Abstract:The 2021 eruption of Fukutoku-Oka-no-Ba (FOB) in the northwest Pacific on 13 August 2021 produced a large volume of pumice that drifted westward for ~1300 km to the Nansei Islands, Japan, and some extent. In February 2022, pumice with similar characteristics to the FOB pumice was deposited along the Gulf of Thailand. The pumice clasts deposited in Songkhla Province, Thailand, were fine-grained with <4 cm in size and rounded. Most of the clasts consisted of clinopyroxene, plagioclase (andesine), and olivine phe… Show more
“…For example, two types of olivine are observed in the FOB pumice: one relatively Fe-rich (Mg# = molar Mg/[Mg + Fe] ~ 65) without compositional zonation and one with a high-Mg (Mg# ~ 90) plateau and decreasing Mg contents toward the rims 18 . The latter type of olivine is observed in or closely associated with the black pumice 18 , 20 . Figure 1 ( a ) Photomicrograph of the boundary between the black pumice (brown glass) and gray pumice (colorless glass).…”
Section: Resultsmentioning
confidence: 94%
“…Visible microlites have not been identified in the gray pumice, whereas the black pumice contains rare clinopyroxene and olivine microlites 18 . The black pumice occurs either as individual clasts or mingled with the gray pumice 18 , 20 .…”
Section: Resultsmentioning
confidence: 99%
“…1 c). Phenocryst mineral assemblages are similar in both pumice types (clinopyroxene, plagioclase, and minor magnetite and olivine), and most minerals have similar compositions, except for those that likely originated in a mafic magma 18 , 20 . For example, two types of olivine are observed in the FOB pumice: one relatively Fe-rich (Mg# = molar Mg/[Mg + Fe] ~ 65) without compositional zonation and one with a high-Mg (Mg# ~ 90) plateau and decreasing Mg contents toward the rims 18 .…”
Section: Resultsmentioning
confidence: 99%
“…The eruption produced a large pumice raft, mainly consisting of gray-colored pumice, which was carried westward by ocean currents for > 1000 km 18 , 19 . The pumice raft arrived first on the Pacific coasts of the Japanese islands and subsequently traveled west for a total of > 5000 km, arriving in the Gulf of Thailand 20 . Large amounts of floating pumice can damage coastal ecosystems and impact the economy 16 , 18 , 21 .…”
Nanometer-sized crystals (nanolites) play an important role in controlling eruptions by affecting the viscosity of magmas and inducing bubble nucleation. We present detailed microscopic and nanoscopic petrographic analyses of nanolite-bearing and nanolite-free pumice from the 2021 eruption of Fukutoku-Oka-no-Ba, Japan. The nanolite mineral assemblage includes biotite, which is absent from the phenocryst mineral assemblage, and magnetite and clinopyroxene, which are observed as phenocrysts. The boundary between the nanolite-bearing brown glass and nanolite-free colorless glass is either sharp or gradational, and the sharp boundaries also appear sharp under the transmitted electron microscope. X-ray absorption fine structure (XAFS) analysis of the volcanic glass revealed that the nanolite-free colorless glass records an oxygen fugacity of QFM + 0.98 (log units), whereas the nanolite-bearing brown glass records a higher apparent oxygen fugacity (~ QFM + 2). Thermodynamic modelling using MELTS indicates that higher oxygen fugacities increase the liquidus temperature and thus induced the crystallization of magnetite nanolites. The hydrous nanolite mineral assemblage and glass oxygen fugacity estimates suggest that an oxidizing fluid supplied by a hot mafic magma induced nanolite crystallization in the magma reservoir, before the magma fragmentation. The oxidation-induced nanolite crystallization then enhanced heterogeneous bubble nucleation, resulting in convection in the magma reservoir and triggering the eruption.
