Tracing past glacial floods in Kangchenjunga

Updated: Sep 20

Satellite imagery is useful, but involving local people in research can often help fill gaps in research of glacial floods


By Dr. Alton C Byers


Glacial lake outburst floods are highly destructive events, usually caused when stored lake water is suddenly released by a triggering event that can include moraine dam failure, snow and debris avalanches, as well as heavy rainfall.


There have been at least 26 major glacial lake outburst flood (GLOF) events in Nepal that we know of, most having occurred since the 1960s and onset of global warming trends, receding glaciers, and new glacial lake formation.


Perhaps most famous is the Langmoche ‘flash flood’ of 1985 in the Thame Valley in Khumbu which killed at least five people, destroyed a nearly completed hydropower facility, and took out bridges for nearly 100km downstream.


However, it would be 20 years more before the acronym GLOF became a household word, at least in Nepal, as well as a major scientific discipline producing dozens of peer reviewed papers each year, my own included


So, it was no coincidence that two years ago a scientific paper about a 1980 GLOF in the Kanchenjunga region in eastern Nepal caught my eye, written by the renowned Japanese geographer Teiji Watanabe in 1998.


The only documentation of the flood that Watanabe could find was a short piece in the The Rising Nepal of 28 June 1980 reporting that a flood had occurred in the Tamor Valley a week or so before. Damage included ‘…all the houses in Olangchung Gola village’, bridges, and downstream settlements, with at least 10 human fatalities.


Using topographic maps and aerial photographs from 1978 and 1992, Watanabe was able to determine that the source of the flood was the Nangama glacial lake, about 8km south of the border with Tibet (Figures 1 and 2).


Oblique aerial photos taken in 1978 and 1992 clearly showed the breached terminal moraine and deposits that not only a GLOF from Nangama had occurred in 1980, but that its debris had blocked a small river to the south, creating a new lake named Chheche by the local people.


For the next 40 years, no GLOFs were reported in the Kanchenjunga region. This was odd, since during the same period Nepal had experienced dozens of GLOFs — twice from the Zhangzango Lake in Tibet (1964 and 1981), the Tama Pokhari due east of the Mt Everest region (1998), and the Langmale flood in the Barun valley (2017).


There had also been dozens more smaller glacier floods which originate from within the glacier itself and consist of stored water from surficial ponds and ice caves. But nothing from Kanchenjunga.

And so we set out from Bhadrapur by jeep on 18 April last year to see if we could update the status of GLOFs and climate change impacts in what had now become the Kanchenjunga Conservation Area. It was an eight hour drive to Taplejung from the Tarai plains up through the beautiful tea plantations of Ilam.


The next day a three hour drive to Tapletok, at that time the end of the ever-lengthening and expanding road. From there we spent the next six weeks on foot in the Kanchenjunga Conservation Area (KCA).


Kanchenjunga is the world’s third highest mountain at 8,586m, located in eastern Nepal on the border of Nepal, Sikkim in India, and Tibet in China. Initially thought to be the highest mountain in the world, several attempts to seriously climb it were made in the early 1900s to 1930s by the Germans and British.


But it wasn’t until 25 May, 1955 that the mountain was first summited by Georg Band and Joe Brown, in a British expedition led by Charles Evans[1], deputy director of the successful 1953 climb of Everest (Band and Brown actually stopped just short of the sacred summit, as per the request of the Maharajah of Sikkim).



The region’s location at the intersection of three floristic provinces — the Indo-Malayan, Palearctic, and Sino-Japanese — create one of the most biologically rich landscapes of the eastern Himalayas. The entire Kanchenjunga Landscape region in Nepal, Bhutan, Sikkim and Tibet encompasses 22 ‘Important Bird and Biodiversity Areas’, 19 protected areas, one UNESCO World Heritage Site, and one Ramsar wetland site. Vegetation zonations include: tropical (below 1,000 m), subtropical (1,000-2,000 m), warm temperate (2,000-2,500 m), cool temperate (2,500-3,000 m), subalpine (3,000-4,000 m), and alpine zones (>4,000 m). There are 5,198 species of plants that have been recorded in the region since botanical investigations first began in the 1840s and continue to this day.

