National Geographic : 2010 Jun
• Institution and the University of Washington documented the draining of a two-square-mile supraglacial lake: More than 11 billion gallons of water disappeared into a moulin in 84 minutes, owing faster than Niagara Falls. e meltwater lake Tedesco is studying has an outlet river that must lead to a gulping moulin. LeWinter and I are determined to nd it. Armed with ice axes, ice screws, and ropes, we set out. We haven't gone a quarter mile before we're sty- mied by holes in the ice. At rst we can thread our way between them, but farther along, the rims are all touching, and we're forced to bound the pools, one knife-edge to the next. It's like playing leapfrog on razor blades. We try an alternate route, following a ridge of ice that parallels the river. is time we make good headway and march across the ice sheet for miles. We can't nd the moulin on foot, but we make an intriguing observation: On the journey out, the holes we were jumping were separate, circular bowls, but on the way back, just half a day later, there's been enough melting so that the holes are connected by swi -running creeks. At camp that night we nd out what Tedesco and Steiner have con rmed about the bottom of the meltwater lake. It is mottled with cryoconite. Cryoconite begins as airborne sediment spread over the ice by wind. It is composed of mineral dust sucked up from as far away as Cen- tral Asian deserts, particles from volcanic erup- tions, and soot. e soot particles come from res both natural and man-made, diesel engines, and coal- red power plants. Cryoconite is not a new phenomenon: Arctic explorer Nils A. E. Nordenskiöld discovered and named the ne brown silt during his visit to the Greenland ice sheet in 1870. Human activities have increased the amount of black soot in cryoconite since Nordenskiöld's day, and global warming has given it new importance. Carl Egede Bøggild is a native Greenlander and geophysicist who has spent the past 28 years studying the ice sheet. Recently Bøggild has focused on cryoconite. "Even though cryoconite n Society Grant This project was funded in part by your National Geographic Society membership.