Formes et dépots glaciaires et périglaciaires de la Serra do Geres-Xurés (Portugal; Galiza) Levé cartographique

[Resumo] Apresentam-se os primeiros resultados de um levantamento cartográfico do pormenor das formas e depósitos glaciários e periglaciários da Serra do Geres-Xurés, levado a efeito por urna equipa de investigadores portugueses e espanhois. Os levantamentos de campo foram realizados nas escalas de 1:5.000 ou 1: 10.000 e tiveram urna importante componente sedimentológica, nomeadamente pelo estudo dos tzlls subglaciários, que se revelaram da maior importancia para o diagnóstico preciso de formas de erosao e de acumula~ao quase sempre pouco nítidas. Esse levantamento nao está ainda completo, mas é possível, desde já, deduzir várias conclus5es acerca da glacia~aoe da morfogénese periglaciária, que sao indicadas no final do texto principal[Résumé] Nous présentons les premiers résultats du levé cartographique détaillé mené par une équipe de chercheurs portugais et espagnols. Les levés de terrain ont été réalisés aux échelles du 1:5.000 ou du 1.10.000. Une attention particuliere a été accordée al'étude des tzlls sous-glaciaires, indispensables au diagnostic rigoureux de formes souvent trop peu claires. Ce levé pas encore terminé, mais il semble possible, des maintenat, de dégager quelques conclusions: 1) Présence, indiscutable, de manifestations glaciaires, tant du coté du Minho que du coté galicien. Cela confume, donc, idées de Schmidt-Thomé et de Coudé-Gaussen. 2) Les formes d' érosion et d' accumulation conservées révelent une glaciation essentiellement de cirque et de vallée. Dans une hypothése de glaciation restreinte, l'épaisseur maximale des langues glaciaires serait de l'ordre de 150 m. Mais ces manifestations représentent, tres probablement, un épisode de retrait des glaciers. L'étude des tills sous-glaciaires suggere, en effet, une glaciation plus ample, avec formation probable d'une calotte de plateau. 3) La répartition spatiale des manifestations glaciaires canographiées montre deux types de contraintes: a) structural, qui commande les directions de grandes vallées englacées; b) climatique, révélant une dyssimétrie NW-SE, avec accumulation préférentielle des neiges du coté oriental (probablement due aun effet d'abri vis-a-vis des vents dominants). 4) Absence d'une morphologie glaciaire typique, ce qui signifie que l'action des glaciers a été peu efficace; elle s'est limitée, pratiquement, a la destruetion et au transport des manteaux d'altérites pré-glaciaires. 5) Monotonie des manÍfestations periglaciaires; il s'agit, surtout, de versant réglés, avec tabliers d'éboulis, et de quelques coulées de solif1uxi6n. Mais c'est ala dynamique cryonivale que revient l'essentiel de l'a1lure des grands versants de la montagne. 6) Absence de pergélisol. Les éboulis et les blocs des grands versants ne sont pas dus ala macrogélifraction. Les actions cryonivales se sont certainement limitées au déchaussemet des blocs, déja préfigurés dans la roche par la fracturation tectonique et par la météoris~tion pré-glaciaire. 7) Absence d'une séparation nette entre l'étage périglaciaire et l'étage glaciaire, al'exception pres du versant galicien. Tout au plus peut-on parler d'un étage forestier (<<étage des arenes», COUDE-GAUSSEN, 1979, 1981), OU les actions cryonivales seraient tres limitees, et d'un étage «glacionival» (ETIICHER, 1988), pres de la limite des neiges persistante

Introducción al patrimonio geológico de interés turístico de la Red Española de Reservas de la Biosfera

160 p.Esta publicación se ha realizado con el objetivo de describir el origen y formación de una buena parte del patrimonio geológico de interés turístico de la Red Española de Reservas de la Biosfera para que éste sea conocido y pueda ser utilizado como motor de desarrollo económico local. La necesidad de dar a conocer este sorprendente patrimonio natural de la Red español de Reservas de la Biosfera fue constatada por su Consejo de Gestores que encargó el trabajo a su Consejo Científico. La publicación tiene la vocación de ser accesible para todos los públicos. Sin embargo, parte de un trabajo bibliográfico profundo abordado con una rigurosa metodología científica. Es además el fruto de una continua colaboración de los editores con las personas gestoras de las Reservas de la Biosfera españolas, así como con varios miembros de su Consejo Científico asesor.Instituto Geológico y Minero de España, Españ

Geogaceta.

