Presenter: Logan Wetherell
Mentor: Josh Roering
Oral Presentation
Major: Geological Science
Surface exposure dates estimated through lichenometric growth rates can be used to document geologic events where other methods of dating rock surface exposure are not applicable. Largest lichen diameter measurements of pioneer species Placopsis lambii were taken at 10 sites with independent ages along the Yachats Basalt in the central Oregon coast to construct a regional growth curve to be used in estimating surface exposure dates. Largest lichen diameters were recorded across 25m2 swaths of non-calcareous rock at each site and recorded to establish two growth phases of P. lambii. Lichen colonization occurs approximately 5 years after surface exposure and lichen diameter increases at 1.2mm/yr to 1.5mm/yr for approximately 20 years. After 20 years, we observed slow linear growth of <0.2mm/yr as biological competition or spatial constraints from nearby P. lambii colonies impeded growth. We expect that P. lambii could be applied as a lichenometric dating species for exposed surfaces where the timescale of rockfall are less than 100 years and can provide useful information of regional rockfall rates.