Tag: Josh Roering

Lichenometric Dating Using Placopsis lambii Applied to the Yachats Basalt, Central Oregon Coast

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.

A Sedimentary Analysis of the Eugene Millrace

Presenter(s): Ethan Niyangoda − Geology

Faculty Mentor(s): Josh Roering

Poster 67

Research Area: Natural Science

The Eugene Millrace, a slowly-flowing 1.5 mile channel which is connected to the Willamette River and flows through East Eugene, has once again become a matter of public interest. Originally designed by Hillyard Shaw and constructed in 1851 to create a millrace for the quickly-industrializing city. Approximately half of the channel is a former side-channel of the Willamette River, and the other half was constructed by man. With the advent of the highly-publicized Knight Campus, which will be built around and possibly atop the Millrace, there has been great speculation into the future of this small but culturally-significant channel. One helpful means of understanding the nature and movement of a river system is to examine its bathymetry (the topography of its channel) and sediment accumulation pattern. In order to do this, we used six- to twelve- foot steel rods, a canoe, a GPS unit, and a tape measure to gauge sediment depth at a given location. To do this, we launched the canoe at several locations and took measurements from the center of the channel and around drainage pipes. This was done once in May 2017 and once in November 2017. We hypothesized that the channel would have mostly uniform, shallow (less than one foot) levels of sediment throughout. This hypothesis was completely wrong, as we discovered that the Millrace in fact has sediment ranging from less than a foot to meters in depth depending on the location measured. This finding could potentially have significant implications for channel dredging during the building and design associated with the Knight Campus.