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Largest Undersea Landslide Revealed on the Great Barrier Reef

Scientists have discovered the remnants of a massive undersea landslide on the Great Barrier Reef, approximately 30 times the volume of Uluru.

The remains of the slip, known as the Gloria Knolls Slide, were discovered 75 km off the Queensland coast near Innisfail. “This is all that remains after a massive collapse of sediment of about 32 cubic kilometres’ volume more than 300,000 years ago,” said Dr Robin Beaman of James Cook University.

Beaman said a debris field of large blocks, or knolls, and numerous smaller blocks, lies scattered over 30 km from the main landslide remains, into the Queensland Trough, to a depth of 1350 metres. “We were amazed to discover this cluster of knolls while 3D multibeam mapping the deep GBR seafloor,” he said. “In an area of the Queensland Trough that was supposed to be relatively flat were eight knolls appearing like hills, with some over 100 metres high and 3 km long.”

A sediment sample from a knoll at a depth of 1170 metres identified a remarkable cold water coral community of both living and fossilised coral species, gorgonian sea whips, bamboo corals, molluscs and stalked barnacles. “The oldest fossil corals recovered off the top of the knoll was 302,000 years, which means the landslide event that caused these knolls must be older,” says lead author Dr Angel Puga-Bernabéu of The University of Granada.

Modelling revealed that the landslide could have led to a tsunami wave measuring 27 metres. However, the wave would likely have been dampened significantly by the presence of any coral reefs.

The researchers say that considerably more seabed mapping and sampling is needed to fully assess the tsunami hazard to the Queensland coast posed by underwater landslides.

With one-third of the Great Barrier Reef situated beyond the seaward edge of its shallower reefs, the researchers say that the discovery of this prominent undersea landslide and its vast debris field reveals a far more complex landscape in the deep Great Barrier Reef than was previously known.