16:00 〜 16:15
[MGI25-03] Towards the assessment of volcanic activity and hazards of Nabukelevu volcano, Kadavu Island, Fiji
キーワード：火砕流、溶岩、プリニー式、地滑り、ナブケレブ
Nabukelevu Volcano, Kadavu Island, is one of the few active volcanoes in Fiji. As part of the SATREPS project, we have begun research to clarify the eruptive history of Nabukelevu volcano and to assess volcanic activity and future hazards in the area. We report on the preliminary results of geological surveys around the volcano. We found several pyroclastic flow and fallout deposits from past eruptions of the volcano in the nearest village. The massive, poorly sorted and lava-block-rich facies in some of the deposits suggests that they were formed by block and ash flows from the collapse of lava domes. Pumice fallout deposits were also found in the deposit sequence, suggesting that a Plinian style eruption occurred in the past eruptive activity, possibly associated with lava dome formation. We plan to carry out chemical analyses of rock samples to clarify the nature of the magma, and dating of carbonized materials to clarify the timing of the eruption. While the explosive eruption of Nabukelevu volcano will be a major hazard in the area, landslides may also be a source of hazard. We have therefore studied collapse materials from recent landslides in the northern area and found that most of them are andesite and dacite lavas rich in phenocrysts. These lavas are the main components of the summit lava dome and are also similar to the pyroclastic flow deposits in the village. It is worth noting that the collapsed lava is very fragile, i.e., it has weak strength. This physical property may be related to the ease with which slope failures can occur. Landslides are thought to be caused by topographical factors such as steep slopes or meteorological factors such as heavy rainfall, but in the case of Nabukelevu volcano the physical properties of the lava may also have a significant influence