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SIXTH INTERNATIONAL CONFERENCE ON GEOMORPHOLOGY

GLACIAL LANDFORMS AND EVOLUTION IN THE PYRENEES (THE GALLEGO RIVER VALLEY,

CENTRAL PYRENEES)

E. Serrano and J.A. Cuchí

FIELD TRIP GUIDE - B9

SIXTH INTERNACIONAL CONFERENCE ON GEOMORPHOLOGY

GLACIAL LANDFORMS AND EVOLUTION IN THE PYRENEES (THE GALLEGO RIVER VALLEY, CENTRAL PYRENEES) Enrique Serrano Cañadas(1) and José Antonio Cuchí Oterino(2) (1)Departamento de Geografía. Universidad de Valladolid. Pº Prado de la Magdalena s/n. 47011 Valladolid, Spain E-mail: [email protected]. Teléfono: +34-983423000. ext 6589. Fax: +34-9834279 (2)Departamento de Agricultura y Economía Agraria. Escuela Politécnica Superior de Huesca. Universidad de Zaragoza. Carretera de Cuarte, s/n. 22071 Huesca. Spain E-mail: [email protected]. Teléfono: +34-974239338. Fax: +34-974239302. 1. Introduction to geomorphology and landscape of the Central Pyrenees The Pyrenees is a mountain range followed by the Spanish-French border. It is located between the plains of the Ebro valley, by the south, and the Aquitane basin by the north The Pyrenees extend from the Cantabrian to the Mediterranean Seas over a length of 435 km in an E-W direction with a maximum width of 150 km. The maximum height of 3.404 m is reached at the peak of the Aneto (Fig. 1).

Jaca

Ainsa

Vignemale3303

Monte Perdido3335

Balaitus3144

3129

1928

1769

Gálleg

o

Ara

gón

Ara

Cinca

Pau

Ossau

0 km 60 km 6

0 km 2000 km 200

42º

40º

38º

36º 8º 4º 0º 4º

Bisaurín2.670

Balaitus3.144

Vignemale3.298

Monte Perdido3.355

Ara

gón

Sub

ordá

n

Osi

a

Ara

gón

Gál

lego

Ara

Ara

Vellós

Cinca

Cin

ca

Hecho

Canfranc

Sallent

Biescas

Sabiñánigo

Jaca

Torla

Broto

Bielsa

0 10km

BERNERA TELERATENDEÑERA

PAN

TICO

SA

ORDESA

Figure 1. Location of the fieldtrip area.

Glacial landforms and evolution in the Pyrenees

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A basic division of the landscape can be established based on the clear difference between the northern and southern Pyrenees. At the north side, the Pyrenees are a narrow strip between the water divide and the plain, with a sharp change between the peaks and the plain. It is wet and densely vegetated area. The Mediterranean influence is only located to the east. The southern Pyrenees house many valleys transversal to the chain, producing compartmentalised depressions in an E-W direction. The Mediterranean influence reaches far to the west, configuring a Mediterranean landscape. The Southern Pyrenees are divided in three sectors, the western, markedly atlantic, the central area, of transition (the fieldtrip area), and the eastern, of Mediterranean characteristics. The geological structure of the Pyrenees reflects a double vergent collisional mountain belt derived from the interaction between the Iberian and European plates (Fig. 2). The compression involved a shortening of the crust, starting from the Lower Cretaceous with the development of reverse faults and thrusts. The Iberian plate would be submerged under the European plate from the Late-Jurassic and for 50 million years the thrust systems that characterise the relief took place. The push towards the north of the African plate involved a thickening and shortening of the crust of around 150 km from the Turonian, and the emerging sierras overlie the Ebro and Aquitane foreland basins. All of them form a double vergent asymmetric thrust system with an overlain south directed thrust fault. Later, the isostatic uplift of the chain, and intense erosive processes favouring the drainage of the Ebro and Aquitane basins and configure the hydrographic network. At the end, a very small and marginal volcanism develops in the district of Olot (East Pyrenees) and fault blocks take place during distensive stages (Seguret, 1972; Muñoz et al. 1986, 1994; Vergés and Muñoz, 1990, 1992, 1997; Teixell, 1998; Capote et al. 2002). The incision of the fluvial network and lesser tectonic re-adjustments determine the present day relief.

Figure 2. Structural map of the Pyrenees. (Modified from Teixell, 1996 and Capote et al. 2002).


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The general structure of the Pyrenees is made up of four large units: 1. The Ebro valley basin as the southern foreland basin. 2. The Southern Pyrenees composed of two series of upper and lower thrust sheets. The upper thrust sheet is formed by a succession of southward overthrusts overlying the Ebro basin. This is made up of three overthrust sheets. From west to east: the Marginal Sierras or Gavarnie thrust sheet, the Cotiella-Montsec thrust sheet and the Boixols thrust sheet, placed between the Upper Cretaceous and the Middle Eocene and deformed during the Upper Eocene and the Oligocene. On the orographic axis of the range, the lower thrust sheets form an antiformal stack of palaeozoic basement rocks, southward vergent. 3. The Northern Pyrenees are formed by a stack of thrust sheets northward vergent that affects the basement and sedimentary cover, developed to the north of the North Pyrenean fault and overthrusting on the Aquitane foreland basin. The overthrusts are much lesser developed than in the northern Pyrenees. That is the reason of the strong morphostructural disymmetry of the Pyrenean chain. 4. The Aquitane basin constitutes the northern foreland basin. In the southern Pyrenees the relief is defined by several morphostructural units (Solé, 1942). These are the Axial Pyrenees, the Inner Sierras, the Middle Depression and the External Sierras. On the fieldtrip all the units will be crossed from south to north (Figure 3), paying attention to the first three ones, defined by different authors (Wensink, 1962; García Ruiz, 1989; Serrano, 1998). - The Axial Pyrenees form the highest relief, with heavy and rounded shapes only sharpened by glacial modelling. The Axial Pyrenees possess great rock and morphostructural diversity, with outcrops of slates, limestones, marbles, schists, sandstones, conglomerates, basaltic rocks and granites. The raising and faulting of several Late Variscan batholiths, during the Alpine tectonics, produced landscapes modelled on granite (Balaitous, Panticosa, Cauterets, Neouvielle, Lys, Llardana Maladetas, Aigues Tortes, Marimanya, Querigut) that form the top of the chain. In the palaeozoic rocks, strongly folded, faulted and thrusted, the structural disposition and lithology determine the detailed landforms. The most resistant materials, the Devonian limestones, generate the most energetic relief areas, while in the slates wide intra-mountain valleys are formed (Valleys of Tena, Benasque, Aure, Arán, Ariége). The valleys have complex morphologies with prominences associated to front thrust and harder rocks. All were shaped by Quaternary glaciers. In the Tena valley there is a great difference between the relief elaborated on slate and limestone materials to the west, and granite rocks to the east, configuring an asymmetrical valley. - The Inner Sierras. Forming part of the south directed upper thrust sheets, with complex structures, slices and by fault-propagation folds, dorsal ramps and thrust fronts. They are made up of calcareous rocks with karstic features intensely remodelled by Quaternary glaciations. They form narrow sierras (Sierras of Abodi, Bernera, Collarada, Telera, Tendeñera, Cotiella, Cadí, etc.) that culminate in the massif of Monte Perdido (3355 m). The sierras of Tendeñera and Telera limit the Tena valley to the south, and constitute a high barrier of an imbricate stack of several slices and by fault-propagation folds, which form the southern limit of the Gavarnie thrust sheet.


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- The Middle Depression. Made up of molasse and turbidite folded rocks vergent toward the south. Differential erosion has generated relief and depressions that follow an E-W direction along the south vergent of the Pyrenees (Pamplona basin, Jaca basin, in the study area, or the Tremp basin). In the Upper Gállego basin this unit is subdivided into two morphostructural areas: The turbiditic unit give voluminous and rounded sierras with sharp unevenness that surpass 2000 m, made up of the Ribera de Biescas, Sobrepuerto and Sobremonte areas. In the south Pyrenean a long depression in an E-W direction has been generated by differential erosion on blue marls. This unit has its northern limit in the form of a thrust front that accentuates the intra-mountain depression characteristic. It forms the Canal de Berdún, subdivided by the sandstones of Sabiñánigo in two lesser depressions, the Val Ancha (broad valley) and the Val Estrecha (narrow valley). - The External Sierras. They are formed by a calcareous and molasse folded unit on a south directed thrust, with prominent relief along the contact with the Ebro basin. The succession of sandstones, marls, limestones, dolomites and conglomerates and the folds and complex thrust define the folded relief, of the Sierras de Santo Domingo and Guara, characterised by imbricate folded thrust. The area host also several perched synclines (Oturia, Peña Oroel, Serra de San Joan) and differential erosive depressions.

Gállego

Ara

Isuela

Alc

anadre

Huesca

JacaTorla

Panticosa

1 2 3 4

5 6 7 8

0 10

km

Figure 3. Morphostructural units of the fieldtrip area. 1, Magmatic complex of Cauterets-Panticosa and granite batholith batolith of Panticosa. 2. Palaeozoic complex of Axil Pyrenees. 3. Mesozoic and Tertiary calcareous rocks of Inner Ranges.


