Waterfalls, floods and climate change: evidence from tropical Australia

Sediments preserved at the base of rare types of waterfalls provide records of terrestrial floods to 30 kyr or more, being approximately 6–10 times longer than that usually obtained from the traditional slackwater method. These coarse-grained sand deposits form ridges and levees adjacent to plunge pools at the foot of unindented escarpments and within gorge overflow bedrock channel systems. The extension of palaeoflood records into the Late Pleistocene allows comparisons to be made between periods of extreme floods and dramatically different climatic regimes. Our results highlight that the last 30 kyr were dominated by alternating periods of extreme and relatively low magnitude floods that correspond to particular climatic regimes. Recent predictions from Global Climate Models suggest that tropical regions will experience dramatic increases in the frequency and magnitude of extreme floods under a future altered climate. Plunge-pool palaeoflood records can be used to at least partially test such predictions by determining whether similar previous climate/flood associations have occurred within a region.