Geomorphology as a tool in regional landslide mapping
Landslides are a widespread feature in the Tasmanian landscape. Mineral Resources Tasmania, through the Federal Government’s National Disaster Mitigation Programme funding, is progressively undertaking regional landslide mapping of urban areas and their surrounds to provide stakeholders such as local councils with information that will assist them in the mitigation of landslide risk. The approach being used includes geological mapping, geomorphological mapping and analysis and the compilation of a landslide inventory. When combined within a GIS framework, these information layers are used to produce a predictive landslide susceptibility assessment based on raster modelling.
This paper outlines the methodologies being used along the coastal strip from Devonport to Boat Harbour Beach in Tasmania’s northwest, concentrating on the geomorphological mapping and analysis. Historical and recent aerial photography, updated geological information and targeted fieldwork are the data sources for this analysis, with various methods being utilised to capture the landform information gained. Examples of landforms the geomorphological analysis has identified include regional basalt surfaces, escarpments, colluvial aprons, marine benches at varying elevations, river terraces, alluvial fans and previously undocumented landslides. The identification of these various key landscape units in the geomorphological analysis has allowed an understanding of the timing of landslide events to be developed. This, in combination with the spatial distribution of landsliding provided by the inventory, gives us the ability to begin assessing the likelihood of landslides in this area of Tasmania. From this we can gain a preliminary idea of the hazard that they present, as hazard involves the knowledge of spatial distribution and likelihood.