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4. Folded Flysch formation of central depression. 5. Folded Eocene marls of central depression. 6. Oligocene-Miocene continental sediments of Guarga syncline. 7. Carbonate cover of External Sierras. 8, Ebro basin, Tertiary. These units present straight-line incisions that evoke the exploitation of transverse tectonic lines to orogenic-strike according to some authors. To others, the existence of a Late-Oligocene infill from which the hydrographic network incides, favoured isostatic uplift, generating the superimposed drainage. That superimposed drainage (e.g. Jaca basin, river Aragon or Canal de Berdún) and antecedent drainage (e.g. north-south main valleys, Gállego, Aragón, Cinca, and so on) are probably mixed in time and place in the Pyrenees. The present day relief has been built up by morphostructural evolution, the hydrographic network and glacial erosion. Pleistocene glaciers occupy the Pyrenean valleys up to 800 m a.s.l. on the southern and 400 m on the northern side of the Pyrenees, with valley glaciers of over 40 km in length. There are still glaciers of small size in the high mountain over 3000 m a.s.l. in places where orientations are favourable (Infierno, Balaitous, Vignemale, Monte Perdido, Posets, Maladetas).

Figure 4. View of Inner Sierra (Partacua and Collarada) and Flysch Fm sierras from Jaca depression. The Larrés glacis (Gl-II) at foreground. The Pyrenees present a gradual transition from the atlantic oceanic climate of the western Pyrenees to the Mediterranean one in the east side. In the central area, the influences of both domains have allowed this sector to be defined as the Upper Aragonese transitional climate zone (Creus, 1980). The limit between the Pyrenees of oceanic and of Mediterranean influences has been established at the Gállego-Ara waterside divide. The Tena valley is situated at the easternmost extreme of the Pyrenees with oceanic influence. It is a valley that presents both influences. The thermal pattern shows a cold climate characterised by strong daily and annual oscillations, with a thermal range of 18ºC at 800 m a.s.l. and 14-15º C at 2100 m a.s.l. The rainfall


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pattern is oceanic, with the maximum in winter and the minimum in summer. The winter is characterised by the accumulation and permanence of snow. The snowpack lasts from the end of November until the beginning of May, varying as a function of orientation and exposure. Snowfall represents 94% of the precipitation in winter at over 2000 m a.s.l., where it remains for over six months, followed by a rapid spring melt (García Ruiz et al. 1985; López-Moreno and García-Ruiz, 2004).

Area Altitude Annual Medial Air Temperature

Climatic characteristics Vegetative period

Human influence

Valleys and down mountains

800-1000 10ºC//18ºC Short winter and hot summer, summer drought.

6-8 months April to November

Human occupation, farming, reforestation

Low slopes and valleys

1000-1600 10ºC / 5ºC Short winter (15-20 days of snow) Cool summer

5 months May to November

Farming, grassland, villages and tourist use.

Middle mountain

1600- 2500 5ºC/ 0ºC Very cold winter (5 months). Snow from November to May

4 months June to September

Meadows above forest line and ski resorts.

High Mountain 2500-3140 2ºC/ -5ºC Long winter (7 months) and cool summer. Summer air temperature <0ºC above 2725 m a.s.l. Presence of permafrost

1-5 months July to August

Rocky high mountain and small glaciers. Ski resorts and mountaineering.

Table 1: Altitudinal climatic and landscape belts of the High Gállego basin In the Upper Gállego, between Sabiñánigo and the Panticosa Spa, there are diverse hydrogeological units: - Unit 1. Quaternary infills of the Ribera de Biescas and El Serrablo. The fluvioglacial and glacial infills, and bottom-valley alluvial cones host a slightly studied aquifer, limited by the impermeable turbidites. It recharges by surface water losses and direct rainfall, and discharges into the Gállego river.

Site Altitude m a.s.l.

Precipitation mm/yr

Mean Annual Temperature

Sabiñánigo. 780 806 10.6 ºC Biescas. 875 1097 9.1 ºC

Balneario de Panticosa 1638 1184 7.0 ºC Table 2: Basic climatic data - Unit 2. Karstic systems of Telera-Tendeñera. These include limestones of the Upper Cretaceous -Cenomanian to Maastrichtian- and sandstones (Marboré formation), and limestones and dolomites of the Paleocene on the top. To the south they thrust over the turbidites of the Middle and Upper Eocene, bringing materials of very different hydrogeological characteristics into contact. The limestone receive high precipitation with a large percentage of snow. On the northern side of the calcareous sierras there are glacial features superimposed on intense karstic shapes, whose origin is clearly prior to the last glaciation (Serrano, 1995). The different hydrogeological behaviour between the calcareous and turbidite formations implies the existence of a spectacular springs, were emerge water infiltrated in the limestones. This scheme is common throughout the western Pyrenees with examples such as the


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Castillo spring at the Veral valley, Rigüelo at the Estarrún valley, Villanúa at the Aragón valley, Santa Elena de Bujaruelo at the Ara valley, Puyarruego at the Bellós gorge or Fornos at Irués headwater. - Unit 3. Aquifers of the granite Batholith of Panticosa. This is a Late-Variscan igneous body intruded in the Devonian limestones and shales. It presents four approximately concentric divisions with a monzogranite nucleus surrounded by light granodiorite, dark granodiorite and an outer zone of quartz gabbrodiorites. At Panticosa Spa basin three aquifers have been identified (Table 3).

Aquifer Temperature Characteristics Surface aquifer

Cold Free. Fed by high mountain stream flows and found in sediment cover, over 30 metres in thickness.

Fissured aquifer

Cold Situated in fractures of plutonic rocks of the high and medium mountain.

Fissured aquifer

Warm 45º

Rising by fissures in the sides and the bottom of the basin infill, it generates in the area of the surrounding peaks and has a residence time longer than 30 years (Tritium=0). Geothermometers suggest descents of around 2.5 km.

Table 3: Aquifers in granite materials at Panticosa Spa basin. The study area constitutes a region of biogeographical transition between Atlantic and Mediterranean conditions, with alpine conditions at over 2500 m a.s.l. The vegetation of the Upper Gállego is of great richness and complexity with a staged altitudinal characteristic of the oceanic-Mediterranean transition in the Pyrenees (Montserrat, 1971; Martínez de Pisón et al. 2001) (Fig. 4).

Altitudinal zones Altitude m. a.s.l

Plant communities

Vegetation Type

Species Human use

Chaparrall Quercus Rotundifolia, Buxus Sempervivens Artostafilus uva ursum

Farming and abandoned fields

Oak forest Quercus Faginea, Quercus pubescens, Acer monspesulanus, Prunus ssp., Buxus sempervivens

Farming and abandoned fields

Submontane Supramediterranean

600 to 1000-1200

Evergreen forest

River communities

Quercus sessiliflora, Fraxinus ssp., Tilus ssp., Acer campestris, Coryllus avellana

Meadows and Fraxinus

Evergreen conifers 1500 and 1700

Pine forest Pinus sylvestris Coryllus avellana, Ilex aquifólium. Regressive formations: Buxus sempervirens and Sarothamnus scoparius.

Montane Oromedite- granean

1000-1200 to 1700

Decidious forest Beech and abies forest

Abies pectinata, Fagus sylvatica

Pastures, abandoned fields and forest

Subalpine 1700 to 2300

Evergreen coniferous forest

Black pine forest, larch forest

Pinus uncinata Juniperus communis Sorbus chamaesmespillus, Rhododendron ferrugineum

Meadows and ski resorts, hydroelectric power.

Alpine 2500 to 3404

Alpine tundra Herb-fields, meadows.

Juniperus communis Poa, Carex, Trifolium, lichens.

Mountain and ski resorts

Table 4: Altitude of vegetation belts of Upper Gallego valleys


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2. Glacial geomorphology of High Gallego basin (Tena Valley and Ribera de Biescas). The Gállego basin was occupied by glaciers in the upper part, in the Ribera de Bisecas Valley and Tena Valley. The Upper Gállego is located between deep valleys (Aragón, Aurín and Ara), and opens in the meridian direction. The Ribera de Biescas is a broad valley shaped by Pleistocene glaciers, limited by the waterside divides on gentle mountains. To the north, the Tena valley is an intra-mountainous valley with its limit at the Atlantic waterside divide. The valley reaches 3151m at the Balaitus, 3082 m at the Infierno, 3005 m at Gran Fache and 3051 m at Argualas peaks. The relief derives from the rock diversity and structural complexity, which generates the succession of morphostructural units described above and the glacial evolution.

