Catálogo de publicaciones - revistas

<jats:title>Abstract</jats:title><jats:p>Wide bedrock valleys and their genetic descendants, strath terraces, can serve as morphological records of past climate that reflect river discharge and sediment load during periods of valley widening. Understanding how changes in sediment load and water discharge create such distinct morphological features is limited by a lack of robust understanding of the specific processes of bedrock valley widening. We present results from the first set of flume experiments specifically devoted to exploring the conditions necessary to create wide bedrock valleys and how bedrock valleys develop through time. We ran six experiments in a weak bedrock substrate representing valley widening in an easily erodible bedrock, with differing amounts of water discharge, sediment load and base level fall. We evaluated valley width, valley wall height, channel mobility, lateral and vertical bed incision and sediment cover on the bed to explore the conditions necessary for the development of wide bedrock valleys and better understand the processes that affect valley widening rates. The results of the experiments show that wide bedrock valleys developed slowly and only under long periods of high sediment conditions, while vertical incision occurred much faster and was easily induced under different forcing mechanisms. We found that high sediment flux, enough to cover the channel bed, was a necessary condition for substantial valley widening. However, sediment cover on the bed was not by itself a sufficient condition to create wide bedrock valleys in our experiments; other factors were also required, particularly mobile channels within the valleys and some channel curvature to induce lateral undercutting. The results from this set of experiments suggest that the creation of wide bedrock valleys has several necessary conditions that must be met, and the development of a wide bedrock valley can be disrupted by slight changes in one of these necessary conditions.</jats:p>

