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The outstanding preservation of Paleolithic decorated caves is related to the buffering properties of their karstic environment. However, long-term monitoring of air/wall temperatures and gas compositions has recently revealed disruption signs in cave microclimates that had been maintained stable for hundreds of centuries. High precision and continuous temperature data records are currently monitored in various prehistoric caves in the South of France. Such operations have been promoted since the late 1990s by the French government for risk assessment and conservation. The most striking feature is the positive drift of underground temperatures (air and wall) which is now obvious in most sites except for Niaux Cave (> 300 m undersurface) and in the deepest parts of Mas-d’Azil and Chauvet Caves (> 50 m undersurface). In tourist caves (Pech-Merle, Mas-d’Azil, Gargas, Villars), the positive thermal trends could not be related to the energy increase brought by visitors which number is now stable, nor to the lighting systems whose energy demand was strongly reduced. In addition, the underground thermal drift nearly starts at the same time in many caves with uncertainties of +/- 1 year: 2012 for Chauvet with +0.4 °C/decade, 2011 for Pech Merle with +0.32 °C/decade, 2011 for Marsoulas Cave with +1.09 to +0.36 °C/decade from the entrance to the deep gallery, 2011 for Gargas with +0.69 °C, +0.54 °C and +0.36 °C for the deeper station. It is worth noting that a 0.3-0.4 °C thermal drift is consistent with that predicted from global warming in these regions. The thermal drifts were already in progress when monitoring began in Villars Cave in 1996 (+0.17 °C to +0.39 °C/decade), in Mas-d’Azil in 2012 and in Bruniquel in 2015. Marsoulas (+1.09 °C/decade) and Mas-d’Azil (more than +1 °C/decade in 6 of the 16 stations) present a much higher drift rate compared with that of surface, which suggests a thermal amplification process. As measurements are performed in heterothermal zones, the long-term thermal drifts are modulated by persisting smoothed and out-of-phase yearly variations. A notable exception is the case of Bruniquel main gallery where the temperature records show a quasi-linear increase. In that case, the decadal evolutions of temperature +0.31 °C, +0.175 °C, and +0.24 °C, are not related to the depth of monitoring stations (32 m, 55 m, and 38 m, respectively) nor to their distances from the entrance. In 2018, those drift rates induced a permanent inversion of thermal gradient in the main gallery. In Gargas, the drift rate is more pronounced in the outer parts of the karst body, thus inducing a continuous evolution of the thermal gradients within the galleries. Such underground microclimate disruption of patrimonial caves is a warning signal of direct threat on the preservation of remains. Karst physical organization and its related underground environment are themselves legacies of past climates; the current functioning of transfer zones of karst aquifers which includes the caves, are directly dependent on the outside climate. A more comprehensive approach and modelling of possible tipping points are urgently needed for conservation issues.

Coastal boulders or mega-clasts, named huracanolitos in Cuba, are found along many rocky shores. They result from storms/hurricanes or tsunamis, but despite being potentially important indicators for hazard assessment, their mode of emplacement is typically unknown. We studied a coastal boulder that is probably the largest one ever described on Cuba Island. Located on a low-lying coral reef terrace on the SE Cuban shore, the reefal limestone boulder is emplaced seaward of the ruins of the Bucanero resort. The latter was built in 1989, suffered from Hurricanes Ivan (2004) and Dennis (2005), and, in October 2012, was totally destroyed by Hurricane Sandy. Despite these extreme climatic events, satellite images obtained since 1962 show no movement of the block. In order to analyse the boulder and its morphological context, we have analysed its position, shape and its morphological environment. To determine its volume, we developed a low-cost, open-source Structure from Motion photogrammetry (SfM) procedure using a simple 3D spherical target (diameter 30 ± 0.2 x 10-3 m). Using various hydrodynamic equations, we calculated the breaking wave height and associated energy responsible for the dislocation of the coral reef terrace and transport of the boulder. To determine the exposure time of the block on the terrace, we performed 36Cl analysis and U/Th dating on post-depositional secondary calcite. From these data, the climatic or tsunamigenic (by earthquake or gravity event) origin is discussed. Notably, mapping and dating of a neighboring coastal landslide were made in order to correlate or not its effect on the setting up of the boulder.Keywords: coastal boulder; extreme-wave deposit; tsunami; hurricane; Cuba

The erosion of sandy beaches can have a profound impact on human activities and ecosystems, especially on developed coasts. The scientific community has, to date, primarily focused on the potential impact of sea-level rise on sandy beaches. While being abundantly recognized at local to regional scales in numerous studies over the last two decades, the contribution of diminishing fluvial sediment supply to sandy beach erosion at the global scale is still to be investigated. Here, we present the first global sand pathway model from land to sea. We show that recent sandy beach evolution trends worldwide are strongly controlled by fluvial sand input to the ocean, and that there is a global convergence of sand at the Equator due to wave-induced longshore transport. The reduction of sand supplies to beaches caused by river-basin changes such as dam constriction has a profound effect on beach stability. Our analysis demonstrates the massive impact of the thousands of river dams on beach erosion worldwide.

In global geochemical cycles, the solid flux from the continent to the ocean is usually reduced to the input of sediments from rivers [1]. However, regional studies have shown that the input of sediments from rocky coast erosion may be a significant part of this flux [2]. So, it is important to consider this input into global cycles and to quantify it over different timescales.On short-term timescales, from the year to the century, coastal erosion is currently quantified with direct measurement of the coastline retreat, between successive time intervals [3]. Extrapolating on timescales longer than a thousand years is difficult. This leads to a lack of data and therefore a gap in knowledge in longer term coastal erosion [4].A solution to quantify long-term erosion of rocky coast is to reconstruct the initial geometry of the coastline and to know the age of its formation. Volcanic islands are suitable objects for this method. Indeed, their initial shape is simple and can be easily reconstructed, and their maximum extension can be dated [5,6,7]. Thus, the topographic reconstruction of a volcanic island allows, by comparison with its current topography, the quantification of volumes lost by erosion. In turn, it becomes possible to obtain values of the rocky coast total retreat on timescales from thousands to hundreds of thousands of years [8].Another and complementary approach to quantify long-term erosion is the use of cosmogenic isotopes. This approach is widely used to date surface exposure and quantify long-term denudation rates in drainage basins [9]. The use of this approach to directly quantify sea-cliffs retreat is completely new. By sampling colluvial deposits resulting from coastal erosion of sea-cliffs, measuring cosmogenic 10Be and 3He concentrations, depending on the cliff lithology, may provide values on the retreat rate of the cliffs on the millennia timescale.It is interesting to test both approaches on volcanic islands. Indeed, their wide geographic distribution provides a diversity of climatic and geodynamic settings allowing to analyze the effects of various factors on long-term coastal erosion. We compare and discuss the results obtained by both methods on the island of Fogo (Cape Verde). [1] Milliman and Farnsworth (2013). Cambridge University Press.[2] Regard et al. (2022). Earth and Planetary Science Letters 579, 117356.[3] Bird (2011). John Wiley & Sons.[4] Prémaillon et al. (2018). Earth Surface Dynamics 6, 651-668.[5] Lahitte et al. (2012). Geomorphology 136, 148-164.[6] Ramalho et al. (2013). Earth-Science Reviews 127, 140-170.[7] Karátson et al. (2016). Geomorphology 253, 123-134.[8] Bossis et al. (in press).[9] Bierman et al. (1996). Earth Surface Processes and Landforms 21, 125-139.

