A vocabulary of landscape — a landscape of words
1467 entries
lichenometry
Lichenometry is the practice of dating a rock surface by measuring the lichens growing on it. Certain slow, steady, disc-shaped lichens grow outward at a rate that can be calibrated against surfaces of known age, such as dated gravestones, so the diameter of the largest thallus on a boulder gives an estimate of how long that boulder has been sitting where it is. It works over roughly the last five hundred years and in some settings much longer.
Etymology
The word is built from the Greek for lichen and the Greek for measure, and it was coined in the 1950s by the Austrian botanist Roland Beschel, who noticed the possibility in a graveyard and then took it to glacier forelands. Lichen itself is Greek and originally meant something that licks or eats around, applied to skin eruptions before it was applied to the organism.
Notes
The main use is dating glacier moraines, since a moraine deposited in a particular year presents a fresh rock surface for colonization, and a sequence of moraines can be put in order and roughly dated by lichen size. The method is also used on rockfall deposits, old walls, and archaeological stonework, and its accuracy is argued over constantly because growth rates vary with rock type, aspect, and how wet the site is.