The gentle slopes along the feet of the low mountains in the inland part of Hyogo prefecture are colluvial slopes, which were developed where rhyolite and chert occur. The area is further characterized by the existence of geomorphological features such as stream capture and formation of wet lowlands. Geomorphological processes which contributed to forming these topographic features were studied on the basis of tephro- and radio-carbon chronologies as well as geomorphological investigations. Volcanic ashes which are recognized in the area are useful in determining the period in which the geomorphological features were formed. They are: DNP (Daisen Namatake pumice; 65, 000-70, 000 y.B.P.); MsP (Misen pumice; 16, 000-18, 000 y.B.P.), derived from Daisen Volcano; and AT (Aira-Tn ash; 24, 700 y.B.P.) and K-Ah (Kikai-Akahoya ash; 6, 300 y.B.P.), derived from volcanoes in southern Kyushu. The colluvial slopes are divided into four surfaces: I, II (further divided into II and II 2), III and IV. The II 2 can be further divided into three parts: c(talus cone), d (debris flow) and f (alluvial fan). The ages of formation of these surfaces are as follows: surface I was formed before the last glacial age; II 1 and II 2, during the first and second halves of the last glacial age, respectively; III, between the late glacial age and approximately 6, 000 years ago; IV, after the formation of the former. The distribution of the colluvial slopes is influenced by the lithology: they are best developed in the area of rhyolite, and next best in that of chert. Rhyolite and chert are easily subjected to freeze-thaw action and discontinuous rock disintegration. The surface II 2 is judged to have been formed in the cold period of the last glacial age, when freeze-thaw action was dominant and broke these rocks into fragments. The facies of I and II 1 indicate that they were formed by the process as II 2. Surface III was formed as an alluvial fan during the period when the climate was getting warmer and wetter. The debris of II 1 is thicker than that of II 2, and was transported by debris flow. This suggests that the formed period was wetter than the latter. Discharge of the basin and lowland lie inland area gradually diminished during the last glacial age, because of the development of colluvial slopes. The colluvium was deposited onto the outlet of Sasayama basin, leading to stream capture. After this event, the drainage of this basin improved. In Hikami lowland, however, wet conditions remained.
Pollen fossils from late Paleolithic site deposits of the Kasuga-Nanokaichi area and the Itai-Teragadani area were analysed with drilling cores. The forest history of the last glacial age in the Tanba district of Hyogo Prefecture may be summarized as follows, based on the result of this work: 50∼40ka ago: Temperate mixed forest (conifer trees dominant). 40∼30ka ago: Temperate mixed forest. 30∼25ka ago: Temperate mixed forest(broadleaved trees dominant). 25∼20ka ago: Temperate mixed forest(conifer trees dominant). Samples from the deposits of 20∼17ka ago, which is regarded as the coldest time of the last glacial age, could not be obtained in this work. Neither subalpine forest nor warm temperate forest were be formed in these districts during the last glacial age, at least until 20∼17ka ago.
The Kasuga-Nanokaichi Site and Itai-Teragatani Site are located in the western district of Tanba, Hyogo Prefecture. We excavated these site from 1984 to 1985, identified the Aira-Tn ash(AT) and constructed an accurate chronology of the artifact assemblages. We found useful data for reconstructing the structure of paleolithic settlements. At the Kasuga-Nanokaichi Site, we excavated about 5, 000 artifacts, which could be divided into more than 20 clusters, three stone clusters and some stone heaps under the AT. These are divisible into at least two cultural layers. The main material of the artifacts is chert; sanukite [andesite] is occasionally found. We consider these assemblages to be one of the Paleolithic traditions in the Chugoku mountains. At the Itai-Teragatani site, AT is divided into two cultural layers. We excavated 11 areas of construction of stone implements, 6 pits, 5 clusters of charcoals, many stone heaps and many stone clusters on the lower layer. We found 2 types of techniques for fabricating stone implements in the two areas. We consider this evidence that the Paleolithic traditions in the Chugoku mountains and the Setouchi region were in contact.
