The Northern Izu-Bonin Arc, one of the intraoceanic arc systems in Western Pacific, is marked by an along-arc arrangement of trench, volcanic front, and backarc rift, and across-arc NE-SW oriented seamount chains. Hachijojima Volcanic Group is located on the volcanic front of this arc, and consists of Nishiyama, Higashiyama, Hachijo-kojima Volcano, and one eroded submarine volcanic edifice. The structure and the evolution process of Hachijojima Volcanic Group are revealed in this topographic study.
The Hachijojima Volcanic Group comprises about ten stratovolcanoes. Eight of them were active during the past 140, 000 years. All these volcanoes were formed on the same submarine basement having a 30-35-kilometer bottom diameter. This might suggest that the volcanoes originated from the same mantle diapir. The volcanoes of the Hachijojima Volcanic Group are classified into two types: basalt-type and andesite-type. Andesitic or dacitic magmas or both sometimes erupted during the late-stage activity of the basalt-type volcanoes.
The NW-SE alignment of flank volcanoes of Nishiyama might indicate the direction of horizontal compressional stress, which is probably caused by a collision between the Izu-Bonin Arc and the Honshu (Japan) Arc in the Izu Peninsula. On the other hand, the instability of the eruption center and the low eruptive rate suggest that the Hachijojima Volcanic Group has been under the influence of a relatively tensional stress field. Crustal deformation caused by the compressional stress associated with the arc-arc collision is less remarkable in Hachijojima than around the Izu Peninsula-Oshima-Miyakejima region. Active backarc rifting associated with N-S-oriented normal faults and monogenetic volcanoes immediately west of the Hachijojima Volcanic Group supports this view. However the E-W tensional stress field in the backarc rift is differant from NW-SE compressional stress field in the volcanic front. The NE-SW alignment of volcanic edifices in Higashiyama is probably controlled by the NE-SW structure which continues from the across-arc seamount chain in the backarc region.

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Multiproxy analyses including grain size, total organic carbon (TOC), total sulfur (TS), total nitrogen (TN), calcium carbonate (CaCO₃) contents, diatom as well as sedimentary properties of the boring core KM-11 (54m in length) collected from a brackish lake, Lake Kamo, are used to reconstruct paleoenvironment and coastal evolution of northeast coast of Sado Island in central Japan. Anoxic and normal marine sediments can be detected by TOC-TS relationship, and the origin of organic matter is inferred from the TOC/TN ratio. Geochemical characteristics of the sediments respond striking to sea-level change. In the Late Pleistocene, fluvial sediments are characterized by high TOC, very low TS and terrigenous organic matter. The overlying coastal marsh sediments are characterized by high TOC and abruptly increasing trend of TS suggesting sea water spilled into the site, and are overlain by estuarine sediments which obviously indicates the beginning of the Holocene transgression. Embayment sediments are characterized by low TOC, marine organic matter and low productivity condition indicating the rapid relative sea-level rise. The maximum Holocene transgression could be inferred between 6, 500 and 5, 000yrs BP. After that fluctuations of relative sea-level are characterized by high TOC, high TS, a mixed type of marine/terrigenous organic matter and high productivity condition to be inferred marine/brackish lagoonal sediments. Diatom floral changes of the core KM-11 also support the geochemical data to interpret the paleoenvironment and evolution of the coastal deposits.

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A large number of Quaternary tephra layers covering terrace surfaces and hill slopes are well preserved in the north Kanto and south Tohoku regions of central Japan. However, previous fission track ages of some of the tephras are considered to be inaccurate, and other radiometric ages dated by K-Ar method reported in previous studies are also insufficient to discuss the tephrochronology.
In this study, eleven Quaternary tephra layers were newly dated by the fission track dating method using zircon crystals. The method includes zeta calibration, which is recommended by the I. U. G. S. The ages obtained are shown as follows, in descending order of the stratigraphy; Shibahara Tephra (SB): 110±20ka, Tagashira Tephra (TG): 160±20ka, APm-U: 130±30ka, Kurodahara Tephra (KdP): 200± 30ka, Nemoto 13 Tephra (Nm-13): 290±60ka, Nemoto 14 Tephra (Nm-14): 290±30ka, Nemoto 16 Tephra (Nm-16) 290±70ka, Tajima Yellow Tephra (TyP): 160±70ka, Hoshitoge Biotite Tephra (HtB): 660±40ka, Nishigo Pyroclastic Flow Deposit (NSG): 790±160ka, Kumado Pyroclastic Flow Deposit (KMD): 1, 400±200ka (errors are 1σ). SB, TG, KdP, Nm-14, HtB were dated using more than 100 zircon grains in order to obtain a high precision, but the remainding procedures used about 30 grains. The fission track ages are reviewed with reference to stratigraphic position, comparison with previous radiometric ages, and consistency with a chronological framework established by previous studies.
All the ages are consistent with the stratigraphic relationships of tephras except for TyP. Fission track ages determined in this study show younger ages than those obtained by the previous studies which did not use the zeta calibration. Our chronological data provide a new time scale for the tephrochronology of the study area. This suggests that changes in the accumulation rate of tephric soil deposits are smaller than estimated by Suzuki (1993). Climatic fluvial terraces formed under glacial conditions of marine isotope stage 6 are now recognizable, in contrast to previous studies. On the other hand, identification of APm-U tephra, correlated to Omachi A Tephra Group, requires further examination.

