1:45 PM - 3:15 PM
[O08-P11] Exploring pumice washed ashore in the Enshu Sea Ⅱ ~Comparison of white pumice and Kawagohira pumice~
Keywords:pumice, volcano, drifting ashore
1 Motivation and Purpose
"Earlier research revealed that the gray pumice obtained in 2021 in the Enshu Sea originated from Fukutoku Okanoba. The origin of the various white pumice collected in the Enshu Sea during the same period is not known. Therefore, this study will identify the origin of the white pumice by shape, mineral, and volcanic glass. Preliminary experiments compared the composition of colored minerals in the white pumice with those of Kawagodaira pumice, Aira Osumi pumice, Kozushima Tenjo-zan pumice, and Niijima Mukouyama pumice, which are candidates for the origin, and found that the type of colored minerals in the white pumice is similar to that of Kawagodaira pumice."
2 Hypothesis
"Kawagodaira volcano in eastern Shizuoka Prefecture erupted pumice in the past. The shape of pumice collected in July 2023 at the mouth of the Kano River, which is connected to Kawagodaira volcano, was similar to one of several types of white pumice collected in the Sea of Enshu. Therefore, we assume that the origin of this white pumice stone is Kawagodaira.
3 Methods
"White pumice collected from the Enshu Sea in February 2021 were classified into 11 types according to appearance, and those that were similar in appearance to Kawagodaira pumice were extracted (Enshu Sea pumice).
3-1 (Mineral composition)
Grain size ranged from 250 µm to 500 µm. Colorless minerals, colored minerals, and rock fragments were counted in the mineral composition, and colored minerals were counted in the colored mineral composition, with at least 200 grains counted.
3-2 (Shape of volcanic glass)
There are two types of volcanic glass: bubble type and pumice type (Machida and Arai). Using binocular stereomicroscopes, the shapes of volcanic glass in samples with grain sizes ranging from 250 μm to 500 μm were observed.
3-3 (Refractive index of volcanic glass)
The refractive indices of volcanic glass contained in samples with grain diameters of 63 μm to 125 μm were measured using a refractive index measuring device.
4 Results and Discussion
4-1 Results of mineral composition
The percentage of volcanic glass was high in all the samples. Enshu Nada pumice, Kano River pumice, and Kawagodaira pumice A were similar.
In the colored mineral compositions, the types of minerals contained were similar, although the proportions differed. Both Enshu Nada and Kano River pumice contained opaque minerals such as orthopyroxene, hornblende, and magnetite.
Kawagodaira pumice A and Kawagodaira pumice B contained small amounts of monoclinopyroxene. The types of minerals contained in the Enshu pumice were similar to those documented for the Kawagodaira pumice by Masujima.
4-2 Shape of Volcanic Glass
All were pumice-type.
(The shape of volcanic glass varies depending on the magma, indicating that they originated from similar types of magma.)
4-3 Measurement of refractive indices of volcanic glasses
The peak refractive indices of each volcanic glass were 1.497-1.498 for Enshu Nada pumice, 1.497-1.499 for Kano River pumice, 1.496-1.497 for Kawagodaira pumice A, and 1.497-1.498 for Kawagodaira pumice B.
4-4 Discussion
The minerals contained in both Enshu Nada Pumice and Kano River Pumice are similar to those of Kawago Plain Pumice A and Kawago Plain Pumice B. The shapes of the volcanic glass contained in the pumice are also similar to those of Kawago Plain Pumice A and B. The shape of the volcanic glass was also similar to that of the Kawagohira pumice A and Kawagohira pumice B. The refractive indices of the volcanic glass were similar to those of Kawagodaira pumice A and Kawagodaira pumice B, and were within the range of values described in the literature.
Therefore, it is highly probable that the white pumice that drifted to the Sea of Enshu and the pumice at the mouth of the Kano River both originated from the Kawagodaira volcano.
5 Reflections and issues
We would like to conduct more detailed surveys in the future to further improve the accuracy of the results of this study. We would also like to determine the origin of other white pumice that drifted ashore in the Sea of Enshu.
6 Acknowledgments and References
We would like to thank Dr. Akira Aoshima, visiting professor at the Fujinokuni Museum of Global Environmental History, and the members of the Earth Science Club of Iwata Minami High School in Shizuoka Prefecture for their cooperation in this research.
[1]Utsunomiya Oar, Mabuchi Ayaka, Yoshida Wakana, 2022, Exploration of drifted pumice in the Sea of Enshu: Comparison with Fukutoku Okanoba pumice, Japan.
[2]Machida, H. and F. Arai, 1992, New Atlas of Volcanic Ash, University of Tokyo Press, 111, 129, 135.
