Twenty-Five Years of Geomorphological Evolution in the Gokurakudani Gully (Unzen Volcano): Topography, Subsurface Geophysics and Sediment Analysis

In the aftermath of pyroclastic density current-dominated eruptions, lahars are the main geomorphic agent, but at the decadal scale, different sets of processes take place in the volcanic sediment cascade. At Unzen volcano, in the Gokurakudani gully, we investigated the geomorphologic evolution and...

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Autores principales:	Christopher Gomez, Yoshinori Shinohara, Haruka Tsunetaka, Norifumi Hotta, Balazs Bradak, Yuichi Sakai
Formato:	article
Lenguaje:	EN
Publicado:	MDPI AG 2021
Materias:	Unzen volcano lahars erosion entropy lidar photogrammetry Geology QE1-996.5
Acceso en línea:	https://doaj.org/article/8a8bae41fa3f498c91c413aa50eaef8a
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spelling	oai:doaj.org-article:8a8bae41fa3f498c91c413aa50eaef8a2021-11-25T17:42:57ZTwenty-Five Years of Geomorphological Evolution in the Gokurakudani Gully (Unzen Volcano): Topography, Subsurface Geophysics and Sediment Analysis10.3390/geosciences111104572076-3263https://doaj.org/article/8a8bae41fa3f498c91c413aa50eaef8a2021-11-01T00:00:00Zhttps://www.mdpi.com/2076-3263/11/11/457https://doaj.org/toc/2076-3263In the aftermath of pyroclastic density current-dominated eruptions, lahars are the main geomorphic agent, but at the decadal scale, different sets of processes take place in the volcanic sediment cascade. At Unzen volcano, in the Gokurakudani gully, we investigated the geomorphologic evolution and how the topographic change and the sediment change over time is controlling this transition. For this purpose, a combination of LiDAR data, aerial photography and photogrammetry, ground penetrating radar and sediment grain size analysis was done. The results show choking zones and zones of enlargement of the gully, partly controlled by pre-eruption topography, but also by the overlapping patterns of the pyroclastic flow deposits of 1990–1995. The ground penetrating radar revealed that on top of the typical lahar structure at the bottom of the gully, side wall collapses were trapping finer sandy sediments formed in a relatively low-energy deposition environment. This shows that secondary processes are taking place in the sediment transport process, on top of lahar activity, but also that these temporary dams may be a source of sudden sediment and water release, leading to lahars. Finally, the sediments from the gully walls are being preferentially oozed out of the pyroclastic flow deposit, meaning that over longer period of time, there may be a lack of fines, increasing permeability and reducing internal pore pressure needed for lahar triggering. It also poses the important question of how much of a past event one can understand from outcrops in coarse heterometric material, as the deposit structure can remain, even after losing part of its fine material.Christopher GomezYoshinori ShinoharaHaruka TsunetakaNorifumi HottaBalazs BradakYuichi SakaiMDPI AGarticleUnzen volcanolaharserosionentropylidarphotogrammetryGeologyQE1-996.5ENGeosciences, Vol 11, Iss 457, p 457 (2021)
institution	DOAJ
collection	DOAJ
language	EN
topic	Unzen volcano lahars erosion entropy lidar photogrammetry Geology QE1-996.5
spellingShingle	Unzen volcano lahars erosion entropy lidar photogrammetry Geology QE1-996.5 Christopher Gomez Yoshinori Shinohara Haruka Tsunetaka Norifumi Hotta Balazs Bradak Yuichi Sakai Twenty-Five Years of Geomorphological Evolution in the Gokurakudani Gully (Unzen Volcano): Topography, Subsurface Geophysics and Sediment Analysis
description	In the aftermath of pyroclastic density current-dominated eruptions, lahars are the main geomorphic agent, but at the decadal scale, different sets of processes take place in the volcanic sediment cascade. At Unzen volcano, in the Gokurakudani gully, we investigated the geomorphologic evolution and how the topographic change and the sediment change over time is controlling this transition. For this purpose, a combination of LiDAR data, aerial photography and photogrammetry, ground penetrating radar and sediment grain size analysis was done. The results show choking zones and zones of enlargement of the gully, partly controlled by pre-eruption topography, but also by the overlapping patterns of the pyroclastic flow deposits of 1990–1995. The ground penetrating radar revealed that on top of the typical lahar structure at the bottom of the gully, side wall collapses were trapping finer sandy sediments formed in a relatively low-energy deposition environment. This shows that secondary processes are taking place in the sediment transport process, on top of lahar activity, but also that these temporary dams may be a source of sudden sediment and water release, leading to lahars. Finally, the sediments from the gully walls are being preferentially oozed out of the pyroclastic flow deposit, meaning that over longer period of time, there may be a lack of fines, increasing permeability and reducing internal pore pressure needed for lahar triggering. It also poses the important question of how much of a past event one can understand from outcrops in coarse heterometric material, as the deposit structure can remain, even after losing part of its fine material.
format	article
author	Christopher Gomez Yoshinori Shinohara Haruka Tsunetaka Norifumi Hotta Balazs Bradak Yuichi Sakai
author_facet	Christopher Gomez Yoshinori Shinohara Haruka Tsunetaka Norifumi Hotta Balazs Bradak Yuichi Sakai
author_sort	Christopher Gomez
title	Twenty-Five Years of Geomorphological Evolution in the Gokurakudani Gully (Unzen Volcano): Topography, Subsurface Geophysics and Sediment Analysis
title_short	Twenty-Five Years of Geomorphological Evolution in the Gokurakudani Gully (Unzen Volcano): Topography, Subsurface Geophysics and Sediment Analysis
title_full	Twenty-Five Years of Geomorphological Evolution in the Gokurakudani Gully (Unzen Volcano): Topography, Subsurface Geophysics and Sediment Analysis
title_fullStr	Twenty-Five Years of Geomorphological Evolution in the Gokurakudani Gully (Unzen Volcano): Topography, Subsurface Geophysics and Sediment Analysis
title_full_unstemmed	Twenty-Five Years of Geomorphological Evolution in the Gokurakudani Gully (Unzen Volcano): Topography, Subsurface Geophysics and Sediment Analysis
title_sort	twenty-five years of geomorphological evolution in the gokurakudani gully (unzen volcano): topography, subsurface geophysics and sediment analysis
publisher	MDPI AG
publishDate	2021
url	https://doaj.org/article/8a8bae41fa3f498c91c413aa50eaef8a
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Twenty-Five Years of Geomorphological Evolution in the Gokurakudani Gully (Unzen Volcano): Topography, Subsurface Geophysics and Sediment Analysis

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