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Natural Hazards and Earth System Sciences An interactive open-access journal of the European Geosciences Union
https://doi.org/10.5194/nhess-2017-110
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
23 Mar 2017
Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Natural Hazards and Earth System Sciences (NHESS).
Morphological analysis of hummocks in debris avalanche deposits around Mt Erciyes, central Turkey
Yuichi S. Hayakawa1, Hidetsugu Yoshida2, Hiroyuki Obanawa3, Ryutaro Naruhashi4, Koji Okumura5, Masumi Zaiki6, and Ryoichi Kontani7 1Center for Spatial Information Science, The University of Tokyo, Kashiwa, 277-8568, Japan
2School of Arts and Letters, Meiji University, Tokyo, 101-8301, Japan
3VisionTech Inc., Tsukuba, 305-0045, Japan
4Earthquake Research Institute, The University of Tokyo, Tokyo, 113-0032, Japan
5Department of Geography, Graduate School of Letters, Hiroshima University, Hiroshima, 739-852, Japan
6Department of Economics and Business, Faculty of Economics, Seikei University, Tokyo, 180-8633, Japan
7Department of Contemporary Sociological Studies, Faculty of Literature, Notre Dame Seishin University, Okayama, 700-8516, Japan
Abstract. Debris avalanche caused by the sector collapse of a volcanic mountain often forms characteristic depositional landforms including hummocks. Not only sedimentological but also geomorphological analyses of debris avalanche deposits (DAD) are crucial to clarify the size, mechanisms, and processes of the debris avalanche. We investigate the morphology of hummocks newly identified in the DAD at the north-eastern flank of Mt. Erciyes in Kayseri, central Turkey, likely formed in the late Pleistocene. Using a remotely piloted aircraft system (RPAS) and the structure-from-motion multi-view stereo photogrammetry (SfM), we obtained high-definition digital elevation model (DEM) and orthorectified image of the DAD surface with hummocks. Detailed geometric features of the hummocks are investigated using the RPAS-derived high-definition DEM. The source volume of the DAD was also estimated by reconstructing the original shape of the mountain body using a lower-resolution satellite-based DEM. For this, topographic cross sections are examined based on the slopes around the scar that are regarded as the remnant topography preserved since the sector collapse. The spatial distribution of hummocks shows an unusual pattern regarding the distance-size relationships, i.e., anomalously concentrated in a certain distance from the source. The hummocks are found to be aligned toward the flow direction of the debris avalanche, suggesting the extensional regime of the debris avalanche. These facts indicate that this debris avalanche did not follow the typical flow type of debris avalanches observed in the other cases. Instead, the topographic constraints by former caldera wall and fault-induced lineaments could have strongly affected the flow course and pattern in this particular case: The pre-existing caldera wall topography could have acted as the topographic barriers for the debris avalanche to force the initial flow to turn northward, and the flow regime to be once compressional followed by extensional at the narrow and steepened outlet valley. Also, the estimated volume of the DAD 12–15 × 108 m3 gives its mean thickness of 60–75 m, which is much deeper than the reported cases of other DADs. This suggests that the debris avalanche could have flown down to the far downstream areas from the presently-observed limit of the DAD extent. Assessments of the DAD including the results of this study can provide further insights into the risk and mitigation of potential disasters in the study area.

Citation: Hayakawa, Y. S., Yoshida, H., Obanawa, H., Naruhashi, R., Okumura, K., Zaiki, M., and Kontani, R.: Morphological analysis of hummocks in debris avalanche deposits around Mt Erciyes, central Turkey, Nat. Hazards Earth Syst. Sci. Discuss., https://doi.org/10.5194/nhess-2017-110, in review, 2017.
Yuichi S. Hayakawa et al.
Yuichi S. Hayakawa et al.
Yuichi S. Hayakawa et al.

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Short summary
This study assesses the applicability of the RPAS-based photogrammetric approach for a high-resolution geomorphometry of hummocks, i.e., characteristic morphological features in the surface of debris avalanche deposits caused by a gigantic sector collapse of a volcanic mountain body. A satellite-based topographic data were also utilized to estimate the source volume of the sector collapse. We provide new, detailed insights into the characteristics of the debris avalanche and potential hazards.
This study assesses the applicability of the RPAS-based photogrammetric approach for a...
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