SPECTACULAR WATERFORMATIONS FORSOLITARYMOUNTAINEERS

ORDISO MOUNTAIN LAKE

torla

9Geo route

GEO-ROUTENETWORK

c Sobrarbe Geopark

Texts: Luis Carcavilla Urquí (IGME) and Ánchel Belmonte Ribas

(Scientific Coordinator Sobrarbe Geopark).

Figures and illustrations: Albert Martínez Rius

Photographs: Luis Carcavilla Urquí

Translation into French and English: Trades Servicios, S.L.

Design and layout: Pirinei, S.C.

CBC project Pyrenees-Monte Perdido, World Heritage (PMPPM)

of the 2007-2013 POCTEFA Program.

1

Taken together, these routes will enable visitors to enjoy the most beautiful parts ofthe Sobrarbe district and also obtain further information on its long geological historydating back over 500 million years.

S OBRARBE GEOPARK GEO-ROUTENETWORK

THE SOBRARBE GEOPARK

The Sobrarbe Geopark is located in the north of the province of Huesca andcoincides with the district of the same name. This area is noted for its many cultural and naturalvalues, most notably its spectacular geology.

In 2006 the Sobrarbe District was declared a Geopark and became part of the EuropeanGeopark Network, sponsored by UNESCO. A Geopark is a district with unique geological features forwhich a sustainable development strategy has been developed. Consequently, the key objective is topreserve its natural and cultural heritage and promote development through the appropriatemanagement of the geological environment. There are currently 60 Geoparks in Europe and 100 in theword. The Sobrarbe Geopark features an exceptional geological environment, with over 100 places ofgeological interest that have been inventoried; many of which can be visited on the Geo-Routenetwork.

More info: www. geoparquepirineos.com

Indeed, the Geo-Route network of theSobrarbe Geopark was created to learn about andunderstand its geological heritage in greater depth.This is a network of 30 self-guided routes that allowvisitors to access the most outstanding geologicalsites in the district and understand their origin,meaning and significance. All Geo-Route havebeen designed so that they can be covered on footand are clearly signposted; in most cases they arebased on official short-route (PR) or long-route(GR)except PN 1, PN 4, PN 5, PN 9, PN 10 and PN 11that combine a stretch of road and vehicle withtrails paths. There is a brochure on each route inorder to facilitate the interpretation of each stop onthe way.

In addition, 11 of these geological routesare located in the Ordesa and Monte PerdidoNational Park, including the territory of the Geopark,and 3 of the Geo-routes are of a cross-bordernature, allowing visitors to enjoy the geologicalheritage of the Pyrenees-Monte Perdido, declared aWorld Heritage Site by UNESCO.

In addition to the Geo-Route network, thereare mountain bike (MTB) routes in the Geopark,some of which feature small information panelsalong the way and there is also a brochure that

MAP OF THE SOBRARBE GEOPARKGEO-ROUTE NETWORK

The various Sobrarbe geo-routes vary in length, difficulty, theme and duration. Consequently, almosteveryone will be able to find a route that suites them.

Geo-Route Geo-Route in National Park of Ordesa and Monte PerdidoGEO 1 PN 1

TorlaBielsa

Fanlo Gistaín

Plan

Lafortunada

Escuaín

SanVictorián

San Juan de Toledo

Foradada

Tierrantona

Boltaña

Laspuña

Puértolas

Ascaso

Escalona

Aínsa

Arcusa

Paúles de Sarsa

Lecina

Bárcabo

PaloSamitier

Abizanda

Broto

Fiscal

Las Bellostas

Nerín

Campo

Víu

2

Gavarnie

GèdreAragnouet

PinetaBujaruelo

MontePerdido

Río

Ara

Río Cinca

Embalse deMediano

Embalse de El Grado

Río

Ese

ra

PP.N. DE ORDESA.N. DE ORDESA YYMONTE PERDIDOMONTE PERDIDO

PPARQUE NAARQUE NATURALTURALDE LADE LA SIERRASIERRA YY

LOS CAÑONES DELOS CAÑONES DEGUARAGUARA

PPARQUEARQUENANATURALTURAL

DEDEPOSETS-POSETS-

MALADETMALADETAA

Viadós

San Juan de Plan

Labuerda

A-1

38

N-260

A-1

38

N-260

Saravillo

Geopark Interpretation Centre

Aínsa: a town between two rivers. Urban geology

Geology: A bird's eye view

Inside the canyon

Breath-taking landscapes of water and rock

Sobrarbe at your feet

Crossing the Jánovas Gully

Iron Age Elements

Whims of water for lonely mountaineersA lake among the oldest rocks inSobrarbe

The hidden lake

A road with tradition

A privileged vantagepoint

Secrets of the Guara Mountains

Geology for the Saint

A passage between two worlds

Water inside the Earth

The Jewel of Cotiella

Treasures of the Posets-Maladeta Nature Park

Ordesa Valley

Mount Perdido

The Roland Gap

Cutas Viewpoints

La Larri

Balcon de Pineta

Añisclo Canyon (lower part)

