Natural EnvironmentMonitoring 2005, No 6, 41-45
USE OF LICHENOMETRY IN GEOMORPHOLOGICAL RESEARCH
Lichenometry is performed by measuring diameters of map lichens, most often of Rhizocarpon geographicum and Rhizocarpon alpicola species, growing on rock surfaces (stones) constituting moraines, talus slopes, debris flows, rock glaciers, landslides and river terraces. Lichens of the Rhizocarpon species allow dating of sediments deposited c. 800 year ago, though best resolution is obtained for younger sediments.
Beschel (1950) was a pioneer of use of lichenometry in geomorphology as he dated moraines of Alpine glaciers. Lock et al. (1973), Innes (1982, 1983, 1985), Bradwell (2004) and McKinzey et al. (2004) describe lichenometric procedures used in geomorphological research. Kotarba (1988, 2001, 2004) and Bajgier (1992), Bajgier-Kowalska (2002, 2003) use lichenometry in Poland. Lichenometry is often used and modernized during researches on age of moraine deposits in Iceland (Jaksch, 1975; Gordon and Sharp, 1983; Maizels and Dugmore, 1985; Caseldine, 1991; Evans et al., 1999; Bradwell, 2001, 2004; Kirkbridge and Dugmore, 2001; D¹bski, 2002; D¹bski et al. 2005; McKinzey et al., 2004).
On the rock surface subject to dating the largest diameters of relatively circular and separate thalli are measured. Age of the surface is calculated based on singular largesr thallus or mean of 5 largest thalli. Obtained value is referred to calibrated growth curve of the lichens. The curve is drawn based on measurements performed on rock surfaces of known age. Recently (Brawdell, 2004; McKinzey et al., 2004) it was found out that for SE Iceland best results bring use of the size-frequency gradient technique performed on the population of Rhizocarpon lichens.
The use of lichenometry in geomorphology has some limitations, e.g.: most often measured lichens Rhizocarpon don.t grow on carbonate rocks, it is essential to pay attention to specific local environmental conditions (e.g. location on a slope, aspect of the rock surface) which can differentiate the pace of lichens growth, colonisation lag time which is not always known (especially in a case of moraine deposits), difficulties in finding sufficient number of lichens thalli. In SE Iceland lichenometry gives best results of rock surfaces exposed 60 to 250 years ago.