Estimating The Occurrence Of Rockfalls In Columnar Basalt

The occurrence of rockfalls from a columnar basalt cliff at the Lal Lal Falls reserve, near Ballarat, Victoria has been estimated using erosion rates and historical data. Erosion rates were calculated from the volume of material removed over the past 3 million years, based on the geomorphological history of the site. Historical data included a rockfall in 1990, which caused the death of two high school students, and another rock topple observed in 1992. A reasonable agreement is found between the volume of material involved in the observed events and the calculated annual erosion rate. In the absence of more reliable data, the method provides a useful estimation of event size and frequency.