Multiple remote-sensing assessment of the catastrophic collapse in Langtang Valley induced by the 2015 Gorkha earthquake

Hiroto Nagai, Manabu Watanabe, Naoya Tomii, Takeo Tadono, Shinichi Suzuki

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

The main shock of the 2015 Gorkha Earthquake in Nepal induced numerous avalanches, rockfalls, and landslides in Himalayan mountain regions. A major village in the Langtang Valley was destroyed and numerous people were victims of a catastrophic avalanche event, which consisted of snow, ice, rock, and blast wind. Understanding the hazard process mainly depends on limited witness accounts, interviews, and an in situ survey after a monsoon season. To record the immediate situation and to understand the deposition process, we performed an assessment by means of satellite-based observations carried out no later than 2 weeks after the event. The avalanche-induced sediment deposition was delineated with the calculation of decreasing coherence and visual interpretation of amplitude images acquired from the Phased Array-type L-band Synthetic Aperture Radar-2 (PALSAR-2). These outline areas are highly consistent with that delineated from a high-resolution optical image of WorldView-3 (WV-3). The delineated sediment areas were estimated as 0.63 km2 (PALSAR-2 coherence calculation), 0.73 km2 (PALSAR-2 visual interpretation), and 0.88 km2 (WV-3). In the WV-3 image, surface features were classified into 10 groups. Our analysis suggests that the avalanche event contained a sequence of (1) a fast splashing body with an air blast, (2) a huge, flowing muddy mass, (3) less mass flowing from another source, (4) a smaller amount of splashing and flowing mass, and (5) splashing mass without flowing on the east and west sides. By means of satellite-derived pre- and post-event digital surface models, differences in the surface altitudes of the collapse events estimated the total volume of the sediments as 5.51 ± 0.09 × 106 m3, the largest mass of which are distributed along the river floor and a tributary water stream. These findings contribute to detailed numerical simulation of the avalanche sequences and source identification; furthermore, altitude measurements after ice and snow melting would reveal a contained volume of melting ice and snow.

Original languageEnglish
Pages (from-to)1907-1921
Number of pages15
JournalNatural Hazards and Earth System Sciences
Volume17
Issue number11
DOIs
Publication statusPublished - 2017 Nov 13
Externally publishedYes

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avalanche
PALSAR
remote sensing
valley
snow
ice
melting
sediment
rockfall
mountain region
tributary
landslide
monsoon
village
Gorkha earthquake 2015
hazard
air
river
rock
simulation

ASJC Scopus subject areas

  • Earth and Planetary Sciences(all)

Cite this

Multiple remote-sensing assessment of the catastrophic collapse in Langtang Valley induced by the 2015 Gorkha earthquake. / Nagai, Hiroto; Watanabe, Manabu; Tomii, Naoya; Tadono, Takeo; Suzuki, Shinichi.

In: Natural Hazards and Earth System Sciences, Vol. 17, No. 11, 13.11.2017, p. 1907-1921.

Research output: Contribution to journalArticle

Nagai, Hiroto ; Watanabe, Manabu ; Tomii, Naoya ; Tadono, Takeo ; Suzuki, Shinichi. / Multiple remote-sensing assessment of the catastrophic collapse in Langtang Valley induced by the 2015 Gorkha earthquake. In: Natural Hazards and Earth System Sciences. 2017 ; Vol. 17, No. 11. pp. 1907-1921.
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