Then he promptly stepped into one, his left leg sinking up to the knee.
''I expected it to be there, based on that crack in the ice,'' the glaciologist at the University of Colorado at Boulder said with a grin. ''I just wanted to test my theory.'' Reuters photographer Bob Strong and I were aware of the perils lurking here when we travelled to Greenland's ice cap to report on climate change, but we didn't expect to find out first hand how perilous this place really is.
We moved our snowmobiles away and vowed not to approach the crevasse, while Steffen's friend, NASA scientist Jay Zwally, did the exact opposite. He methodically poked at the hole with an aluminium pole, enlarging it.
Two days before, the helicopter pilot who was supposed to fly us here fell 18 metres (yards) down a similar crevasse, fracturing his skull. He was lucky to survive.
In the summer, some crevasses turn into moulins -- huge ice tunnels that funnel melt water underneath, lubricating the bedrock and speeding the ice sheet's slide toward the ocean.
Zwally wondered if this too could be a moulin.
He tied himself to a snowmobile and leaned over the crevasse to videotape it. ''I'd say it's at least 15 metres deep and wide enough for several of us to fit in,'' he announced. ''Wegener, are you down there? What would you like for dinner?'' There is a running joke between these scientists that one day the radar they use to measure ice thickness might pinpoint the body of Alfred Wegener, the German author of the continental drift theory who died in 1930 during an expedition.
SWISS CAMP The Swiss-born Steffen has been studying Greenland's ice cap since 1990. He and his colleagues helped show that temperatures are rising significantly here in the winter, spring and fall, while the ice cap is sliding faster into the ocean.
Every year from late April to early June Steffen lives and works alongside other scientists and graduate students at Swiss Camp, a wind-swept outpost of tents on the ice cap.
Temperatures can drop to minus 30 Celsius and a biting wind blows almost incessantly.
Storms create white-outs in which an inexperienced visitor can get lost between tents, a potentially fatal mistake.
Despite the cold, 50 SPF sunscreen barely keeps at bay the sun bouncing off the ice. The toilet is simply a hole in the ice, with no shelter around it.
The scientists are used to the hardships and look forward to coming here every year, driven by a sense of purpose. For visiting journalists working here was tougher than we imagined.
The cold seeps in through every undone button, every open flap and every loose buckle. It drained the batteries in Bob's cameras in a matter of hours and made me think twice about taking notes, because using a pen meant taking off one of the two gloves I wore on each hand.
On the way back from the weather station, we stopped several times to recover equipment or push snowmobiles that had lost traction on smooth patches of ice, twice coming to a halt on top of see-through crevasses.
Luckily they were plugged for now, but soon they will melt open, forcing the scientists to take long detours.
Weary from the cold, we were glad to climb aboard a helicopter and leave ahead of a burgeoning snow storm that confined our host to their tents for two days.
REUTERS LPB BD1008