sierra nevada massif glacial geomorphology and present cold

Transcription

SIXTH INTERNATIONAL CONFERENCE ON GEOMORPHOLOGY
SIERRA NEVADA MASSIF GLACIAL
GEOMORPHOLOGY AND PRESENT COLD
PROCESSES
Antonio Gómez Ortiz, Lothar Schulte, Ferran Salvador Franch, David Palacios
Estremera, Carlos Sanz de Galdeano, José J. Sanjosé Blasco, Luis M. Tanarro García and
Alan Atkinson
FIELD TRIP GUIDE -
A9
SIXTH INTERNATIONAL CONFERENCE ON GEOMORPHOLOGY
FIELD TRIP TO SIERRA NEVADA MASSIF GLACIAL GEOMORPHOLOGY AND
PRESENT COLD PROCESSES
Antonio Gómez Ortiz, Lothar Schulte, Ferran Salvador Franch, David Palacios Estremera, Carlos
Sanz de Galdeano, José J. Sanjosé Blasco, Luis M. Tanarro García and Alan Atkinson
Departament de Geografía Física i Análisi Geográfica Regional. Facultat de Geografía i História. Universitat Central de
Barcelona. Baldiri Reixac, s/n. 08028 Barcelona. e-mail: [email protected]
Introduction
The A9 field trip of the Sixth International Conference on Geomorphology highlights the special
morphobioclimatical nature of Sierra Nevada Massif situated in the southeast of Spain. This
massif is characterized by the existence of high peaks (over 3.400 m), its low latitude (the
southeastern zone of Europe) and its thermopluviometric pattern (long arid periods and intensive
cold). These features make Sierra Nevada and especially its summits be an interesting scientific
area to reconstruct the recent paleoenvironmental Quaternary history of the Mediterranean areas
and to understand the present morphodynamics in cold and arid high areas of temperate latitudes.
The guide is divided into two parts. The first one pays attention to the biophysics features and
particularly to the glacial and periglacial geomorphology of summits. The second part contains
the details of the viewpoints and the most outstanding geomorphological aspects of the field trip.
To sum up, the field trip emphasizes the glacial and periglacial landforms and the cold processes
that characterize the mountaintops from the study of one of the most representative areas of the
range, the “Picacho Veleta unit”.
The final results come from several research projects developed since 1998.
FIRST PART: BIOPHYSICAL ENVIRONMENT OF SIERRA NEVADA SUMMITS
1. Geographical context
Sierra Nevada belongs to the Betic Range that is situated in the southeast of the Iberian Peninsula.
The Range is a southwest-northeast orogen that extends along 520 km from the vicinity of the
Strait of Gibraltar (Atlantic Ocean/Mediterranean Sea) to the La Nao Cape (Mediterranean Sea).
Sierra Nevada is a West-East trending massif that stands out from the depressions and valleys that
surround it (Granada, Baza-Guadix, Guadalfeo, Andarax, etc.). The massif includes the highest
peaks of the Iberian Peninsula (Mulhacén, 3482 m; Veleta, 3396 m; Alcazaba, 3366 m; etc.). It is
at latitude 37º North and 2º45´/3º30´ West in the Andalucía region in Almería and Granada
provinces along 90 km. Its maximum width reaches 40 km and it is 30 km away from the sea.
The morphology of Sierra Nevada is characterized by the predominance of gentle landforms apart
from the western summits affected by Pleistocene glaciations (picture 1 and figure 1). A dense
and incised network of creeks and watercourses compartmentalizes the relief. The ones orientated
to the South discharge into the Mediterranean Sea (Guadalfeo creek, Adra creek, Andarax creek,
etc.) while those orientated to the North discharge into the Guadalquivir River (Genil creek,
Fardes creek, etc.). They show an ephemeral regime due to the arid/semiarid climate of the
western part of the Mediterranean area. Long dry periods are interrupted by autumn high intensity
Sierra Nevada massif glacial geomorphology
storms that make the watercourses overflow, sometimes catastrophically. However, the altitude of
the massif triggers a change in the climate, especially in the summits where the cold and the snow
become important (at 2150 m between October and May the mean temperature is lower than 5º C
and the 47,8 per cent of the mean annual rainfall is as snow). As a result, the thicket and the
sclerophile forest of the lower altitudes disappear in favour of a xerophile grass of festucas at
higher altitudes.
al Río Guadiana
0º
Baza
40º
R. Almanzora
Guadix
GRANADA
Fiñana
R. Genil
37º N
S
ALMERIA
Motril
Adra
Cabo de Gata
N
0
10
20
30 Km
3º W
Figure 1. Geographical situation of Sierra Nevada and the glaciated area.
Picture 1. Aerial photographs of Sierra Nevada western summits
2
A. Gómez Ortiz et al.
Sierra Nevada (known as“Sun Hill/Snow Hill” in Muslim texts of the IX century) has been
affected by anthropic activities since the old times. Currently, many villages are spread all over
the area ascending up to 1550 m high. Their economy is based on farming and tourism trade. The
summits that are home to high value scientific ecosystems and interesting landscapes have been
declared Biosphere Reserve (UNESCO, 1986), Natural Park (Regional Government, 1989) and
National Park (Spanish Government, 1999) (picture 2).
Picture 2. Alcazaba-Veleta area. Highest peaks of Sierra Nevada
2. Geological context
Sierra Nevada is situated in the Inner Betic Zone that is formed by three large tectonically
overlapped complexes. From bottom to top, they are the “Nevado-Filábride”, the “Alpujárride”
and the “Maláguide”. The latter does not crop out in Sierra Nevada. In contrast, the Alpujarride
Complex is found at low altitude areas surrounding the massif. The highest summits of this
complex such as “Alayos”, “Trebenque”, the “Tesoro”, the “Dornajo” and the “Calar de Cantar”
occur at the western part of the massif and they may reach 2000 m high. Although the Alpujarride
Complex is superposed on the Nevado-Filábride Complex, it is not as taller as the NevadoFilábride Complex. Both complexes are formed by metamorphic rocks. Finally, the NevadoFilábride Complex is divided into two thrust nappes: at the bottom the Veleta nappe and at the top
the Mulhacén nappe (figure 2).
In this area, the Veleta nappe is formed by a single unit called “Las Yeguas unit” (Puga, 1971;
Díaz de Federico et al., 1980). The field trip pays attention to Veleta nappe outcrops. This nappe
is made up of over 3000 m thick dark carbonaceous schists (picture 3) (Díaz de Federico et al.,
1980) that alternate with locally thick quartzite beds. We may also find lenses of amphibolites and
scarce serpentinites and epidotites. These rocks are believed to constitute a Palaeozoic basement
affected by Alpine metamorphism.
3
Guéjar·Sierra
C
2528
Mirador Bajo
Charcón
Papeles
S
C
H. Duque
V·P
2435
T
Picón de
Jeres
C
T
T
2215
T
3094
SF
C
Cañadillas
V·P
Horcajo de
Trevélez
Mojón
Alto
La Estrella
S
T
T
T
T
2878
C
Pradollano
Tesoro
Cerro de Trevélez
3182
3109
C
C
Puntal de
Vacares
3129
S
C
C
Puntal de
la Caldera
Mulhacén
3226
3482
Veleta
C
3398
C
Muerto
2891
Alcazaba
3366
S
Tajo de Lagunillos
3157
S
Caballo
3013
C
Tajo de los Machos
C
3081
Trevélez
C
N
Alegas
2720
0
Neogene
Veleta mantle
Alpujárride (T:Trevenque unit,
V·P:Víboras·Padules unit)
Overlaping
Mulhacén mantle
(S:Sabinas unit, C: Caldera unit,
S·F: San Francisco unit)
Fault
1
2 km
Antiformal of Sierra Nevada
Figure 2. Geological context (modified and simplified from Díaz de Federico et al., 1980).
To the top, Triassic quartzite beds alternate with feldspathic micaschists that may reach 200 m
thick.
