A team of scientists mapping the seafloor along Australia's Great Barrier Reef have stumbled upon the remains of a huge underwater landslide. Its estimated 32-km3 volume is around 30 times that of Uluru, the giant red rock in Australia's center, and is thought to have crumbled off the Queensland coast some 300,000 years ago.

Scientists from James Cook University, the University of Granada and the University of Sydney made the discovery while working from a research ship around 75 km (46 mi) off the coast. The team was mapping the floor in an area called the Queensland Trough using 3D multibeam mapping, a technique that bounces sound waves off the seabed to determine water depth, and made some unexpected discoveries.

"We were amazed to discover this cluster of knolls while 3D multibeam mapping the deep Great Barrier Reef seafloor," said James Cook University's Dr. Robin Beaman. "In an area of the Queensland Trough that was supposed to be relatively flat were eight knolls, appearing like hills with some over 100 m high (330 ft) and 3 km (1.86 mi) long."

After discovering the chunks of underwater debris, the researchers worked backwards, using the mapping technique to trace their origins back to the massive landslide, as far as 30 km (18 mi) away. In one of the knolls, the team discovered a community of both living and fossilized cold-water corals, mollusks and barnacles, which played an important role in dating the ancient event.

"The oldest fossil corals recovered off the top of the knoll was 302 thousand years," says Dr. Angel Puga-Bernabéu at the University of Granada, lead author on the study. "Which means the landslide event that caused these knolls must be older."

This type of underwater landslide certainly has the potential to cause a tsunami, and the researcher's modeling for a consequent giant wave places it at around 27 meters (88 ft) tall. A tsunami in this area, however, would most likely be stunted by the presence of the coral reef, which acts as a natural breakwater and absorbs the force of waves. The teams says a lot more research is needed to assess the tsunami risk to the Queensland coast created by landslides of this nature.

Big as it may be, this landslide pales in comparison to some of history's largest submarine land slides. The Storegga Slide in the Norwegian sea around 8,000 years ago saw 3,500 km3 sheared off Noway's continental shelf, while millions of years ago, the Agulhas landslide off South Africa moved as much as 20,000 km3 of sediment, the largest described by scientific literature.

Still, its discovery gives researchers a new understanding of the landscape beneath the Great Barrier Reef, and offers new opportunities to study the marine life that call it home.

The research was published in the journal Marine Geology.