The immediacy of the earth's landscape, with its highly visible and dynamic systems, has long fascinated geologic researchers. The diversity of the earth's surface, formed by the interplay between the lithosphere, atmosphere and hydrosphere, and biologic systems, presents a formidable challenge to interpretation. Exciting opportunities to unravel this puzzle have recently opened up with the development of new Quaternary dating techniques and modern high-resolution topography. In combination with experimental work and numerical modeling, we finally have the tools to begin to understand this complex interface.

My research has three broad focuses. My first focus is on tracing sediment through its entire sequence of production, transport, and deposition. One area of interest is exploring the linkages and feedbacks between geomorphic systems. Because these systems are usually studied in isolation, sediment transfer between them is poorly understood. Of particular interest is movement of sediment between the land-sea interface, which presents the dual challenges of a moving boundary problem and understanding littoral system processes. Another area of interest lies in determining the effects of climate change on erosion and sediment transport rates. Depositional records worldwide show a marked increase in sedimentation rates in the past 2 Ma, with fluctuations in climate fingered as the culprit. Explaining the means by which sediment production and transport rates are increased in such a diverse set of geomorphic systems presents an exciting challenge. To better constrain basin records, I am working on the development of authigenic mineral dating techniques.

The second focus is on understanding the interaction between geomorphic processes and biologic systems. Biogeomorphology is a young field, with the effects of organisms on the landscape ignored until recently. One line of research is determining how beaver-built dams modify stream morphology, sediment transport, and nutrient availability. Another is exploring the feedbacks between forest fires, debris flows, and vegetation regrowth. One of the biggest questions in biogeomorphology is whether the ecosystems contribute a distinct signature to landscape development. Many geomorphic forms are scale invariant, with the same proportions holding over 10 meters as at 10 kilometers. I am interested in the influence organisms and ecosystems have on setting these scaling parameters, which could provide a means to assess their importance in forming the landscape.

A third focus is the feedbacks between erosion and tectonics. One interest is the evolution of geomorphic systems in response to changes in uplift rates. In particular, I am investigating whether properties of stream networks or stream morphology can indicate when an orogenic system reaches steady-state. Another line of inquiry is the rate of response of stream networks and hillslopes to an increase in uplift rates. Another interest is the flexural response to erosion, with a specific concern in the rate of headward migration of knickpoints into plateaus. A third interest lies in perturbation of the geothermal gradient through high fluvial or glacial incision rates. This is not only important for thermochronologic interpretation, but could have implications for metamorphism and magma emplacement.

Tools that I use to understand surface processes include fieldwork, geochemical techniques, experimental work, numerical modeling, and morphologic analysis. One cutting-edge geochemical tool that I use is in-situ cosmogenic nuclides. Formed by highly energetic cosmic rays reaching the earth's surface, their concentration is an indicator of how long material has been at or near the surface, with uses ranging from dating surfaces, to determining erosion rates, to tracing sediment sources. Experimental work, performed at St. Anthony Falls Laboratory, provides the opportunity to control the initial conditions and input parameters of a geomorphic system. This control allows sensitivity analysis, constraining the effect and importance of various factors on the system. Numerical modeling provides another means of sensitivity analysis, and is also important in testing our understanding of the processes acting in geomorphic systems. High-resolution digital elevation models and geographic information systems (GIS) allow unprecedented opportunity for morphologic analysis of features such as stream networks over broad regions. Ground-penetrating radar, which images sub-surface stratigraphy, is useful for comparing natural systems with experimental work and numerical models. The riddle posed by the earth's surface is so broad that no discipline can hope to answer it alone. I am a part of the National Center for Earth-surface Dynamics (NCED), an interdisciplinary team of researchers spanning geology, civil engineering, biology, and chemistry. Centered at the University of Minnesota, the mission of NCED is to develop erosion, transport, and deposition laws for use in a community surface processes modeling effort. Particular focus areas include landscapes and seascapes, basin archives, biogeomorphology, and the similarity of morphodynamic processes across environments and scales. The strong collaborative concern and fostering of cross-disciplinary projects at NCED provide a stimulating environment for surface processes research.