From the beginning of the Tertiary to the end of the Oligocene, different stages of compression
and extension led to the thrusting of the Inner Betic Zone complexes. Subsequently, from the
lower Miocene to the Middle Miocene an important extensional period (Galindo-Zaldívar et al.,
1989; García-Dueñas et al., 1992) caused a readjustment of the tectonic complexes and their units.
The upper units were displaced to the WSW. The deformation was first ductile affecting mainly
the Nevado-Filábride complex. Afterwards it changed to brittle affecting specially the Alpujárride
Complex. Most of the previously overlapped units were sheared and occasionally thrusted.
In spite of the intense tectonic activity no high relieves were formed. The highest ones (1830 m)
are found in the western zone of the massif. Those summits consist of Upper Miocene marine
sediments (Sanz de Galdeano & López-Garrido, 1999) that suggest the main uplift stage occurred
after the Upper Miocene. The lack of eroded sediments from the Nevado-Filábride Complex in
4
the stratigraphical record before the end of the Upper Miocene corroborates the previous
hypothesis.
Picture 3. Carbonaceous micaschists of the Veleta Unit affected by neotectonics and gelifraction processes.
The main uplift period that caused the large antiform structure of Sierra Nevada began in the
Upper Miocene as a result of a NNW-SSE to N-S compression regime (Sanz de Galdeano, 1998;
Sanz de Galdeano & López Garrido, 1999; Sanz de Galdeano & Alfaro, 2004), which is still
active today. The uplift enhanced the incision of an important drainage system. The axis of this
antiform structure has an E-W orientation and it bends to the south in its western zone.
3. Geomorphological Context
Cold quaternary processes concentrate above 2000 m. The snow line was 2400, 2800-2900 and
1965 in the Würm, Tardiglaciar and Messerli glacial phases respectively. The studies have
demonstrated that summits landforms grade into periglacial landforms from the mountaintops
downwards.
3.1. Summits landforms. Pleistocene glaciation
Pleistocene glaciation was first studied at the end of the XIX century, although its existence was
confirmed at the beginning of the XX century (Obermaier, 1916; Dresch, 1937). However, its
geomorphological and paleoenvironmental meaning was not established until halfway through the
last century (Paschinger, 1957; Messerli, 1965; Lhenaff, 1977). Nowadays, Pleistocene glaciation
is well known, although the number of glaciations and their ages have not been recognized yet
(Gómez Ortiz & Salvador Franch, 1998).
The quaternary glaciers of Sierra Nevada Massif were similar to those that exist in dry mountains
such as the High Atlas and Andes rather than in wet mountains such as the Alps or the Pyrenees.
Its latitude contributed to minimize the effect of the Atlantic atmospheric perturbances and to
favour the thermal Mediterranean influence. As a result the snow line was set at a much higher
5
altitude than in other areas of the Iberian Peninsula (2300-2400 m in the North face; 2400-2500 m
in the South face; Messerli, 1965).
Other local factors that helped to characterize its glaciarism were its volume, altitude, preexisting
relief, morphostructure, lithology and slope orientation.
These local and regional factors made the glaciers exist in mountaintops and headwaters of creeks
mainly in the western zone where the summits such as the “Cerro de Trevélez” (2877 m)-“Cerro
del Caballo” (3013 m) reached the highest altitudes (figure 3).
In Sierra Nevada the area occupied by ice and snow masses is characterized by the following
geomorphological features:
a) Influence of tectonic activity and lithostratigraphy on the creation of erosive landforms in
cirques and valleys.
b) Summits defined by either ridges and horns (hörner) or altiplanation terraces.
c) Isolated and well limited accumulation areas. Transfluence passes were scarce.
d) Steep and U-shaped glacial troughs.
e) Moraine deposits of different ages along creeks.
f) A large number of rock glaciers in the highest points of the cirques.
Corral del Veleta
Río Maitena
Río Alhorí
Río Genil
arn
Gu
ó
n
Río
?
Río Monachil
?
?
Río Dílar
Río Dúrcal
Rí
oL
an
jar
ón
Trevelez
Río Puntal
Río Poqueira
Río Trevélez
0
1
2
3
N
5 km
4
Figure 3. Glaciarism of Sierra Nevada. Identification of the Corral del Veleta cirque. 1. Summits; 2. Fluvial network; 3.
Glacial cirques; 4. Glaciers.
6
We may distinguish two types of glacial systems regarding their morphological meaning (table 1):
Table 1. Classification of Glacial systems
__________________________________________________________________________________________________
Type
Glacial system/form
Variety
Examples
__________________________________________________________________________________________________
convergent glacier tongues
Genil, Poqueira, Trevélez
…………………………………………………………………………………………………………….
Cirque and valley not well differentiated
Monachil, Guarnón, San Juan,
Valley
isolated glacier tongue
Lanjarón
……………………………………………………………………..
Cirque and valley well differentiated
Dílar, Vadillo, Maitena
…………………………………………………………………………………………………………………………………
Moraines outside the cirque
Siete Lagunas, Dúrcal, Alhorí,
Lagunillos, Río Chico
……………………………………………………………………………………………………………………
Cirque
Lateral-moraines
Cornavaca, Puerto de Trevélez,
Hoya de la Mora
…………………………………………………………………………………………………………………
Moraines exclusively inside the cirque
Ventisquero del Gallo, Chorrillo,
Peñón Negro, Nigüelas.
__________________________________________________________________________________________________
Cirques
Sierra Nevada cirques were formed in the headwaters of watercourses where the slope was
suitable for the accumulation of snow. Those formed in the South face were favoured by an extra
supply of snow due to the predominance of west winds (picture 4). During the Tardiglaciar and
the Litlle Ice Age, the ice only remained in Cirques. The isolation of cirques, the
compartmentalization of glacial systems and the accommodation to a preexisting relief are
demonstrated by the lack of confluence points and transfluence passes.
Picture 4. Río Seco cirque (South slope of Sierra Nevada)
7
On the other hand, local tectonic structures influenced the erosion activity of glaciers and the
erosional landforms. The formation of thresholds, striated, polished and grooved rock surfaces
and overdeepened basins was controlled by NNW-SSE and NE-SW trending joints and faults
present on bedrock. Some examples are the Veleta (Green Water landscape), Cuenco del Goterón
and Juntillas cirques.
The most outstanding depositional landforms are rock glaciers that tend to fill cirques above
2,800 m. They might be formed during the Early Würmiense (Tardiglaciar) in different phases
(Messerli, 1965; Lhenaff, 1977; Sánchez Gómez et al. 1990). The best examples occur at the
headwater of Dílar creek (Cascajar del Cartujo) and in the Valdeinfierno unit (Genil headwater)
(figure 4).
Glacial cirque headway and
bedrock in process of gelifraction
Puntal del
Goterón
3072
Rock ledge
Polished, raked substratum
Localised fracture network
3371
Alcazaba
Old rock glaciers
Taj
os
del
G
ote
rón
More recent rock glaciers
N
0
50
100 m
B
o
nc
ra
ar
de
ld
Va
i
nf
ei
no
er
Gravity gelifract cone
River systems and irrigation
grassland
Figure 4. Morphology of the Goterón cirque.
Valleys
Glaciers mainly tended to flow along the preexisting fluvial valleys leading to glacier tongues.
However some of them grew along the mountain slopes becoming cirque glaciers (Cornavaca,
Siete Laguna, Alhorí). Glacier tongues were little and didn’t reach long distances. Nevertheless,
glaciers orientated to the North and especially to the Northwest had longer tongues. For example,
the Dílar glacier tongue could reach more than 10 km long. The low latitude of the massif, the fact
that accumulation areas were small and the scarce transfluence caused the early thawing. As a
result the U-shaped glacial geometry of the valleys has disappeared quickly due to erosional
processes.
