CGRG Bibliography of Canadian Geomorphology
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Author : Beschel, R.E.
Date : 1961.
Title : Dating rock surfaces by lichen growth and its application to glaciology and physiography (lichenometry)
Publication : In: Geology of the Arctic, edited by: Raasch, G.O., Toronto: University of Toronto Press, Proceedings of the First International Symposium on Arctic Geology, Calgary, Alberta
Issue : 2:
Page(s) : 1044-1062
Abstract
Most of the arctic and alpine crust lichens, especially the genera Rhizocarpon and Lecidea grow very slowly. This can be concluded indirectly from maximum diameters on rock surfaces of known age or repeated measurements. The over all constant increment after an initially sigmoidal growth allows dating of rock surfaces exposed up to 1000-4500 years BP, depending on the climatic conditions. Lichenometry permits relative dating of events which led to the exposure of bare rock surfaces within the age limit of the lichens in similar macroclimates. This can be converted to an absolute scale if one event is dated by other means, e.g. historical information, or if the growth rate is measured directly. From lichen measurements obtalned in West Greenland, the Alps, and the Ruwenzori Mountains, the synchronlsm of glacier behaviour within the advance Period of modern times (400-40 BP) appears very high. Early hypothermal moraines and boulder streams can be separated clearly from early modern ones, even if other morphological criteria fail. Lichen growth rates are inversely proportional to the hygrocontinentality of the area. This permits calculation of this or similar combined climatic factors through lichenometry, or the predictlon of lichen growth rates from the known climate. Lichenometry is especially useful where dendrochronology is impossible.
Bibliography of Canadian Geomorphology