Table 2 Calculation of correlation between H/L and slope tangent of source area (tan θ) in the case of Khanh waterfall landslide as shown in Fig. 14

Runout distance after collapse (before collapse)

L (L') (m)

520

220

Runout height after collapse (before collapse)

H (H') (m)

120

120

Correlation between H/L (H'/L')

H/L (H'/L')

0.23

0.55

Slope tangent of source area

θ (°)

13

29

Rounding up slope tangent of source area (friction angle)

Rounding up θ (degrees)

15

30

Tangent of rounding up slope tangent of source area

θ

0.27

0.58