Añisclo Canyon (upper part)

Circuit Añisclo Canyon

Escuaín Valley

Otal Valley

Geopark area

Aínsa

Samitier castle and hermitages

Congosto de Entremón

Vero River canyon viewpoints

Ascaso- Nabaín

Near Jánovas

Viu-Fragén-Broto

Ordiso Valley

Lake Pinara and Puerto Viejo

Lake Bernatuara

Bujaruelo Pass

Fiscal-Gradatiello-Peña Canciás

Las Bellostas-Sta. Marina

Espelunga de San Victorián

Collado del Santo

Badaín-Chorro de FornosBasa de la Mora (Ibón de Plan)

Viadós-Ibones de Millars

Torla-Cola de Caballo-Góriz Shelter

Góriz Shelter-Mount Perdido

Góriz Shelter - Roland Gap

Torla-Viewpoints-Nerín

Bielsa-La Larri Valley

Pineta-Balcón de Pineta

San Urbez-Fuen Blanca

Fuen Blanca-Añisclo Pass

Escalona-Puyarruego

Tella, Revilla-Escuaín

Broto -Bujaruelo-Otal Valley

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1 hour

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3

* Theme: T- Tectonics; F- Fossils;K- Karst; R- Rocks; E- Stratigraphy; G- Glaciarism** Combining vehicle and hiking

1

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Nº TRAVEL DIFFICULTY DURATION THEME*

Nº GEO-ROUTE TRAVEL DIFFICULTY DURATION THEME*

PN1

PN2

PN3

PN4

PN5

PN6

PN7

PN8

PN9

PN10

PN11

GEO-ROUTE IN NATIONAL PARK OF ORDESA ANDMONTE PERDIDO

4

GEOLOGICAL HISTORY OF THE SOBRARBE GEOPARK

1THE REMOTEST PAST

2TROPICAL MARINE SEDIMENTATION

3THE FORMATION OF THE PYRENEES

(between 500 and 250 million years ago)

(between 250 and 50 million years ago)

(between 50 and 40 million years ago)

The geological history of the Sobrarbe Geopark goes back over 500 millionyears. Many geological events that have affected the current landscape and relief tookplace over that vast period of time. The geological history of Sobrarbe can be divided into 6different episodes, each of which includes significant moments that led to today's geologicallandscape.

Over a long period of the Palaeozoic, the land nowoccupied by Sobrarbe was a seabed where silt, mud, clay andsand accumulated. Today these sediments have become theshale, sandstone, limestone and quartzite that form the northernmountains and valleys of the District. These rocks were intenselyaltered by the Variscan orogeny: an episode of intense tectonicactivity that affected much of Europe and resulted in a hugemountain range. Numerous folds and faults attest to this pasttogether with granite that was also formed in that era.

The giant mountain range formed in the previous stage washeavily eroded and almost disappeared. Once erosion has almost

swept away the mountain range, the resulting flat land wascovered by a shallow tropical sea. Coral reefs appeared and the

calcareous mud we see today in the shape of limestone, dolomiteand marl, containing abundant marine fossils, accumulated. Thesea fluctuated several times and there were many time when its

depth increased and decreased; however, it practically coveredthe area throughout this episode.

The marine sedimentation process continued during this episode, butunder very different conditions to previous episodes. The sea, whichseparated what is today the Iberian Peninsula from the rest of Europe,gradually dried up. About 45 million years ago, as this sea becamenarrower and sedimentation occurred on the seabed, thousands ofmetres below the surface, on land, the Pyrenees began to develop. I

Folds in Palaeozoic rocks

Fossils of marine organisms in the

Cretaceous limestone

Typical landscape of turbidites outcrops

In Sobrarbe we can find exceptional examples of turbidites, rocks formed in that sea as itaccumulated huge amounts of sediments resulting from the development of the mountain range,while the mountains continued to develop.

PALAEOZOIC

542 m.a. 488 m.a. 443 m.a. 416 m.a. 359 m.a. 299 m.a. 251 m.a. 199 m.a. 145 m.a. 65 m.a. 23 m.a. 2,5 m.a.

