It is one thing to look at satellite images that provide a sweeping view of a glacial lake expanding over time, but it is an entirely different experience to visit the lake and get a ground level perspective. In September 2021, a joint research team from ICIMOD and Kathmandu University carried out a physical investigation of the expanding Lower Barun lake, its dam, and surroundings.

The Lower Barun lake is one of two significant glacial lakes in the Makalu region of Nepal. The other lake – Barun lake – lies at the base of Mount Makalu, the world’s fifth highest mountain, while the Lower Barun lake lies further down the valley. Located at 4,500 masl, in the heart of the Barun valley, in Makalu Barun National Park, the Lower Barun lake is 2.7 km long and 600 m wide. It is situated next to the Makalu Base Camp trekking trail and empties into the Barun River, which then joins the mighty Arun River.

The importance of the Lower Barun lake

The Lower Barun lake was formed by the gradual recession of the Barun Glacier and by meltwater pooling in front of the moraine complex. A large mound of rock, gravel, and soil deposited by previous glacial activity now dams the lake. Through the joint study we conducted with UNDP in 2020, it was identified as the largest potentially dangerous glacial lake in Nepal – one that needed regular monitoring. The findings were based on analysis of geomorphological features using remote-sensing tools and techniques.

However, remote sensing can provide us only so much information particularly on the physical characteristics of lakes, dams, and surroundings. Bathymetry survey is used to measure volume of the lake and map the lake floor and sides. The survey also estimates the pressure from the impounded water on the moraine. Such information helps us to develop potential breach scenarios of water burst through the moraine dam, model the resulting flood, and identify sites for installing early warning systems.

Surface area change of Lower Barun Glacial Lake from 1988 to 2021

The Nhepu of Lower Barun

Mountain communities across the HKH revere mountains and lakes as the abodes of gods and goddesses. For the communities living downstream from the Lower Barun lake, the lake is revered as the abode of their guardian deity, Nhepu. The local people believe that Nhepu protects them from disease, famine and disaster, and communities perform rituals to seek blessings, particularly when starting important activities. Many lakes at high altitudes have remained pristine due to such beliefs and traditions.

As communities consider lakes and mountains as abodes of gods and goddesses, they have deep respect and a spiritual connection with their environment. This also means that disaster events, such as GLOFs, are often perceived as divine retribution for sacred sites being disturbed or defiled by human activity.

Understanding community perspectives

The path to the lake follows the trekking route to Makalu Base Camp, passing through several Sherpa settlements, including Tashigaon, the largest permanent settlement along the route. Community members who we interacted with on our way to the lake were concerned about the cascading danger from the Barun River, which is likely to spill into the right side of the Lower Barun lake by the Shersong valley. They were also apprehensive about our research activities disturbing their guardian deity, which they believe could cause a GLOF. This strong belief among the local people has discouraged several research teams in the past, with some even cancelling their research midway due to inclement weather or team members falling sick. The local people interpret these as signs of Nhepu’s displeasure.

Undertaking research while respecting local traditions

The task at hand for the research team was to survey the lake’s surface and surroundings using an unmanned aerial vehicle (drone), conduct a bathymetry survey to measure the depth, perform a geophysical survey to understand the internal moraine complex, and survey the morphological features in the surroundings to understand potential impact areas to the lake and its dam. These activities required us to walk around the lake and take a boat to its centre. Perceiving some discomfort with our planned activity, we assured the local people that we would not disturb the lake’s sanctity and adhere to all local customs, including seeking the necessary permission from the lake’s guardian deity.

On the morning of 20 September 2021, we invited religious figures from the community, local leaders, and community members to help us perform rituals to appease Nhepu and seek her blessings. We started our work after carrying out the rituals. Every morning, as we headed to the lake for our measurements, we burned incense and juniper leaves as part of a cleansing ceremony. By adhering to local customs and respecting local sentiments, we were able to clearly communicate the intentions of our work. Fortunately, the weather remained pleasant during our fieldwork, further assuring the communities that we had the guardian deity’s blessings.

Working in high mountains can be risky, and the bathymetry survey was particularly challenging with active ice calving into the lake, several large blocks of ice floating to the lake outlet, and ice blocks falling into the lake and disturbing the surface.

The expedition team

Findings and initial observations

Our initial observations show that the lake’s condition matches with findings from our remote sensing-based work. The lake is at risk from meltwater flows from the Barun lake and other adjoining glaciers and glacial lakes in the valley edging their way towards Lower Barun lake. With gradual erosion of the lake’s lateral moraine, the Barun Khola riverbed is almost the same height as the moraine. The river may not change its course and feed into the lake, but in case of high river flows, potentially triggered by avalanches or extreme precipitation, there is a high risk of river water cascading into the Lower Barun lake.

The lake’s dam consists mainly of boulder-sized rocks, which are highly porous. Because there is less finer-sized material between the boulders, the probability of water flowing out from under the dam through the end moraine dam is high.

Since the Lower Barun lake is also expanding, Barun glacier, which feeds the lake, has seen continuous calving of ice because of undercutting from the lake, the dynamics in the crevassed glacier tongue, and repeated action of waves against the glacier front. The data from our fieldwork are being analysed, which we hope will provide better evidence to support early warning systems for people living downstream of the lake.

In many ways, we are inspired by the deep concerns and sentiments of the local communities, and we see the importance of merging science and traditional knowledge to address emerging cryosphere-related challenges, identify hazards, and mitigate risks. Our worldviews may be different, but we share the overall goal of preserving the lake and ensuring the wellbeing of the people living around the lake and downstream.