Glacial lake outburst floods, known as GLOFs, have been a core focus of mountain research in recent years. Interest has grown as glacial lakes have developed and started to threaten communities and infrastructure. In March, GlacierHub covered the growing GLOF database, overseen by the International Consortium on Landslides. Since the beginning of 2016, 32 peer-reviewed, English-language papers examining GLOFs and their impacts have been published online. Half explicitly focused on changes across the Hindu Kush Himalayan (HKH) region.
Glaciers in the HKH region have lost up to 55 percent of their mass since the 1980s, according to a study by the International Centre for Integrated Mountain Development. And glacier-fed lakes in the Central Himalayas grew in surface area by 122 percent between 1976 to 2010, research led by Weicai Wang of the Chinese Academy of Sciences found.
One area in the HKH is of particular interest: the Shyok system. The Shyok River catchment, a tributary of the Indus, has been unleashing powerful GLOFs on the Indus since 1533. In 2013, Kenneth Hewitt and Jinshi Liu examined the catchment via satellite data, providing the most recent analysis to date. Located in northern Pakistan’s Karakoram Range, 25 miles (40 km) east of Siachen Glacier, the valley has been “inaccessible because of security issues” according to Hewitt and Liu.
Shyok’s reputation is a result of the characteristic behaviors of its glaciers, which have a tendency to surge. This means they unpredictably slide down the tributary Chong Khumdan, Sultan Chussku, and Kichik Khumdan valleys and block the flow of the Shyok River. The three glaciers of Chong Khumdan valley— North, Central and South— are the most active, and are thought to have dammed the river 13 times between 1826-1933.
However, since the last GLOF of 1933, the Shyok system has gone quiet.
Hewitt, who has studied the catchment for over 30 years, in 2013 designated the Chong Khumdan Glaciers as posing an “immediate, high risk” of blocking the Shyok River and unleashing a GLOF, based on satellite imagery from 2009. Despite the lateral thinning of each glacier’s trunk, the terminus of the combined North and Central Chong Khumdan Glaciers advanced 1.4 miles (2.2 km) between 1991-2013. The South Chong Khumdan Glacier moved more slowly, nudging forwards 0.16 miles (250 m) over the same period. However, the system has surged to the extent that the Shyok River presently flows through a gap of only 200 feet (60 m).
In a 2007 paper, Hewitt determined that glaciers in the Karakoram can surge up to 4.3 miles (7 km) within a matter of months. He also found that regional surging glaciers have been especially susceptible to recent changes in regional climatic conditions.
The experiences in 1928 and 1929 of a little acknowledged biologist, Frank Ludlow, tell a powerful story about the impacts of the last major GLOF released by the Shyok system.
In 1929, The Himalayan Journal published his findings. A lake had formed as a result of the eastward migration of the Chong Khumdan Glaciers. The glacier had connected with the valley side, and was blocking the meltwaters from a large Rimo Glacier system upriver. Extending 10 miles (16 km) from tip to tip, the lake was shaped like “an irregular crescent with its two horns pointing north-west and south.”
He had judged that it averaged 150 feet (45 m) in depth, and within a 24-hour period, as he camped along the eastern shoreline, the water-level had risen 1.5 feet (45 cm). He estimated that the water was likely rising by 4.5-9 inches (11-22 cm) daily. Ill-equipped to study the lake in any greater detail, Ludlow departed from Shyok within a week.
The next year, he returned, accompanied by J.P. Gunn, an officer of the Punjab Irrigation Department. The lake had grown to 11 miles (18km) in length. The ice dam was beginning to feel the strain. In 1930, Gunn wrote in The Himalayan Journal: “All the time we were down at the dam on 12th August loud creaks and ‘groans’ were heard, lasting some time, as ice‐floes broke off the main body.”
Three days later, the Chong Khumdan Glacier dam broke.
An estimated 356 billion gallons (1.35 billion cubic meters) of water was released on August 15, 1929— enough to fill 540,000 Olympic swimming pools. Gunn observed a “dark chocolate‐coloured flood,” and judged that 10.5 million cubic feet (300,000 cubic meters) of ice were borne off by the floodwaters. The wall of water, mud, and debris stood 85 feet (26 m) high, and travelled a staggering 930 miles (1500 km) down the Indus. Even 740 miles (1194 km) downriver, the flood waters swelled the river up to 26 feet (8 m).
Were a glacial lake in Shyok to form now, it would pose a dire and immediate threat to more than two million people who inhabit downriver. Hundreds of villages, cultivated lands, and infrastructure, including the Karakoram Highway and Tarbela Dam, are at risk. What’s more, glacial lakes in this catchment are known to form and collapse within less than two years.