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The quantification of active tectonics from geomorphological and morphometric approaches most often implies that erosion and tectonics have reached a certain balance. Such equilibrium conditions may however be seldom found in nature, as questioned and documented by recent theoretical studies, in particular because drainage basins may be quite dynamic even though tectonic and climatic conditions remain constant. Here, we document this drainage dynamics from the particular case example of the Bhutan Himalayas. Evidence for out-of-equilibrium morphologies have for long been noticed in Bhutan, from major (> 1 km high) river knickpoints and from the existence of high-altitude low-relief regions within the mountain hinterland. These peculiar morphologies were generally interpreted as representing a recent change in climatic and/or tectonic conditions. To further characterize these morphologies and their dynamics, and from there discuss their origin and meaning, we perform field observations and a detailed quantitative morphometric analysis using Chi plots and Gilbert metrics of drainages over various spatial scales, from major Himalayan rivers to local streams draining the low-relief regions. We first find that the river network is highly dynamic and unstable. Our results emphasize that the morphology of Bhutan does not result from a general wave of incision propagating upstream, as expected from most previous interpretations. Also, the specific spatial organization in which all major knickpoints and low-relief regions are located along a longitudinal band in the Bhutan hinterland, whatever their spatial scale and the dimensions of the associated drainage basins, calls for a common local supporting mechanism most probably related to active tectonic uplift. From there, we discuss previous interpretations of the observed landscape in Bhutan. Our results emphasize the need for a precise documentation of landscape dynamics and disequilibrium over various spatial scales as a first-order step in morpho-tectonic studies of active landscapes.

In northern Brazil, deformational structures control various features of the morphology. These structures are ductile shear zones and regional foliations formed during the brasiliano orogeny in the late proterozoic, and faults formed during the rifting of the margin in the Jurassic—cretaceous and in the late cretaceous and Cenozoic. The morphology features related to these structures include mainly residual alignment of ridges, fault-controlled valleys, and structural fault scarps. In this perspective, this paper presents a review about the morphostrutural control played by brittle and ductile basement structures on the relief in northeastern brazil. Our study indicates that continental denudation have been controlled by both differential erosion and tectonics. In this aspect, the exhumation along NE-SW and E-W striking shear zones originates lineaments, which confine the drainage channels and guide the dissection and sometimes fluvial aggradation. This process results in ridges and valleys that control the flow channels, which become indicators of shear zones and faults. This process is also observed in sedimentary basins, where dissection along fault zones form tectonic valleys that constitute the geomorphic expression of the fault reactivation.

Climate-dependent chemical weathering is found to control the erodibility of bedrock-floored rivers across a rainfall gradient on the Kohala Peninsula, Hawai‘i; river erosion models that incorporate this process could improve the assessment of climatic controls from topographic data and the understanding of climatic feedbacks in landscape evolution models. It is widely assumed that there is a feedback between climate, erosion and tectonics over geological timescales, but the influence of local climate on landscape erosion rates remains poorly understood. Using new field constraints on geochemistry, rock mechanics, and erosion rates along rivers spanning an extreme climate gradient on the Big Island of Hawai'i, this study demonstrates that climate-dependent chemical weathering controls the erodibility of bedrock-floored rivers. Although the strength of this mechanism may vary with tectonic, lithologic and climatic conditions, the quantified relationship between local rainfall and rock erodibility can help with the assessment of climatic controls from topographic data and the incorporation of climatic feedbacks into landscape evolution models. Feedbacks between climate, erosion and tectonics influence the rates of chemical weathering reactions1,2, which can consume atmospheric CO2 and modulate global climate3,4. However, quantitative predictions for the coupling of these feedbacks are limited because the specific mechanisms by which climate controls erosion are poorly understood. Here we show that climate-dependent chemical weathering controls the erodibility of bedrock-floored rivers across a rainfall gradient on the Big Island of Hawai‘i. Field data demonstrate that the physical strength of bedrock in streambeds varies with the degree of chemical weathering, which increases systematically with local rainfall rate. We find that incorporating the quantified relationships between local rainfall and erodibility into a commonly used river incision model is necessary to predict the rates and patterns of downcutting of these rivers. In contrast to using only precipitation-dependent river discharge to explain the climatic control of bedrock river incision5,6, the mechanism of chemical weathering can explain strong coupling between local climate and river incision.

1. IntroductionThe recognition that the present landscape is a product of the long-term interaction of tectonics and climate is one of the fundamental concepts in historical geoscience. Determining the response of the environment to these changes has been further emphasised by attempts to understand the relationship between rates of tectonic activity and sedimentation or erosion and the interplay of these factors with climate change (e.g. Cloetingh et al., 2005). Moreover, the dynamic linkage of erosion and tectonics results in major impacts on changes of the Earth’s climate through the evolution of major continental topography and vice versa.The form of the Earth’s topography actually results from the net interaction of processes operating at a wide range of time scales. These include long- and short-term tectonic uplift, subsidence, phases of glaciation, and climatic and environmental changes. In northern Europe, these processes, operating simultaneously through the Cenozoic, have left a record of changing conditions that have determined the form of the present landscape. The emphasis recently has been on relatively short-term interactions involving quasi-simultaneous uplift followed shortly by incision, paced alongside Late Pleistocene marine isotope stages, and interacting with climatic fluctuations. Here we take a longer view, that of Cenozoic uplift centres changing in intensity and location, and thus sediment feeds and alluvial styles, feeding into a depositional basin

The Edea-Eseka region (EER), a portion of West African Margin located in SW Cameroon between 3°30′—4°00′ N and 10°00′—10°55′ E and submitted to equatorial climate since early Miocene is used here as a proxy for climatic conditions. Geomorphological analysis based on morphometric parameters computed from DEM (30 m) combined with geological maps and field observations were used to constrain geomorphic evolution and landscape adjustment to tectonic processes in this humid zone. Three types of geomorphic indices reflecting specially patterns of differential uplift, those efficient in detecting tilting, and those revealing interactions between erosion and tectonics. - The obtained results show that lithological boundaries and base level controls on landscape are very limited. Tectonic processes, peculiarly uplift induced by faults or tilting at local scale and by mantle dynamics at large scale coupled with climate condition, represent the main factors that drove the geomorphic evolution of this area discriminating three main morphotectonic provinces different by their geomorphic characteristics, uplift and degree of incision. There are, from West to East: (1) the coastal province (CP), deeply incised and built on Douala-Kribi/Campo basin ( - Several geomorphic indices used to evaluate tectonic activities and their average the index of relative active tectonics (IAT) show that tectonic activity differs from one province to another and within each province. Generally, it increases from coast (coastal province) to hinterland (UP). EER are represented by classes 2 and 3 of IAT indicating moderate to high active tectonics. Class 1 revealing the highest tectonic activity, occurs exclusively in the UP. Class 2 corresponding to high tectonic activity happens largely in the south of the IP along the Nyong Fault and the UP where relief are particularly high. Class 3 indicates the moderate relative tectonic in the IP. Class 4 mainly takes place in tectonically low to inactive Douala-Kribi/Campo basin, except along the South part of Sanaga Fault. The development and the evolution of Edea-Eseka region landscape is then acted by a dominant high-uplift rate in SW Cameroon. This tectonic activity apparently incompatible with the passive margin context is however realistic in this area, on one hand justified by the numerous reactivations over time of faults crossing the region that generate earthquakes in some places and on the other hand, by the activity of the Cameroon Volcanic Line, and particularly that of the Mount Cameroon located near the study area. It appears at the end that, due to mantle dynamics, the EER has been rejuvenated under the tectonics and climate forcings, returning to a transient stage of its geomorphic evolution.

