Lichenometry is the process or science of measuring lichens. Lichens are complex plantlike organisms, which show no differentiation into stem, root, or leaf and are composed of a fungus and algae growing in a symbiotic relationship on a solid surface. Lichenometry is a newly evolved surface-exposure dating method with a ninety-five percent with the confidence level having a margin of error plus or minus ten years. This method can be used to date rock falls, debris flows, landslides, moraines and other glacial landforms, and many other geomorphic processes. Lichenometry may, also be used in the identification of blind thrusts and subduction zone thrust that lack easily accessible fault scarps, to detect the frequency and intensity of earthquakes, as well as the relative and/or absolute dates of solid surfaces.
Lichenometry was refined in New Zealand, while varying procedures have devolved all over the world. This procedure is conducted by measuring lichens of the same species at a particular site. Generally, a large sample of the lichen-size population is sampled using digital calipers to measure the maximum diameter of the largest lichens. A growth curve is then created that may be calibrated through the use of dendrochronology, radiometric and/or cosmogenic dating. The data then can be analyzed to answer questions for which the research is being conducted. William Bull is conducting ongoing research on the Earthquake History of the San Andreas Fault.
Several of Bull's research sites are within Sequoia and Kings Canyon National Parks since they are close enough to the San Andreas Fault for coseismal rock falls. Lichenometry is being used to evaluate the earthquake history of San Andreas Fault and Southern Alps in New Zealand. It is also being used on North Central Baffin island to evaluate glacial mass budgets and to analyze debris flows of Chalance torrent, in Valgaudemar of the French Alps.
Roaring River in Kings Canyon National Park is an easily accessible site that allows for the illustration of many aspects of lichenometry. Here it is particularly easy to recognize regional rockfall events that have been triggered by the San Andreas Fault. The lichens growing on these rockfall blocks contain an extremely inclusive record of the faults history. This site even contains a limited number of lichens over 1,000 years of age. Investigations have also been initiated on glacial moraines in the area. Lichenometric dating from moraine crests may mark the end of the responsible glacier's advance. Lichenometric study of these moraines could result in a valuable insight to the Little Ice Age, a particularly cool period between the 16th and 19th centuries that was one to two degrees Celsius cooler than current temperatures.
Overall, lichenometry is a newly evolving procedure that offers promising possibilities for research involving relative and absolute dating.