Eruptive history of Fuji Volcano from AD 700 to AD 1,000 using stratigraphic correlation of the Kozushima-Tenjosan Tephra

Abstract

Abstract:We analyzed refractive index, microstructure, vesicularity of glass from an alien tephra in the upper weathered volcanic ash soil horizon of Fuji Volcano, Izu peninsula, Miyakejima, and Niijima Volcanoes. The glass size increases toward Izu Islands. Based on the vesiculality of glass, the Kozushima-Tenjosan tephra (AD 838) can be distinguished from the Niijima-Mukaiyama tephra (AD 886). Thus, we determined from where the tephra of low refractive index on the flank of Fuji Volcano comes from. Next, using the stratigraphic correlation of the tephra, the detailed stratigraphy of Fuji Volcano during the period of AD 700-1,000 was clarified. It was difficult to determine exact age of each eruption by 14 C dating with 2 sigma error bar (around ±40 years). However, the KozushimaTenjosan tephra horizon can classify Fuji Volcano products those below the tephra and those above the tephra. The Obuchi scoria (OBC), the Kansuyama scoria (KNS), the Nishi-Futatsuzuka scoria on S and SE flanks, the Takamarubi lava flow (Tam) and the Hinokimarubi 2 lava flow (Hnm 2), the scoria associated with the Oniwa-Okuniwa 2 lava flow (Onw 2) on NE and N flanks are below the Kozushima-Tenjosan tephra. The Fudosawa lava flow (Fud), the Obuchimarubi lava flow (Obu), the Higashi-Usuzuka south lava flow (Hum), the Mizugatsuka-hinokimarubi lava flow (Him) on S and SE flanks, the Kenmarubi 2 lava flow (Ken 2), the Tenjin-Igatono scoria (TNG), the Aokigahara lava flow and the Nagaoyama scoria on the NE and N flanks are above the Kozushima-Tenjosan tephra. The Kozushima-Tenjosan tephra was discovered just below the S-24-6 scoria on E flank. The stratigraphy of E flank is rearranged as follows in ascending order: the S-24-5 scoria, the S-24-5-1 scoria (newly defined), the S-24-5-2 scoria (newly defined), the S-24-5-3 scoria (newly defined), the Kozushima-Tenjosan tephra, the S-24-6 scoria, the S-24-7 scoria, the S-24-9 scoria, the S-24-10 scoria.

Integrating the Holocene tephrostratigraphy for East Asia using a high-resolution cryptotephra study from Lake Suigetsu (SG14 core), central Japan

“…Distally, the Iz-Kt is difficult to stratigraphically and geochemically distinguish from the Niijima-Mukai-yama (Iz-Nm) tephra (Sugiuchi and Fukuoka, 2005;Kobayashi et al, 2007;Suzuki et al, 2017;Tsuchiya et al, 2017), which was dispersed during an eruption from Niijima volcanic island (20 km north of Kozushima) and believed to have occurred in AD 886 (Tsukui et al, 2006).…”

Non-crystalline Inorganic Constituents of Soil

“…Mt. Fuji emits scoriaceous tephra (Kobayashi et al 2007;Miyaji 2002). Soil horizons of A1 to C were formed from Hoei, and horizons of 2A1 from Jogan tephra (Fig.…”

Volcanic influence of Mt. Fuji on the watershed of Lake Motosu and its impact on the lacustrine sedimentary record

“…Fuji, three rhyolitic tephra markers are identified in inland trenches, outcrops, and in drilling cores: the Kozushima-tenjosan (KT), the Kawagodaira (Kg) and the Kikai-Akahoya (K-Ah) tephra (Miyaji, 1988;Machida and Arai, 1992;Kobayashi et al, 2007;Nakano et al, 2007). The CE 838 KT tephra is characterized by a low refractive index (1.494-1.497, Kobayashi et al, 2007), similar to those from volcanoes on the Izu Islands (Uesugi, 2003). The Kg tephra is a fine-grained white pumice resulting from the eruption of the Kawagodaira Volcano on the Izu Peninsula with a refractive index around 1.500-1.503 (Takemura et al, 2000).…”