A climber crosses a dangerous crevasse.


On the Move As the group heads out, Koppes thinks about the speed of this glacier. It grinds downhill about 700 meters (2,300 feet) each year. T at’s nothing compared to one glacier in Greenland. Every year, that glacier moves downhill about 15 kilometers (9 miles). It’s the fastest glacier on Earth. As a glacier flows, the bottom and sides drag


more slowly than the middle. T e diff erent speeds tug at the ice. T is can cause real trouble. It cracks the ice. Some cracks, called crevasses, can be deep and dangerous. T ese cracks oſt en become hidden under a


thin crust of fallen snow. In many places, the snow is only a few centimeters thick. It can’t support the weight of a person. For an explorer, a crevasse could be deadly. Koppes saw this danger up close during


another expedition. She and her team were in a helicopter, ready to hop out onto the ice. Her partner leaned out of the helicopter and


poked the snow with a pole. It seemed firm enough. So he jumped out. Bad idea! T e snow gave way. Only the safety rope held by Koppes kept him from plunging to the bottom of a deep crevasse. Koppes learned an important lesson about


glacier safety that day. On today’s hike, she and her team rope themselves together. If someone falls in a crevasse, the rest of the team can pull that person out.


20 NATIONAL GEOGRAPHIC EXPLORER


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