TY  - JOUR
A1  - Miller, Scott R.
A1  - Sak, Peter B.
A1  - Kirby, Eric
A1  - Bierman, Paul R.
T1  - Neogene rejuvenation of central appalachian topography evidence for differential rock uplift from stream profiles and erosion rates
JF  - Earth & planetary science letters
N2  - The persistence of topography within ancient orogens remains one of the outstanding questions in landscape evolution. In the eastern North American Appalachians, this question is manifest in the outstanding problem of whether topographic relief is in a quasi-equilibrium state, decaying slowly over many millennia, or whether relief has increased during the late Cenozoic. Here we present quantitative geomorphic data from the nonglaciated portion of the Susquehanna River drainage basin that provide insight into these end-member models. Analysis of channel profiles draining upland catchments in the northern Valley and Ridge, Appalachian Plateau, Blue Ridge, and Piedmont provinces reveals that a large number of streams have well defined knickpoints clustered at 300-600 m elevation but not systematically associated with transitions from weak to resistant substrate. Cosmogenic Be-10 inventories of modern stream sediment indicate that erosion rates are spatially variable, ranging from similar to 5-30 m/Myr above knickpoints to similar to 50-100 m/Myr below knickpoints. Overall, channel gradients, normalized for drainage area, scale linearly with catchment-averaged erosion rates. Collectively, regionally consistent spatial relationships among erosion rate, channel steepness, and knickpoints reveal an ongoing wave of transient channel adjustment to a change in relative base level. Reconstructions of relict channel profiles above knickpoints suggest that higher rates of incision are associated with similar to 100-150 m of relative base level fall that accompanied epierogenic rock uplift rather than a change to a more erosive climate or drainage reorganization. Channel response timescales imply that the onset of relative base level change predates similar to 3.5 Ma and may have begun as early as similar to 15 Ma. We suggest that adjustment of the channel network was likely driven by changes in mantle dynamics along the eastern seaboard of North America during the Neogene.
KW  - Appalachian Mountains
KW  - stream profile
KW  - knickpoint
KW  - transient erosion
KW  - cosmogenic nuclides
Y1  - 2013
U6  - https://doi.org/10.1016/j.epsl.2013.04.007
SN  - 0012-821X
SN  - 1385-013X
VL  - 369
IS  - 2
SP  - 1
EP  - 12
PB  - Elsevier
CY  - Amsterdam
ER  - 
TY  - JOUR
A1  - Regalla, Christine
A1  - Kirby, Eric
A1  - Fisher, Donald
A1  - Bierman, Paul R.
T1  - Active forearc shortening in Tohoku, Japan - constraints on fault geometry from erosion rates and fluvial longitudinal profiles
JF  - Geomorphology : an international journal on pure and applied geomorphology
N2  - Convexities in the longitudinal profiles of actively incising rivers are typically considered to represent the morphologic signal of a transient response to external perturbations in tectonic or climatic forcing. Distinguishing such knickzones from those that may be anchored to the channel network by spatial variations in rock uplift, however, can be challenging. Here, we combine stream profile analysis, Be-10 watershed-averaged erosion rates, and numerical modeling of stream profile evolution to evaluate whether knickzones in the Abukuma massif of northeast Japan represent a temporal or spatial change in rock uplift rate in relation to forearc shortening. Knickzones in channels that drain the eastern flank of the Abukuma massif are characterized by breaks in slope-area scaling and separate low-gradient, alluvial upper-channel segments from high-gradient, deeply-incised lower channel segments. Average erosion rates inferred from Be-10 concentrations in modern sediment below knickzones exceed erosion rates above knickzones by 20-50%. Although profile convexities could be interpreted as a transient response to an increase in rock uplift rate associated with slip on the range-bounding fault, geologic constraints on the initiation of fault slip and the magnitude of displacement cannot be reconciled with a recent, spatially uniform increase in slip rate. Rather, we find that knickzone position, stream profile gradients, and basin averaged erosion rates are best explained by a relatively abrupt spatial increase in uplift rate localized above a flat-ramp transition in the fault system. These analyses highlight the importance of considering spatially non-uniform uplift in the interpretation of stream profile evolution and demonstrate that the adjustment of river profiles to fault displacement can provide constraints on fault geometry in actively eroding landscapes. (C) 2013 Elsevier B.V. All rights reserved.
KW  - Knickzones
KW  - Fluvial longitudinal profile
KW  - Cosmogenic Be-10 erosion rates
KW  - Basement-involved thrusts
KW  - Futaba fault
KW  - Fukushima Prefecture
Y1  - 2013
U6  - https://doi.org/10.1016/j.geomorph.2013.04.029
SN  - 0169-555X
VL  - 195
IS  - 8
SP  - 84
EP  - 98
PB  - Elsevier
CY  - Amsterdam
ER  -