Even before the pandemic, tourism was limited in the KCA compared to other protected areas of Nepal, perhaps owing to its remoteness and lack of publicity. The vast majority of trekkers visit the Kanchenjunga Base Camp situated north of the Kanchenjunga Glacier.


Five rustic lodges have been built in recent years in Lhonak kharka (pasture), providing food and shelter for the estimated 200 trekkers arriving each spring, and 500 in autumn (the fewer numbers in the spring reflect the difficulty in crossing the still-snow covered passes).


After arriving in the KCA last year, we were faced with the fundamental question of how to go about reconstructing the history of GLOFs in a region with absolutely no written, media, or scientific documentation?


As a start, we decided to interview local people. This is something still somewhat unusual in the physical sciences in general, and in research related to glaciers in particular, for reasons that are not entirely clear.


Glaciologists like to take field measurements, drill ice cores, analyse satellite imagery, and recreate peak flows and flood volumes through the use of sophisticated flood modeling, but for some reason the insights and experience of local people has been strangely lacking in scientific studies of GLOFs.


The original plan was to trek from Tapletok due north to Yangma, and then west to Nangama glacial lake, so that we could see firsthand, and for the first time by scientists, what this place looked like. But by interviewing local people along the way, primarily those over 75, a new story started to take shape —  one that totally changed the original itinerary of visiting Nangama glacial lake only.


It all started when we were told that an older person who was knowledgeable in the region’s history lived in the upper part of Tapletok, about a 20 minute walk away. We left immediately, walking through the rice fields and up a steep incline to a beautiful house overlooking the Tamor River below, the home of Barachan Limbu, 81 (Figure 7).

Limbu had spent 21 years in the Indian Army, and was now enjoying his days at home under the care of one of his daughters, a registered nurse.  He was also a storehouse of local knowledge, and over the next hour described how instead of only one GLOF in the region since the 1980s from Nangama, there had been five major floods that local people still remembered and could describe, including one that happened nearly 100 years ago, in 1921.


Table 3 shows the five floods as identified by Barachan Limbu. The most recent was in 1986, presumably from the Yalung Glacier and within the Shimbuwa River that joins with the Tamor from the east.


The 1980 Nangama flood we knew about, but two floods had occurred in the upper branch of the Tamor River, one in 1963 and one in 1968, were a complete mystery.  And for people to still remember a GLOF from the upper Ghunsa valley that occurred in 1921, nearly one hundred years ago, meant that it must have been one very large flood indeed.


Armed with this new and unexpected information, we decided to alter our journey by branching off to the west and following the Tamor River to the the village of Olanchun Gola, also located on the Great Himalayan Trail route, to try and get the story on the 1963 and 1968 floods.



Once there, we were directed to Kushophula Lama Ukyap, 72, caretaker of the Deki Chholing Gompa built 450 years ago. Ukyap informed us that as opposed to the 1980 Nangama flood destroying the lower part of the village (a physical impossibility, since the Yangma Khola runs to the east of the Tamor River), it was in fact the 1963 Olangchun Gola 1 flood (map symbol 5) that caused the damage to the village.


Flood waters originated in the Tiptola glacial lake to the northwest, which was the source of a second and smaller GLOF in 1968. Approximately 45 houses were destroyed by the 1963 flood, either by undercutting of the river bank below or by a lake that formed when debris blocked the flood downstream for a while.


Most of the people who lost their homes and property moved to Kathmandu. The cause of both the 1963 and 1968 floods was thought to be a result of massive ice avalanches from the Chhochenphu Himal (6,269 m) to the north of the lake (Figures 2 and 9).



We then trekked for two days to Tiptola glacial lake (Figure 9), for the most part following a newly constructed road from Olangchun Gola to the Tiptala Pass (5,095 m) to Tibet. Along the way we meet a group of KCA  employees from the Department of National Parks and Wildlife Conservation, scouting out a new site for a checkpost location.


Wildlife poaching and sales to China were major problems in the region prior to the pandemic, and the checkpost was designed to try and curb the illegal trade. The group was also holding community consultations in an effort to promote the development of home stays as well as more nature-based economic development in the region. Once they had checked our research permits, they expressed a strong support for our work and wished us the best of luck.


