Cobrante, grotte

Le siteLa grotte de Cobrante est située dans la localité de San Miguel de Aras sur la commune de Voto (Cantabrie, Espagne). Elle se trouve vers le fond de la vallée de la Clarín, à mi-hauteur du versant du Monte de Cobrante, à une altitude de 150 m au-dessus du niveau de la mer (fig. 1a). La cavité se développe, après un vaste vestibule renfermant un gisement archéologique, sur environ 500 m. Les gravures paléolithiques se situent dans deux zones intérieures. La première prend place sur la p..

First ground penetrating radar survey on Monte Perdido glacier (Pyrenees)

Producción CientíficaThe project “The Monte Perdido Glacier: Monitoring the glacial dynamic and the associated cryospheric processes as indicators of global change” (National Park´s 2013 Fund) aims to study the recent dynamic and degradation of this ice mass, using geomatic and geophysical techniques in order to estimate thickness and potential volumetric variations. We present the first ground penetrating radar survey, carried out on the northwest section of the lower Monte Perdido Glacier. The survey was conducted along a 270 m transect, using three antennas of different frequencies -500, 200 and 50 MHz- that enabled us to study the glacier´s structure at various maximum depths and spatial resolutions. The results show a first section composed by several seasonal snow layers (2015-2016 winter and spring), a clear snow/ice transition layer, an ice layer and a final basal zone characterised by typical sub-glacial till sediments.Ministerio de Agricultura y Pesca, Alimentación y Medio Ambiente (project 844/2013)Junta de Extremadura - Fondo Europeo de Desarrollo Regional (grant GR15107

Assessment of the structural integrity of the Roman bridge of Alcántara (Spain) using TLS and GPR

El puente romano de Alcántara es el más grande de España. Su preservación es de suma importancia y para ello deben estudiarse diferentes aspectos. El más destacado es la evaluación de su estructura, y esto es especialmente importante ya que el puente permanece en uso. Este documento documenta la forma en que se llevó a cabo la evaluación de la seguridad estructural. Se aplicó la metodología de evaluación de las estructuras existentes. La evaluación preliminar se basó en datos bibliográficos y técnicas no destructivas. Los datos geométricos del puente se obtuvieron mediante el escaneado láser terrestre (TLS), que permitió el análisis de sus deformaciones y la evaluación de su estructura. También se utilizó el Radar de penetración en el suelo (GPR) con diferentes antenas para trabajar a diferentes profundidades y resoluciones espaciales con el fin de analizar los elementos estructurales. A partir de la información anterior, la evaluación de la seguridad estructural se realizó mediante el método de análisis de límites aplicando los trabajos históricos realizados sobre el mismo y los descritos en la normativa de obligado cumplimiento en España (IAP11), estudiando la sensibilidad de la seguridad a los parámetros más relevantes. Se discute el estado de conservación e integridad estructural del puente y se extraen conclusiones sobre las áreas de mayor riesgo y las bases para la siguiente fase de evaluación de la conservación del puente.The Roman bridge of Alcántara is the largest in Spain. Its preservation is of the utmost importance and to this end different aspects must be studied. The most prominent is the assessment of its structure, and this is especially important as the bridge remains in use. This paper documents the way the assessment of structural safety was carried out. The assessment methodology of existing structures was applied. The preliminary assessment was based on bibliographic data and non-destructive techniques. The geometric data of the bridge were obtained by Terrestrial Laser Scanning (TLS), which made possible the analysis of its deformations and assessment of its structure. Ground-Penetrating Radar (GPR) was also used with different antennae to work at different depths and spatial resolutions with the aim of analysing structural elements. From the above information, the assessment of structural safety was made using the limit analysis method by applying the historical works carried out on it and those described in the regulation of obligatory compliance in Spain (IAP11), studying the sensitivity of safety to the most relevant parameters. The state of preservation and structural integrity of the bridge is discussed and conclusions are drawn on the areas of greatest risk and the bases for the following assessment phase of preservation of the bridge.• Junta de Extremadura y Fondos FEDER. Ayuda GR15069 y GR15107, para el grupo de investigación NEXUS y COMPHASpeerReviewe

