Undersea, or submarine, landslides are common features on steep continental margins and the sides of oceanic islands around the world. Submarine slope failure is a natural hazard process that dramatically shapes the seafloor environment and transfers large quantities of sediment from the shelf into the deep basins. They can be triggered by different mechanisms and are important to study due to their ability to generate large and catastrophic tsunamis.

Viper Slide on shelf edgeIn 2007, while on an expedition on the RV Southern Surveyor, we first discovered and mapped a series of underwater landslides along the Great Barrier Reef margin. Some of these landslides surprisingly occurred right at the continental shelf edge, in about 90 m water depth about where sealevel was positioned near the last ice age. The Viper Slide, so named because of its proximity to Viper Reef, represents a collapse of the shelf edge 7 km long with debris up to 5 km spreading down the upper slope.

Smaller shelf edge and upper slope slides were found clustered around the central Great Barrier Reef area, likely related to the oversteepening (steeper gradients) of the upper slope due to the shelf-edge delta developed by the paleo-Burdekin River. Other small slides were found in deeper waters at the base of the continental slope in depths of about 800 m or more where submarine canyons incising into the slope had caused collapses.

Noggin Block on upper slopeTwo huge landslide scarps, up to 20 km long, were found that stretch the full height of the continental slope. The Gloria Knolls slide lies offshore of Cairns and lies in depths 300 to 1000 m. About 20 km downslope are eight knolls, 10s to several 100 m high, that are the remains of the debris from this slide. Also in the central GBR, the Bowl Slide, named due to its proximity to Bowl Reef, is another huge slide stretching from 200 to 900 m.

The Noggin Block in 340 to 470 m, named due to its closeness to Noggin Passage off Cairns, was identified as section of the upper slope about 0.86 km³ that could potentially collapse due to the undercutting of submarine canyons around the edges of the block, leaving it with small pockmarks indicating weakening of the steep headscarps.

These landslide features point to a north-eastern Australian margin that has been greatly influenced by erosion which shapes the seafloor environment in these deeper waters. Research is continuing to how these geological processes have influenced the growth of the Great Barrier Reef, the ages of these dramatic events, and any potential tsunami impact from these landslides.

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

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Additional media

• Peer-reviewed literature – Potential collapse of the upper slope and tsunami on the GBR margin
• Peer-reviewed literature – Submarine landslides on the Great Barrier Reef shelf edge and upper slope
• Conference paper – Submarine landslides in the Great Barrier Reef margin
• Peer-reviewed literature – Gloria Knolls Slide
• Related blog post – Largest undersea landslide revealed on the Great Barrier Reef
• Peer-reviewed literature – Submarine landslide morphometrics and slope failure dynamics along a mixed carbonate-siliciclastic margin, NE Australia