The role of bedrock erodibility in the topography and landscape evolution of the Appalachian Mountains

Mountains linger on the continents long after they are built by tectonic motions. During their erosional decay, these diminishing mountains are subject to modification by changing conditions, including climate, basin dynamics, and renewed tectonics, resulting in complex signals. Another factor that controls the evolution of these landscapes is the material properties of the eroding bedrock, which change through time as rocks are exhumed. Correlations exist between topography and rock type in many ancient mountain ranges, including in the Appalachian Mountains, the type locality of this phenomenon. In sedimentary rocks of the Appalachians, the role of bedrock properties is at least qualitatively clear, but in metamorphic rocks the relationships are murkier. The purpose of this investigation is to determine the degree to which metamorphic rocks of the high Blue Ridge control the landscape and to quantify specifically what makes them durable. This will contribute to understanding of the origin of the Appalachian landscape, as well as to the processes that control erodibility along ancient passive margins. This project also supports a program for developing and adding a field experience as a required element for eighth grade Earth Science classes in a rural Appalachian middle school (~350 students/year), where currently no field trips are included in the curriculum. The specific goals of this project are to measure bedrock properties of complex metamorphic rock of the Virginia and North Carolina Blue Ridge, including rock strength (e.g., point-load testing), discontinuities (e.g., fracture scanlines), mineralogy, and sensitivity to chemical and physical surface processes via laboratory testing (freezing/thawing, heating/cooling, microwave acid digestion, and slake testing). A large data collection effort (~150 locations, >500 samples) will fill a major data gap for the material properties of complex Blue Ridge rock types. Samples will be acquired from both natural and anthropogenic exposures and will be compared to relative topographic position (i.e., ridges and peaks vs. valley bottoms) as well as a host of other geomorphic metrics. Data will be synthesized to test the degree to which bedrock controls topography and ultimately be integrated into a model of what controls long-term erodibility in this setting. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.