Erosion and tectonic uplift are widely thought to be coupled through feedbacks involving orographic precipitation, relief development, and crustal weakening. In many orogenic systems, it can be difficult to distinguish whether true feedbacks exist, or whether observed features are a consequence of tectonic forcing. To help elucidate these interactions, we examine Gongga Shan, a 7556 m peak on the eastern margin of the Tibetan Plateau where cosmogenic 10Be basin-wide erosion rates reach >5 mm/yr, defining a region of localized rapid erosion associated with a restraining bend in the left-lateral Xianshuihe Fault. Erosion rates are consistent with topography, thermochronometry, and geodetic data, suggesting a stable pattern of uplift and exhumation over at least the past 2–3 My. Transpression along the Xianshuihe Fault, orographically enhanced precipitation, thermally weakened crust, and substantial local relief all developed independently in the Gongga region and existed there prior to the uplift of Gongga Shan. However, only where all of these conditions are present do the observed topographic and erosional extremes exist, and their relative timing indicates that these conditions are not a consequence of rapid uplift. We conclude that their collocation at 3–4 Ma set into motion a series of feedbacks between erosion and uplift that has resulted in the exceptionally high topography and rapid erosion rates observed today.

Investigations of tectonic and surface processes have shown a clear relationship between climate-influenced erosion and long-term exhumation of rocks. Numerical models suggest that most orogens are in a transient state, but observational evidence of a spatial shift in mountain building processes due to tectonic-climate interaction is missing. New thermochronology data synthesized with geophysical and surface process data elucidate the evolving interplay of erosion and tectonics of the colliding Yakutat microplate with North America. Focused deformation and rock exhumation occurred in the apex of the colliding plate corner from > 4 to 2 Ma and shifted southward after the 2.6 Ma climate change. The present exhumation maximum coincides with the largest modern shortening rates, highest concentration of seismicity, and the greatest erosive potential. We infer that the high sedimentation caused rheological modification and the emergence of the southern St. Elias, intercepting orographic precipitation and shifting focused erosion and exhumation to the south.

This special issue collects a number of papers mainly reflecting discussions during the “tectonics, sedimentation and surface processes” sessions (TSSP) organized at recent EGU conferences (2012, 2013, 2014), as well as related studies that have appeared in Earth Surface Processes and Landforms over the last two years. The sedimentary record has long been used to invert for deformation at all scales and in all tectonics settings. Growth strata, sediment provenance, sequence stratigraphy and changing depositional environments have all provided first order constraints on quantifying deformation at a range of spatial and temporal scales. At the same time, these studies have motivated much work on the influence of tectonics on both sedimentation patterns and basin fill successions. However, relatively few studies have considered the whole integrated system of catchment erosion, fluvial transport and sediment deposition together, often concentrating on either the basin or the catchment separately. Recently however, methodological progress in quantifying rates of surface processes in the upstream erosion and transfer zones, as well as revived interest in the couplings between surface processes, tectonics and climate, have made it possible to renew our understanding of the interactions between sedimentation and tectonics within the framework of the whole integrated sediment routing system. Although the studies within this special issue are only a fraction of the work presented over the last five years of the TSSP sessions, the manuscripts presented here reflect a selection of the broad content and diversity of studies that integrate both sedimentation and surface processes to understand deformation in the context of sedimentary systems. They highlight and are organized into three active challenges of the field: 1) tectonics and climate into landscapes, 2) signal propagation within sediment routing systems, and 3) modeling of tectonic and surface processes.

Half a century ago, principles of the theory of lithosphere plate tectonics, or plate tectonics, were first formulated. Since then, the theory has become substantially more complicated and tectonic processes and phenomena have been identified that are not described by the theory. This relates to certain types of vertical movements, primarily to the newest uplifts that led to the formation of modern mountain systems. Comparison of geological processes (both those described by the theory of plate tectonics and those unexplained thus far) with data of the seismic tomography of the mantle has made it possible to outline a new tectonic model, according to which the source of observable tectonic manifestations is lateral flows of upper mantle matter, propagating from superplumes—flows of matter and energy rising from the mantle’s bottom. These lateral flows not only move lithospheric plates but also determine structural–substantial transformations of the lithosphere and the upper underlithospheric mantle, which lead to vertical movements and mounting building.

Identifying topographic and erosion rate response to tectonic and climatic forcing remains challenging. This is in part because of the difficulty in isolating the respective roles of climate and tectonics. Here we exploit 2500 thermochronometric data points collected over several decades of research, using a new inverse technique, to image the space-time evolution of erosion rate across the European Alps over the past 35 m.y. The most striking feature of our results is a two- to three-fold increase in erosion rate over the past 2 m.y. exclusively within the Western and Central Alps. This increase appears to be controlled by the inferred high rock uplift rate due to the progressive detachment of the European slab under the Western Alps. The similarity in mean elevation between the Western and Eastern Alps indicates a surprisingly low topographic response to this differential tectonic forcing, and points to the role of enhanced glacial erosion in response to surface uplift.

The discussions on the orogenic evolution during Earth's history converge to the question of a different thermal structure in the Archean compared to the Phanerozoic and the applicability of the plate tectonic paradigm. However, geothermal structures are transient in orogens and are difficult to translate into large-scale tectonics and exhumation rates. Therefore, we propose depth–time data in the Archean Skjoldungen Orogen (SE Greenland, North Atlantic Craton) that allow for reconstruction of an exhumation rate independent of geothermal gradients. The resulting exhumation rate of ca. 0.4 km/Ma is similar to exhumation rates during erosion-controlled processes in modern orogens. These exhumation rates can only be established by erosion time constants similar to modern orogens. The occurrence of erosion-controlled exhumation is best explained by a stiff foreland promoting localized deformation in the orogen. Therefore, a switch from magmatic-dominated processes to localized deformation is proposed in the Skjoldungen Orogen area. This is supported by a change in magma composition and volume, from widespread granodiorite to localized alkaline intrusions. In addition, the involved metasedimentary rocks include detrital zircons of the only 50 Ma older foreland, which also correspond to erosion and tectonics as in modern orogens, i.e. flysh-type sediments. Relatively fast exhumation rates and the structural-magmatic evolution of the Neoarchean Skjoldungen Orogen thus indicate modern-style tectonic processes where stiff Mesoarchean continental crust forms a foreland to a collisional orogen instead of typical accretionary tectonics of weak island arc-like terranes in granite-greenstone terranes.

