A Schmidt hammer was applied for relative-age dating to 48 sites in 5 different massifs of the Cantabrian Mountains (NW Spain). The sample included glacial (moraines, erratics, and polished bedrock) ...and periglacial (rock glaciers, blockfields, and talus slopes) sites from the last glaciation to the present in different geomorphological contexts. The rebound (R) values agree with the morphostratigraphic reconstructions, showing progressively lower values for older deposits. Six stages from the Last Glacial Maximum to the present are inferred. The results differ according to the lithology: i) the quartzites showed higher R-values and very low weathering rates; ii) the granodiorites showed larger differences in R-values reflecting clearly age differences; iii) sandstones appear to be unsuitable for Schmidt hammer measurements in some areas; however, quartzite sandstones provide better results. The rock glaciers formed in different periods after deglaciation (i.e. just after the Last Glacial Maximum, Bölling/Allerød, Holocene), indicate a paraglacial dependence rather than climate-driven landforms. The sampled blockfields stabilized after the (almost) total deglaciation of the cirques, but their origin and significance in this mountainous area remain poorly understood.
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•Six stages from the Last Glacial Maximum to the present are inferred.•Relevant differences between R-value and weathering rates depending on lithology•Paraglacial control rather than climate dependence in the generation of rock glaciers•Blockfields stabilized after the (almost) total deglaciation of the cirques.•More chronological data are required to construct a proper calibration curve for SHD.
This paper provides a synthesis of current data and interpretations on the crustal structure of the Pyrenean-Cantabrian orogenic belt, and presents new tectonic models for representative transects. ...The Pyrenean orogeny lasted from Santonian (~84 Ma) to early Miocene times (~20 Ma), and consisted of a spatial and temporal succession of oceanic crust/exhumed mantle subduction, rift inversion and continental collision processes at the Iberia-Eurasia plate boundary. A good coverage by active-source (vertical-incidence and wide-angle reflection) and passive-source (receiver functions) seismic studies, coupled with surface data have led to a reasonable knowledge of the present-day crustal architecture of the Pyrenean-Cantabrian belt, although questions remain. Seismic imaging reveals a persistent structure, from the central Pyrenees to the central Cantabrian Mountains, consisting of a wedge of Eurasian lithosphere indented into the thicker Iberian plate, whose lower crust is detached and plunges northwards into the mantle. For the Pyrenees, a new scheme of relationships between the southern upper crustal thrust sheets and the Axial Zone is here proposed. For the Cantabrian belt, the depth reached by the N-dipping Iberian crust and the structure of the margin are also revised.
The common occurrence of lherzolite bodies in the northern Pyrenees and the seismic velocity and potential field record of the Bay of Biscay indicate that the precursor of the Pyrenees was a hyperextended and strongly segmented rift system, where narrow domains of exhumed mantle separated the thinned Iberian and Eurasian continental margins since the Albian-Cenomanian. The exhumed mantle in the Pyrenean rift was largely covered by a Mesozoic sedimentary lid that had locally glided along detachments in Triassic evaporites. Continental margin collision in the Pyrenees was preceded by subduction of the exhumed mantle, accompanied by the pop-up thrust expulsion of the off-scraped sedimentary lid above. To the west, oceanic subduction of the Bay of Biscay under the North Iberian margin is supported by an upper plate thrust wedge, gravity and magnetic anomalies, and 3D inclined sub-crustal reflections. However, discrepancies remain for the location of continent-ocean transitions in the Bay of Biscay and for the extent of oceanic subduction. The plate-kinematic evolution during the Mesozoic, which involves issues as the timing and total amount of opening, as well as the role of strike-slip drift, is also under debate, discrepancies arising from first-order interpretations of the adjacent oceanic magnetic anomaly record.
Snowfall in elevated areas of the mid-latitudes has a strong impact on infrastructure, freshwater availability, and the climate system. The Cantabrian Mountains of the northwestern Iberian Peninsula ...are very vulnerable to climate change because of their moderate altitudes, which limits their snowfall. Monitoring snow events is essential for the evaluation of weather and climate prediction models. However, measurement networks are scarce in mountainous areas and have great uncertainties because of blizzards. In this study, a multiphysics ensemble of the Weather Research and Forecasting (WRF) model was designed using three microphysics and two planetary boundary layer (PBL) schemes to simulate nine snowfall events in the Cantabrian Mountains during autumn and winter 2021–2022. The WRF was validated using several snow characteristics, such as liquid water equivalent, snow cover, and snow depth. Liquid water equivalent was evaluated using snow-gauge networks and satellite products in an assessment of snow cover. In addition, a monitoring network of webcams and snow poles was implemented, improving the low density of snow observations in the mountains. The results showed good model performance for detection of snow cover and slight overestimation of liquid water equivalent and snow thickness, which may have been caused by under-catchment that is generally an effect of wind on the measurement systems and by snow compaction, respectively. Morrison microphysics and Mellor-Yamada-Nakanishi-Niino (MYNN PBL) yielded better results for liquid water equivalent at higher altitudes and output greater snow cover. The results help determine the best configurations for snow modelling in the study area to develop future studies of the spatiotemporal patterns of snow distribution.
