In order to understand the long-term geomorphic development of drainage basins that include some Quaternary stratovolcanoes in the upstream area, as occur in Japan, it is necessary to evaluate not only the usual river processes associated with glacial-interglacial alternations but also the influence of sediment supply derived from large-scale volcanic events-for example, the sector collapse of volcanic edifices peculiar to Quaternary volcanoes. From this point of view, this paper discusses the depositional process of “Nakanojo Mud flow (NMf)” and its impact on the fluvial landform development in Nakanojo basin, located in the drainage basin of the Agatsuma river, central Japan.
In Nakanojo basin, a terrace landform is well developed. However, the relation of NMf and long-term geomorphic development has not been discussed in detail by previous works. NMf has been considered to be the debris avalanche deposit associated with the sector collapse of Asama Volcano around 24, 000 years ago.
The main part of Nakanojo Surface is the depositional surface of NMf sediments running onto the existing fluvial terraces composed of the Nakanojo gravel layer formed during the Younger stage of the Last Glacial period. Along with the morphological features of the Nakanojo Surface, such factors as the direction of the long axis of the flow mounds and the 3-D distribution of the mud flow deposit suggest the flow direction and relative magnitude of NMf; within Nakanojo basin, NMf maintained the property of a debris avalanche more than 40m thick, and flowed onto the existing terraces mainly on the attacked slope side 20-30m above the river bed at that time.
In Nakanojo basin, the deposition of NMf strongly disturbed the valley cut and fill sequences which are normally controlled by climatic conditions. It is supposed that the river bed fluctuations had been regulated by this event until the emergence of Isemachi I Surface with its relatively coarse gravels. This period may correspond to the termination of the Last Glacial, which is often characterized by the increase of discharge related to tractive force.

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The present innermost part of Kagoshima Bay corresponds to Aira Caldera, which appeared with a large eruption about 25, 000yrs BP. Shinjima (Moeshima) Island, our study site, is located in the center of Aira Caldera. According to historical records, this island was uplifted from the caldera bottom during the “An'ei volcanic eruption” of Sakurajima in 1779-1780. Therefore, the geology of Shinjima Island ought to record a part of the environmental changes in Aira Caldera.
As a reexamination, geological survey and dating of the Shinjima Island were carried out. The Pleistocene to Holocene series of Sinjima Island is classified into the Susaki Pumice Bed, Moeshima Silt Bed, Moeshima Shirasu Bed, Moeshima Shell Bed, Shinjima Shirasu Bed, descended (air-falled) volcanic ash layers from Sakurajima volcano, and surface soil; they are overlapping in that order. The silt bed on the southern coast was identified as corresponding to the Moeshima Silt Bed on the northern coast on the basis of agreement of the lithologic features and formative ages. The Moeshima Silt Bed was formed in the period between 14, 600 and 7, 800yrs BP. A thick pumice bed on the southern coast was distinguished from the Moeshima Shirasu Bed on the northern coast on the basis of stratigraphic relationship. The former was identified below the Moeshima Silt Bed and named the Susaki Pumice Bed. The formative periods of Susaki Pumice Bed and Moeshima Shirasu Bed were estimated to be about 16±4ka by fission-track dating (before about 14, 600 ¹⁴C yrs BP) and about 7, 800 to 6, 000 ¹⁴C yrs BP., respectively. The origins of both were subaqueous eruption on deep caldera bottom. Subaqueous eruption resulted in deformation of the previous strata and an unconformity between the previous and subsequent strata.
The period when Aira Caldera was submerged under seawater was specified to be between about 11, 700 and 11, 000yrs BP. The outer and inner areas became a seawater environment at about the same time with a rapid rise in sea level, because the south wall of the Aira Caldera opened at that time.
The Moeshima Shell Bed was formed during the period from about 6, 000 yrs BP to 2, 300yrs BP. Progression from the Moeshima Shell Bed with outer sea species to the Shinjima Shirasu Bed with inner bay species occurred in successive steps. The innermost bay changed to a more close condition with the decreasing of outer seawater after about 2, 300yrs BP.

