T55 These Old Mountains Still Got It: Natural Hazards of the Evolving Appalachian Mountain Belt

Sunday, 15 October 2023
1:30 PM - 5:30 PM
317 / 318

USING SCHMIDT HAMMER AND TERRESTRIAL COSMOGENIC NUCLIDE DATING TO UNRAVEL THE TIMING AND MECHANISMS OF ROCKFALL DEPOSITS IN THE BLUE RIDGE ESCARPMENT, NORTH CAROLINA

Paper number: T55-11
Program: Technical Sessions
Time: 4:00 PM – 4:15 PM

Authors

Abstract

The Blue Ridge Escarpment in the Appalachians is characterized by steep and high relief. Increased slope activity in the past has led to the accumulation of impressive rockfall deposits in the valleys, including blocks up to 10 m high. To mitigate potential future hazards, especially in the face of climate change, it is critical to understand the timing and mechanisms of their origin. Three well-preserved rockfall sites (Pacolet River, Tryon Peak, and Buffalo Creek Park) have been investigated using terrestrial cosmogenic nuclides (TCN) Be-10 dating and the Schmidt Hammer methods. These provide the first age estimates of rockfall deposits in North Carolina with twelve Be-10 ages of 161±10 to 9.9±2.7 ka. Differences in mean rebound (R-values) for 30 boulders at each site were not significant: 27.5±4, 28±3, and 29.3±3 for Pacolet, Tryon, and Buffalo Creek Park, respectively. Based on the correlation between age and elevation of the samples (r = -0.7), the deposits are likely the result of numerous catastrophic collapses occurring at intervals of thousands of years. The Pacolet River deposits are arranged in multiple clusters of large gneiss blocks of up to 30 m in length between the source cliff and the river. Older boulders are present along the valley floors with ages up to 161±10 ka while boulders closer to the detachment wall date to at least 41.4±3.4 ka. R-values decrease gradually with elevation drop (r=-0.7), which likely indicates that multiple events responsible for the deposits happened consecutively due to the gradual incision of the Pacolet River. The Buffalo Creek Park site contains mostly smaller fragments with a few large boulders (≤30 m diameter) and exhibits a weak correlation between R-values and elevation, with higher values on the hillslope toe. This configuration showed that Buffalo Creek Park rockfall likely occurred as a single event with a minimum age of 95.5±15.4 ka. Similarly, R-values of the Tryon site correlate weakly with elevation (r=0.3), while sediments date to between 19±4.2 and 9.9±2.7 ka. For all sites, there is no apparent relationship between size of boulder and elevation, suggesting that hillslopes are dominated by non-local transport at a steady state.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-391698

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