Marine geologists from Australia's James Cook University said 3-D mapping techniques have revealed a slab of seafloor a quarter of a cubic mile in size -- the remains of an ancient underwater landslide -- are perched on the continental shelf off the coast of Queensland, Sky News reported Friday.
"Undersea landslides are a well understood geological process, but we didn't know there were any on the Barrier Reef," university geologist Robin Beaman said.
"It is sitting on top of a submarine canyon, cutting into the slopes and it is in the preliminary stage of collapse."
The research vessel Southern Surveyor made the discovery on the deepest part of the reef where researches said they've found dozens of submarine canyons.
"It is slowly giving way although it remains stable under current conditions," Beaman said.
Exactly when it would collapse is unclear, he said.
"But it is absolutely going to collapse and when it does it will fall 1 kilometer [3,200 feet] into the adjacent basin.
"This will generate a localized tsunami that will affect the Queensland coastline, which is around 40 miles away," he said.
"We're not trying to alarm people, but we need to know it is there and what could happen when it falls."