Field Notes: The Polar Field Services Newsletter

GrIT details: Threading the Needle

Robin Davies (left) and Kevin Emery probe a crevasse, a combined tactic that helps the team more quickly identify the strike angle and width of the crevasse. Photo: Jen Mercer

During the last few days, the Strategic Crevasse Avoidance Team (SCAT) has passed out more flags than the Grand Marshall at a Fourth of July parade. Of course, the flags fluttering in SCAT’s wake are of the black variety used to mark crevasses.

The team is picking its way through some pretty tumbled territory on the Greenland ice sheet. ”It was a difficult day today for the ground-penetrating radar (GPR) team,” Allen Cornelison reported yesterday, 5 April. “But they did make some headway. They found multiple crevasses that were not on the satellite imagery.”

"Kevin on the skidoo next to crossed black flags marking a crevasse," Robin explains. "Look closely and you’ll see a line of whiter patches of snow running in a line at 45 degrees across the picture. That’s the line of the crevasse: it’s a wide one with a sagging bridge. We couldn’t see it at all at the point were Allen stopped us with the GPR (were Kevin is) but looking back from higher up the slope it became obvious. This crevasse is one side of the eye of the needle." Photo: Robin Davies

Allen’s report a day earlier mentioned SCAT had found a crevasse that had opened up to 12 feet wide, with a sagging bridge that Allan Delaney could see on the GPR imagery—a common occurrence in Antarctica, but a first in Greenland for the radar expert, Cornelison mentioned.

We heard from Robin Davies later: “We had to find a route that took us between two parallel crevasses. We zig-zagged back and forth, turning each time the GPR detected the crevasses, until we made it through. A technique we refer to as “threading the needle.”

Crevasse avoidance made for a lot of zig-zags. “Those of us watching the tracker this evening thought they had turned around because they could not get through,” Cornelison remarked. “But as it turns out, it was just time to come back to camp. This is decent news: they were not stopped in their tracks.”

SCAT Track: The green dots depict “bread crumbs” left by the SCAT along the route they’ve travelled. The blue line is the 2008 GrIT route. Image: Allen Cornelison

That these crevasses were undetected by satellite suggests just how important the SCAT’s job is prior to the inland traverse start-up. Nothing can replace boots-on-the-ground, especially boots belonging to these fine people: Allan Delaney, a retired CRREL radar expert, who pioneered ground-penetrating radar crevasse detection techniques while leading the United States Antarctic Program’s (USAP) effort to find a safe route to the South Pole, and who was recently coaxed from retirement to continue contributing to the GrIT; Jen Mercer, an earth sciences PhD and USAP research veteran; Kevin Emery, expert rock-climber and mountaineer, who has taught a myriad of people to explore high-altitude, difficult terrain all over the world, including the USAP; and Robin Davies—well, the polar chapter in his career began with the British Antarctic Survey in 1974, but it is only one of many storied adventures.

Clockwise from left: Jen Mercer, Allan Delaney, Kevin Emery, and Robin Davies take a break from route-making. Photo: Robin Davies