The concept of interplay between mantle convection and tectonics goes back to about a century ago, with the proposal that convection currents in the Earth's mantle drive continental drift and deformation (Holmes, 1931). Since this time, plate tectonic theory has established itself as the fundamental framework to study surface deformation, with the remarkable ability to encompass geological and geophysical observations. Mantle convection modeling has progressed to the point where connections with plate tectonics can be made, pushing the idea that tectonics is a surface expression of the global dynamics of one single system: the mantle-lithosphere system. Here, we present our perspective, as modelers, on the dynamics behind global tectonics with a focus on the importance of self-organisation. We first present an overview of the links between mantle convection and tectonics at the present-day, examining observations such as kinematics, stress and deformation. Despite the numerous achievements of geodynamic studies, this section sheds light on the lack of self-organisation of the models used, which precludes investigations of the feedbacks and evolution of the mantle-lithosphere system. Therefore, we review the modeling strategies, often focused on rheology, that aim at taking into account self-organisation. The fundamental objective is that plate-like behaviour emerges self-consistently in convection models. We then proceed with the presentation of studies of continental drift, seafloor spreading and plate tectonics in convection models allowing for feedbacks between surface tectonics and mantle dynamics. We discuss the approximation of the rheology of the lithosphere used in these models (pseudo-plastic rheology), for which empirical parameters differ from those obtained in experiments. In this section, we analyse in detail a state-of-the-art 3-D spherical convection calculation, which exhibits fundamental tectonic features (continental drift, one-sided subduction, trench and ridge evolution, transform shear zones, small-scale convection, and plume tectonics). This example leads to a discussion where we try to answer the following question: can mantle convection models transcend the limitations of plate tectonic theory? (C) 2016 Elsevier B.V. All rights reserved.

We integrate analysis of present-day topography with a synthesis of current knowledge of the geology, deformation history, exhumation history, and the pattern of erosion rates to address the controversies surrounding the surface uplift history of the Bolivian Andes and the relative roles of climate and tectonics in the evolution of this mountainous landscape. Using metrics of channel steepness ( k sn , a measure of channel slope normalized by drainage area), local relief (over a 2.5 km radius), and hillslope gradient we identify and map a suite of previously unrecognized perched, low-relief upland landscape patches in northern Bolivia that define a long-wavelength (∼300 km) topographic ramp with an ∼3.5 km elevation drop from SE to NW. We interpret these low-relief patches as the remnants of a formerly continuous low-relief landscape formed on grade with the foreland that has been uplifted and warped since formation. The 11–7 Ma Cangalli Formation on-laps the northern end of this ramp and suggests a shared history and common baselevel with the well-known ca. 12–9 Ma San Juan del Oro erosion surface in southern Bolivia. Patterns of rock and surface uplift rate implied by this interpretation are consistent with those inferred independently from analysis of channel steepness ( k sn ), the distribution of fluvial hanging valleys, reconstruction of channel profiles, and the distribution of published low temperature thermochronometric ages. These data reinforce earlier interpretations for 2–3 km surface uplift in the Bolivian Andes in the last 12 Ma. The marked contrast in topography across the Santa Cruz bend (∼18°S) appears largely controlled by differences in tectonics conditioned by inherited geologic contrasts and we show that post–12 Ma erosion and exhumation in northern Bolivia are controlled primarily by tectonics, not climate. However, the pattern and style of uplift in many locations suggests warping over deep structures in absence of significant shortening, consistent with the observation that exhumation patterns cease to be coupled to patterns of contractile deformation post-11–15 Ma. Tectonically controlled topography strongly focuses rainfall and may enhance erosional efficiency and thus erosion rates in zones of high rainfall, but no data from this study area demands this. Moreover, we find no evidence for a tectonic response to the modern rainfall pattern. We speculate that differences in the pattern of deformation and uplift across the Santa Cruz bend appear to be accommodated by a crustal-scale relay ramp.

[1] The Hangay mountain range, a dome in central Mongolia, provides a window into understanding how climate influences the erosion and resulting geomorphic and sedimentary signatures of continental topography. Specifically, asymmetric erosion of the Hangay, associated with a distinct orographic precipitation gradient, offers a natural experiment for exploring uplift, erosion, and the isostatic response to erosional unloading. The flat-topped Hangay peaks preserve low-relief remnant surfaces that provide markers of rock uplift. This makes it possible to map the deformation of a former planar surface during doming and hence to estimate the total extent of erosion by the difference from present day topography. Erosion into the Hangay surface has been significant but incomplete; the morphology of the range indicates a nonequilibrium landscape that may have persisted for millions to tens of millions of years, implying a long response time in this semiarid climate. The extent of erosion across the range correlates with mean annual precipitation. Variability in present-day peak heights across the north-south climatic and erosional gradient provides empirical support for the generally accepted theory that climate-driven erosion will increase the height of mountain peaks by generating greater surface uplift through isostasy. Correction for this isostatic response makes it possible to reconstruct primary surface uplift of the Hangay. Results highlight the importance of considering the interplay between climate, erosion, and uplift in shaping intracontinental topography and thus when interpreting the geomorphic, sedimentary, and geodynamic signatures associated with such topography.

In many regions, tectonic uplift is the main driver of erosion over million-year (Myr) timescales, but climate changes can markedly affect the link between tectonics and erosion, causing transient variations in erosion rates. Here we study the driving forces of millennial to Myr-scale erosion rates in the French Western Alps, as estimated from in situ produced cosmogenic 10Be and a newly developed approach integrating detrital and bedrock apatite fission-track thermochronology. Millennial erosion rates from 10Be analyses vary between ~0.27 and ~1.33 m/kyr, similar to rates measured in adjacent areas of the Alps. Significant positive correlations of millennial erosion rates with geomorphic measures, in particular with the LGM ice thickness, reveal a strong transient morphological and erosional perturbation caused by repeated Quaternary glaciations. The perturbation appears independent of Myr-scale uplift and erosion gradients, with the effect that millennial erosion rates exceed Myr-scale erosion rates only in the internal Alps where the latter are low (

The inception of plate tectonics on Earth and its subsequent evolution are discussed on the basis of theoretical considerations and observational constraints. The likelihood of plate tectonics in the past depends on what mechanism is responsible for the relatively constant surface heat flux that is indicated by the likely thermal history of Earth. The continuous operation of plate tectonics throughout Earth's history is possible if, for example, the strength of convective stress in the mantle is affected by the gradual subduction of surface water. Various geological indicators for the emergence of plate tectonics are evaluated from a geodynamical perspective, and they invariably involve certain implicit assumptions about mantle dynamics, which are either demonstrably wrong or yet to be explored. The history of plate tectonics is suggested to be intrinsically connected to the secular evolution of the atmosphere, through sea-level changes caused by ocean-mantle interaction.