Figure 5. Geomorphologic sketch of Tena valley (Martínez de Pisón and Serrano, 1998). 1. crests, ridges and peaks. 2, rivers. 3, lakes, reservoir. 4, glacial cirques. 5, overdeepened basin. 6, rock bar. 7, glacial trough limit. 8, Palaeoglacial diffluence. 9, moraine. 10, till. 11, supraglacial till (palaeo debris covered glacier). 12, proglacial terraces. 13, rock glacier. 14, ice patches. 15, glacier. 2.1. Glacial evolution and morphology The Tena Valley is located at the head of a broad glacial set whose tongue to Sabiñánigo was almost 40 km long. The shapes of glacial origin characterise the organization of the relief and mountain landscape (Figure 5). The eastern sector of the Tena Valley (Bolática, Caldarés, Aguas Limpias valleys), outcroped by granites, is characterised by its higher peaks and complex physiography, with “alpine” glacial landforms, and a greater proliferation of lakes and watercourses. In the western sector (Lana Mayor, Escarra, Culivillas), slates outcrops are predominant -without granites- and this area is limited to the west by calcareous cover. It is lower and simpler, without great evenness, and the glacial landforms -cirques, rock bar and basins- are


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less clear. The morphostructural dissymmetry of the valley has generated a marked glacial dissymmetry. The Ribera de Biescas, on the other hand, is formed by a homogeneous glacial trough of 31 km in length, which opens up into a wide valley when it reaches the Jaca depression. The erosion landscape was produced by a relatively moderate but persistent glacial feed from the heads (Figure 6). An ice thickness of 600 m has been recorded at the glacial maximum in Escarrilla and Panticosa, 400 m. in Santa Elena and 400 m in the Ribera of Biescas, with a sharp drop in the sector of Satué-Sabiñánigo. Erosion landform analysis shows several glacial morphogenic phases.

Figure 6. Glacial trough of Pondiellos valley in the Axial Pyrenees, Tena valley. Contributions to the knowledge of the glacial landforms and evolution of the Upper Gállego basin began in the XIX century with Schrader (1836), who dealt with the upper mountain, while Mallada (1878) and Penk (1885) dealt with the glacial deposition landforms and the lateral obturation complexes of the Gallego Valley. These works were followed by Vidal Box (1933), Panzer (1948) and Solé Sabarís (1942), who made a first approach within the pluriglacial theory. More detailed studies on Quaternary glaciation problems carried out by Casas & Fontboté (1945), Fontboté (1948) and Barrère (1952, 1953, 1966, 1975). Martí-Bono (1977, 1978), Menéndez & Martí (1973), Montserrat (1992), García Ruiz et al. (2003); González et al. (2004), Sancho et al. (2004) and Peña et al. (2004) worked on chronological problems. There are also cartographic contributions (Barrère, 1966; García Ruiz & Puigdefábregas. 1982; García Ruiz, 1989, Serrano,


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1991), studies on present day glaciers (Martínez de Pisón & Arenillas, 1988, 1992; Martínez de Pisón et al. 1995, 1997, 1998) and rock glaciers (Serrano & Rubio, 1989; Chueca, 1989, 1992; Serrano and Agudo, 1998, Serrano et al. 1995, 1999). Studies also have been made on the upper mountain phases, Lateglacial and Little Ice Age in the Tena Valley (Serrano and Agudo, 1989, 2004; Serrano, 1991, 1998). Contributions on glacial geomorphology and the Quaternary evolution have been made on the Gállego valley (García Ruiz, 1989; Serrano, 1991, 1995, 1998; Martínez de Pisón and Serrano, 1996; García Ruiz et al. 2001) and also syntheses including the Upper Gállego (Serrano and Martínez de Pisón, 1994; García Ruiz and Martí Bono, 1994; Peña et al. 1998, Chueca et al. 1998, Gutiérrez Elorza et al. 2002). The following are the glacial phases in the Upper Gállego, as they are understood at present knowledge state: 2.1.1. The pre-maximum phase. The blocks and mega blocks scattered throughout the Espierre and La Sía valleys have a glacial origin (Penck, 1885; Fontboté, 1948, Serrano, 1998). They may be classified as remnants of till or proglacial deposits but are related neither to the main glacial landforms nor to the existing deposits. In Yesero they are all located over the ancient bottom of the valley where there is also a lateral lake complex. The valley bottom deposits include scattered granite blocks and supra-glacial till covered by lake and slope deposits. These sedimentary records and erosion landforms point to a stage previous to the main glacial landforms. This is mainly deduced from the reworked till included in recently altered ancient hillside deposits; the lack of well preserved landforms, their uneasy connection with the major glacial phase and their relationship with pre-glacial topography. They are remnants of an ancient cold phase, deposits created on a different morphology to those of the present and the Pleniglacial. Its features have been correlated to the slope and fluvial landforms previous to the Pleniglacial (Serrano, 1991, 1998) and this phase may be located in the Middle Pleistocene, as has been indicated in other places in the Pyrenees. 2.1.2. The Pleniglacial: Ice maximal expansion The landforms related to the Pleniglacial phase (G.Ph.A) are the most important in glacial morphology. They are the most representative in the upper Gallego basin, and they constitute a large number of deposition and erosion landforms (Figure 7). The pleniglacial landforms in the stabilisation maximum phase indicate glacial thickness of 300 m in Ribera de Biescas, 400 m in Santa Elena and 600 in the Tena Valley. The largest ice extension in the Gállego Valley is performed by the three pulsations registered in the lateral morainic complexes and in the frontal one in Senegüé-Sabiñánigo (Serrano, 1991). We can differentiate: a Maximal Expansion Pulse (G.Ph 1, Sabiñánigo phase) marked by the external moraines in the lateral complexes of La Ribera de Biescas and Tena Valley, and by the sedimentary records at the Satué depression and Sabiñánigo area; an Intermediate Regressive one (G.Ph 2, Aurín Phase), related both to the Aurín moraine and to the intermediate moraines located in the Ribera de Biescas lateral complexes; and the Inner Stabilisation one (G.Ph 3, Senegüé phase), represented by the Senegüé frontal moraine and the inner lateral ones in Escuer, Oliván and Gavín. All belong to the same phase, being the result of smaller pulsations in the Pyrenean Pleniglacial (G.Ph. A.).


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Balaitus

Gran Fache

Brazato

Telera

Tendeñera

Escarra

El Portalet

Aurín

Gál

lego

Erata

Cotefablo

N

0 1km

Figure 7. Last Glacial Maximum in the Upper Gállego basin and main flow line. The black areas are the Pleistocene lateral moraine and obstruction lakes complex. On the northern side of the Pyrenees the glacial maximum has been established prior to 38000 B.P. with some retraction and stability periods until 26000-24000 B.P. when the definitive retraction and deglaciation began (Mardones. 1982; Jalut et al, 1982; Mardones & Jalut, 1983; Herail et al. 1987; Andrieu et al, 1988). Recently, OSL dating has been made on several terraces and moraines in the Cinca Valley, with an OSL age of between 49000 and 66200 years B.P. (Sancho et al. 2003). In the same way, OSL dating of moraines and terraces has been performed in the Sabiñánigo area (Sancho et al. 2004; Peña et al. 2004). The analysis of moraines gives an OSL age of 35700 years B.P.-MIS3a- for G.Ph.3, indicated by the Senegüé moraine; an age of 85000 years B.P.-MIS 5a- is attributed to the Aurín complex (G.Ph 2) and, finally, the age obtained for G.Ph1 is 155800 years B.P. -MIS 7- by means of the dating of a terrace (811 m a.s.l.) is related to a roched


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moutoneé hill (807 m a.s.l.). The uncertain morphostratigraphic relationship between the glacial feature (lowest) and proglacial deposit (highest) and our prior morphostratigraphic interpretation (Serrano, 1991, 1998) connecting the terrace with the level of glacis II (Gl-II, prepleniglacial) does not, for the moment at least, permit this age to be put down to G.Ph1 (Sabiñánigo phase), indicated by Satué-Sabiñánigo glacial features. The hypothesis of an MIS 7 is only supported by dating of fluvial sediments of presumed glacial origin but not by any evidence of sediments of unequivocal glacial origin, such as till. Whatever the case, the Gállego Pleniglacial phase (G.ph.A) is prior to the last Northern European glacial maximum and the period of maximum cold (18000-20000 years B.P.). The Gállego Pleniglacial phase would have its maximum before 35700 years B.P. and hypothetically the frontal moraine complex of Senegüé-Sabiñánigo would have an age of 85000-35000 years B.P. From this age, deglaciation started in the lower areas. 2.1.3. The Late-Pleistocene retraction phases. After the maximal glacial stage a continuous and complex retraction took place (Figure 8). It had small pulsations that created deposition landforms always in the inner Tena Valley up to the Santa Elena Canyon. This phase has been divided (Serrano, 1991, 1998) into different episodes: - Late-Pleistocene retraction I (G.Ph.4a) or Búbal phase. This contains small landforms set in a confused disposition. These may be signs of a smaller equilibrium related to a dynamic variation of the glacial tongue itself, resulting in a local morphogenetic phase in Santa Elena. Nevertheless, it does not mean a stable climatic phase. - Late-Pleistocene retraction II (G.Ph.4b), Disjunction phase (Lanuza and Panticosa moraine complexes). This phase is well-defined and can be found in the river Gállego, Lanuza and Escarrilla complexes, as well as those at Panticosa. This last phase is the so-called "disjunction phase" by Barrère (1963), since the glacial tongues remained definitely separated and enclosed within the mountains. By that time, the glaciers had left the main valley and only remained in the Panticosa basin -the Caldarés tongue-, and in Lanuza -the Aguas Limpias-Gallego tongue-. These disconnected tongues are responsible for the deposition of two lateral moraine complexes into the Tena valley (Lanuza and Panticosa) that show the climatic character of this pulsation. By correlation with the north Pyrenean side, the Late-Pleistocene retraction was produced following the last stopping period, dated about 26000-24000 years B.P. (Mardones, 1982; Andrieu et al., 1988). These authors believe that a progressive retraction until its retreat to the upper valleys was produced about 16000-15000 years B.P. This chronology has been confirmed in the Tena Valley by Montserrat (1992), García Ruiz et al. (2001, 2003) and González et al. (2004). The peat bog and lake deposits in marginal areas of the Tena Valley point to an early glacial disappearance and a new pulsation phase around 20000 years B.P. (Monserrat, 1992; González et al. 2004). This phase is related to “Disjunction phase” in larger glaciers of Caldarés and Aguas Limpias, when the eastern side of the Tena Valley was occupied by tongue glaciers of tens of km in length.


