What Triggers Glacial Lake Outburst Floods? Why Uttarakhand?

What we know about GLOFs and what triggers them?

Flash floods caused by the outburst of glacial lakes are called as Glacial Lake Outburst Flood (GLOF).

(Photo: The Quint)

Video Producer: Shohini Bose

Video Editor: Ashutosh Bhardwaj

Fourteen people are feared dead and at least 170 others are reportedly missing after a flash flood triggered by a glacier burst wreaked havoc in Uttarakhand's Chamoli district, on 7 February, Sunday.

While the exact reasons behind the disaster are still being ascertained, thousands of people living close to the Alaknanda and Dhauliganga rivers had to be evacuated.

As political leaders extended their consolations, several environmentalists and climate activists are trying to draw attention to India’s climate crisis that gets largely ignored in policy-making. They have blamed mindless developmental projects and human interventions for destroying the Himalayan ecology, that they say, triggered this calamity.

But what do we know about GLOFs and what triggers it?

What is a Glacial Outburst?

According to India’s Central Water Commission (CWC) website, flash floods caused by the bursting of glacial lakes are called Glacial Lake Outburst Flood (GLOF).

Such floods happen when glacial meltwater breaks through moraine dams which are deposits of ice and debris collected from a glacial sheet. When large glacial sheets retreat, they leave behind a huge impression on the ground where water collects and moraines usually act as natural dams for these lakes.

But with rising water levels, moraine dams may collapse causing the water to burst out and create floods or a GLOF which impact downstream communities and infrastructure.

Another way that a GLOF can get triggered are when waves are formed due to avalanches or rockfalls or glacial ice that end up breaking moraine dams. Dam failures can also happen due to water seepage.

GLOFs are known to occur in Himalayan regions where such lakes had often been formed by landslides.

“GLOFs have immense potential of flooding in downstream areas, causing disastrous consequences due to release of large volumes of water in very short interval of time. Most often, the consequences arising out of such situations are highly unpredictable primarily due to lack of availability of sufficient data regarding rainfall intensity, location of landslide, impounded volume and area and physical conditions of lakes/ water bodies. Therefore, Glacial Lakes and Water Bodies in Himalayan Region need to be closely monitored,” the CWC website says.

Can climate change increase the frequency of GLOFs?

The short answer is yes, absolutely!

GLOF disasters are not a new phenomenon. For example, an article titled 'Glacial Lake Outburst Flood Disasters and Integrated Risk Management in China' that was published in the International Journal of Disaster Risk Science, says that in the past 65 years, over 21 GLOF disasters have been recorded and nearly 30,000 people have been killed in the Peruvian Cordillera Blanca.

Research has shown that human intervention and climate change can escalate GLOF disasters.

As per the aforementioned article, "In the past 20 years, glaciers in these regions have retreated and thinned rapidly as a response to regional climate warming, leading to the formation of new glacial lakes and the expansion of existing glacial lakes. These areas are located in the border belt between the Indian and the Eurasian plates, where tectonic seismic activity is also frequent and intense. Earthquakes have often compromised the stability of mountain slopes, glaciers, and moraine dams, resulting in an imbalance in the state of glacial lakes and an increase of loose materials in valleys. It is foreseeable that the possibility of GLOFs and disaster occurrence will be great in the context of frequent earthquakes and continued climate warming."

Are potentially dangerous glacial lakes monitored?

The work of monitoring of glacial lakes/water bodies was taken up by Central Water Commission (CWC) during XIth plan period. CWC signed an MOU with National Remote Sensing Centre (NRSC), Hyderabad in 2009 for making an inventory and monitoring of Glacial Lakes / Water Bodies in the Himalayan region catchment which contributes to rivers flowing in India using satellite imageries, remote sensing and GIS techniques.

According to a 2020 report published The International Centre for Integrated Mountain Development, a Nepal-based intergovernmental learning and knowledge sharing centre, there are 47 potentially dangerous glacial lakes (PDGLs) within the Koshi, Gandaki, and Karnali river basins of Nepal, the Tibet Autonomous Region of China, and India.

What happened in Uttarakhand?

While some reports say that the Nanda Devi glacier had broken off triggering an avalanche followed by a flood in the Alaknanda and Dhauli Ganga rivers, the exact cause of the calamity is yet to be ascertained.

On Monday, 8 February, a DRDO team of snow and avalanche experts from its newly-created Defence Geo-Informatics Research Establishment visited the site for assessment.

The director of the Wadia Institute of Himalayan Geology, Kalachand Sain, said two teams of glaciologists will leave Dehradun on Monday morning.