The combination of large, temperate glaciers and rapid crustal convergence in the Saint Elias Mountains (southeastern Alaska, USA, and Yukon Territory and British Colombia, Canada) provides an exceptional opportunity to study the interactions between the tectonic and surface processes that have shaped most active orogens on Earth during much of the Quaternary. This research first provides a review of thermochronometric data sets recording exhumation under two major glacier systems of the Saint Elias Mountains, the Bagley-Bering and the Seward-Malaspina systems. These data sets are integrated over the single glacier systems and used in conjunction with glaciological data to investigate the interactions of glacial erosion and tectonics. Despite their proximity, the glaciological processes and geological settings of these two glacial systems differ significantly. On the east side of the orogen, sediments eroded from bedrock underneath the Malaspina Glacier reflect regions of rapid erosion under the slowly moving Seward Ice Field. Because the Seward Ice Field overlies a localized zone of major faulting and rapid exhumation, the strained and fractured bedrock is primed for erosion. On the west side, the Bering Glacier is the primary outlet for the Bagley Ice Field, which covers half of the crest of the orogen; however, few if any of the sediments at its terminus originate from under the Bagley Ice Field. Sediment transport is likely hindered by subglacial freeze-on processes that reduce the sediment-carrying capacity of subglacial rivers, though glacial surges are likely exceptions that deposit sediment far beyond the active margin of the glacier. Our study concludes that the widely invoked concepts of glacial erosion should be used with caution, as oversimplification can fail to account for important site-specific differences in geologic and glacial conditions.

Geodynamic models of collisional orogens suggest that precipitation gradients profoundly influence spatial patterns of exhumation and deformation in active collisional mountain ranges. A basic tenet of this hypothesis is that in unglaciated areas, spatial patterns of long-term precipitation, erosion and exhumation should be correlated. A correlation of this type has been observed in the Eastern Himalaya, where uplift of the Shillong Plateau by Pliocene time drastically reduced monsoonal rainfall in the Himalayan range downwind. Existing apatite fission-track data suggest that the resulting precipitation gradient caused a twofold gradient in long-term erosion rates across an area with similar geology, suggesting a strong influence of climate on the region's geomorphic and tectonic evolution. We extend this dataset by presenting 53 new bedrock apatite and zircon fission-track ages from deeper within the rain shadow. We expected latest Miocene to Pliocene apatite ages, similar to previously published ages from neighboring areas in the rain shadow. Instead, apatites as young as 1.3 ± 0.2 Ma and zircons as young as 4.5 ± 1.0 Ma (2σ) demonstrate that spatial gradients in precipitation do not correlate with variations in long-term erosion and crustal strain as predicted by geodynamic models. Thermal–kinematic modeling of these data suggests that local exhumation patterns reflect gradients in rock uplift dictated by fault kinematics in this rapidly deforming area, despite a dramatic precipitation gradient. These findings both highlight the need to better understand how erosive processes scale with precipitation amount and intensity in such settings, and suggest a disconnect between the predictions of orogen-scale geodynamic models and the relationship between erosion and tectonics at the regional scale.

Uplift of the surface of mountain belts requires forces that are comparable in magnitude to those associated with plate motion, and therefore determination of rates of surface uplift could provide important information on the dynamics of mountain ranges. Rates of uplift of the surfaces of mountain ranges have not, however, been quantified sufficiently well that they provide useful constraints on those processes. Many reports off surface uplift in mountain ranges are based on mistaking exhumation of rocks or uplift of rocks for surface uplift, and provide no information whatsoever on the rates of surface uplift.

What is the influence of glacial processes in driving erosion and uplift across the European Alps? It has largely been argued that repeated erosion through glaciation sustains isostatic uplift and topography in a decaying orogen. But, some insist that the Alps are an orogen still actively uplifting (e.g., Hergarten et al., 2010). We add insight to this debate by isolating the role of post-glacial topographic forcing on erosion rates. To do this, we quantify the topographic signature of past glaciation on millennial scale erosion rates in previously glaciated and unglaciated catchments at the easternmost edge of the Austrian Alps. Newly measured catchment-wide erosion rates, determined from cosmogenic 10Be in river-borne quartz, correlate with basin relief and mean slope. GIS-derived slope-elevation and slope-area distributions across catchments provide clear topographic indicators of the degree of glacial preconditioning, which further correlates with erosion rates. Erosion rates in the eastern-most, non-glaciated basins range from 40 to 150 mm/ky and likely reflect underlying tectonic forcings in this region, which have previously been attributed to recent (post 5 Ma) uplift (Legrain et al., 2015). By contrast, erosion rates in previously glaciated catchments range from 170 to 240 mm/ky and reflect the erosional response to local topographic preconditioning by repeated glaciations. Together, these data suggest that Holocene erosion across the Eastern Alps is strongly shaped by the local topography relict from previous glaciations. Broader, landscape-wide forcings, such as the widely debated deep mantle-driven or isostatically-driven uplift, result in lesser controls on both topography and erosion rates in this region. Comparing our data to previously published erosion rates across the Alps, we show that post-glacial erosion rates vary across more than two orders of magnitude with poor topographic indicators of controls. This high variation in post-glacial erosion may reflect combined effects of direct tectonic and modern climatic forcings, but is strongly overprinted by past glacial climate and its topographic legacy.

The steep topography of mountain landscapes arises from interactions between tectonic rock uplift, valley incision and landslide erosion on hillslopes. An analysis of more than 15,000 landslides in the eastern Himalaya, mapped from satellite images, shows that steep uplands primarily respond to uplift and river incision by increases in landslide erosion rates rather than by steepened hillslope angles.

By combining geochemical data and geodynamical models, evidence is provided to address the existence and style of Archaean plate tectonics, a topic of vigorous debate for decades. Using careful analyses of lithostratigraphic Archaean assemblages and numerical model results, we illustrate that a short-term episodic style of subduction was a viable style of tectonics in the early Earth. Modeling results show how, due to the low strength of slabs in a hotter Earth, frequent slab break-off events prevented a modern-style long-lived subduction system, and resulted in frequent cessation and re-initiation of the subduction process on a typical time scale of a few million years. Results fit with geochemical observations that suggest frequent alternation of arc-style and non-arc-style volcanism on a similarly short time scale. Such tectonics could provide the link between early pre-plate tectonic style of tectonics (or stagnant-lid convection) and modern-style plate tectonics, in which short-term episodes of proto-subduction evolved over time into a longer-term, more successful style of plate tectonics as mantle temperature decayed.

The Earth's surface is shaped by tectonics and climate. This simple statement implies that we should, in principle, be able to use the landscape as an archive of both tectonic rates and of changes to climate regime. To solve this inverse problem, and decipher the geomorphic record effectively, we need a sound understanding of how landscapes respond and erode in response to changes in tectonic or climatic boundary conditions. Rivers have been a major focus of research in this field because they are patently sensitive to tectonic and climatic forcing via their channel gradient and discharge. Theoretical, field, and numerical modeling techniques in the last few years have produced a wealth of insight into the behavior of fluvial landscapes, while the increasing availability of high-resolution topographic models have provided the data sets necessary to address this research challenge across the globe. New work by [Miller et al. (2012)][1] in Papua New Guinea highlights the progress we have made in extracting tectonics from topography due to these developments, but also illustrates the problems that still remain. This paper reviews our current knowledge of how fluvial landscapes record tectonics at topographic steady-state and under “transient” conditions, assesses why the climate signal has proven so challenging to interpret, and maps out where we need to go in the future. [1]: #ref-17

Interaction between surface processes and deep tectonic processes plays a key role in the structural evolution, kinematics and exhumation of rocks in orogenic wedges. The deformation patterns observed in analogue models applied to natural cases of present active or ancient mountain belts reflect several first order processes that result of these interactions. Internal strain partitioning due to mechanical behaviour of a thrust wedge has a strong impact on the vertical component of displacement of tectonic units that in return favour erosion in domains of important uplift. Such strain partitioning is first controlled by tectonic processes, but surface processes exert a strong feed back on wedge dynamics. Indeed, material transfer in thrust wedges not only depends on its internal dynamics, it is also influenced by climate controlled surface processes involving erosion and sedimentation. Effects of erosion are multiple: they allow long term localization of deformed domains, they favour important exhumation above areas of deep underplating and combined with sedimentation in the foreland they contribute to maintain the wedge in a critical state for long time periods. The simple models illustrate well how mountain belts structure, kinematics of tectonic units and exhumation are determined by these complex interactions.