•Monitoring system of snow events in Cantabrian Mountains has been developed.•We selected nine snowfall events during autumn and winter 2021–2022.•Three microphysics and two PBL parameterizations were tested.•Morrison microphysics and MYNN PBL yielded better results at higher altitudes.
Deglaciated mountainous areas are usually affected by a great range of paraglacial processes that involve progressively denudation of glacial imprints. This study focuses on paraglacial processes and ...glacial landform preservation in six zones located in two catchments of the Cantabrian Mountains (NW Spain). These zones are adjacent but display important topographic, lithologic and glaciation style differences. An analysis of how these variables conditioned the intensity and diversity of paraglacial processes in these zones was investigated through a detailed study of their relief, lithology and paleo glacier surface using GIS. A comprehensive cartography of paraglacial landforms was also accomplished, considering landslides, alluvial fans and rock glaciers that show signs of having been conditioned by glaciation. Moraines and debris-mantled slopes were also included in the analysis to examine their grade of preservation depending on the studied variables. Data comparison show that differences in glaciation style influenced paraglacial processes. In the ancient icefield area, relief modification by glacial action was limited and scarce paraglacial processes occur. By contrast, in the upper areas located in the southern ranges where an alpine-style of glaciation was installed, paraglacial processes were very active, generating many rock glaciers. Lithology explains some paraglacial landforms distribution: 1) Landslides are associated with incohesive (sandy and shale) rocks; 2) Rock glaciers mainly occur in quartzite areas; 3) In limestone areas subterranean drainage contributes to glacial landscape preservation, but suffosion dolines affect some glacial deposits. Topography is also a key factor in paraglacial processes: 1) Moraines are well-preserved in gently sloping valleys, but rare in the steeper where they are usually transformed into moraine (or debris)-mantled slopes; 2) Alluvial fans are more frequent in the steeper valleys, but more dissected by postglacial river action. 3) Elevation and orientation show little influence on paraglacial landforms, except in the generation of some periglacial features such as rock glaciers.
Natural conditions that explain the triggering of snow avalanches are becoming better-known, but our understanding of how socio-environmental changes can influence the occurrence of damaging ...avalanches is still limited. This study analyses the evolution of snow avalanche damage in the Asturian Massif (NW Spain) between 1800 and 2015, paying special attention to changes in land-use and land-cover patterns. A damage index has been performed using historical sources, photointerpretation and fieldwork-based data, which were introduced in a GIS and processed by means of statistical analysis. Mapping allowed connecting spatiotemporal variations of damage and changes in human-environment interactions. The total number of victims was 342 (192 dead and 150 injured). Results show stability in the number of avalanches during the study period, but a progressive decrease in the damage per avalanche. Changes in land use explain the evolution of damage and its spatial/temporal behaviour. The role played by vegetation cover is at the root of this process: damage was the highest during the late 19th and early 20th centuries, when a massive deforestation process affected the protective forest. This deforestation was the result of demographic growth and intensive grazing, disentailment laws and emerging coal mining. Since the mid-20th century, the transformation of a traditional land-management system based on overexploitation into a system based on land marginalization and reforestation, together with the decline of deforestation due to industrial and legal causes, resulted in the decrease of avalanches that affected settlements (mostly those released below the potential timberline). The decrease of damage has been sharper in the western sector of the Asturian Massif, where oak deforestation was very intense in the past and where lithology allows for a more successful ecological succession at present. Taking into account that reforestation can be observed in mountain environments of developed countries worldwide, and considering present initiatives conducted to counteract its negative cultural effects by means of grazing and clearing operations, planning is imperative, and this research provides useful information for environmental management policies and risk mitigation in avalanche prone areas.
•Evolution of snow avalanche damage is studied over a 215-year period.•A synthetic damage index is created, mapping its variations over time and space.•The evolution of damage is closely related to human-induced changes in vegetation cover.•Deforestation explains the concentration of damages in the late 19th century.•Changes in land use management explain the decrease of the damage, mainly since the 1960s.