“…For example, two types of olivine are observed in the FOB pumice: one relatively Fe-rich (Mg# = molar Mg/[Mg + Fe] ~ 65) without compositional zonation and one with a high-Mg (Mg# ~ 90) plateau and decreasing Mg contents toward the rims 18 . The latter type of olivine is observed in or closely associated with the black pumice 18 , 20 . Figure 1 ( a ) Photomicrograph of the boundary between the black pumice (brown glass) and gray pumice (colorless glass).…”
Section: Resultsmentioning
confidence: 94%
“…Visible microlites have not been identified in the gray pumice, whereas the black pumice contains rare clinopyroxene and olivine microlites 18 . The black pumice occurs either as individual clasts or mingled with the gray pumice 18 , 20 .…”
Section: Resultsmentioning
confidence: 99%
“…1 c). Phenocryst mineral assemblages are similar in both pumice types (clinopyroxene, plagioclase, and minor magnetite and olivine), and most minerals have similar compositions, except for those that likely originated in a mafic magma 18 , 20 . For example, two types of olivine are observed in the FOB pumice: one relatively Fe-rich (Mg# = molar Mg/[Mg + Fe] ~ 65) without compositional zonation and one with a high-Mg (Mg# ~ 90) plateau and decreasing Mg contents toward the rims 18 .…”
Section: Resultsmentioning
confidence: 99%
“…The eruption produced a large pumice raft, mainly consisting of gray-colored pumice, which was carried westward by ocean currents for > 1000 km 18 , 19 . The pumice raft arrived first on the Pacific coasts of the Japanese islands and subsequently traveled west for a total of > 5000 km, arriving in the Gulf of Thailand 20 . Large amounts of floating pumice can damage coastal ecosystems and impact the economy 16 , 18 , 21 .…”
Nanometer-sized crystals (nanolites) play an important role in controlling eruptions by affecting the viscosity of magmas and inducing bubble nucleation. We present detailed microscopic and nanoscopic petrographic analyses of nanolite-bearing and nanolite-free pumice from the 2021 eruption of Fukutoku-Oka-no-Ba, Japan. The nanolite mineral assemblage includes biotite, which is absent from the phenocryst mineral assemblage, and magnetite and clinopyroxene, which are observed as phenocrysts. The boundary between the nanolite-bearing brown glass and nanolite-free colorless glass is either sharp or gradational, and the sharp boundaries also appear sharp under the transmitted electron microscope. X-ray absorption fine structure (XAFS) analysis of the volcanic glass revealed that the nanolite-free colorless glass records an oxygen fugacity of QFM + 0.98 (log units), whereas the nanolite-bearing brown glass records a higher apparent oxygen fugacity (~ QFM + 2). Thermodynamic modelling using MELTS indicates that higher oxygen fugacities increase the liquidus temperature and thus induced the crystallization of magnetite nanolites. The hydrous nanolite mineral assemblage and glass oxygen fugacity estimates suggest that an oxidizing fluid supplied by a hot mafic magma induced nanolite crystallization in the magma reservoir, before the magma fragmentation. The oxidation-induced nanolite crystallization then enhanced heterogeneous bubble nucleation, resulting in convection in the magma reservoir and triggering the eruption.
“…On 13-15 August 2021, there was an explosive phreatomagmatic eruption at the volcano that produced a large pumice raft that was carried westward by ocean currents for > 1000 km (Maeno et al, 2022;Metz, 2022;Yoshida et al, 2022a). The pumice raft arrived rst on the Paci c coasts of the Japanese islands and subsequently traveled west for > 5000 km, arriving in the Gulf of Thailand (Yoshida et al, 2022b We performed a comprehensive study of the nanolite-bearing glass in the FOB pumice, including TEM analysis, Fe K-edge XANES (X-ray absorption near edge structure) microanalysis, and thermodynamic modelling. The investigated sample (AYA-2) contains a clear boundary between the gray and black pumice and was collected from the northeastern coast of Amami Ōshima (28°28.4′N, 129°42.9′E) on October 18th, 2021 (Supplementary Fig.…”
Nanometer-sized crystals (nanolites) play an important role in controlling eruptions by affecting the viscosity of magmas and inducing bubble nucleation. We present detailed microscopic and nanoscopic petrographic analyses of nanolite-bearing and nanolite-free pumice from the 2021 eruption of Fukutoku-Oka-no-Ba, Japan. The nanolite mineral assemblage includes biotite, which is absent from the phenocryst mineral assemblage, and magnetite and clinopyroxene, which are observed as phenocrysts. The boundary between the nanolite-bearing brown glass and nanolite-free colorless glass is either sharp or gradational, and the sharp boundaries also appear sharp under the transmitted electron microscope. X-ray absorption fine structure (XAFS) analysis of the volcanic glass revealed that the nanolite-free colorless glass records an oxygen fugacity of QFM + 0.98 (log units), whereas the nanolite-bearing brown glass records a higher oxygen fugacity (~ QFM + 2). Thermodynamic modelling using MELTS indicates that higher oxygen fugacities increase the liquidus temperature and thus induced the crystallization of magnetite nanolites. The hydrous nanolite mineral assemblage and glass oxygen fugacity estimates suggest that an oxidizing fluid supplied by a hot mafic magma induced nanolite crystallization in the magma reservoir. The oxidation-induced nanolite crystallization then enhanced heterogeneous bubble nucleation, resulting in convection in the magma reservoir and triggering the eruption.
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