El registro sedimentario del Cuaternario Reciente en el Lago Redó D'Aigües Tortes (Pirineos Centrales)

[Resumen] El estudio del registro sedimentario del lago Redó d'Aigües Tortes (Pirineos Centrales) permite analizar la evolución paleoambiental en los alrededores del lago desde el final del Último Ciclo Glaciar hasta la actualidad (Pleistoceno Superior-Holoceno). El relleno sedimentario se inicia alrededor de los 13500 años BP con la sedimentación de ritmitas glaciolacustres que indican la presencia de glaciares en la zona de influencia del lago hasta el inicio del Holoceno (9980 años BP). Durante el Holoceno, la sedimentación es predominantemente de tipo orgánico aunque algunas intercalaciones detríticas puedan corresponder tanto a fluctuaciones climáticas como a fenómenos de inestabilidad en las laderas que bordean el lago (deslizamientos y/o aludes).[Abstract] The study of the sedimentary record from Lake Redó d'Aigües Tortes (Central Pyrenees) allows us to recognize the paleoenvironmental evolution in the surrounding area since the end of the Last Glacial Cycle (Upper PleistoceneHolocene). The sedimentary filling begins at about 13500 years BP with the sedimentation of glaciolacustrine rhythmites showing the existence of glaciers in the cirque area up to the beginning of the Holocene (9980 years BP). During the Holocene, the prevailing organic sedimentation is interrupted by detritic levels that would correspond either to climatic fluctuations or to landslides / snow avalanches in the slopes bordering the lake

Structure des grands bassins glaciaires dans le nord de la péninsule ibérique: comparaison entre les vallées d'Andorre (Pyrénées orientales), du Gállego (Pyrénées centrales) et du Trueba (Chaîne Cantabrique).

Les grandes vallées glaciaires de la Péninsule Ibérique sont situées dans la chaîne pyrénéo-cantabrique, principalement dans le bassin de l'Èbre. Ainsi, les vallées d'Andorre, de la Noguera Pallaresa et de la haute vallée du Gállego, dans les Pyrénées, ont eu des appareils glaciaires longs de 42, 50 et 40 km respectivement. Dans les vallées du Sil (bassin du Miño) et du Trueba, dans la Chaîne Cantabrique, ils atteignaient 42 et 16,5 km (Serrano-Cañadas, 1996 ; Gómez-Ortiz et al., 2001 ; Turu & Peña, 2006a et b ; Redondo-Vega et al., 2006). L'une des caractéristiques géomorphologiques de la plupart de ces vallées est l'existence d'une dépression morphologique du substratum dans les parties moyennes et terminales, interprétée comme la conséquence de l'érosion glaciaire. Dans tous les cas, on observe une architecture litho-stratigraphique commune (Vilaplana & Casas, 1983 ; Bordonau et al., 1989 ; Bordonau, 1992 ; Turu et al., 2002) représentée par trois unités géoélectriques : une unité inférieure très épaisse, avec des résistivités électriques basses (70 - 200 Ohms par mètre), qui traduit la présence de matériaux fins considérés comme d'origine lacustre ; une unité intermédiaire, moins épaisse, avec des valeurs de résistivité plus élevées (400 - 800 Ohms par mètre), pouvant être interprétée comme un système fluvio-deltaïque pro-glaciaire et une unité géoélectrique supérieure, avec des valeurs de résistivité très variables (100 - 1500 Ohms par mètre), constituée de sédiments alluviaux subactuels. La comparaison des données de type géophysique et géomécanique (sismique à réfraction et essais pressiométriques) montre que l'unité intermédiaire, considérée comme d'origine fluvio-deltaïque, présente des valeurs de vitesse sismique anormalement élevées, ainsi que de hautes valeurs de consolidation. Cette observation effectuée pour la première fois dans la vallée d'Andorre (Turu, 2000) montre des remarquables corrélations entre les hautes vitesses sismiques et les valeurs élevées de consolidation, ainsi que la très nette corrélation entre les hautes valeurs de consolidation et les tills sous-glaciaires. Elle permet d'interpréter l'unité intermédiaire comme essentiellement glaciaire et de remettre en question le modèle simple d'une séquence de comblement lacustre et deltaïque proposé jusqu´à maintenant