8
Rock ledge
Middle Mulhacén moraines
Narrow valley
Eroded slope ledge
Majada moraines
River system
Other ledge
Hoya del Capitán moraines
(Veleta-Río Seco-Milhacén
confluence)
Polished and raked bedrock
Moraine matter indistinguishable
from Majada
Erosive high plateau
Bedrock subjedt to gelifraction
Crescent mark
Ice mass
Developed cirques with uneven
edges
Slope debris soligelifluidal slides
Ravine, antique snowy
Moraine matter flows
Middle Sabinar moraines
Soligelifluction flows and lobes
Middle Río Seco moraines
Water in soft matter
Río Veleta
Slope rupture
Río Mulhacén
Río Seco
Peñones
Negros
La Majada
Barr
anc
o de
l Sa
bina
r
Hoya del
Capitán
Río Poquerira
Alto del
Chorrillo
N
0
0,9 km
Figure 5. Morphology of the Hoya del Capitán cirque (Poqueira valley).
9
Only those moraines deposited in low-gradient valleys (glaciers formed on cirque thresholds and
on open thalweg valleys) such as the ones present in Poqueira, San Juan, Cornavaca and Lanjaron
glacial systems, preserve their original morphology. In those places, several different stages of
moraines formation can be identified. Each stage may be related to a glacial period (figure 5). All
the moraines identified in the massif had similar features. They are sharp-crested ridges made up
of a poorly sorted mixture of debris embedded in fine matrix. In the absence of good absolute
dating, they have been dated depending on their morphosedimentary features and their
distribution in the valleys. Outer, inner and intermediate moraines are supposed to be PrewürmWürm, Würm-tardiglaciar and würm respectively. The Poqueira glacial system is a good
example. Here, stepped moraine ridges occur between the altitudes of 1750 m and 3150 m
3.2. Altiplanation terraces and slopes landforms. Periglaciarism
Sierra Nevada slopes were affected by periglacial processes during and after glacial
morphodynamics leading to grèzes litées on hill slopes even at low altitude (1100 m in the Laroles
Valley). The periglaciarism of the massif was first pointed out by Dresch (1937), although UlrichBrosche (1978) and Soutadé & Baudière (1971) were the ones who showed its morphological
meaning and effects on the present dynamics of ecosystems.
The most outstanding feature of Sierra Nevada periglaciarism is the existence of altiplanation
terraces. They are attributed to old remains of periglacial erosional surfaces. The edaphological
studies conducted in altiplanation terraces (Sánchez Gómez, 1989) suggest that they behaved as
cryoplanation surfaces and they didn’t host fjeld type ice caps. On the other hand, periglacial
processes led to patterned grounds, stone pavements, gelifluction lobes and stone accumulations
depending on the topographic gradient (table 2 and picture 5). In addition, during the Tardiglaciar,
a great volume of debris was accumulated leading to the previously mentioned rock glaciers. The
snow deflacted from the altiplanation terraces was accumulated in the cirques orientated to the
south. This fact controlled the dynamics of the existent rock glaciers such as the ones situated in
Poqueira and Lanjaron valleys.
Picture 5. Patterned ground in the Cerro de los Machos pass
10
Table 2. Topmost altiplanation terraces and landforms
_____________________________________________________________________________________________
Altiplanation terrace
1
2
3
4
5
6
7
8
_____________________________________________________________________________________________
Caballo
M
15,8
0,8 3013
2940
WNW
14,1
ABE
............................................................................................................................................…………………………….
Tajos Altos
M
38,7
1,5 3003
2940
NW
5,5
ABE
0,5 2920
............................................................................................................................................……………………………
Lanjarón-Elorrieta
M
33,7
1,0 3100
3080
SW
19,1
ADE
0,2 2890
............................................................................................................................................……………………………
Cañar
M
47,7
1,7 3081
3020
NW
6,1 ABCE
0,3 2980
............................................................................................................................................……………………………
Cerro de los Machos
M
9,4
0,4 3320
3240
N
10,1
ABD
0,4 3160
............................................................................................................................................……………………………
Allanada del
M
32,3
0,7 3440
3400
S
8,5
ABD
del Mulhacén
0,3 3380
............................................................................................................................................……………………………
El Cuervo
M
16,1
1,5 3152
3100
S
3,4
ABC
0,2 3100
............................................................................................................................................……………………………
La Atalaya
M
26,2
1,5 3158
3100
S
3,8
ABE
0,1 3100
............................................................................................................................................……………………………
Jeres-Cerro PeladoM
96,4
3,5 3182
3100
S
2,3 ABCE
-Horcajo
1,2 3100
.........................................................................................................................................……………………………..
Las Albardas
M
236,9
4,5 2919
2900
S
1,2 ABCE
1,5 2860
___________________________________________________________________________________________
1. Substratum (M. micaschists); 2. Area (ha); 3. Maximun length and width (km); 4. Highest and lowest points (m);
5. Average altitude; 6. Predominant orientation; 7. Average slope (%); 8.Significant landsforms (A. Cryoplanation
terraces; B. Tors; C. Mer de roches; D. Patterned grounds; E. Gelifluction lobes).
___________________________________________________________________________________________
4. Little Ice Age
During the Little Ice Age, (XV-XIX centuries), while the Alpine and Pyrenean glaciers expanded,
the high peaks of Sierra Nevada Massif hosted small glaciers. This fact allows stating that this
historical cooling period reached the Mediterranean latitude. Since halfway through the 18th
century (Ponz, 1797; Boissier, 1839; Hellmann, 1881; Quelle, 1908; Solé Sabarís, 1942) travellers
and scientists already informed about the existence of probably the most important ice mass of the
massif formed during the Little Ice Age. It was situated in the “Corral del Veleta” cirque at the
headwaters of the Guarnón Creek and it left moraine ridges of different ages of deglaciation
(Gómez Ortiz et al. 1996; Schulte, 2002b) (figure 6).
The geophysical (seismic and electrical profiles) and borehole data point out the present existence
of a frozen mass at 1.90 m underground covered of debris in the eastern side of the cirque where
the glacier lasted up to halfway through the 20th century (Gómez Ortiz et al. 1999). The frozen
body may be associated with an alpine permafrost situated between the back wall and the
Tardiglaciar lip moraines of the cirque. Periodical thermal checks suggest that it may be
undergoing a degradation process.
11
Figure 6. Topography of Sierra Nevada Massif (Bide, 1893).
5. Morphodynamics of summits
The climatic conditions of Sierra Nevada summits are defined by the aridity and the thermal and
nival regime (long periods of gelifraction processes on soils). Those conditions allow the
development of the important cold processes that characterize arid mountains. The combined
effect of cold, ice, snow and wind is very effective above 2.700 m in the South face.
Table 3. Present cryonival processes and landforms
Site
Preferential situation
Cirque
Transition bottomwall (talus)
Glacial Valleys
“Borreguiles”
Rocky walls
Cirque heads and
headwaters of creeks
Altiplanation terraces
>3000m
Slopes
Upper part >29003400m
Middle part 25002900m
Main processes
Weathering
Gelifraction
Transport
Avalanche,
landslides
rock
Landform
and
biogeographical affinity
falls
Protalus ramparts, talus
cones, block streams and
lobes
Gelifraction
Rock falls
Block slopes and cones
Physical/chemical
Cryoturbation
and Lobes vegetated by
solifluction
Carex, Ranunculus and
Sphagnum
Gelifraction, deflation and cryoturbation either may preserve preexisting
landforms (patterned grounds and mers de roches) or form new ones
(patterned ground and stone lobes).
Psicroxerphite grass (Festuca indigesta, F. Pseudoeskia)
Gelifraction, deflation, cryoturbation and meltwater runoff either preserve
preexisting landforms (debris-mantled slopes) or form new ones (stone
lobes). Psicroxerophite grass (Festuca indigesta, F. pseudoeskia) and low
growing junipers (Genista baetica)
Gleifraction,
Cryoturbation,
Stone lobes, gelifruction
wetting-drying,
solifluction, meltwater benches, patterned
deflation
runoff, creep
Cold processes are variable. Gelifraction is favoured by the low strength of the substratum
(fractured micaschists that led to block accumulations at the toe of vertical walls). Solifluction
and cryoturbation are especially important in loose detrital deposits. Their action results in either
a slow migration of superficial debris along the slopes or the formation of debris terraces,
12
depending on the topographic gradient. The scarce vegetation cover is always a passive agent as it
is unable to inhibit those movements. The resulted landforms, cryonival processes and altitude are
connected as shows Table 3.
