Carlos Martí-Bono

Glacial and Fluvial Deposits in the Aragón Valley, Central-Western Pyrenees: Chronology of the Pyrenean Late Pleistocene Glaciers

Abstract The ragón alley glacier (entral estern yrenees) has been studied since the late nineteenth century and has become one of the best areas in the yrenees to study the occurrence of leistocene glaciations and the relationships between moraines and fluvial terraces. New morphological studies and absolute ages for moraines and fluvial terraces in the ragón alley allow a correlation with other yrenean glaciers and provide solid chronologies about the asynchroneity between global last glacial maximum and the maximum ice extent. Six frontal arcs and three lateral morainic ridges were identified in the illanúa basin terminal glacial complex. The main moraines (1 and 2) correspond to two glacial stages (oxygen isotopic stages 6 and 4), dated at 171 ± 22-ka and 68 ± 7-ka, respectively. From a topographical point of view, moraine M1 appears to be linked to the 60 m fluvioglacial terrace, dated in a tributary of the ragón iver at 263 ± 21-ka. The difference in age between 1 moraine and the 60 m fluvioglacial terrace suggests that the latter belongs to an earlier glacial stage ( 8). Moraine 2 was clearly linked to the fluvioglacial 20 m terrace. Other minor internal moraines were related to the 7–8 m terrace. The dates obtained for the last glacial cycle (20–18-ka) are similar to other chronologies for Mediterranean mountains, and confirm the occurrence of an early in the entral yrenees that does not coincide with the global .

Forests and Their Hydrological Effects in Mediterranean Mountains - The Case of the Central Spanish Pyrenees

Abstract This article considers the effects of forests on the hydrology of a Mediterranean mountain area. Variations of climate factors, discharge, interception, and water table depth in the San Salvador forested experimental catchment in the Central Spanish Pyrenees were studied and the results compared with those from two deforested catchments. The hydrological response of the San Salvador catchment had the following properties: 1) it had both smaller peak flows and smaller low flows than the deforested catchments; 2) most rainstorm events produced almost no discharge response; 3) the intensity of precipitation had no influence on the magnitude of peak flows; and 4) depth to the water table was the most important factor in the relationship between precipitation and discharge. These results confirm that forest conservation reduces floods and soil erosion, particularly on steep slopes.

Temporal variability in hydrological response within a small catchment with badland areas, central Pyrenees

Abstract The lower Araguás catchment, central Pyrenees, is characterized by extensive badlands (25% of the total catchment), whereas the upper catchment is covered by dense plantation forest. The catchment (45 ha) has been monitored since October 2005 with the aim of studying its hydrological response. The 44 floods recorded over this period were analysed to identify the factors that control the rainfall—runoff relationship. The first relevant feature of the catchment was its responsiveness. The catchment reacted to all rainfall events, but the irregular nature of the hydrological response was the most characteristic feature of the response. No single variable could explain the response of the Araguás catchment. It was found that stormflow coefficients mainly depend on the combination of rainfall volume and antecedent baseflow. A significant correlation was observed between maximum rainfall intensity and peak flow values. The shapes of the different hydrographs are very similar, regardless of the peak flow magnitude; they show a short time lag, relatively narrow peak flow, and steep recession limb. This indicates a large contribution by overland flow, resulting mainly from the generation of infiltration excess runoff in badland areas.

Morphometry of glacial cirques in the Cantabrian Range (Northwest Spain)

Two study areas were selected in the Cantabrian Range, in northern Spain, in order to analyse the morphometric characteristics of Pleistocene glacial cirques in a relatively mar- ginal glacial environment. The Western Massif of Picos de Europa (WMPE) (highest altitude at 2,596 m) is characterised by Alpine-like relief and a geological landscape mainly dominated by calcareous outcrops. The sierras of Southwest Asturias (SSWA) (highest altitude at 2,002 m) is a typical Palaeozoic landscape of Appalachian-like relief and is dominated by old erosion surfaces. A statistical analysis found few relationships between environmental factors (altitude, aspect and lithology) and cirque morphometry in the WMPE. Glacial cirque development in this area is therefore likely to be more influenced by structural processes (such as differential erosion and fractures) and karstic erosion. In contrast, a clear increase in cirque size is observed with increasing altitude in the SSWA. In both study areas, cirques are predominantly distrib- uted in areas with N and NE aspects, but particularly so in the SSWA which is of lower alti- tude than the WMPE. In the SSWA but not the WMPE, the horizontal dimensions of the cirques tend to increase more rapidly than the vertical dimensions, supporting the allometric model of glacial cirque development in this area.

