glacial landforms and evolution in the pyrenees

Transcripción

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).
Pau
u
sa
Os
42º
Balaitus
3144
0
Aragón
Vignemale
3303
40º
km 6
3129
Monte Perdido
3335
Jaca
38º
1769
0 km 200
36º
8º
Ara
o
eg
ll
Gá
4º
0º
4º
a
nc
Ci
1928
Ainsa
Balaitus
3.144
Vignemale
3.298
SA
Bisaurín
TI
PA
N
TELE
RA
Cinc
a
ÑERA
TENDE
Ara
Canfranc
ORDESA
ón
Torla
Biescas
Broto
Cinca
Gállego
Arag
Hecho
Osia
ERA
3.355
s
lló
Ve
Aragón
Subor
dán
Sallent
BERN
Monte Perdido
CO
2.670
Jaca
0
km
10
Figure 1. Location of the fieldtrip area.
Sabiñánigo
Ara
Bielsa
Glacial landforms and evolution in the Pyrenees
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).
2
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.
3
- 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.
Panticosa
Torla
Jaca
Ara
adre
o
Huesca
Alcan
Isuela
G
g
álle
km
0
10
1
2
3
4
5
6
7
8
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.
4
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
5
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
Valleys
and 800-1000
down
mountains
Low slopes and 1000-1600
valleys
Middle
mountain
1600- 2500
High Mountain
2500-3140
Annual Medial Climatic characteristics
Vegetative
Air Temperature
period
10ºC//18ºC
Short winter and hot summer, 6-8 months
summer drought.
April
to
November
10ºC / 5ºC
Short winter (15-20 days of 5 months
snow)
May
to
Cool summer
November
5ºC/ 0ºC
Very cold winter (5 months). 4 months
Snow from November to May
June
to
September
2ºC/ -5ºC
Long winter (7 months) and
1-5 months
cool summer. Summer air
July
to
temperature <0ºC above 2725
August
m a.s.l.
Presence of permafrost
Human influence
Human occupation,
farming, reforestation
Farming, grassland,
villages and tourist
use.
Meadows
above
forest line and ski
resorts.
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
Sabiñánigo.
Biescas.
Balneario de Panticosa
Altitude
m a.s.l.
780
875
1638
Precipitation
mm/yr
806
1097
1184
Mean Annual Temperature
10.6 ºC
9.1 ºC
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
6
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
Surface
aquifer
Fissured
aquifer
Fissured
aquifer
Temperature
Cold
Cold
Warm
45º
Characteristics
Free. Fed by high mountain stream flows and found in sediment cover, over 30 metres in
thickness.
Situated in fractures of plutonic rocks of the high and medium mountain.
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
Submontane
Supramediterranean
Montane
Oromedite- granean
Altitude
m. a.s.l
600
to
10001200
Plant
communities
Evergreen forest
10001200
to
1700
Evergreen
conifers
1500 and 1700
Decidious forest
Subalpine
1700
to 2300
Alpine
2500
3404
Evergreen
coniferous forest
to Alpine tundra
Vegetation
Type
Chaparrall
Species
Quercus
Rotundifolia,
Buxus
Sempervivens
Artostafilus
uva
ursum
Oak forest
Quercus
Faginea,
Quercus
pubescens, Acer monspesulanus,
Prunus ssp., Buxus sempervivens
River
Quercus sessiliflora, Fraxinus ssp.,
communities Tilus ssp., Acer campestris, Coryllus
avellana
Pine forest
Pinus sylvestris Coryllus avellana,
Ilex
aquifólium.
Regressive
formations: Buxus sempervirens and
Sarothamnus scoparius.
Beech and Abies pectinata,
abies forest
Fagus sylvatica
Black pine Pinus uncinata
forest, larch Juniperus communis
forest
Sorbus
chamaesmespillus,
Rhododendron ferrugineum
Herb-fields,
meadows.
Juniperus communis
Poa, Carex, Trifolium, lichens.
Human use
Farming and
abandoned
fields
Farming and
abandoned
fields
Meadows
and
Fraxinus
Pastures,
abandoned
fields and
forest
Meadows
and
ski
resorts,
hydroelectri
c power.
Mountain
and
ski
resorts
Table 4: Altitude of vegetation belts of Upper Gallego valleys
7
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
8
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,
9
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 supraglacial 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.).
10
Balaitus
Gran Fache
El Portalet
Escarra
Brazato
Tel
e
ra
Tendeñera
Cotefablo
Erata
rín
Au
Gá
lle
go
N
0 km 1
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 5ais 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
11
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.
12
lleg
o
lleg
B
Gá
Gá
ego
Gáll
Balaitus
ín
Aur
ín
Aur
ín
Aur
A
Balaitus
o
Balaitus
C
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).
13
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 Lateglacial 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.
14
3005 Gran Fache
A
0
2918
1 km
Araitille
2220
2900
Infierno
3082
