Mass Movements of Warrumbungle National Park, New South Wales, Australia

Abstract

The Warrumbungle Range is the mountainous eroded remnant of an Early Miocene shield volcanic complex located in the central west of New South Wales. A high-severity wildfire in Warrumbungle National Park in January 2013 was followed by intense rain, causing a number of debris flows. Several flows impacted on infrastructure such as roads and culverts and posed a severe risk to public safety, prompting a broader assessment of mass movement hazard within the park. High resolution LiDAR DEM revealed 542 locations with evidence of mass movement processes that pre-date the fire. The most common types of mass movement visible in the DEM are rotational slumps (353, 65%). The distribution of these indicated stratigraphic control, with 50% of slumps within 440 m of the volcanics-sandstone geologic contact, and typically occurring within unconsolidated volcanic colluvium and/or in situ deeply weathered volcanics. Debris flows are the next most common mass movement type after rotational slumps. Debris flow scour channels generally occurred on colluvial slopes in more elevated sites, within the volcanic rocks. DEM-extracted morphometric data was used to identify areas of debris flow hazard in WNP. Several large mass movements are morphometrically different, with some evidence for formation under different hydro-climatic conditions. A simple conceptual model of how mass movements contribute to the evolution of the Warrumbungle Range is proposed involving groundwater, deep weathering, slope retreat by mass failure, colluvial deposition and periodic incision by debris flows.