We propose a method, along with an examination of its limitations, for estimating the crustal movement rate around a drilling site by reconstructing lake-level history with high temporal resolution. Sediment drilling was conducted off the mouth of the Echi-gawa river in the eastern part of Lake Biwa. At depths shallower than 35 meters, over 130 measurements of sand ratio in surface sediments were collected, allowing for the establishment of an empirical formula relating sand content to water depth.

Using a modern analogue method and this empirical formula, the paleowater depth for each drilled sediment sample was estimated. The sedimentary age of each drilled sample was determined based on an age model constructed from carbon-14 dating. By combining the water depth estimates with the above-sea-level height of each sediment layer, the historical lake-level changes were reconstructed. These lake-level changes were interpreted as a combination of crustal movement and short-term variations due to climatic factors, and an approximation model for lake-level changes was derived.

The analysis yielded an average crustal movement rate of 0.7 mm/year. However, various sources of error are likely present within the estimation process. Nonetheless, the obtained rate aligns with values reported by other methodologies.

The 3.5-2.3 Ma Yoneyama Formation distributed in and around Kashiwazaki City consists of volcanic rocks over 2,000 m thick. The volcanic activity is divided into four stages based on periodic intercalation of volcanic conglomerate and sandstone and on upward felsification cycles in the formation. The Tanne Member (450 m thick) of the first stage is subdivided into the lowest, lower, middle, and upper parts. Our research on the volcanostratigraphy and sedimentary facies of the member revealed the volcanic history of three steps. (1) During the deposition of the lowest and lower parts, volcanic bodies grew through building and collapse of the edifice in shallow marine environments. (2) A large volcanic island appeared during the deposition of the middle part with prevalent high-temperature reddish oxidization facies. (3) At the time of sedimentation of upper part, the volcanic activity declined to form abrasion platforms and the magma composition changed from basaltic to andesitic/dacitic. The growth-to-stabilization history of the volcanic island and the secular changes in magma composition (felsification) seem to become important clues to elucidate the origin of the periodic volcanic activities in the Plio-Pleistocene Yoneyama area.

We conducted geochemical analyses of whole-rock major and trace elements including rare earth elements of the Yamakunigawa Granitic rocks. The Yamakunigawa Granitic rocks are divided into three facies in terms of petrographical features: the hornblende - biotite tonalite facies, biotite granodiorite facies and two- mica granite facies. The hornblende - biotite tonalite facies, which are mainly composed of medium-grained weakly foliated hornblende - biotite tonalite, are distributed in the southern part of this granitic body. The biotite granodiorite facies, which are mainly composed of medium-grained weakly foliated biotite granodiorite, are distributed to south and north of the hornblende - biotite tonalite facies. The two-mica granite facies, which are mainly composed of medium-grained weakly foliated two-mica granite, are scattered in the northern plains. These granitic rocks have undergone plastic deformation, and so there are elongated recrystallized quartz grains. Variations of many elements of the whole-rock chemical compositions of these facies are continuous. But in part of element, there are gaps between the biotite granodiorite facies and two- mica granite facies. This suggests that the hornblende - biotite tonalite facies and biotite granodiorite facies were derived from same magma, but the two-mica granite facies might be derived from different magma.

The late Miocene to Pliocene igneous rocks occur between Tsunan and Shiga Kogen areas in the northeastern margin of the Utsukushigahara Zone of the North Fossa Magna region. These rocks are classified into the volcanic rocks in the Nishitajiri Formation (TH-series), the Takai volcanic rocks (CA-series), and the Neogene intrusive rocks. We newly obtained 5.77 ± 0.51 Ma K-Ar age from the Takai volcanic rocks. This indicates that the volcanic activity that formed the Takai volcanic rocks spanned the late Miocene to the early Pleistocene.

Based on the petrological and geochemical studies, Sr- and Nd-isotope compositions differ between the TH-series and the CA-series volcanic rocks. This feature is different from that in the Early Pleistocene volcanic rocks of the same region, where both the TH- and CA-series rocks were derived from isotopically similar sources. Additionally, the alkali contents of both rock series are lower than those in the Early Pleistocene rocks.

Based on the trace elements compositions, the basaltic magmas of the TH series rocks are inferred to be mantle melts generated by addition of slab fluids with high Sr isotope ratio. The CA series rocks are also derived from the similar fluid fluxed mantle melting but with lesser amount of slab fluid. It is also possible that the low-Nd isotopic crustal materials were assimilated during magmatic differentiation as shown by the elevated Zr-Hf relative to Sm in the fractionated rocks. In addition, the Nd isotope ratios of the volcanic rock in Nishitajiri formation and the Masugatayama volcanic rocks suggest the regional spread of distribution the HND group (high-Nd group) volcanic rocks.

Diatom fossils were detected from the Miocene Zaimokugawa Member of the Ikokuma Formation in the western part of Shimokita Peninsula, Northeast Japan. In this report, this unit is proposed as member for the Zaimokugawa Formation in previous work. The flora from this member contains Denticulopsis praedimorpha v. praedimorpha suggesting that this formation is assigned to D. praedimorpha Zone (NPD5B) (around the boundary between middle and upper Miocene). This is the first report on the age of this member. Furthermore, this member intercalated in the lower part of Ikokuma Formation consisting of andesitic pyroclastic rocks. The age of the Zaimokugawa Member constrains the age when the eruption of that pyroclastics started.

This paper describes the “Gravestone group at Mitsuya”, which is graves for victims at the 1888 eruption of Bandai Volcano. This gravestone group does not appear on any known disaster records and can be considered an important remains at the 1888 eruption of Bandai volcano.

The disaster caused at the 1888 eruption of Bandai Volcano left about 500 people dead or missing. The reason for the large number of deaths and missing was that they were caught in rock avalanche and mud flow caused by the collapse of Kobandai-san.

The Nagasaka district of this paper is located on the eastern foot of Bandai Volcano, with the Nagase River flowing on the southeast side of the district. At the 1888 eruption of Bandai volcano, debris flow flowed into the Nagase River and attacked Nagasaka. And at the southeast of Nagasaka where the debris flow had accumulated, many corpses were found. The corpses found here were temporarily buried in the debris flow field. Even after that, human bones were occasionally found, and the residents at Nagasaka built graves at a hill in Mitsuya and held memorial services.

The above is the history of why the “Gravestone group at Mitsuya” was created.