SECOND PART: ITINERARY, VIEW POINTS AND ANALYSIS
The field trip is designed to visit the Veleta unit situated in the highest area of the western massif.
The way up is easy. A restricted-access bypass reaches the mountaintop ridges. The explanation
of the glacial and periglacial processes and landforms is carried out from significant viewpoints.
The field trip consists of four stops (figure 7):
1. Carihuela pass;
2. Picacho del Veleta Peak
3. Corral del Veleta cirque
4. Cerro de los Machos pass
Figure 7. Itinerary and viewpoints.
13
1. Carihuela pass.
Carihuela Pass (3199 m) is one of the main communication routes between the North and the
South faces of Sierra Nevada. Many years ago, people from the Alpujarra villages were obliged to
cross it to get to Granada city. Thanks to its situation it acts as a junction point of three glacial
valleys: Veleta, Lagunillos-El Nevero and Dílar. In addition, Carihuela Pass shows excellent
views of the Mulhacén-Loma del Tanto-Chorrillo Ridge and the Veleta cirque and valley head.
1.1. Cirque and headwater of the Veleta valley.
The Veleta cirque, also called Aguas Verdes cirque is orientated towards the SSE and it is formed
by several cirques. It is limited by the “Tesoro Cut (Loma Púa)-Raspones de Río Seco” and
Veleta and Machos Peaks of more than 3300 m high. During the Last Glacial Maximum
transfluent ice flowed through Río Seco, Valdeinfierno and Dílar valleys and some peaks acted as
horns (Veleta, Tajos de la Virgen, Púlpito).
Corral del
Veleta
Corral de
Valdeinfierno
Veleta
3.398 m
Circo de
Río Seco
Loma
Púa
N
0
300
1
900 m
2
3
Río Veleta
4
5
6
7
8
9
10
Figure 8. Morphology of the Veleta cirque. 1. Horn; 2. Sep-walled cirque; 3. Ledge, furrow; 4. Joints and faults families;
5. U-shaped valley; 6. Glacial basin hewn through a tectonic fault; 7. Bedrock subject to gelifraction and remains of
glacial abrasional surfaces; 8. Hanging valley and transfluence pass; 9. Ice cap (Corral del Veleta cirque); 10. Late-melting
glacier (Vasares del Veleta).
14
The snow deflated from the Altiplanation terraces of the Picacho del Veleta peak fed the Veleta
Cirque. Even at the present times snow-patches orientated towards the South survive in the
surroundings of the Cilindro shelter in summer. The Veleta, Río Seco and Mulhacén glaciers
formed the Poqueira glacial system that reached 6.4 km in length and led to a sequence of stepped
moraines. Their tongues reached the altitude of 1704 m. The zone of ablation occurred at an
altitude of 1980 m in the “Hoya del Capitán” basin.
In the Veleta Cirque, erosional landforms such as overdeepened glacial basins (Aguas Verdes,
Púlpito and Cabras ponds) and incised channels (Chorreras Negras) were controlled by the
lithology and structure of the substratum (figure 8). This is made up of low shear strength
micaschists affected by a NW-SE and NE-SW trending alpine faults. Rockfall deposits
accumulate at the toe of vertical walls.
The Veleta glacial trough is a straight, wide and U-shaped valley of four km long (picture 6) that
starts soon after the cirque threshold is surpassed. In its right margin we find several knickpoints
and small hollows cut into bedrock blocked by rock glaciers. In its left margin the hanging Púlpito
cirque and moraines are at 125 m above the main channel. Hanging lateral moraines occur in both
valley sides.
Picture 6. Veleta glacier head and Aguas Verdes pond
2. Picacho del Veleta peak
The Veleta Unit forms part of the antiform structure axis that generates the highest peaks ridge of
Sierra Nevada. This unit is made up of dark carbonaceous micaschists and light quartzites. On the
other hand, it hosts the Picacho del Veleta peak (3,398 m), which became a horn during the
Pleistocene, and several cirques that surround it such as the Veleta cirque orientated towards the
Southeast and the Corral del Veleta cirque towards the North).
15
The Picacho del Veleta peak connects with the Machos Peak through a gentle pass to the east and
with the headwaters of Dílar and Monachil creeks to the west. Its top shows one of the most
beautiful panoramic view of the massif (picture 7).
Picture 7. Picacho del Veleta peak
2.1. Thermal record from the Picacho del Veleta peak borehole
Periodic temperature measurements of the permafrost allow distinguishing annual and centuriesold changes in the energy balance. The european PACE project (Permafrost and Climate in
Europe) established the first permafrost systematic monitoring network in the european
mountains. The stations were placed from Janssonhaugen (Svalbard) to Sierra Nevada (Spain)
(Janssonhaugen (Svalbard) – Tarfalaryggen (Sweden) – Juvvasshoe (Norway) – Schilthorn and
Stockhorn (Switzerland) – Stelvio Pass (Italy) – Sierra Nevada (Spain)) (Harris et al., 2003; figure
9). In Sierra Nevada drillholes were conducted in the Picacho del Veleta peak (3,397 m high) up
to 114,5 m deep at 3,380 m high by rotary-percussion drilling technique. In a first stage 30 and in
a second stage 10 thermal sensors were placed inside a protection PVC pipe (figure 10).
First phase (2001 and 2002)
According to the rules of the PACE project, during 2001 and 2002 the first thermal cable included
30 Yellow Spring Instruments YSI 44006 type NTC thermistors (negative temperature coefficient
thermistor). The electrical resistivity of the sensors was 2.95 x 104Ω at 0ºC. They were calibrated
in VAW (Versuchsanstalt für Wasserbau, Hydrologie und Glaziologie) that belongs to ETH.
Their absolute accuracy was ±0.05ºC.
The thermal profiles of figure 11 show the record of the only two temperature measurements
obtained (September 8th 2001 and August 27th 2002 at 12:00 am GMT). The absence of
permafrost in the Picacho del Veleta Peak is suggested by: a) The temperature values of the 2002
survey were above 2.15 ºC and b) the existence of water at 80 m deep.
16
0
250
Svalbard, Noruega (UO-NO)
500 km
Tarfala, Suecia (SU-SE)
Jotunheimen, Noruega
(UO-NO y TEDAT-UK)
Cardiff, Gran Bretaña (UWC-UK)
(Geotechnical Centrifuge Centre)
Zugspitze, Alemania (JLUG-DE)
Corvatsch, Suiza
(ETH-CH y UZ-CH)
Valtellina, Italia (TUDSR-IT)
Zermatt and Shilthorn,
Suiza (JLUG-DE)
Sierra Nevada, España (UCM/UB-ES)
40003500-
4
8
5
3000-
6
7
25003
2000-
2
Altitude, meters
15001000500030
1
40
50
60
70
80
Latitude, degrees North
1. Janssonhaugen Svalbard
2. Tarfalaryggen
3. Juvvasshoe
4. Stockhorn
5. Stelvio Pass
6. Schilthorn
7. Murtèl-Corvatsch
8. Veleta Peak, Sierra Nevada
Figure 9. Geographical situation and altitude of permafrost monitoring stations in European mountains (PACE).
The temperature of both thermal profiles are almost similar from 1.20 m deep downwards. There
is just 0.15º C difference that is less than the deviation of the instrumentation. At 7 m deep the
temperature sets at around 2.45 ºC. Below this depth the variation of temperature was minimum.
The zero annual amplitude (ZAA) was set at 20 m deep. Under this depth there weren’t
significant temperature variations.