Recent and ongoing transformations of the Nevado Coropuna tropical cryosphere (Central Andes): the Ground-Penetrating Radar perspective

The evaluation of presence and origin of ground-ice in the non-glaciated peripheral areas of Nevado Corpuna can contribute to a more refined estimation of its real extent, as well as of the ongoing and recent transformation processes (i.e. permafrost aggradation/degradation). We carried out GPR surveys in sectors immediately outside the glacial tongues which diverge from the glaciated area, both on rock glaciers and debris-covered glaciers. The data acquisition was made with an unshielded antenna operating at a central frequency of 25 MHz, and according longitudinal and cross profiles. We defined a processing sequence particularly effective in removing in air-reflections generated by isolated blocks on the surface, and the numerous point-source diffractions. The signal-to-noise ratio consents a data imaging interpretable up to 25-30 m of depth, according to the estimated velocity of GPR waves propagation. In some sectors we calibrated the GPR data (depth and reflection amplitude) with those obtained from Vertical Electric Sounding. The rock glaciers examined show a reflective pattern consistent with a permafrost that extends from 2-4 m to more than 20 m depth. The GPR reflections also depict a permafrost stratigraphic architecture, and potential deformation structures in the frozen layers (i.e. shear planes). The GPR profiles made on debris-covered glaciers show a high-amplitude reflection consistent with the presence of near-surface (2-3 m depth) (sedimentary) ice, which in depth exhibits a radar facies less characterized by reflection events than those of rock glaciers. Also in this case an ice stratigraphy and potential deformation features in layers highly rich in ice are visible. The GPR data allowed a view of ice-ground presence in the ice-free areas in Nevado Coropuna and can be integrated with the glaciological evolution of the last decades to build a forecasting model that considers the transformation from clean-ice to debris-covered glacier or permafrost landforms

A search for ultra-high-energy photons at the Pierre Auger Observatory exploiting air-shower universality

The Pierre Auger Observatory is the most sensitive detector to primary photons with energies above ∼0.2 EeV. It measures extensive air showers using a hybrid technique that combines a fluorescence detector (FD) with a ground array of particle detectors (SD). The signatures of a photon-induced air shower are a larger atmospheric depth at the shower maximum (X$_{max}$) and a steeper lateral distribution function, along with a lower number of muons with respect to the bulk of hadron-induced background. Using observables measured by the FD and SD, three photon searches in different energy bands are performed. In particular, between threshold energies of 1-10 EeV, a new analysis technique has been developed by combining the FD-based measurement of X$_{max}$ with the SD signal through a parameter related to its muon content, derived from the universality of the air showers. This technique has led to a better photon/hadron separation and, consequently, to a higher search sensitivity, resulting in a tighter upper limit than before. The outcome of this new analysis is presented here, along with previous results in the energy ranges below 1 EeV and above 10 EeV. From the data collected by the Pierre Auger Observatory in about 15 years of operation, the most stringent constraints on the fraction of photons in the cosmic flux are set over almost three decades in energy

Study on multi-ELVES in the Pierre Auger Observatory

Since 2013, the four sites of the Fluorescence Detector (FD) of the Pierre Auger Observatory record ELVES with a dedicated trigger. These UV light emissions are correlated to distant lightning strikes. The length of recorded traces has been increased from 100 μs (2013), to 300 μs (2014-16), to 900 μs (2017-present), to progressively extend the observation of the light emission towards the vertical of the causative lightning and beyond. A large fraction of the observed events shows double ELVES within the time window, and, in some cases, even more complex structures are observed. The nature of the multi-ELVES is not completely understood but may be related to the different types of lightning in which they are originated. For example, it is known that Narrow Bipolar Events can produce double ELVES, and Energetic In-cloud Pulses, occurring between the main negative and upper positive charge layer of clouds, can induce double and even quadruple ELVES in the ionosphere. This report shows the seasonal and daily dependence of the time gap, amplitude ratio, and correlation between the pulse widths of the peaks in a sample of 1000+ multi-ELVES events recorded during the period 2014-20. The events have been compared with data from other satellite and ground-based sensing devices to study the correlation of their properties with lightning observables such as altitude and polarity