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Volume 17, issue 5 | Copyright
Nat. Hazards Earth Syst. Sci., 17, 749-764, 2017
https://doi.org/10.5194/nhess-17-749-2017
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 22 May 2017

Research article | 22 May 2017

Anomalous winter-snow-amplified earthquake-induced disaster of the 2015 Langtang avalanche in Nepal

Koji Fujita1, Hiroshi Inoue2, Takeki Izumi3, Satoru Yamaguchi4, Ayako Sadakane5, Sojiro Sunako1, Kouichi Nishimura1, Walter W. Immerzeel6,7, Joseph M. Shea7,8, Rijan B. Kayastha9, Takanobu Sawagaki10, David F. Breashears11, Hiroshi Yagi12, and Akiko Sakai1 Koji Fujita et al.
  • 1Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
  • 2Disaster Risk Research Unit, National Research Institute for Earth Science and Disaster Resilience, Tsukuba, Japan
  • 3Graduate School of Urban Environmental Sciences, Tokyo Metropolitan University, Hachioji, Japan
  • 4Snow and Ice Research Center, National Research Institute for Earth Science and Disaster Resilience, Nagaoka, Japan
  • 5Langtang Plan, Kamakura, Japan
  • 6Department of Physical Geography, Faculty of Geosciences, Utrecht University, Utrecht, the Netherlands
  • 7International Centre for Integrated Mountain Development, Khumaltar, Kathmandu, Nepal
  • 8Centre for Hydrology, University of Saskatchewan, Saskatoon, Canada
  • 9School of Science, Kathmandu University, Kathmandu, Nepal
  • 10Faculty of Social Sciences, Hosei University, Tokyo, Japan
  • 11GlacierWorks, Marblehead, MA, USA
  • 12Faculty of Education, Art and Science, Yamagata University, Yamagata, Japan

Abstract. Coseismic avalanches and rockfalls, as well as their simultaneous air blast and muddy flow, which were induced by the 2015 Gorkha earthquake in Nepal, destroyed the village of Langtang. In order to reveal volume and structure of the deposit covering the village, as well as sequence of the multiple events, we conducted an intensive in situ observation in October 2015. Multitemporal digital elevation models created from photographs taken by helicopter and unmanned aerial vehicles reveal that the deposit volumes of the primary and succeeding events were 6.81±1.54 × 106 and 0.84±0.92 × 106m3, respectively. Visual investigations of the deposit and witness statements of villagers suggest that the primary event was an avalanche composed mostly of snow, while the collapsed glacier ice could not be dominant source for the total mass. Succeeding events were multiple rockfalls which may have been triggered by aftershocks. From the initial deposit volume and the area of the upper catchment, we estimate an average snow depth of 1.82±0.46m in the source area. This is consistent with anomalously large snow depths (1.28–1.52m) observed at a neighboring glacier (4800–5100ma.s.l.), which accumulated over the course of four major snowfall events between October 2014 and the earthquake on 25 April 2015. Considering long-term observational data, probability density functions, and elevation gradients of precipitation, we conclude that this anomalous winter snow was an extreme event with a return interval of at least 100 years. The anomalous winter snowfall may have amplified the disastrous effects induced by the 2015 Gorkha earthquake in Nepal.

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We create multiple DEMs from photographs taken by helicopter and UAV and reveal the deposit volumes over the Langtang village, which was destroyed by avalanches induced by the Gorkha earthquake. Estimated snow depth in the source area is consistent with anomalously large snow depths observed at a neighboring glacier. Comparing with a long-term observational data, we conclude that this anomalous winter snow amplified the disaster induced by the 2015 Gorkha earthquake in Nepal.
We create multiple DEMs from photographs taken by helicopter and UAV and reveal the deposit...
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