The field of tectonic geomorphology is in a state of tension. The widespread availability of high-quality, high-resolution digital topographic data encourages the development of simple morphological ‘tools’ which can be used to deduce recent tectonic evolution. Meanwhile, process geomorphologists recognize that current models have a significant empirical basis, and lack insight into the underlying physics of erosion processes. Most tectonic geomorphology research is concerned with rivers, but glaciers, debris flows and hillslope processes also play a key role in hypotheses linking climate to tectonics, via surface processes, while submarine geomorphology has barely been investigated in a tectonic context. Studies combining field data collection, exposure, burial and low-temperature thermochronologic dating, digital topographic analysis, laboratory experiments and numerical models are successfully incorporating physics into geomorphic process ‘laws’, and demonstrating key tectonic geomorphology hypotheses. The approaches required for further progress have been outlined, but many exciting challenges remain.

orogenic wedges; Interaction between surface and tectonic processes plays a key role in the structural evolution, kinematics, and exhumation of rocks in orogenic wedges. The deformation patterns observed in analog models show that strain partitioning has a strong impact on the vertical component of displacement of tectonic units, which in return favors erosion in domains of important uplift. Partitioning is controlled by tectonic processes and by climate-dependent surface processes, including erosion and sedimentation. The effects of partitioning include localization of deformed domains, exhumation above areas of deep underplating, and steady-state maintenance of wedges for long time periods. Simple models illustrate well how the morphostructural evolution of mountain belts is determined by these complex interactions.

It has been debated whether rivers or glaciers are more effective agents of erosion. A global compilation of erosion rates reveals that both are capable of generating rates of erosion that match or exceed the highest rates of rock uplift. Since the late nineteenth century, it has been debated whether rivers or glaciers are more effective agents of erosion1. The dramatic landscapes associated with glaciated terrain have often led to the argument that glaciers are more erosive than rivers, and recent studies have documented the topographic signature of an ice-controlled limit of mountain height known as the ‘glacial buzz-saw’2,3. Here we present a new global compilation of erosion rates, which questions the conventional view of glaciers and erosion. In regions of rapid tectonic uplift, erosion rates from rivers and glaciers both range from 1 to over 10 mm yr−1, indicating that both are capable of generating erosion rates matching or exceeding the highest rates of rock uplift. Moreover, a comparison of erosion rates over timescales ranging from 101 to 107 years indicates that glacial erosion tends to decrease by one to two orders of magnitude over glacial cycles, whereas fluvial erosion rates show no apparent dependence on time. We conclude that tectonics controls rates of both fluvial and glacial erosion over millennial and longer timescales and that the highest rates of erosion (>10 mm yr−1) generally result from a transient response to disturbance by volcanic eruptions, climate change and modern agriculture.

The St Elias orogen in Alaska is one of the world’s highest coastal mountain ranges. An age analysis of detrital material in active sediment systems in the inaccessible ice-covered valley bottoms reveals localized exhumation that is driven by coupling between erosion and active tectonic rock uplift.

Simple physical arguments, analogue experiments and numerical experiments all suggest that the internal dynamics of actively deforming collisional mountain ranges are influenced by climate. However, obtaining definitive field evidence of a significant impact of climate on mountain building has proved challenging. Spatial correlations between intense precipitation or glaciation and zones of rapid rock-uplift have indeed been documented in numerous mountain ranges, and are consistent with model predictions. More compelling evidence — such as tectonic changes in response to (rather than just coincident with) climate change — has, however, rarely been documented. Triggered by a climate-driven increase in erosion rate, friction-dominated mountain ranges are expected to show a number of simultaneous responses: a decrease in the width of the range, a temporary increase in sediment yield, a persistent increase in the rate of rock uplift and a reduction in the subsidence rate of surrounding basins. The most convincing field evidence for such a coordinated response of a mountain range to climate change comes from the European Alps and the St Elias range of Alaska. Field studies and experimental research during the past two decades have provided considerable evidence for a significant influence of climate on tectonics. Recent advances suggest that model predictions can guide future fieldwork aimed at substantiating this view.

The interactions among climate, erosion, and tectonics have long been of interest to geologists, but have not yet been united into a single theoretical framework. In this study, representations of orographic precipitation and fluvial erosion are combined with the concept of a critical wedge orogen. The idealized framework captures the basic system dynamics. It also allows for a formal analysis of the precipitation and tectonic interactions in terms of feedback factors and gains, and so permits a quantitative comparison of their relative strengths. The constraint of self-similar growth in a critical wedge orogen acts as a tectonic governor, whereby changes in orogen size are strongly damped. We determine that this negative tectonic feedback is stronger than the precipitation feedback, which may be negative or positive depending on whether precipitation increases or decreases with orogen size. For an extreme positive feedback unconstrained runaway growth is possible, ultimately leading to plateau formation. When orographic precipitation leads to a significant rain shadow, there is a strong partitioning of rock uplift rates that favors the wet, windward flank of the orogen. This flank also dominates the response of the whole orogen to changes in climate or tectonic forcing, except in the case where a large fraction of the eroded material is recycled into the wedge. Finally, it is demonstrated that the response time of the orogen depends on the feedbacks, and is proportional to the gain of the system.

Unraveling the relative roles of erosion and tectonics in shaping the modern topography of active orogens requires datasets documenting spatial and temporal patterns of exhumation, surface uplift and climatic forcing throughout orogenic growth. Here we report the results of biotite 40 Ar/ 39 Ar incremental heating and single-grain laser-fusion experiments from a nearly vertical, ∼1000 m age-elevation transect in the central Nepalese Himalaya. Age-elevation relationships constructed from these data suggest very slow cooling in this part of the Himalayan crystalline core during the Early Miocene, accelerating to only moderate rates at ∼10 Ma. If we assume purely vertical exhumation and a steady-state thermal structure, the exhumation rates implied by these data are ≪0.1 mm/yr prior to 10 Ma and ∼0.5 mm/yr from ∼10–7 Ma. The acceleration in cooling rate at 10 Ma requires a change in kinematics that may be linked to large-scale changes in climate, or to more local tectonic perturbations. Although we do not presently have enough data to assess the relative roles of regional vs. local drivers, these data provide a new constraint on exhumation through the Miocene that must be honored by any model of Himalayan evolution. © 2008 Elsevier B.V. All rights reserved.

