Landslides in Tertiary Basalts at Murrurundi, Australia

Abstract

The principal geomorphic feature of Eastern Australia is the Great Dividing Range. It is intermittently capped by Tertiary basalts, which are variously preserved as plateaus or steep-sided ridges. In contrast to most of the Australian landscapes, the Tertiary basalts form steep, topographically immature landforms that are prone to slope instability. This paper looks at the characteristics of the basalts and their associated alteration horizons, which, in combination, make them susceptible to landsliding on a large scale. The very different physical and chemical weathering characteristics of the basalt and the altered materials are contrasted and used to explain a complex landsliding mechanism that is triggered by failure in an amygdaloidal horizon capped by a palaeosol, and then sustained by characteristics of the basalt and its derived soils. Process rates are inferred to range from relatively rapid to very slow, throughout the different stages of instability. The role of anthropogenic factors on slope stability is discussed.