Abyssal storms create huge seabed ditches, which have the potential to wreak havoc with offshore oil and gas exploration.
It's often possible to trace the route of a tornado using the path of destruction it leaves behind.
Underwater, similar events occur. While no barns are imploded, the seafloor is carved up in such a way that those thinking of developing oil and gas reserves at these depths may want to proceed warily.
Looks like the ocean bottoms of the world have their own versions of Tornado Alley.
Like the midwestern United States, geography plays a part. Underwater currents follow the contour of the land. When these currents become strong enough, they are considered abyssal storms, with currents moving at speeds of up to 2 knots. While this speed may not seem excessive, the amount of water moved is. The result is furrows carved out as sediments are removed from the ocean floor.
Dr. William Bryant, a professor in the department of oceanography at Texas A&M University and a recognized authority on the geology of the Gulf of Mexico, has been studying these furrows partly out of curiosity and partly with an eye toward their potential impact on oil and gas exploration.
In 2000, he led an expedition of almost 40 scientists and observers, making deepwater dives between Galveston, Texas, and Key West, Fla., with the submersible Alvin. The team encountered an abyssal storm during one of its dives, and it also found furrows that extended for miles.
"The furrows reflect a fundamental piece of sediment transportation," Bryant said. "This is how muddy sediments are eroded by currents." He said scientists first discovered furrows about 35 years ago, and since then they have studied them in the lab by running moving currents over mud in a flume. "They found the same thing - the current formed grooves in the flume," he said. "We're seeing the same feature in the ocean, only it's 10,000 times larger."
The area of research is significant because it encompasses the Sigsbee Escarpment and the western Mississippi Fan Fold Belt, active areas of interest for oil and gas exploration. Bryant said the furrows the team discovered are probably a result of the Gulf of Mexico's "loop current," which enters the Gulf near the Yucatan Peninsula, loops its way around the Gulf and then exits near Florida. The current generates large eddies that spin to the west, and the furrows are concentrated along those contours.
Bryant's next adventure will be offshore Nova Scotia, where he expects to find furrows at the base of the continental slope. Seismic data have shown evidence of furrows offshore Brazil and Oman, and they're likely to exist offshore Angola and Nigeria.
Seismic data also indicate the presence of "fossil furrows," which have since been buried by sediments. "If they're filled with sand, it's possible that they could be reservoirs," Bryant said. "Companies have seen these long linear features on seismic records and thought they were sand ridges, but now they're thinking they might be furrows."
On the seafloor, however, they're more likely to be a major pain than an opportunity for exploitation. "They can cause significant problems for pipelines," Bryant said, adding that the furrows look like "a plowed field."
"If you have to engineer around a furrow that's 10 m (34 ft) deep and 50 m (164 ft) across, you've got a pretty big ditch there," he said. "It's hard to do. You either have to trench it in or use flexible pipe, which is very expensive."
Nor are the furrows to be confused with some static geological feature - in many cases the currents are still actively digging them. They tend to form when sea levels are higher, such as modern times, and fill when sea levels are lower, such as during an ice age, Bryant said.
The oil and gas industry has shown significant interest in the phenomenon, not surprisingly. Bryant said the currents probably are not strong enough to take out drill pipe or seafloor structures, but engineers have to know the parameters and design for them. Knowing the path of the currents helps, and many companies are using current meters to measure conditions under the water.
Meanwhile, the A&M team will be on the lookout for these fascinating deepwater obstacles. "Wherever we can expect to find swift currents, we're almost sure to find furrows," Bryant said.

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