Lichenometric dating of rock surfaces in the northern cascade range, usa

Abstract

This study presents a growth curve developed from direct and indirect growth rates of hizocarpon geographicum lichens from study sites on ounts aker, ainier, dams, and ood in the northern ascade ange of the western . Our observations of direct growth rates are based on 31 measurements of 11 lichens growing on different surfaces. This direct growth rate dataset is complemented by indirect growth rates based on measurements of the largest lichen observed on 20 different surfaces over 24–33‐yr periods. The direct and indirect datasets produce statistically indistinguishable mean radial growth rates of 0.48 and 0.50-mm yr⁻¹, respectively. Statistical analysis of zero and first order fits of our growth rate data suggests that lichen growth is best characterized by the average of our mean growth rate (zero order) models at 0.49-mm yr⁻¹. Our revised growth curve for the study area extends the applicable range for dating rock surface in the study area to the seventeenth century, approximately 175 years longer than previous calibrated curves.

Key words:

• lichenometry
• lichenometric dating
• Cascade Range

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Acknowledgements

The authors would like to thank the Mazamas nonprofit mountaineering education organization located in Portland, Oregon for supporting the data collection effort.