider motion, and the influence of the vertical motion of the slider on the wave is dominant. As the falling angle of the slider increases from \(45^{\circ}\) to \(70^{\circ}\), the vertical acceleration component of the gravity of the slider increases, that of the flow resistance decreases due to the decrease in the area of vertical incoming flow (\(Bz\)), which causes the total horizontal acceleration of the slider to increase. The maximum wave increases due to the increase in the total vertical acceleration of the slider. Of course, this is only the qualitative analysis, while quantitative analysis requires many formulae derivations and experimental  
Figure 13: The temporal evolution of the water elevation in \(\mathrm{G_{1}}\) and \(\mathrm{G_{2}}\) with the submarine landslide: (a) \(\theta=30^{\circ}\); (b) \(\theta=50^{\circ}\); and (c) \(\theta=70^{\circ}\).  
data to verify, which will be further studied in future work. In addition, the critical angle does not have to be 45\({}^{\circ}\), which also needs further research. However, when the initial submersion condition of the slider is partial submersion and complete submersion, the situation changes. Specifically, the maximum wave height of the partial subaerial and submarine landslide-induced tsunamis will still decrease as the falling angle increases (increasing but not exceeding 45\({}^{\circ}\)) but the increase in the maximum wave height after 45\({}^{\circ}\) is not obvious to them. In other words, the hazard of the subaerial landslide-induced tsunami is greater under a small or large falling angle and that of the partial subaerial and submarine landslide-induced tsunami is greater under a small falling angle.