Returning to Olanchun Gola several days later, we next set out for the village of Yaphu to the north (Figure 2). Along the way on the Yaphu River we saw two bears, a possible red panda, a variety of resplendent sun birds, and old growth stands of junipers, hemlocks, and fir trees with diameters of 1 meter+ (Figures 4, 5, and 6).


A road was being built on an upper ridge to the west to Yaphu, but the path along the river and old growth forests also contained painted boulders with surveyor’s markings that suggested a road might be built along the river as well. A number of people that we interviewed felt that such a road was not needed, would result in the destruction of the old growth forests, and have negative impacts on the adventure tourism trade as a result.


As tourism will definitely return to the region at some point in time, officials and local communities might do well to heed these words of warning, or lose a valuable source of income as well as incentives for biodiversity conservation.


At Yangma, we met Tahwa Lama, 71, an eyewitness to the 1980 Nangama flood (Figure 10) who remembered grazing his yaks in what had been three distinct pasture areas covering approximate 4.5 km2below the terminal moraine when the GLOF occurred. He heard a deafening noise and a large dust cloud descending from the lake area, followed by a wave that rose above the high-water mark, “like a fountain,” and accompanied by “strange sounds” (some GLOFs in Nepal have been described as creating deep, deafening moaning sounds as they slosh down the river).


Water then began to slowly emerge from the terminal moraine, growing larger and larger by the minute in terms of discharge. The flood that followed was “big, muddy, with stones clashing against each other” (sparks created by rocks may cause the gunpowder smell often reported during a GLOF, and have even been linked to local forest fires).


Floodwaters rose and lowered at intervals, indicating the pulse-like nature reported for GLOFs elsewhere in Nepal. Lama said that Chheche Pokhari, located at the foot of the Nangama valley, was formed from the blockage of the Pabuk Khola by flood sediments and debris (Figures 2 and 10).


Another interpretation of the flood, as reported by Damling Lama Sherpa, 62, also of Yangmais that the lake had been inhabited by a local deity or spirit (Khangba), similar in appearance to a giant turtle, who became angry with the local people and caused the GLOFs as a consequence. Just before the flood he could hear “strange sounds” which presumably came from the Khangba.



The turtle then floated down valley in the flood waters until it reached the bridge at Yangma village. Refusing to go under the bridge, the turtle’s body blocked the flood water, resulting in a temporary lake upstream that damaged hillslopes and grazing land, but which drained when it decided to continue downriver.

The flood was also linked by religious leaders to the fact that “modern people have become wicked, so bad things happen”, a frequently heard lament and correlation in highland Nepal that links greed, the erosion of traditional practices, and lack of respect for gods, deities, and spirits with negative consequences, both physical (earthquakes, floods) and social (death, suffering).

Our final visit of a GLOF site was to the Lhonak Glacier, en route to the Kanchenjunga base camp north (Figure 2 and 15). This was the source of the 1921 Lhonak GLOF which is of particular interest because, nearly 100 years after its occurrence, it was still mentioned to by people throughout the Tamor watershed.


Lakpa Chhetan Sherpa, 88, of Ghunsa (Figure 16) said that his ancestors had come from Tibet and settled at Khangpachen, a goth (yak pasture) downstream of the Lhonak Glacier, some 500 years ago, where they farmed and herded yak.


When the flood destroyed all of their fields in 1921 his grandfather, whose wife was among the fatalities of the flood, moved to Ghunsa, where the family has lived ever since. Lakpa Chhetan Sherpa also reported that another small flood of the Ghunsa River had occurred in “either August or September” of 2011, the approximate time that a deadly earthquake (6.9 magnitude) centered in the Kanchenjunga region occurred that killed an estimated 111 people, which brought our total number of new, unreported floods from the Kanchenjunga Conservation Area up to a remarkable six, in addition to the 1980 Nangama GLOF.


The massive breach in the terminal moraine of Lhonak, and deposits of debris at the foot of the moraine, are testimony to the power that the flood must have possessed (Figure 15). In fact, most people probably walk by such features and ignore them for the beautiful snow and ice peaks jutting above, never realising that they are walking in the middle of a catastrophic event that changed people’s lives, livelihoods, and view of the world nearly 100 years ago. We certainly wouldn’t have known anything about the glacial lakes and moraines that we visited if we hadn’t consulted with local people along the way.