Ponencia presentada en la 34a Sesión Científica de la Sociedad Geológica de España, celebrada en la Facultad de Ciencias de la Universidad del País Vasco, Campus de Leioa (Bilbao) el día 30 de mayo de 200

Formation and internal structure of a regenerated coastal sand dune (Biosphere Reserve of Urdaibai, Basque Country)

During a 3 year sand-dune regeneration project in the Laida beach (Biosphere Reserve of Urdaibai) both dune formation process and sedimentary features have been monitorized. The measured bimodal wind regime controls both the formation of bipolar sedimentary structures at different scales and the growth of the sand dune. Main depositional and erosiona! processes controlling sand dune development and the preserved internal sedimentary structures are shown in this pape

Sand-dune regeneration in the Biosphere Reserve of Urdaibai (Biscay, Basque Country)

Promoted by local authorities, a sand-dune regeneration project in the Laida beach (Biosphere Reserve of Urdaibai) started in October 2001. During the first year, two different phases of sedimentary development were observed. Semester 7 (autumn and winter) showed a significant sand accumulation (>3500 m3) due to the dominant NW winds that reached an average velocity greater than 4 m/s. On the other hand, semester 2 (spring and summer) exhibited SE-dominant winds with average velocities between 7-2 m/s. Sand deposition was nill during this period. The final result has been the formation of a supratidal area of 6250 m2 with almost 8 m of maximum height (above national ordnance datum) on this sandy estuarine environmen

Sand-spit accumulations at the mouths of the eastern Cantabrian estuaries: The example of the Oka estuary (Urdaibai Biosphere Reserve)

The majority of the eastern Cantabrian estuaries occur on a coast with waves approaching dominantly from a NW direction. However, at their mouths sand-spit accumulations occur on their eastern margin. These sedimentary features have extended westwards, although the main littoral transport path on this coast is dominantly eastwards. The origin, morphology and development of these sand accumulations can be considered unusual, because they do not show the expected sedimentary response. Through a multidisciplinary approach (surface sediment analysis, morphodynamic, oceanographic and meteorological monitoring, and mathematical modelling) developed during the period May 2005–April 2006 in the Oka estuary, it has been possible to establish a genetic, hydrodynamic and morphodynamic sedimentary model for these estuaries. The main factors to determine the origin of these sedimentary features are wave intensity and direction, wave refraction and diffraction processes, spatial orientation and morphology of estuarine mouths, tidal range and the intensity and direction of tidal currents. On this coast, but elsewhere due to the influence of headlands, usually situated in the western margin of the estuarine mouths, wave diffraction and a variation in energy occur along the approaching waves. Consequently, wave set-up is forced in the eastern side of the estuarine mouths. Because of this induced wave pressure gradient an energy-compensation is needed and thus wave induced currents towards southwest originate. The action of the tidal currents is also important. In this paper a cyclical sedimentary transport pattern for the nearshore zone around the mouths of these estuaries is described. This process is taking place under tidal influence that induces wave set-up and breaking processes and reinforces also the sedimentary transport towards the estuarine inlet. The combination of all these hydrodynamic and sedimentary processes has produced these “anomalously-oriented” sedimentary features

The negative effect of dredging and dumping on shorebirds at a coastal wetland in northern Spain