Cambrian Ordovician Silurian Devonian Carboniferous Permian Tria Jurassic Cretaceous Palaeogene Neogene Quaternary

EPISODES: 1

5

SOBRARBE GEOPARK

4THE SOBRARBE DELTAS

5THE ICE AGES

6 TODAY

(between 40 and 25 million years ago)

(last 2,5 million years)

Once the mountain range and its foothills had formed,erosion began to transform it. The river valleys widened and

the present river network began to be formed. On severaloccasions during the Quaternary, mainly over the last two

and a half million years, various cold spells occurred,covering the mountains with snow and ice. The last major

ice age reached its peak about 65,000 years ago. Hugeglaciers covered the valleys and mountains and shaped the

landscape, effectively eroding some places andaccumulating sediment in others. The landscape of the

entire northern section of the District was shaped by thoseancient glaciers.

Today, erosion processes are slowly and graduallywearing away the mountain range. This erosion occurs in

many ways: through the action of rivers, erosion on theslopes, karst dissolution, etc. The landscape that we see

today is only an instant in a long evolutionary processthat is on-going, but now with the participation of man

who is changing the environment like no other livingbeing is capable.

The formation of the mountain range caused thegradual disappearance of the sea, which was becomingshallower and elongated. About 40 million years ago, asystem of deltas marked the transition between the area thathad emerged and later stages of this marine gulf. Althoughthis period was relatively short, huge amounts of sedimentaccumulated, which can be found today in the southern partof the District converted into marl, limestone and sandstone.Once the sea had retreated definitely from Sobrarbe, therelentless effects of erosion became all the more intense ifpossible. About 25 million years ago, active and dynamictorrents accumulated huge amounts of gravel that, over time,became conglomerates, such as those that form the bulk ofPeña Canciás.

Glaciers like the ones we see today in the Alps covered

the Pyrenees at that time

Río Cinca, agente modelador actual

Conglomerates: rocks formed from rounded

fragments of other rocks

MESOZOIC CENOZOIC

199 m.a. 145 m.a. 65 m.a. 23 m.a. 2,5 m.a.

Tria Jurassic Cretaceous Palaeogene Neogene Quaternary

2 3 4 5 6

EPISODES REPRESENTED IN THE GEO-ROUTES

Episode 1: Variscan orogeny - Episode 2: Tropical marine sedimentation - Episode 3: The formation of thePyrenees - Episode 4: The Sobrarbe deltas- Episode 5: The ice age - Episode 6: Today

Nº GEO-ROUTE EPISODES

Ordesa Valley

Mount Perdido

The Roland Gap

Cutas Viewpoints

La Larri

Balcon de Pineta

Añisclo Canyon (lower part)

Añisclo Canyon (upper part)

Circuit Añisclo Canyon

Escuaín Valley

Otal Valley

PN1

PN2

PN3

PN4

PN5

PN6

PN7

PN8

PN9

PN10

PN11

2 5 6

2 3 5 6

2 3 5 6

2 3 5 6

1 3 5

2 3 5 6

2 5 6

2 3 5

3 6

3 6

1 3 5 6

Nº GEO-ROUTE EPISODES

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

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17

18

19

Geopark Interpretation Centre

Aínsa: a town between two rivers.Urban geology

Geology: A bird's eye view

Inside the canyon

Breath-taking landscapes of water and rock

Sobrarbe at your feet

Crossing the Jánovas Gully

Iron Age Elements

Whims of water for lonely mountaineers

A lake among the oldest rocks in Sobrarbe

The hidden lake

A road with tradition

A privileged vantagepoint

Secrets of the Guara Mountains

Geology for the Saint

A passage between two worlds

Water inside the Earth

The Jewel of Cotiella

Treasures of the Posets-Maladeta Nature Park

1 2 3 4 5 6

3 6

2 3 6

2 3 6

2 4 6

3 6

3 6

5 6

5 6

1 5

1 2 5 6

1 2 5

4 6

2 6

2 3

2 3

2 6

2 5 6

1 5 6

7

8

Geo route

SPECTACULAR WATERFORMATIONS FORSOLITARY MOUNTAINEERS

This route takes us to LakeOrdiso, one of the remotest inSobrarbe, on a clearly visible and,above all, long path. The reward willbe to visit a unique geological event.The mountain lake receives water froma small upwelling, and a few kilometresfurther downstream from the lake, itrushes into a chasm that acts as ahuge natural basin. The water appearsagain at the end of Ordiso Valley,creating a waterfall. Therefore, thisroute visits a unique river, a surface

and underground water course, whichproves that the underground rocks inthis area hide much more than youmight expect.

