10:45 〜 11:00
[SVC28-07] 軽石いかだ噴出量の迅速な定量化に向けて必要なもの―福徳岡の場2021年噴火および近年の類似例を通した試み
★招待講演
キーワード：福徳岡ノ場、軽石いかだ、海底火山
The 2021 eruption of Fukutoku-Oka-no-Ba demonstrated that the pumice rafts from underwater volcanic eruptions can be a major hazard to ship traffic, aquacultures, industrial plants, and harbour infrastructures. Despite satellites having detected the rafts 2 months earlier, nobody was prepared for the stranding of the pumice rafts. It was because we currently do not have a method to evaluate the level of threat from the pumice rafts. A major challenge especially lies in the estimation of their volume, which has never been determined reliably.
I analysed the geometries of the pumice rafts from Fukutoku-Oka-no-Ba (2021) and compared to the past raft-forming eruptions such as Havre (2012) and Volcano F (2019). The total sizes of the rafts continuously expanded over time in all eruptions, indicating the ubiquitous role of thickness for their spreading. The morphological change of some rafts over time shows the transition from a coherent raft to a raft with a lagoon inside that also supports the spreading process in the rafts. The spreading is believed to be driven by the buoyancy of pumices stacked in the water column, hence the spreading rate would be faster as the raft was thicker. The actual spreading rates of the rafts significantly vary between the eruptions and are consistent to the model. Further observations in the relationship between the raft thickness and their spreading rate enable us to calculate the volume of the pumice rafts in a few days after the eruption.
I analysed the geometries of the pumice rafts from Fukutoku-Oka-no-Ba (2021) and compared to the past raft-forming eruptions such as Havre (2012) and Volcano F (2019). The total sizes of the rafts continuously expanded over time in all eruptions, indicating the ubiquitous role of thickness for their spreading. The morphological change of some rafts over time shows the transition from a coherent raft to a raft with a lagoon inside that also supports the spreading process in the rafts. The spreading is believed to be driven by the buoyancy of pumices stacked in the water column, hence the spreading rate would be faster as the raft was thicker. The actual spreading rates of the rafts significantly vary between the eruptions and are consistent to the model. Further observations in the relationship between the raft thickness and their spreading rate enable us to calculate the volume of the pumice rafts in a few days after the eruption.