LOW RATES OF BEDROCK OUTCROP EROSION IN THE CENTRAL APPALACHIAN MOUNTAINS INFERRED FROM IN SITU 10BE CONCENTRATIONS
Outcrop erosion rates in the Potomac River basin (n=46) range from 1.0±0.11 to 66±4.8 m/My, average 15±1 m/My, and have a median of 7.1±0.6 m/My; outcrop erosion rates in the Susquehanna River basin (n=26) range from 1.8±0.2 to 28±2 m/My, average 10±0.7 m/My, and have a median of 8.3±0.7 m/My. The average bedrock outcrop erosion rate for the region is 13±1 m/My which is greater than the few other erosion rates measured on bedrock outcrops in the region (4-7 m/My, Reuter, 2005, Hancock and Kirwin, 2007; Duxbury, 2008). Outcrop erosion rates are significantly indistinguishable from the average basin rate of 12 m/My for 62 Potomac River sites (Trodick, this meeting) and significantly lower than the average basin rate of 20 m/My for 79 Susquehanna River sites (Reuter, 2005). Similar rates of erosion for bedrock outcrops and drainage basins suggest that the Central Appalachians as a whole have reached a general state of equilibrium. This is in contrast to some studies which suggest an increase in relief near our study sites (Reuter, 2005; Hancock and Kirwin, 2007).
We observe a weak, positive correlation between bedrock outcrop erosion rates and relief in meters within a 5km radius (R2=0.24; p<0.0001), and an even weaker positive correlation between bedrock outcrop erosion rates and elevation (R2=0.11; p=0.0042). A weak, negative correlation is observed between bedrock outcrop erosion rates and latitude (R2=0.14; p=0.0013). Bedrock outcrop erosion rates were analyzed against mean annual precipitation and temperature but no correlations were significant.