Publication Date:
2011-02-22
Description:
The southern Appalachians represent a landscape characterized by locally high topographic relief, steep slopes, and frequent mass movement in the absence of significant tectonic forcing for at least the last 200 Ma. The fundamental processes responsible for landscape evolution in a post-orogenic landscape remain enigmatic. The non-glaciated Cullasaja River basin of southwestern North Carolina, with uniform lithology, frequent debris flows, and the availability of high-resolution airborne lidar DEMs, is an ideal natural setting to study landscape evolution in a post-orogenic landscape through the lens of hillslope-channel coupling. We limit our investigation to channels with upslope contributing areas 〉2.7 km2, a conservative estimate of the transition from fluvial to debris-flow dominated channel processes. We utilize values of normalized hypsometry, hypsometric integral, and mean slope vs. elevation for 14 tributary basins and the Cullasaja basin as a whole to characterize landscape evolution following upstream knickpoint migration. Our results highlight the existence of a transient spatial relationship between knickpoints present along the fluvial network of the Cullasaja basin and adjacent hillslopes. Metrics of topography (relief, slope gradient) and hillslope activity (landslide frequency) exhibit significant downstream increases below the current position of major knickpoints. We capture the transient effect of knickpoint-driven channel incision on basin hillslopes by measuring the relief, mean slope steepness, and mass movement frequency of tributary basins and comparing these results to the distance from major knickpoints along the Cullasaja River. We present a conceptual model of area-elevation and slope distributions that may be representative of post-orogenic landscape evolution in analogous geologic settings. Importantly, our model explains how knickpoint migration and channel-hillslope coupling is an important factor in tectonically-inactive (i.e. post-orogenic) orogens for the maintenance of significant relief, steep slopes, and weathering-limited hillslopes. Copyright © 2011 John Wiley & Sons, Ltd.
Print ISSN:
0197-9337
Electronic ISSN:
1096-9837
Topics:
Geography
,
Geosciences
Permalink