When the ice is too thick
15th April 2011
What happens when the ice is too thick for a ship to break through, especially when that ship is carrying 12 months of food and other supplies?
This scenario was the reality in February when the Aurora Australis set off intending to sail first to Mawson to supply provisions 200 metres across the water of Horseshoe Harbour and then on to Davis to conduct resupply and collect returning expeditioners.
However, a week before the ship was due to leave Hobart, the failure of the sea ice to break out from Mawson was looking sufficiently ominous that the Antarctic Division chartered a large Sikorsky S76 helicopter in case it became necessary to conduct a ‘fly-off’ from the ship. In addition, cargo was stowed independently in the ship’s hold in such a way that access for one station would not disturb cargo bound for the other, just in case the ship had to reverse its planned route. As it happened, this was a fortunate contingency plan.
Ice conditions continued to worsen as the ship made way, and it went first to Davis to collect 2 Squirrel helicopters in case of a Mawson fly-off. The closer the Aurora came to Mawson, the heavier the sea ice became, both thicker and more extensive than normal.
Resupply over water was now impossible, but initially the ship couldn’t even get close enough to do a fly-off! The traditional access to station up Iceberg Alley, a narrow but well charted 45 nm channel, had in excess of 2.5 metres of ice on it and 1 metre of snow. The maximum the ship can tackle is 2 metres of ice. Snow acts as a sponge and makes it even more difficult for the ship to break through.
After a recce flight by the voyage leader, field training officer and the ship’s captain, an alternative much longer but little-used route was eventually chosen through a polynya (an area of relatively ice-free water surrounded by pack ice), through which the ship was able to make way to within 33 nm of the station.
Once in position, it was a case of ‘all hands to the deck’ to offload the cargo as quickly as possible in case the ice worsened. A total of 120 flights (each of about 45 minutes), using all 3 helicopters lifted over a 100 tonnes of cargo, much of which had to be laboriously repacked from large containers originally destined for barges into smaller packages suitable for helicopter lift.
To maximise the time and efficiency of the operation, a make-shift helipad was made on the sea ice off the ship’s bow to enable 2 helicopters to load simultaneously. Ship’s crew and expeditioners worked very well together to keep the re-packaged cargo flowing both onto the ice and into the hangar on board the ship.
Congratulations to all involved! Despite such an unconventional resupply that differed in almost every way from the original plans, most of the cargo was successfully deployed and Mawsonites can look forward to a comfortable winter.