THE GEOMORPHIC INFLUENCE OF WILDFIRE ON STABILISED DUNE FIELDS, AN EXAMPLE FROM THE COOLOOLA SAND MASS, AUSTRALIA

Wildfires are a major source of dune activation; however, few studies have evaluated their influence on relic (stabilised) dune field development. In this study, we assess the onlapping parabolic dune sequences at the sub-tropical Cooloola Sand Mass, an ideal chronosequence in eastern Australia, to understand fires contribution to their evolution. Our field based measurements and forward numerical models demonstrate that dune hillslopes evolve (erode and deposit) in two distinct phases. Initially, stabilised dunes go through a rapid phase of topographic adjustment (0.47 ± 0.08 cm yr^-1) associated with the dominance of episodic sediment transport (dry-ravel and sheetwash) due to wildfire on over steepened gradients. This phase continues for ~1.5 kyr until hillslope gradients are lowered below their angle of repose (33°). Once sufficiently lowered, the dunes evolve through a gradual evolution (0.08 ± 0.05 cm yr^-1) associated with continuous sediment transport (biogenic soil creep and granular relaxation) despite the continued presence of fire. This evolution can be explained by nonlinear sediment transport with 33° These findings of dual transport regimes and fire frequency are confirmed by stratigraphic records and age-depth modelling at excavated dune foot-slopes and highlights the importance of fire to both ecologic and the geomorphic development of dune profiles.