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A B C

Aurín

Aurín

Aurín

Gálle

go

Gálle

go

Gálle

go

Balaitus Balaitus Balaitus

Figure 8. Pleistocene glacial evolution in the Upper Gállego basin. A, The Last Glacial Maximum (G.Ph.A). B, LatePleistocene I, Búbal phase (G.Ph.4a). C, LatePleistocene II, the disjunction phase(G.Ph.4b). 2.1.4. Glacial phases in high mountain: Late-glacial. Almost the entirety of the deglaciation was produced after the Late Pleisocene retraction. Afterwards, three morphogenetic phases totally different from the previous retraction occurred in the upper mountain (Figure 9). This is characterised by small glaciers of less than one km length and located in the highest cirques. In this episode the glaciers extended around the highest peaks. In the Panticosa and Balaitus massifs there are several glacial front complexes and lateral moraines (Serrano and Agudo, 1988; Serrano, 1991, 1998; Serrano and Martínez de Pisón 1998) that point to different episodes. Remnants of depositional glacial landforms can be found in many cirques above 2300 m a.s.l. at Ibones Azules, Espelunz, Arnales, Lana Cantal, Punta Zarra, Pecico, Brazato, Letrero, Batanes, Baldairán-Ferreras and Sierra de Tendeñera and there are also rock glacier complexes. Three areas with different glacial behaviour can be distinguished according to their location, lithology and height. The largest glaciers are found in the metamorphic zone, better fed because of their exposure to the cold fronts from west and their greater height. In the granite zone the ice feed is less favoured and so glaciers are associated with northern exposures. Here, the evolution with two periods, pointed out in the metamorphic zone, is of geomorphic importance (Figure 10). Both in the southern zone and in Tendeñera there is a single period, again because of the little importance that glacial processes had on those areas. The morphological evidence shows two main phases:

- High mountain pulse I (G.Ph 5a), an expansive one. The morphogenesis is basically glacial, with glaciers close to 1 km long. There are also rock glaciers -the only ones that show great development- accompanied by an intense periglacial activity (Serrano, 1990, 2004).


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Figure 9. Glacial evolution in the Tena valley (Martínez de Pisón y Serrano, 1996). A and B. First and second LatePleistocene dynamic retraction phases (G.Ph.4a and b). C and D, Lateglacial I and II phases (G.Ph.5a and b).

- High mountain pulsation II (G.Ph 5b). The most important morphological evidence of this phase is found at a greater altitude than the previous ones; moreover, it is scarcer. These circumstances imply the existence of glacial processes encouraged by altitude and exposure conditions, as well as periglacial processes forming rock glaciers.

Starting from glacier extension and location, and by correlation with the bibliography (Taillefer, 1968, 1985; Mardones & Jalut, 1983; Vilaplana, 1983; Montserrat & Vilaplana. 1987) these landforms have been related to the Late-glacial period (Serrano, 1991, 1998) and their chronology has been established between 13000 and 10000 years B.P. Palynologic analysis only detects a cold phase in the Late-glacial (Monserrat, 1992; González et al., 2004) but the geomorphologic features allow us to establish two glacial morphogenetic phases. Both are included in the Late-glacial because, studying the morphological position of the moraines and the lichen cover, it has been established that they are very close in time (Serrano, 1991; 1998). Based on palynology analysis (Duplessy etal., 1981; Ruddimann & Mcintyre, 1981; Jalut & Mardones, 1984), the first pulse has hypothetically been assigned to the first episode of the Old Dryas, and the second one is located in the recent Dryas.


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Figure 10. Lateglacial and Holocene readvances in the Panticosa massif area. A, Lateglacial I phase (G.Ph.5a). B, Lateglacial II phase(G.Ph.5b). C, the Little Ice Age readvance (G.Ph.6). 1, crests, ridges and peaks. 2, hydrographical net. 3, glaciers. 4, ice patch. 5, rock glaciers. 6, protalus lobes.


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2.1.5. High mountain phase III, the Little Ice Age. This phase (G.Ph 6) represents the last cold pulsation of some morphogenetic importance in the high Gállego basin (Figure 10). The remnants found in the Infierno massif northern slope, Tendeñera north face and Balitus massif belong to this stage. They constitute small moraine complexes showing frontal, lateral and retraction accumulations. During this period the glacial morphogenesis had a limited importance. They are only located in very local places where conditions were most suitable. The main features are: steep walls, peaks above 3000 m a.s.l. and cirques above 2600 m a.s.l. exhibiting N and NE exposures. The glacial phase has been attributed to the glacial reappearing between the XVIth and XIXth centuries, the Little Ice Age. In the Infierno and Balaitus massifs, from historical papers, Martínez de Pisón & Arenillas (1988) have checked the existence of ice tongues which started their retraction in the 1880s. Some large and cracked tongues were located and described by scientists and climbers like Russel in 1867, Lequeutre in 1874 and Mallada in 1878. In 1898 Schrader (1936) indicated two glaciers in the Infierno massif, one more in Pondiellos and four in Balaitus. Two glaciers, now disappeared, existed in the Tendeñera Range in this period (Serrano, 1995). The Little Ice Age is a complex glacial phase with at least three pulsations between the XVIII and XIX centuries, and a quick and recent deglaciation (Serrano et al., 2002). 2.1.6. The present day glaciers and geomorphic dynamic. In the Upper Gállego there are two clearly differentiated active morphogenic environments. The upper timberline environment (Barrio & Puigdefábregas, 1987; García Ruiz et al. 1988; Serrano et al. 1998; Martínez de Pisón et al. 2001) has predominantly soil saturation processes, solifluction and freezing and thawing cycles, which act on land free of vegetation. The forest mountain, in which snow and periglacial processes are weakened and the forest stabilises the slopes. On these, the steep falls and human intervention lead to intense and occasional morphogenetic processes. - The glaciers and high mountain: The period between the last expanding phase and the present day is characterised by the nearly complete upper mountain deglaciation. It has known occasional glacial advances and annual variations until recent decades (Martínez de Pisón & Arenillas, 1988; Martínez de Pisón et al., 1991, 1997; Serrano et al. 2002). A strong retraction has been suffered by glaciers during the last decade. Nowadays, the latest period of retraction is occurring, and it may be in its final phase. The ice-patches of Frondellas and Latour in Balaitus massif, the ice patches of Punta Zarra and the little glaciers of Infierno massif are the only features of glacier dynamic in the Tena Valley (Figure 11). Only a single glacier remains with landforms showing some movement, located in the western cirque of the north face of the Infierno. This feature marks the end of the morphogenesis caused by ice and glacial dynamics in the field trip area, now characterised by an active periglacial dynamic. It is a deglaciated high mountain dominated by vigorous periglacial and nival processes. We must point out the presence of the Argualas rock glacier, an ice body of 20 m medium width and a medium movement on the axis of 22.5 cm a-1. The slopes of the high mountain are the domain of active solifluction, generated by periglacial processes above 2400 metres. These processes generate debris sheets, protalus lobes, protalus rampart, avalanche landforms and deposits, rock glaciers and above all lobe and sheet solifluction, producing intense source to sink sediment transfer processes which make the high mountain a very dynamic morphogenetic environment. Below 2400 metres the melting snow, periglacial


17

processes and the action of man through intensive deforestation generate a highly active environment in which mass movements predominate in extremely varied proportions and intensities. Both deep (slope slides) and surface mass movements (solifluction sheets and lobes) are very common, becoming characteristic of large deforested surfaces (as occurs around El Formigal).

