Imja Lake Research Articles

Evolution and Controls of Large Glacial Lakes in the Nepal Himalaya

Glacier recession driven by climate change produces glacial lakes, some of which are hazardous. Our study assesses the evolution of three of the most hazardous moraine-dammed proglacial lakes in the Nepal Himalaya—Imja, Lower Barun, and Thulagi. Imja Lake (up to 150 m deep; 78.4 × 106 m3 volume; surveyed in October 2014) and Lower Barun Lake (205 m maximum observed depth; 112.3 × 106 m3 volume; surveyed in October 2015) are much deeper than previously measured, and their readily drainable volumes are slowly growing. Their surface areas have been increasing at an accelerating pace from a few small supraglacial lakes in the 1950s/1960s to 1.33 km2 and 1.79 km2 in 2017, respectively. In contrast, the surface area (0.89 km2) and volume of Thulagi lake (76 m maximum observed depth; 36.1 × 106 m3; surveyed in October 2017) has remained almost stable for about two decades. Analyses of changes in the moraine dams of the three lakes using digital elevation models (DEMs) quantifies the degradation of the dams due to the melting of their ice cores and hence their natural lowering rates as well as the potential for glacial lake outburst floods (GLOFs). We examined the likely future evolution of lake growth and hazard processes associated with lake instability, which suggests faster growth and increased hazard potential at Lower Barun lake.

Decision-Making Methodology for Risk Management Applied to Imja Lake in Nepal

Glacial retreat causes the formation of glacier lakes with the potential of producing glacial lake outburst floods (GLOFs). Imja Lake in Nepal is considered at risk for a GLOF. Communities in the path of a potential Imja GLOF are implementing adaptation projects, yet no quantitative data or guidance is available to understand the benefits of these projects or how to weigh benefits against the cost of implementation. We develop and demonstrate a decision-making methodology for GLOF risk management, incorporating available scientific information and uncertainty. The methodology consists of (1) identifying flooding scenarios, (2) evaluating scenario consequences, and (3) performing an economic analysis of proposed adaptation projects. The methodology is applied to assess benefits in Dingboche of lowering Imja Lake by 3, 10 and 20 m. The results show that the baseline case (no lake lowering) has the lowest expected cost because of low valuation of agricultural land and homes in the literature. Nonetheless, the result is sensitive to changes in the analysis variables. We also found that lowering the lake by 10 or 20 m is efficient according only to the methodology used here; however, considering only direct economic damages and literature cost estimates, the costs outweigh the benefits for these projects.

Factors controlling the accelerated expansion of Imja Lake, Mount Everest region, Nepal

AbstractThis study explores the link between area increase of Imja Tsho (Lake) and changes of Imja Glacier (area ~25km2) under the influence of climate change using multitemporal satellite imagery and local climate data. Between 1962 and 2013, Imja Lake expanded from 0.03±0.01 to 1.35±0.05 km2 at a rate of 0.026±0.001 km2 a-1. The mean glacier-wide flow velocity was 37±30ma-1 during 1992–93 and 23±15ma-1 during 2013–14, indicating a decreasing velocity. A mean elevation change of –1.29±0.71ma-1 was observed over the lower part of the glacier in the period 2001–14, with a rate of –1.06±0.63ma-1 in 2001–08 and –1.56±0.80ma-1 in 2008–14. We conclude that the decrease in flow velocity is mainly associated with reduced accumulation due to a decrease in precipitation during the last few decades. Furthermore, glacier ablation has increased due to increasing maximum temperatures during the post-monsoon months. Decreased glacier flow velocities and increased mass losses induce the formation and subsequent expansion of glacial lakes under favourable topographic conditions.

Changes in Rongbuk lake and Imja lake in the Everest region of Himalaya

Abstract. The Himalaya holds the world record in terms of range and elevation. It is one of the most extensively glacierized regions in the world except the Polar Regions. The Himalaya is a region sensitive to climate change. Changes in the glacial regime are indicators of global climate changes. Since the second half of the last century, most Himalayan glaciers have melted due to climate change. These changes directly affected the changes of glacial lakes in the Himalayan region due to the glacier retreat. New glacial lakes are formed, and a number of them have expanded in the Everest region of the Himalayas. This paper focuses on the two glacial lakes which are Imja Lake, located at the southern slope, and Rongbuk Lake, located at the northern slope in the Mt. Everest region, Himalaya to present the spatio-temporal changes from 1976 to 2008. Topographical conditions between two lakes were different (Kruskal-Wallis test, p < 0.05). Rongbuk Lake was located at 623 m higher than Imja Lake, and radiation of Rongbuk Lake was higher than the Imja Lake. Although size of Imja Lake was larger than the Rongbuk Lake in 2008, the growth speed of Rongbuk Lake was accelerating since 2000 and exceeds Imja Lake in 2000–2008. This trend of expansion of Rongbuk Lake is anticipated to be continued in the 21st century. Rongbuk Lake would be the biggest potential risk of glacial lake outburst flood (GLOF) at the Everest region of Himalaya in the future.

Water Quality of High-Altitude Lakes in the Sagarmatha (Everest) National Park, Nepal

The aim of this research was to analyze physical and chemical characteristics of high altitude lakes (Gokyo lake series, Imja lake, Pyramid lake) of the Sagarmatha National Park, Khumbu region located above 4500 m altitude. The lake water was studied for three years (2008, 2009 and 2010) to compare the annual changes in the parameters. The findings created a database for present status of high land lakes of Nepal, which can be used for the management of lakes as well as to study the impact of tourism on water quality. The lake water quality in general still stands good in terms of standards for drinking water (WHO, Nepal standard) but degradation process has started. Total nitrogen in water samples was lower than the WHO standard but an increase in the nitrate nitrogen has been recorded. Similarly, total phosphorrous quality was also found increased.

