3:00 PM - 3:15 PM
[SVC32-06] Structural state of plagioclase in volcanic ash collected in response to the eruption of Sakurajima Volcano
Keywords:Sakurajima, volcanic ash, plagioclase, structural state
Volcanic ash is a mixture of pyroclastic materials from various stages of volcanic activity, and identifying the origin of magma and the time of crystal growth is widely recognized as an important theme in volcano research. Preliminary surveys to date have shown that the structural state of plagioclase contained in volcanic ash changes sensitively in response to volcanic activity (scale and number of eruptions, amount of ashfall, etc.), and that the structural state of plagioclase is a useful indicator for monitoring the progress of volcanic activity. In particular, it has been confirmed that plagioclase in volcanic ash erupted during periods of frequent eruptions tends to show a lower degree of order. However, through preliminary surveys, several issues have become clear in order to use the structural state of plagioclase contained in volcanic ash erupted from Sakurajima as an indicator for linking it to monitoring volcanic activity.
In this presentation, the author reports the results of an analysis of samples collected once a month by installing collection trays at elementary and junior high schools on Sakurajima Island and in Tarumizu City so as to surround Sakurajima, as an effort to ensure the amount of samples to be collected in response to volcanic eruptions.
As an example, the values of the site with the highest collection volume from November 2023 to October 2024 were compared with the values of the nearest ashfall observation site in Kagoshima Prefecture. The collection volumes of both sites were generally correlated, but at Kyowa Elementary School (Kaigata), the collection site for this survey collected more samples, and at Kurokami Elementary School (Kurokami) in July 2024, the collection site for this survey collected significantly more samples. In the future, the author plans to verify whether the collection volume corresponds to the amount of ashfall, including by referring to ashfall observations by weather radar.
The plagioclase crystals were isolated from the volcanic ash collected in response to the eruption, and powder X-ray diffraction data was measured. Volcanic ash should be considered while keeping in mind the magma from which it originated, the time of crystal growth, the effects of sorting in the atmosphere after eruption, and the compositional zoning structure within the same crystal (phenocryst), and it should be noted that the diffraction data obtained in powder X-ray diffraction experiments reflect the average structure of the crystal. In order to determine the structural state of plagioclase, the diffraction peaks that serve as indicators will be separated into multiple plagioclase peaks with different compositions and degrees of Al/Si order, and the heterogeneity of the samples will be discussed.
In the future, the author also plans to confirm whether the temporal changes in the crystal structure of plagioclase that accompany the rise and fall of volcanic activity are consistent with observation data based on geophysical methods.
In this presentation, the author reports the results of an analysis of samples collected once a month by installing collection trays at elementary and junior high schools on Sakurajima Island and in Tarumizu City so as to surround Sakurajima, as an effort to ensure the amount of samples to be collected in response to volcanic eruptions.
As an example, the values of the site with the highest collection volume from November 2023 to October 2024 were compared with the values of the nearest ashfall observation site in Kagoshima Prefecture. The collection volumes of both sites were generally correlated, but at Kyowa Elementary School (Kaigata), the collection site for this survey collected more samples, and at Kurokami Elementary School (Kurokami) in July 2024, the collection site for this survey collected significantly more samples. In the future, the author plans to verify whether the collection volume corresponds to the amount of ashfall, including by referring to ashfall observations by weather radar.
The plagioclase crystals were isolated from the volcanic ash collected in response to the eruption, and powder X-ray diffraction data was measured. Volcanic ash should be considered while keeping in mind the magma from which it originated, the time of crystal growth, the effects of sorting in the atmosphere after eruption, and the compositional zoning structure within the same crystal (phenocryst), and it should be noted that the diffraction data obtained in powder X-ray diffraction experiments reflect the average structure of the crystal. In order to determine the structural state of plagioclase, the diffraction peaks that serve as indicators will be separated into multiple plagioclase peaks with different compositions and degrees of Al/Si order, and the heterogeneity of the samples will be discussed.
In the future, the author also plans to confirm whether the temporal changes in the crystal structure of plagioclase that accompany the rise and fall of volcanic activity are consistent with observation data based on geophysical methods.