[3]Masujima, J., 2010, Sources of hornblende with volcanic glass in pottery clay, Shizuoka Earth Science, 101, 15-28.
"Earlier research revealed that the gray pumice obtained in 2021 in the Enshu Sea originated from Fukutoku Okanoba. The origin of the various white pumice collected in the Enshu Sea during the same period is not known. Therefore, this study will identify the origin of the white pumice by shape, mineral, and volcanic glass. Preliminary experiments compared the composition of colored minerals in the white pumice with those of Kawagodaira pumice, Aira Osumi pumice, Kozushima Tenjo-zan pumice, and Niijima Mukouyama pumice, which are candidates for the origin, and found that the type of colored minerals in the white pumice is similar to that of Kawagodaira pumice."
2 Hypothesis
"Kawagodaira volcano in eastern Shizuoka Prefecture erupted pumice in the past. The shape of pumice collected in July 2023 at the mouth of the Kano River, which is connected to Kawagodaira volcano, was similar to one of several types of white pumice collected in the Sea of Enshu. Therefore, we assume that the origin of this white pumice stone is Kawagodaira.
3 Methods
"White pumice collected from the Enshu Sea in February 2021 were classified into 11 types according to appearance, and those that were similar in appearance to Kawagodaira pumice were extracted (Enshu Sea pumice).
3-1 (Mineral composition)
Grain size ranged from 250 µm to 500 µm. Colorless minerals, colored minerals, and rock fragments were counted in the mineral composition, and colored minerals were counted in the colored mineral composition, with at least 200 grains counted.
3-2 (Shape of volcanic glass)
There are two types of volcanic glass: bubble type and pumice type (Machida and Arai). Using binocular stereomicroscopes, the shapes of volcanic glass in samples with grain sizes ranging from 250 μm to 500 μm were observed.
3-3 (Refractive index of volcanic glass)
The refractive indices of volcanic glass contained in samples with grain diameters of 63 μm to 125 μm were measured using a refractive index measuring device.
4 Results and Discussion
4-1 Results of mineral composition
The percentage of volcanic glass was high in all the samples. Enshu Nada pumice, Kano River pumice, and Kawagodaira pumice A were similar.
In the colored mineral compositions, the types of minerals contained were similar, although the proportions differed. Both Enshu Nada and Kano River pumice contained opaque minerals such as orthopyroxene, hornblende, and magnetite.
Kawagodaira pumice A and Kawagodaira pumice B contained small amounts of monoclinopyroxene. The types of minerals contained in the Enshu pumice were similar to those documented for the Kawagodaira pumice by Masujima.
4-2 Shape of Volcanic Glass
All were pumice-type.
(The shape of volcanic glass varies depending on the magma, indicating that they originated from similar types of magma.)
4-3 Measurement of refractive indices of volcanic glasses
The peak refractive indices of each volcanic glass were 1.497-1.498 for Enshu Nada pumice, 1.497-1.499 for Kano River pumice, 1.496-1.497 for Kawagodaira pumice A, and 1.497-1.498 for Kawagodaira pumice B.
4-4 Discussion
The minerals contained in both Enshu Nada Pumice and Kano River Pumice are similar to those of Kawago Plain Pumice A and Kawago Plain Pumice B. The shapes of the volcanic glass contained in the pumice are also similar to those of Kawago Plain Pumice A and B. The shape of the volcanic glass was also similar to that of the Kawagohira pumice A and Kawagohira pumice B. The refractive indices of the volcanic glass were similar to those of Kawagodaira pumice A and Kawagodaira pumice B, and were within the range of values described in the literature.
Therefore, it is highly probable that the white pumice that drifted to the Sea of Enshu and the pumice at the mouth of the Kano River both originated from the Kawagodaira volcano.
5 Reflections and issues
We would like to conduct more detailed surveys in the future to further improve the accuracy of the results of this study. We would also like to determine the origin of other white pumice that drifted ashore in the Sea of Enshu.
6 Acknowledgments and References
We would like to thank Dr. Akira Aoshima, visiting professor at the Fujinokuni Museum of Global Environmental History, and the members of the Earth Science Club of Iwata Minami High School in Shizuoka Prefecture for their cooperation in this research.
[1]Utsunomiya Oar, Mabuchi Ayaka, Yoshida Wakana, 2022, Exploration of drifted pumice in the Sea of Enshu: Comparison with Fukutoku Okanoba pumice, Japan.
[2]Machida, H. and F. Arai, 1992, New Atlas of Volcanic Ash, University of Tokyo Press, 111, 129, 135.
[3]Masujima, J., 2010, Sources of hornblende with volcanic glass in pottery clay, Shizuoka Earth Science, 101, 15-28.