A new approach to lichenometry: dating single-age and diachronous surfaces

Abstract

A new approach to lichenometry, based on large samples of the single largest lichen on each boulder, is presented. On surfaces of uniform age, lichen sizes measured in this way are near normally distributed, so the mean value can be used in constructing lichenometric-dating curves. By combining mean values from several sites, statistically defined confidence limits can be assigned to predicted dates. In a pilot study, dates obtained for 'Little Ice Age' moraines of two glaciers in southern Norway are consistent with those obtained using other approaches. Unlike standard lichenometry, the new approach can be used to investigate the age-frequency of boulders on diachronous surfaces formed by continuous or periodic accretion or disturbance. It has been used successfully to access the record of late-Holocene snow avalanche activity retained on avalanche boulder ramparts in upper Jostedalen, western Norway. Pilot studies are also presented of its use on a talus slope, solifluction lobes and periglacial patterned ground. Although there are some problems and limitations to its use, in many circumstances these are likely to be outweighed by the advantages of the new approach over standard lichenometry.