In 1911, there occurred a large landslide on the steep slopes of Mt. Hieda, Nagano prefecture, to which much attention was paid by geologists at the time. So much debris was produced that the river bed of the Ura, a tributary of the Hime River, was raised over 50 metres.
In this paper, the author firstly clarifies the recent development of the mountain slopes and valleys, and then attempts to evaluate the importance of the severe erosion along the Ura River as a source of the bed load in the lower reaches of the Hime River.
The results obtained are summarized as follows:
1) The large landslide on Mt. Hieda occurred on the slope of this highly dissected strato-volcano, and is closely related to the heavy rain which fell four days before the occurrence, but is fundamentally due to the nature of the fragile rocks containing solfataric clay with abundant joints (Fig. 1, geological map).
2) The landslide debris originally swept 6 kilometres down the valley and dammed the Hime River at its confluence with the Ura. The debris was deposited in the valley, elevating the valley floor a maximum of about 100 metres and steepening the gradient. The quantity of mudflow deposit is estimated roughly at 1.5×10⁸ m³.
3) The surface of the mudflow deposit is comparatively rugged with many flow mounds (Fig. 2). Just after the catastrophe, the superimposed river bed started incising itself due to the decrease in material provided from the slopes. The mudflow dammed the Hime River at the confluence, forming a lake. When this dam itself was washed away during the floods in the following year, a knick point was formed on the lower reaches of the Ura River, but this disappeared before it had time to migrate far upstream because of rapid downcutting in the upper reaches and consequent deposition along the lower reaches. Vertical erosion was rapid in earlier stages but lateral erosion became more important during later stages.
4) The mass eroded during the past 50 years is calculated to be 2.4×10⁷ m³. The Ura introduced such heavy loads into the Hime that the river bed of the latter was elevated a maximum of 30 metres and caused an increase in the gradient below the point of confluence due to the bed load which may well persist for a long time (Fig. 4).
5) From the standpoint of the source of bed load, it can be considered that the materials of the Hime below the confluence were derived from the three sources; (a) Mt. Hieda and its mudflow deposits, (b) Mt. Kazafuki ((a) and (b) were transported by the Ura), (c) the upper area of the Hime River. The proportions of debris supplied by each river were found by calculation from the lithologic analysis of gravel as follows: (a) 41%, (b) 26%, (c) 33%. Area of the region (c) is twenty one times as large as the combined area of the regions (a) and (b), which indicates the high rate of erosion in the latter. Consequently, it was found that more than half of the gravels of the Hime River came from the Ura River dissecting the mudflow deposits of 1911, although the Ura is only a small tributary of the Hime.
6) In conclusion, it was found that the erosion in the Ura River during the past 50 years has progressed enough to show a conspicuous topographic change in the bottom of the valley, and that the heavy load resulting from the rapid erosion has a strong influence on the stability of the Hime River.

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The island of Kyûshû is well characterized by the abundance of volcanoes such as Unzen, Aso, and Kirishima. Major land uses on the slopes of these volcanoes are cultivated fields, grasslands, and forests. According to the ratio of these land uses, these volcanic areas can be divided into three types: cultivated-field-dominant, grassland-dominant, and forest-dominant. Unzen belongs to the cultivated-field-dominant type, and Aso grassland-dominant, whereas Kirishima represents the forest-dominant type in general. The primary aim of this paper is to analyze the reasons why the forest-dominant type is to be found in the Kirishima volcanic region with reference to physical conditions, historical changes in land use, ownerships of the land, productivity, and so on.
The reasons for this trichotomous division may be explained by both physical and social factors. The physical factors are closely related to the nature of surface features and rocks of respective volcanoes; whether the slopes are gentle and wide or not, or the valleys in unit area are many or not.
Social reasons are equally important for making this division, because, if the physical factors are decisive, the ratio between the three types of land uses will not differ from place to place. Therefore we also have to study social factors. Among them productivity of land is the most important, because the owner of the land will like to use it so as to attain the highest possible income. Like the opinions of many other researchers, the present writer thinks that forest land is the most productive or profitable among the three types of land use on volcanic slopes. For this reason many grasslands have changed to forests on Kirishima.
In the volcanic region of Aso, however, most grasslands have not so changed to forests as in the case of Kirishima. This is primarily because of the fact that many of the grasslands of Aso have long been and are even now owned by a great number of farmers in common and so the subdivisions and aff orestations have been largely checked for the farmers of the area. On the contrary, grasslands and forests have been widely owned by the national govenment in the Kirishima volcanic region, which fact has enabled considerable afforestation there.
In short, it is known that both physical and social factors are decisive for the formation of present land uses on the volcanic slopes in Kyûshû. Such factors were surveyed in the volcanic region of Kirishima in comparison with Aso and, to a lesser degree, with Unzen.

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In Japan where the capitalist system developed in support of the military econmy, the principle of military priority was also applied to the use of land, and so lands suitable for the construction of factories were often removed from private use and used for military purposes.
With the end of World War II, the large military establishments were released for public use, and there has been a tendency for these sites to be utilized for such uses as the building of factories.
In Japan the former military bases have come to be used, as the property of the national government, bor contributing to the economic development in the post-War period.
In the Kantô District, there were about 1, 100 military establishments accounting for about 430km². Of this area, today 44% is used as farmlands, 30% for public establishments or services, 14% for American military uses, 8% for use of the Japanese Defense Agency and the remaining 4% for factory sites.
There were 38 military airbases for the defense of the capital area within 20-60 km of Tokyo, and if the former military training grounds are also included, then these former establishments comprise a very large and flat area well-suited for the establishment of large-scale factories and industrial tracts. Therefore :since 1950, there has been an increasing tendency for just such developments.
Also the former military bases which had been converted into farmlands are now being changed over into factory sites, and today 33% of these farmlands are designated as suitable sites for factories.

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