Shako Chho emerges as Sikkim’s most vulnerable glacial lake

BIJOY GURUNG

State proposes solar-powered pumping system to lower lake level; DPR forwarded to NDMA for consideration

GANGTOK, : After more than two and a half years of detailed studies and painstaking field visits, the Sikkim government has identified three glacial lakes in North Sikkim as posing the highest risk of a Glacial Lake Outburst Flood (GLOF), with Shako Chho identified as the most vulnerable.

The State government has accordingly proposed mitigation measures to the Government of India, including a solar-powered pumping system to lower the water level of Shako Chho, a medium-sized glacial lake which is located above Thangu and contains around 27 million cubic metres of water.

The proposed pumping system by Department of Science & Technology (DST) aims to lower the lake’s existing water level further by around 20 metres over a period of two to three years. The objective is to reduce the volume of water in the lake and thereby lower the potential impact of an avalanche or other natural event that could trigger a GLOF.

A Detailed Project Report (DPR) for using solar-powered pumps to lower the water level of Shako Chho has been submitted to the Sikkim State Disaster Management Authority (SSDMA), which has forwarded it to the National Disaster Management Authority (NDMA). The proposal is currently under consideration, it was informed.

The urgency for detailed studies and mitigation measures comes in the backdrop of the October 2023 GLOF-induced flash floods that caused widespread destruction downstream in the northern and eastern riverine belts of Sikkim and further downstream in North Bengal along the Teesta River. The recent GLOF which has devastated Nepal on August 26 has also heightened concerns among people in Sikkim.

However, DST officials here said that the level of threat from the identified lakes in Sikkim is not comparable to the recent disaster in Nepal based on the studies conducted so far, while cautioning that preparedness is essential given the State’s highly seismic nature and difficult Himalayan terrain.

National Disaster Management Authority (NDMA) has identified 189 high-vulnerability glacial lakes in the Indian Himalayas, including 40 high-hazard glacial lakes in Sikkim. This means one out of every four high-risk glacial lakes identified in India is located in Sikkim. Of these 40 glacial lakes in the State, 16 have been categorised under the highest-risk classification.

Since August 2024, the State Department of Science & Technology (DST), along with concerned State departments and Central agencies, has visited and studied 13 of these 16 highly vulnerable glacial lakes, mostly in North Sikkim.

All these sites are located above 17,000 feet and are extremely difficult to access, requiring preparations similar to those for a mountaineering expedition.

The most recent multi-disciplinary study expedition, involving scientists, engineers and geologists, was conducted from July 23 to August 8 this year. During the expedition, Automatic Weather Stations (AWS) were installed at Kerang near Gurudongmar Lake and at Dolma Sampa, located below the Lhonak Valley.

On Tuesday, DST Minister Pintso Namgyal Lepcha, Principal Secretary Dr Sandeep Tambe, Secretary-cum-Principal Director Dhiren Shrestha and senior engineers briefed the media in Gangtok on the extensive glacial studies carried out by the State, their findings and the mitigation measures proposed to the concerned Central agencies.

Minister Lepcha said the DST and concerned State departments, along with Central agencies such as the NDMA and Central Water Commission (CWC), have been consistently studying high-risk glacial lakes, mapping their potential threats and examining the best possible mitigation measures under the direction of Chief Minister Prem Singh Tamang-Golay.

“People of Sikkim are concerned due to the recent natural disasters in the neighbouring country but in Sikkim’s context, such level of threat is not there as per the studies till now. But anything can happen in future and that’s why we conducted these extensive studies and are preparing precautionary measures,” the minister said.

The DST Principal Secretary explained that one of the main objectives of the glacial lake studies is to determine the volume of water contained in the lakes, as the volume of water is a major factor in determining the potential impact of a GLOF.

A specialised unmanned boat is deployed on the lake and remotely controlled to measure and quantify the volume of water at different points within a glacial lake.

The second major aspect of the study focuses on the strength and stability of the natural dam that holds back the lake, including whether it can withstand an avalanche entering the lake.

Sub-surface geological studies are carried out using specialised equipment to assess the stability of the natural dam and determine the strength of the terminal moraine. Scientists and engineers examine whether the moraine is composed of hard rock or softer material and whether water is permeating through the structure.

The lateral moraine is also studied to assess the potential threat posed by an avalanche striking the lake.

