Geological Evidences for a Large Tsunami Generated by the 7.3 ka Kikai Caldera Eruption, Southern Japan

NASA Astrophysics Data System (ADS)

Yamada, M.; Fujino, S.; Satake, K.

2017-12-01

The 7.3 ka eruption of Kikai volcano, southern Kyushu, Japan, is one of the largest caldera-forming eruption in the world. Given that a huge caldera was formed in shallow sea area during the eruption, a tsunami must have been generated by a sea-level change associated. Pyroclastic flow and tsunami deposits by the eruption have been studied around the caldera, but they are not enough to evaluate the tsunami size. The goal of this study is to unravel sizes of tsunami and triggering caldera collapse by numerical simulations based on a widely-distributed tsunami deposit associated with the eruption. In this presentation, we will provide an initial data on distribution of the 7.3 ka tsunami deposit contained in sediment cores taken at three coastal lowlands in Wakayama, Tokushima, and Oita prefectures (560 km, 520 km, and 310 km north-east from the caldera, respectively). A volcanic ash from the eruption (Kikai Akahoya tephra: K-Ah) is evident in organic-rich muddy sedimentary sequence in all sediment cores. Up to 6-cm-thick sand layer, characterized by a grading structure and sharp bed boundary with lower mud, is observed immediately beneath the K-Ah tephra in all study sites. These sedimentary characteristics and broad distribution indicate that the sand layer was most likely deposited by a tsunami which can propagate to a wide area, but not by a local storm surge. Furthermore, the stratigraphic relationship implies that the study sites must have been inundated by the tsunami prior to the ash fall. A sand layer is also evident within the K-Ah tephra layer, suggesting that the sand layer was probably formed by a subsequent tsunami wave during the ash fall. These geological evidences for the 7.3 ka tsunami inundation will contribute to a better understanding of the caldera collapse and the resultant tsunami, but also of the tsunami generating system in the eruptive process.

JPRS Report. Science & Technology: Japan.

DTIC Science & Technology

1988-12-09

Molding Technology [Takashi Kasai , Akihiko Hirota; KIKAI TO KOGU, May 88] 106 Injection Molding Technology [Toshiyuki Iwahashi; KIKAI TO KOGU, May 88...Development Shu Isa -Planning Office Fumio Sato —Control Office Shizuka Kudo - Patent Office Taro Inoue —Technical Information Office Takeshi...the possibility that a more serious situation could occur. Fumio Kaneko, who is in charge of the marine sector, joined the company in 1971 after

Sub-Saharan Africa Report

DTIC Science & Technology

1987-04-01

election, for only then can they successfully fight what they see as the threat of a black government resulting from government policy. The...careful. What is happening in Bisho and Mabatho can easily spill over to our comfortable South Africa. History has proved that these things have a...see what support they they can lend to getting rid of the National Party Govern- ment. Different A series of tenuous alliances is enticing- ly

Tsunami deposits associated with the 7.3 ka caldera-forming eruption of the Kikai Caldera, insights for tsunami generation during submarine caldera-forming eruptions

NASA Astrophysics Data System (ADS)

Geshi, Nobuo; Maeno, Fukashi; Nakagawa, Shojiro; Naruo, Hideto; Kobayashi, Tetsuo

2017-11-01

Timing and mechanism of volcanic tsunamis will be a key to understand the dynamics of large-scale submarine explosive volcanism. Tsunami deposits associated with the VEI 7 eruption of the Kikai Caldera at 7.3 ka are found in the Yakushima and Kuchinoerabujima Islands, 40 km south -southeast of the caldera rim. The tsunami deposits distribute along the rivers in their northern coast up to 4.5 km from the river exit and up to 50 m above the present sea level. The tsunami deposits in the Yakushima area consist of pumice-bearing gravels in the lower part of the section (Unit I) and pumiceous conglomerate in the upper part (Unit II). The presence of rounded pebbles of sedimentary rocks, which characterize the beach deposit, indicates a run-up current from the coastal area. The rip-up clasts of the underlying paleosol in Unit I show strong erosion during the invasion of tsunami. Compositional similarity between the pumices in the tsunami deposit and the juvenile materials erupted in the early phase of the Akahoya eruption indicates the formation of tsunami deposit during the early phase of the eruption, which produced the initial Plinian pumice fall and the lower half of the Koya pyroclastic flow. Presence of the dense volcanic components (obsidians and lava fragments) besides pumices in the tsunami deposit supports that they were carried by the Koya pyroclastic flow, and not the pumices floating on the sea surface. Sequential relationship between the Koya pyroclastic flow and the tsunami suggests that the emplacement of the pyroclastic flow into the sea surrounding the caldera is the most probable mechanism of the tsunami.

