[M-GI25] Holocene paleoenvironment, paleoclimate, and paleohazards in the Pacific Islands

[MGI25-09] In search of paleotsunami deposits on Viti Levu Island, Fiji

*後藤 和久¹、ゴフ ジェームス²、マロダリ ジョジ³、クマー ニレシュ⁴、石澤 尭史⁵、笠井 克己¹、中田 光紀¹ (1.東京大学大学院理学系研究科、2.ニューサウスウェールズ大学、3.鉱物資源局、4.南太平洋大学、5.東北大学)

Fiji is located in the central part of the South Pacific. Although there is no tsunamigenic subduction zone close to Fijian islands, Fiji has potential to be affected by large distant tsunamis generated along remote subduction zones such as Tonga Trench and large submarine volcanic eruptions like the 2022 Hunga Tonga-Hunga Haʻapai (HT-HH) event. Also, there is a risk of tsunamis generated by local submarine landslides (Lau et al., 2018). Notwithstanding the high tsunami risks, paleotsunami research in Fiji is scarce (Goff et al., 2020). In this study, we carried out preliminary site surveys on Viti Levu Island to explore its paleotsunami history. Generally, the southern coast of the island is a wave-dominated coast with coral reefs while the northern coastline is dry, with calm conditions and tide-dominated deltas with mangrove forests developed along the coast. As a result of such settings, terrestrial sediments along the northern coastline are generally dry with limited preservation potential for high-energy event deposits. Southern coasts on the other hand have higher potential to preserve such event deposits, although there are few coastal plains. For instance, we found multiple sandy event deposits in the wetlands landward of the Kiuva beach dunes, where the pumice, possibly including the 2022 HT-HH, is scattered over the beach surface. Some of these event deposits, which should be older than the 2022 HT-HH event, contain large pumice fragments. In a similar manner, some sand layers and coral boulders, both of which can be interpreted as event deposits, are also observed along the southwestern coast of the island. Although further analyses are required to identify the origin of these deposits, Viti Levu Island appears to be an important target to study the paleotsunami history of Fiji.

Acknowledgments: This research was supported by SATREPS, JST/JICA and JSPS.