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A palynological study was made of the marine sediments from the maximum transgression period of Oxygen Isotope Stage 7.3 at Miyakodai, Kakogawa (134°53′49″E, 34°48′43″N), in the Harima Plane facing the northeastern coast of the Seto Inland Sea, Japan. We revealed a temperate deciduous broad-leaved forest consisting of Fagus and Quercus subgen. Lepidobalanus, and pine forest spread out in the Miyakodai area in Substage 7.3. The sediments are tephrostratigraphically correlated to marine clay Ma 11 (2) of the Osaka Group. They yield pine and beech pollen in common, as well as very low values of Quercus subgen. Cyclobalanopsis, or other warm temperate elements. Nevertheless, the Miyakodai deposit differs from the typical Ma 11 beneath the Osaka Plain in the absence of Pseudotsuga pollen. By contrast, previous studies have shown that abundant Quercus subgen. Cyclobalanopsis occurs in the Takatsukayama clayey layer (Ma 9/Stage 11 equivalent) at Tarumi, Kobe, to the east of Miyakodai. These palynological differences are most likely the result of palaeoclimatological differences between the Middle Pleistocene interglacials. In this case Substage 7.3 was significantly cooler than Stage 11, even in its highest sea-level stand, which leads to the deposition of Ma 11 (2) marine clay.

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Landforms from around the prodelta to the deltafront were reconstructed from grain size distributions of two sediment cores (Kaizu and Ooyamada) obtained from the Kiso River delta. Relations between the landform and the accumulation rate based on ¹⁴C ages are also discussed. Both cores show the typical deltaic succession of prodelta (MM-I or -II), deltafront slope (US-I), and deltafront platform (US-II). However, the characteristics of grain size distributions from each core are varied, corresponding to the core location. At the Ooyamada core, which is located at the edge of the plain, bimodal sediment (MM-II) was deposited under the influence of small tributary influx of the western Yoro Mountains, with the prodelta environment. At the lobate deltafront slope (Unit US-I), sediments were mainly supplied along the main axis of the river during flooding. Typical deltafront successions are preserved in the Kaizu core, which was estimated to be located along the main axis of the lobe. In contrast, the Ooyamada core was estimated to be located at the outer edges of the lobe, with smaller sediment supply, coarse and wellsorted sediments(around 2∅); it was relocated from the upper deltafront platform (Unit US-II) with waves of coastal process, and its sediments were preserved in a higher ratio. Accumulation rates of the two cores reflect the landform reconstructed above. A high accumulation rate was recorded in the Kaizu core (-56.8mm/yr) with its higher sediment flux from the river, and a low accumulation rate was recorded in the Ooyamada (-12.6mm/yr) core with its smaller sediment flux from the river and the preservation of relocated sediments.

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The peat of the Pleistocene Keihoku Formation at Keihoku, northern Hokkaido, is covered by tephra which is correlated to Aso-4. Pollen assemblages just below the tephra are dominated by Picea, which coexisted with Larix, Abies, and Betula. These assemblages indicate a cold and dry climate, which corresponds to the pollen assemblages just below Aso-4 at other points in Hokkaido. Larix-rich pollen assemblages accompanied Cyperaceae and Thalictrum, whereas Larix-rare assemblages included abundant Lysichiton pollen and remarkable Sphagnum spores. This reflects local wetland conditions at Keihoku around the Aso-4 fall, such as larch forests growing on the sedge bog or with skunk cabbages on the sphagnum bog.

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The author examines the temporal correspondence between geochronological settings and archaeological chronology in order to reconsider human-environment interactions during the Final Pleistocene in eastern Honshu Island. The discussion concentrates on two primary issues: (1) research problems with particular reference to the archaeological findings on numerical chronology, using radiocarbon dates; and (2) the relationships between geochronological settings and relative archaeological chronologies, using a calibrated radiocarbon time scale on the eastern part of Honshu Island during ca. 24, 000-11, 000cal BP.
The archaeological chronology during this period has been divided into seven phases: Backed point industry, Point industry, Microblade industry, Biface industry and plane pottery group, Slender-clay-ridges pottery group, Crescent-impressed and cords-marked pottery group, and Cord-wrapped-stick-pattern pottery group. Based on calibrated radiocarbon dates using the CalPal_2004_Jan, the groups seem to be placed at 2.3-2.0ka cal BP, 2.1-1.9ka cal BP, 1.8 (2.0)-1.5ka cal BP, 1.7-1.5ka cal BP, 1.5 (1.6)-1.4 (1.3)ka cal BP, 1.35-1.15ka cal BP, and after 1.1ka cal BP, respectively. The beginning of the use of pottery seems to be placed in the transitional period from stage Ib to stage II (beginning 15, 500cal BP). The slender-clay-ridges pottery group seems to coincide with the abrupt warming period of stage II. In addition, the beginning of the Cordwrapped-stick-pattern pottery group corresponds to the transition to stage IV (beginning 11, 500cal BP). Although the comparison between relative archaeological frameworks and geochronological ones is rather comprehensive, the archaeological study of this period is specifically required for the establishment of reliable correspondence.

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