The Japanese Islands, which underwent significant crustal movements in recent times, have been inhabited over a long period of time. Therefore, abundant evidence of paleo-earthquakes is expected to exist on archaeological objects. The author presents examples of this evidence from three points of view, as follows. 1) Deformation of tumuli: Kondayama and Hakuchohjinja tumuli, which had been constructed on an active fault, were displaced about 1.8m vertically by a historical earthquake. The earthquake is inferred to have occurred in the year 1510 and to have been of magnitude 7.1. 2) Trace of paleo-earthquake discovered by archaeological excavation: Evidences of liquefaction were clearly observed at Kitogenishikaidoh, Hotarudani, and Kizugawakashoh Sites. The ages of the earthquakes which caused the liquefaction at these places were estimated by archaeological method. 3) Submergence by paleo-earthquake: A fault scarp, formed by the earthquake that occurred in 1611, dammed up the rivers forming a small lake on the western fringe of the Aizu Basin. Some villages and roads had to be moved beyond the lake. Submergence by paleo-earthquake is similarly observed on the shores of Lake Suwa and Lake Biwa.
The purpose of this paper is to elucidate the change in the topographical environment of the plains after the end of the prehistoric age, and also to clarify the relationship between the change and the land use. Geomorphological analysis for environmental reconstruction is employed. It consists of four different analyses: landform surface analysis, landform zone analysis, micro landform analysis I and micro landform analysis II. The purpose of landform surface analysis is to clarify the topographical change taking place in a time frame of 104 years (for example, the formation of terraces). Landform zone analysis can clarify the topographical change on a scale of 103 years order (for example, delta formation). These two analyses correspond to what was formerly called the history of topographical development. On the other hand, micro landform analysis I and micro landform analysis II are connected with the investigation of archaeological excavation. The purpose of micro landform analysis I is to clarify topographical change on a scale of 102 years. For example, a natural levee must have greatly influenced the location of a village. In micro landform analysis II, what is looked at is the topographical change which occurs every time a river floods. In geomorphological analysis for environmental reconstruction, we pay attention not to “natural topography” but to “topography of the human living environment”. In other words, geomorphological analysis for environmental reconstruction is not a mere history of topographical development; it includes the history of natural disasters and of land development. As the subject of our research, we used the Mihara Plain on Awaji Island in Setonaikai. In Shichigawa Okitaminami site, part of delta I in the Mihara Plain, minute topographical changes and the appearance of the land used from the end of Yayoi era to the Kofun (old tomb) era-about 1, 700 years ago-can be clarified by geomorphological analysis for environmental reconstruction. The following is a summary: 1) The area surrounding the Shichigawa Okitaminami site was a shallow sea bed at the height of the Jomon transgression (stage III, about 6, 400y.B.P.). This sea area became a lagoon 2, 600y.B. P., when the sea level changed and a sand spit was formed at the inlet (stage IV). 2) The accretion of natural deposits progressed rapidly here from the end of the Yayoi era to the beginning of the Kofun era. This accretion caused the area where rice fields could be developed to spread down the river. The loam brought by the flood has a negative aspect in that it buries the rice field and a positive aspect in that it changes swampland into dry land with high productivity. 3) The rice fields are divided by a footpath in accordance with the level of the ground so that the difference in the height of each division would not exceed six centimeters. Where the incline is steep the rice field was smaller, where the ground is flat, the rice field is larger. 4) When floods or accumulation occur, the rice fields revert to their original state. Therefore it can be assumed that this process occurred without delay in the Mihara Plain. 5) Rice fields of stage IV16 are of two different kinds: high and dry, and low and wet. The fields can also be classified as good or bad in terms of the water supply.