In addition, glaciers carved theOrdiso Valley and when we visit it, wewill be able to observe the evidence ofits ice-related origins. Finally, the viewsfrom the track of the Viñemal, of theMount Perdido Massif and of OtalValley would, in themselves, be worthtaking this Geo-Route.

ORDISO MOUNTAIN LAKE

9

9

1

2

5

3

6

4

OPCION 1

OPCION 2

i

10

L É G E N D E

i

1

500 m

Parking

Home Geo-Route

Tour Geo-Route

Optional Tour

Number of stop

Signpost

N

GRANITE BLOCKS IN THE ARA?

From San Nicolás de Bujaruelo we must head north, towards Ordiso Bridge. Wehave two options: OPTION 1: At the end of the track that leads to San Nicolás de Bujaruelo, where thebarrier that prevents the passage of cars is located, we take the clearly visible path towardsOtal. After about 20 minutes, we shall reach the turnoff to Otal Valley (indicated), wherethe Femalla Fountain is located. Here, we shall turn right (indicated) towards theheadwaters of the Ara and, after about 200 metres, cross the river on the Oncins Bridge.

OPTION 2: At the rear of the main buildingin San Nicolás de Bujaruelo, we shall takethe path that crosses the river over thebridge and then we shall turn left towardsthe head of the Ara Valley - Otal Valley(indicated). This well-marked path runsthrough the meadows by the River Ara. Afterabout 20-25 minutes we shall arrive at theforest track, near Oncins Bridge.

Option 1 is more cumbersome but takes us past the fountain. Option 2 is a nicepath, but you must be more careful not to stray from it.

Whichever option we have chosen, from Oncins Bridge we must head northalong the GR11 (white and red signs), uphill, towards the head of the Ara-Vignemal-Ordiso (signposted). The track soon begins to gain altitude and overcomes some steephills through the woods. After 15 minutes from Oncins Bridge, we shall come to a clearingin the woods and get a view of the spectacular Otal Valley and of its waterfall, which weshall see later on from above.

The track continues and after about 30 minutes, it passes next to a waterfall onour right where the water drops onto limestone rocks. After 10 minutes from the waterfall,we shall reach a fence that crosses the track, and that is usually open and only 5 minuteslater we shall come to a shepherd's hut.

Here, we must leave the main track and the GR11 and make our way down tothe river on the left (west), in the direction of the bridge over the River Ara, which is clearlyvisible from the hut. The first Stop will be at Ordiso Bridge (75 minutes from the car park).

San Nicolás de Bujaruelo. In order to reach this point, we will have to go tothe town of Torla and then continue along the road to Pradera in OrdesaValley (Ordesa y Monte Perdido National Park). At Puente de los Navarros,

where the barrier that prevents the access of private vehicles to the Pradera car parkin the summer is located, we shall turn left towards Bujaruelo (indicated). This is thebeginning of a seven kilometre long unpaved track, although suitable for all types ofvehicles, which runs past the Bujaruelo campsite and ends near the San Nicoláscamping area. The path starts behind the main building.

iSTARTING POINT:

11

stop1 75’

The explanation is that ice

excavated the Ara Valley during the

Quaternary ice ages; the most recent of

which peaked in the Pyrenees about 65,000

years ago.

At that time, the Ara Valley was

occupied by a glacier measuring over 36

kilometres long, ending nearly 5 kilometres

beyond Sarvisé.

This glacier, one of the longest on

the Spanish side of the Pyrenees, collected

ice from the Vignemal (3,298 m) and joined

with those in the Ordiso, Otal, Tendeñera

and, above all, Ordesa valleys. Precisely at

the confluence with the Ordesa Valley, the

glacier would have been 400 metres thick,

which gives us an idea of its magnitude.

Glaciers, in addition to being

important erosive agents, also transport

materials. The rocks they erode at their

origins or that fall on the ice surface are

driven down the valley as if they were on an

enormous conveyor belt.

Once the ice retreats after an ice

age, we can find these rocks that had been

transported by the glacier along its route,

as is the case with these granite boulders.

Large rocks that are dragged and

abandoned by the ice far from their places

of origin are known as erratics. On the climb

to the Ordiso Valley, we shall come across

more. Fig. 3. Details of granite erratics brought to this point by the ancientAra glacier.

12

Along the river, before crossing it,

we shall see that there are many granite

blocks in the vicinity; some that are quite

large. We will already have encountered

some on the track leading to this point,

partially hidden among the vegetation. If

the nearest granite outcrops are more than

5 kilometres from here (Panticosa area);

how did these blocks get here?

Fig. 1. View of Ordiso Bridge. Granite blocks can be seen in the

background.

Fig. 2 View of the head of the Ara Valley where the beginning of the

glacier was and a large granite boulder.

