Damnably Big Waves

In September of 2004, Hurricane Ivan approached the Gulf of Mexico. It was a Category 5 storm with sustained winds of 130 mph. In the offshore oil fields, 75% of the manned oil platforms (574 platforms) and 59% of the drilling rigs (69 rigs) were evacuated. When the storm passed, five rigs were adrift and seven sunk outright. Numerous platforms were heavily damaged. Seabed pipelines were shifted as much as 300 feet, many were leaking, and some couldn’t be found at all, buried beneath tons of mud that had slid down submarine canyon walls.

By a fortuitous accident, the Naval Research Laboratory had deployed 14 instrument packages on the bottom of the Gulf as part of a project measuring ocean currents. Several of the instruments were also capable of measuring the heights of waves passing overhead. They lay directly in the path of Ivan.

Oceanographers are apparently not immune from a fondness for pet names. The instrument packages, officially called current profiler moorings, looked vaguely like a barnacle clinging to a half-tide rock. They called them barnys.

To save battery life, the barneys were programmed to awake only eight and a half minutes every eight hours. Although their sleep periods were staggered, none were awake when the height of the storm passed overhead.

They were, however, awake as the hurricane approached their position on the continental shelf about 100 miles south of Mobile Bay. While they were awake, the barnys recorded a wave set averaging 66 feet at 10 second intervals. Ten seconds—hardly long enough to catch your breath. During that narrow window when the barney’s were recording, one wave passing overhead was 91 feet from crest to trough. It was not a rogue.

If a wave 91 foot tall swept across New York harbor it would stand as tall as the Statue of Liberty’s shoulders.

Extrapolating from the available data, the scientists at the Naval Research Laboratory estimated that when the eye wall of the hurricane passed over the hibernating barneys, extreme wave heights were likely greater than 130 feet. Only the Statue of Liberty’s torch would have remained above water.

These were not rogue waves—the random conspiracy of several waves or the magnifying effect of a boundary current. These were sets of waves behaving as you would expect. Damnably big waves, I’ll grant you.

"The implication is waves generated by hurricanes are much larger than previously suspected. Waves in excess of 90 feet aren’t rogue but are fairly common during hurricanes," said William Teague, a member of the Naval Research Team and co-author of a report on their findings published in Science, August 2005.

God help the sailor in the path of such seas.

Technorati tags: , , ,


One thought on “Damnably Big Waves”

Leave a Reply

This site uses Akismet to reduce spam. Learn how your comment data is processed.