The mean recession rate of Kegon Falls is examined, estimating original location and age. Two locations (LI and LII) at which the waterfall originated are estimated based on the distribution of Kegon lava, while the age of origination is considered to be the same as that of the Kegon lava eruption, i.e., 20, 000 years ago. Two values of the mean recession rate obtained are 0.018 m/y for the case of LI and 0.10 m/y for the case of LII. On the other hand, the recession rate can be evaluated, as an order estimation, using the empirical equation of the authors (Hayakawa and Matsukura, Earth Surf. Process. Landforms, 28, 2003), which shows relationships between the recession rates of waterfalls and the ratio of the erosive forces of rivers to bedrock resistance. The values of parameters used in the index of force/resistance ratio are obtained from existing data and field measurements for Kegon Falls. Substituting them into the equation, the recession rate is calculated to be in the order of 0.009-0.019 m/y. This result suggests that the recession rate for the case of LI is suitable for Kegon Falls.