ORDISO VALLEYWe shall cross the bridge and start to make our way up a clearly visible path

that reaches beyond the threshold of the valley. There are no milestones or

markers; however, there is no missing it. Once we have reached this point, we

shall follow the path beside the river (almost always dry in summer, along the valley floor until

we reach the ruins of a shed (40 minutes from the previous Stop).

The Ara is one of the unique riverson the Spanish side of the

Pyrenees. There are no dams on its68 kilometre course and, therefore,

it is the only large Pyrenean river that preservesits natural dynamic features. Another two

routes visit other sections of this river: Geo-Route 8 visits the Sorrosal Valley and the

spectacular waterfall at its confluence with theRiver Ara at the town of Broto; and Geo-Route

7, which visits the Foz de Jánovas, carved bythe River Ara.

THE RIVER ARA!!

Glaciers also excavated the OrdisoValley. In this case, the glacier was a tributaryof the Ara glacier. The source was where theupper Ordiso mountain lake is now situated,where we will end the route. From that point,it flowed to the west until it met with the mainvalley glacier (Ara). As it was a smallertributary emptying into the main glacier, its

erosive effect was limited and this is why thereis a significant difference in altitude betweenthe floor of the Ordiso Valley and the floor ofthe Ara Valley (almost 200 metres).Consequently, from the bridge at the previousStop we have had to climb the hill that marksthe "threshold" where the confluence of thetwo glaciers took place.

40’

13

stop2

Fig. 4. Reconstruction of the area 65,000 years ago when ice covered the Ara and Ordiso valleys.

ARA

VALLEY

Torla

SOASO

VALLEY

ORDESA

VALLEY

San Nicolás deBujaruelo

BUJARUELO VALLEY

ORDISO

VALLEY

VALLE DE

OTAL

ORDISO

GLACIER

ARA

GLACIER

ORDESA

GLACIER

BUJARUELO

GLACIER

OTAL GLACIER

SOASO

GLACIER

Ordiso Valley also has other uniquegeological features. Many large limestoneblocks appear near the end of the valley;most having fallen from nearby slopes.

On the other hand, the stream wehave been following, carves its way downinto the rocks forming sections of deepravines. But this is not all; there are manygroundwater springs that contribute morewater to the stream, even if we can find notributaries on the surface: the water comesfrom underground. This is not the onlyunique hydrogeological feature of OrdisoValley. At the end of the valley, there is awaterfall also originated by undergroundwater. This spring cannot be seen from thetrack; we will have to leave the path andclimb to the top of the waterfal (Fig.7).

These hydrogeological peculiaritiesare mainly due to the type of rock found inthe valley. These are l imestone rocksformed of calcium carbonate, which aredissolved by runoff water that filters downtaking advantage of slabs, fractures andfissures in the rock, in a process known askarstification.Fig. 7.View of a point where underground water comes to the surface.

The water has travelled several kilometres.

Fig. 5. Ordiso Valley as seen from the head of the valley. Beyond Stop 2, the shape of a glacial valley becomes clear; however, it is even more so

when we make our way higher to the following Stops, where we can enjoy this view. 1- Valley threshold; 2- Stream fed by underground spring.

Fig. 6. Waterfall fed by underground springs.

14

Ara Valley

Ordiso

Valley

TROUGH

GLACIER

The result is the formation of aseries of underground tunnels that channelthe water. Thus, rainwater filters into theground and flows back to the surface inother places; in this case several kilometresaway. If we go to the top of the waterfall,we shall find that there is not one single

upwelling but that the water emerges fromvarious points near each other. In addition,the existence of a thick type of soil does notmake it easy to find springs. We shall onlyfind small f looded areas where smallstreams originate and join to form the riverthat flows through the Ordiso Ravine.

GRALLERA DE ORDISO

From the ruins of the shed, we shall take a short path and cross the river. Weshall then turn left (southwest) and make our way up a grassy slope following

the paths and stone markers. The markers indicate the route, although they may behidden in the long grass in summer. The track climbs the moraine and heads towards asmall ravine where the markers disappear; however, the direction is clear: we have tocontinue uphill, to a point from where we shall enjoy excellent views of the gaping mouthof Ordiso Cave (1 hour and 15 minutes from the semi-ruined shed at Stop 2).

To reach the foot of the cave, we have to leave the track although the best viewof the cave is precisely from a certain distance. Consequently, it is not necessary to goall the way (in addition, access is difficult).

Fig. 8. The huge mouth to the Grallera de Ordiso, which resulted in a rock arch.

