A devastating flash flood, accompanied by a mudslide and debris, swept through Thame village in Solukhumbu district. Screenshot from YouTube video by Anand Nepal. Fair use.

This story by Sonia Awale was first published on the Nepali Times. An edited and shortened version is republished below as part of a content-sharing agreement with Global Voices.

At exactly 9 am on August 16th, a 4.5 magnitude earthquake hit Xizang on the Tibetan Plateau. Four hours later, 65 kilometres away in Nepal, a glacial lake burst unleashing a cascade of destruction downstream.

It is not certain if that nearby tremor caused the lake to burst — either because an avalanche on the south ridge of Mt Tengi Ragi Tau fell into it, or heavy monsoon rain led to the collapse of a moraine.

Either way, the snowmelt emptied into another lake below and unleashed a debris flow that roared down the valley to the village of Thame. Fortunately, children at a school had gone home early that Friday and inhabitants had time to climb to safety when they heard the approaching roar. There were no fatalities.

Thame was not as lucky on August 4th, 1985, when a bigger lake in an adjacent valley, Dig Tso, burst after an avalanche fell on it. Twelve people were swept away by the ensuing flood, a newly built hydropower plant was destroyed, and a section of the Everest trekking trail was washed away.

Glaciologist Tenzing Chogyal Sherpa remembers his mother telling him that their home in Namche Bazaar was spared because it was on higher ground.

“But she told us that with trails destroyed, food and supplies couldn’t reach us. At one point, her family had to survive on rotten potatoes,” recalls Sherpa, who works at the Kathmandu-based International Centre for Integrated Mountain Development (ICIMOD) and uses remote sensing to map climate-induced hazards in the Himalayas.

He says the Thame flood this week was a reminder of the inherent risk of living in the mountains — a risk which is significantly magnified by ongoing climate breakdown.

“To the south, we have Lumding Tso, a potentially dangerous glacial lake that also empties into the Dudh Kosi river, and to the west in Rolwaling is Tso Rolpa, a lake that is now three kilometres long. And to the north is Dig Tsho, which burst in 1985,” says Sherpa.

Dik Tsho (Dig Tsho) glacial lake in Namche, Nepal. Image via Flickr by Matt Westoby. CC BY-NC-ND 2.0.

“We are facing one of the worst disasters since the Dig Tso flood. This is a wake-up call, not just for us in Khumbu region, but for the entire Himalaya to rethink our ways, find alternatives to reduce the risks, and explore measures to protect ourselves,” he adds.

The Thame flood was a smaller disaster compared to the flood that destroyed the Melamchi headworks in 2021, the massive Sikkim flood last year, or the debris flow that ravaged Kagbeni village in Mustang District of the Himalayas. All were caused by glacial lake bursts or moraine collapses due to extreme rainfall.

Anil Pokhrel of the National Disaster Risk Reduction and Management Authority (NDRRMA) flew to Thame on the morning of August 17th to inspect the glaciers above the village. He confirmed that two of five small glacial lakes below Tashi Lapcha pass had caused the flood. Satellite data shows that till two years ago, there were only four lakes.

Across the Himalayan mountain range, there are now thousands of new glacial lakes that do not even have names. In Nepal, the 20 most dangerous ones are located in the centre and east of the country, but there are dozens of enlarged lakes in China which drain into tributaries of rivers that flow into Nepal like the two Bhote Kosis, Arun and Tama Kosi.

Some of these lakes are infamous because of their volume, the rate at which they are expanding, and the potential danger they pose to populations downstream — like Tso Rolpa, Imja Tso and Thulagi.

But the Thame flood, and others like the Nare Lake outburst below Ama Dablam mountains in 1977 show that even smaller lakes can cause massive damage.

Even a relatively small flood like the one in Thame can be damaging far downstream. The debris flow moved swiftly downstream, destroying a bridge worth NPR 80 million (USD 596,000) on the Dudh Kosi in Okhaldhunga. Most villages downstream had been evacuated, so there were no casualties. If the flood had been bigger, it would have threatened major hydropower projects on the Dudh Kosi.

Thame is at an elevation of 3,840 metres, but Pokhrel of NDRRMA says he was surprised by how warm it was up there this week. “It felt like Kathmandu,” he says. “And satellite imagery shows accelerated melting of the upstream in the past month which could have led to the cascading collapse of the two lakes.”

In his preliminary report after observing the Thame, Pokhrel notes that the Forsey Precipitation Monitoring Station near the glacial outburst point was recording a total of 65 millimetres of rainfall per day. He wrote:

On August 16th, the temperature rose to a maximum of 15.9°C. On the same day, at the Rakhuwabazar Precipitation Monitoring Station in Khotang district near the Dudh Kosi River, the water level rose from 4.29 meters at 5:10PM to 5.53 meters at 5:40PM.

Glacial lake outbursts and debris flows are going to be more destructive and frequent in Nepal in the coming years, making them a fact of life. Seismic risk in the Himalayas adds to the dangers posed by the climate emergency.

Local communities and governments have no option but to adapt by installing early warning systems, planning smaller decentralised hydropower schemes, moving settlements and infrastructure higher, and conducting detailed hazard mapping.

“Thame showed us we cannot only rely on satellite mapping, and why in-situ observation is so important in a country with such a diverse topography and climate as ours,” says Sherpa. “There are more than 50,000 glaciers in the Himalayan region and we haven’t even studied one percent of them.”

Despite the scarcity of field data, there have been considerable advances in remote sensing technologies that have helped fill this gap in data and help understand the changing cryosphere. ICIMOD’s report shows that glacier mass loss has increased by 65 percent in recent decades. The report also warns that the risk of flooding could increase much more in the coming century.

Because so many of Nepal’s rivers are transboundary, a bilateral early warning mechanism with China is also urgent. Because of the scale of the danger, Nepal needs resources from the international community for adaptation, as well as loss and damage reparation to cope with future risks.

Tenzing Chogyal Sherpa co-founded a global advocacy campaign called #SaveOurSnow last year to provide local communities with agency to deal with climate-induced risk.

Through #SaveOurSnow Sherpa hopes that Himalayan communities can draw international attention to monsoon extremes, drying springs, winter droughts and heat waves so that they can adapt and survive. Sherpa says:

 As glaciers melt and lakes expand, disasters like Thame will be more frequent, we have to adapt. We need to tell our stories to the world, even as they continue to debate on the topic, we are already facing the brunt of it without having caused it ourselves. At local levels, we have to get back on our feet and prepare for what's coming.