Lichenometry in Iceland, results and application

International audienceThis paper proposes a review of the use of lichenometry in Iceland since 1970, using different techniques to solve the chronology of geomorphic processes. Most users have sought to date proglacial landforms in two main areas: around the southern ice-caps of Vatnajökull and Mýrdalsjökull and in the Tröllaskagi peninsula in the north. Based on the results of over 35 published studies, lichenometry has been widely applied in Iceland, proposing numerical ages (absolute dating) and relative ages (relative dating) of different surfaces. Increasing awareness of methodological limitations of the technique, together with more sophisticated data processing, has led some authors to claim that lichenometric 'ages' are robust and reliable. However, the different measurement techniques used make it difficult to compare regions or studies in the same area. These problems are exacerbated in Iceland by rapid environmental changes across short distances and more generally by lichen species mis-identification in the field. Moreover, the reliability of lichenometric dates is discredited by their lack of correspondence with tephrochronologic data, whatever the lichenometric method used. Finally, the accuracy of lichenometry quickly weakens after few decades of surface exposure and the method loses rapidly any absolute aptitude. At the end, absolute dates proposed in the literature are not very trustworthy, and lichenometry should be used for relative dating only