LATE-HOLOCENE SNOW-AVALANCHE ACTIVITY IN SOUTHERN NORWAY - INTERPRETING LICHEN SIZE-FREQUENCY DISTRIBUTIONS USING AN ALTERNATIVE TO SIMULATION MODELING

Recent work by McCarroll (1993, 1994) suggests that a new approach to lichenometry can be used to date diachronous surfaces. Size-frequency distributions of largest lichens obtained from the diachronous surface s of avalanche boulder ramparts comprise two elements: an equilibrium population growing on boulders deposited throughout the Holocene, and overlapping populations growing on groups of boulders deposited by eve nts during the last 300 years. In this study, almost 10 000 lichens we re measured on two groups of closely similar ramparts. The number of v ery large lichens is used to predict the form of the equilibrium distr ibution, which is then removed, leaving a corrected distribution which reflects the age-frequency of surface boulders deposited during the ' Little Ice Age'. The results confirm that maximum avalanche activity o ccurred during the 19th century, but a minor peak at one site suggests that avalanche activity was enhanced during the mid-18th century.