In carrying out archaeological excavations and studies on remains of rice paddy fields, many problems cannot be solved without the help of the methods and techniques of natural science. Several such problems of considerable importance are detecting the sites, analyzing for what purpose they were used, clarifying the system for their utilization, establishing their chronology, estimating the harvest, determining the factors allowing for the existence of the rice paddy fields, their surrounding environment, and the effects of their cultivation on the natural environment. Observation of the soil section combined with pollen analysis has been successfully used in detecting the horizon of the site. Investigation of macro-remains of culture plants and other weeds contributed to recognition of the difference between rice paddy fields and dry agricultural fields, or to determining whether a rice field was dry or wet. Conventionally, in estimating a rice harvest, not only archaeological, but also bibliographical or agricultural methods have been applied. Analysis of plant opal, developed in recent years, reveals itself as a method superior to these conventional ones. To analyze the factors which made possible the establishment of the site, the methods mentioned above-for example, reconstruction of paleo-vegetation based on the pollen analysis-have been used. Recently, a method which could be referred to as micro-scale topographyenvironment analysis has been used successfully in investigating the relationship between rice field cultivation and topography and water supply. The number of branches of archaeology in which methods of natural science can be used successfully will increase also in the future. We should be aware, however, that analysis of archaeological material seldom yields any positive result unless the archaeologist, in consultation with the natural scientist, has a clear aim in utilizing such analyses. Establishing a data base to accumulate the archaeological data yielded by methods of natural science is necessary; such a data base may be useful for many disciplines in archaeological studies. More important, however, is the careful observation of sites in situ to establish the correct chronology of multi-layered archaeological sites and to estimate the time gap between succeeding layers, because the factors controlling the duration of cultivation of a rice field are multidimensional.
Two formation patterns are recognized archaeologically for surviving rice paddy fields which were covered with soil. The first is the case of flooding: thick alluvial soil covered the fields. The other is volcanic activities, in which volcanic ash exploded over the fields; this pattern is characteristic of Gunma Prefecture. This study is focused on both horizontal analysis, by reconstruction of its distribution pattern by means of micro-geographical method, and vertical analysis by the observation of the cross-cut sections in order to determine their superimposition at each site. To know its distribution over a broad area which was prospected by observing the ground surface, aerial photographs and large-scale maps are helpful. Also, an interdisciplinary approach is especially important for this kind of research.
The three layers of tephra that erupted from Haruna (_??__??_) volcano and Asama (_??__??_) volcano covered most of the rice fields in the district of Gunma in the Kofun period (from 4c to 6c A. D.). So considerable damage might have been done to the society of that time. The writer of this report wants to make clear what measures the rulers managed to take against these volcanic disasters. We have no historical records of the volcanic activities in Japan prior to the Kofun Period because of the lack of written records. But we can determine the time or the season of tephra effusions by archaeological means, mostly typological methods of analyzing pottery from the horizons both above and below each of the three tephra layers. The time and the season of tephra effusions that the writer has conclusively identified are as follows. 1) The tephra in the lowest horizon (Asama C pumice: As-C) had erupted in the late autumn of the middle of the 4c A. D. from Asama volcano; footmarks of cultivaters or planters on the muddy paddy fields and morphologic plans of the rice fields remaining just below each of the three tephra layers prove this. 2) The tephra in the middle horizon (Haruna Futatsudake (_??__??__??_ )ash: Hr-FA) erupted in the early summer of the beginning of 6c A. D. from Haruna volcano. 3) The tephra in the uppermost horizon (Haruna Futatsudake pumice: Hr-FP) erupted in the early summer of the middle of 6c A. D. At Dodo (_??__??_) Site in Gunma Pref., we found four horizons of rice fields just below the tephra layers; three horizons were proved to be in the Kofun Period; quite the same rectangular divisions of rice field were found from the horizons both above and below each of the three tephra layers. This fact shows that the rice fields had never been abandoned since then but were cultivated further on the tephra layers. The writer thinks that the rulers of that time forced the people to restore the rice fields injured in the volcanic disasters, immediately after the effusion, in order to keep their systems of control or maintain their bases of food production.
