In humid uplands landsliding is the dominant mass wasting process. In the western Southern Alps of New Zealand landslides are scale invariant and have a power-law magnitude frequency distribution. Independent studies from other regions suggest that this is a general property of landsliding. This observation is of critical importance to the evaluation of the impact of events of different length scales over different time intervals on landscape evolution. It is particularly useful when estimating regional geomorphic rates, because it constrains the frequency and overall significance of extreme events, which cannot otherwise be evaluated. By integrating the complete response of the system, we estimate the regional denudation rate due to landsliding to be 9 ± 4 mm yr -1 . Sediment discharge from the western Southern Alps is dominated by landslide-derived material.

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Abs•act, Foreland basin stratigraphy can be considered as the result of three interacting processes:thrust deformation, which builds the tectonic load, sedimentary and erosional processes which redistribute that load, and the flexural response of the lithosphere. The resultant stratigraphy of foreland basins is commonly composed of a small number of shallowing and coarsening upward cycles bounded by regional unconformities. To understand the development of these unconformities, we present a simple model of these three processes, coupling an evolving thrust wedge on a linear elastic plate with erosion and sedimentation defined by the diffusion equation applied to topography. Our model demonstrates the development of regional unconformities without recourse to either eustasy or complex viscoelastic models for the continental lithosphere. The model describes the thrust wedge-foreland basin system in terms of four parameters: (1) the effective elastic thickness of the foreland plate (Te), (2) the sediment transport coefficient (K), (3) the thrust wedge advance rate, (4) the surface slope of the thrust wedge. The model is applied to the Oligocene-Miocene North Alpine Foreland Basin (NAFB) of eastern Switzerland. The stratigraphy of the NAFB can be simplified into two large-scale shallowing upward cycles separated by an unconformity at the base of the Burdigalian (22 Ma). Geological information is taken from the NAFB to estimate suitable values for the parameters listed above. Assuming a linear elastic lithospheric rheology, the Te value is estimated at 10 + 5 km from decompacted sediment columns. Data to constrain the sequential development of the thrust wedge come from structural geology. The early stages (40-24 Ma) of compression involved a relatively low-angle thrust wedge with an advance rate of approximately 2-4 mm/yr. At about 24 Ma the wedge advance slowed down and thickened by underplating crystalline basement of the foreland plate. The value for the transport coefficient has been estimated from previous studies. Prior to attempting to simulate the broad-scale geometry of the NAFB the role of each parameter was assessed individually. The values for Te and K are held constant throughout the simulation of the NAFB at 7.5 km and 500 m2/yr, respectively. The geometry of the base Burdigalian unconformity is reproduced by variations in the parameters describing the thrust wedge. The surface slope angle of the wedge is increased from 2.5 ø to 4 ø over 0.2 m.y., and the rate of thrust advance is decreased from 2 mm/yr to 0.2 mm/yr, during the thickening event between 24 and 23.8 Ma. The rejuvenation of the internal parts of the thrust load causes backtilting of the foreland basin sediments and, after a time lag, erosion of the distal stratigraphy over the forebulge, so simulating the base Burdigalian unconformity. Platt, J.P., Dynamics of orogenic wedges and the uplift of high-pressure metamorphic rocks, Geol. Soc. Am. Bull., 97, 1037-1054, 1986. Price, R.A., Large scale gravitational flow of supracrustal rocks, South...

Earth's landscape, shaped by the interplay between tectonics and climate, is a dynamic interface over which many biogeochemical cycles operate. The mass fluxes associated with the physical, biological and chemical processes acting across the landscape involve the transport of particulate sediment and solutes. Sediment is moved from source to sink -from the erosional engine of mountainous regions to its eventual deposition -by the sediment-routing system. The selective long-term preservation of elements of the sediment-routing system to produce the narrative of the geological record is dictated by processes operating in Earth's lithosphere. Making the connection between these two levels of enquiry -between the forces shaping present-day erosional and depositional landscapes and the long-term historical record -requires integration and ingenuity. If successful, we may indeed "see a world in a grain of sand" as the poet William Blake suggested.The growing field of study of Earth surface processes is uniting the normally disparate disciplines of solid Earth geology, geomorphology and atmospheric and oceanographic sciences. Conference sessions are packed with contributions on Earth surface processes and new journal sections are devoted to it. These developments are not a result of a sudden conversion to an environmentalist agenda, but of a growing realization of the myriad of interactions, and the strength of the associated mass fluxes, that operate across the critical zone comprising Earth's surface. Understanding Earth surface processes therefore provides vital insights into how Earth functions as a system.For Earth surface processes to be a vibrant new discipline, rather than a rebranding of conventional reductionist thinking, integration is required at different levels. One level is the integration of the physical, chemical and biological processes that shape Earth's surface and that drive its mass fluxes, investigated at the so-called human timescale -over the period for which we have historical records. The second level of integration is over larger spatial and temporal scales. Making the connections between these two levels is the exciting challenge that faces a wide range of natural scientists today.