Back in the US, it was March of 2020 before I was finally able to start transcribing the recorded interviews and designing a framework for a scientific research paper. While rumours of a strange global virus were circulating, I contacted Mohan Bahadur Chand, a recently-minted PhD student at Hokkaido University and, coincidentally, one of Teiji Watanabe’s students.


Mohan’s 2020 PhD thesis was, in fact, about the development of glacial lakes in the Kanchenjunga region, and he was rapidly able to document the occurrence of five of the six GLOFs reported by local informants using before and after remote sensing images, mostly through the presence of flood scars, breached terminal moraines, and deposits.

He also located two additional smaller GLOFs that had not been mentioned, probably because they were smaller and located in remote regions near glaciers. Mohan had been aware of these events through his own research work, but he had been unable to assign approximate dates to their actual occurrence until provided with the results of the project’s oral history component.


Jonathan Lala, graduate student in engineering at the University of Wisconsin Madison, developed a numerical simulation model of the Nangama GLOF that strongly suggested that it was triggered by an ice/debris avalanche of some 800,000 m3of material, just like local people had thought, causing a surge wave that breached the terminal moraine and released an estimated 11 million cubic meters of water, with debris from the flood damming the Pabuk Khola river 2km below to form what is today known as Chheche Pokhari—just like local people had said.


Milan Shrestha, an anthropologist at Arizona State University, provided the methodological framework for oral history as a tool in recounting past GLOF events. He also provided essential information about mountain cultures and religious beliefs that helped immensely with our understanding and interpretations of many of the interviews conducted.  


Plant ecologist Elizabeth Byers, when not photographing wild flowers for her new Himalayan wildflower app, was responsible for taking many of the field measurements of the Nangama glacial lake and terminal moraine that Jonathan Lala considered to be essential to his numeric modeling.


And Teiji Watanabe, whose article from over 20 years ago about the Nangama GLOF sparked the launch of our 2019 expedition, shared his vast expertise and more recent thoughts about the continued dangers of glacial lakes in the Kanchenjunga region.


Together, the different contributions resulted in our scientific paper published earlier this month in the journal Sustainability, ‘Reconstructing the history of glacial lake outburst floods in the Kanchenjunga Conservation Area, east Nepal: an interdisciplinary approach’.


In summary, the experience demonstrated the benefits and utility of using interdisciplinary research approaches to the better understanding of past and poorly documented GLOF events in Nepal and elsewhere, especially in remote, data-scarce high mountain environments rarely visited by scientists. Modern technologies and tools such as Geographical Information Systems, satellite imagery, and flood modeling are becoming increasingly sophisticated and valuable to our understanding of our changing world, but they have their own temporal and analytical limitations as well.


Involving local people in research can often help to fill these gaps in surprising ways. The research also demonstrates that while development agencies are busy writing up guidelines for mountain people to adapt to climate change and hazard risk impacts, these same people have been doing so for decades, if not for centuries.


They suffer (each flood mentioned killed many people and destroyed millions in infrastructure), they find ways to adapt (move to Ghunsa, graze the cattle higher), and they press on. Their resilience in the face of a history of unexpected GLOFs could provide some valuable lessons for us all, as we face the shock and completely unanticipated challenges imposed by COVID-19 and the global pandemic.

Alton C Byers, PhDis a Senior Research Associate and Faculty at the Institute for Arctic and Alpine Research (INSTAAR), University of Colorado at Boulder. A scientific version of this article, recently published in Sustainability, can be downloaded for free here.



Acknowledgements: The author would like to thank the local people of the Kanchenjunga Conservation Area for both their hospitality and generous sharing of their knowledge of historic glacial lake outburst floods. Staff of the Kanchenjunga Conservation Area are also thanked for the invaluable work that they are doing in biodiversity conservation as well as in the nature-based economic development of the region. Partial support for the expedition’s field costs was provided by the National Science Foundation.


[1]See: Mick Conefrey, 2020. The Last Great Mountain: The First Ascent of Kangchenjunga. Mike Conefrey Books.


This article first appeared in Nepali Times on July 25th, 2020. The article has been reposted along with the photos with explicit consent from the author.

eARThumanities at NYU Abu Dhabi

@2020 Geopolitics & Ecology of Himalayan Water