3082
2500
2160
2894
2000
1640
2194
2758
2702
3005 Gran Fache
B
0
2918
1 km
Araitille
2220
2900
Infierno
3082
2500
2160
2894
2000
1640
2194
2758
2702
3005 Gran Fache
C
0
2918
1 km
Araitille
2220
2900
Infierno
3082
3082
2500
2160
2894
2000
1640
2194
2758
2702
1
2
3
4
5
6
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.
15
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
16
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
17
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.
18
Sorripas
le
l
Gá
go
Lárrede
III
830
Senegüé
II
2
2
2
3
1
2
2
1
III
2
ín
ur
A
III
2
1
Satué
Latas
II2
2
II
900
Aurín
le
ál
go
G
Sabiñánigo
2II
2
3
III
III
II
Sardás
1I
III
II
II
2
II
1
6
11
II
0
2
m
1000
2
3
4
5
7
8
9
10
12
13
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.
19
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).
Senegüé
(M-707)
m
D FC
S
S
Aurín
T
l sgB
m
D FC
S
T
l sgB
H
Dmm
Fm
Dcm
Dmm
Fm
1
2
Fm
Dmm
1
Dmm, matrix supported,
massive diamicton
Dcm, matrix supported,
reworked diamicton
Fm, massive fines
S,
soils.
H,
Human alterations
L, silt
s, sand
g, pebbles
B, boulder
Figure 13. Lithostratigraphic log of Senegüé and Aurín moraines.
20
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.
21
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.
22
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.
23
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.
24
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).
25
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).
26
In the Gorge of Santa Elena there are several springs, belonging to the karst systems of TeleraTendeñera (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.
27
* * *
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.
28
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.
29
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).
Sallent de
Gállego
Portalet
N-260
27
12
To Jaca
10
Panticosa
To Ordesa
National Park
Biescas
N-330
/E-7
Sabiñánigo
52
Arguís
To Jaca
HUESCA
To Lérida
Almudevar
-7
/E
23
A
47
Zuera
28
To Bilbao
Villanueva de
Gállego
To Barcelona
To Madrid
0
20 km
ZARAGOZA
To Madrid
* * *
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
30
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).
2816
Brazato
A
2571
Panticosa
Spa
W
E
Marcadau
Pass 2341
B
2207
Pnaticosa
Spa
Panticosa
1184
1091
SW
1
2
3
4
5
6
NE
7
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.
31
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
32
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
33
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
34
ordered the spa to be built, and it has since passed through phases of prosperity and decadence,
studied by Montserrat (1996).
Garmo Negro
Collado de
3051
Pondiellos
S
S
Argualas
3046
S
G
G
G
Cd
Cd
Cd
Ht
G
Ac
Ac
Ac
G
Ca
Ca
Cd
Ca
FL
FL
S
1
G
2
3
4
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:
35
· 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
36
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
37
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.
38
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
39
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.
40
- 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.
41
Tendeñera
Tendeñera
Tendeñera
GM
M1
T
Ss
D
D
M2
Af
Ss
U
Ss
U
Lanuza M2
M2
Ss
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.
42
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).
43
El Portalet
1794
N
2165
0 m 500
S
Port
Vieux
1862
S
S
S
1767
S
S
S
S
S
S
2053
S
S
S
Espelunciecha
S
S
S
S
Culivillas
1600
S
S
S
S
S
lego
S
Gál
S
Campo
de Troya
2224
1544
2
3
4
5
6
7
8
9
10
1544
11
12
13
14
16
17
18
S
S
1
15
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.
44
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 glacierand 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 AtlánticMediterranean 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.
45
From the Pass, limit of the French Pyrenees National Park , there is a magnificent view of the
peak of Midi dÓssau (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 DÓssau 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.
46
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52
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 TeleraTendeñera 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 DÓssau 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.
53

glacial landforms and evolution in the pyrenees

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