Feb 9, 2017

Ancient Undersea Landslide Discovery Sheds New Light on Great Barrier Reef

Scientists studying Australia's Great Barrier Reef have discovered an ancient undersea landslide which dumped an estimated 8 cubic miles of rock and debris on the ocean floor and could have triggered a tsunami of up to 20 feet high.

Researchers said Wednesday the slip and vast debris field of large blocks, or knolls, at its edge reveals a far more complex reef landscape than was previously known.

"In an area of the Queensland Trough that was supposed to be relatively flat were eight knolls, appearing like hills with some over 100 [feet] high and [nearly 3 miles] long," Dr. Robin Beaman, from James Cook University, said.

Remnants of the slip, known as the Gloria Knolls Slide, were first found in 2007 while scientists were carrying out three-dimensional mapping of the Queensland Trough, a deep basin that runs adjacent to the reef.

After finding the knolls poking up from the sea floor, scientists spent years mapping the area to find the landslide that caused the underwater hills, which are located about 47 miles offshore at a depth of between 4,000 to 4,600 feet.

A sediment sample from the largest knoll, taken at a depth of about 4,000 feet, revealed the presence of a cold-water coral community which allowed researchers to date the event.

"The oldest fossil corals recovered off the top of the knoll were 302,000 years old — which means the landslide event that caused these knolls must be older," lead researcher Dr. Angel Puga-BernabĂ©u, a former postdoctoral researcher from the University of Sydney who is now with the University of Granada, said in a statement.

The landslide was a "catastrophic collapse" that pushed debris about 20 miles from the base of the slip, Beaman said.

Modeling also showed a potential tsunami wave of up to 30 feet high. However, the wave's impact would likely have been dampened by the vast coral reef system, researchers said.

The findings, published in the journal Marine Geology, shed new light on the deepest reaches of the Great Barrier Reef, the world's largest coral reef ecosystem.

"Prior to 2007 we just didn't know what the deep Great Barrier Reef landscape looked like," Beaman said. "This is building up a far more detailed picture of how complex it is down there."

Already the team of international researchers have been surprised by the marine life they have found in the deep-sea conditions where temperatures can drop to 39 degrees Fahrenheit and it is pitch black.

"There was lot of marine life. We found both living and dead cold water corals," Beaman said. "They are very different to the shallow water cousins and don't rely on sun light at all."

Westerly view of the Gloria Knolls lying in the Queensland Trough downslope of the Gloria Knolls Slide. Depths are colored red (shallow) to blue (deep), over a depth range of about 1500 meters.
A better understanding of the geological structure of the seafloor will also help improve oceanographic knowledge of the area, Beaman said.

The Great Barrier Reef is one of the most biodiverse natural systems on earth and is home to about 1,400 coral reef species and 1,625 species of fish.

Samples taken from the deep water coral community included gorgonian sea whips, bamboo corals, molluscs and stalked barnacles.

Read more at Discovery News

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