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Eruption scenario and hazard assessment at a basaltic volcanic island: a preliminary result on Gaua volcano, Vanuatu

Yuki Yasuda 1, Fukashi Maeno1, Osamu Ishizuka2, Tatsuji Nishizawa3, Janvion Cevuard4, Ricardo William4, John Junior Niroa4, Mie Ichihara1

  • Affiliations: 1Earthquake Research Institute, The University of Tokyo, Tokyo, Japan; 2Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan; 3Mount Fuji Volcanic Disaster Research Center, Mount Fuji Research Institute, Yamanashi, Japan; 4Vanuatu Meteorology and Geohazards Department, Port Vila, Vanuatu

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 93

  • Programme No: 3.16.20

  • Theme 3 > Session 16

Abstract

Basaltic volcanic islands exhibit a variety of explosive eruption styles, from small-scale phreatomagmatic explosions to large caldera-forming eruptions. The eruptions may become complicated and more hazardous due to interaction between magma and seawater. We focus on Gaua volcano, an active oceanic volcanic island in Vanuatu with a diameter of ~20 km that has a ~8 × 6 km summit caldera. We aim to understand the eruption history, the processes that have produced the various eruption styles, and their impacts, and use these to assess hazards. We present preliminary results, including stratigraphy and chemical compositions of representative deposits, obtained through mapping and sampling at coastal outcrops and at the caldera rim. Some coastal sections in the north are thin and dominated by a scoria lapilli fallout and a lapilli tuff, whereas other coastal sections in the west consist of lava flows and overlying pyroclastic current and fallout deposits. The thickest pyroclastic current deposit (likely derived from a caldera-forming eruption) shows alternating massive and stratified facies, and the stratified facies shows evidence of magma--water interaction such as abundant accretionary lapilli and cross stratification. We also identified several satellite cones along the coast. These small cones indicate that magmatic eruptions occurred near the coast due to the fissure formation reflecting the regional stress field. The new survey results provide insights into the potential hazards associated with large basaltic islands such as Gaua and may help to construct accurate hazard maps that mitigate the impacts of future eruptions.