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[SVC34-P18] Mineralogical Characteristics of Volcanic Ash during the 2019-2020 Eruptions of Aso Volcano
Aso Volcano erupted intermittently from July 2019 to June 2020, preceded by small eruptions on April 16, 2019, and from May 3 to May 5, 2019. The volcanic ash from these small eruptions consisted of altered minerals and rock fragments, indicating phreatomagmatic eruptions (Miyabuchi et al., 2020). Subsequently, from14th May tolate July the juvenile ash proportion increased, confirming that the eruptions transitioned into magmatic eruptions.
This study examines the mineralogical characteristics of volcanic ash during the transition from phreatomagmatic to magmatic eruptions and during magmatic eruptions. Mineral compositions were analyzed using XRD and SEM-EDS on volcanic ash samples collected between April 2019 and June 2020. Optical microscopy and SEM-EDS were also used to observe the texture of volcanic ash particles.
The volcanic ash from the eruption on April 16, 2019, isyellowish-white and primarily composed of spherical native sulfur particles smaller than 0.5 mm, with pyrite and alunite adhering to the sulfur particles. From April 17 to 20, the ash consists of yellowish-white or light gray rock fragments, with many plate- and pipe-shaped fragments. During the eruption from May 5 to 8, the volcanic ash is mainly composed of spherical aggregated ash particles (0.5 mm). Micro-sized calcium sulfate (less than 5 µm) ,silica and pyrite(about 30 µm) adhere on the surface of the particles.
The volcanic ash from June 24 to July 5 contains small amounts of black glass fragments and altered rock fragments in white to dark gray. From July 5 to 16, the ash contains fewer glass fragments compared to the earlier samples, but the majority is composed of yellowish-white altered rock fragments and spherical native sulfur particles around 0.5 mm. These samples increase the juvenile proportion and textures compared to the earlier eruptions, indicating a transition to magmatic eruptions.
From July 16 to May 1 of the following year, the volcanic ash showed slight changes in particle size, predominantly light gray to dark gray, with fine particles (<0.1 mm). These particles are mainly composed of black glass fragments, transparent glass fragments, and free crystals, with small amounts of altered rock fragments and aggregated volcanic ash.
These results indicate that the 2019–2020 eruptions of Aso Volcano initially expelled altered rock fragments and spherical sulfur particles from hydrothermal systems and the crater lake from April 16 to May 5. However, between July 5 and 16, as activity intensified, the eruptions began to expel volcanic ash containing magmatic fragments. From July 16 onward, a noticeable change in the composition of volcanic ash occurred, marking the transition to magmatic eruptions. The eruptions between July 5 and 16 suggest the involvement of hydrothermal processes or the expansion of the crater.
Future research will focus on more detailed mineralogical analyses and tracking temporal changes in volcanic activity to further clarify the evolving material composition and better understand the eruption systems at Aso Volcano.
This study examines the mineralogical characteristics of volcanic ash during the transition from phreatomagmatic to magmatic eruptions and during magmatic eruptions. Mineral compositions were analyzed using XRD and SEM-EDS on volcanic ash samples collected between April 2019 and June 2020. Optical microscopy and SEM-EDS were also used to observe the texture of volcanic ash particles.
The volcanic ash from the eruption on April 16, 2019, isyellowish-white and primarily composed of spherical native sulfur particles smaller than 0.5 mm, with pyrite and alunite adhering to the sulfur particles. From April 17 to 20, the ash consists of yellowish-white or light gray rock fragments, with many plate- and pipe-shaped fragments. During the eruption from May 5 to 8, the volcanic ash is mainly composed of spherical aggregated ash particles (0.5 mm). Micro-sized calcium sulfate (less than 5 µm) ,silica and pyrite(about 30 µm) adhere on the surface of the particles.
The volcanic ash from June 24 to July 5 contains small amounts of black glass fragments and altered rock fragments in white to dark gray. From July 5 to 16, the ash contains fewer glass fragments compared to the earlier samples, but the majority is composed of yellowish-white altered rock fragments and spherical native sulfur particles around 0.5 mm. These samples increase the juvenile proportion and textures compared to the earlier eruptions, indicating a transition to magmatic eruptions.
From July 16 to May 1 of the following year, the volcanic ash showed slight changes in particle size, predominantly light gray to dark gray, with fine particles (<0.1 mm). These particles are mainly composed of black glass fragments, transparent glass fragments, and free crystals, with small amounts of altered rock fragments and aggregated volcanic ash.
These results indicate that the 2019–2020 eruptions of Aso Volcano initially expelled altered rock fragments and spherical sulfur particles from hydrothermal systems and the crater lake from April 16 to May 5. However, between July 5 and 16, as activity intensified, the eruptions began to expel volcanic ash containing magmatic fragments. From July 16 onward, a noticeable change in the composition of volcanic ash occurred, marking the transition to magmatic eruptions. The eruptions between July 5 and 16 suggest the involvement of hydrothermal processes or the expansion of the crater.
Future research will focus on more detailed mineralogical analyses and tracking temporal changes in volcanic activity to further clarify the evolving material composition and better understand the eruption systems at Aso Volcano.