In the largest-ever study of glacial lakes, researchers using 30 years of NASA satellite data have found that the volume of these lakes worldwide has increased by about 50% since 1990 as glaciers melt and retreat due to climate change.
The findings, published in the journal Nature Climate Change, will help researchers assessing the potential hazards to communities downstream of these often-unstable lakes and help improve the accuracy of sea level rise estimates by advancing our understanding of how glacial meltwater is transported to the oceans.
Glaciers are retreating on a near-global scale and this study provides scientists with a clearer picture of how much of this water has been stored in lakes.
“We have known that not all meltwater is making it into the oceans immediately,” said lead author Dan Shugar of the University of Calgary in Canada. “But until now there were no data to estimate how much was being stored in lakes or groundwater.” The study estimates current glacial lake volumes total about 37.4 cubic miles (156 cubic kilometres) of water, the equivalent of about one-third the volume of Lake Erie.
Shugar and his collaborators from governments and universities in Canada, the United States and the United Kingdom, working under a grant from NASA’s High Mountain Asia programme, initially planned to use satellite imaging and other remote-sensing data to study two-dozen glacial lakes in High Mountain Asia, the geographic region that includes the Tibetan Plateau and surrounding mountain ranges, including the Himalaya.
“We wrote scripts in Google Earth Engine, an online platform for very large analyses of geospatial data, to look only at High Mountain Asia, and then decided to look at all glacial lakes in the world,” Shugar said. “From there, we were able to build a scaling relationship to estimate the volume of the world’s glacial lakes based on the area of this large population of lakes.”
The team ultimately analysed more than 250,000 scenes from the Landsat satellite missions, a joint NASA/US Geological Survey programme. A decade ago it would not have been possible to process and analyse this volume of data. The team looked at the data-in five time steps beginning with 1990 to examine all the glaciated regions of the world except Antarctica and analyse how glacial lakes changed over that period.
Shugar pointed out that while water from melting glaciers stored in lakes is a relatively small contributor to overall sea level rise, it can have a major impact on mountain communities downstream of these glacial lakes.
Glacial lakes are not stable like the lakes in which most people are used to swimming or boating because they are often dammed by ice or glacial sediment called a moraine, which is composed of loose rock and debris that is pushed to the front and sides of glaciers.
They can be quite unstable and can burst their banks or dams, causing massive floods downstream. These kinds of floods from glacial lakes, known as glacial lake outburst floods, have been responsible for thousands of deaths over the past century, as well as the destruction of villages, infrastructure and livestock.
A glacial lake outburst flood affected the Hunza Valley in Gilgit-Baltistan in May 2020. The flood from a lake at the base of the Shishper glacier left the people of Hasanabad in fear. The floods displaced at least 20 residents in the downstream village of Hassanabad and damaged a half-built power station.
Akber Hussain, a villager in his late 50s, looked helpless as he and his family packed up household items.
Hussain and other residents across the village made desperate efforts to save the wooden panels that made up the structure of their mud homes. They feared that within hours everything they owned would be swept away by rapid currents of glacier meltwater.
At least three families were moved to a tent provided by the Aga Khan Agency for Habitat, an NGO that helps communities prepare for and respond to natural disasters, as they had no way of constructing a new home.
“My lands have either been swept away by the floods or are at constant risk of being destroyed,” Hussain told The Third Pole.
Explained: Glacier surge and glacial lake
A glacier surges when ice in its lower layers melts faster than the top layers. Though surging is not a common occurrence, when it does take place it happens in large glaciers as a result of sudden warming. As lower layers melt, a huge amount of ice sits on top of thawed ice and meltwater, causing the top layer to slip and move down the slope: a glacier surge. If the surge is strong, the top layer moves beyond the original snout (end of the glacier), and begins to melt quickly. This can lead to a flood.
A glacier typically melts drop by drop at the snout. Some of those drops percolate into the ground, others form a very small stream and then flow down the mountain slope. Ultimately those streams join to form a river. As global warming accelerates glacial melt, more water is released than the stream or the ground can hold. Meltwater accumulates at the snout, forming a glacial lake.
Since 2018, the advancing Shishper glacier has moved down the slope and blocked the outlet of the nearby Muchuhur glacier, resulting in the creation of an ice-dammed glacial lake.
High temperatures accelerate glacial melt, swelling the lake. A breach would result in a glacial lake outburst flood (GLOF) that could damage thousands of homes in the Hunza valley.
In October last year, the Shishper glacier surged again. The freezing temperature then slowed down the flow of the water. But as the temperature rose in the spring, glacial melt accelerated and water started flowing, leading to the GLOF.
What is a GLOF?
A glacial lake outburst flood (GLOF) is caused by a sudden release of water from a glacial lake. This happens when the lake swells up because the glacier is melting faster. The lake bursts out in flood when the weight and volume of the water cannot be contained by its banks anymore. This has the potential to do immense damage.
In 2015, a crisis unfolded in Chitral valley, where flash floods and GLOFs killed three people, destroyed houses and swept away roads and infrastructure. Around 250,000 were left stranded.
In neighbouring India, the 2013 GLOF in Uttarakhand impacted more than 100,000 people, led to the deaths of thousands, and caused immense damage to infrastructure. GLOFs have killed people in Nepal and threatened entire valleys in Bhutan.
“Surging glaciers like Shishper have lakes underneath the ice in the ablation zone [area where melting exceeds ice accumulation], mostly near the terminus [the snout or end of the glacier],” said Ghulam Rasul, the regional programme manager at the International Centre for Integrated Mountain Development (ICIMOD).
