Earthquakes and Lichenometry
Thursday, October 18, 2007 9:50:27 AM
To get a better understanding of how earthquakes work, it is necessary to study past earthquakes. Here it is important to estimate when the earthquake in question actually took place, which may be difficult for prehistorical events. Several dating methods are available, like tree-ring dating, varve chronology and others. But they are not all even accurate or precise.
Lichenometry is accurate and has tightly clustered precision. It can be used on rockfalls caused by earthquakes. Lichenometry is the study of dating a surface using lichens as age markers: lichens increase in size radially as they grow. Measuring the diameter of the largest lichen on a rock surface can thus be used to determine the time the rock has been exposed. Lichen can be preserved on old rock faces for up to 10,000 years, providing the maximum age limit of the technique. The use of lichenometry is of increased value for dating deposited surfaces over the past 500 years as radiocarbon dating techniques are less efficient over this period. Different lichens have different growth rates, and the local climate also influences the growth rate. Slow growing lichens date older events than fast growing lichens. Obviously it is necessary to determine the lichen species and local growth rate, before measuring the diameter makes any sense.
Lichens are plant-like colonies of fungi and algae that grow together (in symbiosis) on the exposed surface of rocks. Lichens are often the first to settle in places lacking soil.
Lichenometry can, of course, also be used to date rock art or stonewalls, if you should be interested - see A Study of Lichens and Lichenometry. Lichens are, by the way, very sensitive to pollution from the atmosphere, which causes them not to grow in highly polluted areas. “Luckily” we have lichens on beautiful monumental stones in our garden, but my wife doesn’t seem to be so happy about that.