Tsho Rolpa Research Articles

Glacial hazard assessment at Tsho Rolpa, Rolwaling, Central Nepal

Recession of glaciers throughout the Himalayas is resulting in the development of a growing number of high-altitude proglacial lakes that are retained behind natural moraine dams. Some of these have failed catastrophically and the consequential Glacier Lake Outburst Floods (GLOFs) have resulted in substantial damage and loss of life downstream. With growing populations in remote valleys coupled with the demand for substantial growth in the capacity for hydro-electric power for export, the risk of further disasters is increasing. Accordingly, His Majesty's Government of Nepal has undertaken a series of studies since 1985 to investigate the risks associated with such glacial lakes. This photofeature encapsulates aspects of the work undertaken between 1994 and 1997 at Tsho Rolpa, which is thought generally to be the largest and most dangerous glacial lake in Nepal. The present project at Tsho Rolpa is the first of its kind in Nepal and represents the first time that such detailed glacial hazard assessment has been undertaken through to the development of a full remediation scheme in Nepal. Tsho Rolpa lies about 110 km north east of Kathmandu at the eastern end of the Rolwaling Valley (Fig. 1) and immediately south of Gauri Sankar (7146 m). The lake (Fig. 2) is about 3.5 km long by 0.5 km wide and is up to 135 m deep. It is fed by Trakarding Glacier (Fig. 3) to the southeast which is itself a composite glacier supplied by several glaciers from among the peaks to the east and south east of

Hydrodynamics of a Supraglacial Lake and Its Effect on the Basin Expansion: Tsho Rolpa, Rolwaling Valley, Nepal Himalaya

The thermal structure and hydrodynamics of supraglacial Tsho Rolpa Lake (27°51′N, 86°29′E) in the Nepal Himalaya were examined in the premonsoon of 1996. We continuously measured flow velocity, water temperature, and turbidity with moored self-recording current meters, temperature data loggers, and turbidimeters. Vertical measurements (every 0.2 m in depth) of water temperature and turbidity were also made by lowering a self-recording sonde. Tsho Rolpa Lake (surface area, 1.39 km2 at present) has increased in size since late 1950s (surface area, 0.23 km2 in 1958) by both glacial ice melt below the lake bottom and the retreat of the glacier terminus. Lake stratification is defined by suspended sediment concentration (SSC) rather than by temperature. The suspended sediment is mostly silt and clay (d < 15.6μm), which is supplied by the meltwater discharge from a subaqueous tunnel portal into the lake at the glacier terminus. The sediment is transported to the deepest zone of the lake by underflows and diffused by advection by the other currents into the upper zone. The observations revealed that a diurnal valley wind produces a vertical water circulation in the quasi-isopycnal surface layer, which is about 27 m deep. This circulation transports the surface water, heated mostly by solar radiation, toward the glacier terminus and consequently forces relatively warm water (>~5°C) into continual contact with the glacier terminus. This warm water contact could induce calving of the upper glacier-ice by increasingly melting the subaqueous lower part.

Hydrodynamics of a Supraglacial Lake and its Effect on the Basin Expansion: Tsho Rolpa, Rolwaling Valley, Nepal Himalaya

The thermal structure and hydrodynamics of supraglacial Tsho Rolpa Lake (27°51′N, 86°29′E) in the Nepal Himalaya were examined in the premonsoon of 1996. We continuously measured flow velocity, water temperature, and turbidity with moored self-recording current meters, temperature data loggers, and turbidimeters. Vertical measurements (every 0.2 m in depth) of water temperature and turbidity were also made by lowering a self-recording sonde. Tsho Rolpa Lake (surface area, 1.39 km2 at present) has increased in size since late 1950s (surface area, 0.23 km2 in 1958) by both glacial ice melt below the lake bottom and the retreat of the glacier terminus. Lake stratification is defined by suspended sediment concentration (SSC) rather than by temperature. The suspended sediment is mostly silt and clay (d < 15.6μm), which is supplied by the meltwater discharge from a subaqueous tunnel portal into the lake at the glacier terminus. The sediment is transported to the deepest zone of the lake by underflows and diffused by advection by the other currents into the upper zone. The observations revealed that a diurnal valley wind produces a vertical water circulation in the quasi-isopycnal surface layer, which is about 27 m deep. This circulation transports the surface water, heated mostly by solar radiation, toward the glacier terminus and consequently forces relatively warm water (>~5°C) into continual contact with the glacier terminus. This warm water contact could induce calving of the upper glacier-ice by increasingly melting the subaqueous lower part.

High-altitude glacial lake hazard assessment and mitigation: a Himalayan perspective

Abstract Glaciers throughout the Himalayas have been receding rapidly over the last few years. In the areas vacated by the ice snouts lakes have formed behind large moraine dams. As with their Andean counterparts, these lakes can pose significant threats to downstream towns, roads and power schemes. For a developing country like Nepal, for example, the prospective loss of economically vital infrastructure and food-producing land can be devastating, in addition to the human misery. The Tsho Rolpa glacier lake has formed by the retreat of Trakarding Glacier at the head of the Rolwaling Valley in northern Nepal. The lake is now over 3 km long and contains an estimated volume of 80 x 10 6 m 3 . The snout of Trakarding Glacier terminates in the lake which, at its western end, is dammed by an ice-cored moraine. It is feared that the lake could be the source of a major glacier lake outburst flood (known locally as a ‘GLOF’) which could destroy the nearby villages of Na and Beding, as well as trekking routes, vital bridges, etc. , further downstream. At Khimti, 80 km downstream from Tsho Rolpa, a new hydroelectric power scheme is being built and could potentially be at risk. It is known that the local glaciers in the Rolwaling Valley have been the source of many GLOFs in historical as well as contemporary times. The last GLOF destroyed several houses and valuable farm land at Beding in July 1991. Following an initial GLOF-risk assessment in September 1994, a trial siphon was installed at Tsho Rolpa in May 1995. This is the first time that such measures have been used in the Nepalese Himalayas. Since then further remediation measures have been proposed and are awaiting funding. The nature of the glacial hazards at Tsho Rolpa and the engineering mitigation measures being proposed are described. Furthermore, it is concluded that an integrated national policy on glacial hazards should be developed urgently.

Acts of God are not the problem

Mountain tourism both increases the risks posed by mountain hazards and also provides the economic opportunity to effectively cope with those hazards. Salient points and recommendations from participants in “Mountain Hazards, Mountain Tourism” e-conference include:Although climate change is increasing the likelihood of glacial lake outburst floods (GLOFs), we now have the scientific tools to monitor and quantify such hazards. Unfortunately, those tools are not being used on a regular basis. This increases the hazard of media sensationalism, which in turn increases the risk of serious economic damage as well as lost scientific credibility. Contrary to published reports, the hazard mitigation project at Tsho Rolpa in Rolwaling was left in an incomplete state and without provision for scientific monitoring; the lake still poses a great risk. More attention must be paid to the human component of mountain hazards. Ethnic cleansing programs such as the current disaster in Bhutan cause suffering and economic damage on a scale that beggars most natural events. A useful step toward the rational confrontation with all sorts of disasters (not just those that impact mountains) would be the conversion of King Gyanendra’s palace into a Disaster Management University. &#x0D; &#x0D; Himalayan Journal of Sciences Vol.4(6) 2007 p.11-19