Rates of erosion and landscape change along the Blue Ridge escarpment, southern Appalachian Mountains, estimated from in situ cosmogenic ¹⁰Be

Abstract

The Blue Ridge escarpment, located within the southern Appalachian Mountains of Virginia and North Carolina, forms a distinct, steep boundary between the lower‐elevation Piedmont and higher‐elevation Blue Ridge physiographic provinces. To understand better the rate at which this landform and the adjacent landscape are changing, we measured cosmogenic beryllium‐10 (10Be) in quartz separated from sediment samples (n = 50) collected in 32 streams and from three exposed bedrock outcrops along four transects normal to the escarpment, allowing us to calculate erosion rates integrated over 104–105 years. These basin‐averaged erosion rates (5.4–49 m Myr−1) are consistent with those measured elsewhere in the southern Appalachain Mountains and show a positive relationship between erosion rate and average basin slope. Erosion rates show no relationship with basin size or relative position of the Brevard fault zone, a fundamental structural element of the region. The cosmogenic isotopic data, when considered along with the distribution of average basin slopes in each physiographic province, suggest that the escarpment is eroding on average more rapidly than the Blue Ridge uplands, which are eroding more rapidly than the Piedmont lowlands. This difference in erosion rates by geomorphic setting suggests that the elevation difference between the uplands and lowlands adjacent to the escarpment is being reduced but at extremely slow rates. Copyright © 2016 John Wiley & Sons, Ltd.

Erosion rates and sediment flux within the Potomac River basin quantified over millennial timescales using beryllium isotopes

“…10 Bei erosion rates are correlated to mean basin slope in the Potomac River basin (R 2 = 0.115; p = 0.008); this correlation, while significant, is much weaker than the correlations between 10 Bei erosion rates and slope found in other nonglaciated basins in the Appalachian Mountains: R = 0.54 for the Blue Ridge Escarpment (Linari et al, 2016); R = 0.42 for the Great Smoky Mountains (Matmon et al, 2003); R 2 = 0.58 for the Susquehanna River basin (Reuter, 2005). As a whole population, 10 Bei erosion rates in the Potomac Basin (n = 61) are correlated with mean basin elevation (R = 0.160; p = 0.001) and mean annual precipitation (R 2 = 0.146; p = 0.002; Hijmans et al, 2005), but not with basin relief (R 2 = 0.034; p = 0.156) or basin area (R 2 = 0.022; p = 0.253); 10 Bei erosion rates exhibit a weak but significant correlation (R 2 = 0.065) -after rounding (p = 0.047) -with latitude, which is a proxy for distance from the Last Glacial Maximum ice-sheet margin.…”

“…The duration over which erosion is integrated is determined by the time it takes to erode through one cosmic-ray attenuation depth, ~60 cm of rock, and thus isotope concentration is inversely related to landscape stability (Lal, 1991) and biased toward the surface and recent erosion history. In slowly eroding, areas, such as the Appalachian Mountains, which occupy much of the Potomac River basin, 10 Bei erosion rates integrate over 10 4 to 10 5 yr (e.g., Duxbury et al, 2015;Hancock and Kirwan, 2007;Linari et al, 2016;Matmon et al, 2003;Portenga et al, 2013;Reusser et al, 2015).…”

Retracted: Background rates of erosion and sediment generation in the Potomac River basin, USA, derived using in situ 10 Be, meteoric 10 Be, and 9 Be

“…7; cf. Linari et al, 2016;Matmon et al, 2003;Reuter, 2005). As whole populations, 10 Be i and 10 Be m / 9 Be reac sediment generation rates are also correlated with mean basin elevation and mean annual precipitation, but not with basin relief or basin area (Table 1); 10 Be i sediment generation rates are correlated with latitude, which we use as a proxy for distance from the Last Glacial Maximum ice-sheet margin.…”

“…The duration over which erosion is integrated is determined by the time it takes to erode through one cosmic-ray attenuation depth, ~60 cm of rock, and thus isotope concentration is inversely related to landscape stability (Lal, 1991). In slowly eroding, old mountain ranges, such as the Appalachians in the Potomac River basin, 10 Be i erosion rates are integrated over 10 4 to 10 5 yr (e.g., Duxbury et al, 2015;Hancock and Kirwan, 2007;Linari et al, 2016;Matmon et al, 2003;Portenga et al, 2013;Reusser et al, 2015).…”

The relative roles of inheritance and long-term passive margin lithospheric evolution on the modern structure and tectonic activity in the southeastern United States

“…A number of competing theories exist on the persistence of elevation and steep topography. These range from theories that require no postorogenic uplift and posit persistent topography due to dynamic equilibrium and lithologic variability (Hack, 1980;Baldwin et al, 2003;Matmon et al, 2003) to those that do require recent uplift (e.g., Hack, 1982), which may be due to various epeirogenic processes (e.g., Pazzaglia and Brandon, 1996;Fischer, 2002;Moucha et al, 2008;Flament et al, 2013;Linari et al, 2016) or climatic variability (e.g., Molnar, 2004).…”