17
467.0
468.0
3.098,08
116m-Borehole
Sierra Nevada, Veleta Peak, Spain
3.095,5
3.000
1
Altitude: 3380 m; Depth: 114,5 m
3.050
2.900
4.102.0
4.102.0
2.950
3.000
3.0
50
3.10
0
3.053,5
3.073,0
3.065,5
3.095,5
3.15
0
3.072,5
3.200
3.137,0
3.250
3.200
3.150
3.3
00
3.329,0
3.250
3.100
1
3.299,0
3.352,5
3.319,5
0
3.35 0
3.30
3.398
3.323,5
3.298,5
3.324,5
Cerro
de lo
c hos
s Ma
Veleta Peak
3.135,0
3.145,0
4.101.0
3.127,0
467.0
100
0
100 m
3.014,0
4.101.0
468.0
Figure 10. Location of the Picacho del Veleta peak borehole.
The Picacho del Veleta peak thermal record shows that there isn’t an increase of temperature due
to geothermal gradient. Actually, between 20 m and 100 m deep the thermal gradient is 0.004ºC
m-1 and it may be even negative. This fact has been also observed in other european mountains
included in the PACE project (Isaksen et al., 2001; Harris et al., 2003).
The influence of thermal flows from the Corral de Veleta (North) and Aguas Verdes (Southeast)
cirques walls might explain this phenomenon. The mean annual ground surface temperature
(MAGST) has been estimated around 2.6ºC. The 20 m deep bh1 thermal profile carried out in
Flüela Pass in the Swiss Alps at an altitude of 2470 shows a similar behaviour. The absence of
permafrost possibly inhibits the development of a geothermal gradient (Luntschg et al., 2004).
Second phase (2002 a 2004)
A new cable equipped with ten autonomous thermal sensors of the Type UTL-1 (supplied by
Geotest AG firm, Switzerland) substituted the previous NTC thermistors due to technical
problems in august 2002. The number of sensors decreased and the temperature deviation
increased (from ±0.05ºC to ±0.27ºC) in comparison with the previous thermal cable. Sensors
recorded temperature every two hours.
18
The thermal record allows reconstructing the maximum and minimum values from September
2002 to August 2004 (figure 12). The maximum temperature variation occurred just 20 cm below
the surface and the zero annual amplitude (ZAA) was at 20 m deep as in the first phase thermal
measurements. The extreme minimum temperature was -1.2 ºC at 20 cm deep. From 80 cm deep
downwards, temperature was no longuer negative. Therefore, only the upper 80 cm of the ground
is undergoing temperature changes above and below 0ºC. The mean annual ground surface
temperature (MAGST) was around 2.3 ºC, three tenths less than in the first phase survey. This
difference may be attributed to the less sensitivity of the UTL-1 sensors. The average annual
atmospheric temperature measured by the UTL-1 sensors at the Picacho del Veleta peak (3395 m)
was 0.83 ºC from September 21st 2003 to September 20th 2004 (figure 13).
Geothermal profile of the 115m-borehole of the Veleta Peak (3.380 m)
Upper profile
Schulte, 2003
Total depth (115 m)
Figure 11. Geothermal log of the Picacho del Veleta peak (8-9-2001 y 27-8-2002).
The average ground temperature data recorded in Picacho del Veleta peak borehole (figure 14)
every four months from September 1st 2003 to August 26th 2004 suggests: a) there isn’t
permafrost as it was already observed in the first phase survey, b) The ZAA is located at 20 m
deep, c) The lowest temperature values happened during spring in the first 5 m of the ground and
during summer between 5 m and 10 m deep, d) Solar radiation at the Corral cirque side walls may
explain the lack of a geothermal gradient as it was stated for the 2001-2002 period, and f) the
unknown thermal effect of the flowing water found at the base of the borehole.
19
Annual ground temperature amplitudes within
the Veleta Peak borehole (3380 m a.s.l.)
-21.5°C
28.06°C
Annual air temperature amplitude 2003-04*
Ground temperature [°C]
-4 -2 0
0
2
4 6
8 10 12 14 16
3380 m a.s.l.
MAGST
10
ZAA
20
30
40
50
60
Maximum and minimum temperatures 01.09.2002 - 28.08.2003
Maximum and minimum temperatures 01.09.2003 - 26.08.2004
Temperature (ºC)
Figure 12. Annual ground temperature amplitude within the Veleta peak borehole (3380 m) (2202-2204)
Autumn
Winter
Sping
Summer
Figure 13. Air temperature in the Veleta peak (2003-2004 field survey).
20
Conclusions
The positive temperature values recorded by the thermistors, the mean annual ground surface
temperature (MAGST) of around 2.3 ºC and the occurrence of water at different depths suggest
the lack of alpine permafrost. As a result, the postnival expansive thermal wave quickly
counteracts the negative values accumulated at the surface. Ground temperature values are 2.5 ºC
higher than the ones recorded by the PACE borehole in Schilthorn (46 ºN, Switzerland) at 2,900
m high (Harris et al., 2003).
Below the ZAA the positive thermal gradient remains constant probably due to its proximity to
the side walls of the Cirque. This fact has been also observed in the Stockhorn and Schilthorn
boreholes despite the present existence of permafrost (Harris et al. 2003). The lack of permafrost
in Sierra Nevada does not allow the calculation of the geothermal gradient and the possible
influence of the present climatic change (Lachenbruch & Marshall, 1986). The surface-wave
radiation reaches 20 m deep. The monitored boreholes of Tarfalaryggen (Sweden) and Juvvasshoe
(Norway) show the same value (Isaksen et al., 2001). The seasonal lag of the radiation wave is
recorded at a depth of 7 m.
Mean seasonal ground temperatures within
the Veleta Peak borehole (2003-2004)
Temperature [°C]
3395 m
3380 m
a.s.l.
Figure 14. Mean seasonal ground temperature within the Veleta peak borehole (3380 m) (2003-2004).
2.2. Permafrost distribution model in the Veleta unit
The first model of permafrost distribution in a Mediterranean area was developed in the Veleta
Unit (Tanarro et al., 2001). The model established a statical relationship among BTS data (Bottom
21
Temperature of the Winter Snow Cover), altitude, solar radiation and snow cover. According to
Gruber & Hoelzle (2001), this relationship decisively influences on the occurrence of permafrost.
121 BTS temperature measurements were carried out at the base of the snow cover when it was
more than 80 cm thick and two months stay. Haeberli (1973) points out that permafrost exists
when the BTS temperature obtained under these conditions is below -3ºC BTS temperature values
below -3ºC were recorded in the north face of the Picacho del Veleta peak and the northern wall
of the Corral del Veleta cirque. The variables that might control these values were the altitude, the
potential solar radiation and the snow cover during summer. The altitude was established from a
1:10.000 scale digital elevation model (DEM). The potential solar radiation values were obtained
using the SRAD model. This model developed by Moore et al. (1993) allows determining the
solar radiation distribution from July to October when the snow cover is minimum and radiation
is maximum. The minimum radiation values occurred at the northern wall of the Corral del Veleta
cirque. A raster type model of the snow cover in summer time was obtained by the aerial
photographs of four years (1957, 1985, 1989 and 1999) in July. The different zones were
classified depending on the existence or the lack of snow.
A multiple regression analysis of the four variables was applied to develop a permafrost
distribution model using ArcInfo GIS software. The function used was (Gruber y Hoelzle, 2001):
BTS = 11.789 - 0.0054 * Altitude + 0.131 * Radiation + 0.095 * snow thickness in summer
Three different methods validated the model (figure 15). Firstly, the occurrence of a cryokarst
(collapse structures) informed that permafrost was undergoing degradation processes. Secondly,
the temperature under the snow cover was constant (-5ºC). Finally, seismic refraction and
geoelectrical resistivity surveys showed characteristic physical properties of the ice mass. For
example, different areas presented resistivity values of 562.220 Ohm/m
According to the model, permafrost occurs at the north face of the Picacho del Veleta peak and
the back wall of the Corral del Veleta cirque. The model informs that solar radiation is the
variable that best fit the permafrost distribution. Therefore it seems that permafrost existence in
the Picacho del Veleta peak is controlled by the topography that favours the occurrence of areas
where solar radiation is minimum and snow patches remain. Future BTS data of a larger number
of points and the establishment of a ground thermal control network at different depths will
improve the current model.
