Rock Properties as Controls on Free‐face Debris Fall Activity

A free face composed of basalt flows showed, over a 72 week observation period, considerable variation in yield (kg or m 3 ) of fallen material. Yield peaks in spring and autumn were recorded but small contributions were made from all flows throughout the year. The incidence of frost action cannot account for all of the yield peaks. An explanation of free‐face weathering can best be given by taking the microcrack crack system into account in relation to some simple rock properties. Although there are several factors involved, microcrack density and coefficient of loosening are useful indicators of flow behaviour. An explanation of rock removal which takes material properties into account as well as environmental or climatic conditions is to be preferred and can be applied as a general model for all climates.