<jats:title>Abstract</jats:title><jats:p>There is a need for geomorphology to integrate better with related disciplines, especially in Critical Zone science. To help satisfy this integration, geomorphology's knowledge‐base should extend into biotic as well as geological processes via ‘open data’. To aid information exchange between disciplines, the use of decimal latitude‐longitude (dLL) topographic geo‐referencing is advocated to identify locations of investigations, images and data in accord with the FAIR principles for data: findability, accessibility, interoperability and reusability. While local place names (toponyms) have their uses, they do not provide good location information. Identification of detailed locations using dLL referencing should be used in written, especially published, reports of investigations. Author‐date citations are traditionally used to identify geomorphic knowledge, which can be enhanced when linked to dLL‐specified locations and data such as sample sites and laboratory data. Ways in which dLL specifications might be used in geomorphology and associated disciplines are explored and some geomorphological problems associated with ‘steepland’ landscape domains are presented. Examples show how dLL data can be incorporated into the literature, whereby authors can help provide and develop geomorphic ‘information surfaces’ by using geo‐referencing to enhance ‘open’ science via the FAIR principles.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The mass transport rate of wind‐borne particles, and indeed the fluid stress required for their entrainment, is strongly governed by inter‐particle cohesion arising from water retained through adsorption and capillary force. This paper reports on a series of wind tunnel experiments in which high‐speed photography was used to record the motion of dry sand particles as they impinged on test beds of systematically varied target gravimetric pore water content (0% ≤ <jats:italic>W</jats:italic> ≤ 10%). The wind friction velocity was preset to 0.33 m s<jats:sup>−1</jats:sup>, sufficient to maintain a saltation cloud above an upwind strip of dry sand, which then was blown over the wetted surface. Discrete particle trajectories were identified in the camera images using expected particle area searching–particle tracking velocimetry (EPAS‐PTV). Adding progressively more water produced an exponential decrease in the normalized particle number density over the test surface. The largest response was achieved by wetting the bed surface to just 2%. To reduce the number of particles by a further 40%, it was necessary to add eight times more water, signifying a diminishing return regarding water use. Relative to particles either rebounding or splashed from a dry bed, the total particle velocity increased incrementally by a factor between 1.5 and 2 with increasing water content. Increasing amounts of pore water were associated with progressively higher saltation trajectories, reaching a plateau beyond <jats:italic>W</jats:italic> ~8%. The spatio‐temporal adjustment in the sand cloud was observed to be extremely rapid. There is no consensus in the literature on how to measure the water content that effectively governs aeolian transport. In this study, all approaches to sampling <jats:italic>W</jats:italic> produced strong correlation (R<jats:sup>2</jats:sup> ≥ 0.85). Sampling the topmost grains, however, provided the most accurate prediction of the normalized number density over the full range of water content.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Downslope movements of 12 stones (10–27 cm in diameter) were determined from time‐series images for 21 years on a Japanese alpine debris slope (inclination 12°). The process of stone movements was analysed on the basis of frost heave and soil temperature records, with particular attention to the stone size transported by needle ice and the effect of climate change on stone movements. Soil heaving mainly due to needle‐ice growth occurred 24–85 times yr<jats:sup>−1</jats:sup> with an annual maximum and cumulative amounts of 1.8–5.5 cm and 17–58 cm yr<jats:sup>−1</jats:sup>, respectively. Stones moved downslope at rates of 5–20 cm yr<jats:sup>−1</jats:sup> (mean 11.7 cm), the velocity correlating with the stone size, although small stones with a height of less than about 3 cm do not reduce needle‐ice activity very much. On an assumption of a linear relationship between the two variables, needle ice can transport stones with a diameter of as large as 30 cm. Both annual mean air/soil temperatures and needle‐ice activity slightly increased through the monitoring period. Climatic warming may have raised the frequency of needle ice by shortening the snow‐covered period.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Intraplate settings far from tectonic plate boundaries are normally thought to be tectonically inactive regions in which the landscape evolves via the slow downcutting of fluvial systems. When identified, tectonic reactivations are thought to be of too low an amplitude and not cause any change in the landscape. However, in the absence of datable markers of tectonic deformation, the landscape can be used as a passive marker of intraplate tectonic activity. In this study, we investigate the northern boundary of the Ponta Grossa Arch in the southeastern portion of the Brazilian passive margin. We mapped and studied the spatial and temporal (relative) relationships between brittle structures and geomorphic markers of base level changes. Drainage anomalies (knickpoints and high <jats:italic>k</jats:italic><jats:sub><jats:italic>sn</jats:italic></jats:sub> values) are correlated with structural/tectonic lineaments in which we recognize strike‐slip and transtensional faults with right‐lateral and left‐lateral kinematics. Through mapping and analysis of structural data, we constrained the underlying structural framework. The fault data demonstrate the counterclockwise rotation of the maximum stress field, which moved from the NE–SW orientation (at the Cretaceous‐Paleogene boundary) to N‐S to reach the current WNW‐ESE position. Together, the data suggest that, though subtle and low‐magnitude, the evolution of intraplate stress field forms a dynamic forcing of intracontinental landscape change.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Bauxitic clays, clayey bauxites and bauxites are residual products formed from the weathering of aluminosilicate‐rich parent rocks under wet and warm conditions. These deposits show a complex interplay between remobilisation of pre‐existing kaolinitic soils and depositional micro‐environments.</jats:p><jats:p>In the southern Ribeira belt, Brazil, a paleoweathering surface developed on the continental shelf of the Capiru Group passive margin strata and on its basement/source rocks. This weathering cycle gave rise to a paleosol profile on the continental domain and a karstic paleotopography on the emerged carbonate shelf. The surface and karstic nets were later caped and filled with Al‐rich materials, typical of remobilised soils, bauxitic clays, clayey bauxites and pods of karst‐type bauxites.</jats:p><jats:p>The age of the disconformity is Pre‐Brazilian/Pan‐African, implying a Neoproterozoic age for the weathering surface. In this study, we investigate the relationship among disconformities, paleosols and karst topography to better understand the stratigraphic control, chemical composition and mineralogy of the Al‐rich materials. We interpret this horizon as the remnants of a (meta‐)paleoweathering surface that can serve as a valuable key bed for stratigraphic correlation and paleogeographic reconstructions.</jats:p><jats:p>We propose that the triggering process for the genesis of the paleosol profiles, bauxitic material and bauxite pods was a coupled mechanism between favourable climate and uplift along the northern margin of the Curitiba–Angola craton, creating a karstic topography that allowed the down‐plain transport of Al‐rich materials. In a later stage, these deposits were metamorphosed, developing a series of Al silicates in unusual paragenesis, typical of Al‐rich protoliths.</jats:p><jats:p>The presence of these paragenesis, along with the recognition of the disconformity–paleoweathering surface pair, could be a useful tool to understand the paleoenvironmental and paleogeographic evolution of highly deformed terrains.</jats:p>

<jats:title>Abstract</jats:title><jats:p>In this study, we map different types of channel geomorphic units in a sediment‐starved, residual‐flow reach before and after an artificial flood. Bedload particles of a previous sediment augmentation measure are tracked with passive integrated transponder tags, and water depth and flow velocity are recorded across 10 cross‐sections. The analysis focuses on the influence of channel geomorphic units on bedload transport and river morphology. Our hypotheses are (i) that during low‐magnitude bed‐forming floods with sediment pulse migration, existing channel geomorphic units influence bedload transport, and more specifically, (ii) that their type influences the retention rate of bedload particles. Furthermore, we hypothesise that (iii) the density of channel geomorphic units is linked to the hydromorphological diversity of a river section. We provide evidence that supports the first two hypotheses and contradicts the third one. We consider our results to be transferable to similarly regulated reaches based on an analysis of site‐specific conditions and alternative explanatory factors. Further research is needed to transfer the results to varying flood and sediment supply conditions in unregulated reaches.</jats:p>