Understanding the role that climate, erosion and tectonics play in determining the mean relief, elevation and general form of a mountain range over time has become the focus of much recent research in the field of tectonic geomorphology. A crucial constraint in these studies is the long-term exhumation rate, which is increasingly being examined using detrital minerals from the sedimentary rock record that represent the eroded remnants of the orogen. A classic field area of such studies is the Himalayan orogen — the Earth's largest mountain range. We describe here a novel approach that uses the in situ analysis of Nd isotopes by laser ablation multicollector inductively coupled plasma mass spectrometry of fission-track dated apatite grains to unambiguously tie them to their source regions. We demonstrate the capability of this new approach on several modern and Holocene river sand samples from the Himalayan orogen and determine, because of the large isotopic differences in the constituent tectonostratigraphic units, both the location and magnitude of long-term erosion. In agreement with previous studies we are able to show that in the Central and Eastern Himalaya long-term denudation is focussed within the High Himalayan Crystalline Series (HHCS) at average rates of not, vert, similar 2 mm/yr. Average long-term rates are similar in the Western Himalaya sampled by the Indus River and largely reflect erosional denudation of the Western Indian Himalaya and the Western Syntaxis (the Nanga Parbat Haramosh Massif and South Karakoram Metamorphic Complex). Notably, the Asian continent supplies significantly more apatites to the mouth of the Indus than they do to the Bengal delta. The ability to reconstruct the patterns of long-term erosion in the Himalaya using detrital apatites from a few samples collected from major transverse drainages provides confidence in the utility of this approach to examine the locations and magnitude of long-term erosion in the past.

Research in landscape evolution over millions to tens of millions of years slowed considerably in the mid-20th century, when Davisian and other approaches to geomorphology were replaced by functional, morphometric and ultimately process-based approaches. Hack's scheme of dynamic equilibrium in landscape evolution was perhaps the major theoretical contribution to long-term landscape evolution between the 1950s and about 1990, but it essentially ‘looked back’ to Davis for its springboard to a viewpoint contrary to that of Davis, as did less widely known schemes, such as Crickmay's hypothesis of unequal activity. Since about 1990, the field of long-term landscape evolution has blossomed again, stimulated by the plate tectonics revolution and its re-forging of the link between tectonics and topography, and by the development of numerical models that explore the links between tectonic processes and surface processes. This numerical modelling of landscape evolution has been built around formulation of bedrock river processes and slope processes, and has mostly focused on high-elevation passive continental margins and convergent zones; these models now routinely include flexural and denudational isostasy. Major breakthroughs in analytical and geochronological techniques have been of profound relevance to all of the above. Low-temperature thermochronology, and in particular apatite fission track analysis and (U–Th)/He analysis in apatite, have enabled rates of rock uplift and denudational exhumation from relatively shallow crustal depths (up to about 4 km) to be determined directly from, in effect, rock hand specimens. In a few situations, (U–Th)/He analysis has been used to determine the antiquity of major, long-wavelength topography. Cosmogenic isotope analysis has enabled the determination of the ‘ages’ of bedrock and sedimentary surfaces, and/or the rates of denudation of these surfaces. These latter advances represent in some ways a ‘holy grail’ in geomorphology in that they enable determination of ‘dates and rates’ of geomorphological processes directly from rock surfaces. The increasing availability of analytical techniques such as cosmogenic isotope analysis should mean that much larger data sets become possible and lead to more sophisticated analyses, such as probability density functions (PDFs) of cosmogenic ages and even of cosmogenic isotope concentrations (CICs). PDFs of isotope concentrations must be a function of catchment area geomorphology (including tectonics) and it is at least theoretically possible to infer aspects of source area geomorphology and geomorphological processes from PDFs of CICs in sediments (‘detrital CICs’). Thus it may be possible to use PDFs of detrital CICs in basin sediments as a tool to infer aspects of the sediments' source area geomorphology and tectonics, complementing the standard sedimentological textural and compositional approaches to such issues. One of the most stimulating of recent conceptual advances has followed the considerations of the relationships between tectonics, climate and surface processes and especially the recognition of the importance of denudational isostasy in driving rock uplift (i.e. in driving tectonics and crustal processes). Attention has been focused very directly on surface processes and on the ways in which they may ‘drive’ rock uplift and thus even influence sub-surface crustal conditions, such as pressure and temperature. Consequently, the broader geoscience communities are looking to geomorphologists to provide more detailed information on rates and processes of bedrock channel incision, as well as on catchment responses to such bedrock channel processes. More sophisticated numerical models of processes in bedrock channels and on their flanking hillslopes are required. In current numerical models of long-term evolution of hillslopes and interfluves, for example, the simple dependency on slope of both the fluvial and hillslope components of these models means that a Davisian-type of landscape evolution characterized by slope lowering is inevitably ‘confirmed’ by the models. In numerical modelling, the next advances will require better parameterized algorithms for hillslope processes, and more sophisticated formulations of bedrock channel incision processes, incorporating, for example, the effects of sediment shielding of the bed. Such increasing sophistication must be matched by careful assessment and testing of model outputs using pre-established criteria and tests. Confirmation by these more sophisticated Davisian-type numerical models of slope lowering under conditions of tectonic stability (no active rock uplift), and of constant slope angle and steady-state landscape under conditions of ongoing rock uplift, will indicate that the Davis and Hack models are not mutually exclusive. A Hack-type model (or a variant of it, incorporating slope adjustment to rock strength rather than to regolith strength) will apply to active settings where there is sufficient stream power and/or sediment flux for channels to incise at the rate of rock uplift. Post-orogenic settings of decreased (or zero) active rock uplift would be characterized by a Davisian scheme of declining slope angles and non-steady-state (or transient) landscapes. Such post-orogenic landscapes deserve much more attention than they have received of late, not least because the intriguing questions they pose about the preservation of ancient landscapes were hinted at in passing in the 1960s and have recently re-surfaced. As we begin to ask again some of the grand questions that lay at the heart of geomorphology in its earliest days, large-scale geomorphology is on the threshold of another ‘golden’ era to match that of the first half of the 20th century, when cyclical approaches underpinned virtually all geomorphological work. Copyright © 2007 John Wiley & Sons, Ltd.

The glacial way of wearing away The rate at which glaciers erode landscapes is an important but poorly constrained relationship. Herman et al. tackle this issue by considering the Franz Josef alpine glacier in New Zealand. The amount of sediment piling up at the edge of the glacier provided erosion rates, whereas remote sensing allowed for simultaneous tracking of glacial motion. The result was a nonlinear relationship, suggesting that fast glaciers are much more effective at gouging landscapes. This could explain the paradox of why long-term erosion rates are so much lower in polar regions with more permanent glaciers. Science , this issue p. 193

Plate tectonics is the paradigm in the Earth system science that links solid Earth processes acting within and on the surface of the Earth with processes that have lead to the evolution of the atmosphere and hydrosphere. The processes and phenomena that connect these parts of the Earth system are driven by magmatism and volcanism. This link is much stronger than the classic correlation between plate tectonic boundary type (i.e., convergent or divergent boundaries), magma generation, and volcanic phenomena acting on millennial or greater timescales. Magmatic and tectonic systems interact at timescales of seconds to years, leading to the triggering of volcanic eruptions by large magnitude earthquakes, and earthquakes by magmatic activity.