15

stop31h.15’

From the track, we can see theenormous opening of the Grallera deOrdiso. This is actually a natural arch withthe entrance at the top, and that leads to aravine. The cave also provides waterfiltered from an area 500 metres away andabout 150 metres higher up on the southernside of Mount Año (see Stop 5). This cavehas underground galleries measuring overone kilometre and reaches a depth of 113metres. The stream that emerges from thiscave filters into the ground a little furtherdown and reappears at the surface onceagain at the springs we saw at Stop 1.

This is not the only karst feature in

the vicinity. There are also several sink-holes, fi ltration areas and limestonepavements nearby. However, to see them,we would have to leave the track and tourthe area.

Limestone pavements are typicalkarst formations created by the dissolutionof rocks containing calcium carbonate andare recognisable as they produce groovesor cavities on rocky surfaces. Sinkholes arealso a typical karst feature. They are closeddepressions of various sizes formed by adissolution process that starts at the topand works down or by the collapse of anunderground cavity.

Fig. 9, 10 y 11. Details of some of the karst features in the area: limestone pavement, filtering area and sinkhole.

Fig. 12. Route indicating some of the unique points seen from Stops 2, 3 and 4.

16

2

5

6

4

IBÓN DE ORDISO

PEÑA DEORDISO

2.319 3

COLLADO DETENDEREÑA

2.391

PUERTO DE ORDISO 2.684 MONTAÑA

DEL AÑO BARRANCO DEFERRERAS

SINKHOLE

UPWELLING

SINKHOLE

UPWELLING OTAL V

ALLEY

OR

DIS

O V

AL

LE

Y

HILLTOP We shall continue to make our way up the hill towards the top. The path

disappears and the markers scarce but the path we have to take is clear; up the

valley and up a grassy slope. After a false plateau, we shall come to the hilltop

that overlooks the rest of the valley from an altitude of about 2,300 metres (2 hours from the

ruins of the shed at Stop 2).

From the hil ltop, two interestingfeatures need mentioning. The first is that, ifwe look straight ahead, as we arrived, weshall see a huge depression that looks like avalley.

However, when we proceed to thenext Stop, we shall find that its lowest point,which we cannot see from here because itis on our right hidden by the slope, does notconnect with any stream. Therefore, whatwe have is not a valley, but an enormousdepression of karstic origins formed by thedissolution of the limestone rocks that formthese mountains.

For the other observation, we shallhave to turn around and look in thedirection from where we came. From here,we shall enjoy an excellent view of Mount

Viñemal (3,298 metres), one of the greatgiants of the Pyrenees, the southern slopesof which belong to Sobrarbe, while thenorthern slopes belong to France.

We may have already noticed italong the way because it is a huge mass ofrock that stands out in the landscape givenits size and its bright colour (Fig. 14). Thiscolour is partly due to the fact that itsstructure includes white limestone, formingwhat is popularly known as "the Viñemalmarble factory".

This is highly recrystall izedlimestone, which provides this typical andstriking clear colour. This phenomenon alsoappears in other places in the AragonesePyrenees, such as La Larri or in Otal.

Fig. 13. Karstic depression of the Ordiso sinkhole, seen from the hilltop at Stop 4.

45’

17

stop4

ORDISO MOUNTAIN LAKE

(hidden)

SINKHOLESINKHOLE(hidden)(hidden)THE STREAMTHE STREAM

FLOWING FROMFLOWING FROMTHE ORDISOTHE ORDISO

MOUNTMOUNTAIN LAKEAIN LAKE

KARSTIC DEPRESSIONKARSTIC DEPRESSION

Furthermore, in the basin that hasformed on this side of Viñemal, we can seethe small ice field of the Central Peak (Fig.14). This is a small mass of ice that, as otherPyrenean glaciers, has suffered a significantdecline in its volume in recent years. Thecurrent glaciers and ice fields on theSpanish side of the Pyrenees are small andsurvive in cirques at altitudes around threethousand metres. They are known as cirqueglaciers because they only exist near theglacier head or cirque and are not largeenough to expand into the valleys. They areactually masses of ice, remnants of largerglaciers that formed during colder eras,especially during the so-called Little IceAge; a cold cycle from the fourteenth tothe nineteenth centuries.

