Dr. Devin McPhillips is awarded the NSF Earth Sciences Postdoctoral Fellowship to implement a program of research and education at the University of Vermont. The project's goal is to evaluate how the style and rate of surface erosion responds to glacial-interglacial climate change. The particular focus is on landscapes that were never covered by glacial ice. Dr. McPhillips will compare concentrations of the cosmogenic radionuclide Be-10 from modern stream cobblestones to concentrations in nearby terrace deposits of glacial-stage cobblestones. First, bulk concentrations will be used in a conventional manner to understand the variability of erosion rates in high- and low-order streams. Second, the statistical distribution of individual cobble concentrations will be used to estimate the relative importance of 'deep' versus 'shallow' erosive processes, such as landslides and hillslope diffusion. The results will provide insight into the mechanisms of erosion, including potentially destructive mass movements.
Several students will be trained in geomorphology in the course of the project. Dr. McPhillips will co-advise at least one undergraduate student and act as mentor for graduate students at the University of Vermont. The undergraduate(s) will participate in field work and develop a complementary senior thesis project. The senior thesis will provide the student(s) with a strong foundation in research and further the professional development of Dr. McPhillips as teacher as well as a scientist.
Measuring the response of complete landscapes (hillslopes and stream channels) to climate change is difficult, in a large part because hillslopes are very seldom preserved in the geologic record. However, this measurement is extremely important for the the fields of geomorphology and, increasingly, tectonics. The scientific goal of this project was to determine how the changing climate at the end of the last Ice Age affected the landscape in tropical Andes Mountains, where glacial ice never reached. The project was also designed to train undergraduate students to conduct independent research. In order to measure landscape change, we used the cosmogenic isotope Be-10 to measure the spatial distribution of erosion rates and erosion processes. By sampling stream terrace deposits, we were able to measure Be-10 concentrations from Late Pleistocene time (that is, at the end of the last Ice Age). We also made measurements in modern sediments. Although Be-10 is often used to measure erosion rates, we helped to pioneer its use for measuring erosion processes. Landslides and sand-grain-by-sand-grain "diffusive" erosion are two types erosion processes, for example. Our study had three important results. First, erosions rates show that the landscape response was restricted to the upper reaches of the stream network. The density of stream channels increased during the Late Pleistocene, which was wetter than the modern climate. Second, the mix of erosion processes did not change much, even though the climate did. Specifically, big landslides are as common today as in the past. Third, single-clast Be-10 methods are an effective tool for measure past erosion processes such as landslides. These results are important because they support theoretical and model predictions about the landscape response to climate. This will help to predict future changes in response to our changing modern climate. The single-clast Be-10 technique could also be used to better understand landsliding and related hazards in the United States. In the Andes, the constant rate of landsliding suggests that the climate had about the same number of large storms in the past as today. This implication is important for interpreting of many geologic records. Finally, the similarity of erosion in the past and present suggests that large, global climate changes are not necessarily important for the development of high mountains, at least in the absence of glacial ice. In addition to the scientific contributions, two undergraduate students completed semester-long research studies in support of project goals. They developed skills in field mapping, analysis, and scientific writing, as well as the broader skills of designing and carrying out a large project. Both received college credit. One student is now a graduate student in volcanology, and the other teaches at the high school level.
