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Volume 18, issue 2 | Copyright

Special issue: The use of remotely piloted aircraft systems (RPAS) in monitoring...

Nat. Hazards Earth Syst. Sci., 18, 429-444, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 07 Feb 2018

Research article | 07 Feb 2018

Characteristics of debris avalanche deposits inferred from source volume estimate and hummock morphology around Mt. Erciyes, central Turkey

Yuichi S. Hayakawa1, Hidetsugu Yoshida2, Hiroyuki Obanawa3, Ryutaro Naruhashi4, Koji Okumura5, Masumi Zaiki6, and Ryoichi Kontani7 Yuichi S. Hayakawa et al.
  • 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 avalanches caused by volcano sector collapse often form characteristic depositional landforms such as hummocks. Sedimentological and geomorphological analyses of debris avalanche deposits (DADs) are crucial to clarify the size, mechanisms, and emplacement of debris avalanches. We describe the morphology of hummocks on the northeastern 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 and multi-view stereo (SfM–MVS) photogrammetry, we obtained high-definition digital elevation model (DEM) and orthorectified images of the hummocks to investigate their geometric features. We estimated the source volume of the DAD by reconstructing the topography of the volcano edifice using a satellite-based DEM. We examined the topographic cross sections based on the slopes around the scar regarded as remnant topography. Spatial distribution of hummocks is anomalously concentrated at a certain distance from the source, unlike those that follow the distance–size relationship. The high-definition land surface data by RPAS and SfM revealed that many of the hummocks are aligned toward the flow direction of the debris avalanche, suggesting that the extensional regime of the debris avalanche was dominant. However, some displaced hummocks were also found, indicating that the compressional regime of the flow contributed to the formation of hummocks. These indicate that the flow and emplacement of the avalanche were constrained by the topography. The existing caldera wall forced the initial eastward flow to move northward, and the north-side caldera wall forced the flow into the narrow and steepened outlet valley where the sliding debris underwent a compressional regime, and out into the unconfined terrain where the debris was most likely emplaced on an extensional regime. Also, the estimated volume of 12–15×108m3 gives a mean thickness of 60–75m, which is much deeper than the reported cases of other DADs. This suggests that the debris avalanche must have flowed further downstream and beyond the current DAD extent. Assessments of the DAD incorporating the topographic constraints can provide further insights into the risk and mitigation of potential disasters in the study area.

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Short summary
This study assesses the applicability of the RPAS-based photogrammetric approach for a high-definition 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. 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...