Terrace profiles along rivers based on accurate correlations of terraces and geochronological examination are needed to reveal regional crustal deformation from the distribution of river terrace surfaces. Tephra beds, which are intercalated or cover terrace sediments, are used as beneficial information to correlate terrace surfaces accurately. On the other hand, in cases lacking tephric sediments, the correlation of terrace surfaces is mainly based on geomorphic characteristics, such as degree of dissection, relative elevation, and geologic properties, such as facies of sediments and weathered degree of terrace gravels. A terrace surface correlation based on qualitative indicators may cause uncertainty or variability depending on the criteria defined in each study. In this research, weathered degree of gravels in terrace sediments is introduced as another quantitative indicator to validate or compensate for the terrace surface correlation. The examination process is as follows. The research target is the Hiji-kawa River in western Shikoku, along which many terrace surfaces (P, HH, H, M, and L) are distributed. Few tephric sediments exist in terrace sediments. The 0.6 Ma tephra is intercalated at the upper part of P Surface deposits. 0.3 Ma tephra is intercalated at the upper part of Hf1 Surface deposits. An analysis of volcanic ash grains suggests that M surfaces are covered with Aso-4 tephra (85 to 90 ka). First, the ages of other non-aged-terrace surfaces are estimated based on height differences from aged-terraces. Second, real density values are measured for several gravels collected from 15 stages of terrace sediments. Finally, measured real density values are normalized by measured values of current riverbed gravels. Relative density values (RDV) show a negative correlation with ages of terrace surfaces. The research results suggest that RDV is very useful for estimating the ages of terrace surfaces without tephric sediments. The average uplift rates of the middle stream and downstream along the Hiji-kawa River are calculated to be 0.17-0.18 mm/yr. There are no nick points in the current riverbed slope and the spatial distribution of each terrace surface. These results indicate that there is no local topographic deformation due to faulting and folding around the Hiji-kawa River valley.