Este trabajo muestra las principales características de los canchales situados en el entorno de La Becerrera, en la vertiente oeste del macizo de Las Ubiñas (cordillera Cantábrica). Para el estudio ...se ha generado la cartografía de detalle de los canchales y sus áreas fuente mediante el uso de técnicas de análisis cartográfico y trabajo de campo. El posterior tratamiento de las variables estadísticas ha mostrado la relación entre las proporciones de las áreas fuente y los canchales, siendo la longitud y la superficie del área fuente, dos factores muy importantes en la dimensión de los canchales. Las características del área fuente y la topografía del terreno donde se asientan los canchales, afectan de manera significativa en su morfología. Los canchales adoptan dos morfologías principales, taludes y conos, asociados estos últimos a la presencia de canales en el área fuente. La orientación del área fuente y del canchal pueden diferir debido a la presencia de canales de aludes en cabecera. Las pendientes de los canchales son homogéneas correspondiéndose con el ángulo de reposo de los derrubios.
This paper provides a review of the evolution of palaeomagnetic directions and sequence of tectonic events in the European Variscan belt during Late Palaeozoic times. These data are correlated with ...palaeomagnetic records from Gondwana and Baltica in order to provide a large-scale geodynamic framework during the Carboniferous to Permian. The Early Carboniferous palaeomagnetic records reported mainly from the Rhenohercynian and Saxothuringian magmatic arcs indicate a 70° anticlockwise rotation, while Late Carboniferous to Permian magnetic directions from various rocks of western and central Europe are consistent with 120° clockwise rotation of the eastern and central parts of the Variscan belt. Our review of the chronology of tectonic events is based on a robust database of geochronologically constrained deformation, metamorphic and magmatic events, which allow discretizing the 80Ma long orogenic evolution into five principal events. In this scenario, the Variscan belt can be regarded as a linear sub-plate, isolated from Gondwana and Laurussia by the Rhenohercynian and Palaeotethysian oceans during Devonian times. This linear composite belt was segmented by transform faults and boundaries in the Late Devonian to Early Carboniferous times (360–335Ma) during progressive E–W closure of Rhenohercynian ocean synchronously with collision between Saxothuringian and Moldanubian blocks. Subsequent relocation of subduction to the northern boundary Palaeotethysian ocean was responsible for N–S shortening almost orthogonal to the ancient sub-plate N–S elongation at around 335–325Ma. This deformation resulted in dextral reactivation of transform boundaries associated with anticlockwise rotation of intermittent blocks. At the end of this rotation, the faults were parallelized to the Teysseire-Tornquist zone – the southern margin of Baltica, while the lozenge-shaped blocks of the former Variscan sub-plate were further shortened during continuous contraction. This evolution can fully explain the ≈70° anticlockwise rotation from Cn3 to Cn2 palaeomagnetic directions, which are regarded as successive Carboniferous magnetizations. Subsequently, the Variscan belt suffered a giant transtensional event from 325 to 310Ma that was related to the development of extensional syn-magmatic core complexes over the whole belt and significant dextral reactivation of earlier NW–SE trending transform faults. This extensional event was associated with important tilts recorded by Cp magnetic overprint resulting from a major thermally induced remagnetization. During this event new sets of sinistral transfer NNE–SSW trending faults originated, that partly reactivated boundaries of the principal tectonic zones. Blocks delimited by second-order sinistral and first-order dextral faults, then rotated in a clockwise manner by ≈80°. The whole system subsequently suffered a period of NNE–SSW shortening that affected the Variscan belt namely along the former Laurussian and former Variscan sub-plate contact in the north and in the south, where the giant Cantabrian orocline developed at around 310–300Ma due to hard collision with Gondwana. This deformation is associated with the clockwise rotation of Laurussia together with the accreted northern sector of the Variscan belt, and the anticlockwise of Gondwana. This clockwise 30° rotation is achieved by A1 remagnetizations, while the southern part of Iberia suffered anticlockwise rotation. The final stage of rapid clockwise rotation affecting the northern limb of the Iberian Arc including Corsica and Sardinia is attributed to giant N–S extension affecting the whole Variscan belt at the onset of Permo-Triassic opening of the Tethys ocean. This complex evolution is regarded as a result of the readjustment of inhomogeneous and thermally and mechanically instable mobile space in between reorganizing the Gondwana and Laurussia megaplates and the opening of the Palaeotethys ocean during the final stages of formation of the Pangea supercontinent. Finally, the palaeomagnetically constrained rotations and tectonic evolution of the Variscan belt are explained using a pinned model of “internal” and “external” rotations of blocks driven by activation of dextral shear zones by N–S compression and E–W transtension in particular.
•70° of anticlockwise rotation of the belt followed by 120° of clockwise rotation in the Carboniferous - Permian•Complex and polyphase wrench dominated deformation related to final amalgamation of the Pangea supercontinent•Readjustment of thermally and mechanically instable space in between reorganizing Gondwana and Laurussia and opening of Paleotethys•The rotations are explained using a pinned model of “internal” and “external” rotations of blocks due to dextral shear during Early Carboniferous N-S compression and late Carboniferous – Permian E-W transtension
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