Large Nankai Trough earthquake and tsunami found in lacustrine deposits through late Holocene-time along the western coast of Kii Peninsula, southwestern Japan

NASA Astrophysics Data System (ADS)

Okamura, M.; Matsuoka, H.; Tsuzuki, M.; Toraya, K.

2015-12-01

We continue paleo-seismic studies through Late Holocene-time in coastal marsh ponds along the Nankai Trough . These ponds which are co-seismic subsidence areas have continuous muddy sediment stratigraphy and sporadic tsunami induced coarse material. Well controlled age data has been collected from the core-sample that contains plant remains under anoxic sedimentary environment . Total 21 cores collected from two coastal ponds Ashihama-ike and Zasa-ike which locate behind beach-ridge along southeastern coast of Kii Peninsula under Tokai/Tonankai Earthquake assumption areas. Tsunami events are recognized after eighty AMS C-14 dating through recent (core top) to 7300 yBP interval. Among these interval, two remarkable events found in sediment, which are 2050yBP to 2300yBP (=2K event) and 1000yBP to 1100 yBP. 2k event consists thick sand, well rounded gravel in chaotic mud and wood fragment derived from forests surrounding lakes. Later event is correspond to the historical Ninna Nankai earthquake (AD887, 26 August under the old lunar calendar).　Rather small events are occurred in 3500yBP and 1100yBP. These events are found from both of two ponds which has two kilometers in distance each other. Cores bottom are composed of 7400yBP huge-tsunami event caused simultaneously by the Kikai-caldera eruption (over 170 cubic km ejecta) is just covered with the Kikai-Akahoya (K-Ah) tephra. The 2K and volcanic tsunami events have also found widely, not only Kii Peninsula but southern Shikoku (Tokushima Pref. and Kochi Pref.) and Kyushu through the Nankai Trough.

Morphological and molecular characterization of a new genus and new species of parazoanthid (Anthozoa: Hexacorallia: Zoantharia) associated with Japanese Red Coral

NASA Astrophysics Data System (ADS)

Reimer, J. D.; Nonaka, M.; Sinniger, F.; Iwase, F.

2008-12-01

The Order Zoantharia has long been taxonomically neglected primarily due to difficulty in examining the internal morphology of sand-encrusted zoanthids. However, recent work using molecular markers has shown an unexpectedly high diversity of previously “hidden” taxa (families and genera) within Zoantharia (=Zoanthidea, Zoanthiniaria). In this study, unidentified sediment-encrusting zoanthid specimens ( n = 8) were collected from living Japanese Red Coral Paracorallium japonicum (Family Coralliidae) during precious coral harvesting by Remotely Operated Vehicle (ROV) and manned submersible (February 2004-January 2006) at depths of 194-250 m at six locations between Ishigaki-jima Island and Kikai-jima Island, southern Japan. DNA sequences (mitochondrial 16S ribosomal DNA [mt 16S rDNA], cytochrome oxidase subunit I [COI], nuclear internal transcribed spacer of ribosomal DNA [ITS-rDNA]) unambiguously place these specimens in a previously undescribed, new monophyletic lineage within the family Parazoanthidae. Corallizoanthus tsukaharai, gen. n. et sp. n. is the first reported zoanthid species associated with the family Coralliidae and unlike other described gorgonian-associated zoanthids ( Savalia spp .) does not secrete its own hard axis. Morphologically, C. tsukaharai sp. n. is characterized by generally unitary polyps and bright yellow external coloration.