Figure 11. Glaciers of Tena valley (from Martínez de Pisón, 1994) A, Balaitus massif, southern side. 1, ice patch of Frondellas. 2, Ice patch of Balaitus. B, Infierno massif, northern side. 1, Eastern glacier of Infierno. 2, Western glacier of Infierno. - The forest mountain: Below 1600 metres conditions of geomorphological stability are present, with scarce mass movements and very rare alluvial heads. Only slow frost creep processes affect the steeper forested slopes and permit the observation of a dynamic that neither generates soil loss nor outstanding morphogenetic features. The inactive or active slide slopes also constitute unstable environments inherited from previous phases and determined by lithological and structural organization. In the lower areas (800-1250 metres), greatly altered by human activity, intense geomorphological processes are generated in favour of the abandoning of cultivated land and the restoration of a natural dynamic. In the low areas and glacial troughs, lithological alternation, limestone drainage, saturation of slates and postglacial strain produce instability of the


18

slopes and slope slides of great dimensions, rotational and translational slide slopes or rock fall are generated. These partially occupy the valley bottoms, visible in Panticosa, El Furco, Las Saras, la Costera Ordenal or Lanuza. 3. The fieldtrip in high Gállego. The Tena Valley fieldtrip begins in Zaragoza, at the centre of the Ebro Valley, in a semi-arid and steppe landscape, smoothed by the irrigated land. To the foot of the Pre-Pyrenees to the north of Huesca, the route crosses the north side of the Ebro sedimentary basin formed by continental Miocene rocks. The alpine tectonic closed a wide depression at the end of the Tertiary, partially infilled by alluvial fans from the Pyrenean rivers. At its apex, gravels were deposited which became conglomerates. A little further south sands were deposited with abundant palaeochannels, and later muds and clays. The evaporation of the waters reaching the arid centre of the depression led to considerable thicknesses of gypsum and halite. The later opening up towards the Mediterranean generated a strong erosive process and the creation of fluvial terraces and glacis systems, mapped by Alberto et al. (1984). The route initially follows the fluvial terraces of the river Gállego, studied by Benito (1989). Areas of gypsum are also crossed which show infilled dolines and flat floored little valleys (named vales). From Zuera it crosses the ancient desert of La Violada, transformed by the irrigation in the 1960s. From Almudebar, the road crosses the Monegros irrigation channel and a monocline hill of mud material is ascended. It gives way to la Hoya de Huesca, a broad depression excavated by the rivers Isuela and Flumen. From this point a first sight is made of the Pyrenean front and, at the foot of the Pre-Pyrennean sierras, “Los Somontanos” (a name of undeniably Latin root whose meaning is “under the mountain”). Diverse staged levels of glacis characterise them, as studied by Rodríguez Vidal (1986). The glacis descend a gentle ramp towards the centre of the Ebro depression and they are covered by gravel sheets of modest thickness, today occupied by cereal, almond, olive and vineyard crops. To the north of the city of Huesca the Pre-Pyrenees are the beginning of the Upper Aragonese mountain (External Sierras). It presents a complex structure, in thrusting scales formed by limestones of Upper Triassic to Middle Eocene of Guara Fm.(Millán,1996). By the south, the External Sierras are connected to the Tertiary conglomerate in the border between the Ebro basin and the Pyrenees. On the Miocene conglomerate the typical features named “Mallos”, isolated conglomerate towers and needles have been built up close to the calcareous hills. To the north, the Pyrenean front thrusts are followed by diverse depressions carved in the Eocene marls outcrops. The differential erosion between limestone and marls shapes depressions characterised by structural crests and successions of glacis, studied by Pierre Barrère (1951, 1975) and which is used today as a reservoir basin. After crossing the Arguis depression, the sandstones of the Oligocene age form the Monrepós pass. This pass offers a magnificent view of the intra-Pyrenean depressions formed by sandstones and marls, dominated by the conglomerate perched synclines of Santa Orosia, Oroel and San Juan de la Peña, as well as the Inner Sierras, with the highest peaks, Monte Perdido (3353 m), Tendeñera (2853 m) and Telera (2764 m). From the pass we go down, crossing the syncline of the river Guarga. In Rapún, after crossing the river Guarga, the layers gain in verticality.


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Sorripas

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830

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Figure 12. Geomorphologic sketch of Senegüé-Sabiñánigo area (modified from Serrano, 1991). 1, rivers. 2, homocline formed on sandstone. 3. ridge on marls. 4, moraine. 5, till. 6, fluvioglacial terrace I. 7, fluvioglacial terrace II. 8, Depresión infill by lacustrine sediments. 9, fluvial terrace. 10, glacis (I, oldest level; II, main level; III, younger level). 11, glacial trough limit. 12, scarp, 13, village.


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In Sabiñánigo the easternmost extreme of the Canal de Berdún is reached, a wide depression elaborated in middle Eocene blue south Pyrenean marls (Larrés and Pamplona marls), here divided in two smaller valleys, the Val Ancha and the Val Estrecha, separated by the alignment of Capitiellos, monoclyne crests of the sandstone of Sabiñánigo. The depression is modelled by successive levels of glacis (Barrère, 1975, Serrano, 1998) staged to the wide fluvioglacial plain that occupies the bottom of the valley (Figure 12). There are three levels of glacis (Figures 14 and 15): - The upper level (Gl.I), named “Coronas” (“Crowns”), represented by small topmost remains. - The level of “main”glacis (Gl.II), in which Barrère (1975) distinguished between the glacis-cono features, like the one that descends from the valley of the Aurín, and the front-glacis, associated with a slope dynamic (photo X). - The lowest level (Gl.III), It is a highly compartmentalised level which has been related with the glacial landforms of the bottom of the valley (Serrano, 1998).

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ines

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Figure 13. Lithostratigraphic log of Senegüé and Aurín moraines.


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Figure 14. Glacis of Senegüe area, Val Ancha. Gl-II, main glacis. Gl-III, younger glacis level. Stop 1: The frontal morainic complex of Senegüé The small village of Senegüé is situated over a frontal morainic arch found in the central part of the Gállego valley. The moraine is formed by a succession of lodgement and supraglacial till, with the alternation of facies Dmm and Fm, which generate an arch perched to the exterior and with a strong interior slope, curved and closing the valley (Figures 12 and 13). From the moraine a wide range of the glacial and fluvioglacial landforms of the Sabiñánigo proglacial plain can be seen. To the south the ancient fluvioglacial terrace forms the main plain, linking to the lower glacis levels (GlII). In the morphology now deteriorated by a quarry , a small depositional glacial landform formed by till (Dmm and Dcm facies) (Figure 13) is observed (Barrère, 1966; Serrano, 1991, 1998). The Aurín moraine would indicate a phase of greater extension of the glacier of the Gállego, and recently has been dated at 85000 years B.P. (Peña et al. 2004; Sancho et al. 2004). Downstream a wide fluvioglacial plain continues (T-I), with erosive steps associated with the moraine described. The remains of till and the moraines of the Lárrede sector to the NE of Senegüé, the till of Latas and the glacial erosive landforms of Sabiñáñigo, spread throughout the area studied, would be witnesses to the greater glacial phase, whose front would reach the sandstone crests of Sabiñánigo-El Puente. All the glacial landforms are inscribed below the staged glacis, and in relation to the last level (Gl.III). The observation of the geomorphological history of the Pyrenees during the Pleistocene is possible. Towards the north, the glacial trough of the Gállego is shaped in the turbidites of the Echo Group (Flysch), with deposits and slide slopes, and a wide alluvial fan that descends from the lateral valleys.


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Figure 15. Long profile of Senegüé-Sabiñánigo area (modified from Serrano, 1996). S1, planation surface. RH1, oldest palaeohydrographical net. RH2, palaeohydrographical net 2. G-I, oldest glacis level. G-II, main glacis level. G-III, younger glacis level.

* * *

From Sabiñánigo the national road N-260 (Trans-Pyrenean road) continues down the valley of the river Gállego, dominated by turbidites of the Upper Eocene. The bottom of the valley is characterised by glacial and fluvioglacial infills, as well as diverse alluvial fans, which together form a hydrogeological unit. The source of sediments of these alluvial fans are in the lateral moraines of the valley and in the alluvial heads, with a highly active dynamic that confers sectorial characteristics on the alluvial fans (Gómez-Villar, 1996) with highly active sectors together with less active and partially vegetated ones, or inactive ones, occupied by meadows. This unit houses a slightly studied aquifer, limited by impermeable turbidites. It is fedded by stream water losses and direct rainfall and discharges to the Gállego river. It is used to supply Sabiñánigo, from a well, situated upstream of Senegué. Stop 2. Lateral morainic complex of Sobremonte and the Arás steep riverbank. The route follows the glacial valley of the Gállego, with affluents in perched valleys and active alluvial fans, such as the sadly famous “Barranco of Arás”, near of Biescas, The 7th of August 1996 there was a flash flow that swept away a camp-site, killing 87 people.


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Figure 16. The Sombremonte lateral moraine complex. A. Geomorphologic sketch of Sobremonte area. 1, crests, ridges and peaks 2, rivers. 3, scarp. 4, moraine. 5, till. 6, reworked till. 7, glacial trough limit. 8, rock bar. 9, overdeepened basin. 10, lacustrine sediment. 11, alluvial fan. 12, fluvial deposits. 13, villages. B, long Profile of Sobremonte valley. 1, subtract. 2, till. 3, lacustrine deposits. 4, slope deposits.

The lateral valley of Sobremonte constitutes a valley perched over the glacial trough of the Gállego, whose tongue deposited a wide lateral morainic complex (Figure 16). It is formed by three lateral moraines that block the valley, generating three obstruction lakes which were formed and functioned successively in time. An outer moraine (G.Ph1) closed the valleys of Betés and Aso at 1200 m a.s.l., forming large lakes that together now make up the flattened and fertile bottom valley, still occupied by the meadows and cattle. A second moraine (G.Ph. 2) is situated at 1150 m a.s.l., and produced a single lake, where the village of Yosa is now found. Finally, a third moraine (G.Ph3) formed a smaller lake in the wide intermoraine depression. In this last moraine the spectacular erosive landforms, the “dames coiffés” type, are situated. They are locally denominated “the Priest and the Hausekeeper”, and have been classified as sites of geomorphological interest, given the rarity and singular nature of these landforms in the southern Pyrenees (Figure 19). The successive glacial phases have been correlated (Serrano, 1991, 1998) to the phases registered in the sector of Sabiñánigo, with an outer (G.Ph.1), middle (G.Ph.2) and inner (G.Ph.3), the latter related to the moraine of Senegüé. This sequence of phases can be seen in all the lateral valleys.


