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Titel |
The 2012 Seti River flood disaster and alpine cryospheric hazards facing Pokhara, Nepal |
VerfasserIn |
Jeffrey Kargel, Gregory Leonard, Lalu Paudel, Dhananjay Regmi, Samjwal Bajracharya, Monique Fort, Sharad Joshi, Khagendra Poudel, Bhabana Thapa, Teiji Watanabe |
Konferenz |
EGU General Assembly 2014
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Medientyp |
Artikel
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Sprache |
Englisch
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Digitales Dokument |
PDF |
Erschienen |
In: GRA - Volume 16 (2014) |
Datensatznummer |
250096916
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Publikation (Nr.) |
EGU/EGU2014-12448.pdf |
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Zusammenfassung |
We have identified the likeliest cause of the Seti River disaster of May 5, 2012, in which a
flash flood killed or left missing 72 people. A cascade of deadly physical Earth processes
combined with imprudent habitation on the lowest flood terraces and floodplain. The process
cascade started with rockfalls into the Seti River gorge (observed via repeat ASTER
imaging). The last rockfall—one to several weeks prior to the disaster-affected a knickpoint
in the Seti River gorge and impounded glacial meltwater and spring snowmelt. The trigger
was a large rock/ice avalanche originating from cornice ice on Annapurna IV, where part of
the mass was channeled into the impoundment reservoir. That violent ground-surge event,
plus possibly an air blast caused by a violent gravity flow of airborne debris—then burst the
rockfall dam. This was not a glacier lake outburst flood. Glaciers were involved in the
disaster by supplying meltwater, which was impounded by the rockfall dam, by
triggering the disaster with collapse of cornice ice, and by contributing ice to the
landslide and outburst flood. Debuttressing of moraine debris and ancient glacial lake
sediment by retreat and thinning of glaciers also may have played a role—this is
the only possible indirect link of the disaster to climate change. The rockfall and
avalanche mass movements occurred independently of climate change. The narrow
and easily blocked Seti River gorge was a key factor in the 2012 disaster, and it
remains a unique component of this physiographic setting. A similar flood in this area
may happen by a different cascade of Earth surface processes. An enormous mass
of ancient unconsolidated glaciolacustrine and moraine sediment—many cubic
kilometers—was discovered and is vulnerable to production of debris flows and
hyperconcentrated slurry flows. Some aggravating processes occurring in the Sabche
Cirque are related to climate change. Glaciers in that area are melting, and small
lakes are forming. Although the lakes were not implicated in the 2012 disaster, the
possibility exists for a small glacial lake outburst flood to trigger a larger mass
movement. Such a debris flow could reach Pokhara directly. More likely, a debris
flow in the Sabche Cirque could form another temporary and potentially dangerous
impoundment dam in the gorge. Furthermore, the type of rockfall blockage that produced
2012’s natural impoundment reservoir is likely to happen repeatedly. Hence, there is
a high capacity of the Earth system in this area to produce comparable or even
bigger flash floods or mass flows. The likelihood of a further disaster is magnified by
imprudent habitation of the river channel and lower floodplain. Of all the changes to the
Pokhara Valley, human encroachment on the flood plain is the factor most related to
increasing vulnerability, but it is also the one factor that could be remedied by a
complete ban on construction on lower terraces, if that is politically feasible. Warning
systems could help, but fairly relocating people in jeopardy would be more effective.
Supported by NASA/USAID SERVIR Applied Sciences and USAID Climbers’ Science. |
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