Glaciolacustrine deposits formed in an ice-dammed tributary valley in the south-central Pyrenees: new evidence for late Pleistocene climate

Combined geomorphic features, stratigraphic characteristics and sedimentologic interpretation, coupled with optically stimulated luminescence (OSL) dates, of a glacio-fluvio-lacustrine sequence (Linás de Broto, northern Spain) provide new information to understand the palaeoenvironmental significance of dynamics of glacier systems in the south-central Pyrenees during the Last Glacial Cycle (≈130 ka to 14 ka). The Linás de Broto depositional system consisted of a proglacial lake fed primarily by meltwater streams emanating from the small Sorrosal glacier and dammed by a lateral moraine of the Ara trunk glacier. The resulting glacio-fluvio-lacustrine sequence, around 55 m thick, is divided into five lithological units consisting of braided fluvial (gravel deposits), lake margin (gravel and sand deltaic deposits) and distal lake (silt and clay laminites) facies associations. Evolution of the depositional environment reflects three phases of progradation of a high-energy braided fluvial system separated by two phases of rapid expansion of the lake. Fluvial progradation occurred during short periods of ice melting. Lake expansion concurred with ice-dam growth of the trunk glacier. The first lake expansion occurred over a time range between 55 ± 9 ka and 49 ± 11 ka, and is consistent with the age of the Viu lateral moraine (49 ± 8 ka), which marks the maximum areal extent of the Ara glacier during the Last Glacial Cycle. These dates confirm that the maximum areal extent of the glacier occurred during Marine Isotope Stages 4 and 3 in the south-central Pyrenees, thus before the Last Glacial Maximum. The evolution of the Linás de Broto depositional system during this maximum glacier extent was modulated by climate oscillations in the northern Iberian Peninsula, probably related to latitudinal shifts of the atmospheric circulation in the southern North-Atlantic Ocean, and variations in summer insolation intensity

Reaching the boundary between stellar kinematic groups and very wide binaries. The Washington Double Stars with the widest angular separations

Aims. I look for and characterise very wide binaries and multiple systems with projected physical separations larger than s = 0.1 pc, which is generally believed to be a sharp upper limit to the distribution of wide binay semimajor axes. Methods. I investigated in detail 30 Washington Double Stars with angular separations rho > 1000 arcsec. I discarded 23 of them as probably unbound systems based on discordant astrometry, photometry, spectral types, and radial velocities. The remaining seven systems were subject to a comprehensive data compilation and derivation (multi-wavelength photometry, heliocentric distance, multiplicity, age, mass, metallicity, membership in young kinematic group). Results. Of the seven very wide systems, six have projected physical separations larger than the hypothetical cutoff at s = 0.1 pc; four of them have separations s > 0.2 pc. Although there are two systems in young kinematic groups (namely HD 136654 and BD+32 2572 in the Hyades Supercluster, and AU Mic and AT Mic AB in the beta Pictoris moving group), there is not a clear prevalence of young systems (tau < 1 Ga) among these very wide binaries. Finally, I compare the binding energies of the seven systems with those of other weakly bound systems in the field.Comment: A&A, accepted (this version: as sent to language editor

