Friday, 12 October 2012

The Biggest Waves (Penny Holliday)

Waves crash over the bow of RRS Discovery
In February 2000, the people on board RRS Discovery endured an experience they will never forget. Cruise 245 was the 68th occupation of the Ellett Line, a repeat hydrography section in the Rockall Trough, and the aim was to collect rare winter data. Winter is a particularly interesting time from a physical oceanography perspective with convective mixing to 800 m below the surface, and a huge amount of heat released to the atmosphere from the ocean. We soon found out why this time series, which was started in 1975 by David Ellett, had so little winter data.

D245 Wave data
For most of the cruise we were battered by ferocious storms. Of the 25 days at sea, science work was possible on only 9. The science programme was in tatters, and so were people nerves. The storms were relentless and as the ship rolled and pitched, no-one got any sleep and ribs were broken. The ship's officers and crew worked continually to keep us safe and to try to salvage something of the science we had planned. But the sight of the Captain (Keith Avery) and often the Chief Engineer (Ian McGill) on the Bridge at all hours, looking very worried, and saying they had never seen weather so bad, is something I hope not to experience again.

There was damage to the ship. An interior window between the main lab and the computer room shattered as the ship flexed. During a roll of 33° at 4am the starboard lifeboat came loose and was banging loudly against the side of the ship. Crew were dispatched to secure it, and watching them go out into the raging storm was the worst moment for me. They did the job though, and all came safely back inside.

During a 12-hour period on 8-9 Feb 2000, a total of 23 waves exceeded 20m (peak-to-trough height). The biggest wave was over 29m, and significant wave height reached 18.5m, the highest ever recorded.

Penny Holliday, Co-Chief Scientist of Discovery  Cruise 245

Read Susan Casey's version of this story on Gizmodo as an excerpt from her book "The Wave".