Day 3: What lies beneath?
By Chris La Rosa
When you are 260 kilometres offshore, surrounded by an expanse of featureless blue waters, it’s hard not to wonder what lies beneath you. That’s exactly where I find myself aboard RV Investigator as part of this CSIRO research voyage. The simple answer is that it happens to be 320 metres deep, however, that is just part of the story.
Research scientists are busy working to map the seafloor and investigate undersea phenomenon about which little is known. Using sophisticated multi-beam echosounding equipment, the team is able to create a detailed image of the seafloor beneath the ship. These systems allow the team to measure an arch of up to 150º downward from the hull of the ship. This means that as the RV Investigator cruises along in 300m of water, researchers are capable of mapping a 1200-1500m wide swath of the bottom.
3D view of the Bowl Slide on the central Great Barrier Reef continental slope. This image stretches across 23km of the reef edge and 18km out across the basin. The seafloor is artificially coloured by depth, with red being the shallow reefs ~100m in depth, down to the purple representing ~900m depth. The landslide debris can be seen spreading downslope across the basin floor away from the scarp.
On this voyage, the mapping team, led by Dr Robin Beaman from James Cook University (JCU), has been exploring sites linked to underwater landslides. One recently discovered slide, the Swain Slide, occurred when an area of the shelf located at the outer edges of the Great Barrier Reef collapsed and material slid down the slope into deeper water. Dr Beaman tells me that the available evidence suggests this likely took place between 10,000–18,000 years ago which is considered relatively recent on a geologic timescale. Findings from this voyage’s mapping exercise show that there is little sediment covering the debris field, indicating that it happened not that long ago.
Dr Robin Beaman analysing incoming data on the Bowl Slide.
What next for the research team? Well after measuring 179km² of seafloor, it was determined that the slide is wider than previously thought and will therefore require further voyages to complete the mapping. In addition, it is hoped that future voyages may involve direct sampling of the seafloor to better understand the composition of the slide material. This will also assist researchers in pin-pointing exactly when the slide occurred. Team member Chris Yule (JCU) explains that ‘ground truthing’ or bringing up material from bottom, will greatly improve their understanding of the slide and could help confirm a number of findings from this voyage.
The mapping team hard at work.
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