Geometr&#237;a y dep&#243;sitos de las cubetas glaciolacustres del Pirineo

Six lacustrine Quaternary basins of glacial origin from the Pyrenees have been studied by using both geomorphological methods and electric soundings. The localities studied are glacial overdeepened basins (Esterri d'Aneu, Noguera Pallaresa valley; Benasque, Esera valley and Bono, Noguera Ribagor&#231;ana valley), proglacial lacustrine basins formed by a morainic-ridge obstruction (Seminari de Vilaller, Noguera Ribagor&#231;ana valley), juxtaglacial lacustrine basins formed also by a morainic obstruction (Ta&#252;ll, Noguera de Tor valley) and lacustrine basins formed by bedrock faulting of the slopes after glacial wastage (Basses d'Ules, Garona valley). The high contrast between the resistivities from the bedrock and the Quaternary deposits allows us to determine not only the thickness of the Quaternary deposits but also the several Quaternary units by using electric soundings. Generally three Quaternary units are present over the paleozoic bedrock: a basal glaciolacustrine unit with a low resistivity, a middle fluviodeltaic unit of variable resistivity though higher than the resistivity from the glaciolacustrine unit, and an upper alluvial and/or fluviotorrential unit with high resistivities. The thickness of the Quaternary deposits is very variable, ranging from more than 300 meters in the Esterri d'Aneu overdeepened basin to a few meters in the Basses d'Ules basin.<br><br>Mediante la combinaci&#243;n de m&#233;todos geomorfol&#243;gicos y sondeos el&#233;ctricos, se han estudiado 6 cubetas lacustres cuaternarias de origen glacial en el Pirineo. Esterri d'Aneu, Benasque y Bono son unos claros ejemplos de cubetas de sobreexcavaci&#243;n glacial. El Seminari de Vilaller constituye un ambiente lacustre proglacial debido a un cierre morr&#233;nico. El lago de Ta&#252;ll como ejemplo de un ambiente lacustre yuxtaglacial debido tambi&#233;n a una obturaci&#243;n morr&#233;nica y la laguna de Les Basses d'Ules, en el valle de Ar&#225;n, formada a partir de procesos de fracturaci&#243;n del substrato rocoso despu&#233;s de la retirada del glaciar del Garona. Debido al elevado contraste entre la resistividad de los diferentes materiales cuaternarios de recubrimiento y el substrato rocoso, se ha podido determinar mediante sondeos el&#233;ctricos el espesor del cuaternario y diferenciar las diversas formaciones que lo constituyen. En general, aparecen 3 formaciones cuaternarias sobre el substrato rocoso paleozoico: una unidad glaciolacustre que es relativamente conductora, una unidad fluviodeltaica de resistividad variable pero con valores m&#225;s elevados que la anterior, y una unidad superior de resistividades muy variables seg&#250;n la cubeta y que, en general, es m&#225;s resistente. La potencia del relleno cuaternario es muy variable seg&#250;n la cubeta. As&#237; encontramos espesores de m&#225;s de 300 metros de media en la cubeta de Esterri d'Aneu y de tan solo unos pocos metros en Les Basses d'Ules

Three-level modulation techniques to reduce instantaneous common mode voltage in induction machines

Problems on inverter motor drives such as bearing currents are introduced due to common mode voltages. Different solutions are proposed on literature, for two-level or multilevel inverter. Instantaneous zero common mode voltage by using a three-level inverted could be achieved. This paper proposes a commutation strategy that allows zero common mode voltage by using medium vectors, and also a new representation as a plane on the commutation space is defined which is called zero common mode voltage plane. On this defined plane, every turning vector fulfil this property. Simulations and experimental results clearly show method's efficiency

Long-term entrenchment and consequences for present flood hazard in the Garona River (Val d'Aran, Central Pyrenees, Spain)

On 18 June 2013, a damaging flood of the Garona River (Val d'Aran, Central Pyrenees, Spain) caused losses exceeding EUR&thinsp;100&thinsp;million. Few studies have related flood events to the geologic, tectonic and geomorphologic context. This study deals with both short- and long-term processes by studying the upper reach of the Garona River on different timescales and space scales. There has been a clear entrenchment tendency of the drainage network since the Miocene. Post-orogenic exhumation and uplift of the Axial Pyrenees determines the recent and active tectonics of the area and leads to fluvial incision. The last Upper Pleistocene glaciation affected Val d'Aran and gave rise to a destabilization period during the glacial–interglacial transition, marked by a postglacial incision tendency. Mean entrenchment rates between 0.68 and 1.56&thinsp;mm&thinsp;yr^&minus;1 since deglaciation have been estimated. The assessment of the 2013 flood, characterized by the predominance of vertical incision and bank erosion, suggests that the long-term tendency of the fluvial system is reflected in short-term processes. The study of the geologic and geomorphologic evolution, combined with the analysis of this 30&ndash;50-year return period flood event, helps to improve flood risk management by providing contextual information that can constrain predictions and help guide choices and decisions. In fact, the millennial entrenchment tendency is shown at the human scale, which is considered useful for river management, but could be imperceptible in detailed hydrodynamic and channel morphology studies that describe river dynamics mostly at the 10&ndash;15-year timescale