3. Corral del Veleta Cirque
The Corral del Veleta is the oldest cirque of the Guarnón glacial system. It is located at the toe of
the North face of the Picacho del Veleta peak in the headwater of the Guarnón creek. It is a 600 m
long oval hollow whose back wall is 300 m high. During the Little Ice Age it hosted a small
glacier that has already disappeared. However, several ice masses remain trapped in the eastern
side of the cirque. Those ice bodies are probably undergoing degradation processes.
22
Figure 15. Possible Permafrost in the Veleta unit.
23
3.1. Holocene glacial fluctuations
Introduction
During the XX century important studies about the evolution of glaciers have led to a better
understanding of the Holocene climatic changes (Maisch, 1981; Röthlisberger, 1986; Zumbühl &
Holzhauser, 1999). The morphological, sedimentological and dendrochronological record of
different european mountain ranges such as the Alps and the Scandinavian Range informs about
the youngest and oldest Holocene glacial fluctuations with chronological precision (e.g. Wanner
et al., 2000; Karlén & Kuylenstierna, 1996).
On the other hand, a large number of studies developed since the end of the XIX century in South
Europe evidence the glacial variability that existed in high mountain ranges. Messerli (1967)
pointed out the altitudinal and latitudinal distribution of glaciers during the Holocene and
Pleistocene glaciarism in the Mediterranean areas. However, the correlation and reconstruction of
the climatic changes in the Mediterranean regions isn’t easy due to the shortage of welldifferentiated Holocene moraines, the insufficient geochronological data, The insufficient
stratigraphic record and the absence of written texts referring to the extension of glaciers.
In the Iberian Peninsula, the understanding of glacial fluctuations started in the nineties of the XX
century. For example, lichenometric dating and written texts of the Maladeta Cirque (central
Pyrenees Range) suggest that the Pyrenees Range underwent four ice expansion periods during
the Little Ice Age in 1600-1620 AC, 1820-1830 AC, 1915-1925 AC and 1985-1995 AC (Chueca
Cía & Julián Andrés, 1996). The rest of the mountain ranges of the Iberian Peninsula had a poor
record of moraine deposits that difficults the reconstruction of the recent climatic changes. Apart
from the Pyrenees, Sierra Nevada massif shows the greatest information.
For the last 130 years Sierra Nevada has become an interesting area to study end and lateral
moraines ridges due to the volume and geographical situation of the massif (Obermeier, 1916;
Paschinger, 1957; Messerli, 1965, Gómez et al., 1996; Schulte, 2002a). The Corral del Veleta
cirque located in the Guarnón valley and the Hoya del Mulhacén cirque situated in the
Valldecasillas valley are two of the most outstanding areas of the massif.
Upper Pleistocene moraines of the Guarnón valley
The Guarnón valley hosts a moraine deposited during the maximum ice advance of the last
glaciation at an altitude of 1790 m and three post-LGM (Last Glacial Maximum) moraines at
2010 m, 2250 m and 2360 m above sea level (Gómez et al., 2002).
The youngest Tardiglacial moraine (LPM or Late Pleistoce Moraine) may be correlated with the
outer end and lateral moraine ridges of the Corral del Veleta cirque situated at an altitude of 2.980
m (figure 15). The LPM consists of heterogeneous, up to metric-scale blocks that are
perpendicularly orientated to the glacier flow direction. Its absolute age is unknown due to the
absence of radiometric dating. However, its spatial configuration and topography indicate a
tardiglacial age, probably Younger Dryas. The tardiglacial equilibrium line altitude (ELA) was
lower than the Holocene ELA (figure 16). This fact suggests that the glacier exceeded the cirque
threshold flowing along the Guarnón valley during the Tardiglacial. The reconstruction of the
Tardiglacial glaciation and ELA was carried out by Schulte et al. (2002 a) by the dating of
lacustrine sediments found in the overdeepened basin of the Hoya del Mulhacén cirque.
24
467.5
LEGEND/LEGENDA
468.0
Late Glacial (Morrenas Tardiglaciares)
moraines
Holocene moraines (Morrenas Holocenas)
L.I.A. Moraines, Hm4a (Morrenas de la PEH)
2.850
L.I.A. Moraines, Hm4b (Morrenas de la PEH)
Holocene moraines (Rampa morrénica)
Smoothened rock surface (Sustrato pulido y estriado)
Glacio-nival hollows (Nichos glacio-nivales)
2.900
Perennial ice slab (Placas de hielo perennes)
4.102.0
4.102.0
Rockwall (Pared rocosa)
Rocky outcrops (Afloramientos rocosos)
2.950
Scree slope of rock fall (Taludes de gravedad)
Rock avalanches (Desprendimientos)
Pronival ramparts (Crestas pronivales)
3.000
3.0
50
3.10
0
3.053,5
3.073,0
3.065,5
3.095,5
Diffused ridges (Crestas indiferenciadas)
Active ice-creep (Lengua de bloques activo por
tongue
crio- reptación)
Active ice-creep (Formas activas por crio-reptación)
features
Inactive ice-creep (Formas inactivas por crio-reptación)
features
Sorted circle (Círculo de piedras)
3.15
0
3.072,5
Sorted stripes (Banda de piedras)
Debris flows (Colada de derrubios)
Dead-ice depression (Depresión por fusión de hielo muerto)
3.200
Blocks field (Campo de bloques )
3.137,0
(Lóbulos de solifluxión
Stone-banked
solifluction lobes con frente de piedras)
Gelifluxión lobes (Lóbulos de gelifluxión)
3.250
Slide scars (Grietas de deslizamiento)
Mudflow (Flujo de detritos)
Peat (Turberas “Borreguiles”)
3.3
4.101.5
00
3.329,0
Removed material
(Material removido de
from diverse genesis génesis diversa)
4.101.5
Principal escarpment (Escarpes principales)
Structural steps (Escalones estructurales )
3.250
3.350
3.300
3.352,5
Pico del Veleta
3.398
3.319,5
3.299,0
e
ro d
Cer
3.323,5
3.298,5
cho
Ma
Los
s
Channels (Canales)
Break of slope by
(Ruptura de pendiente por
covered structural steps escalones estructurales cubiertos)
Lakes (Lagos)
Fluvial network (Red fluvial)
3.324,5
100
467.5
0
100
468.0
Figure 16. Morphology of the Corral del Veleta cirque.
Holocene moraines of the Corral de Veleta cirque
They occur closer to the back wall of the cirque than the Late Pleistocene moraines between the
altitudes of 2996 m and 3060 m. We have mapped five end and lateral moraine ridges of different
ages.
Every ridge shows its own size and geomorphological and sedimentological features (figure 16).
The HM1 (first Holocene moraine formation period) is associated with the maximum extension of
the glacier flowing over the cirque threshold. Its front that ended at an altitude of 2996 m has
become blurred due to erosional processes. Moraine deposits are thin due to the steep slopes of
the cirque.
The HM2 may be related to different ice advance periods. The moraine deposits formed during
this phase are made up of a great amount of fine-grained sediments (<2 mm) that constitute the 60
per cent of the total. Blocks (36%) and pebbles (29 %) become the most representative sizes of
the coarser fraction (>2 mm; 40% of the total) (measurement point number 7, cross-section CV98-T2, figure 2) (figure 17).
The amount of fine-grained sediments allows distinguishing HM2 moraines from HM3, HM4a
and HM4b ones. Gelifraction processes acting during a long time may explain the great amount of
fine and medium size clasts. In this context, it seems that the present atmospheric temperature
values may corroborate the former hypothesis. The thermal sensors situated in the Picacho del
Veleta peak at an altitude of 3395 m and 300 m above the HM2 moraines, have recorded 134 days
(36,6 %) in which the temperature was around 0º C between September 21st of 2003 and
September 20th of 2004.
25
The HM3 period led to a 30 cm thick subglacial and ablation till that comprises subangular,
coarse and middle size clasts (52 %) and little fine size matrix.
