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Journal Articles

Local tephra as an age-determination tool; Example of 2.3 ka Yakedake volcano tephra in Nagano Prefecture, central Japan

Kojima, Satoru*; Kagami, Saya; Yokoyama, Tatsunori; Kariya, Yoshihiko*; Katayama, Yoshikazu*; Nishio, Gaku*

Proceedings of 5th International Workshop on Rock Mechanics and Engineering Geology in Volcanic Fields (RMEGV 2021) (Internet), 6 Pages, 2021/09

A local tephra embedded in a hand-auger boring core drilled at near-shore of Kinugasanoike Pond about 4.6 km NE of Mt.Yakedake, one of the most active volcanoes in central Japan, is composed mainly of several kinds of volcanic glass shards (microlite-bearing, blocky, fluted and micro-vesicular types) with minor amounts of crystal minerals including quartz, plagioclase, hornblende, biotite, and pyroxene. Plant remains recovered from the horizon 10 cm below the tephra layer yield $$^{14}$$C ages of 2,331-2,295 (19.2% probability distribution) and 2,270-2,155 (76.2% probability distribution) cal yrs BP. We measured major element compositions of 241 individual glass shards using Electron Probe Micro Analyzer. They are plotted on the SiO$$_{2}$$-K$$_{2}$$O, SiO$$_{2}$$-Na$$_{2}$$O+K$$_{2}$$O, and FeO$$^{ast}$$-K$$_{2}$$O diagrams in a region different from those of major regional tephras distributed in central Japan. The clast and chemical compositions coincide with those of a tephra embedded in the Nakao pyroclastic flow deposits distributed about 2 km NNW of Mt. Yakedake dated as around 2,300 cal yrs BP. The tephra could be used as a local marker of 2,300 cal yrs BP in the southern part of Northern Japan Alps.

Journal Articles

Dating of buried wood logs and fragments for high resolution reconstruction of landslide histories; Case studies in the Japanese Alps region in the historical times

Yamada, Ryuji*; Kimura, Takashi*; Kariya, Yoshihiko*; Sano, Masaki*; Tsushima, Akane*; Li, Z.*; Nakatsuka, Takeshi*; Kokubu, Yoko; Inoue, Kimio*

Sabo Gakkai-Shi, 73(5), p.3 - 14, 2021/01

We discuss the applicability of dating methods for determining landslide chronologies in relation to the type of samples and the sampling location. Case studies are carried out with fossil wood samples buried in the colluvial soil of large-scale landslides occurred in two areas of the Japanese Alps region. Ages are determined by accelerator mass spectrometry radiocarbon dating and dendrochronological analysis using the oxygen isotope composition of tree ring cellulose. Most of ages for Dondokosawa rock avalanche are concordant with the period of AD 887 Ninna (Goki-Shichido) earthquake. Ages for Ohtsukigawa debris avalanche are not concentrated in a specific period. In order to obtain accurate age of large-scale landslide, utilizing buried large diameter tree trunk or branches with the good preservation condition has a lot of advantages because it allows us to compare the landslide chronology with historical records of heavy rainfall and large earthquakes.

Journal Articles

Progress of divertor simulation research toward the realization of detached plasma using a large tandem mirror device

Nakashima, Yosuke*; Takeda, Hisahito*; Ichimura, Kazuya*; Hosoi, Katsuhiro*; Oki, Kensuke*; Sakamoto, Mizuki*; Hirata, Mafumi*; Ichimura, Makoto*; Ikezoe, Ryuya*; Imai, Tsuyoshi*; et al.

Journal of Nuclear Materials, 463, p.537 - 540, 2015/08

 Times Cited Count:21 Percentile:84.82(Materials Science, Multidisciplinary)

Journal Articles

Development of divertor simulation research in the GAMMA 10/PDX tandem mirror

Nakashima, Yosuke*; Sakamoto, Mizuki*; Yoshikawa, Masayuki*; Oki, Kensuke*; Takeda, Hisahito*; Ichimura, Kazuya*; Hosoi, Katsuhiro*; Hirata, Mafumi*; Ichimura, Makoto*; Ikezoe, Ryuya*; et al.

Proceedings of 25th IAEA Fusion Energy Conference (FEC 2014) (CD-ROM), 8 Pages, 2014/10

Oral presentation

Yakedake Nakao tephra; An Attempt to use the local tephra as a Late Holocene age marker for the southern part of the Northern Japan Alps

Nishio, Gaku*; Kagami, Saya; Yokoyama, Tatsunori; Kariya, Yoshihiko*; Kojima, Satoru*

no journal, , 

We attempt to use local tephra derived from nearby volcanoes as an age marker. The Kamikochi area in the southern part of the Northern Alps is strongly affected by the Yakedake volcano. We prepared distinctive tephras, (1) one sample of glassy volcanic ash in hand auger boring cores drilled at the near-shore Kinugasanoike Pond, about 4.7 km northeast of Mt. Yakedake and (2) two samples of glassy volcanic ash in the Nakao pyroclastic flow deposites, which is considered to be a product of the last magmatic eruption about 2,300 years ago, distributed about 1.5 km north-northwest of Mt. Yakedake. We investigated the clast composition of these tephras and the chemical composition and refractive index of volcanic glass. Approximately 70% of the clasts were volcanic glasses, and most of them were vesicular and blocky types. These glasses were characterized by high SiO$${2}$$, K$$_{2}$$O, Na$$_{2}$$O and low Al$$_{2}$$O$$_{3}$$, FeO, which were clearly distinguishable from the volcanic glasses in Quaternary widespread tephras. The refractive indices of 30 volcanic glasses for each tephra were 1.4958-1.5011 with a peak in the range of 1.497 to 1.499. The results of this study indicate the tephra from Kinugasanoike Pond were erupted from Mt. Yakedake about 2,300 years ago. Therefore, the tephra with the above characteristics can be used as a useful age marker for the southern part of the Northern Alps about 2,300 years ago.

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