Long-term coastal erosion is not yet well studied given that it is difficult to quantify. The quantification of long-term coastal erosion requires a proper reconstruction of the coast’s initial geometry. It is also important to determine the timing of the start-up. Volcanic islands are good candidates fulfilling these two conditions: their initial shape is roughly conical and the age of the lavas that generated this geometry is easily measured. We have developed a method to reconstruct the initial shape of simple volcanic edifices from aerial and submarine topographic data. The reconstructed initial shape and associated uncertainties allow us to spatially quantify the coastal erosion since the building of the island. This method is applied to Corvo Island in the Azores archipelago. We calculated the initial radius and peak elevation of the island to be approximately 3.8 km and 1 km, respectively. We calculated that, due to coastal erosion, the island has lost a volume of 6.5 ± 2.7 km3 corresponding to a reduction of roughly 80 % of its surface area since it was first built. Taking the large uncertainty in the age of the topmost lava flows (90 to 770 ka) into account, our reconstruction yields a conservative range of long-term coastal erosion rates between 7 and 370 mm/yr. These values are consistent with the orders of magnitude of short-term coastal erosion rates measured on similar lithologies. Lastly, we show a strong correlation between long-term coastal erosion and the spatial distribution of the waves. Specifically, we highlight a stronger erosion control by moderate and usual waves than by storm waves. The next step will be to apply this method to other volcanic islands in order to: (i) strengthen and consolidate the method, and (ii) verify the correlations observed in the present study.

In global geochemical cycles, the solid flux from the continent to the ocean is usually reduced to the input of sediments from rivers [1]. However, regional studies have shown that the input of sediments from rocky coast erosion may be a significant part of this flux [2]. So, it is important to consider this input into global cycles and to quantify it over different timescales.On short-term timescales, from the year to the century, coastal erosion is currently quantified with direct measurement of the coastline recession, between successive time intervals [3]. Extrapolating on timescales longer than a thousand years is difficult. This leads to a lack of data and therefore a gap in knowledge in longer term coastal erosion [4].A solution to quantify long-term erosion of rocky coast is to reconstruct the initial geometry of the coastline and to know the age of its formation. Volcanic islands are suitable objects for this method. Indeed, their initial shape is simple and can be easily reconstructed, and their maximum extension can be dated [5,6,7], although this age can be difficult to estimate. Thus, the topographic reconstruction of a volcanic island allows, by comparison with its current topography, the quantification of volumes lost by erosion. In turn, it becomes possible to obtain values of the rocky coast total recession on timescales from thousands to hundreds of thousands of years [8]. Moreover, the wide geographic distribution of volcanic islands provides a diversity of climatic and geodynamic settings allowing to analyze the effects of various factors on long-term coastal erosion.Here we propose an improvement of this erosion quantification by accounting for the submarine morphology. Applying this approach for different volcanic islands, we carried out a statistical analysis of the impact of several factors that control long-term coastal erosion. This analysis allows us hierarchize these factors. This is the first step towards the formulation of long-term coastal erosion universal laws and towards the quantification of rocky coast sediment influx in global cycles. [1] Milliman and Farnsworth (2013). Cambridge University Press.[2] Regard et al. (in press).[3] Bird (2011). John Wiley & Sons.[4] Prémaillon et al. (2018). Earth Surface Dynamics 6, 651-668.[5] Lahitte et al. (2012). Geomorphology 136, 148-164.[6] Ramalho et al. (2013). Earth-Science Reviews 127, 140-170.[7] Karátson et al. (2016). Geomorphology 253, 123-134.[8] Bossis et al. (in press).

The eroding rocky coasts export sediment to the ocean, the amount of which is poorly known. At the global scale it could amounts 0.15-0.4 Gt/a (1). Recent evaluations of large retreat rates on monitored sections of sea cliffs indicate it can be comparable to the sediment input from medium to large rivers. We quantify rocky coast input to the ocean sediment budget at the European scale, the continent characterized by the best dataset.The sediment budget from European rocky coasts has been computed from cliff lengths, heights and retreat rates. For that, we first compiled a large number of well-documented retreat rates; the analysis of whom showed that the retreat rates are at first order explained by cliff lithology (GlobR2C2, 2). Median erosion rates are 2.9 cm/a for hard rocks, 10 cm/a for medium rocks and 23 cm/a for weak rocks. These retreat rates were then applied to the European coast classification (EMODnet), giving the relative coast length for cliffs of various lithology types. Finally the cliff height comes from the EU-DEM (https://ec.europa.eu/eurostat/web/gisco/geodata/reference-data/elevation).Due to data availability, we only worked on ~70% of the whole Europe, corresponding to a 127,000 km-long coastline (65,000 km of rocky coast). We calculated it originates 111±65 Mt/a, corresponding to 0.38 times the sediment input from rivers from the equivalent area (3.56 106 km2), calculated after Milliman and Farnsworth (3)’s database (290 Gt/a). A crude extrapolation to the 1.5 106 km-long Earth’s coastline reaches an amount of 0.6-2.4 Gt/a, an order of magnitude less that the sediment discharge from rivers (11-21 Gt/a, e.g., 3).This up-to-now overlooked sedimentary source must further be explored for: (i) its effects on the geochemical ocean budget; (ii) the rising sea level control on the cliff retreat rates; and (iii) the characteristics and location of sediment deposition on ocean margins. References(1) Mahowald NM, Baker AR, Bergametti G, Brooks N, Duce RA, Jickells TD, Kubilay N, Prospero JM, Tegen I (2005). Atmospheric global dust cycle and iron inputs to the ocean: ATMOSPHERIC IRON DEPOSITION. Global Biogeochemical Cycles 19. DOI: 10.1029/2004GB002402(2) Prémaillon M, Regard V, Dewez TJB, Auda Y (2018). How to explain variations in sea cliff erosion rates? Insights from a literature synthesis. Earth Surface Dynamics Discussions:1–29. DOI: https://doi.org/10.5194/esurf-2018-12(3) Milliman J, Farnsworth K (2011). River Discharge to the Coastal Ocean: A Global Synthesis. Cambridge University Press

The Atacama rocky coast in Northern Chile is a tectonically active region that displays a particular morphological assemblage along its extension. There is a major morphostructural element named the Great Coastal Cliff (GCC) that runs parallel to the coastline for almost 1000 km in hyper-arid conditions. This cliff reaches heights between 800 and 2000 m a.s.l. and its continuity is only interrupted by a few, great fluvial valleys that drain from the High Andes and by several, small creeks of the Coastal Cordillera. At the mouth of these creeks and valleys, it is possible to recognize sequences of staircased marine terraces formed and preserved by the interplay between the tectonic uplift, sea-level changes, and marine erosion action. The Pan de Azúcar National Park (~26°) is a segment of the Atacama rocky coast which exhibit a morphological segmentation along strike into three domains that shows how the GCC is limited by areas characterized by marine terraces: one domain with a high, steep scarp (>500 m) that sits on top a single shore platform, and two domains with a further inland, degraded cliff (heights 1.5 m2/yr (1.5 m3 for one meter of coast length) to develop the morphology of the GCC without stair-cased terraces. Instead, much lower erosion rates of 0.25-0.5 m2/yr or less are necessary to reproduce a shorter cliff with different terraces, i.e. low erosion rates to preserve terraces. This erosion variability is likely due to alongshore gradients in erosion efficiency by sediments-fed beaches that act as natural barriers against incoming waves, dissipating their energy. These sediments are provided by creeks with large catchment areas that discharge into the Pacific Ocean.