“Glacial hazard is a new threat to humanity because of climate change. Whatever we are doing, it is for the first time and that is why it takes more time. It is innovative work which has to be done in very difficult terrain. We have covered and studied 13 lakes out of 16 lakes and now we have detailed information to prepare and propose mitigation measures,” said Dr Tambe.

Officials said the biggest threat that can lead to flash floods from glacial lakes is the volume of water contained within them. Containing or reducing the volume of water in the lakes through appropriate measures therefore appears to be the most feasible approach to mitigating the potential impact.

Three glacial lake clusters in North Sikkim have been identified as posing the most potent threat - Shako Chho, the North and South Lhonak lakes, and the Gurudongmar Lake cluster.

Among these, Shako Chho has been identified as the highest-risk lake because it does not have a natural outlet, according to DST officials.

Water is currently seeping out through its terminal moraine, which officials said could potentially become unstable. The lake drains directly towards Thangu village, where several Defence establishments are also located, making it a potential risk to both civilians and Defence personnel.

Officials described both the lake and its terminal moraine as fragile.

“Extensive studies have been done at this lake and all have concluded that it is very risky. Experts have told us not to touch the lake at all and not to do any engineering measures. They have recommended non-invasive projects for pumping out the water from the lake,” said Dr Tambe.

According to DST officials, a solar-powered pumping system has been identified as the most viable mitigation option for Shako Chho to gradually lower its water level.

Once the water level is reduced, the potential threat is also expected to decrease. However, officials are still examining what type of pumps can operate effectively at an altitude of around 17,000 feet.

There is no electricity supply at the site, while water freezes during winter. Officials also have to determine how the pumping system can be installed and operated without creating additional risks to the fragile lake and its surrounding ecosystem.

The use of solar energy has been considered because of the significant logistical constraints at the site. The nearest power grid is around 20 km away, while transporting fuel for conventional mechanical pumps would require head-loading over steep and difficult terrain, making conventional pumping systems economically and operationally unfeasible.

A solar-powered pumping system has therefore been identified as the most viable option.

Shako Chho is a medium-sized lake with an estimated total water volume of around 27 million cubic metres.

We want to reduce the water level further by 20 metres over two to three years so that when an avalanche comes, the waves and flood are contained within the lake, said the DST officials.

Officials explained that once water bursts out of a glacial lake, it gains momentum and can acquire enormous force as it moves downstream, carrying boulders and debris along with it. This can significantly increase the destructive potential of a GLOF. Hence, best preventive efforts should be made to contain the outburst of water within the lake itself.

Asked whether a GLOF can be completely prevented, DST officials said Sikkim’s location in the young fold mountains of the Himalayas and its status as a highly seismically active zone make it impossible to rule out sudden natural events.

Earthquakes, they noted, cannot currently be forecast, making preparedness and risk reduction particularly important.Preparedness is most important and we have been taking mitigation measures besides sensitising the people on what steps to take when a GLOF-like event happens, the officials said.

Following the Sikkim GLOF of October 2023, the State government constituted the Sikkim Commission on Glacier Hazard, whose report is currently at the final stage.

Sikkim has 84 glaciers, each covering an area of more than one square kilometre, underlining the need for continued monitoring, scientific studies and preparedness measures to reduce the risks associated with glacial hazards.

The State has also been strengthening its monitoring and early-warning capabilities by installing monitoring and automatic weather systems at Kerang near Gurudongmar Lake, Shako Chu, and Lhonak Lakes.

BOX

Glacial Lakes in Sikkim: Key Facts

189 - High-vulnerability glacial lakes identified across the Indian Himalayas

40 - High-hazard glacial lakes in Sikkim

16 - Sikkim lakes classified under the highest-risk category

13 - High-risk lakes studied by the State and Central agencies so far

3 - Glacial lake systems identified as posing the most potent threat in North Sikkim

84 - Glaciers in Sikkim covering more than one sq km each

17,000+ ft - Approximate altitude of the high-risk lake sites studied

Why Shako Chho is a Concern

Location: North Sikkim

Water volume: Around 27 million cubic metres

Altitude: Around 17,000 ft

Key concern: No natural outlet

Natural dam: Terminal moraine considered fragile

Downstream area: Thangu village

Potentially exposed: Civilian population and Defence establishments

Proposed measure: Solar-powered pumping system

Target: Lower water level by around 20 metres

Timeline: 2-3 years

Status: DPR forwarded to NDMA; proposal under consideration