The purpose of this symposium is to verify the merits and demerits of the extensive land transformation for the Quaternary Research, the history of land transformation during the Quaternary Period, and the regionality of disasters and environmental degradation caused by land transformation, from the viewpoint of the Quaternary Research. Besides, the methodology for the study of the artificial environments formed by land transformation, as well as the technology for land reclamation and environmental conservation are also sought from the angle of the Quaternary Research.
In the land transformation studies geomorphology mainly deals with two aspects: i.e., direct transformation and induced geomorphic processes. This paper is concerned with the latter from the perspectives of climatic geomorphology. Climatic geomorphology that attaches importance to the following aspects constitutes the essential part of environmental geomorphology applicable to land transformation studies and environmental management: 1) spatial variability in land conditions, 2) spatial variability in geomorphic processes characteristic of regional and local climatic conditions, 3) variability in space and time in climatic variables operating as geomorphic agents, and 4) nature and resources of the land produced through the past climatic/environmental oscillations. Based on this framework, general tendencies and implications of accelerated erosion and man-induced land deterioration in Japan are summarized so as to formulate the spatial variability in the form and intensity of induced geomorphic processes under different climatic conditions. It becomes clear that the transformation of the land surface form and cover almost always results in the enhancement of geomorphic processes characteristic of regional and local climatic conditions. Combined effects of land transformation and climatic anomalies often cause geomorphic hazards due to rapid gullying, mass movements, etc. Examples of intensification of human impact on the land caused by recent climatic anomalies are reviewed briefly. The author hopes that the concepts of environmental geomorphology introduced here may shed a new light on the fields of civil engineering responsible for a better modification and the management of terrestrial environment. In Japan, the conception that most of land properties including soils are the product of the past climatic/environmental changes and hence a non-renewable resource has hitherto been very weak. The soildification of this conception requires a positive discussion among the related fields of Quaternary research.
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.
The increasing number and expanding area of artificial land formations has caused a rapid and large increase in the number and size of contract archaeological projects. These excavations, which are carried out all over the Japanese archipelago, have revealed a great deal of new and important information about Japanese archaeological sites. The fortunate result of this contract work has been that archaeologists are now better able to explain the Japanese prehistoric past. Sadly, however, we are faced with the serious problem that, because our archaeological theory and techniques of excavation are still limited, we are unable to recover all of the crucial and important information about these sites. Futhermore, the sites and their environs, are important not only for their historical value but also for the characteristic and irreplaceable atmosphere they bring to our daily lives. Artificial land formations not only destroy a vast number of sites but also threaten the atmosphere and meaning attached to these places and surroundings. Today, these problems concern not only individual archaeologists or even the field of archaeology, but they are also social and political matters which must be resolved by the entire community. We have yet to find a way of resolving these pressing issues.
The formative processes of archaeological sites are connected with the effects of topographical environment. In this regard, this paper deals with the result of the excavations in the Yoshida campus of Kyoto University, situated in the north-eastern part of the City of Kyoto. In the area these effects are mainly recorded on the change of sediment formation which consists of sand beds and covers a marginal part of the Kitashirakawa alluvial fan. It should be pointed out that the formation date of the Yellow Sand Bed, the key bed of the area, is confirmed to be the early Middle phase of the Yayoi period judging from the artefacts and from the fact that the Bed was worn out after the formation by the old Takano River, having made a step at the east of the Higashi-Oji Avenue. The step was readjusted with a different level about 2.5m high from the west side, as we see it now, at the Edo period. It is seen that the water-courses have changed topographical environments and man has made the best use of these kinds of changes from the prehistoric age to the present.
