Tipped as a ‘Ticking Time Bomb,’ the Thorthormi glacial lake has a worst-case-scenario outburst projection since 2010, DUE to melting glaciers
Studies have always warned that Thorthormi Lake could burst at any time. Although it is not known when, experts openly point out that it is definitely bound to happen, which earned it the tag as a ‘ticking time bomb’.
Residents of Thanza village in Lunana were in for a shocker at dinner time on October 30, sending them running for their belongings to flee a possible Glacial Lake Outburst Flood (GLOF) situation when alarm bells triggered from the Thorthormi Lake monitoring station in Lunana.
Field verification staff from the National Centre for Hydrology and Meteorology (NCHM) later that night found out ‘abrupt changes’ in the water level of Thorthormi. Displacements of icebergs and new erosions on the moraine walls of Thorthormi’s subsidiary lakes I and II were also observed.
The NCHM meanwhile hinted towards a possible spillage of Thorthormi’s water into the adjacent Raphstreng Lake which is merely 3 kilometers away approximately. If this happens, it would mean disaster as two water bodies will converge and overflow, causing disaster and havoc in the low lying areas and settlements.
GLOFs are catastrophic discharge of water from glacial lakes. As the glaciers retreat, they leave behind reservoirs of water which grow in size over time. The walls which hold the water in place are structurally unstable and weak, and undergoing constant changes. This increases the risk of breach in these walls and a sudden, devastating discharge of large quantities of water.
These GLOF events have increased in frequency in the latter part of the twentieth century, resulting in loss of life, property and livelihoods in Bhutan and the Himalayan region. Bhutan’s very own devastating GLOF in 1994 from Luggye Tsho killed 20 people, numerous Yaks and damaged dozens of houses and other source of livelihoods and pastureland. Studies have confirmed the presence of 25 ‘potentially dangerous’ glacial lakes in Bhutan, and Thorthormi is one of them.
Moreover, the Lunana area is a basin with altitudes of 4300-4500 meters (m) between the main Himalayan divide and mountains and plateau with 5000-5500m altitudes to the south. The large glaciers are located in the Lunana basin, while smaller glaciers are on plateaus that stretch to the south from the basin.
Field observations and investigation by map and satellite images indicate that supra glacial lakes on the glaciers tend to connect with each other and grow to a large lake rapidly. Lunana is seeing this happen since the 1970s due to retreat and/or melting of glaciers, which subsequently resulted in the 1994 event.
According to research, Luggye, Raphstreng and Thorthormi Lakes are the three potentially dangerous glacial lakes in the Lunana region. These glacial lakes contain large volumes of water, are bound to each other and interact sensitively through water flux and erosion. Constant and regular monitoring of glaciers and glacial lakes is required to prepare necessary mitigation activities.
Thorthormi glacier had no supra glacial ponds on it during the 1950s but now there are numerous ponds that are enlarging and becoming interconnected. The lake measured only 1.28 sqkm in 2001 but is now by far the largest glacial lake in Lunana with a total surface area increase to 3.42 sqkm and ‘still growing’.
These growing and merging processes of lakes pose great threat. According to the Department of Geology and Mines (DGM), the worst case scenario of the changes is a combined GLOF of these lakes with resultant outflow of over 53 million cubic metres of water, three times catastrophic than the 1994 GLOF.
The Throthormi is located between Luggye and Raphstreng Lakes, raising concerns over the stability of the moraine dam which has been decreasing in its size over the years.
If there is a breach, a chain reaction would be caused if one of the lakes in Lunana bursts open. The Raphstreng Lake where earlier artificial canalizing had been carried out would not be able to hold the water from the Thorthormi in case it leaks due to a moraine wall failure.
What causes the outbursts?
It’s the spillage of melting ice. Bhutan has more than 700 glacial lakes but they are melting at an alarming rate due to climate change and rise in temperature.
A significant portion of ice and billions of gallons of water is lost annually from the mountains of Bhutan. Bhutan lost 17 gigatons of glacier ice summing up to a staggering 17,000 trillion liters of water between the years 2004 and 2020.
The NCHM has found out that if the temperature rise by 1 degree celsius, Bhutanese glaciers will shrink by 25 percent and if there is a steady climate, 10 percent of Bhutanese glaciers will vanish in few decades.
According to Hydrologists in the country, in 1957, Thorthormi was a glacier. However, due to climate change event over 2004, the glacier has changed to a lake. This loss of glaciers led to flash floods, debris flow and landslides similar to the 1994 event and therefore, culminated in the devastating flash floods of Gelephu, Phuentsholing and Lhuntse in July this year.
NCHM has further updated ‘17 potential dangerous’ lakes in the Punatsangchhu basin since 2021, aptly phrased as the ‘Ticking Time Bombs’ by glaciologists around the globe.
Tashi Namgyal from Thimphu