(IF 2.45; Q2); International audience; We explore the coastal morphology along an uplifting 500 km-long coastal segment of the Central Andes, between the cities of Chala (Peru) and Arica (Chile). We use accurate DEM and field surveys to extract sequences of uplifted shorelines along the study area. In addition, we consider continental pediment surfaces that limit both the geographical and vertical extent of the marine landforms. We establish a chronology based on published dates for marine landforms and pediment surfaces. We expand this corpus with new 10Be data on uplifted shore platforms. The last 12 Ma are marked by three periods of coastal stability or subsidence dated ~12-11 Ma, ~8-7 Ma and ~5–2.5 Ma ago. The uplift that accumulated between these stability periods has been ~1000 m since 11 Ma; its rate can reach 0.25 mm/a (m/ka). For the last period of uplift only, during the last 800 ka, the forearc uplift has been accurately recorded by the carving of numerous coastal sequences. Within these sequences, we correlated the marine terraces with the sea level highstands (interglacial stages and sub-stages) up to MIS 19 (790 ka), i.e., with a resolution of ~100 ka. The uplift rate for this last period of uplift increases westward from 0.18 mm/a at the Peru-Chile border to ~0.25 mm/a in the center of the study area. It further increases northwestward, up to 0.45 mm/a, due to the influence of the Nazca Ridge. In this study, we document an unusual forearc cyclic uplift with ~4 Ma-long cycles. This periodicity corresponds to the predictions made by Menant et al. (2020) based on numerical models, and could be related to episodic tectonic underplating (subducting slab stripping) beneath the coastal forearc area.

The current retreat of the world's coastline has a profound impact on human activities and ecosystems. The scientific community has primarily focused on the potential impact of sea level rise. At the global scale, the contribution of river sand loads to coastal erosion has been overlooked. Here we present the first global sand pathway model from land to sea. Our model reveals that sand tends to accumulate towards tropical regions. We show that the recent shoreline evolution is significantly controlled by the imbalance in the sand budget, challenging the idea that sea level rise due to climate change is currently the main driver of coastal erosion. Our model highlights that the significant reduction in sand supply due to tens of thousands of river dams and its consequences on coastal erosion could be avoided by an effective sustainable management policy.

International audience

Several rivers of Chile from the latitude 30 degrees-38 degrees have been sampled during a stable anticyclonic period (October 2008). Firstly, our aim was to evaluate the dissolved chemical composition (major and trace elements) of poorly known central Chilean rivers. Secondly, we used a co-inertia analysis (see Doledec and Chessel in Freshw Biol 31:277-294, 1994) to explore the possible relationships between the concentrations of elements and the environmental parameters [surface of the basin (km(2))/mining activity (%)/average height (m)/watershed mean slope (%)/% of the surface covered by vegetation, sedimentary rocks, volcano-sedimentary rocks, volcanic rocks, granitoid rocks/erosion rate (mm/year)]. Globally, the major elements concentration could be explained by a strong control of mixed silicate and carbonate and evaporate lithology. The statistical treatment reveals that the highest metal and metalloids loads of Tinguiririca, Cachapoal, Aconcagua, Choapa, Illapel and Limari could be explained by the contribution of the mining activities in the uppermost part of these watersheds and/or by the higher geochemical background. Indeed, it remains difficult to decipher between a real mining impact and a higher geochemical background. Even if these rivers could be impacted by AMD process, the size of these watersheds is capable of diluting AMD waters by the alkaline character of tributaries that induce acid neutralization and decrease the level of metals and metalloids.

We explore the coastal morphology along an uplifting 500 km-long coastal segment of the Central Andes, between the cities of Chala (Peru) and Arica (Chile). We use accurate DEM and field surveys to extract sequences of uplifted shorelines along the study area. In addition, we consider continental pediment surfaces that limit both the geographical and vertical extent of the marine landforms. We establish a chronology based on published dates for marine landforms and pediment surfaces. We expand this corpus with new 10Be data on uplifted shore platforms. The last 12 Ma are marked by three periods of coastal stability or subsidence dated ~12-11 Ma, ~8-7 Ma and ~5-2.5 Ma ago. The uplift that accumulated between these stability periods has been ~1000 m since 11 Ma; its rate can reach 0.25 mm/a (m/ka). For the last period of uplift only, during the last 800 ka, the forearc uplift has been accurately recorded by the carving of numerous coastal sequences. Within these sequences, we correlated the marine terraces with the sea level highstands (interglacial stages and sub-stages) up to MIS 19 (790 ka), i.e., with a resolution of ~100 ka. The uplift rate for this last period of uplift increases westward from 0.18 mm/a at the Peru-Chile border to ~0.25 mm/a in the center of the study area. It further increases northwestward, up to 0.45 mm/a, due to the influence of the Nazca Ridge. In this study, we document an unusual forearc cyclic uplift with ~4 Ma-long cycles. This periodicity corresponds to the predictions made by Menant et al. (2020) based on numerical models, and could be related to episodic tectonic underplating (subducting slab stripping) beneath the coastal forearc area.

International audience; The widening and deepening of river valleys occur at different rates. This co evolution is largely undocumented over thousands of years. Uncertainties on incision and widening laws limit the ability of models to reproduce erosion rates and responses to tectonics and climate over geologic timescales. We studied two 1 km deep canyons in northern Chile, both characterized by valley widening after the upward migration of a major knickzone but with a diachronous incision initiation. We use 10Be concentrations measured in colluvial deposits to quantify the erosion rates E of along stream valley flanks. We observe that E increases in the knickzone, with well defined relationships (R2 = 0.7): E increases quasilinearly with the valley bed slope and decreases with the valley width (exponent ∼ 0.4). Our results suggest that E decreases with time but that valley flank weathering may sustain a significant lateral erosion rate. Our results provide data for testing erosion laws governing valley widening.

River sediment grains are transported and stored episodically in different reservoirs (terraces, alluvial fans, foreland basin, etc.). The residence time of sediment grains in each reservoir has important implications for the paleo-environmental interpretation established from these grains, and their stratigraphic record, as well as for soil contamination, when these grains come from contaminated sources. The recycling of old sediments, via erosion of an old reservoir (e.g. foreland basin erosion), is a known problem. What is less well recognised is that the recycling of a minority of very old grains can strongly bias the average residence time of a grain population deposited in a stratum. In this case, the time-dependent paleo-environmental properties of a population of grains, such as the degree of weathering, or the concentration of cosmogenic isotopes, can then be biased. Several lines of evidence for this phenomenon, inherent to fluvial transport processes, have emerged, though reconstructing the residence time distribution of a grain population over long times (>>ka) remains a challenge. Using a landscape evolution model coupled with grain transport, we show that at the scale of a piedmont, grains can remain several hundred ka before being evacuated. At the scale of a river in Northern Chile, we used the concentration of 10Be in individual pebbles to show that some pebbles remain stored for several tens of ka before being evacuated to the river outlet. In addition, the distribution of residence times can also provide information on the nature of the diffusive processes that control the fluxes of exported sediment. These results suggest that the characterisation of grain-by-grain properties in a grain population can not only help to avoid possible interpretation biases but also provide constraints for models of long-term fluvial sediment outfluxes.