Erosion of orogenic mountain ranges exhumes deeply buried rocks and controls weathering, climate, and sediment production and transport at a variety of scales. Erosion also affects the topographic form and kinematics of orogens, and it may provide dynamic feedbacks between climate and tectonics by spatially focused erosion and rock uplift. Thermochronology measures the timing and rates at which rocks approach the surface and cool as a result of exhumation. Relatively well-understood noble gas and fission-track thermochronometric systems have closure temperatures ranging from ∼60 to ∼550°C, making them sensitive to exhumation through crustal depths of about one to tens of kilometers. Thus, thermochronology can constrain erosion rates and their spatial-temporal variations on timescales of ∼105–107 years, commensurate with orogenic growth and decay cycles and possible climate-tectonic feedback response times. Useful methods for estimating erosion rates include inverting ages for erosion rates using crustal thermal models, vertical transects, and detrital approaches. Spatial-temporal patterns of thermochronometrically determined erosion rates help constrain flow of material through orogenic wedges, orogenic growth and decay cycles, paleorelief, and relationships with structural, geomorphic, or climatic features.

Bedrock fission-track analysis, high-resolution petrography and heavy mineral analyses of sediments are used to investigate the relationships between erosion and tectonics in the Western Alps. Along the Aosta Valley cross-section, exhumation rates based on fission-track data are higher in the fault-bounded western block than in the eastern block (0.4–1.5 vs. 0.1–0.3 mm yr−1). Erosion rates based on the analysis of bed-load in the Dora Baltea drainage display the same pattern and have similar magnitudes in the relative sub-basins (0.4–0.7 vs. 0.04–0.08 mm yr−1). Results highlight that climate, relief and lithology are not the controlling factors of erosion in the Western Alps. The main driving force behind erosion is instead tectonics that causes the differential upward motion of crustal blocks.

Despite much progress, many questions remain regarding the potential dynamic coupling between atmospheric and lithospheric processes in the long-term evolution of mountain belts. As a complement to recent efforts to discover the interrelationships among climate, topography, erosion, and rock deformation under conditions of mass-flux steady state, we explore orogen response to changes in climate and tectonic influx. We derive an analytical model that predicts a powerful climatic control on orogen evolution and distinct, potentially diagnostic, responses to climatic and tectonic perturbations. Due to isostatic compensation, the near-surface rock uplift rate during transients is tightly coupled to climate-modulated erosional efficiency. System response is approximately exponential, with a characteristic response timescale that is inversely proportional to the climate- and lithology-modulated erosional efficiency, and is largely insensitive to initial conditions, tectonic influx, and both the sign and magnitude of perturbations.

The geology of Western and Central Europe is significantly influenced by the Variscan orogen that developed during Devonian and Carboniferous time. Numerical models are essential in understanding and quantifying the involved endogenous and exogenous processes and their interactions. These are mainly based on the large-scale mass redistribution caused by erosion and fluvial sedimentary transport. The sedimentary mass flux leads to changing loads on the lithosphere and affects therefore the evolution of the orogen and the foreland-basin. The complex feedback-mechanism of the surface and tectonic processes is studied by three-dimensional elastic–plastic numerical models. The calculated uplift rates are used to model the interaction between tectonic and surface processes such as erosion and sedimentation. An iterative application of the numerical models for the tectonic and surface processes yields a detailed view of the evolution of the foreland-basin. The tectonic model itself (excluding surface processes) already shows some of the palinspastically reconstructed important features of the lower Carboniferous like the London-Brabant Massif, and the northward propagation of the Variscan deformation front. The results obtained from the coupled analysis can be compared to studies of the sedimentary record (i.e. time, thickness, and sedimentation rates) and other geological concepts (i.e. stability of geological provinces). The results demonstrate that both processes are essential in understanding the complex structural evolution of the Variscides and their foreland. The numerical approach on the tectonic–surface process interaction can also be applied easily to other geological settings.

When converting temperature-time curves obtained from geochronology into the denudation history of an area, variations in the isotherm geometry should not be neglected. The geothermal gradient changes with depth due to heat production and evolves with time due to heat advection, if the deformation rate is high. Furthermore, lateral variations arise due to topographic effects. Ignoring these aspects can result in significant errors when estimating denudation rates. We present a numerical model for the thermal response to thrust faulting, which takes these features into account. This kinematic two-dimensional model is fully time-dependent, and includes the effects of alternating fault activation in the upper crust. Furthermore, any denudation history can be imposed, implying that erosion and rock uplift can be studied independently to each other. The model is used to investigate the difference in thermal response between scenarios with simultaneous compressional faulting and erosion, and scenarios with a time lag between rock uplift and denudation. Hereby, we aim to contribute to the analysis of the mutual interaction between mountain growth and surface processes. We show that rock uplift occurring before the onset of erosion might cause 10% to more than 50% of the total amount of cooling. We applied the model to study the Cenozoic development of the Sierra de Guadarrama in the Spanish Central System, aiming to find the source of a cooling event in the Pliocene in this region. As shown by our modeling, this temperature drop cannot be caused by erosion of a previously uplifted mountain chain: the only scenarios giving results compatible with the observations are those incorporating active compressional deformation during the Pliocene, which is consistent with the ongoing NW-SE oriented convergence between Africa and Iberia. © 2004 Elsevier B.V. All rights reserved.

An analysis of the evolution of river channels on Hawaii's Big Island shows that a key factor is the effect of local rainfall on bedrock strength — rather than its effect on river discharge, as is often assumed. See Letter p.223 It is widely assumed that there is a feedback between climate, erosion and tectonics over geological timescales, but the influence of local climate on landscape erosion rates remains poorly understood. Using new field constraints on geochemistry, rock mechanics, and erosion rates along rivers spanning an extreme climate gradient on the Big Island of Hawai'i, this study demonstrates that climate-dependent chemical weathering controls the erodibility of bedrock-floored rivers. Although the strength of this mechanism may vary with tectonic, lithologic and climatic conditions, the quantified relationship between local rainfall and rock erodibility can help with the assessment of climatic controls from topographic data and the incorporation of climatic feedbacks into landscape evolution models.

The hypothesis that abrupt spatial gradients in erosion can cause high strain rates in active orogens has been supported by numerical models that couple erosional processes with lithospheric deformation via gravitational feedbacks. Most such models invoke a 'stream-power' rule, in which either increased discharge or steeper channel slopes cause higher erosion rates. Spatial variations in precipitation and slopes are therefore predicted to correlate with gradients in both erosion rates and crustal strain. Here we combine observations from a meteorological network across the Greater Himalaya, Nepal, along with estimates of erosion rates at geologic timescales (greater than 100,000 yr) from low-temperature thermochronometry. Across a zone of about 20 km length spanning the Himalayan crest and encompassing a more than fivefold difference in monsoon precipitation, significant spatial variations in geologic erosion rates are not detectable. Decreased rainfall is not balanced by steeper channels. Instead, additional factors that influence river incision rates, such as channel width and sediment concentrations, must compensate for decreasing precipitation. Overall, spatially constant erosion is a response to uniform, upward tectonic transport of Greater Himalayan rock above a crustal ramp.

