Featured image above shows landslide and tsunami simulations at 0m, -50m and -70m sea-level scenarios and landslide distribution and geomorphology. Credits: Webster et al, University of Sydney.

What has developed into the Great Barrier Reef was not always a barrier reef – it was once a fringing reef and did not offer the same protective quality. This is because the coast at this time was much closer to the source of the tsunamis, says lead author of the paper, Associate Professor Jody Webster, from the Geocoastal Research Group at the University of Sydney.

The research shows a shallow underwater landslide occurred 20,000–14,000 years ago, which caused a tsunami 2–3 metres high. The tsunami could have impacted Aborigines living at the time along estuaries and on islands off the paleo-coastline, which has since receded under the rising sea levels that followed the last ice age.

Animation of ancient tsunami:

A submarine landslide 70m below sea-level causes a tsunami, which travels along the paleo-coastline. Credit: Dr Jon Hill, University of York.

The 7km-wide landslide occurred off the edge of the continental shelf causing the tsunami on the paleo-coastline lying between Airlie Beach and Townsville.

Details of the discovery of the submarine landslide and tsunami were published this week in Marine Geology. The international team of researchers used sophisticated computer simulations to recreate what the tsunami would have looked like.

Webster says similar landslides under the sea could occur without our knowledge.

“There is a relatively low chance that a similar submarine landslide with the potential to cause a tsunami of up to three metres or more would happen today,” Webster says.

“However, if one did occur, our findings suggest that the Great Barrier Reef is doing us a great service because of its ability to absorb some of that potential wave energy.”

Just how much energy would be absorbed and what the extent of damage could be done by rising sea levels and tsunamis or king tides is the subject of future research.

In reaching their findings, Dr Jon Hill from the University of York created visual simulations of the tsunami impact at today’s sea level, as well as at a depth of -70m, where the paleo-coastline was before it receded to its current position and was replaced at the shelf edge by the formation of the Great Barrier Reef.

The research team has named the submarine landslide the Viper Slide because of its location adjacent to Viper Reef.

“The discovery of the Viper Slide is the first solid evidence that submarine landslides existed on the Great Barrier Reef,” says Dr Robin Beaman from James Cook University – a member of the expedition that mapped the slide.

The early edition of the paper, ‘Submarine landslides on the Great Barrier Reef shelf edge and upper slope: a mechanism for generating tsunamis on the north-east Australian coast?’, was published by the international journal Marine Geology.

This article was first shared by The University of Sydney on 25 November 2015.