The landform of the Chugoku mountains was transformed considerably in some places by the unique mining method called Kannanagashi between about 1600 and 1923. Kannanagashi is the method by which workers cut out a large quantity of weathered rock and wash out with running water the small amount of iron sands contained therein.This paper aims at discussing the landform transformation caused by Kannanagashi and the associated formation of the alluvial plains in the four river basins of the Sanin district.It is fairly easy to distinguish a Kannanagashi site (stope) from other kinds of landforms because it is characterized by unnatural cliffs, ditches and artificially cut hills. Numerous stopes are seen in the middle and upper river basins. Many of them are, in particular, concentrated into several parallel belts extending in an ENE-WSW direction (Fig. 2). Such densely distributed areas correspond with the places having the following three natural conditions: where granitic rock with iron sands such as granodiorite or diorite is distributed; where a deep weathered crust on an erosion surface has developed; and where plenty of water for Kannanagashi is available.The total area of the scopes is estimated to be 7.8×107m2. It occupies nearly 4 percent of the area of the middle and upper river basins. The approximate volume of the waste earth discarded as a result of Kannanagashi is estimated at between 3.8×108m3 and 5.4×108m3.The outflow of a large volume of waste earth into the rivers has caused the expansion of the delta fronts in the Hii and Iinashi Rivers and the widening of the sand-bar in the Hino River. Six borings drilled in the fan-like delta of the Iinashi River reveal a sand-and-gravel bed nearly 4 meters thick covering a deep silt-and-clay bed containing organic matter and fossil shells throughout. The upper bed is mainly composed of angular granitic particles and a number of iron slags which were thrown away by the iron works and the blacksmiths. This facies shows that the fan-like delta of the Iinashi River has been formed mainly by sediments from waste earth discarded as a result of Kannanagashi.
Disposition of beach ridges vis-a-vis paleo river courses has helped in recognizing several abandoned delta lobes and reconstructing the stages in the progradation of various deltas on the east coast of India. The sea level was more than 100m below the present level, around 13 ka, in this region and the maximum Holocene transgression has risen to _5m around 6 ka, from where it has fallen to the present level with at least 3 relatively stationary levels in between, as can be inferred from the orientation of different sets of beach ridges. The delta progradation, at present, is mostly by the growth of spits and lagoon-filling.
The purpose of this paper is to document the total area of kanna-nagashi sites (stopes) and the area occupied by rice fields lying within these stopes, and to estimate the quantity of earth moved by kanna-nagashi in the Takahashi and Tojo (a tributary) River basins in the Chugoku Mountains.In Japan iron was produced only by the traditional iron sand smelting method, tatara, until western style smelting was introduced in 1853, and the tatara method continued to be used until the 1920s. The iron sand used as raw material is found in small quantities (about 0.35%) in weathering granitic rocks. It was collected by breaking up weathered rocks and sorting them in running water. This method of mining was known as kanna-nagashi. Mountains and hills in many parts of the Chugoku mountains have been much deformed by kanna-nagashi.The main results may be summarized as follows:1. Numerous kanna-nagashi stopes are distributed in the upper parts of the Tojo river basin (Fig. 1). Most of the stopes are geomorphologically located in the gentle piedmont slopes and mountain ridges, and geologically located in the regions consisting of granite or granito-diorite.2. Most of the rice fields lying in the stopes are located on gentle piedmont slopes.3. The total area of stopes, estimated by the interpretation of aerial photographs, is 2, 673 hectares in the Tojo River basin and 570 hectares in the main Takahashi Riever basin; the area in rice fields is 288 hectares in the Tojo River basin and 71 hectares in the main Takahashi River basin.4. The quantity of earth moved by kanna-nagashi can be estimated by two methods, the documentary method and the geomorphological method. For the documentary method, the following data were used:1) the ratio of the volume of iron sand collected to that of earth cut; 2) the volume of iron sand collected at one stope for one year; 3) the number of stopes; 4) the ratio of iron sand used for tatara to the tatara output; 5) the volume of iron sand used for one tatara for one year; 6) the output of one tatara for one year; 7) the number of tatara; and 8) the period, which was about 220 years, from the beginning of the 18th century to the 1920s.Judging from the above calculations we concluded that the quantity of earth moved was 1.9×108m3-2.3×108m3 in the Tojo River basin and 4.1×107m3-6.6×107m3 in the main Takahashi River basin.For the geomorphological method, the area of stopes and the heights of man -made cliffs and kanna-zankyu (mounds left in the stopes) were measured. From these calculations, the quantities of earth were 1.5×108m3-2.2×108m3 in the Tojo river basin and 3.3×107m3-4.8×107m3 in the main Takahashi river basin.5. The reason for the great difference between the volumes calculated by the documentary method and those calculated by the geomorphological method for the main Takahashi River basin is the shortage of historical records. So we suppose that the figure calculated by the geomorphological method is closer to the actual volume of earth moved.
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.
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