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Both glacial and fluvial processes are key elements in molding landscapes in high mountain environments--glaciers are highly efficient erosional agents and producers of sediment but are restricted spatially, while rivers can transmit such signals through landscapes and flush this sediment out of mountain belts and into sedimentary basins. However, little research has focused on the manner in which these two agents of landscape change interact, especially on longer time scales. We analyze a suite of catchments that drain the previously glaciated Ladakh Batholith in the northwest Indian Himalaya; which preserve the oldest known moraine succession in this mountain chain. We describe and quantify the rates, processes, and time scales of postglacial recovery of the fluvial system across a previously unstudied time interval of [10.sup.5]-[10.sup.6] yr. We demonstrate that glacial modification of the upper reaches of a catchment can have profound first-order influence on the hydraulic scaling of the channel downstream, where increasing degree of glacial modification systematically and nonlinearly elevates the channel concavities of downstream reaches above the expected value range of 0.3-0.6. We also demonstrate that the response time of these systems as they recover must exceed 500 k.y., which is longer than any previously reported estimate for recovery times from glaciations, but is comparable with estimates from many tectonically perturbed landscapes. doi: 10.1130/B30048.1

We present new field data from rivers draining across active normal faults that incise across the same lithology at the fault, have been subjected to similar climatic regimes and tectonic settings, and were perturbed by a well-documented increase in fault slip rate ca. 1 Ma. In spite of these similarities, the rivers exhibit markedly different long profiles and patterns of catchment incision. We use channel slope and hydraulic geometry data for each river to calculate bed shear stresses ([tau]b), and show that there is no simple relationship between peak [tau]b and the relative uplift rates across the faults, U, which differ by a factor of four. The long-term average sediment supply to each channel (Qs), estimated from time-averaged catchment erosion rates, can explain the [tau]b versus U data if bedload modulates bedrock incision rate, E, in a strongly nonlinear way. Together these field data allow us, for the first time, to evaluate theoretical predictions of the role of sediment on river profile evolution and to quantify the magnitude of the effect in natural systems. Keywords: geomorphology, erosion, transient response, faulting.

We present detailed data of channel morphology for a river undergoing a transient response to active normal faulting where excellent constraints exist on spatial and temporal variations in fault slip rates. We show that traditional hydraulic scaling laws break down in this situation, and that channel widths become decoupled from drainage area upstream of the fault. Unit stream powers are ~4 times higher than those predicted by current scaling paradigms and imply that incision rates for rivers responding to active tectonics may be significantly higher than those heretofore modeled. The loss of hydraulic scaling cannot be explained by increasing channel roughness and is an intrinsic response to tectonic forcing. We show that channel aspect ratio is a strongly nonlinear function of local slope and demonstrate that fault-induced adjustment of channel geometries has reset hillslope gradients. The results give new insight into how rivers maintain their course in the face of tectonic uplift and illustrate the first-order control the fluvial system exerts on the locus and magnitude of sediment supply to basins. Keywords: rivers, tectonics, faulting, channel geometry, geomorphology.

Rift-basin stratigraphy commonly records an early stage of slow subsidence followed by an abrupt increase in subsidence rate. The physical basis for this transition is not well understood, although an increase in extension rate is commonly implied. Here, a numerical fault-growth model is used to investigate the influence of segment linkage on fault-displacement-rate patterns along an evolving normal fault array. The linkage process we describe is controlled by a stress feedback mechanism, which leads to enhanced growth of optimally positioned faults. Model results indicate that, even with constant extension rates, slow displacement rates prevail during an initial phase of distributed extension, followed by an increase in displacement rates as strain becomes localized on linked fault arrays. This is due to the dynamics of fault interactions rather than mechanical weakening. Comparison of model simulations with rift-basin subsidence and stratigraphic patterns in the Gulf of Suez and North Sea suggests that the occurrence and timing of rapid basin deepening can be explained by the mechanics of fault-zone evolution, without invoking a change in regional extension rates.

We present a source-to-sink analysis to explain sediment supply variations and depositional patterns over the Holocene within an active rift setting. We integrate a range of modelling approaches and data types with field observations from the Sperchios rift basin, Central Greece that allow us to analyse and quantify (1) the size and characteristics of sediment source areas, (2) the dynamics of the sediment routing system from upstream fluvial processes to downstream deposition at the coastline, and (3) the depositional architecture and volumes of the Holocene basin fill. We demonstrate that the Sperchios rift comprises a 'closed' system over the Holocene and that erosional and depositional volumes are thus balanced. Furthermore, we evaluate key controls in the development of this source-tosink system, including the role of pre-existing topography, bedrock erodibility and lateral variations in the rate of tectonic uplift/subsidence. We show that tectonic subsidence alone can explain the observed grain size fining along the rift axis resulting in the downstream transition from a braided channel to an extensive meander belt (>15 km long) that feeds the fine-grained Sperchios delta. Additionally, we quantify the ratios of sediment storage to bypass for the two main footwall-sourced alluvial fan systems and relate the fan characteristics to the pattern and rates of fault slip. Finally, we show that ≥40% of the sediment that builds the Sperchios delta is supplied by ≤22% of the entire source area and that this can be primarily attributed to a longer-term (∼106 years) transient landscape response to fault segment linkage. Our multidisciplinary approach allows us to quantify the relative importance of multiple factors that control a complex source-to-sink system and thus improve our understanding of landscape evolution and stratigraphic development in active extensional tectonic settings. [ABSTRACT FROM AUTHOR]