S
Spot 5
Elevation: 3.090 m
pot 4
Elevation: 3.086 m
80
90
90
80
80
70
80
80
70
70
60
70
70
60
60
50
60
60
50
50
40
50
50
40
40
30
40
40
60 º
45º
/
45
º
º
º / 60
º
30
º/
º/
15
/ 30
º
º
/ 90º
60º
º
45
º
0 10 20 30 40 50 60 70 %
0º / 15
15 º
30º
º
º
0 10 20 30 40 50 60 70 %
0º / 15
15 º
30º
/4
/ 30
º
º
5º
/6
90º
90º
0º
0º
/6
60º /
90º
90º
90º
90º
60º /
4 5º
5º
45º
60º
60º /
60º
º
60º /
º/
90º
60
0º
60º /
º/
º/
º
/4
/ 30
0 10 20 30 40 50 60 70 %
30
º/
45
º
0º / 15
º
15º
/ 30
Flujo
Clast dip angle
Clast dip angle
0 10 20 30 40 50 60 70 %
0 10 20 30 40 50 60 70 %
45
º
0 10 20 30 40 50 60 70 %
15º
/ 30
º
30
º
45
º
30
º/
/
45
º
º
45
º
º/
º
60 º
4 5º
30
45
º
º
º
º/
º
/ 90
/ 60
90 º
º
º
% 60 50 40 30 20 10 0 10 20 30 40 50 60 %
0º / 15
Flujo
0º / 15
º
30
60 º
4 5º
º
> 50 cm
Clast orientation respect to
flow direction
45º
30
º/
0
º
/ 60
º
º
15
º/
/4
5º
3 0º
º
º
º
25-50 cm
> 50 cm
30
/ 45
10
15º
º
10-25 cm
25-50 cm
º/
30º
4.5-10 cm
20
10
/ 30
15º
/ 30
º
2-4.5 cm
30
10-25 cm
30
º
15º
º/
/ 90
45º
45
Flujo
0º / 15
30
º
60 º
º/
45
40
20
flow direction
30
º
50
4.5-10 cm
Clast dip angle
0º / 15
30
º/
/ 90
º
45º
/ 60
º
60º
º
/ 30
15º
45
Flujo
45
60
60 º /
º/
45
/6
60º /
0 10 20 30 40 50 60 70 %
/4
5º
> 50 cm
60 º
Clast dip angle
º
45
/4
5º
30º
/ 30
10
25-50 cm
º
/
45º
cm
60
% 60 50 40 30 20 10 0 10 20 30 40 50 60 %
/ 90
60 º
0 10 20 30 40 50 60 70 %
0º / 15
º
15º
/ 90
º
45º
/ 60
º
60º
0 10 20 30 40 50 60 70 %
70
30
% 60 50 40 30 20 10 0 10 20 30 40 50 60 %
º/
30
º/
60 º
º
0º / 15
º
0 10 20 30 40 50 60 70 %
º
10-25 cm
flow direction
º
º / 90
/
45º
º
º
60
60 º
80
70
0
30
/ 30
15º
º
30º
/ 30
º
º
/ 30
0º / 15
15º
Flujo
0º / 15
º
30
45º
/
º
º / 60
45
/ 45
15
º/
º
º
5º
0 10 20 30 40 50 60 70 %
º
Perennial
ice slab
3120
0º / 15
º
/4
/ 30
45º
0 10 20 30 40 50 60 70 %
0 10 20 30 40 50 60 70 %
º
º
/ 90
20
0
% 60 50 40 30 20 10 0 10 20 30 40 50 60 %
Clast dip angle
Clast dip angle
15 º
30º
Flujo
15º
45º
Clast dip angle
0 10 20 30 40 50 60 70 %
0º / 15
/ 90
45º
/ 60
60º
º
0º / 15
/
/
45º
60 º
30º
º/
30
/ 30
15º
0º / 15
Flujo
60 º
90 º
60º
º
/ 45
45º
/ 60
º
º
/ 60
º
/ 90
60º
% 60 50 40 30 20 10 0 10 20 30 40 50 60 %
> 50 cm
flow direction
% 60 50 40 30 20 10 0 10 20 30 40 50 60 %
30º
45 º
60º
/ 90
º
15
60
º
º / 90
0º / 15
% 60 50 40 30 20 10 0 10 20 30 40 50 60 %
25-50 cm
0º / 15
flow direction
10-25 cm
0
flow direction
30
flow direction
4.5-10 cm
10
> 50 cm
0
80
40
4.5-10 cm
30
> 50 cm
0
> 50 cm
0
90
2-4.5 cm
30
20
25-50 cm
10
25-50 cm
10
10-25 cm
º/
25-50 cm
10
10-25 cm
2-4.5 cm
30
º/
20
10-25 cm
20
4.5-10 cm
15
20
4.5-10 cm
0º / 15
4.5-10 cm
90
50
2-4.5 cm
15
2-4.5 cm
30
Clast size
%
100
cm
60
2-4.5 cm
2-4.5 cm
%
100
º
90
cm
0º / 15
90
30
Spot 7
Elevation: 3.093 m
Clast size
%
100
cm
30
%
100
Spot 6
Elevation : 3.094 m
Clast size
Clast size
90
15
º/
Clast size
cm
%
100
cm
º
Clast size
%
100
0º / 15
Spot 3
Elevation : 3.088 m
Spot 2
Elevation : 3.106 m
Clast size
cm
0º / 15
Spot 1
Elevation : 3.117 m
%
100
m
3130
N
Corral del Veleta, Sierra Nevada (Spain)
Section CV-98-T2
Rock fall talus
1
20º
3110
10º 2
<5º
LIA moraines
Hm4b HM4a
LIA flutes
3100
40º
10º
3090
3
<5º
4
5º
40º
10º 5
6
Holocene moraine Hm2
7 <
5º
40
º
3080
3060
3050
0
50
100
150
200
L.M. Tanarro, 1998
3070
Figure 17. Morphosedimentological cross-section.
Moraines ridges of HM4a and HM4b are sinuous, their thickness shows variations and they
overlay older Holocene moraine deposits. They are made up of angular blocks that constitute 65
% of the total. We didn’t find fine-grained sediments (measurement points numbers 5 and 6,
cross-section CV-98-T2, figure 9) (figure 17). Subglacial till shows streamlined features such as
glacial flutes (measurement points numbers 5 and 6, cross-section CV-98-T2) (figure 17).
Chronology of the Holocene glaciation in the Corral del Veleta cirque
The absolute ages of HM1, HM2 y HM3 are unknown but it seems that they happened during the
Holocene. We can ensure that HM1 and HM2 periods are older than the Little Ice Age. The
Holocene age of HM3 is doubtful. We believe that HM3 may occur at the beginning of the Little
Ice Age or during medieval times as its deposits are little weathered (Röthlisberger, 1986;
Zumbühl & Holzhauser, 1999).
The HM4b period led to an inner moraine ridge that represents the youngest deposit of the Corral
del Veleta cirque. The HM4b is associated with the last glacier advance that happened in 1876
AC (Hellmann, 1881). This ice expansion event may be correlated with the glaciers advance of
the Alps in 1850 AC (Röthlisberger, 1986; Zumbühl & Holzhauser, 1999) and the middle
Pyrenees between 1820 AC and 1830 AC (Chueca Cía & Julián Andrés, 1996).
26
The morphoestratigraphical distribution of the HM4a moraine ridges informs that HM4a deposits
had to be oldest than the HM4b ones. The 210Pb dating of the lacustrine sediments of a pond
situated between Hm4a and Hm4b moraine ridges (Schulte, 2002a, 2002c) indicates that the
HM4a period may be related to an ice expansion during the Little Ice Age. This period may be
correlated with the early glaciers advance in the Alps (1570–1650 AD; Röthlisberger, 1986: 308;
Wanner et al., 2000) and the middle Pyrenees (1600-1620; Chueca Cía & Julián Andrés, 1996).
