Hurricane season and Gulf oil pipelines. Trouble ahead?

Hurricanes roaring across the Gulf of Mexico create strong enough underwater waves to dig up and potentially bust open oil pipelines that run across the ocean floor, according to a new study that recorded the currents created by the massive storms.

The massive Deepwater Horizon oil spill in the Gulf has focused attentions on the potential for more such environmental disasters, particularly now that the 2010 hurricane season has started. Scientists and officials are not only worried about how a storm might exacerbate the current spill, but the potential for it to cause another one, possibly by causing a rupture in an oil pipeline.

At least 31,000 miles (50,000 kilometers) of pipelines snake across the floor of the Gulf, according to the Minerals Management Service, and hurricanes have long been known to cause a range of damage to them, from dents to full ruptures.

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After 2004's Hurricane Ivan, the MMS cited 168 pipeline damage reports; after Rita in 2005, it was 243; and there were 299 in the wake of devastating Hurricane Katrina, said Bill Teague of the U.S. Naval Research Laboratory at Stennis Space Center in Mississippi.

The numbers Teague cited were based on a 2006 MMS report stated that Ivan "produced high levels of pipeline damage, many resulting from mudslides and excessive movement in the Mississippi Delta region." The report listed separations of pipelines and rises as the No. 1 type of damage reported from the 168 cases, with "unknown" coming in at No. 2 with 25 incidents and bent risers at No. 3 with 24 reports. Other types of damage included dents, pipeline movements and kinks.

Teague's study did not investigate whether any of these cases of damage had resulted in a leak.

Ivan's scouring

Teague and his colleagues got an unprecedented view of the forces that can cause this damage when the eye of Ivan, a Category 4 storm, passed over a network of sensors moored to the ocean floor that were put in place to monitor currents along the continental shelf of the Gulf.

The sensors showed that strong currents along the seafloor scoured the seabed, picking up sediment from some places and piling it up in others.

The howling winds of hurricanes can generate strong currents, but the researchers found that it was the surface waves that Ivan generated that in turn created the most powerful currents on the seafloor. These waves can rise to 66 feet (20 meters) or more above the ocean's surface — the team measured one at 91 feet (28 meters), which Teague said he thinks is the highest wave ever measured by instruments.

"That is a big wave," he said.

The currents generated by the waves loft large amounts of sediments, which clouded the water up to 82 feet (25 meters) above the seafloor. Sediments were washed away from underneath the team's sensors, causing them to sink down to the new ocean bottom.

The scouring of sediments could create underwater mudslides — akin to avalanches on land — that could cause damage to oil pipelines.

Persistent effect

Because the waves have a much more powerful effect on this seafloor scouring, even a weaker, slow-moving hurricane could cause damage, because its speed would allow it time to build up large waves, even if its winds weren't as fierce.

"It doesn't take a Category 4 storm to do this," Teague told OurAmazingPlanet.

Another point that was learned from the study of Ivan's scouring was that the effects persisted for more than a week after the storm had passed.

The study couldn't say the exact ways in which pipes are damaged or what the likelihood of having a major rupture and subsequent spill would be, said Teague, who could smell the current oil spill from his office just 10 to 15 miles from the Gulf coast. But the researchers hope that their study could help engineering efforts to protect structures and pipelines in the face of an impending storm.

The study is detailed in the June 10 issue of the journal Geophysical Research Letters.

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