Soil history and debris avalanche deposits along the Illawarra scarpland

Abstract

Two major periods of avalanching have occurred along the Illawarra scarpland. The older, the Scarborough formation, is characterized by a very thick, acid, weathered zone, similar to the lower mottled horizons of laterite profiles. The younger, Keira formation, has relatively shallow red and yellow earth profiles developed in it. Although its profile of deep weathering has some features in common with laterite, the Scarborough formation is not part of the general laterite surface, but represents a separate period of prolonged stability and weathering. The debris-avalanches are thought to have been deposited during excessively wet climatic conditions in the past, and they represent an alternate form of instability compared with the dry phase instability proposed for the K-cycle history of milder hillslope terrain near Nowra.