Recently large-scale land transformations especially for residential development have been progressing around the suburbs of the cities. There are several types of land transformation in building residential areas on the hills. The types differ according to geomorphic and geologic characteristics and also by the development of construction instruments. They are called a step-shaped cutting, a flat-type by cutting and filling, and a filled-up-valley type. Since much artificial ground which consists of fill has appeared around the suburbs of the cities, we cannot neglect it in a geological map. It should be treated as a special geologic unit, i.e., an artificial formation. Residential areas built by fill are often deformed by natural phenomena like, earthquakes and rainfalls. When a slump or slide occurs on an inclined land-surface composed of fill, the sliding plane is generated not only on its basal surface but also in the inner part of fill containing mud or clay. Even on the flattened surface which fills up a valley, there occur some deformations like slide, slump and subsidence. Compared with natural sediments, the artificial formation consequently bears some irregularities and differences as well as some characteristics, resulting from its processes. It is pointed out that there is some similarity between the artificial sediments which form a filled-up-valley type residential area and the debris laid on the natural valley floor. It is necessary to investigate the geomorphic development of the valley among the geology of young artificial sediments, for maintaining such artificially formed land in safety.
Land transformation on hilly land usually aims at grading steeper slopes and creating gentle or nearly flat land surfaces. The process contains cutting the soil mantle at a higher portion, transporting it and filling a lower portion with it. A large-scale land transformation could mean that a large part of the original soil loses its exposure on the new surface by burial or removal. The criterion for it may be the exposure width (along the slope direction) of the soil being less than half of the total width of the new surface which is composed of filled material in the lower part and exposed material beneath the soil in the upper part, leaving the original soil between the both. Geometry tells us that the thinner the soil and the steeper the slope, the more the said criterion is satisfied. One should limit the soil, as pedology does, to the one having A and B horizons or A horizon when B horizon is lacking. Thickness of soil thus defined is usually no more than 1-2 meters on slope, hence satisfying the criterion in most cases. C horizon and even unconsolidated or semiconsolidated geological bed may often get utilized as new soil material. New soils can be treated as a man-made immature type because in fill zone, on the one hand, the original soil profile is hidden deep beneath the disturbed or mixed fill material either of the original soil itself or of non-soil material and in cut zone, on the other hand, C or D horizon of the original profile is brought to the surface. It is worth notice that a large-scale land transformation changes a complicated land form into a simpler one but makes the distribution of the soil materials more complicated. Before the transformation the soil is located parallel to the land surface, but after that the new surface is divided into three different zones: fill, original soil, and cut. The horizontal distribution pattern of the zones is variable and irregular depending on the initial land form and the mode of transformation. A tendency of regularity, however, is found as follows: in the original soil and the cut zones the soil horizons appear reversely to those in the normal profile, the upper the horizon the lower the position of the appearance, while in the fill zone the upper part of the original soil profile comes first nearer to the bottom.
The relationship between soil condition and tree growth on artificially graded land surface was studied in the Tama New Town, located in the western suburbs of the Tokyo Metropolis, as a typical case of hill land development. In this case edaphological management, especially controlling of soil physical conditions, is one of the important soil conservation works for landscape planting. As a result of the soil survey of the planted sites, five soil types are classified from the viewpoint of tree planting; that is, Coarse soils, Clayey volcanic ash soils, Sandy soils, Newly accumulated volcanic ash soils and Protected top soils (mainly Volcanogenerous Ando soils). The occurrence of these soil types was determined by the difference of surface geology and the method of grading. The characteristics of sites as planting bed were affected by the earth works for grading. Common characteristics of these soils were a high rate of the solid phase and low permeability. The result of tree growth survey shows that 53 percent of surveyed planted trees (Quercus serrata, Pinus thunbergii etc.) was poor in growth. The occurrence of dead branches and the volume of verdure correlated to the growth of both annual rings and new shoots. Therefore the soil condition should be appraised by these two indicators. The growth of trees on the Preserved top soils was better than that on the Volcanic ash soils and the Sandy soils. Coarse soils bring the worst result of growth. The growth of the root system was mainly influenced by the soil water contents and the soil aeration. Soil condition influenced the distribution of tree roots, too. Overwet or overdry condition of the planting bed soils within the transformed sites is caused by artificial soil compaction. The lack of large porosity which guarantees root respiration is also due to soil compaction. The ratio of solid phase of compacted soils was over 50 percent, and it characterizes transformed soils on the hill lands. Systematic understanding of the relationships among landform, geology, soils and vegetation will contribute to the development of the method of land-transformation assessment and environmental conservation planning.