These glaciers formed because theaverage annual temperature dropped andthe amount of snow that fell increased,leading to an accumulation of snow,especially at the end of spring andbeginning of summer. Therefore, thesummers were shorter, and the effect of thesun was less intense. Glaciers are extremelysensitive to environmental change andrespond very quickly to positive or negativevariations. Studies conducted on Pyreneanglaciers have provided some clues tounderstanding how the melting processoccurs. The increase of the averagetemperature in summer causes the snowthat has accumulated throughout the yearto melt, leading to the melting of ancientglacier ice, which, in turn, causes areduction in the size of the glacier each

year. In the summer months, there is a dailymelting cycle, i.e. melting in the mornings,freezing at night. It has been calculatedthat the flow of water generated by themelting process reaches its maximum leveltwo hours after this highest dailytemperature is reached. Thus, calculationsmade on the glacier of the Picos delInfierno have shown that some years it haslost one metre of its thickness and its fronthas retreated up to 8 metres. This meansthat, under current thermal and climaterhythms, the Pyrenean glaciers wil ldisappear within a few decades. These aregeological elements that are becomingextinct.

A small moraine has formed at thefront section of this ice field: anaccumulation of ochre coloured sedimentsthat were transported by the glacier andthat seen from above has a crescentshape, which corresponds to the shape ofthe front section of the ice field (Fig. 15).

Fig. 14. View of the "Viñemal marble factory", a prominent feature in the landscape.

Fig. 15. Detailed view of the Viñemal central peak glacier and

the moraine.

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White limestone / marble

Glacier

Moraine

THE SINKHOLE.From the hilltop, we must make our way down to the river (which will almost

certainly be dry) towards our right. You cannot miss the sinkhole because it is

the lowest point in the depression and the river flow into it.

(10 minutes from the previous Stop).

From the previous Stop, we hadfigured out that there was no way out of thevalley opposite (we are now at the lowestpoint of it). In other words, the streams flowingtowards its lowest point were prevented bythe lay of the land to continue their way downthe valley. The reason is that this entiredepression is of karstic origins and the water,after flowing a short distance on the surface,reaches the bottom of the depression andfilters into the ground through a sinkhole(Fig.xx). In fact, this sinkhole acts as a natural

collecting point for the water from themountain lake we shall visit at the next Stop. Itis strange to see a river disappear from thesurface and filter into the ground through alarge hole. After filtering into the ground, thewater emerges once again at the Grallera deOrdiso (Stop 3), after covering more than onekilometre underground. We know this is thecase because, years ago, a harmlesscolouring agent was added to the water thatfiltered into the ground at this point in order tosee where it emerged again.

Fig. 16. View of the stream flowing from the Ordiso mountain lake (left) and of the sinkhole through which the water filters.

10’

Fig. 17. View of the stream and sinkhole from another angle. The arrow indicates the direction of the water.19

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IBÓN DE ORDISO (ORDISO MOUNTAIN LAKE)From the sinkhole, we shall follow the river course towards the mountain lake,

which we shall reach after walking along paths that appear and disappear,

although the direction is clear (20 minutes from the previous Stop).

We finally come to the Ordismountain lake, one of the most remote andlonely in Sobrarbe, located at an altitude of2,340 metres. We can observe it from many

points, but we recommend walking to thewestern end, where we will be able to seethe point where the water that feeds thelake emerges.

Fig. 18. View of the Ordiso mountain lake, one of the most remote in Sobrarbe.

20’

Fig. 19. View of the Ordiso mountain lake. The lighter coloured edges indicate the accumulation of sediment.

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Fig. 20. View of the underground water emerging to feed the Ordiso mountain lake.

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The mountain lake elongated; itslongest side measures about 150 metres.The northern section appears to be partiallyfi l led-in, given that the rain washesabundant sediments into the lake from thehigher part of the cirque (Fig. 19).

A singularity of this lake is that it isrelatively small given the size of the basinsurrounding it. Undoubtedly, the karsticnature of the area is partially responsible forthis. While the stream that originates at thelake filters into the sinkhole we saw at Stop4, the lake also receives underground water(Fig.xx). In other words, the karstic nature ofthe terrain affects the circulation of waterin the lower part of the valley and also inthe higher sections.

Although mountain lakes are someof the most typical elements of Pyreneanlandscapes, they are not particularlyabundant in Sobrarbe. This is due to the

nature of the rocks that emerge in thehigher mountain areas in this district.Mountain lakes are formed becauseglaciers erode the ground unevenly,forming troughs in places where thethickness of the ice is greatest or where therocks display some pronounced weakness.When the ice retreats, the basinaccumulates the runoff and rainwater,originating a mountain lake of varyingdimensions.

Therefore, the formation ofmountain lakes is closely related to the typeof rock. Consequently, granitic rocks aremore favourable when it comes to theformation of these basins, especially if theyhave several grains. However,metamorphic and sedimentary rocks, whichare usually less resistant to erosion, do notgenerate these forms as the erosion takesplace more evenly, grinding away theentire floor of the valley.