The mechanics and petrological signature of a collisional mountain belt can be significantly influenced by topographic and erosional effects at the scale of large river gorges. The geomorphic influence on crustal scale processes arises from the effects of both stress localization due to existing topography, and also erosional removal of advected crustal mass. The shear stress concentration and normal stress amplification due to topographic gradients and loads divert strain away from existing topographic loads, while concentrating strain into topographic gaps. Efficient erosional removal of material within topographic gaps with widths of at least the thickness of the brittle crustal layer results in differential advection of crustal material. Concentrated exhumation within a gap leads to thermal thinning of the upper brittle layer of the crust, removing the highest strength part of the continental crust and significantly reducing the integrated crustal strength beneath the topographic gap. A rheological weak spot, triggered by efficient incision, grows in intensity as strain becomes increasingly concentrated within the weak region. The growth of extreme topography of an isolated massif requires that the process of creation of the massif is related to the weakening process and can result from the velocity pattern produced by erosional-rheological coupling. As a result, distinctive thermal/mechanical regions develop within the crust in response to these river-influenced velocity patterns and these regions impose a characteristic signature on material advecting through. The signal is one in which the region of highest topography is bracketed by two high-strain zones between which concentrated advection produces lozenges of sillimanite and dry melt stability approximately 20 kilometers beneath the summit. Above these lozenges is a thermal/mechanical boundary layer containing an active hydrothermal system driven by steep thermal, topographic and mechanical gradients. These thermal mechanical regions are fixed with respect to a crustal reference frame. Passage of rock beneath and through these regions under these conditions produces the distinctive petrology and structure of mantled gneiss domes and is recorded within the moving petrological reference frame. Such erosional-rheological coupling can explain the occurrence of some high-grade gneiss domes in ancient collisional belts as well as the presence of active metamorphic massifs at both ends of the Himalayan orogen.

The geologic evidence for worldwide uplift of mountain ranges in the Neogene is ambiguous. Estimates of paleoelevation vary, according to whether they are based on the characteristics of fossil floras, on the masses and grain sizes of eroded sediments, or on calculations of increased thickness of the lithosphere as a result of faulting. Detrital erosion rates can be increased both by increased relief in the drainage basin and by a change to more seasonal rainfall patterns. The geologic record provides no clear answer to the question whether uplift caused the climatic deterioration of the Neogene or whether the changing climate affected the erosion system in such a way as to create an illusion of uplift. We suggest that the spread of C4 plants in the Late Miocene may have altered both the erosion and climate systems. These changes are responsible for the apparent contradictions between data supporting uplift and those supporting high elevations in the past.

The functional relationship between erosion rate and topography is central to understanding both controls on global sediment flux and the potential for feedback between tectonics, climate, and erosion in shaping topography. Analysis of a high-resolution (10-m-grid) DEM transect across the convergent orogen of the Olympic Mountains reveals a non-linear relation between long-term erosion rates and mean slope, similar to a model for hillslope evolution by landsliding in steep terrain. The DEM data also reveal a relation between mean slope and mean local relief. Coarser-scale (1-km-grid) global analysis of the relation between erosion rate and mean local relief reveals different trends for areas with low erosion rates and tectonically active mountain ranges, with the composite relation being well-described by non-linear models. Together these analyses support the emerging view that erosion rates adjust to high rates of tectonically driven rock uplift primarily through changes in the frequency of landsliding rather than hillslope steepness, and imply that changes in local relief play a minor role in controlling landscape-scale erosion rates in tectonically active mountain ranges. - 2002 Elsevier Science B.V. All rights reserved.

The proposal that climate change can drive the uplift of mountain summits hinges on the requirement that glacial erosion significantly enhances the relief of a previously fluvially sculpted mountain range. We have tested this hypothesis through a systematic investigation of neighbouring glaciated and nonglaciated drainage basins on the eastern side of the Sierra Nevada, CA. We present a simple, objective method for investigating the relief structure of a drainage basin, which shows noticeable differences in the spatial distribution of relief between nonglaciated and glaciated basins. Glaciated basins on the eastern side of the Sierra Nevada have only ∼80 m greater mean geophysical relief than nonglaciated basins. This “extra” relief, though, is attributable principally to the larger size of the glaciated basins, as geophysical relief generally increases with basin size. The glaciers on this side of the range were only responsible for relief production if they substantially increased headward erosion rates into low relief topography, such as an elevated plateau, and thus enlarged previously fluvial basins. We carried out a preliminary morphometric analysis to elucidate the importance of this effect and found that the glaciers of the eastern Sierra Nevada may have eroded headward at considerably faster rates than rivers, but only when they were not obstructed from doing so by either competing larger glaciers in adjacent valleys or transfluent ice at the head of the basin. Our results also suggest that, in temperate regions, alpine glaciers are capable of eroding downward at faster rates than rivers above the equilibrium line altitude (ELA). Although we can rule out significant peak uplift in response to local relief production, in the special case of the Sierra Nevada the concentration of mass removal above the ELA could have contributed to flexural uplift at the edge of a tilting block.

International audience; As several modeling studies indicate, the structural expression and dynamic behavior of oro-genic mountain belts are dictated not only by their rheological properties or by far-field tectonic motion, but also by the efficiency of erosion and sedimentation acting on its surface. Until recently, numerical inves-tigations have been mainly limited to 2-D studies because of the high computational cost required by 3-D models. Here, we have efficiently coupled the landscape evolution model Cascade with the 3-D thermome-chanically coupled tectonics code FANTOM. Details of the coupling algorithms between both codes are given. We present results of numerical experiments designed to study the response of viscous-plastic crustal materials subjected to convergence and to surface processes including both erosion and sedimentation. In particular, we focus on the equilibration of both the tectonic structures and on the surface morphology of the orogen. We show that increasing the efficiency of fluvial erosion increases the frontal thrust angle, which in turn decreases the width of the orogen. In addition, the maximum summit elevation of the orogen during transient evolution is significantly higher in those models showcasing surface processes than those that do not. This illustrates the strong coupling between tectonics and surface processes. We also demon-strate that an along-strike gradient of erosion efficiency can have a major impact upon the landscape mor-phology and the tectonic structure and deformation of the orogen, in both the across-strike and along-strike directions. Overall, our results suggest that surface processes, by enhancing localization of deforma-tion, can act as a positive forcing to topographic building.

Triangular interactions among climate, erosion and tectonics happen during the course of formation and development of a mountain range. In this study mountain range of Nyainqentanglha of Himalaya has been focused to assess which element played the vital role in this case. Altitude data of the catchments have been used as the primary key of analysis. Significant concentration of catchment areas near glacier equilibrium line altitudes (ELA) proved the presence of glacial buzzsaw mechanism. Swath analysis confirmed the presence of Teflon peak. Finally web of interrelationship has been explored behind the development of this mountainous range.