Several of the glaciers that flow into this valley surge, meaning they cycle through periods when they flow forward several times faster than usual. Since the valley is narrow and has a river running through it, surging glaciers regularly dam the river and create flood hazards. The floods occur when water pooling up behind the tongue of the advancing glacier suddenly breaks through the natural ice dam and cascades down the gorge.

Khurdopin has surged most recently. After years of little movement, the glacier began a rapid advance in October 2016, accelerating to a rate of roughly 20 meters (65 feet) per day by the spring of 2017—one of the fastest rates observed for a glacier in this region. As ice and sediment pushed into the river, a sizable lake pooled up in March 2017. Jakob Steiner of Utrecht University and the Mountain Hydrology Group has been monitoring the growth of the lake using imagery collected by Landsat 8 and Planet Labs, a commercial satellite company.

By July 2017, the river had carved an outlet through the glacial debris before the lake could grow extremely large, but Steiner’s group continued to keep a watchful eye on this area because of how much debris the glacier pushed into the river. The surge increased the thickness of the end of the glacier by as much as 80 meters (260 feet), according to Steiner. The photograph above, taken by Waheed Anwar of Focus Pakistan, shows the tip of the sediment-coated glacier pushing into the river on May 15, 2017. The camera is pointed upstream toward Khurdopin glacier.