[1] Regional grain size trends in fluvial successions can reveal important information regarding the dynamics of sediment routing systems. Self-similar solutions for downsystem grain size fining have recently been proposed to explore how key variables, such as the spatial distribution of deposition, sediment discharge, and sediment supply characteristics, control spatial distribution of grain size in fluvial successions over time scales of 10 4 -10 6 years. We explore the sensitivity of these solutions to changes in key variables and assess their applicability to ancient fluvial successions. Several sensitivity analyses are presented to investigate the relative control of the key model variables on the spatial pattern of down-system grain size fining in fluvial successions. Sensitivity analyses demonstrate that (1) an increase in the initial value of sediment discharge to a basin causes a decrease in the rate of grain size fining in fluvial successions, an effect that becomes nonlinear for large values of initial sediment discharge; (2) a short-wavelength/ high-amplitude subsidence regime generates a greater rate of down-system grain size fining and a long-wavelength/lower-amplitude subsidence regime generates a lesser rate of down-system grain size fining in fluvial successions; and (3) an increase in the spread of grain sizes in the sediment supply generates a greater rate of down-system grain size fining. We apply this modeling technique to grain size data sets collected from two time surfaces within conglomerates of the Upper Eocene Montsor Fan Succession of the Pobla Basin, Spanish Pyrenees. These data sets exhibit approximately self-similar grain size distributions; further, the observed increase in down-system grain size fining associated with smaller depositional system lengths provides support for the application of self-similar solutions to fluvial successions. By applying these solutions to carefully collected grain size data from fluvial successions, we are able to relate explicitly the initial grain size supplied to the system, the spatial distribution of subsidence and the sediment discharge into the basin to the rate of grain size fining in fluvial successions. This method thus offers a powerful means of elucidating sediment routing system dynamics over time.

In regions undergoing active tectonics, the coupling between the tectonic displacement field, the overlying landscape and the redistribution of mass at the Earth's surface in the form of sediment routing systems, is particularly marked and variable. Coupling between deformation and surface processes takes place at a range of scales, from the whole orogen to individual extensional fault blocks or contractional anticlines. At the large scale, the attainment of a steady-state between the overlying topography and the prevailing tectonic conditions in active contractional orogens requires an efficient erosional system, with a time scale dependent on the vigour of the erosional system, generally in the range 106–107 years. The catchment–fan systems associated with extensional fault blocks and basins of the western USA are valuable natural examples to study the coupling between tectonic deformation, landscape and sediment routing systems. Even relatively simple coupled systems such as an extensional fault block and its associated basin margin fans have a range of time scales in response to a tectonic perturbation. These response times originate from the development of uniform (steady-state) relief during the accumulation of displacement on a normal fault (c. 106 years), the upstream propagation of a bedrock knickpoint in transverse catchments following a change in tectonic uplift rate (c. 106 years), or the relaxation times of the integrated catchment–fan system in response to changes in climatic and tectonic boundary conditions (105–106 years). The presence of extensive bedrock or alluvial piedmonts increases response times significantly. The sediment efflux of a mountain catchment is a boundary condition for far-field fluvial transport, but the fluvial system is much more than a simple transmitter of the sediment supply signal to a neighbouring depocentre. Fluvial systems appear to act as buffers to incoming sediment supply signals, with a diffusive time scale (c. 105–106 years) dependent on the length of the system and the extent of its floodplains, stream channels and proximal gravel fans. The vocabulary for explaining landscapes would benefit from a greater recognition of the importance of the repeat time and magnitude of perturbations in relation to the response and relaxation times of the landscape and its sediment routing systems. Landscapes are best differentiated as ‘buffered’ or ‘reactive’ depending on the ratio of the response time to the repeat time of the perturbation. Furthermore, landscapes may be regarded as ‘steady’ or ‘transient’ depending on the ratio of the response time to the time elapsed since the most recent change in boundary conditions. The response of tectonically and climatically perturbed landscapes has profound implications for the interpretation of stratigraphic architecture.

Changes to the tectonic boundary conditions governing erosional dynamics in upland catchments have a significant effect on the nature and magnitude of sediment supply to neighbouring basins. While these links have been explored in detail by numerical models of landscape evolution, there has been relatively little work to quantify the timing, characteristics and locus of sediment release from upland catchments in response to changing tectonic boundary conditions that are well-constrained independently. We address this challenge by quantifying the volume and

The Pyrenees represents an orogen that developed diachronously, from east to west, between the Late Cretaceous and Miocene. Here, we use detrital zircon fission-track thermochronological analyses and U-Pb geochronology, interpreted within the context of the thermal and tectono-sedimentary development of the orogen, to construct a 3-stage model for south-central Pyrenean sediment routing system evolution as follows: (1) Late Cretaceous to Paleocene: Oblique convergence and topographic growth initiates in the eastern Pyrenees. After erosion and removal of the "cover layer", south-central Pyrenean basins are supplied with zircons cooled during the Late Cretaceous (ϳ78 Ma), with a fission-track lag time of ca. 15 Myr, that record early Pyrenean exhumation. The zircons are sourced from the eastern, not central, Pyrenees. Orogen-parallel sediment routing systems dominate; (2) Early to Middle Eocene: After a period of quiescence, plate convergence rates increase. Uplift of the central Pyrenees supplies the south-central Pyrenean basins with zircons sourced from the central Pyrenean cover layer. Out-of-sequence thrusting recycles the early foredeep deposits and their associated thermochronological signals. The sediment routing systems begin to transition from orogen-parallel to orogen-transverse states; (3) Late Eocene to Miocene: Uplift and exhumation of the western Pyrenees begins. Zircons exhumed and cooled during the Oligocene (ϳ30 Ma) in response to duplex stacking in the central Axial Zone, reach the south-central Pyrenean wedge-top and foreland basins with a lag time of ca. 3 Myr. Orogen-transverse sediment routing systems become fully established. Our results extend the exhumational history of the Pyrenees beyond that shown from bedrock studies and reveal that significant topography existed in the Pyrenees in the Paleocene. Furthermore, our data demonstrate the successive change from orogen-parallel to orogen-transverse sediment dispersal along strike, coeval with diachronous mountain growth. This study has implications for understanding the evolution of synorogenic sediment routing systems, migrating depocenters and the redistribution of mass by surface processes that may drive any coupling with tectonics during oblique orogenic development.