Academic Affiliation: University of Oregon
Research Mentors: Joshua Roering
Writing Mentor: Joshua Roering
Nathan studies Geosciences at the University of Oregon. In addition to his academic interests, he has competed for Princeton Division I track and field as a middle distance runner. He has enjoyed the RESESS program, first as an intern in the summer of 2012 and then again in the summer of 2013, as it allowed him to build his scientific network and introduced him to a cohort of truly top-notch, fun-loving future scientists. Nathan spent his past summer in the Coastal Range of Oregon, collecting soil samples from landslides to determine their absolute age using their color, a technique currently not well understood and one that could revolutionize quaternary sediment dating.
Obtaining accurate chronological data for landslides is critical to understanding their causes as well as their dynamics. The ability to easily and inexpensively date various parts of a landslide can provide insight not only into the “When” of landslides but also on the “How” and “Why” as well. In this study, we apply visible near-infrared (VisNIR) spectroscopy as a means to date landslide soils in a setting with uniform climate and bedrock lithology. In our Oregon Coast Range site, as sandstone-derived soils weather over time, pedogenic hematite accumulates and alters the color of the soil at a quantifiable or discernable rate. This rate having already been established through a soil chronosequence study, we can use the redness of a soil as a proxy for soil age. This is a potentially economical dating method as it does not rely on expensive radioisotopes and requires only a small amount of sample to process. We collected 39 B-horizon soil samples from 7 different slides and used VisNIR spectroscopy to identify the soil residence time of the landslides. The majority of the samples possessed ages between 75,000 and 150,000 years of age, though several slides registered ages over 200,000 years. The average percent error associated with the landslide ages was ~30-35%, although this value was lower for younger slides (<100,000 years) and greater for slides (>200,000 years). Younger slides were more homogenous in age while older slides exhibited more variability. Additionally, there was lower variability in auger-collected samples when compared to samples collected from road-cuts. Our results suggest that VisNIR spectroscopy may prove a more useful dating method on younger, less disturbed landslides but fail to truly capture the age of older, more complicated slides due to its reliance on a specific pedogentic model for hematite weathering as well as the increased risk for complex slide history. This method could be useful in a regional characterization of landslide chronology for similar biomes and provide scientists with a currently lacking catalogue of ancient landslide ages. Such a catalogue could provide significant insight into the mechanisms and potential triggers of bedrock landslides.