Dating Glacial Moraines with Lichenometry
When a glacier temporarily stabilizes during its retreat, some of the sediment it is carrying gets deposited as glacial moraines. Moraines are most often composed of poorly sorted (wide range of grain sizes) sediment called glacial till. They can be deposited on the side (lateral moraine) or at the snout (terminal moraine) of a glacier. Moraines not only mark a previous location of a glacier, but they can be dated to provide a timeline of events.
One of the ways to date young Holocene aged moraines is with a technique called lichenometry. The green (algae) and black (fungus) symbiotic lichen, Rhizocarpon geographicum, is one of the first colonizers of exposed rock surfaces. These lichens grow slowly and can last hundreds of years. A growth curve can be calculated based on climate conditions and rock composition in an area. Once this is established, the five largest lichens found on any one moraine can be measured in millimetres and averaged to determine the approximate age of the moraine.