Dredging and/or dumping actions at coastal environments are a common phenomenon worldwide. The re-working of dumped sediments from their disposal sites to places of great ecological value can have a very strong impact on the ecosystems through deep changes over the communities and the trophic web. Using a relevant dredging-dumping episode carried out in 2003 at Urdaibai, one the chief estuary areas in northern Iberia, we tested the consequence of this action on the subsequent use of the zone by shorebirds. The surface sediment characteristics before and after the dredging and dumping actions were also compared. The dredging at Urdaibai showed a negative effect on bird abundance in three out of the eight species tested overall (dunlin, grey plover, common ringed plover). Highest-ranked models supported a decrease in their population sizes two years after the event. In this scenario, local authorities should be appealed to take dredging and dumping effects into account in order to improve the estuary management.Peer Reviewe

Morphodynamic consequences of dredging and dumping activities along the lower Oka estuary (Urdaibai Biosphere Reserve, southeastern Bay of Biscay, Spain)

Dredging and dumping in the lower Oka estuary (southeastern Bay of Biscay) during 1973–2003 have modified its pattern of sedimentary transport and morphology. An analysis of these activities through time and morphodynamic response of the estuarine system is presented. The relationships between both processes have been established.A Geographical Information System (GIS) has been used to create a temporal cartographic series of the changing patterns of estuarine sedimentary environments, identify the anthropogenic changes generated and observe the consequent responses of the estuarine system. The GIS has proven to be a very useful tool to monitor and evaluate the natural and human induced morphological evolution of the lower Oka estuary during the last 50 years. In the absence of dredging and dumping (1957–1973), the estuary had a distinct pattern of flood and ebb channels. Flood channels are deeper than ebb channels at their mouth, and progressively becomes shallower in the direction of the flooding tide. On the other hand, ebb channels form a seaward extension of the fluvial main channel. Both types of channels are prone to be evasive and braiding was common. During the period of study, the channels showed low natural variability relative to their location and spatial extension. The dredging and dumping carried out between 1973 and 2003 altered the natural flood/ebb channel distribution and modified sedimentary dynamics. Dredging caused the isolation of meanders of the ebb channel, the rapid infilling of the new dredged areas, and affected the flood channels thus producing the necessity for regular dredging, approximately every 5 years.Observation of the natural response of the estuarine system after the dredging and dumping makes it possible to state that, at present, the lower Oka estuary is not in a state of morphodynamic equilibrium and has a tendency to lose its capacity gradually. Dredging and dumping have accelerated this process and have increasingly unbalanced sedimentary regime

An evaluation of the Rouse theory for sand transport in the Oka estuary, Spain

The Rouse profile has been traditionally used to represent the vertical distribution of suspended sand in a marine benthic boundary layer. Yet it is one of the biggest unknowns in estuarine morphodynamics, largely due to uncertainties of the ratio of the sediment fall velocity to bed friction on which the Rouse exponent (R=ws/?ku?) is based. A field campaign was carried out at three different locations in the Oka estuary, northern Spain, in order to examine these uncertainties. Each location differed in grain size and flow condition thus offering a wide range of settings. The first survey was inside the estuary (wave sheltered, flood tide dominated and relatively broad estuary section), the second was at the distal ebb delta (ebb tide dominated and narrow estuary section), and the third was over the wave exposed proximal ebb delta (wave/flood tidal current combined flows and open sea). The aim of this study is to evaluate the applicability of the Rouse (1937) theory for the distribution of sand in suspension throughout a turbulent benthic boundary layer. A modified version of a Helley–Smith sampler was used to trap sand and measure the vertical distribution of sand in the water column. As well, a 1200 ADCP was used to measure flow velocity and backscatter together with an ADV (turbulence). The sand traps were found to have a sampling efficiency of 44%. The grain size at all stations was finer near the surface and coarser near the bed. The sand transport inside the estuary (Station 1) is inwards dominant. By contrast, the sand concentration during the ebb tide was ten times higher than during the flood tide at Station 2 and even higher at Station 3, which suggests that the sand transport over the ebb delta is seawards. The average Rouse parameters for Stations 1, 2, and 3 are 0.48±0.035, 0.78±0.23, and 0.46±0.06 respectively, which correspond to a coefficient of proportionality of the movability number, (?) of 4 ( Van Rijn, 1993). These differ from previous findings of Villatoro et al. (2010) and Amos et al. (2010b)