The global solid flux from continent to ocean is usually reduced to the input of sediments from rivers, and is estimated at approximately 20 Gt/year. Another input of sediments to ocean is coastal erosion, but this flux is difficult to estimate on a global scale and it is often neglected, perhaps wrongly according to regional studies [1,2]. Most studies attempting to quantify coastal erosion have focused on the coasts of developed countries and are limited to the timescale of decades or less [3]. The difficulty in quantifying long-term coastal erosion is that there are still many uncertainties about the factors controlling coastal erosion on this time scale, and it would be necessary to know the initial geometry of coastlines to calculate an eroded volume.Volcanic islands, as geomorphological objects, seem to be very good objects of study to remedy these limitations. Indeed, many young volcanic islands are made of only one central edifice with a strong radial symmetry despite its degradation by erosion [4,5]. By knowing the age of an island and by comparing reconstructed shape with current shape, we can calculate a total eroded volume and an integrated average coastal erosion rate on the age of the island. Moreover, due to their geographical, petrological and tectonic diversity, volcanic islands allow to compare the influence of different factors on long-term coastal erosion, such as climate, wave direction and height, rock resistance or vertical movements. Thus, we will be able to prioritize them to propose coastal erosion laws that would applicable to all rocky coasts.Here we built on previous works that have used aerial geospatial databases to reconstruct the initial shape of these islands [6,7] but we improve this approach by using offshore topographic data to determine the maximum and initial extension of their coasts. From both onshore and offshore topographies, we determine a long-term mean coastal erosion rate and we quantify precisely its uncertainty. Using the example of Corvo Island, in the Azores archipelago, we show how our approach allows us to obtain first estimates of long-term coastal erosion rate around this island. References [1] Landemaine V. (2016). Ph.D. thesis, University of Rouen.[2] Rachold V., Grigoriev M.N., Are F.E., Solomon S., Reimnitz E., Kassens H., Antonow M. (2000). International Journal of Earth Sciences, 89(3), 450-460.[3] Prémaillon M. (2018). Ph.D. thesis, University of Toulouse.[4] Karátson D., Favalli M., Tarquini S., Fornaciai A., Wörner G. (2010). Journal of Volcanology and Geothermal Research, 193, 171-181.[5] Favalli M., Karátson D., Yepes J., NannipierI L. (2014). Geomorphology, 221, 139-149.[6] Lahitte P., Samper A., Quidelleur X. (2012). Geomorphology, 136, 148-164.[7] Karátson D., Yepes J., Favalli M., Rodríguez-Peces M.J., Fornaciai A. (2016). Geomorphology, 253, 123-134.

Submerged marine terraces potentially provide crucial information on past sea-level variations and paleo-coastline locations that may be used to estimate long-term coastal erosion rates. The Normandy coastline has recently been surveyed using a shallow water high-resolution mapping system. We identified a new continuous submarine platform, called the inner platform, limited by a shore parallel edge located between -9 m and -10 m (NGF) along the Normandy chalk coastline. A lower rock platform, called the outer platform, ranging from about -14 m to -17 m (NGF) appears locally. This corresponds to inherited preserved submarine terraces created during a past sea level highstand. The high cosmogenic 10Be concentration measured at the end of Mesnil-Val inner shore platform (including intertidal and subtidal shore platforms) is attributed to the last glacial cliff location at 6.5 ky ± 1 ky. From the spatial edge location of the inner platform in Normandy, we estimated cliff retreat rates since 6.5 ky ± 1 ky ranging from 0.051 ± 0.008 m/y to 0.090 ± 0.014 m/y from place to place. Comparisons with the current coastal chalk cliffs indicate a mean retreat rate estimated over the contemporary period suggesting such long-term retreat rates are 33% to 57% lower than the contemporary ones (0.10 m/y to 0.18 m/y). This confirms a contemporary acceleration of chalk cliff system retreat rates.

International audience; Sea cliff morphology and erosion rates are modulated by several factors, including rock control that reflects both lithology and rock structure. Erosion is anticipated to preferentially exploit ‘fractures’, broadly meant as any discontinuity in an otherwise continuous medium, where the rock mass is weakest. Unpicking the direct control of such fractures on the spatial and temporal pattern of erosion remains, however, challenging. To analyse how such fractures control erosion, we monitored the evolution of a 400 m-long stretch of highly structured sedimentary cliffs in Socoa, Basque Country, France. The rock is known as the Socoa flysch formation. This formation combines decimetre-thick turbidites composed of repeat triplets of medium to strong calcareous sandstone, laminated siltstones and argillaceous marls. The sequence plunges at 45° into the sea with a shore-parallel strike. The cliffs are cross-cut by two normal and reverse fault families, with 10–100 m alongshore spacing, with primary and secondary strata-bound fractures perpendicular to the bedding, which combined delimit the cliff rock mass into discrete blocks that are exploited by the erosion process. Erosion, and sometimes plucking, of such beds and blocks on the cliff face was monitored using ground-based structure-from-motion (SfM) photogrammetry, over the course of 5.7 years between 2011 and 2017. To compare with longer time change, cliff-top retreat rate was assessed using SfM-orthorectified archive aerial photographs spanning 1954–2008. We show that the 13,250 m2 cliff face released 4500 blocks exceeding 1.45 × 10−3 m3, removing a total volume of 170 m3. This equates to an average cliff erosion rate of 3.4 mm/year, which is slightly slower than the 54-year-long local cliff-top retreat (10.8 ± 1.8 mm/year). The vertical distribution of erosion reflects the height of sea water inundation, where the maximum erosion intensity occurs ca. 2 m above high spring-tide water level. Alongshore, the distribution of rockfall scars is concentrated along bed edges bounding cross-cutting faults; the extent of block detachment is controlled by secondary tectonic joints, which may extend through several beds locally sharing similar mechanical strength; and rockfall depth is always a multiple of bed thickness. Over the longer term, we explain block detachment and resultant cliff collapse as a cycle. Erosion nucleates on readily exploitable fractures but elsewhere, the sea only meets defect-free medium-strong to strong rock slabs offering few morphological features for exploitation. Structurally delimited blocks are quarried, and with sufficient time, carve semi-elliptic scars reaching progressively deeper strata to be eroded. Lateral propagation of erosion is directed along mechanical weaknesses in the bedding, and large episodic collapses affect the overhanging slabs via sliding on the weak marl beds. Collapse geometry is confined to one or several triplets of turbidite beds, but never reaches deeper into the cliff than the eroded depth at the foot. We contend that this fracture-limited model of sea-cliff erosion, inferred from the Socoa site dynamics and its peculiar sets of fractures, applies more broadly to other fractured cliff contexts, albeit with site-specific geometries. The initiation of erosion, the propagation of incremental block release and the ultimate full failure of the cliff, have each been shown to be fundamentally directly controlled by structure, which remains a vital control in understanding how cliffed coasts have changed in the past and will change in the future.

