Post cyclone mud antidunes on the De Grey Rivier in Northwest Australia

Following Category 5 Cyclone Zelia, the De Grey River delta in northwestern Australia experienced extreme flooding, significant sediment deposition, and widespread erosion. The De Grey is a dryland ephemeral river draining the arid interior of the Pilbara and flowing toward the Indian Ocean. After the cyclone-driven flood pulse passed, the system quickly returned to its dry state, exposing extensive new sediment surfaces.

To characterize the geomorphic and sedimentologic changes, we integrated satellite imagery, drone photography, LiDAR, trenching, laser particle analysis, and age dating to produce pre- and post-flood maps. These datasets guided the selection of field sites for drilling and augering. We excavated multiple trenches ranging from 4 ft by 4 ft pits to a ~50-ft-long cut bank exposure.

The cut bank revealed a sharply eroded face overlain by fresh splay deposits. Within this exposure, we documented striking sedimentary structures, including laterally continuous mud-wave antidunes that extended across the entire cleared bank. These features occurred in sets and could be traced as far down-section as visibility allowed.