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Figure 17. Discharge on the Sobremonte area on the 7th of August, 1996 (García Ruiz et al. 1996). 1, basin limit. 2, minor basin limits. 3, fluvial net. 4, Discharge measurement points. 5, Discharge estimation (m3.s-1). The postglacial incision, highly energetic due to the steep drop between the trough bottom and the perched valley, has generated a deep gorge and an alluvial fan that occupies the bottom of the valley. Like the rest of the alluvial fans the valley, they are characterised by their compartmentalisation in terms of differentiated dynamics (Figure18). It is now possible to see the walls used by the traditional system to combat the flooding of fields worked in marginal areas of the fan. This fully dynamic alluvial fan, fed with materials by lacustrine and morainic deposits, possesses an intense functionality associated with extreme meteorological events, such as that of the summer of 1996, studied by several authors (Figure 17) (García Ruiz et al. 1996; White et al. 1997; Benito et al. 1998; Gutiérrez et al. 1998). Intense rainfall in the basin of Betés, which reached over 500 mm hr–1, with over 250 mm of total rainfall and reaching a maximum flow of 500 m3.s-1, led to a catastrophic flash flow that blocked the apex of the fan, reoccupied functional areas prior to the regulation of the fan (1957) and swept away the camp-site at Biescas.


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Figure 18. Geomorphologic sketch of Ribera de Biescas area (modified of Serrano, 1996). 1, rock bar. 2, alluvial plain. 3, fluvial terrace. 4, braided channel. 5, alluvial fan, inactive area. 6, alluvial fan, active area. 7, floodplain.

Figure 19. “Dames coiffés” features, a geomorphosite named “El cura y la casera” (the Priest and Housekeeper), on the lateral moraine of Sobremonte. (drawn by E. Martínez de Pisón, 1996).


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Stop 3: Santa Elena Hermitage. The entry to Tena Valley. To the north of Biescas, the spectacular thrust of limestone outcrops over flysch Fm is reached. The Inner Sierras (Telera and Tendeñera) are cut by a deep gorge formed by the river Gállego, by which the historical Tena valley is accessed. The gorge is formed by calcareous sub-vertical strata folded in an overturned fold. They are limestone and sandstone from Cenomanian to Maastrichtian ages, and limestone and dolomites of the Paleocene age, rock succession studied in Tendeñera and the valley of Ordesa (Van der Voo, 1966; Van de Velde, 1967). The Gállego river flow by a narrow subglacial gorge shaped in the limestone. The bottom of the valley is infilled by an alluvial fan that has been greatly deteriorated by public works of the road, fed by the lateral moraines of the barranco of El Puerto. Near the access road to the foot of the scarps on the southern slope, an interesting stratified debris of periglacial origin was studied (Martí Bono, 1978), which has now almost disappeared due to quarrying.

Figure 20. Topographic map of karstic springs in Santa Elena area.

Figure 21. Topography of Santa Elena cave (IEES, 1979).


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In the Gorge of Santa Elena there are several springs, belonging to the karst systems of Telera-Tendeñera (Figures 20 and 21). At the level of the road in front of a small hermitage, the terminal area of the barranco of El Puerto is found. It is a beautiful example of a dry valley at its head, and in its final part appears a series of springs (Traconeras). They have a clear karstic behaviour with staged functioning in relation to the volume of rainfall or the snow melt. On the left bank, in the valley of Asieso, at the foot of the limestone wall, appear the springs of Batanes. The water, of calcium bicarbonate type, it is used to supply the village of Biescas. Upstream, several springs appear high over the thalweg. The most spectacular is that of Santa Elena, which has formed a build-up of tuffa perched over the river Gállego (Figure 22). In its interior varve glacial sediments and granite boulder of glacial origin are found.

Figure 22. The Hermitage and tuffa building of Santa Elena (February 2004). The “gloriosa” of Santa Elena, as the spring next to the hermitage is called, is long known for its periodic flow increases without any apparent reason, as described by L. Mallada in the XIX century. The phenomenon has been interrupted several times. At the XVII century, the phenomenom was imputed to the sins of the people of the valley. Much more recently, to the effect of the excavation of an underground gallery between the Bubal dam and the electricity station at Biescas. But from 2002 the phenomenon has returned. A little further to the north, another spring can be seen, also on the left side of the river Gállego, known as “respomuso”, which supplies a small electricity station. A third, not visible, over Hoz de Jaca has, by means of tracers, been related to losses from the Ibón de Asnos (2100 m.), situated at the Panticosa ski station. The gorge of the Gállego divides two sub-units of the northern branch of the Jaca basin. To the west lies sub-unit 2.04 (Peña Ezcaurri-Peña Telera), with a total surface of 399 km2, of which 184 are considered permeable. To the east the sub-unit 2.05 (Tendeñera – Monte Perdido) begins. This is 576 km2, of which 269 are permeable. Annual underground resources of 112 Hm3 are assigned to the former and 207 Hm3 to the latter.


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* * *

Upstream of Santa Elena, the Tena valley opens, limited by the northern walls of the Sierras of Tendeñera and Telera, which is formed by the root of the southern thrust displaced over the Palaeozoic. The alternation of Devonian slate and limestone means that differential erosion has generated wide basins in the slate, and glacial rock bar in the limestone. In the Búbal dam area the remains of lateral moraines can be seen, indicating the existence of a glacial front. Stop 4: Saqués Viewpoint: Glacial morphology and slopes dynamic in the Tena valley. Opposite the abandoned village of Saqués, a viewpoint permits us to observe the morphology of the Tena valley, a characteristic intra-mountainous valley of the axial Pyrenees. The complex folds -the overturned anticline of the Mandilar is visible- studied in detail by Wensink (1962) and mapped by Ríos et al. (1991) can be seen. Over the Palaeozoic unit, the cretaceous and Tertiary calcareous cover is superimposed. The root of the Gavarnie thrust is observed, with a vertical morphology, which rests on the Palaeozoic.

Figure 23. Geomorphologic sketch of Saqués Pueyo area in the Tena valley (Serrano, 1998). Present day occupied by Búbal reservoir. 1, slope slide. 2, Caldares palaeochannel. 3. Long rock bar. 4, alluvial fan. 5, fluvial terraces and floodplain. 7, river. 8, scarp.


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The valley presents a glacial morphology characterised by the succession of rock bars and overdeepened basin, and a glacial trough reworked on slopes by sliding processes (Figure 23) of the Holocene age related to the geological structure and postglacial strains (Bixel et al. 1985; Serrano, 1998). On the eastern side, the slope slides of San Lorenzo, Tochar, Canarellas and Las Magas confer the current morphology. Opposite the Saqués viewpoint, we can observe the rotational slide slope of San Lorenzo, 1250 m. in length, whose root is situated in the thrusting contact between the impermeable Gotlandian slates and the permeable Devonian limestone (Figure 24). The surface runoff is concentrated there and postglacial strain permits the slope movement, related to the structural control and hydrological dynamic. Later, sliding has been reworked and an alluvial fan divides it in two.

Figure 24. Rotational slide slope of San Lorenzo. Ss, slide slope. D, Devonian limestones and slates. D1, Devonian limestone. G, Silurian slate. C, Cretaceous cover of Tendeñera range. C1, Cenomanian to Campanian limestone. C2,

Campanian-Maastrichtian limestones and sandstone (Marboré Formation). C3, Palaeocene limestones and dolomites.


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The vertical walls of the Sierras of Tendeñera and Telera show successions of avalanche tracks. The snow dynamic shaped both the walls and their bases. The different intensities of snow avalanches produce different geomorphic responses. The snow avalanches that reach the base of the wall show a morphology differentiated between the avalanche cones at the foot of the wall and the materials dispersed on the slope, where the avalanche dynamic reworks the lateral moraine complexes (Serrano, 1995).

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Between Saqués and Escarrilla we cross the river Gállego, leaving a deep sub-glacial gorge on the left of the access, crossing the rotational slide slope of Las Saras to the overdeepened basin of the Panticosa village. It is characterised by a longitudinal and a transversal rock bar shaped by diffrential erosion between the Devonian shales (the overdeepened basin) and limestone (the rock


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bars). In the confluence between the rivers Caldarés and Bolatica there is a moraine lateral complex of the Disjunction glacial phase (G.Ph.4b). Ascending towards the Spa of Panticosa by the valley of the Caldarés, the El Escalar Gorge, a well configured glacial trough, is passed. The morphological changes are appreciated between the first part, shaped in the Devonian limestone and schists, and the upper part, modelled in granite and characterised by the verticality of the walls, the perched glacial valleys and avalanche prints on slopes and bottom of the valley. The vertical walls, avalanche tracks, active mixed cones and stream flow deposits are the main features of the glacial trough of Caldarés. Stop 5: The Panticosa Spa: a singular hydrogeological and glacial site. The Panticosa Spa is at 1638 m in a deep basin of glacial over-excavation, surrounded by peaks of over 3000 metres, which goes to make up a place of enormous value as a landscape, more so as a result of human intervention. The spa is the oldest summer tourist centre in the Pyrenees of Aragón1. The mean annual rainfall of 1184 mm and a mean annual temperature of 7ºC, an important winter snow cover and the presence of thermal waters characterise the environmental conditions. The spa is placed on the granitic batholite of Panticosa. This has an approximately circular shape of 7 km in diameter and a surface close to 40 km2. It is an igneous intrusion intruded during the Variscan tectonic. It presents an approximately concentric zonation, with a nucleus of monzogranite surrounded by light and dark granodiorites and quartz gabbrodiorite. The basin of the spa is distributed between the two inner units (Figure 25).