Identification of glacier motion and potentially dangerous glacial lakes in the Mt. Everest region/Nepal using spaceborne imagery

Abstract. Failures of glacial lake dams can cause outburst floods and represents a serious hazard. The potential danger of outburst floods depends on various factors like the lake's area and volume, glacier change, morphometry of the glacier and its surrounding moraines and valley, and glacier velocity. Remote sensing offers an efficient tool for displacement calculations and risk assessment of the identification of potentially dangerous glacial lakes (PDGLs) and is especially helpful for remote mountainous areas. Not all important parameters can, however, be obtained using spaceborne imagery. Additional interpretation by an expert is required. ASTER data has a suitable accuracy to calculate surface velocity. Ikonos data offers more detail but requires more effort for rectification. All investigated debris-covered glacier tongues show areas with no or very slow movement rates. From 1962 to 2003 the number and area of glacial lakes increased, dominated by the occurrence and almost linear areal expansion of the moraine-dammed lakes, like the Imja Lake. Although the Imja Lake will probably still grow in the near future, the risk of an outburst flood (GLOF) is considered not higher than for other glacial lakes in the area. Potentially dangerous lakes and areas of lake development are identified. There is a high probability of further lake development at Khumbu Glacier, but a low one at Lhotse Glacier.

The expansion mechanism of Himalayan supraglacial lakes: Observations and modelling

Himalayan Journal of Sciences Vol.2(4) Special Issue 2004 pp. 118-120

Glacial Lake Outburst Floods in the Sagarmatha Region

Abstract Glacial lake outburst floods (GLOFs) are common natural hazards in the Himalaya. These floods, usually of large magnitude, can severely affect fragile mountain ecosystems and their limited economic activities. In this study, GLOF hazard in the Sagarmatha region (national park and buffer zone) was assessed using dam break and hydrodynamic modeling. The available data from the Dig Tsho GLOF of 1985 were used to validate many of the model outputs. The technique was further applied to GLOF hazard assessment of Imja Lake, the largest and potentially most dangerous glacial lake in the region. The peak outflow discharge of an Imja GLOF is estimated at 5463 m3/s. The peak discharge attenuates to about 2000 m3/s at the boundary of the buffer zone at about 45 km from the outburst site. Finally, a GLOF vulnerability rating map was prepared and an assessment of vulnerable settlements was carried out. The study was found to be a cost-effective means of obtaining preliminary information on the extent and impac...

モレーン堰止型氷河期の熱循環に与える地形の影響―ヒマラヤのイムジャ湖とツォー・ロルパ湖との比較―

The observations in the pre-monsoon seasons of 1996 and 1997 indicated that two moraine-dammed glacial lakes, Tsho Rolpa and Imja, in the Nepal Himalayas have the different thermal structure in spite of the similar solar radiation, air temperature and wind system at the weather stations. The difference of thermal conditions in the lakes possibly results from the depletion in wind velocity over Imja Lake, which is caused by the screening of the upwind end-moraine to dead-ice zone 20-25 m higher than the lake surface. In order to clarify the topographic screening effect, three-dimensional numerical simulations of airflow around Tsho Rolpa and Imja Lakes were performed by building up a topographic model of actual size in the calculation domain. Simulated results indicated that the wind velocity at 2 m above the Imja Lake surface is 33-42 % smaller than that above the Tsho Rolpa Lake surface for the constant wind velocites of 1-5 m/s at 2 m above the points corresponding to the weather stations. This evidences the significant screening effect on the thermal structure of Imja Lake, since the wind force per unit lake area is proportional to the square of wind velocity at a certain height above the lake surface. The airflow simulations indicate that, as a barrier, the glacier terminus (ice cliff) leeward of Imja Lake decreases the wind velocity near the lake surface as much as does the upwind end-moraine to dead-ice zone.

Hydrological and thermal regimes in a supra-glacial lake: Imja, Khumbu, Nepal Himalaya

Supraglacial Imja Lake (lake level, 5010 m a.m.s.l.), Khumbu, Nepal Himalaya, has increased its size on the tongue of Imja Glacier since the 1950s. In order to clarify the mechanism of the lake expansion, the physical conditions, water budget and heat budget of the lake were examined by measuring water temperature, water turbidity, lake level, meteorology and water discharge. These measurements were carried out in the monsoon season of July 1997, when the glacier melt occurred in the ablation area with air temperature of more than 0°C. Density stratification in the lake is built up by an effect of water pressure on lake water, but, neglecting the effect, lake water density is defined by suspended sediment concentration rather than temperature. Glacier-melt water from the subaqueous part of the glacier terminus mixed with lake surface water of 4–8°C, and diffused the water of about 3°C into the deeper zone of the lake. This advective, thermal diffusion occurs by sediment-laden underflow and relatively clear density interflow. The sediment-laden underflow is induced by intermittent glacier-melt sediment discharge at the terminus, while the density interflow is probably produced by continuous glacier-melt water discharge. Calculation of water budget of the lake indicates that meltwater inflow at the glacier terminus and surface water outflow at the outlet determine the hydrological conditions of the lake. The net heat transfer by melting of the terminal ice and dead ice, connected to the lake expansion, was evaluated by calculating the heat budget of the lake.