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Coastal sand dune fields have been formed from large deposits of Shirasu ignimbrite sand such as volcanic glass and pumice from Shirasu plateau in Kagoshima Prefecture. In Fukiagehama dune field, dunes I and II were formed between 5, 200 and 1, 000yrs BP. Dune III was formed around the 18th century. Dune IV was formed artificially around the 19th century by sand arrestation work. Dunes I and II consist of large portions of quartz grains, while dunes III and IV consist of Shirasu sand (volcanic glass and pumice) originating from Shirasu ignimbrite. In Shibushi dune field, dunes I, II and III were formed between the late-Jomon period and the 18th century, and dune IV was formed between the late-Edo Era and early Meiji Era. Dune V was formed artificially by sand arrestation work after World War II. Dunes I, II, and III consist of large portions of quartz sand, while dunes IV and V consist of Shirasu sand. The abrupt changes in dune sand composition between the two dune fields may reflect the changes in the discharge of Shirasu sand from the Shirasu plateau to the coastal area caused by landform transformation due to agricultural development. The intensity of landform transformation increased beginning in the 17th century in Kagoshima (as all over the Japanese Islands). In Satsuma area, agricultural landform transformation was accelerated from 1651 to the end of the Edo Era. Agricultural development in the Ohsumi area was extensively carried out beginning in the early Meiji Era.
As a result of vegetational denudation due to agricultural landform transformation on the Shirasu plateau, soil erosion in the form of sheet flood and gully erosion occurred frequently. Construction of irrigation channels just under the Shirasu cliff, ended the gully erosion of Shirasu. Human-induced soil erosion, however, became prevalent around the 17th century on the Shirasu plateau. Agricultural land transformation on the plateau gave rise to great changes in the discharge of soil from the Shirasu plateau to coastal areas. The formation ages of sand dunes which consist of Shirasu sand coincide with the agricultural landform transformation of Satsuma and Shibushi.

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Abundant fossil beetles were obtained from the Lower Pleistocene Ookui Formation in Kitamimaki-mura, Kitasaku-gun, Nagano Prefecture, Central Japan. These fossils are composed of ground and aquatic beetles, such as Carabidae, Dytiscidae, Hydrophilidae, and Donaciinae of Chrysomelidae. Several fossils of ground beetles are identified with three interesting species, Hemicarabus maeander, Apotomopterus maacki, and Chlaenius gebleri. Among them, H. maeander is not distributed in Honshu where the fossil occurred, but can be found in Hokkaido, Chejudo, Sakhalin, N. E. China, Mongolia, East Siberia, and North America at the present time. The fossil finding indicates that the widely and continuous distributional range of this species seemed to become discontinuous, and extinct in Honshu after the Early Pleistocene. Thus, this species can be considered as a geographic relict species in Honshu during the Pleistocene. The paleoenvironment of the Upper member of the Ookui Formation based on beetle fossils seems that there were mainly low moor of reeds accompanied with areas of still water. These beetle assemblages, especially including H. maeander and C. gebleri, suggest presence of low moor which is similar to those found in Hokkaido during the Upper member of the Ookui Formation deposited.

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A volcanic ash layer was discovered in two sediment cores from the Kaga coastal plain, Ishikawa Prefecture. Three radiocarbon dates, obtained from wood and molluscan shells above and below the ash layer, indicate that its eruption occurred between ca. 8, 800 and ca. 8, 270yrs BP. From the age, distribution and mineral assemblage of the ash layer, it is considered to correlate with the Midagahara ash layer derived from Hakusan volcano, located 50km south of the Kaga coastal plain.

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