Geomorphological consequences of fraquent and infrequent rainfall and hydrological events in Pyrennez Mountains of Spain

Various aspects of pluviometric andhydrological events have been studiedworldwide, one of which is the geomorphichazards as the intensity of the eventsexceeds various geomorphic thresholds.During the last few years, rainstorms ofdifferent intensities have occurred in theCentral Spanish Pyrenees, including one ofexceptional character. Large, historicaldebris flows have been studied, as well asthe actual sediment transport in smallexperimental catchments. This study showsthat during the most frequent eventssuspended sediment transport is the commongeomorphic process. Bedload is mobilizedseveral times per year while small rockavalanches and channelized debris flowshave a return period of at least 5 years.Hillslope debris flows are triggered byrainfall events with a 25–30 year returnperiod. Reactivation of large, deep massmovements is linked to rainfalls of around100 year return period (between 130 and160 mm in 24 hours). Catastrophicgeomorphic processes occur whenprecipitation exceeds a 100 year returnperiod, as was the case of the Biescascampsite disaster. Geomorphic processestriggered by intense rainfall events havecaused major damage and human disastersbut the hazards have been reduced by theintroduction of several control measures,including reforestation, the constructionof check-dams, canalization of riversegments and improved flood forecasting.

Sediment yield and transport in badlands located in the Inner Depression (Araguás Basin, Central Pyrenees)

This study shows the analyses of suspended sediment transport from badland areas developed in the Inner Depression (Central Pyrenees). The importance of these morphologies is related to its frequency, and to the high impact that they produce on the drainage net, because of their intense geomorphological dynamics. The occurrence and development of these morphologies is associated to two main factors: the geological characteristics of the substratum constituted by marls, and the strong climatic seasonality of the submediterranean climate. The area has been studied since 2004, through the selection of a small basin, which was monitored with sensors and plots for observation of weathering and erosion processes (between January 2004 and December 2006). This instrumentation was completed with a gauging station (October 2005) on the main drainage (Rebullesa ravine) that facilitates the record of hydrological response and suspended sediment transport. This paper shows an analysis, based on 79 recorded events between October 2005 and April 2007. The results, that correspond to a short period of time, have allowed pointing out some general characteristics of hydro-sedimentological responses in these morphologies: very high hydrological response, even during the driest period; great capacity of sediment yield and exportation, with punctual concentrations than can reach more than 1000 g·l-1, and the strong sensibility against climatic seasonality. Likewise, it was observed that precipitation intensity is well correlated with sediment concentration, especially during the driest periods, which demonstrates that the main runoff generation process is associated to infiltration excess mechanisms (Hortonian flow). Palabras clave: carcavas, respuesta hidrologica, concentracion de sedimento, transporte en suspension.

The Ordesa and Monte Perdido National Park, Central Pyrenees

The Ordesa and Monte Perdido National Park was created in 1918 and enlarged in 1982 to highlight and protect spectacular high mountain relief dominated by limestone. Alpine tectonics resulted in the piling-up of south-verging thrust sheets leading to the thick sedimentary successions exposed in impressive vertical cliffs. The presence of massive limestones has favoured the development of deep canyons and karst landforms, including karren, dolines, and caves with large shafts. Quaternary glaciations contributed to increase the geomorphic diversity, forming cirques and stunning U-shaped valleys. Small glaciers from the Little Ice Age still remain on the north-facing slopes of the Monte Perdido. Periglacial processes in the most elevated areas of the National Park, as well as erosion in thick soils developed on marly limestone have produced unique geomorphological features.

Hydrological functions of a small mountain cathment with badland morphologies in the Central Pyrenees

The Araguas catchment has been monitored since 2004 to study weathering, erosion and the hydrological and sediment response in order to understand the dynamics of a badland area in a relatively humid environment. This paper studies the main hydrological characteristics of the Araguas catchment, a representative badland area in a subhumid mountain environment. 79 floods have been recorded between October 2005 and April 2007. The results 119 Cuadernos de Investigacion Geografica 2009 No 35 (1) pp. 119-139 ISSN 0211-6820