Differentiations of plant stands and their arrangements were examined in relation to the small- and micro-scale geomorphic units on hilly lands and alluvial plains. It was suggested that four types of plant communities were distinguishable on a hilly land and they occupied 1) crest slope, upper side slope and nose, 2) lower side slope and foot slope, 3) head floor and 4) bottomland, respectively. An alluvial plain was divided into three sections: 1) a section consisting of estuary the coast of which was occupied by a type of mangrove forest, 2) a section of delta covered by the other type of mangrove forest, 3) a section of a floodplain on which a freshwater swamp forest was prominently distributed. The plant communities were further differentiated according to the microscale geomorphic subdivision in each section. The plain was outlined in the course of deposition during the Holocene transgression and have been differentiated by the processes that followed. As a result, the vegetational differentiation was interpreted in terms of these historical and present land-forming processes. It was also shown that the number of plant species in each small-scale geomorphic unit was as small as two thirds to half of that in a hilly land as synthesized geomorphic unit in intermediate-scale.
The biomass, feeding strategies and ecological role of termites in the tropical rain forest and savanna ecosystems are discussed in relation to the human impacts on these ecosystems. A speculation is given on the balance of biological community from a coevolutionary viewpoint with reference to the process through which some species of termites become pests of cultivated plants.
Volcanic ash soils show peculiar engineering properties owing to their abundant moisture contents. So there are many problems in connection with land reclamation of these soils. Engineering properties of these soils were examined with emphasis on the phenomenon of softening and hardening. The following results were obtained. (1) The dry density of compaction soil samples were effected more by soil genesis and moisture contents than by external force. Younger tephra (Tachikawa Loam Formation) showed a low degree of dry density. (2) The degree of softening and hardening depended on the age of tephra. Younger tephras (post-Tachikawa Loam, Tachikawa Loam and Musashino Loam Formations) showed low degrees of softening with much recovery of strength. (3) The same tephra, containing much moisture, softened to a large degree, with less hardening. With little moisture, the degree of softening was low with more hardening. This phenomenon could be explained by the relation between soil moisture and structure. (4) At the soil fill, the permeability fell by compaction. So it is necessary to set up surface and subsurface drainage, pipe drain and sedimentation tank. (5) Volcanic ash soils with humic materials are not suitable for construction from the viewpoints of strength and permeability, but for the green tract of land.
Slope failure is strongly influenced by geological phenomena in the Quaternary. For instance, slope failure is often found in an area of remarkable upheaval in the Quaternary, the terminal area of a peneplane, the surrounding area of a Quaternary fault, an alteration zone and a strongly weathered area. These geological phenomena should be well grasped in land transformation and furthermore, changes by land transformation themselves should also be considered. The latter changes include stress release, change of cut plane and progress of deterioration. To evaluate exactly these geological phenomena in the Quaternary and influences by land transformation, it seems effective to analyze past slope failures in detail under various geological and topographical conditions.
Natural gas has been produced very much in the east-coast area of the Boso Peninsula which is located in the Kanto natural gas field. In order to produce natural gas, however, it is necessary to pump up the fossil brine water containing natural gas, so that the environmental damage by the natural gas spouting from underground, so-called “Uwagasu”, is observed in case of over pumping in the natural gas field. Many inhabitants on the natural gas field also suffer from the environmental damages mentioned above. On the other hand, those on the natural gas field try to use the Uwagasu damaging the environment as fuel energy and continue to do it conveniently. That is, they succeed in getting the benefits of the Uwagasu. When the spouting natural gas decreases accompanying the decreasing production of natural gas, they rather desire the natural gas industry to pump up more fossil brine water containing natural gas. The gas pressure in the secondary reservoir (mainly the lower part of Holocene deposits) of the natural gas rising upward from its reservoir of great depth is controlled artificially by the beneficial relation between the inhabitants and the natural gas industry. Such a phenomenon as the change of the reservoir-pressure mentioned above seems to keep the relations of dynamic equilibrium between man and nature due to the relations among human groups.