International audience; The Ebro Basin constitutes the central part of the southern foreland of the Pyrenees. It was endorheic during the Cenozoic and accumulated sediments. By the end of the Miocene, erosion and river incision reconnected the basin to the Mediterranean Sea, establishing a post-opening drainage network. Those rivers left terraces that we study in this work. We first synthesize previous works on river terraces that are widely dispersed in the basin. We provide new age constraints, up to 3 Ma, obtained thanks to cosmogenic nuclides using both profile and burial methods. We derive a unified fluvial terrace chronology and a homogenized map of the highest terraces over the entire Ebro Basin. The dated terraces labeled A, B, C, D, and E are dated to 2.8±0.7 Ma, 1.15±0.15 Ma, 850±70 ka, 650±130 ka, and 400±120 ka, respectively. The chronology proposed here is similar to other sequences of river terraces dated in the Iberian Peninsula, around the Pyrenees, and elsewhere in Europe. The oldest terraces (A, B, C) are extensive, indicating they form a mobile fluvial network while from D to present, the network was stable and entrenched by 100 to 200 m-deep valleys. The transition from mobile to a fixed fluvial network is likely to have occurred during the Middle Pleistocene Transition (MPT, between 0.7 and 1.3 Ma), when long-period/high-intensity climate fluctuations were established in Europe. We estimate that between 2.8-1.15 Ma and present, the incision rates have tripled.; Le bassin de l’Ebre constitue le centre du piémont sud-pyrénéen. Il a été endorhéique et a accumulé une épaisseur importante de sédiments au cours du Cénozoique. Vers la fin du Miocène, l'érosion et l'incision fluviale ont reconnecté le bassin à la mer Méditerranée, en établissant un nouveau réseau de drainage. Les rivières constituant ce réseau ont laissé des terrasses que nous étudions dans le cadre de ce travail. Nous faisons d'abord une synthèse des travaux antérieurs sur les terrasses fluviales, qui sont largement dispersées dans le bassin. Ensuite, nous fournissons de nouvelles contraintes d'âge, jusqu'à 3 Ma, obtenues grâce aux nucléides cosmogéniques utilisant à la fois des méthodes de profil d’exposition et d'enfouissement. Enfin, nous en déduisons une chronologie unifiée des terrasses fluviales et une carte homogénéisée des terrasses les plus hautes sur l'ensemble du bassin de l'Ebre. Les terrasses, que nous notons A, B, C, D et E, sont datées respectivement de 2,8±0,7 Ma, 1,15±0,15 Ma, 850±70 ka, 650±130 ka et 400±120 ka. La chronologie proposée ici est similaire à d'autres séquences de terrasses fluviales datées dans la péninsule ibérique, autour des Pyrénées, et ailleurs en Europe. Les terrasses les plus anciennes (A, B, C) sont étendues, ce qui témoignent d’un réseau fluvial mobile alors que depuis la formation des terrasses D jusqu’à aujourd'hui, le réseau était stable et canalisé le long de vallées de 100 à 200 m de profondeur. Le passage d'un réseau fluvial mobile à un réseau fluvial fixe s'est probablement produit pendant la transition du Pléistocène moyen (entre 0,7 et 1,3 Ma), lorsque des fluctuations climatiques de longue période et de forte intensité ont été établies, comme l'ont déjà proposé Gibbard et Lewin (2009) pour les rivières européennes. Nous estimons qu'entre 2,8 et 1,15 Ma et la période actuelle, les taux d'incision ont triplé.

The geochemical and physical properties of terrigenous sediment stacked in sedimentary basins are used as proxies for the paleo-environmental conditions that prevailed during their period of deposition. Nevertheless, sediment grains have a stochastic transit from mountain sources to sedimentary basins: a fraction of grains are stored for a long time while others are recycled from old deposits. Consequently, the temporal representativity of a population of grains in a sedimentary stratum is uncertain. The potential recycling of old material is a major concern in the reconstruction of paleo-environments and this recycling is usually difficult to evaluate. In particular, the distribution of grain residence times in basins, between sources and sinks, is out of reach. Here we use a landscape evolution model that traces grains to analyse the distribution of residence times in an alluvial apron at the foot of a mountain relief. We study an end-member scenario that is the least favourable for the storage of grains: when the mountain is eroding at the same rate as rock is uplifting. In this case, the alluvial apron behaves as a by-pass zone, when averaging sediment flux over Ma, and the storage of grains of any size should be minimal. Yet, the model predicts that some grains are stored for hundreds of thousands of years before exiting the alluvial apron. Consequently, the mean residence time of sediment grains is much higher than the observed residence time of 95% of the grains exported by the alluvial apron rivers. This process may explain very long residence times found in fluvial systems by geochemical methods based on bulk measurements of sediment. Furthermore, it suggests that grains stored for a very long time, although a minority, can bias time-dependent proxies.(C) 2020 Elsevier B.V. All rights reserved.

Shortening of the continental lithosphere is generally accommodated by the growth of crustal wedges building above megathrusts in the mantle lithosphere. We show that the locus of shortening in the western margin of South America has largely been controlled by the geometry of the slab. Numerical models confirm that horizontal subduction favors compression far from the trench, above the asthenospheric wedge and steeply dipping segment of the subducting slab. As a result, a second crustal wedge grows in the hinterland of the continent, and widens the Andes. In the Bolivian orocline, this wedge corresponds to the Eastern Cordillera, whose growth was triggered by a major episode of horizontal subduction. When the slab returned to a steeper dip angle, shortening and uplift pursued, facilitated by the structural and thermo-chemical alteration of the continental lithosphere. We review the successive episodes of horizontal subduction that have occurred beneath South America at different latitudes and show that they explain the diachronic widening of the Andes. We infer that the present-day segmented physiography of the Andes results from the latitudinally variable, transient interplay between slab dynamics and upper plate tectonics over the Cenozoic. We emphasize that slab flattening, or absence thereof, is a major driving mechanism that sets the width of the Andes, at any latitude.

Sea cliff shapes and erosion rates are controlled by several factors. Among them, rock resistance, whose strength results from lithology and rock structure, are pointed as major factors. Erosion is expected to focus on discontinuities where the rock mass is weakest (faults, fractures, joints and strata bounds), but understanding the control of discontinuities on the spatial and temporal pattern of erosion remains challenging. To analyze and quantify how rock structures control erosion, we monitored the evolution of a 400-m-long stretch of well-structured sedimentary cliffs: the Socoa cliff (Basque Country, France). The rock, known as the Socoa flysch formation, is a 45°-seaward-tilted, shore-parallel-striking, decimeter-thick repeating sequence of sandstone, mudstone, marl and limestone beds. Cliff-face erosion was observed and quantified using 6 ground-based Structure-from-Motion (SfM) surveys, spanning 5.7 years between 2011 and 2017. To compare with longer term data, a multi-decadal (54 years) cliff-top retreat rate was also assessed using SfM-orthorectified archive aerial photographs spanning the period 1954-2008. During the ground-based survey, the 13 250 m² cliff face released 4500 blocks larger than 1.45*10-3 m3 for a total rock volume eroded of 170 m3. This rock lost volume equates to an average cliff retreat rate of 3.4 mm/yr. It is slightly slower than the 54 years-average cliff top retreat rate of 10.8 ± 1.8 mm/yr. In elevation, the maximum erosive activity is positioned about 2 m above high spring tides. The geographic position of rock scars is controlled by tectonic discontinuities. Alongshore, hot-spots of erosion are focused where major faults cross-cut the cliff face. Around these geographic hotspots, the depth of detached blocks is controlled by bed thickness, removing one or several beds at once. The surficial extent of detached blocks on the cliff-face is controlled by orthogonal secondary tectonic joint sets. These joints do not stop on lithological bed limits but rather on mechanical limits encompassing several lithological beds at once. As a process, we explain block detachment and cliff collapse by a cycle of erosion nucleation on discontinuities, radial erosion propagation around the nuclei and finally, cliff collapse crisis affecting the cliff top. We demonstrate that block production is concentrated around faults (nucleation) that focus erosion and allows for the radial development of sea caves close to cliff foot. Then, block production occurs mainly around those caves by radial detachment processes at free edges or fractures (propagation). It may lead, exceptionally, to high-magnitude events, during which slab collapse can affect the cliff from base to top (crisis).

