By Dr David Whitehouse
BBC News Online science editor
A team of engineers has begun constructing one of the most difficult "roads" ever attempted: a 1,600-kilometre (1,000 miles) overland route to the South Pole.
Road construction: It is a hazardous business
It is hoped that the snow highway will some day become a regular surface route from McMurdo Station on the Antarctic coast to the Amundsen-Scott base, freeing up ski-equipped supply planes for other missions.
Over the next two years, the engineers will slowly mark out the trail. If successful, it will show tractors can be a reliable and efficient way of getting fuel and food to the South Pole.
The route will be the first over-snow, heavy-equipment traverse by the US Antarctic programme since 1968, although the Russians regularly supply their Vostok base by tractor convoys.
In principle, the route is simple: just head south. Or rather, east from McMurdo Sound then traverse the Ross Ice Shelf, ascend the Leverett Glacier and turn due south for the Pole.
The pathfinding engineers reported that the first 48 km (30 miles) were relatively easy but then they had to cross an ice-shear zone.
Project manager John Wright told the Antarctic Sun newspaper: "The shear zone is the single, unavoidable obstacle that any traverse outbound from McMurdo contemplating travel on the Ross Ice Shelf must face."
In one previous excursion in 1991, the surface gave way under a tractor moving across the shear zone. The crew were rescued several hours later, but the tractor is still there.
The hazardous belt of crevasses is there because the Ross Ice Shelf moves faster than the McMurdo Ice Shelf. The ice between them has one end held back while the other is pushed forward, leading to multiple fractures.
Ice 'pot holes'
To make the road safe, the engineers had to find and fill in every crevasse on the route.
A jeep-sized tracked vehicle, called a Pisten Bully, led the way, peering ahead with a ground-penetrating radar held in front on a boom. When a crevasse was found, it had to be dynamited open and then filled.
A crevasse must first be opened...
Eventually, after much toil, the snow dumped into the crevasse would compact itself, leaving a solid, safe surface for the bulldozers to smooth over.
The entire shear zone moves north towards the sea at the rate of up to a metre a day, so the road will have moved significantly in a year. Flags will mark the road and form a grid around the shear-zone.
"You damn sure better not get off the road," Wright says. "The place is full of crevasses."
Forge the trail
In total, the engineers completed about 140 km (87 miles) of road before the Antarctic winter set in.
Next Antarctic spring, a larger convoy of tractors and trailers will set out for the Leverett Glacier, the chosen route through the Transantarctic Mountains.
If all goes well, in 2004-05, the convoy will go the full distance to the South Pole and back, carrying cargo to demonstrate it can be done.
...and then filled in
"The idea is to forge this trail, not a road, but a trail, that may become a snow road in future years," Wright says.
It is estimated that a convoy of tractors pulling full trailers could deliver supplies to the South Pole without using as much fuel as aircraft. Of course, it would take longer - 30 days instead of six hours.
Equipment too large to be carried in an aircraft could be delivered, allowing a new phase of scientific research to be carried out at the South Pole.
Images courtesy of Antarctic Sun/National Science Foundation