<jats:title>Abstract</jats:title><jats:p>The movement of active dunes is tightly linked to climatic conditions (e.g., wind regime, temperature and precipitation) as well as human influence (e.g., grazing, dune fixation and greening). Dune migration rates can be studied to draw conclusions of changing wind conditions over time. The Gonghe Basin (GB), located on the north‐eastern Tibetan Plateau (TP), offers a good testing ground for these assumptions. The intramontane basin is highly influenced by two major wind regimes: the mid‐latitude Westerlies and the East Asian summer monsoon. To investigate environmental changes, this study combines optical remote sensing techniques with climatic datasets. High‐resolution satellite images of the last five decades, such as CORONA KH‐4B, are used to map dunes and calculate their respective migration rates. Further, height information was extracted as well. Climatic changes from the ERA‐5 reanalysis dataset and normalized difference vegetation index (NDVI) values were processed alongside. Relating the dunes' surface processes to climate model data shows an accordance between slowing migration, expanding vegetation and a decrease in sand drift potential. From 1968 to present time, an average dune migration rate of 7.3 m a<jats:sup>−1</jats:sup> was extracted from the satellite images, with an overall reduction of −1.81 m a<jats:sup>−1</jats:sup>. The resultant drift potential (RDP) values for the GB are calculated to be below 10 m<jats:sup>3</jats:sup> s<jats:sup>−3</jats:sup> with a spatial decrease, following a direction from the NW to the SE, fitting well with a corresponding decrease in the migration rates. Our results indicate a good agreement between the development of aeolian landforms and the ERA‐5 climate reanalysis model data, even in a high‐altitude setting with complex topography, which is known to influence such datasets.</jats:p>

<jats:title>Abstract</jats:title><jats:p>There is a global stabilization of coastal dunes, during which, the trajectory of vegetation expansion was rarely studied and, thus, still remains unclear. In this study, patterns and driving factors of vegetation expansion during dune stabilization were examined in three coastal dunefields in Victoria, Australia. Results show that the trajectory of vegetation expansion is fundamentally determined by dunefield topography. At the dunefield scale, vegetation colonization can take place at different parts in dunefield, including (1) the landward margins, where the ecosystem is frequently dominated by woody species and the soil is more mature with higher nutrients and water content; (2) the interdune depressions, where is usually dominated by lower elevations and shelters; and (3) the seaward deflation basins and plains, where vegetation shows a more discontinuous and patchy distribution. At the individual dune scale, vegetation usually expands vertically from the dune toe towards the upper dune slope at both the lee side and stoss face of dunes/dune ridges. The deflation basins are more likely to be free of vegetation establishment. Pre‐existing vegetation also plays a critical role in dune re‐vegetation, and subsequent vegetation expansion takes place around the vegetation patches, more usually towards the downwind direction, probably because it can provide seeds for subsequent vegetation spread. Once established, it can also change the micro‐climates by providing shelter, increasing the surface roughness and changing the wind regimes. More importantly, existing vegetation can form a ‘fertility island’ with higher nutrients, organic matter and water‐holding capacity. Conceptual models depicting the trajectory of vegetation expansion were also generalized. This research provides an original perspective and innovative insight into the patterns and driving factors of vegetation expansion during dune stabilization, under the background of global coastal ‘greening’, which could be helpful to identify opportunities for management interventions.</jats:p>

<jats:title>Abstract</jats:title><jats:p>Landslides following the development of slope instability can have serious consequences. Geophysical surveys have potential to aid in the understanding of landslides and their instability. This study described a landslide that occurred under particular geomorphological and meteorological conditions in Erenler (Sakarya, NW Türkiye) using electrical resistivity tomography (ERT) and multi‐channel analysis of surface waves (MASW) surveys and mechanical drillings. Data showed that the landslide is characterized by downslope movement of an altered clay unit over a claystone unit. The traditional landslide model used to interpret geoelectric data involves sliding of a relatively low‐resistivity material over higher resistivity bedrock. Here, the ERT survey showed a relatively high‐resistivity sliding material moving over relatively low‐resistivity bedrock units corresponding to the claystone unit. The relatively lower resistivity of the whole study area was related to the clay‐rich materials detected in the boreholes. This low‐resistivity unit was detected at high velocity in the MASW section, and it was understood that this layer was a compact structure acting like bedrock. The detected slip surfaces, landslide scars and slip surface toe indicate that the movement character of the landslide is retrogressive. The study results showed that the integrated and comparative use of different geophysical methods effectively reduces interpretation uncertainties and potential errors and leads to much better landslide characterization.</jats:p>