From here, we recommend movingabout one hundred metres to the south totake a look at the neighbouring Otal Valley,of which we shall enjoy an incrediblepanoramic view from this point. We will beable to observe its perfect troughmorphology (glacial valley, in a U shape,compared to typical river valleys that havea V shape) as it was also occupied by atributary glacier of the Ara Valley. It is avalley that, in spite of its simple

appearance, hides a complex tectonicstructure. In fact, the southern slopes ofOtal Valley, the one opposite us, mark theboundary between Mesozoic andPalaeozoic materials in this part of thePyrenees (Fig 21.

Thus, the higher part of the slope,including the sharp ridges, is formed ofcalcareous rocks from the Mesozoic andCenozoic.

Fig. 21. The southern slopes of Otal Valley mark the boundary between calcareous rocks from the Mesozoic-Cenozoic and those from the Palaeozoic,

clearly distinguishing two great units in the Pyrenees: the Axial Zone to the north (towards us), where ancient Palaeozoic rocks predominate;; and the

Inland Ranges to the south, where landscapes such as Ordesa and Mount Perdido, Tendeñera or Otal originated. The difference between the rocks

and the mountain landscapes in both areas is very clear.

However, the lower part of thes lope, the val ley f loor and the s lope weare s tand ing on a re fo rmed o fcalcareous rocks but f rom the Devonian(Palaeozoic) . The t ime lapse betweenthe format ion of these types of rock,which today appear on top of eachother , exceeds 300 mi l l ion years .

However , the mos t impor tantfact i s that th i s conf igurat ion i s due tothe complex tectonic s t ructure of th i sarea ( F i g . 2 2 ) .

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Rocks from the Mesozoic-Cenozoic

Rocks from the Palaeozoic

Anyone who wishes to walk furtherand extend this excursion can make theirway to the highest mountain lake in Ordiso(30 minutes) and to the Ordiso mountain

pass (2,555 m), where there are amazingviews of the Tena Valley, Sabocos, theTendeñera summit and the Mount Perdidomassif.

N

Fig. 22. Geological diagram of this sector of the

Pyrenees. As in figure 19, we can see that the boundary

between the Palaeozoic and the Mesozoic rocks is

located in Otal valley, precisely on the hillside opposite us.

ORDISO

VALLEY

MESO

ZOIC

CENOZOIC

PALA

EOZO

IC

TorlaORDESA

VALLEYRiver AraBujaruelo

OTAL

VALLEY

SPECTACULAR WATER FORMATIONS FOR SOLITARY MOUNTAINEERS

ORDISO MOUNTAIN LAKE>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> PRACTICAL INFORMATION

ROUTE: Mesón de Bujaruelo - Ordiso Mountain Lake ( Ibón de Ordiso). It runs along part of the GR 11.

TYPE OF ROUTE: Linear (return along the same route).

DIFFICULTY: Medium-high. The first part of the route, as far as Ordiso Bridge, runs along a well-markedtrack. After that point, you will have to follow some markers or pathways that are not always clear andsometimes disappear. Therefore, although the route does not present any technical difficulties, care must betaken and a bit of intuition is needed.

DURATION: 4.5 hours. (one way) The return trip is downhill and requires another 3 hours. Long and toughroute.

LENGTH: 27 kilometres (return)

GRADIENT: 1,000 metres up and 450 metres down.

STARTING POINT: San Nicolás de Bujaruelo. In order to reach this point, we will have to go to the town ofTorla and then continue along the road to Pradera in Ordesa Valley (Ordesa y Monte Perdido National Park).At Puente de los Navarros, where the barrier that prevents the access of private vehicles to the Pradera carpark in the summer is located, we shall turn left towards Bujaruelo (indicated). A seven-kilometre unpavedtrack starts here, although it can be used by all types of vehicles. It ends near the San Nicolás campsite, andthe path starts behind the main building.

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9 www.geoparquepirineos.comGEO-ROUTEof Sobrarbeof Sobrarbe

Trekking sticks may be useful on the grassy sections of the route. At the head of the Ordiso Valley (even abovethe lake), there are a lot of cattle; therefore, it is advisable to take your own water as almost all the rivers areused by the cows. This is a long route and its main attraction is Ordiso Valley, consequently all the Stopssuggested are in this sector of the route.

IMPORTANT: This Geo-Route visits a mountainous area, the conditions of which depend on the weather.

The route is not difficult or dangerous, but it does require knowing how to walk in the mountains. The map

included serves to identify the Stops, but is not enough to find your way on the route. It is imperative that

you take a hiking map of the area, and it is highly advisable to take a GPS.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> COMMENTS

2500

2250

2000

1750

1500

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> PROFILE GEO-ROUTE6 5 4

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