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Sharnie Kim ABC News 21 Dec 12;

Researchers mapping the sea floor near the Great Barrier Reef say they have found a giant slab of collapsing sea floor that could trigger a tsunami in the future.
Audio: Sharnie Kim reports from Cairns (AM)

Marine geologists at James Cook University say it is only a matter of time before the slab, known as the Noggin Block, collapses.

Dr Robin Beaman says the slab is the remains of an underwater landslide deep in the Great Barrier Reef.

"It's actually up on the top of the continental slope in about 350 metres of water," he said.

"This block, which is about one cubic kilometre ... is in the very slow, early stages of starting to break away from the edge of the Great Barrier Reef."

He says the Noggin Block is stable at the moment, but warns a collapse could be catastrophic.

"The only thing that we could find that would trigger a block breaking away on that scale [would be] a very large earthquake in the near vicinity. That is very unlikely," he said.

"If it were to break away catastrophically, that is break away really quickly, what that would do is it would create a surface wave above it. It would actually cause a tsunami.

"That tsunami would travel across the Great Barrier Reef, it's about 70 kilometres offshore, and it would impact the local area, the North Queensland area."

It would take about an hour for the tsunami to hit nearby coastal areas like Mourilyan Harbour and Clump Point.

Dr Beaman and his colleagues hope use their sonar mapping technique to find more underwater areas at risk of collapsing.

"We should be aware that these things exist," he said.

"We don't really know when such a block might collapse. All I can say is sometime it eventually will."

The research is published in the journal Natural Hazards.

Slab of Barrier Reef sea floor breaking off: scientists
Channel NewsAsia 21 Dec 12;

SYDNEY: A huge slab of sea floor near the Great Barrier Reef is in the early stages of collapse and could generate a tsunami when it finally breaks off, researchers warned Friday.

Marine geologists from Australia's James Cook University have been using advanced 3D mapping techniques on the deepest parts of the reef -- below diving depth -- since 2007 and have discovered dozens of sub-marine canyons.

On a recent trip, they came across the one cubic kilometre slab of sea floor, the remains of an ancient underwater landslide, which is perched on the continental shelf.

"Undersea landslides are a well understood geological process but we didn't know there were any on the Barrier Reef," geologist Robin Beaman told AFP.

"We found this one large block that stood out. It is sitting on top of a sub-marine canyon, cutting into the slopes and it is in the preliminary stage of collapse."

He stressed that no one knew when a collapse may occur, "whether tomorrow or even in our lifetime", but that people should be aware that it was there.

"It is slowly giving way although it remains stable under current conditions," he said.

"But it is absolutely going to collapse and when it does fall it will fall one kilometre into the adjacent basin.

"This will generate a localised tsunami that will affect the Queensland coastline, which is around 70 kilometres (40 miles) away.

"We're not trying to alarm people, but we need to know it is there and what could happen when it falls," he added.

The geologists who made the discovery, which was published in the journal Natural Hazards, were travelling on the Southern Surveyor, an Australian maritime research vessel.

This is the same ship on which scientist Maria Seton last month discovered that a South Pacific landmass identified on Google Earth and world maps as Sandy Island does not exist.

-AFP/fl