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24 Jul 2019 | Cryosphere

Reassessing Tsho Rolpa glacial lake

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Morphological view of the lake’s end moraine dam and surroundings (Photo: Sudan Maharjan/ICIMOD)

Tsho Rolpa is a large, potentially dangerous glacial lake in Nepal that has been the subject of extensive research and monitoring for decades, with the Government of Nepal even placing it on its priority list in 1997. By 2000, mitigation activities had successfully reduced the lake’s level by 3 m, but the threat of an outburst still looms. The lake has been consistently expanding over the last 60 years and now encompasses an area of 1.6 km2, which roughly translates to around 148 standard-sized football fields. Studies have documented a 3.3% increase in the lake’s area from 2010 to 2015. An outburst flood would be catastrophic for downstream communities.

Researchers are now reassessing the state of Tsho Rolpa – located around 115 km northeast from Kathmandu in Dolakha District at an altitude of 4,560 masl – using state-of-the-art tools and technology. A field expedition to the site from 7 to 21 May 2019, led by ICIMOD and its partners, investigated the present condition of the lake and its dam and surrounding morphological conditions. The lake is directly fed by Tarkading Glacier, which continued to retreat at a rate of 60 m annually from 2009 to 2019.

The ICIMOD field expedition team also investigated Naa, Beding, Gongar Khola, and Singati villages, located directly downstream of the lake Around 6,000 households are at risk from a potential glacial lake outburst flood (GLOF), and cultivated lands, forests, and infrastructure lie in the path. This is particularly worrying because Nepal experiences the most severe GLOF-induced national-level socioeconomic impacts. A 2011 ICIMOD study reported that of 21 critically dangerous glacial lakes in Nepal, only two have been subjected to proper mitigation activities. There is consequently an increasing need to develop a reliable GLOF hazard risk assessment and warning tools to improve preparedness and build resilience at the community level.

The field expedition to Tsho Rolpa is a first step towards narrowing the research gap in exploring the latest monitoring and modelling technologies to support practical GLOF risk mitigation applications. The team observed that the lake continues to expand as a result of the rapid melting of an adjoining glacier and continues calving of surrounding ice cliffs. On the basis of the observations, the team recommended conducting bathymetric surveys in at least two-year intervals, monitoring displacement of the end moraine dam, and installing a hydro-meteorological station to monitor changes in lake features and to detect changes in the hydrological processes.

The findings from this expedition will help researchers expand their activities to other critical glacial lakes in Nepal and help the government scientifically plan effective early warning and risk mitigation strategies.

The field expedition was jointly carried out by researchers from the School of Engineering, Newcastle University; Central Department of Geography, Tribhuvan University; Himalayan Cryosphere, Climate and Disaster Research Center (HiCCDRC), Kathmandu University; and ICIMOD.

1. The exponential growth of Tsho Rolpa over 38 years (1977–2015) (Background image: Google Earth)

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