Danger of another flood as water continues to flow from the lake in Hunza valley in northern Pakistan.
"A loud rumble echoed and water started trickling down with soil and rocks. Villagers immediately left their homes and fled to safety," recounted Manzoor Hussain. Hussain lives in Hassanabad, a village in the Hunza valley high in the Hindu Kush Himalayas in northern Pakistan.
It was siesta time on May 30 when the rumbling started. "It was not the first time, so people in the village knew what was happening. They were aware of glacial lake outburst floods [GLOFs]. They thought it was a GLOF at the Shishper glacier," said Hussain.
In fact, a lake near the Machuhar glacier had burst its banks, causing a flood that submerged farms, the local power plant and part of the Karakoram Highway. Most residents had to sleep in tents afterwards.
Was this a GLOF, where the failure of an unstable natural dam releases meltwater from a glacier? The question is complicated by the Karakoram Anomaly, which describes the advance of glaciers in the region in contrast to the retreat of other glaciers in the Himalayas and globally. Expert opinion is divided.
Zaheer Uddin Babar, the focal person for GLOFs in the Gilgit Baltistan Disaster Management Authority, said, "We can’t interlink the recent incident with a GLOF. Satellite images received from SUPARCO [Pakistan’s Space & Upper Atmosphere Research Commission] are not indicating any glacial lake. It may be the water spilled out from a lake on the surface of the Machuhar glacier. The water flow was as low as 3,000 cusecs [cubic feet per second] only." In some parts of the Hindu Kush Himalayas, water flow after a GLOF has been recorded at around 100,000 cusecs.
The villagers thought the May 30 incident was a GLOF because they had experienced one with a water flow of 7,000 cusecs in 2019, when a 1.5 kilometre-wide lake burst its banks. That time, a large section of the Karakoram Highway, a bridge, two power plants, some offices, over 100 houses, the water supply pumphouse and most farms were submerged.
Shishper is a surging, or advancing, glacier. It formed around the beginning of the twentieth century, when what was then the Hassanabad glacier in the north of the Hunza valley split into two. Machuhar is the other glacier formed by this split. Like the overwhelming majority of glaciers in the Hindu Kush Himalayas, Machuhar is receding due to the warming caused by climate change. There are over 15,000 glaciers in this tallest and youngest mountain range of the world, which stretches from Afghanistan to Myanmar. The number keeps changing as receding glaciers split into two or more.
The surge of one glacier while its neighbour melts is creating a strange situation. Babar said Shishper has been surging quickly; it moved forward two kilometres in 2018-19, though there has been no indication of a surge since November 2019. But the earlier surge blocked the drainage route of the Machuhar glacier. As a result, a lake has formed at the snout, or mouth, of the Machuhar glacier, and is getting bigger as climate change gathers pace and the rate of melt increases.
Blocking the water flowing down from the Machuhar glacier also means blocking this water supply to the Hunza River, a tributary of the transboundary Indus River.
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