Influence of particle aggregation on the tephra dispersal and sedimentation from the October 8, 2016, eruption of Aso volcano
Abstract The phreatomagmatic eruption at Aso volcano on October 8, 2016, released PDC and fallout up to 320 km from the vent, providing an opportunity to study the dispersal and sedimentation of tephra bearing wet and dry aggregates. We investigated fresh air-fall tephra and conducted both dry- and...
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| Format: | Article |
| Language: | English |
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SpringerOpen
2020-07-01
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| Series: | Earth, Planets and Space |
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| Online Access: | http://link.springer.com/article/10.1186/s40623-020-01233-y |
| _version_ | 1818557818701086720 |
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| author | Tomohiro Tsuji Naoki Nishizaka Kozo Ohnishi |
| author_facet | Tomohiro Tsuji Naoki Nishizaka Kozo Ohnishi |
| author_sort | Tomohiro Tsuji |
| collection | DOAJ |
| description | Abstract The phreatomagmatic eruption at Aso volcano on October 8, 2016, released PDC and fallout up to 320 km from the vent, providing an opportunity to study the dispersal and sedimentation of tephra bearing wet and dry aggregates. We investigated fresh air-fall tephra and conducted both dry- and wet-sieving to assess the size distribution of both aggregate-bearing deposits on the ground and particles in the plume prior to aggregation. The tephra was asymmetrically distributed in the ENE direction, with a relatively wide distribution and small maximum grain sizes north of the depositional axis, reflecting different wind directions at each altitude. The secondary accumulation maxima at 4–8 km NE from the vent was characterized by the segregation of lapilli followed by accretionary pellets that were rapidly created by aggregation in the wet plume, thereby enhancing the removal of airborne ash. Coalesced aggregates possibly arose from salt precipitation processes. For dry aggregates fallen in medial-to-distal regions, observed deposition duration and fall velocity calculations concluded that fine ash was deposited not as individual particles but as aggregates. Most grain-size distributions along the dispersal axis based on the two sieving methods used were multimodal, with the coarser mode fining according to distance from the vent and the finer mode stabilizing at around 4ϕ; this is interpreted as resulting from the mixture of grain-size distributions with different origins, i.e., the normal settling of individual clasts and particle aggregation. The wet-sieved total grain-size distribution included 20.4 wt% fine ash compared with only 2.4 wt% fine ash in the dry-sieved distribution, suggesting that aggregated particles accounted for 18 wt% of the deposit. Total grain-size distributions based on wet-sieving showed extremely poor sorting that could be explained by the following causes: the release of coarse-grained ejecta originating from the host rock of the crater, fine particles due to fragmentation from a phreatomagmatic eruption, the supply of water and salt from the crater to the plume, and aggregation enhancement of the fine ash on the ground, reflecting the effect of the crater lake as external water source. |
| first_indexed | 2024-12-14T00:04:35Z |
| format | Article |
| id | doaj.art-35af06b957404461a5b86c319f40ffd4 |
| institution | Directory Open Access Journal |
| issn | 1880-5981 |
| language | English |
| last_indexed | 2024-12-14T00:04:35Z |
| publishDate | 2020-07-01 |
| publisher | SpringerOpen |
| record_format | Article |
| series | Earth, Planets and Space |
| spelling | doaj.art-35af06b957404461a5b86c319f40ffd42022-12-21T23:26:06ZengSpringerOpenEarth, Planets and Space1880-59812020-07-0172111910.1186/s40623-020-01233-yInfluence of particle aggregation on the tephra dispersal and sedimentation from the October 8, 2016, eruption of Aso volcanoTomohiro Tsuji0Naoki Nishizaka1Kozo Ohnishi2Graduate School of Sciences and Technology for Innovation, Yamaguchi UniversityShikoku Electric Power Co. LtdShikoku Electric Power Co. LtdAbstract The phreatomagmatic eruption at Aso volcano on October 8, 2016, released PDC and fallout up to 320 km from the vent, providing an opportunity to study the dispersal and sedimentation of tephra bearing wet and dry aggregates. We investigated fresh air-fall tephra and conducted both dry- and wet-sieving to assess the size distribution of both aggregate-bearing deposits on the ground and particles in the plume prior to aggregation. The tephra was asymmetrically distributed in the ENE direction, with a relatively wide distribution and small maximum grain sizes north of the depositional axis, reflecting different wind directions at each altitude. The secondary accumulation maxima at 4–8 km NE from the vent was characterized by the segregation of lapilli followed by accretionary pellets that were rapidly created by aggregation in the wet plume, thereby enhancing the removal of airborne ash. Coalesced aggregates possibly arose from salt precipitation processes. For dry aggregates fallen in medial-to-distal regions, observed deposition duration and fall velocity calculations concluded that fine ash was deposited not as individual particles but as aggregates. Most grain-size distributions along the dispersal axis based on the two sieving methods used were multimodal, with the coarser mode fining according to distance from the vent and the finer mode stabilizing at around 4ϕ; this is interpreted as resulting from the mixture of grain-size distributions with different origins, i.e., the normal settling of individual clasts and particle aggregation. The wet-sieved total grain-size distribution included 20.4 wt% fine ash compared with only 2.4 wt% fine ash in the dry-sieved distribution, suggesting that aggregated particles accounted for 18 wt% of the deposit. Total grain-size distributions based on wet-sieving showed extremely poor sorting that could be explained by the following causes: the release of coarse-grained ejecta originating from the host rock of the crater, fine particles due to fragmentation from a phreatomagmatic eruption, the supply of water and salt from the crater to the plume, and aggregation enhancement of the fine ash on the ground, reflecting the effect of the crater lake as external water source.http://link.springer.com/article/10.1186/s40623-020-01233-yTephra dispersalSedimentationGrain-size distributionAggregationPhreatomagmatic eruptionAso volcano |
| spellingShingle | Tomohiro Tsuji Naoki Nishizaka Kozo Ohnishi Influence of particle aggregation on the tephra dispersal and sedimentation from the October 8, 2016, eruption of Aso volcano Earth, Planets and Space Tephra dispersal Sedimentation Grain-size distribution Aggregation Phreatomagmatic eruption Aso volcano |
| title | Influence of particle aggregation on the tephra dispersal and sedimentation from the October 8, 2016, eruption of Aso volcano |
| title_full | Influence of particle aggregation on the tephra dispersal and sedimentation from the October 8, 2016, eruption of Aso volcano |
| title_fullStr | Influence of particle aggregation on the tephra dispersal and sedimentation from the October 8, 2016, eruption of Aso volcano |
| title_full_unstemmed | Influence of particle aggregation on the tephra dispersal and sedimentation from the October 8, 2016, eruption of Aso volcano |
| title_short | Influence of particle aggregation on the tephra dispersal and sedimentation from the October 8, 2016, eruption of Aso volcano |
| title_sort | influence of particle aggregation on the tephra dispersal and sedimentation from the october 8 2016 eruption of aso volcano |
| topic | Tephra dispersal Sedimentation Grain-size distribution Aggregation Phreatomagmatic eruption Aso volcano |
| url | http://link.springer.com/article/10.1186/s40623-020-01233-y |
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