Submarine landslides on the Great Barrier Reef shelf edge and upper slope: A mechanism for generating tsunamis on the north-east Australian coast?

Abstract

Shallow (<200 m) submarine landslides influence margin evolution and can produce devastating tsunamis, yet little is known about these processes on mixed siliciclasticcarbonate margins. We have discovered seven landslides along the shelf edge and upper slope of the central Great Barrier Reef (GBR), Australia. The largest shelf edge landslide is investigated in detail and represents a collapse of a 7 km long section of the shelf edge at 90 m water depth with coarse debris deposited up to 5.5 km away on the upper slope down to 250 m. The precise timing and triggering mechanisms are uncertain but available chronologic and seismic stratigraphic evidence suggest this event occurred during the last deglacial sea-level rise between 20 and 14 ka. Regional bathymetric data confirms that these shelf edge and upper slope slides are restricted to the central GBR between latitude 18° and 19°S, suggesting a spatial relationship between the extensive Burdekin paleo-fluvial/delta system and shallow landslide activity. This study highlights an important local mechanism for the generation of tsunamis on this margin type, and numerical simulations under present conditions confirm a 2 to 3 m tsunami wave could be produced locally. However, we consider that the risk of such slides, and their resulting tsunamis, to the modern coastline is negligible due to their relatively small size and the capacity of the GBR to dissipate the wave energy.

Gloria Knolls Slide: A prominent submarine landslide complex on the Great Barrier Reef margin of north-eastern Australia

“…However, this is not the case for the GBR margin, where the maximum rates of sediment supply to the slopes occurred during the late transgression (Dunbar et al, 2000;Page et al, 2003). In the central GBR, many upper slope landslides have been identified nearby a large deltaic system (paleo-Burdekin River lying ~150 km to the south-east; Webster et al, 2016). However, the GKS study area lacks any large deltaic or fluvial systems similar to the paleo-Burdekin River that may provide large amounts of sediment to the slope.…”

“…Run-up heights at the adjacent coast would depend on the sea-level position, the overall physiography of the margin, the period, size and direction of the incoming waves, beach morphology, bottom friction, and other parameters. It has also been suggested that the presence of the shelf reefs, if in existence at the time (Webster and Davies, 2003), would decrease tsunami amplitudes at the coastline to half or less (Baba et al, 2007;Webster et al, 2016). For example, the impact of a modelled 2 m high tsunami wave generated by a smallscale landslide (~0.025 km 3 ) in the southern central GBR, would have reached the coast with a height of 0.5 m (Webster et al, 2016).…”

“…It has also been suggested that the presence of the shelf reefs, if in existence at the time (Webster and Davies, 2003), would decrease tsunami amplitudes at the coastline to half or less (Baba et al, 2007;Webster et al, 2016). For example, the impact of a modelled 2 m high tsunami wave generated by a smallscale landslide (~0.025 km 3 ) in the southern central GBR, would have reached the coast with a height of 0.5 m (Webster et al, 2016). Nonetheless, a tsunami caused by the collapse of GKS would have been significant even if dampened by shelf reefs.…”

“…Earthquakes are one of the most important triggering mechanisms of slope failures (Locat and Lee, 2002; and it is suggested that frequent large earthquakes might limit the landslide volume on such active margins (Tappin et al, 2007;Völker et al, 2012). However, studies on submarine mass-wasting are relatively scarce on modern carbonate or mixed carbonatesiliciclastic passive margins (Hine et al, 2002;Puga-Bernabéu et al, 2013a;Principaud et al, 2015;Tournadour et al, 2015;Webster et al, 2016). Given that one of the preconditioning factors for landslide generation might be the presence of weak layers in the sedimentary succession (Haflidason et al, 2003;Laberg et al, 2003;Harders et al, 2010), it is important to note that the intrinsic characteristics of mixed carbonate-siliciclastic margins are the variable lithologies with different rheologic properties which vary spatially and temporally.…”

Carbonate slope re‐sedimentation in a tectonically‐active setting (Western Sicily Cretaceous Escarpment, Italy)

“…Slope architecture also depends on the controlling factors of sediment shedding occurring on platform tops and/or their adjacent slopes (Spence & Tucker, ; Playton et al ., ; Reijmer et al ., 2015a). Controlling factors of slope architecture include: (i) sea‐level fluctuations (for example, Bahamas: Hine et al ., ; Schlager & Ginsburg, ; Eberli & Ginsburg, ; Reijmer et al ., , , 2015a; Wunsch et al ., ; Mulder et al ., ; Great Barrier Reef: Webster et al ., , ; Puga‐Bernabéu et al ., , ; Maldives: Betzler et al ., ); (ii) tectonics (for example, Southern Provence: Floquet & Hennuy, ; Hennuy, ; Floquet et al ., ; Reijmer et al ., 2015b; Pyrenees: Drzewiecki & Simo, ; general reviews: Payros & Pujalte, , and references therein; Playton et al ., , and references therein); and (iii) the system growth itself (Canning Basin: Playton & Kerans, ,b; Delaware Basin: Playton & Kerans, ). In addition, the downslope movement of sediment‐laden flows covers a variety of processes that may coexist within a single gravity flow event.…”