ON JAKOBSHAVN GLACIER, Greenland (AP) -- The pilot eased his five-ton helicopter toward the glacier's rumpled surface, aiming for the lightest of setdowns atop one of the fastest-flowing ice streams on Earth.

David Holland's voice suddenly broke in on the intercom.

"Carl doesn't like this!" the scientist shouted. "Carl says it's snow bridges!" - drifts that can hide a deep crevasse.

The chopper pulled up sharply and veered off over the chaotic icescape of white knobs and pinnacles and bluish glints of meltwater, on to another, safer landing spot where Carl Gladish, Holland's lanky, ponytailed assistant, stepped cautiously off the skid and onto the ice, under the thudding rotor blades, to swiftly carry out his assigned task.

It was one of eight 2-minute touchdowns on which the New York University research team positioned instruments to measure the movement and internal cracking of Jakobshavn Glacier, a risky operation meant to shed light on one more tiny piece of the giant puzzle called Greenland. ...

Back up at Summit, two young Dartmouth College engineering graduates put one potential answer on display, testing the tiny, tractor-like "Yeti" autonomous robot over the ice. Like humans, Yeti could deploy ground-penetrating radar, meteorological gear and other research tools, say its designers, who envision hundreds crisscrossing Greenland offering up-to-the-minute data.