Rasul, who was previously director-general at the Pakistan Meteorological Department, added: “When an ice mass drifts downward in the early summer, these lakes are bulldozed to release the accumulated water. As the glacier advances, the ice mass blocks the flow much like an ice dam, which again has high potential to generate flooding downstream.”
ICIMOD has described the glacier’s surge in the past as “unpredictable”, “sporadic” and “risky”. Shishper has surged at least three times since 2018 when it moved 1,800 metres and blocked the stream starting from the snout of the Muchuhar glacier. This led to the formation of a glacial lake.
Though the damage last month was limited due to precautionary measures and mitigation efforts, a new study suggests episodes like this will become more frequent and devastating.
Researchers from the University of Geneva and the Xinjiang Institute of Ecology and Geography of the Chinese Academy of Sciences said in a study published last month that glacial lake outburst floods will become much more common in the high mountain ranges of Asia.
“The highest GLOF risk is at present centred in the eastern Himalaya, where the current risk level is at least twice that in adjacent regions. In the future, GLOF risk will potentially almost triple as a consequence of further lake development, and additional hotspots will emerge to the west, including within transboundary regions,” said the study authors.
Markus Stoffel, professor of earth and environmental science at the University of Geneva and a co-author of the study, said in a statement: “The speed at which some of these new hazardous situations are developing surprised us. We are talking a few decades not centuries – these are timeframes that demand the attention of authorities and decision-makers.”
People live in fear of GLOFs
Rasul of ICIMOD said that the Shishper glacier in Hunza “is a partially debris-covered surging glacier which has developed supraglacial lakes”.
“In the early summer, when the melt rate increases, these lakes hold a huge volume of water then suffer an outburst beyond their capacity,” he told The Third Pole.
Rasul added: “[The outburst] carries mud, boulders and a gushing momentum of water with huge potential to cause damage to human settlements, land and infrastructure downstream. This is almost a regular annual feature of this glacier.”
Rasul said that another factor is the glacier’s meandering gorge, which fills the lake with meltwater. In the winter this happens gradually and is gently released when the lake overfills. But in early summer accelerated melting fills it rapidly. This, in addition to the glacial surge, makes the water burst the lake’s banks.
“Increasing temperatures, accelerated melting and enhanced drift velocity have resulted in such disasters,” he said.
“For communities living downstream, surging and bursting glaciers are always a risk,” he said, adding that the lake outburst “creates havoc”.
“Livelihoods in these mountain communities are linked with small-scale patchy agricultural lands and fruit orchards, which are badly eroded by such outbursts,” he said.
The threat of floods has given Hassanabad villagers sleepless nights for the past three years.
The 1,300-metre-wide, 600-metre-tall Shishper glacier is just 4km from the highway and Hassanabad village, where there are about 170 households.
Last year, floods induced by the glacier were quite severe. Several homes, acres of land, trees and two power stations were affected, resulting in a serious power crisis in the entire Hunza district.
According to authorities, up to 20 houses in the village are at serious threat in the event of a moderate flood, with more than 80 houses under threat if there is high-scale flooding from the glacier water.
Community leader Tariq Jamil said that historically, the Shishper glacier and adjoining Muchawar glacier surged concurrently in cycles of 40-45 years. “But during the recent cycle, only the Shishper glacier surged. The moving of the single glacier created a gap in between the two and caused the formation of a huge glacier lake.”
Jamil said that in 2019, “the glacier surged by at least seven metres within 24 hours”.
He also said that since 2018, 80% of the land along the glacier water stream has been eroded. “But so far no compensation has been given to the affectees by the government.”
GLOF mitigation steps
Just before the flood in late May, the Gilgit-Baltistan government declared an emergency in some parts of the district and began evacuations as a precautionary measure. The authorities also diverted traffic on the Karakoram Highway from 15-18 May towards the Negar side. The highway is the sole land route between Pakistan and China.
“We constructed long, deep channels to drain the water which helped to reduce 90% of water-erosion losses,” he said. But the water flow was so fast and high that the protective channels were again damaged.
He highlighted the need to “construct a strongly protected channel with the capacity to outflow water of at least 10,000 cubic feet per second”.
“The constant threat is always there and we need more effective measures to avoid future losses,” said Jamil.
Wali Khan, director-general of the Gilgit-Baltistan Disaster Management Authority, said that a higher level of damage was initially expected. However, controlled release, excavation of the channel and mitigation work done at vulnerable spots enabled the discharge of water in a controlled manner.
Although he said the current threat has subsided, “glaciers can surge at any time and we cannot rule out future risks”.
“We remain vigilant and will tackle the situation. The federal government has also committed to helping us,” said Khan, adding that the inclusion of the Shishper glacier in the GLOF-II project of the UNDP would help with effective mitigation.
What is the GLOF-II project?
The GLOF-II project is a joint initiative between Pakistan’s Ministry of Climate Change and the UNDP. Building on measures piloted by GLOF-I, the GLOF-II project is described by the UNDP as aiming to empower communities to identify and manage risks associated with GLOFs and related impacts of climate change, strengthen public services to lower the risk of disasters related to GLOFs, and improve community preparedness and disaster response.
Farrukh Bashir, director of the Meteorological Department in Gilgit-Baltistan, said that last year the department installed an early warning system at the Shishper glacier and assessed glacier surge and lake formation potential.
“In light of the risk assessment, coordinated measures by government and local communities were taken to channelise the water to safely drain the flood water from the lake. This helped to reduce losses as well as panic among the communities,” Bashir told The Third Pole.
A multidisciplinary team with a glaciologist, climatologist, hydrologist, geologist and civil engineer should be formed to suggest some structural and non-structural measures to reduce the risk of disaster and save lives of vulnerable downstream communities, suggested Rasul.