Research Interests
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.
Selected Publications
Recent Research Support
- NSF, co-PI, National Center for Earth-surface Dynamics Science
and Technology Center
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