1:45 PM - 3:15 PM
[O06-P07] Exploration of Drifted Pumice in the Sea of Enshu: Comparison with Pumice from Fukutoku-Oka-no-Ba
Keywords:drifted pumice, Fukutoku-Oka-no-Ba, the Sea of Enshu
Fukutoku-Oka-no-Ba volcano in the Ogasawara Islands erupted on August 13-15, 2021, spewing a large amount of pumice. It is known that the pumice stone drifted to various places including Okinawa, but it is unknown if it drifted to the coast of the Sea of Enshu from Irako Cape in Aichi Prefecture to Omaezaki in Shizuoka Prefecture. Therefore, the purpose of this study is to elucidate the timing, origin, and characteristics of pumice stone drifting in the Enshu Sea, and finally to clarify the process of drifting and drifting of pumice stones.
First, pumice were collected from the Enshu Sea in December 2021, March and May 2022. The pumice collected from the Enshu Sea and pumice from Okinawa, which is Fukutoku-Oka-no-Ba pumice, were chemically analyzed and compared with the chemical composition of Fukutoku-Oka-no-Ba pumice (Yoshida et al,2022). Pumice that were found not to originate from Fukutoku-Oka-no-Ba were analyzed for mineralogy to determine their origin. The shape, grain size, circularity, type, and density of pumice from the Enshu Sea and Okinawa were also compared.
The results showed that only white pumice was found in the December 2021 and March 2022 surveys, but both white pumice and gray pumice were found in May 2022. The chemical composition of the gray pumice among the drifted pumice from the Sea of Enshu is consistent with that of the Fukutoku-Oka-no-Ba pumice. On the other hand, white porous pumice shows different chemical composition from Fukutoko-Oka-no-Ba pumice, and mineral analysis results show that some of them are consistent with Kawagodaira pumice, Kozuzima Tenjozan tephra, Niijima Mukouyama tephra, and Osumi descending pumice. Furthermore, the gray pumice from the Enshu Sea has a smaller shape dispersion and grain size and a larger circularity than the pumice from Okinawa, while the white porphyry pumice varied in shape, grain size, and circularity. The Fukutoku-Oka-no-Ba pumice was classified into two types, and there was little difference between the Okinawa and Enshu Nada gray pumice in terms of type proportions, while the density of the Enshu Nada gray pumice was greater than that of the Fukutoku-Oka-no-Ba pumice in Okinawa.
The gray pumice from the Enshu Sea that drifted from March to May 2022 is considered to be Fukutoku-Oka-no-Ba pumice, which is considered to have been eroded. White porous pumice that drifted to the Enshu Sea before December 2021 are likely to be Kawagodaira pumice, Kozushima Tenjozan tephra, Niijima Mukaiyama tephra, and Osumi fall pumice, and are considered to have been weathered and eroded for a long period of time.
In the future, the origin of the white porous pumice that could not be determined in this study will be identified, and the drifting and drifting process of the drifted pumice will be clarified.
First, pumice were collected from the Enshu Sea in December 2021, March and May 2022. The pumice collected from the Enshu Sea and pumice from Okinawa, which is Fukutoku-Oka-no-Ba pumice, were chemically analyzed and compared with the chemical composition of Fukutoku-Oka-no-Ba pumice (Yoshida et al,2022). Pumice that were found not to originate from Fukutoku-Oka-no-Ba were analyzed for mineralogy to determine their origin. The shape, grain size, circularity, type, and density of pumice from the Enshu Sea and Okinawa were also compared.
The results showed that only white pumice was found in the December 2021 and March 2022 surveys, but both white pumice and gray pumice were found in May 2022. The chemical composition of the gray pumice among the drifted pumice from the Sea of Enshu is consistent with that of the Fukutoku-Oka-no-Ba pumice. On the other hand, white porous pumice shows different chemical composition from Fukutoko-Oka-no-Ba pumice, and mineral analysis results show that some of them are consistent with Kawagodaira pumice, Kozuzima Tenjozan tephra, Niijima Mukouyama tephra, and Osumi descending pumice. Furthermore, the gray pumice from the Enshu Sea has a smaller shape dispersion and grain size and a larger circularity than the pumice from Okinawa, while the white porphyry pumice varied in shape, grain size, and circularity. The Fukutoku-Oka-no-Ba pumice was classified into two types, and there was little difference between the Okinawa and Enshu Nada gray pumice in terms of type proportions, while the density of the Enshu Nada gray pumice was greater than that of the Fukutoku-Oka-no-Ba pumice in Okinawa.
The gray pumice from the Enshu Sea that drifted from March to May 2022 is considered to be Fukutoku-Oka-no-Ba pumice, which is considered to have been eroded. White porous pumice that drifted to the Enshu Sea before December 2021 are likely to be Kawagodaira pumice, Kozushima Tenjozan tephra, Niijima Mukaiyama tephra, and Osumi fall pumice, and are considered to have been weathered and eroded for a long period of time.
In the future, the origin of the white porous pumice that could not be determined in this study will be identified, and the drifting and drifting process of the drifted pumice will be clarified.