At the global scale and on geological time scales, mechanical erosion and chemical weathering budgets are linked. Together, these processes contribute to the formation and the degradation of the Earth’s critical zone and to the biogeochemical cycles of elements. While the weathering of hot and humid shields areas exhibit low weathering rates because of the depth of the mature depleted soil mantle there, shields areas dominate the continents areas over intertropical regions and, therefore, represent a significant proportion of the global delivery of dissolved matter to the oceans. In addition, these environments are under supply-limited conditions (the weathering rate is limited by the low rates of the erosion) and thus particularly sensitive to long-term variability erosion rates. Despite this importance, weathering-erosion budgets and rates estimation in these environments is sparse, and generally performed at a local scale (soil profiles) or, when performed at a larger catchment scale, the intra cratonic characteristics variabilities (e. g. the diversity of mechanical erosional regimes) are usually not singled out.In the present study, we explored the variability of the weathering intensity of the Ogooué sub-basins (Western central Africa, Gabon) as a function of their geomorphologic, tectonic and lithological setting variability. We analyzed major and trace elements concentration and the strontium and neodymium isotopes of water, suspended matter sediments and bedload sampled in 24 Ogooué tributaries (September 2017 campaign). Our results show that shield areas exhibit a high variability of chemical weathering intensity, which follows the erosional regime characteristics of the studied sub-basins, likely related to their tectonic activity. Three regions can be distinguished: The Bateke plateau (East sub-basins - PB), is composed of pure sandstones (quartz) and is inert in term of tectonic activity and therefore in term of erosion and weathering budget; the northern sub-basins (NB) are subjected to low tectonic activity and exhibit slightly higher erosion and weathering intensity than PB region and, by comparison, southern sub-basins (SB) exhibits uplift activity which is traduced by more intensive erosion and weathering processes.The annual dissolved solid budget of the Ogooué basin is ~2.52 t.yr-1 for a rate of 11.7 t.km-2.yr-1. According to the source discrimination method performed based on the geochemical analysis, the atmospheric inputs contributes to around 20% to the TDS, the silicate weathering contribution dominates the dissolved exports throughout 70% of its production while the carbonates weathering lowly contributes to the TDS production.By comparison to the other large shields rivers, this basin exhibit a lower range of chemical silicate weathering rate than most of the world’s large rivers, with values similar to those of the Congo River. This new dataset provides a key information to complete the World River chemistry database, which is limited for inter-tropical regions, especially in tectonically quiescent environments. Moreover, this study provides new data for tropical shields contexts allowing for the exploration of the interactions between erosion rates and climate in the control of continental weathering rates, and their relationships with long-term carbon cycle and short-term biogeochemical cycles.

The downstream increase in valley width is an important feature of fluvial landscapes that may be evident to anyone: even if local exceptions exist, wide fluvial valleys in plains are distinctive of narrow upstream mountainous ones. Yet, the processes and rates governing along-stream valley widening over timescales characteristic of landscape development (>1-10 ka) are largely unknown. No suitable law exists in landscape evolution models, thus models imperfectly reproduce the landscape evolution at geological timescales, their rates of erosion and probably their response to tectonics and climate. Here, we study two 1 km-deep canyons in northern Chile with diachronous incision initiation, thus representing two time-stage evolutions of a similar geomorphic system characterized by valley widening following the upward migration of a major knickzone. We use 10Be cosmogenic isotope concentrations measured in colluvial deposits at the foot of hillslopes to quantify along-stream valley flank erosion rates. We observe that valley flank erosion rate increases quasi-linearly with valley-bed slope and decreases non-linearly with valley width. This relation suggests that lateral erosion increases with sediment flux due to higher channel mobility. In turn, valley width exerts a negative feedback on lateral valley flank erosion since channels in wide valleys have a lower probability of eroding the valley sides. This implies a major control of river divagation on valley flank erosion rate and valley widening. Our study provides the first data for understanding the long-term processes and rates governing valley widening in landscapes.

The topography of continents is a dynamic interface that evolves in response to several external (tectonics, mantle dynamics, climate) or internal factors to the geomorphic system. If these systems tend naturally toward a steady-state, they often show transient regimes as evidenced by retreating knickpoints, fluvial captures or migrating divides. These two last phenomena are indicative of drainage reorganization and imply the growth of a network at the expense of another. Yet, the rate of drainage network growth is very poorly known. To our knowledge for example, only one study (Craddock et al., 2010) has attempted to constrain the rate of growth of a natural drainage network, in the specific case of a growth by sequential captures of endorheic systems.Our aim here is to constrain the mechanism, timing and rates of network growth and drainage reorganization in a natural setting located in southwest France (Aude river catchment), in a current anorogenic setting in the northern foreland of the Pyrenees.Geomorphic evidence indicate that this catchment is enlarging with about 40 km of displacement of its main divide in the last few hundreds of thousand years (precise timing under investigation). The Aude river and main tributaries show flight of strath terraces that converge downward over ~150 km long distance. This specific fan-shape of paleo-longitudinal profiles implies an upward increase of fluvial incision that we interpret as the consequence of a long-term growth of the Aude drainage network. The dating of these terrace system using cosmogenic isotopes (in-situ 10Be depth-profiles and 10Be-26Al burial isochrones) and Electron Spin Resonance (ESR) is under progress and will allow us to quantify the longitudinal trend of differential incision through time, which we will use to estimate the rate of drainage network growth and divide migration. To support these results, an analysis of the catchment-wide erosion rates on both sides of the migrating divide is also performed. First preliminary results indicate catchment-wide erosion rates of 0.06-0.08 mm.yr-1 in the Aude river catchment.In complement to this natural case study, the main question of network growth dynamic is also addressed through laboratory-scale experiments performed at the Géosciences Environnement Toulouse (GET) laboratory. The first results show that the divide migration rate related to drainage network growth depends positively on the uplift/base level fall rate. In the detail, the divide migration rate is however non-linear, it evolves step by step with periods of acceleration when cyclic retreating knickpoints hit the divide.

The Cotentin Peninsula (Normandy, France) displays sequences of marine terraces and rasas, the latter being wide Late Cenozoic coastal erosion surfaces, that are typical of Western European coasts in Portugal, Spain, France and southern England. Remote sensing imagery and field mapping enabled reappraisal of the Cotentin coastal sequences. From bottom to top, the N Cotentin sequence includes four previously recognized Pleistocene marine terraces (T1 to T4) at elevations < 40 m as well as four higher and older rasas (R1 to R4) reaching 200 ± 5 m in elevation. Low-standing marine terraces are not observed in the central part of the Peninsula and a limited number of terraces are described to the south. The high-standing rasas are widespread all over the peninsula. Such strandline distributions reveal major changes during the Late Cenozoic. Progressive uplift of an irregular sea-floor led to subaerial exposure of bathymetric highs that were carved into rocky platforms, rasas and marine terraces. Eventually, five main islands coalesced and connected to the mainland to the south to form the Cotentin Peninsula. On the basis of previous dating of the last interglacial maximum terrace (i.e. Marine Isotopic Stage, MIS 5e), sequential morphostratigraphy and modelling, we have reappraised uplift rates and derived: (i) mean Upper Pleistocene (i.e. since MIS 5e ~ 122 +/− 6 ka, i.e. kilo annum) apparent uplift rates of 0.04 ± 0.01 mm/yr, (ii) mean Middle Pleistocene eustasy-corrected uplift rates of 0.09 ± 0.03 mm/yr, and (iii) low mean Pleistocene uplift rates of 0.01 mm/yr. Extrapolations of these slow rates combined with geological evidence implies that the formation of the sequences from the Cotentin Peninsula occurred between 3 Ma (Pliocene) and 15 Ma (Miocene), which cannot be narrowed down further without additional research. Along the coasts of Western Europe, sequences of marine terraces and rasas are widespread (169 preserve the MIS 5e benchmark). In Spain, Portugal, S England and other parts of western France, the sequences morphostratigraphy is very similar to that of Cotentin. The onset of such Western European sequences occurred during the Miocene (e.g. Spain) or Pliocene (e.g. Portugal). We interpret this Neogene-Quaternary coastal uplift as a symptom of the increasing lithospheric compression that accompanies Cenozoic orogenies. © 2017 Elsevier B.V., We thank the ANR GiSeLE as well as the INSU programme Sulamer Hople for funding.

