As global warming shrinks glaciers along the world’s highest peaks, glacial lakes in Nepal are increasingly at risk of bursting the natural dams containing them - endangering the lives of tens of thousands in communities below, experts say.
Nepalese authorities have identified about 20 “priority” lakes at risk of leading to glacial lake outburst floods (GLOFs), and are using various methods to reduce the volume of water in some of them.
“With climate change causing the rapid melting of glaciers, the glacial lakes are growing so quickly that the risk of a disaster occurring throughout the Himalayas is increasing,” said Pradeep Mool, of the International Centre for Integrated Mountain Development (ICIMOD), a Kathmandu-based organization funded by eight countries that researches climate change and mountain ecosystems.
“GLOFs come very fast, carry great big boulders; they can push down rock walls and destroy river banks. The destructive impact is very, very high,” Mool told IRIN by phone from Kathmandu.
GLOFs occur when the natural dams of ice or rock containing glacial lakes collapse because the lake has rapidly increased in size or its walls are shattered by earthquakes or avalanches. The resulting floods can cause rivers downstream to rise up to 35 metres, destroying everything in their path for up to 100km in only eight hours, he added.
According to an ICIMOD report released in May, Nepal experiences more than 1,000 earthquakes a year, has 2,323 glacial lakes and is particularly vulnerable to GLOFs. The UN Development Programme (UNDP) says GLOFs have occurred in the recent past roughly every 2-5 years.
“Given the variety of parameters that can cause an outburst, a country like Nepal that sits right in the seismic zone is very much at risk,” Mool said.
Nepalese officials became acutely aware of the potential damage GLOFs can cause in August 1985, when the Dig Tsho glacial lake in Nepal burst, destroying a hydropower plant and 30 houses, 14 bridges, and farmland extending 42km into Bhote Koshi Valley.
GLOFs have occurred in high altitude mountains around the world, causing millions of dollars of damage to infrastructure, villages and farms, as well as claiming lives. In 1941 an outburst flood killed 4,500 people in the city of Huaraz, Peru. A 1968 GLOF in the Swiss Alps disgorged 400,000 cubic metres of debris, severely damaging the village of Saas Balen.
The ICIMOD report said a standardized glacial lake inventory is being prepared for the Hindu Kush-Himalayan region and will be used for GLOF risk assessment.
The Hindu Kush-Himalayan region, covering eight countries from Afghanistan to the southwestern borders of China, has nearly 8,800 glacial lakes, including 203 that experts have identified as potentially dangerous - in Bhutan, China, India, Nepal and Pakistan, according to ICIMOD.
According to the Nepalese Department of Hydrology and Meteorology, over the past 50 years, temperatures in the Nepalese Himalayas have increased by an average of 0.04 degrees Celsius each year, causing glaciers to retreat 60 metres per year, creating new lakes and swelling them.
“Satellite imagery of the Himalayan basins is revealing very fast-growing lakes,” said Vijaya Prasad Singh, assistant country director for UNDP in Nepal.
One remarkable example is Imja Tsho, a lake that did not exist in 1960. Fed by the Imja glacier in the Everest region, which is retreating 74m per year, the lake now covers nearly 1sqkm, ICIMOD said.
Since the 1985 Dig Tsho GLOF, the Nepalese government, in coordination with the World Bank, the UNDP, ICIMOD and local NGOs, has been trying to monitor and mitigate the threat, and prepare and inform communities in the valleys below.
In 2000, the Department of Hydrology and Meteorology (DHM) and ICIMOD constructed an outlet channel to funnel lake water away and lower the water level of Tsho Rolpa, one of three “high priority” lakes in Nepal perched above valley communities - and home to about 67,000 villagers.
“The channel has kept Tsho Rolpa steady. We are monitoring the other glacial lakes, but at this point there isn’t much we can do,” said Om Ratna Bajrachary, senior divisional hydrologist at the DHM.
In addition to outlets, other methods include controlled breaching of the dam, pumping or siphoning water from the lake, or tunnelling through or under the barrier, ICIMOD said.
DHM also built an early warning network of sensors and sirens in 19 villages downstream of Tsho Rolpa, but Bajrachary said the system had not yet been activated because of a lack of resources.
UNDP, meanwhile, has trained more than 100 people - including government officials and workers from community-based organizations - from two vulnerable districts in search and rescue and first aid, said Deepak KC, project officer with the UNDP’s Bureau for Crisis Prevention and Recovery.
This article was produced by IRIN News while it was part of the United Nations Office for the Coordination of Humanitarian Affairs. Please send queries on copyright or liability to the UN. For more information: https://shop.un.org/rights-permissions