BEIJING, Nov. 22 (Xinhuanet) -- A newfound submarine landslide off the African coast that rumbled some 930 miles (1,500 kilometers) down a slightly sloped seafloor before coming to rest some 60,000 years ago is the most colossal event of its kind ever discovered.

"What causes huge submarine landslides is still being hotly debated," study leader Peter Talling, University of Bristol, told LiveScience. "A very large earthquake occurred in the area we studied in the 1960s without triggering a large underwater landslide. We cannot be sure how this landslide was triggered."

Scientists find underwater landslides interesting because they're known to sometimes generate huge tsunamis.

"It was one of the largest movements of material ever to occur on our planet," Talling explained. "This mass was ten times that transported to the ocean every year by all of the Earth's rivers. The flow was sometimes over 150 kilometers [93 miles] wide, spread across the open sea floor."

Talling and colleagues dropped 1-ton dart-shaped weights to the seafloor in 200 locations, some as deep as 2.5 miles (4 kilometers), then winched sediment samples back to their ship to analyze them and learn how the debris had moved.

"The landslide disintegrated into a very fast-moving flow of sand and mud," Talling said. "We followed the trail left by this flow, which is a layer of sand and mud on the sea floor."

The study gives scientists a better understanding of how deep-sea mudflows work ─ and just how far they can move.

Most of the material stayed suspended in the ocean for the bulk of its 930-mile journey until the seafloor gradient changed slightly, from 0.05 degrees to 0.01 degrees (a typical soccer field, for comparison, has a gradient of less than 1.00 degrees to allow drainage).

(Agencies)