The Penmarc’h granitic coastal domain, SW Brittany (Western France), offers the opportunity to address the little investigated issue of erosional processes in a granitic coastal context. From land to sea, the granitic coast is composed of 1) an aerial marine terrace ( 10 Be) analyses, supplies new constraints on the weathering and denudation processes recorded by the Penmarc’h platform in Quaternary times. The role of at least two denudation events is emphasized: (i) a >1.8 m-thick level of granitic material is assumed to have been removed by erosion during the MIS5 sea-level highstand, both in the offshore domain and in the low part of the marine terrace; (ii) an additional 0.6 m-thick level of the granitic substratum was later removed during the last Holocene transgression, mainly in the marine domain. The lack of any morphological step between the subaerial marine terrace and the shore platform is here attributed to the combined effect of multiple factors, including (i) a Quaternary tectonic quiescence, (ii) a major eustatic transgression (MIS5) shaping both the shore platform and the low part of the marine terrace, (iii) the mechanically strong behaviour of the granitic basement with regard to erosion, and (iv) the moderate influence of the Holocene sea-level stillstand (since 6 ka) on the shore platform. Thanks to 10 Be content analysis, a range of vertical erosion rates of ca. 3–6 m⋅Ma −1 is obtained for the onshore domain, showing no discernable difference between the intertidal and aerial erosion rates. From that result, it is thus determined that the long-term development of the Penmarc’h granitic shore platform was mainly driven by marine erosive processes during the MIS5 and Holocene marine transgressions, whereas subaerial erosive processes prevailed after the MIS5 event.

Chile is an elongated country, running in a north-south direction for more than 30 along a subduction zone. Its climate is progressively wetter and colder from north to south. This particular geography has been used positively by a growing number of studies to better understand the relationships between erosion processes and climate, land use, slope, tectonics, volcanism, etc. Here we review the erosion rates, factors, and dynamics over millennial to daily periods reported in the literature. In addition, 21 new catchment mean erosion rates (suspended sediment and Be-10) are provided, and previous suspended sediment-derived erosion rates are updated. A total of 485 local and catchment mean erosion rates are reported. Erosion rates vary between some of the smallest values on earth (10(-5) mm/a) to moderate values 10 Ma) response time of rivers to surface uplift in north-central arid Chile. Over millennia, data provide evidence for the progressive contribution of extreme erosion events to millennial averages for drier climates, as well as the link between glacier erosion and glacier sliding velocity. In this period of time, a discrepancy exists between the long-term offshore sedimentological record and continental decennial or millennial erosion data, for which no single explanation appears. Still, little information is available concerning the magnitude of variation of millennial erosion rates. Over centuries, data show the variable role of groundwater in the dynamics of suspended load and document a decrease in erosion over hundreds of years, probably associated with historical harvesting.

International audience

Intense storms or earthquakes in mountains can supply large amounts of gravel to rivers. Gravel clasts then travel at different rates, with periods of storage and periods of displacement leading to their downstream dispersion over millennia. The rate of this dispersion controls the long-term downcutting rate in mountainous rivers as well as the grain-size signature of climate and tectonic variations in sedimentary basins. Yet, the millennial dispersion rates of gravel are poorly known. Here, we use 10Be concentrations measured in individual pebbles from a localized source along a 56 km-long canyon in the Central Andes to document the distribution of long-term gravel transit rates. We show that an inverse grain-size velocity relationship previously established from short-term tracer gravel in different rivers worldwide can be extrapolated to the long-term transit rates in the Aroma River, suggesting some universality of this relationship. Gravel are also dispersed by large differences in the mean transport rates independent of gravel size, highlighting that some gravel rest at the river surface over tens of thousands of years. These different transport rates imply a strong spreading of the gravel plumes, providing direct proof for the long-term river buffering of sediment signals between mountainous sources and sedimentary basins. The inferred distribution of residence times suggests the first evidence of anomalous diffusion in gravel transport over long timespans.

In Northeastern Venezuela, since 10 Ma, the tectonic setting is dominated by the eastward translation of the Caribbean Plate accommodated mainly by the E-W El Pilar strike-slip fault. However, to the south, in the Monagas Fold and Thrust Belt (MFTB), evidence of active compression has been identified in the southern limit of the Urica dextral fault. The objective of this study is to integrate geomorphological, dating terraces and 2D-3D seismic data in four zones of the MFTB: Tarragona, Punta de Mata, Jusepin, and Amarilis to understand the tectonics relationship between surficial and deep deformation in the area. These zones show surface deformations such as topographic uplifts, tilted, folded and faulted terraces, and drainage anomalies. The age of the river terraces obtained through 10Be and 26Al methods indicates that these terraces were formed in the late Pleistocene. The oldest terrace, located in the Tarragona zone, has a maximum exposure age of 90 ± 5 ka and the youngest, located in the Punta de Mata zone of 15 ± 5 ka. Additionally, we calculated an uplift rate of 0.3–0.4 mm/y for Plio-Pleistocene units using the deformation of the Late Miocene Unconformity (LMU). This rate coincides with the vertical deformation rate average calculated from terraces dating, which suggests that the deformation rate in the MFTB has not changed significantly for the last 5.3 Ma. The ridges observed at the surface and the structural highs interpreted from seismic sections indicate that the uplifting has been active up to the present through the activation of deep thrusts. We propose that the deformation on the surface is linked to the Tarragona, Pirital, Furrial thrusts, and the Amarilis backthrust activity and the youngest thrusts developed in the Carapita Formation. However, this surface deformation decreases towards the SSE away from the Urica fault; therefore, the neotectonic deformation is believed to be caused by the horsetail termination activity at the southern limit of the Urica fault.

International audience; We present numerical models to study how changes in the process of subduction may explain the observed Quaternary uplift of the Andean forearc region. Indeed, most segments of the South American Pacific coasts between 16 and 32° S have been uplifting since the Lower Pleistocene, following a period of stability of the forearc region. Models confirm that local uplift is expected to occur above ridges, this phenomenon being predominant in central Peru where the Nazca Ridge is subducting. We investigate the effects of slab pull, interplate friction and convergence velocity on the vertical displacements of the overriding plate. We propose that the global tendency to coastal uplift is accompanying the deceleration of the Nazca-South America convergence that occurred in the Pleistocene. In contrast, forearc subsidence may accompany increasing convergence velocities, as suggested by the subsidence history of the South America active margin.

South Cameroon is located in a tropical and tectonically quiescent region, with landscapes characterized by thick highly weathered regolith, indicative of the long-term predominance of chemical weathering over erosion. Currently this region undergoes huge changes due to accelerated mutations related to a growing population and economical developments with associated needs and increasing pressures on land and natural resources. We analysed two of the main south Cameroon rivers: the Nyong River and Sanaga River. The Sanaga catchment undergoes a contrasted tropical climate from sub-humid mountainous and humid climate and is impacted by deforestation, agriculture, damming, mining and urbanization, especially in the Mbam sub-basin, draining the highly populated volcanic highlands. By contrast, the Nyong catchment, only under humid tropical climate, is preserved from anthropogenic disturbance with low population except in the region of Yaounde (Mefou sub-basin). Moreover the Nyong basin is dam-free and less impacted by agriculture and logging. We explore both denudation temporal variability and the ratio between chemical and physical denudation through two catchment-averaged erosion and denudation datasets. The first one consists of an 11-year long gauging dataset, while the second one comes from cosmogenic radionuclides CRNs, here beryllium-10 (Be-10)] from sand sampled in the river mainstreams (timescale of tens to hundreds of thousands of years). Modern fluxes estimated from gauging data range from 5 to 100m/Ma (10 to 200t/km(2)/yr); our calculations indicate that the usual relative contribution of chemical versus physical denudation is 60% and 40%, respectively, of the total denudation. Beryllium-10 denudation rates and sediment fluxes range from 4.8 to 40.3m/Ma or 13 to 109t/km(2)/yr, respectively, after correction for quartz enrichment. These fluxes are slightly less than the modern fluxes observed in Cameroon and other stable tropical areas. The highest Be-10-derived fluxes and the highest physical versus chemical denudation ratios are attributed to anthropogenic impact. Copyright (c) 2016 John Wiley & Sons, Ltd.

