UVM Theses and Dissertations
Format:
Print
Author:
Sullivan, Colleen L.
Dept./Program:
Geology
Year:
2007
Degree:
MS
Abstract:
The Blue Ridge escarpment, located within the southern Appalachian Mountains of Virginia and North Carolina, forms a distinct, steep boundary between the less rugged lower-elevation Piedmont and higher-elevation Blue Ridge physiographic provinces. The rugged topography of the Blue Ridge escarpment and the antiquity of the passive margin of eastern North America have lead to questions about the rates and patterns of erosion that have acted on the escarpment over time.
It is generally agreed that great escarpments, like the Blue Ridge escarpment, are the result of rifting. There are two primarily accepted models explaining the evolution of passive margin escarpments: evolution from slow and irregular inland erosional retreat of the primary rift shoulder and drainage divide, and evolution from rapid and significant erosion immediately following rifting with subsequent stability of the resulting passive margin. The passive margin of eastern North America is old; rifting terminated ~200 Ma. Thus, a clear understanding of the processes controlling the erosion and evolution of the Blue Ridge escarpment may provide insight about the geomorphic evolution of similar escarpments on younger passive margins.
To understand better the geomorphic evolution of the Blue Ridge escarpment and to investigate how quickly this landform and its adjacent physiographic provinces are changing, I measured cosmogenic ¹⁰Be in sediment (n=47) from stream basins (n=29) and in exposed bedrock (n=3) along four transects normal to the escarpment. I used a GIS database to select basins with a wide variety of parameters that may influence erosion rates, such as basin size, average basin slope, landscape position and relative position of the Brevard fault zone. These ¹⁰Be measurements allowed me to model erosion rates on the scale of 10⁴-10⁵ years. Basin averaged cosmogenic erosion rates measured on and near the Blue Ridge escarpment are slow (6.5-38 m My⁻¹) These erosion rates are generally consistent with those measured elsewhere in the southern Appalachians and show a positive relationship between erosion rate and average basin slope. Thermochronologically estimated rates of erosion are similarly slow (8-29 m My⁻¹). Analysis of these basin averaged erosion rates in conjunction with the existing thermochronologic data for the escarpment, indicates that the majority of erosion that shaped the Blue Ridge escarpment occurred immediately following rifting in the Mesozoic, and since then, the escarpment's position has generally remained stable.
The cosmogenic data, when considered along with the distribution of basin slopes in each physiographic province, suggest that the escarpment is eroding more rapidly than the Blue Ridge, which is eroding more rapidly than the Piedmont. If this relationship has been maintained over time, the escarpment has been retreating and lowering but at extremely slow rates.
It is generally agreed that great escarpments, like the Blue Ridge escarpment, are the result of rifting. There are two primarily accepted models explaining the evolution of passive margin escarpments: evolution from slow and irregular inland erosional retreat of the primary rift shoulder and drainage divide, and evolution from rapid and significant erosion immediately following rifting with subsequent stability of the resulting passive margin. The passive margin of eastern North America is old; rifting terminated ~200 Ma. Thus, a clear understanding of the processes controlling the erosion and evolution of the Blue Ridge escarpment may provide insight about the geomorphic evolution of similar escarpments on younger passive margins.
To understand better the geomorphic evolution of the Blue Ridge escarpment and to investigate how quickly this landform and its adjacent physiographic provinces are changing, I measured cosmogenic ¹⁰Be in sediment (n=47) from stream basins (n=29) and in exposed bedrock (n=3) along four transects normal to the escarpment. I used a GIS database to select basins with a wide variety of parameters that may influence erosion rates, such as basin size, average basin slope, landscape position and relative position of the Brevard fault zone. These ¹⁰Be measurements allowed me to model erosion rates on the scale of 10⁴-10⁵ years. Basin averaged cosmogenic erosion rates measured on and near the Blue Ridge escarpment are slow (6.5-38 m My⁻¹) These erosion rates are generally consistent with those measured elsewhere in the southern Appalachians and show a positive relationship between erosion rate and average basin slope. Thermochronologically estimated rates of erosion are similarly slow (8-29 m My⁻¹). Analysis of these basin averaged erosion rates in conjunction with the existing thermochronologic data for the escarpment, indicates that the majority of erosion that shaped the Blue Ridge escarpment occurred immediately following rifting in the Mesozoic, and since then, the escarpment's position has generally remained stable.
The cosmogenic data, when considered along with the distribution of basin slopes in each physiographic province, suggest that the escarpment is eroding more rapidly than the Blue Ridge, which is eroding more rapidly than the Piedmont. If this relationship has been maintained over time, the escarpment has been retreating and lowering but at extremely slow rates.