Traditional iron industry, called tatara, had flourished in the Chugoku mountains till the beginning of the twentieth century. The iron sands used as raw materials are found in small amounts in weathered granitic rocks. Such iron sands were collected in a unique mining method called kannanagashi. In this mining process, workers cut out huge quantities of weathered granitic rocks and sorted out the iron sands in running water. There are mountains and hills that have been much deformed by kannanagashi in many parts of the upper Hi Hino and Takahashi river basins.
This paper aims to establish the role which the human managed geomorphic process of kannanagashi has played in the development of the natural environment of the Hii river basin. For this purpose, the author has documented the geomorphological features and the distribution of kannanagashi sites (stopes) and has evaluated the volume of the waste thrown away in the process of kannanagashi by means of field survey, and the interpretation of aerial photos and large scale maps.
The main results may be summarized as follows:
1. The present landforms of the stopes are classified into two types : one is the landforms which have not been changed since the abondonments. Another is the landforms which were further transformed into agricultural lands. It is fairly easy to distinguish those rnan-made landfooms from other natural ones even from the aerial photos, because they are comprised of many unnatural cliffs, artificially cut hills (Kannazankyu) and large round gravels derived from core stones.
2. Numerous stopes are distributed in the upper Hii river basin. These, in particular, form dense belts extending E-W in the vicinity of Yokota and in the upper reaches of R. Kamedake (Fig. 6). Most of the stopes are geomorphologically located in the gentle slopes of the piedmonts and the mountain ridges, and geologically located in the regions consisting of grano-diorite or diorite rocks. However, such stopes are not seen in the grano-diorite region around the town of Daito because it was difficult to channel water for kannanagashi. The total area of stopes is estimated to be 3.5×10⁷m².
3. It is possible to get an approximate volume of the discarded waste by measuring the areas of stopes and the heights of unnatural cliffs and kannazankyu. As a result of culculation, it is estimated that the waste of 1, 5×10⁸_??_2.2×108m³ has been discarded in the process of kannanagashi in the Hii river basin especially over the past 300 years. The figures are nearly the same as those reported by Fujiwara (1980) and Akagi (1981) through many historical records.
In this study, it becomes clear that the landform deformation caused by kannanagashi was much greater than estimated in the Hii river basin.