Japan Geoscience Union Meeting 2019

Presentation information

[J] Poster

S (Solid Earth Sciences ) » S-VC Volcanology

[S-VC38] Active Volcanism

Mon. May 27, 2019 10:45 AM - 12:15 PM Poster Hall (International Exhibition Hall8, Makuhari Messe)

convener:Yuta Maeda(Nagoya University), Takahiro Miwa(National research institute for earth science and disaster prevention), Takeshi Nishimura(Department of Geophysics, Graduate School of Science, Tohoku University)

[SVC38-P13] Eruption age determination of the latest two lava flows and characteristics of volcaniclastic materials from the recent activity of Yokodake Volcano, Japan

*Hiroya Nitta1, Takeshi Saito1, Yorinao Shitaoka2 (1.Shinshu University of Science and Technology, 2.Department of Environment System, Faculty of Geo-environmental Science, Rissho University)

Keywords:Yokodake Volcano, Latest lava, Eruption age determination, TL dating, Volcaniclastic materials from the recent activity

Yokodake volcano, which effused nine lava flows (Y1~Y9), is the only active volcano belonging to Yatsugatake volcano groups in central Japan. Eruption ages of Y1-Y8 lava were not determined distinctively. To evaluate the latest activity of Yokodake volcano, we carried out paleomagnetic studies and tried to estimate the eruption ages of the Y8 and Y9 lava flows. However, several candidates for paleomagnetic ages were remained (Nitta and Saito, 2018, JPGU; Nitta and Saito, 2018, fall meeting of the volcanological society of Japan). In this study, we applied thermoluminescence (TL) dating for Y8 and Y9 lava and viscous remanent magnetization (VRM) dating for Y9 lava. In addition, the volcaniclastic layers were found just above the Y9 lava and around the surface of the summit region. We will report characteristics of the volcaniclastic layers, discussing the recent activities of this volcano.

TL dating was performed by using poly-minerals (ca 10~50 µm) sample extracted from Y8 and Y9 lava. TL age of Y8 sample was 3.3 ± 1.2 ka. Y9 lava sample didn’t emit TL intensity. As for Y9 lava, we tried to estimate the age using VRM. However, the estimated ages were widely scattered. We conclude eruption age of the Y8 lava is ca. 3.3 ka, which is consistent with our previous paleomagnetic age of 3.35~3.85ka. On the other hand, five eruption ages of Y9 lava (0.60 ka, 1.80 ka, 1.90~1.95 ka, 2.20∼2.25 ka, 2.4~2.45 ka) are still remained.

We recognized light gray volcanic ash deposit just above Y9 lava which composed of sand to silt size and contained carbonaceous material. It may be comparable to NYk-1 tephra (Okuno, 1995). Four volcaniclastic layers were found at summit region and the lower layer is a possibility of being correlated with NYk-2 tephra (2.35~2.15 cal ka BP; Okuno and Kobayashi, 2010). Two volcaniclastic layers above NYk-2 tephra seem to be derived from Yokodake volcano, suggesting at least two volcanic eruptions were occurred after NYk-2 tephra eruption.