1091

Panticosa1184

PnaticosaSpa

MarcadauPass 2341

2207

PanticosaSpa

Brazato2816

2571

1 2 3 4 5 6 7

SW NE

W E

A

B

Figure 25. Morphostructural profiles of Panticosa area (Geology from Wensink, 1962, Devon, 1972, Ríos et al. 1991 and Santana 2002). A, 1, monzogranite. 2, light granodiorite. 3, dark granodiorite. 4, gabbrodiorite quartz. B, 1, Devonian

1 The Panticosa Spa is now being submitted to an important rehabilitation process by the company NOZAR. By safety reasons at the works, there are problems of access to some points of interest. A visit to the springs of San Agustín and (optional) Belleza is proposed. The visit to Tiberio springs depends on the state of works.


32

slates. 2, Devonian limestone. 3, granites. 4, slates and schist of metamorphic zone developed around the margin of Panticosa igneous intrusion. 5, Quaternary infill.

Figure 26. Geomorphologic sketch of Panticosa area (modified from Serrano1998). 1, crest and peaks. 2, river. 3, lake. 4, glacial cirque. 5, overdeepened basin and rock bar. 6, glacial trough limit. 7, moraine. 8, relict rock glacier. 9, active rock glacier. The batholite is strongly fractured and compartmentalised in blocks, and is crossed by dikes of diverse nature (Figure 27). In the surroundings of the spa, sub-vertical dykes of diabase and of diorite porphyry are abundant, with thicknesses of the order of decimetres to metres. There is a


33

dominant alignment, in the north-northeast direction, cut by another lesser family of the southeast direction.

Figure 27. Geological sketch of vein and dykes distribution on Panticosa spa area (From Martínez Bayo, 2000, in Sánchez, 2003). The basin of the spa has an evident glacial origin and is partially infilled by till, slope debris and fluvial sediments brought by the river Caldarés and tributaries (Figure 26). In the basin several fractures of N-S, E-W and NW-SE directions come together. The overdeepened basin has been caused by the accumulation of ice that came from the valleys of Brazato, Lavaza, Bachimaña, and Argualas, working on tectonic weakness. These valleys are today perched over the basin -Brazato at 300 m, Argualas at 250 m-, with rock bars that configure its slopes and have an influence on the slope dynamic (Figures 28 and 29).The thickness of the ice accumulated in the basin of the


34

spa surpassed 480 m, as indicated by the truncated crests. The shape of the glacial tongue at the maximum can still be appreciated.

Figure 28. View from the Panticosa Spa glacial overdeepened basin. The thermal waters in the basin of the spa have long been known of, and indeed Roman coins were found there in 1951. At the beginning of the XIX century, the Spanish King Fernando VII


35

ordered the spa to be built, and it has since passed through phases of prosperity and decadence, studied by Montserrat (1996).

Ht

1 2 3 4

Cd Cd

Cd

Ca

Ca

Ca

FLFL

Argualas3046

Garmo Negro3051 Collado de

Pondiellos

G

G

G

GGG

S

S

S

S

Cd

Ac

Ac

Ac

Figure 29. View of western side of Panticosa Spa glacial overdeepened basin. 1, slates and schist of metamorphic zone developed around the margin of Panticosa igneous intrusion. 2, granites of Panticosa igneous intrusion. 3, slope debris. 4, moraines. In the XVII century the existence over the basin of the natural springs of Laguna and Belleza was known. The Hígado and Herpes springs have been used for taking water since the middle of the XVIII century. The ancient San Agustín hot spring was found by chance in 1881 and at the beginning of 1950 the well of Tiberio was excavated. The name derived from the find of some Roman coins. Between 1985 and 1991 a horizontal drilling was performed in San Agustín and Hígado, leading to the disappearance of several traditional springs. In 1991 the Carmen well, near of Tiberio, was explored by vertical drilling and 182 metres was reached. The well is artesian, with a weak spontaneous flow and a temperature of around 35ºC. Other deep wells were also attempted in the proximities of the electric power station. In recent years, other thermal points have been found through geotechnical drillings related to the works on the spa, with temperatures of up to 50ºC, now in the study phase. The spa is now in a major re-building and development process under the project of the architect Rafael Moneo, who is renewing all the buildings of interest (Casino, several hotels) and building a centre for sportpeople, and a thermal palace. The hydrogeology of the spa can be summarised in the presence of three aquifers:


36

· Cold surface aquifer. Free. Fed by the streamflow of the Caldarés, Brazatos and Argualas creeks. It is lodged in the debris cones and talus of the basin, whose thickness can surpass 30 metres in the central area. The water table level is the level of the Baños lake, controlled by a trapdoor. · Cold fissured aquifer. Situated in the fractures of the igneous rocks surrounding the basin. Visible after periods of rain and snow melt. · Hot fissured aquifer. It also springs up through fissures, on the slopes and on the bottom of the basin infill. The aquifer is supplied by the surrounding peaks area and has a residence time of over 30 years (Tritium= 0). The geothermometers suggest a vertical deep flow of the order of 2,5 kms. The discharge is modest and it has been used in therapeutic applications. These are very basic thermal waters of low mineralization with a pH of over 9.0, a smell of hydrogenous sulphur, nitrogen bubbling and the formation of biofilmes of a gelatinous kind. On the access road outside the spa, there is a modest hot spring known as the Escalar, also of a sulphurous thermal character, although it has a different hydrochemistry to that of the spa.

Figure 30. Panticosa Spa view, snow avalanche fences and map of snow avalanches and avalanche fences distribution in Panticosa spa area (Sáez, 1994). The Spa of Panticosa and its accesses are found in a high mountain area where snow avalanches of different sizes take place each year (Figure 30). They have caused damage and victims and create a highly dangerous environment in winter. In 1915, an aerosol avalanche that descended from Peak Argualas destroyed the Hotel of the Pradera and caused serious damage to other


37

buildings (Figure 31). Historically, the winter damage to the installations of the spa hit the low profitability of the establishment (Montserrat, 1996), with the need to continuously perform fences in the avalanche tracks from the end of the XIX century. The road accesses are also often affected by snow avalanches. One of them, possibly due to thawing in April 1971, caused the deaths of two public works employees. In 2001, a period of abundant and large snow avalanches around Panticosa Spa left the spa cut off due to an avalanche of wet snow. Weeks later, a very large wind slab snow avalanche on the slope of the peak Argualas taked ten mountaineers. Fortunately, by the quick response of the Mountain Rescue Team of the Guardia Civil all were saved, the last one after spending four hours under the snow. Owing to this danger, different works to improve protection have been carried out, and these continue. They are of several kinds: empty walls (visible on the accesses), fences (above all on the avalanche track that descends towards the hydroelectrical station, Figure 30), roofs on the road, divert wedges on buildings (Hydroelectric station) and Gazex type systems (Argualas slopes).

Figure 31. The effect of an snow avalanche on the Casino of Panticosa Spa in February 1915. Pictures from Edición F.H.Jaca. The geological structure, glacial features, post-glacial, periglacial, snow and alluvial processes, and human activity have formed an area of high landscape and cultural value, in which the transformations of the last 200 years, including the recent climate change and tourist occupation, have led to considerable landscape changes, with an increase in urban development, both natural and induced by man (gardens, slopes), re-vegetation and weakness of geomorphic processes on


38

slopes (Figure 32). Today, it is an urban leisure area with a high impact on the natural environment, but which has acquired a historical value deriving from its urbanism, architecture and history, in contrast with the surrounding rocky high mountain (Figure 33), which confer on the basin of the spa a place of high geomorphological interest in itself, an added value as an outstanding cultural landscape due to its geomorphological and human values.


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Figure 32. Landscape evolution (building, gardens, slope vegetation and slope dynamic) in the glacial overdeepened basin of Panticosa Spa.

Figure 33. The Infierno massif. (Martínez de Pisón, 1996). 1, Infierno peak (3082 m). 2, marble outcrop of Infierno. 3, Glaciers. 4, L.I.A. moraines. 5, proglacial stream. 6, Ibón Azul (Blue lake). 7, slope debris. 8, granite. Stop 6: The Lanuza area: morainic complex of the Disjunction Phase and postglacial landforms. Upstream of Escarrilla basin a glacial rock bar shaped in Devonian limestone is passed before reaching a wide overdeepened basin in a dissymmetrical glacial trough, now occupied by the Lanuza reservoir (Figure 34). The dissymmetry possesses a structural character, as the northern slope is a thrust front in the Devonian limestones, whereas the south follows the north vergent strata of the calcareous outcrop of Pacino. On the northern slope several features are visible (Figure 36): - Till lodged on the slopes, remains of a lateral moraine, at 1750 m a.s.l., belonging to the glacial maximum when the ice had a thickness of 600 metres in this area.

