Sarah Das sat down on the ice sheet, opened her backpack, and took out a cinnamon Pop-Tart. She chewed quietly, needing a moment to recharge. For the last 90 minutes she had hiked around a massive, deep crack, split by a rushing river and smaller streams of melted ice sheet water. Somewhere in these channels she needed to find a place to dump in nine pounds of a harmless tracing dye. She will use it to trace the water’s flow under the ice, over 40 kilometers of bedrock, to Greenland's coast.

Her goal is to see how long it takes, and in what concentration the dye appears, in order to begin mapping this under-ice pathway. But if she didn’t find an ideal spot in the river to dump in the dye, she worried that it wouldn’t make it into the moulin—a hole in the ice draining the fast flowing river. An inaccurate pour, she feared, would compromise her experiment.

She and her team members scouted upstream of the moulin for the safest, easiest access. After finishing her snack, she crouched on a wide, flat ice bank near a swirling pool and mixed a scoop of water with a tablespoon of powdered dye in a yellow bucket. A few dark pink dots splattered, staining the ice.

Finally, she tilted the bucket over the flowing water. Team members were poised to help; Chris Linder pointed his camera lens at the water, Ian Joughin and Kristin Poinar waited with a video camera on a high ledge to her west to record the flow, and Mark Behn stood on the opposite ledge to time how long it took the dye to flow down.

“You guys ready?” Sarah yelled above the rushing river. “Here goes!”

Read on about today's adventure here.