Glacial Floods

By Dhurjati Mukherjee

The nature and scale of disasters are becoming increasingly hazardous, affecting millions of people across the world. This is starkly evident in the very recent glacial flood disaster in Nepal. The catastrophe was of such magnitude that the death toll reportedly rose to about 1000, while more than 2,500 people were reported missing, including around 275 Indians, according to Nepal’s disaster response agency.

T\he disaster was reportedly triggered by the bursting of a glacial lake formed following a landslide. Satellite imagery reviewed by The New York Times indicated that the lake had breached, unleashing a massive flood and causing widespread devastation.

Scientists at the International Centre for Integrated Maintain Development (ICIMOD) estimate that a large volume of ice and rock debris resulted in a powerful surge of water, sediment and boulders downstream. Such cascading behaviour has been witnessed before in the Himalayas, reviving comparisons with the 2021 Chamoli tragedy in Uttarakhand when a massive rock and ice avalanche triggered a deluge, killing 200 people and destroying two hydropower projects. According to geoscientists, a rock-ice avalanche is dangerous because it may set in motion a chain reaction. Experts pointed out that warm temperatures are adding to the instability of high mountain environments.

The flash floods in Nepal and Tibet were according to geologists set off by a dual high-altitude landslide and glacial avalanche that unleashed huge volumes of water. Disaster experts are of the opinion that such events are difficult to predict. Moreover, the collapse being sudden, it would have been extremely difficult to warn in advance.

As per available statistics, there are 2070 glacial lakes in Nepal, 21 of which are classified as high risk, as per a 2020 report by the ICIMOD. There are many more surrounding lakes in the Himalayan areas of China and India. There were altogether 135 GLOF (glacial lake outburst flood) events in the Karakoram region from 1900 to 2000, and the present century has already witnessed around 85. As the region is full of glaciers – around 22,800 sq. km in the Himalayas and the area is warming faster than the planet, the region is susceptible to more such floods.

Higher temperatures and rainfall are accelerating this change and that is the reason why such events occur from June to August. Scientists see a lot of glaciers melting in the coming years and, by some estimates, 65 per cent of the ice mass region could disappear by 2100.

In such a situation, roughly 1 million people who live within 10 km of a glacial lake are susceptible to the growing risk of disasters and it would be necessary to relocate them away from narrow river valleys and go easy on infra projects in mountainous areas. 

There is need to give credence to IPCC’s special report on oceans and cryosphere which confirmed that glacial lake outburst floods are expected to become more frequent as warming continues because the same warming that shrinks glaciers is what fills and destabilises lakes downstream of them. An Indian Institute of Tropical Meteorology assessment found that the Indo-Gangetic plain witnessed its mean southwest monsoon rainfall decline by roughly 0.5 mm per day per decade between 1951 and 2924, a genuine drying trend across the belt that includes Bihar. Thus, it is evident that there are sharper, more concentrated bursts even as the season’s average falls.

As regards India, it needs to be stated that this country witnesses the highest number of fatalities from GLOF, similar to the one witnessed in Nepal. This has been revealed by experts from a global consortium belonging to six-seven countries. It would be pertinent to mention that a paper titled ‘Glacial Outburst Flood Risks, Response Strategies & Adaptation Gaps in the Hindu Kush Himalayan Region’, which covers data from 1995 to 2025, found that China witnessed 199 GLOFs, followed by Pakistan (152) and India (62) and Nepal (5).

The paper rightly pointed out that climate factors meaning acceleration of warming, specially since the start of this century, led to the increasing frequency of such avalanches.  It is significant that the study noted “The predominance of moraine and ice-damned lakes in the HKH (Hindu Kush Himalayan) GLOF events, accounting for around 80 per cent of observed outburst and almost all recorded fatalities reflects the inherent instability of these dam types under warming conditions”.

It can definitely be stated that with satellites available now, the situation is much easier though prediction, as experts pointed out, may be a difficult proposition. Moreover, countries exposed to these mountains and glaciers like China, Pakistan, Nepal and Bhutan should coordinate to keep people safe across borders. But this has not happened till date. India’s National GLOF Risk Mitigation Programme marked 195 glacial lakes at risk and follows five key priorities such as assessment, monitoring, early warning, mitigation and community awareness. There is also a high-level coordination committee on GLOF risk reduction.  

India took some positive steps after October 2023 when global rocks of 14.7 cubic metre collapsed in South Lhounak Lake in Sikkim generating a 20 m high displacement wave, wiping out several hydropower assets and settlements on its way downstream. The government also allocated Rs 150 crore for the National GLOF Risk Mitigation Programme for four Himalayan states having high risk glacial lakes.   

While the government has started giving some attention to the question of lake outburst, there is need to take lessons from the Sikkim tragedy followed by one in Chamoli in 2025 and then the recent one of our neighbour. It is necessary to install glacial regions in the mountainous areas that can transmit data directly to monitoring stations. Added to this, AI systems may be used to spot changes in these glaciers and create their risk profiles. Many other countries have adopted similar systems.

Experts warn that a far greater disaster could strike the region if adequate safety measures are not strictly enforced and vulnerable populations are not relocated to safer areas, preferably at least 5–10 km away from glaciers and glacial lakes. There is an urgent need for an inter-governmental mechanism involving India, Bhutan and Nepal, and perhaps China, to formulate a coordinated long-term strategy for monitoring glaciers, assessing risks and preventing or mitigating GLOFs. Given that glaciers and glacial lakes do not recognise national boundaries, regional cooperation, real-time data sharing and an effective early-warning system are imperative.  — INFA