The Appalachians stretch 4000 km from Georgia to the Canadian Maritimes. They are old and enduring mountains. First uplifted in the Paleozoic, parts of these mountains still rise up over 2000 meters above the Atlantic. How quickly is a mountain range such as the Appalachians eroding today? How quickly did it erode in the past? Are short and long term erosion rates similar, implying steady rates of denudation over time? The goal of this research is straightforward, to understand rates of Appalachian highland and piedmont erosion over space and time. We will apply a relatively new technique (cosmogenic nuclide analysis of sediment, soil, and rock) to the old question of Appalachian landscape evolution and integrate our new findings with existing data sets. The proposed measurements will compliment several recent and on-going efforts to quantify rates of erosion for this well-studied, ancient orogen. Specifically, cosmogenic nuclides record erosion integrated over a shorter time (shallower depth) than U/He which in turn records a shorter time/lower temperature/shallower depth than fission tracks and pressure-temperature-time paths deduced from mineral assemblages. Considering all the data sets together, we anticipate being able to assess the variability (or lack thereof) of denudation rates over time in terms of processes responding primarily to structure, rock- type, climate, and/or epeirogeny (tectonics). The study will focus on the southern Appalachians. Our interdisciplinary approach will incorporate the collection of significant new isotopic data. Measuring in-situ-produced 10Be in fluvial, colluvial, and terrace sediments as well as in ridge-top and sub-colluvial bed-rock samples collected from a carefully selected set of 6 drainage basins, we will quantify sediment production and rock-denudation rates over the 10,000 to 100,000 year time scale. Measurement of U/He in samples from the same basins will provide denudation rate estimates over longer time frames. Drainage basins have been chosen specifically so that the roles of lithology, relief, and climate in controlling erosion rates can be estimated. Our study will build upon a decade of orogen-scale studies that have elucidated dynamic interactions between the surficial processes that erode rocks and deep earth processes that uplift rocks. These studies are traditionally and necessarily focused on constructional and steady-state orogens. Our study seeks to understand a decaying orogen in order to address the poorly understood conspiracy of deep-earth and surficial processes that results in the persistence of ancient orogens as significant topographic features. The timing and setting for our proposed study is ideal. Extensive Appalachian thermochronologic data have been collected, new helium studies are underway, the siliciclastic sediment load in the offshore post-rift sediment basins is well-documented, long-term landscape evolution has been quantified, and stream sediment yield databases are available. Most importantly, a pilot study has been completed in the Great Smokey Mountains (Matmon et al., in press) demonstrating the viability of our proposed approach. This proposal has a strong educational component that includes field, laboratory, and data analysis training and mentoring at the undergraduate and graduate levels. Students involved in this project will get hands on experience with sophisticated analytical tools and will, as is the tradition for UVM graduate students, interact with a wide variety of USGS geologists and present their work for scrutiny at professional meetings.