Haruna volcano, situated in the central part of Japan, erupted twice in the 6th century, from Futatsu-dake crater. The first eruption, which occurred in the early part of the 6th century, was set set off by a low-temperature phreatomagmatic eruption. The initially ejected very fine ash accumulated as accretionary lapilli and muddy rainfalls. Later, the eruption changed to hot pyroclastic flow effusions, which contained many essential lithics. These pyroclastic flow effusions included small-scale phreatic eruptions. The ash had formed ash clouds that then accumulated on each pyroclastic flow deposit. This tephra sequence was named the Haruna-Shibukawa tephra formation(Hr-S). These pyroclastic flow encroached on an older village, Nakasuji, situated on the eastern flank of Haruna volcano. The pyroclastic flow (S-5) burned and destroyed many houses. Because its deposit was very thinly laminated, it took the form of a hot pyroclastic surge, which spread over the eastern side of Haruna volcano, causing widespread damage there before changing to mud flows and floods and damaging rice fields in the area. The second eruption, which occurred in the middle or later part of the 6th century, is characterized by plinian eruptions and pyroclastic flow effusions. This tephra sequence was named the Haruna-lkaho tephra formation (Hr-I). The pumice ejected in the plinian eruptions was deposited, in a layer about 3cm thick, on Soma city, 200km from the vent. An older village, Kuroimine, situated about 10km from the vent, was buried by a layer of pumice about 200cm thick. Because pumice oxidized by the flames of burning houses is observed from the bottom to near the top of the pumice fall deposit, we can confirm that the greater part of the pumice accumulated during a period of hours. A house was crushed by the coarser part of the pumice fall deposit (1-6). The pyroclastic flows, which caused columns to collapse, moved and accumulated along the valleys before changing into mud flows and floods. They also caused heavy damage to rice fields and farms. In Gunma Prefecture, it may well be that villages, rice fields, and farms damaged by volcanic eruptions in the same way as Nakasuji village and Kuroimine village were damaged will be discovered. The data in relation to past volcanic hazards, obtained by joint research between archaeology and volcanology, will contribute to predicting volcanic disasters.
Paleoenvironmental reconstruction of the Holocene since 8, 000 years ago, based on detailed archaeological excavation and geological and paleobotanical studies, including fossil pollen assemblage, plant macrofossil assemblage, and fossil wood assemblage, has been performed on the sediments in the dissected valley at the Akayama Site (35°50′55″N, 139°45′10″E), about 15km north of Tokyo, in the southeastern part of the Ohmiya Upland, central Kanto Plain. From the results, 5 epoch-making events (E-1 to E-5) and 6 paleoenvironmental stages (I to VI, divided based on their events) were identified. An event is characterized by an erosion and a subsequent drastic change of the sedimentary environment in the valley. Both Stage I(ca 8, 000-6, 500y.B.P.) and Stage II (ca 6, 500-5, 300y.B.P.), corresponding to the Earliest and Early Jomon Ages in archaeology, are characterized by a landslide or collapse of the precipice along the marginal upland ridge, and the reclamation by them or their secondary sediments in a valley under a marine or brackish environment. The sea reached a level 3m above its present level in late Stage I. During both stages, a warm-temperate deciduous broad-leaved forest composed of mainly Quercus subgen. Lepidobalanus stood on the upland to scarp, and Polygonum thunbergii, Chrisoplenium, and Carex communities covered the ridge at the edge of the water, in the valley. Stage III(ca 5, 300-4, 000y.B.P.) corresponds to the Middle Jomon Age, and is distinguished by a standing of Alnus japonica forest in the valley and an invasion of Aphananthe and Celtis in the upland to scarp forest. The deposition of clayey soil containing many Castanea-Castanoposis and Mallotus plant fossils is evidence of the destruction of the forest and the cultivation or semicultivation of Castanea on the scarp to upland. Stage IV (ca 4, 000-2, 200y.B.P.) corresponding to the Late and Later Jomon Ages is defined as an invasion of Fraxinus mandshurica, Aesculus turbinata and Acer to the Alnus forest in the valley, and the beginning of a wide expansion of Cryptomeria, Chamaecyparis group and Quercus subgen. Cyclobalanopsis on the upland. These facts testify to a cooler and wetter climate than that in previous stages. During this stage, part of the bottom forest was destroyed by man, and then manufacturing of Aesculus products was begun. Stage V (ca 2, 200-500y.B.P.) and Stage VI (since 500y.B.P.), later than the Yayoi Age in terms of archaeology, were characterized by a strong impact of man on vegetation and by a swampy valley bottom in which Cyperaceae and Gramineae communities stand. Almost all of the scarp and bottom forests have disappeared mainly as a result of human activities.