Glof: The Looming Threat

GLOF (Glacial lake Outburst Flood) has recently been in the news after a major disaster in Nepal, with a lot of discussion happening around the same. A Glacial Lake is a huge water body with millions of litres of water and molten ice. It is a result of glacial melting which can be attributed primarily to global warming, leading to an increase in the number and size of glacial lakes across the globe. This is further aggravated by human intervention and development around glacial catchment areas. Many of these glacial lakes are susceptible to outburst floods, which has far-reaching consequences on downstream infrastructure and livelihoods.

Glacial lakes are formed through two different methods. Melting and retreat of glacier margin causes water to be collected between the glacier and the abandoned frontal rock debris, resulting in what is known as Moraine-dammed lake. The frontal rocky ridge or moraine acts as a dam for such a lake. The other scenario is that of Ice-dammed lakes where the movement of the glacier blocks the drainage and causes the resultant water to accumulate into a lake. As glacial lakes increase in size, they become hazardous since their support in the form of ice and sediment (moraine ridge) is quite unstable. The volatility of slopes and glacial lakes is further aggravated in young and seismically active mountains like Himalayas, where hazard chains and avalanches are a common occurrence.

Global Lake Outburst Flood is caused by the rupture of the dam holding back the glacial lake. The dam is either a moraine (ridge left behind by a receding glacier) or a glacier (which has blocked the flow of water). The dam rupture could be caused by any of the following reasons :
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Sudden inflow of material into the lake, possibly due to avalanches, rockfalls or pieces of glacial ice-melts, causing displacement of water overtopping the moraine.
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Rapid inflow of water from an upstream glacier.
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Abnormal rainfall or snowmelt causing sudden increase in the water level of the lake.
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Earthquakes.
GLOF leads to release of abnormally huge quantities of water over a very short span of time. The extremely high flow of water coupled with river bed erosion creates havoc on the downstream plains by massive inundation. The sudden release of water, rapid occurrence and abnormally high water discharge combined with boulders, mud, ice and trees adds to the widespread destruction, resulting in loss of life and property. These intrinsic and extrinsic hazard drivers can cause largely unpredictable, rapid, and fatal draining of lake water, which may transform into debris or hyper-concentrated flow as the flood entrains sediment. Such floods often culminate in landscape changes and alter regional climate. 

Ice-dammed lake outbursts result in lower discharge and are relatively less destructive as compared to moraine-dam outbursts. However, since moraine-dam outburst causes dam destruction, it cannot re-occur, whereas ice-dammed outbursts can occur repetitively by the lake getting refilled multiple times. Due to the nature of their formation, the threat from moraine-dammed outbursts increases with glacier retreat while that of ice-dammed outburst increases with glacier growth. Since global warming is causing glacier melting and hence retreat, we will see more of moraine-dammed outburst floods in future. Additionally, with a growth in lake size increasing the risk of overtopping failures, we have an increased probability of outburst floods being triggered and heightened potential flood volume, which are among the main factors contributing to the disaster. 

Glacial Lake Outburst Floods are characterised by a metric - GLOF Susceptibility score, which evaluates the likelihood of a glacial lake to breach and cause an outburst flood. It takes into account lake dimensions (volume, depth), dam properties (material, slope) and environmental factors (seismic activity, avalanche, warming, development). Dam slope is recognized as a critical factor affecting both the stability of the dam and the erosive potential of the downstream channel. Machine learning algorithms, data-driven and objective methods are extensively used to establish the relationship between triggering factors and probability of occurrence.

In the Himalayan region, glacial lakes and water bodies have demonstrated an increasing water spread over recent years. The region has lost over 40% glacial mass in past four decades, thereby creating a significantly high number of glacial lakes in the vicinity. Jammu & Kashmir happens to be one of the vulnerable parts of the country, with a persistent risk of GLOF, despite no outburst in the past. As far as this region is concerned, outbursts frequently start with rapid mass movement into the lake, often due to slope failure from the adjoining mountains, leading to displacement waves and overtopping the dam, causing moraine dam incision and resulting in a sudden discharge of lake water. As the flood propagates farther downstream, it transforms into debris flow and hyper-concentrated or secondary debris flow, depending on the geologic and topographic characteristics of the river channel and available sediment.

The discharge during GLOF is rapid and huge, without any sufficient time for any proactive remediation or warning. We need to look at possible Early Warning Systems, at least to safeguard lives and critical infrastructure. National Disaster Management Authority has charted out a proactive approach to mitigate the risk of GLOFs. Some of these remedial measures are :
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Identification of potentially vulnerable lakes based on field observations, geological characteristics and surrounding conditions.
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Tracking of temperature fluctuations, precipitation, and climate patterns influencing glacial melt and lake stability.
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Monitoring of glacial lake water levels, river discharge, and downstream flood risks.
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Analysing temperature trends, rainfall, and seismic activity to assess the risk of sudden lake bursts.
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Simulation of existing water bodies and remote monitoring through connected devices/ drones to detect any changes, which could trigger an alarm.
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Diversion of water flow, wherever possible, through controlled channels and flow retention structures.
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Restriction and control of development activities in GLOF prone areas.
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Studying glacial dynamics, climate change impacts, and AI based flood forecasting models.
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Simulation of potential flood paths, helping forecasters predict downstream impacts.
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Promoting watershed management, reforestation, and ecosystem-based flood mitigation strategies.
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Risk Indexing of Glacial Lakes and ranking such lakes based on their likelihood of failure and potential damage they could cause in the event of an outburst flood.
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Integrate GLOF metrics into hydropower feasibility studies and Disaster Management policies.
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Creation of rapid response teams and training of tour operators and local communities.
In Jammu & Kashmir, glacial thinning is occurring at an accelerated rate compared to other parts of the Himalayas. This reduction in glacial extent has also spurred the formation and expansion of glacial lakes at an alarming rate, exhibiting a 26% growth in lake surface area over 30 years, with 155 glacial lakes in existence at present. According to a research study, five glacial lakes in Kashmir namely Bramsar, Nundkol, Bhagsar, Chirsar and Gangabal have high GLOF susceptibility. Besides, there is a serious threat on Warwan basin in Kishtwar area, the lake having demonstrated a threefold growth in two decades, with some glacial lakes in quite proximity to hydroelectric projects on the Chenab river. Sonamarg-Ladakh corridor is also vulnerable due to unstable glacial lakes and high tourist activity around the area. The issue demands focused attention as this includes strategic concerns pertaining to Hydropower projects and Leh highway, besides loss of life and property.

Glacial lake outburst floods demonstrate the serious impact of changing mountain environments on downstream population and the risk. Understanding these risks and looking for possible mitigations along with early warning systems are essential for protection against major disasters. It is time for a proper Early Warning System to be put in place and initiate awareness campaigns amongst the downstream population about possible risks, preparedness and mitigations. The recent disaster in Nepal should act as a wakeup call for all regions sitting on susceptible Glacial lakes.

The author is a technocrat with expertise in Data Analytics, Cyber Law and Digital Forensics. He is currently acting as consulting advisor/ mentor to several startups and an ardent supporter of causes pertaining to Environment and Sustainability.