Rocky coast erosion (i.e. cliff retreat) is caused by a complex interaction of various forcings that could be marine, subaerial or due to rock mass property. It turns into variable erosion rates (over 4 orders of magnitude at least, from 1 mm yr−1 to 10 mm yr−1). While numerous local studies exist and explain erosion processes on specific sites, there is a lack at global scale. In order 5 to quantify and rank the various parameters influencing erosion rates, we compiled existing local studies in a global database called GlobR2C2 (for Global Recession Rates of Coastal Cliffs). This database records erosion rates, cliff setting and measurement specifications; it is filled from peer reviewed articles and national databases. In order to be homogeneous, marine and climatic forcings were recorded from global models and reanalysis. Up to now, GlobR2C2 contains 58 publications which represents 1530 cliffs studied and more than 1680 erosion rate estimates. A statistical analysis was conducted on this 10 database to explore links between erosion rate and forcings at global scale. Rock resistance, inferred through Hoek and Brown (1997) criterion, is the strongest signal explaining variation in erosion rate. Median erosion rates are of 2.9 cm yr−1 for hard rocks, 10 cm yr−1 for medium rocks and 23 cm yr−1 for weak rocks. Concerning climate, only the number of frost days (number of day per year below 0 °C) for weak rocks shows a significant, positive, trend with erosion rate. Every other relations with both climatic and marine forcings are very spread and non-significant.

(IF 4.64; Q1); International audience; Many islands of the eastern Indonesian Archipelago exhibit Late Cenozoic sequences of coral reef terraces. In SE Sulawesi, on the Tukang Besi and Buton archipelagos, we identified 23 islands bearing such sequences. Remote sensing imagery and field mapping combined to U/Th and 14C dating enable to establish a chronologic framework of the reef terrace sequences from Wangi-Wangi, Buton as well as on the neighbouring, smaller islands of Ular, Siumpu and Kadatua. We identified the terraces from the last interglacial maximum (MIS 5e) at elevations lower than 20 m except on W Kadatua where it is raised at 34 ± 5 m. Such elevations yield low to moderate Upper Pleistocene uplift rates (

Millennial catchment–mean erosion rates derived from terrestrial cosmogenic nuclides are generally based on the assumption that the lithologies of the parent rock each contain the same proportion of quartz. This is not always true for large catchments, in particular at the edge of mountainous plateaus where quartz-rich basement rocks may adjoin sedimentary or volcano-sedimentary rocks with low quartz content. The western Central Andes is an example of this type of situation. Different quartz contents may be taken into account by weighting the TCN production rates in the catchment. We recall the underlying theory and show that weighting the TCN production rate may also lead to bias in the case of a spatial correlation between erosion rate and lithology. We illustrate the difference between weighted and unweighted erosion rates for seven catchments (16 samples) in southern Peru and northern Chile and show variations up to a factor of 2 between both approaches. In this dataset, calculated erosion rates considering only granitoid outcrops are better correlated with catchment mean slopes than those obtained without taking into account the geological heterogeneity of the drained watershed. This dataset analysis demonstrates that weighting erosion rates by relative proportions of quartz is necessary to evaluate the uncertainties for calculated catchment–mean erosion rates and may reveal the correlation with geomorphic parameters. Copyright © 2015 John Wiley & Sons, Ltd.

Cosmogenic nuclides in river sediment have been used to quantify catchment-mean erosion rates. Nevertheless, variable differences in 10Be concentrations according to grain size have been reported. We analyzed these differences in eleven catchments on the western side of the Andes, covering contrasting climates and slopes. The data include eight sand (0.5–1 mm) and gravel (1–3 cm) pairs and twelve sand (0.5–1 mm) and pebble (5–10 cm) pairs. The difference observed in three pairs can be explained by a difference in the provenance of the sand and coarser sediment. The other sand–pebble pairs show a lower 10Be concentration in the pebbles, except for one pair that shows similar concentrations. Two sand–gravel pairs show a lower 10Be concentration in the gravel and the other five pairs show a higher 10Be concentration in the gravel. Differences in climate do not reveal a particular influence on the 10Be concentration between pairs. The analysis supports a model where pebbles and gravel are mainly derived from catchment areas that are eroding at a faster rate. The five gravel samples with high 10Be concentrations probably contain gravel that were derived from the abrasion of cobbles exhumed at high elevations. In order to validate this model, further work should test if pebbles are preferentially exhumed from high erosion rate areas, and if the difference between pebbles with high 10Be concentrations and sand decreases when the erosion rate tends to be homogeneous within a catchment.

International audience; We estimate using gravity data the thickness of post-glacial unconsolidated sediment filling two major glacial valleys in northern Pyrenees: the Gave de Pau valley between Pierrefitte-Nestalas and Lourdes, and the Garonne valley between Saint-Béat and Barbazan. One hundred and eighty-four new gravity data complete 74 measurements obtained from the International Gravimetric Bureau database. Negative residual anomalies resulting from the presence of small-density unconsolidated sediment approach 4 mgal in both the Gave de Pau and the Garonne valleys. Estimating the sediment thickness requires knowing the density contrast between Quaternary sediments and the underlying bedrock. Supposing this density contrast is 600 kg/m3, the maximum estimated thickness of post-glacial sediment is ∼ 230 and 300 meters, and the volume of sediment is 2.1 and 3.2 km3 in the Gave de Pau and Garonne valleys, respectively. In both valleys, the depth of Quaternary sediment suddenly increases at the confluence between two major glacial valleys (Gave de Pau – Gave de Cauterets, and Garonne – Pique confluences). Overdeepened basins are less deep downstream when approaching terminal moraines (Lourdes and Barbazan area), illustrating that the efficiency of glacial erosion depends on the ice flux flowing through valleys.

(IF 0.99; Q3); International audience; Elevations of the shoreline angles of marine terraces have long been used to infer Pleistocene sea levels and/or uplift rates. We attempt to use morphologic properties of sequences of marine terraces – terrace width and slope – in order to track if these constitute a pattern showing similar alternations at different sites and if this alternation is comparable to the signal from the sea level highstand succession – duration and sea level – for Middle-Late Pleistocene. To do so, we focus on sequences of marine terrace including more than 10 successive strandlines from San Clemente Island and Santa Cruz (both in California, USA). We generated and analyzed 30 topographic profiles in order to confirm the occurrence or lack of each terrace, and to characterize their width and slope. To complement the observation of tenuous trends, we used additional data from previous works at Point Reyes (California, USA), Altos de Talinay (central Chile), San Juan de Marcona (central Peru) and South Taranaki (Northern Island, New Zealand). These additional data strengthen the observations made at San Clemente and Santa Cruz and prove that the most prominent terrace observed is usually carved during the Marine Isotopic Stage 5 (MIS5). Moreover, some terraces appear better expressed than the others: those formed during MIS7, MIS9 plus one of those formed during MIS15, MIS17 or MIS19 highstands. The terraces formed during MIS11 are not preeminent, contrary to what expected from its long highstand duration.