- Lateral moraine attached to the slope, situated at 1300 m a.s.l., which continues until the Escarrilla rock bar of Escarrilla. It indicates an ice thickness of 50 m in Lanuza, descending towards Escarrilla, with a very close front, over 1200-1300 m a.s.l., although there are no frontal moraines. It indicates a phase in which the glacier of Aguas Limpias and the massif of Balaitus would have their front in this area. It constitutes a glacial phase correlated with that of Panticosa, when the glacier of the Gállego would have


40

divided in two tongues, which is the reason why it has been denominated the Disjunction Phase (G.Ph 4b).

Figure 34. Geomorphologic sketch of Lanuza area (modified from Serrano, 1991). 1, wall and scarp. 2, height. 3, contour line, interval 100 meters. 4, river. 5, Devonian slate. 6, Devonian limestone. 7, rock bar and abraded surface. 8, glacial trough limit. 9, glacial overdeepened basin. 10, till. 11, alluvial fan. 12, slope slide. 14, village.


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- At the foot of the scarps, covering the whole of the slope, inactive stratified debris of 5.90 m in thickness are located on the lateral moraine. - Alluvial fan of Lanuza, belonging to a phase of postglacial incision, which occupies the bottom of the valley where the village of Lanuza is located. - Alluvial fan fitted into the previous one, of lesser development, and now partially flooded by the reservoir. On the northern side the landforms are: - Morainic remains in the low areas belonging to the phase of Lanuza, and erratic disperse blocks on the slopes. - Postglacial slope slides, among which is the so-called Lanuza slide slope (Figure 35). This is a rotational slide slope generated in the contact between the Devonian limestone and slate, both with vergent strata to the slope of the flank of the overturned and thrust anticline of the Pacino. This slide occupies a wide part of the slope and shapes the bottom of the valley. With the construction of the reservoir of Lanuza it has been reactivated, with re-adjustments in its frontal part that have led to damage to the access road to Sallent and El Portalet.

Figure 35. View from the east of the rotational slope slide of Lanuza.


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Tendeñera

Tendeñera

Lanuza

M2

M1

M2

U

U Ss

Ss

SsSs

Af

M2

D

D

T

GM

Tendeñera

Figure 36. Palaeogeographic reconstruction and present day morphological features of Lanuza area. 1, The last glacial maximum at Lanuza area (G.Ph1). 2, the LatePleistocene II, the disjunction phase in Lanuza area. 3, Present day features. G.M. limit of ice in the LGM. M1, lateral moraines of LGM. T, glacial trough limit. M2, moraines of disjunction phase (G.Ph.4b). U, rock bar with abraded surface on Devonian limestone. D, postglacial slope debris. Af, postglacial Lanuza alluvial fan. Ss, postglacial slope slides.


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Stop 7: Portalet area and Midi de Ossau view. The road from France continues along the Gállego, ascending towards Formigal ski resort , shows a large set of valleys perched over the main trough, that of Aguas Limpias at the beginning of which Sallent de Gállego is located. The upper area, dominated by glacial features, is characterised by gentle slopes, determined by the dominant lithology, slates, clay slates and schists of Devonian age, with interlocking limestone. The valley is dissymmetric, and the contrasts with the eastern mountains -which culminate at over 3000 metres in the massifs of Balaitous and Argualas- are visible from the valley (Figure 37).

Figure 37. The glacial overdeepened basin of Sallent de Gállego and glacial cirques of the high mountain of Pondiellos (Tena valley). In the upper part between the urban area of the Formigal, dominated by the reef limestone of the Peña Foratata and the El Portalet pass, the remains of the glacial phases can be seen in an early deglaciated environment, since the low altitude of the peaks did not guarantee the permanence of the glaciers (Figure 38). The remains of pro-glacial terraces can be appreciated, now very deteriorated by the work on the ski stations, from the glaciers coming from Culivillas and the cirques of Anayet. These landforms can be correlated with the phase of glacial disjunction and the early deglaciation of the rest of the southern area has been confirmed (Martínez de Pisón and Serrano, 1996; González et al. 2004).


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SS

S

S

S

S

S

S S

S

S

S

S

S

S

S

SS

S S

S

S

S

S

El PortaletEl Portalet

Culivillas

Espelunciecha

PortVieux

PortVieux

Gállego

Campode TroyaCampode Troya

2224

1794

2165

1862

1544

1600

17672053

S S 1544

1 2 3 4 5 61 2 3 4 5 6

7 8 9 10 11 127 8 9 10 11 12

13 14 15 16 17 1813 14 15 16 17 18

N

0 500m0 500m

Figure 38. Geomorphologic sketch of Portalet area. 1, crest and peaks. 2, scarp. 3, river and lake. 4, Devonian shales and limestones. 5, Westphalian shales, limestones and sandstones. 6. Stefanian andesites of Ossau. 7, moraines. 8, relict rock glacier. 9, lacustrine infill. 10, proglacial terraces. 11, alluvial fan. 12, fluvial cutting. 13, slope debris. 14, slope slide. 15, solifluction sheets and lobes. 16, height. 17, buildings. 18. Spain-France border line.


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The whole sector shows an active dynamic of slopes, both actual and inherited. The presence of slope slides, slides and solifluction are dominant on all the slopes of this area, with important mass movements that indicate the instability of the slopes. This area is characterised by the impervious substrate, the presence of fines by substrate weathering, the lithosoils land human intervention, first with cattle-farming use, and now tourism, which favours the saturation of the surface formations. The rainfall and the spring melt of the snow cover make possible high water availability in the soil. A wide flow landforms system, relic landforms -slope slide, rock glacier- and active -solifluction lobes and sheets, rock fall, debris talus and cones- can be seen between Formigal and El Portalet Pass (Figure 39).

Figure 39. View of Paco de Culivillas from the north (from the road to El Portalet pass ). D, debris slope. L, solifluction lobes. GR, relict rock glacier. T, erosional headwater. El Portalet Pass is a glacial diffluence between the Gállego and Ossau basins, in the Atlántic- Mediterranean waterside divide, forming the frontier between Spain and France. It is located in a fracture zone of NW-SE direction, where karstified Westfalian and Devonian limestones crop out. It is now occupied by a glacial complex, with successive moraines and an infilled basin of an age that can possibly be correlated with those of Culivillas and Lanuza.


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From the Pass, limit of the French Pyrenees National Park , there is a magnificent view of the peak of Midi d´Ossau (Figure 40) (Ossau Valley, Bearn, France). It is a narrow tower made up of volcanic dacites. It is a structural relief constituted by a ring dyke surrounding a large pre-alpine volcanic caldera (about 7 km in diameter), eroded, truncated by Upper Variscan faults and thrusted on itself during the Pyrenean orogeny. Differential erosion has dismantled the breccias and ignimbrites, leaving highlighted the dacites and forming the isolated and beautiful peak, surrounded by glacial and periglacial features of great interest.

Figure 40. View of Midi D´Ossau peak from the border line. A, andesites of Ossau. P, Westphalian shales. Ss, slide slope. S, solifluction lobes and sheets. T, water stream terraces. On the southern slope of the Pass, the deterioration of the landforms and ecosystems stands out as a result of aggressive intervention to adapt the valley to the practice of skiing, which has led to a high landscape impact, the absolute alteration of the geomorphological dynamic, with the disappearance of landforms, elements and processes, as well as the impoverishment of the geodiversity of an emblematic and protected area as is the Ordesa Viñamala Reserve of the Biosphere.


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ROAD LOG:

Departure from the Conference Hall at 8,00.

0-127 km A-23 and N-330 (E-7) Motorway to Huesca and road to Sabiñánigo.

127-130 km Road N-260 to Senegüé village. Coffee stop at Senegüé. 15 minutes walk along a track without difficulties by frontal moraine. Stop at a panoramic point to see the main geomorphological features of Senegüé Sabiñánigo fluvioglacial terraces (stop 1).

130-142 km Road N-260 to Biescas. We will stop 5-10 minutes next to the road (stop 2) to see the Arás alluvial fan, the glacial morphology and effects of flash flow.

142-150 km Road N-260 until the Santa Elena Gorge.15 minutes walk along a track without difficulties to see the hydrogeological features and karstic springs of Telera-Tendeñera Sierras.

150-153 km Stop at a panoramic point next to Saqués village to see the main glacial features of Tena valley and the slide slope of San Lorenzo (Stop 4).

153-163 km Local road to Panticosa Spa. We will visit the Spa area (Stop 5). 15 minutes walk around the slopes of Panticosa basin along a relatively steep track. The hike will not pose difficulties to those persons with regular physical conditions. The walk permit us to see the main geomorphological features and to observe the avalanche dynamic on slopes. In the Panticosa Spa we will stop for lunch.

163-175 km The coach go down by the local road and we will take the road N-260 to France. We will stop on Lanuza Dam (Stop 6) to see the geomorphological features of glacial processes and the slide slope of Lanuza.

175-195 km Road N-234 to El Portalet. We will stop in Portalet (Stop 7) to see the glacial features of high Gállego and a Midi D´Ossau panoramic view.

195-345 km Road N-260, N-330 and Highway A-23 to Zaragoza (about 2 hours).

Expected arrival time to the Conference Hall: 20,30.