The studied glacio-lacustrine sediments form a 14 cm thick rhythmite sequence of silts and sands
that is overlying gravel and block size subglacial till of the HM4a period. Therefore, the lacustrine
sequence was sedimented after HM4a. The rhythmite sequence is formed by different
sedimentary units. The age of a sample taken at 7 cm deep was 1908 AC. If we suppose that the
sedimentation rate has been constant, we may hypothesize that its deposition started 200 to 250
years ago halfway of the XVIII century (Schulte, 2002b). Therefore, the HM4a period might be
associated with an advance of glaciers at the beginning of the Little Ice Age and it might be
correlated with the ice expansion recorded in the Alps in the 1570-1650 AC (Röthlisberger, 1986:
308; Wanner et al., 2000).
The Little Ice Age deglaciation was fast. In 1899 Rein’s measurements of the extension of the
Corral del Veleta cirque glacier demonstrated that the ice mass had reduced half its area in just 13
years. It seems that the glacier disappear throughout the first half of the XX century (Gómez et al.,
1999). According to Rodríguez et al. (1996), the thermal and pluviometric record of La Cartuja
station located in Granada city at an altitude of 774 m (1902-1994) and University Youth Hostel
station situated in Sierra Nevada massif at an altitude of 2.550 m (1960-1994) points out a
significant change in the rainfall regime. This change consists in a decrease in winter rainfalls and
an increase in summer rainfalls.
Correlation problems
It is difficult to correlate the glacial fluctuations observed in the Corral del Veleta cirque with the
ones recorded in the Alps due to the lack of chronological data. These data allow highlighting the
following thoughts: a) The distribution of moraines at different altitudes indicates that the snow
line has migrated to the mountaintops. Using the Höfer method (1879) we have estimated a 628 m
upward migration of the snow line in Sierra Nevada after the Last Glacial Maximum. In contrast,
Maisch (1981) considered that in the Alps the snow line underwent a 1200 m migration during the
same period of time; b) Pleniglacial and tardiglacial periods represent important morphological
stages in the South of the Iberian Peninsula; c) In the Corral del Veleta cirque, we have detected
two periods of glaciers advance during the Little Ice Age. They are known as HM4a (the oldest
stage) and HM4b that is considered to be the youngest period and to be form during the second
half of the XX century. Both periods (HM4a and HM4b) may be correlated with ice expansion
events of the Alps and Pyrenees.
Schulte (2002a) tried to establish a relationship between the glacier advances in the Guarnón
valley and the fluvial terraces of the Aguas River in the Vera Depression situated close to the
Mediterranean coast 150 km away from Sierra Nevada massif. The correlations are still difficult
and doubtful despite the number of moraine ridges and terrace levels are the same and the fact
that Pleistocene sedimentary units are different from the Holocene ones.
The discrepancy of absolute ages comes from the dating methods used. AMS radiocarbon dating
is difficult because sediments of semiarid environments contain a little amount of organic matter
27
and pollen grains. Cosmogenic nuclides accumulation and thermoluminescence dating methods
may be used in the coming future in spite of their probable age deviation. In addition, future
research should focus on determining the absolute chronology of the Sierra Nevada glacial
fluctuations so as to know the effects of climatic changes in the Mediterranean mountain ranges
and surroundings.
3.2. Geophysics and permafrost
During the 1995 summer there wasn’t snow cover in the Corral del Veleta cirque. This fact
allowed us to distinguish the different landforms. Talus cones, gelifruction lobes and rock glaciers
occurred between the western wall of the cirque and the LPM (Late Pleistocene Moraine).
Table 4. Electrical and seismic sounding. Features.
__________________________________________________________________________________________________
Zone A
Zone B
Zone C
Zone D
…………………………………………………………………………………………………………………….
Geographical
Western zone
Middle zone
Eastern zone
Eastern
zone situation
……………………………………………………………………………………………………………………………
Average altitude
3062 m
3086 m
3105 m
3123 m
…………………………………………………………………………………………………………………………………
Logs length
92,5 m
92,5 m
42,5 m
192,5
…………………………………………………………………………………………………………………………………
Average depth
14 m
14 m
10 m
25 m
…………………………………………………………………………………………………………………………………
Landform
debris fan
moraine ridge
rock glacier
rock glacier
…………………………………………………………………………………………………………………………………
Maximum
minimum 153
minimum 451
minimum 3431
minimum 150
Resistivity (Ohm/m)
maximum 4862
maximum 5702
maximum 58914
maximum 562220
…………………………………………………………………………………………………………………………………
Seismic velocity (m/s )maximum 4200
maximum 3800
maximum 3600
maximum3600
__________________________________________________________________________________________________
The existence of ice masses (permafrost) covered by debris was suggested by the interpretation of
vertical electrical sounding carried out during the 1995 summer. Later electrical and seismic
sounding of the PACE project (Permafrost and climate in Europa) developed by Terradat-LTD &
ETH in 1995, highlighted the existence of high resistivity deep layers exclusively in the eastern
zone of the Corral del Veleta (table 4).
Table 5. Physical features of the core
_________________________________________________________________________________________________
Reach
Thickness Lithology
Sedimentogical and petrographical features
………………………………………………………………………………………………………………………………..
A
120 cm
Micaschist
Non weathered heterometric blocks in a consolidated
structure at the rock
glacier front
………………………………………………………………………………………………………………………………….
B
30 cm
Sediment
Micaschist, gravels and sand embedded in melting ice
fragments
………………………………………………………………………………………………………………………………….
C
40 cm
Ice masses
C1 (15 cm). Frozen mass with micaschist clasts. The ice is
formed by
amorphous crystals and it contains lots of air
passages.
……………………………………………………………………………...
C2 (25 cm). Dense and crystalline ice mass.
__________________________________________________________________________________________________
28
A borehole was carried out in August 1999 at an altitude of 3105 m in the front of a rock glacier
in the eastern zone of the cirque (zones C and D) 250 m away from the Lagunilla del Corral pond
(Table 4). There, the highest resistivity values (58914 and 562220 Ohm/m) (figures 18 y 19) and
the type of landforms (gelifruction lobes with transverse ridges and rock glaciers) suggested the
possible existence of deep ice masses. The drill core was continuous and reached 190 cm deep
(table 5 and Picture 8).
Picture 8. Borehole log of the permafrost top in the Corral del Veleta cirque
The existence of frozen sediments from 1,20 m deep downwards, the high resistivity of zone D
(562220 Ohm/m) and the location of ice bodies in the first 50 cm under the ground in other places
of the debris-mantled slope of the Corral de la Veleta cirque, ensures the occurrence of alpine
permafrost in the eastern zone of the cirque. The permafrost would be covered by debris and it
would occupy 3200 m2. Its origin is associated with the deglaciation of the Corral del Veleta
glacier after the Little Ice Age at the end of the XIX century. Halfway through the XX century the
glacier had already become a single ice body situated in the eastern zone of the cirque. Debris
material covered it becoming a motionless black glacier. This origin explains its distribution and
the irregular depth of the permafrost top.
In Sierra Nevada massif, we are only sure that permafrost exists in the Corral del Veleta cirque,
although BTS results indicate that it may also occur in other places such as the Cerro de los
Machos peak (3240 m). Permafrost survival lies in the insulating effect of the debris cover. In
addition, the topography and orientation of the Corral del Veleta cirque made its eastern zone be
an especially cold place. Solar radiation is minimum and snow cover remains most of the year. As
a result, the underlying ice melts slowly although the thermal measurements we are carrying out
inform that the solar radiation effect reaches the top of the permafrost (Gómez Ortiz et al., 2004)
29
3.3. Relationship between slope geological processes and snow cover
Rockfalls from the walls of the Corral del Veleta cirque has led to a debris-mantled slope affected
by gelifluction lobes, debris flows and rotational landslides. The existence of permafrost may
explain the formation of these slope movements (Gómez Ortiz et al., 2001). Every winter the
debris-mantled slope is covered by several metres of snow that usually remains all the year.
The insulating effect of the snow cover may protect the substratum from temperature changes
(Gómez Ortiz et al. 2003). Besides, ice fixes the blocks and prevents slope movements (Thorn,
1988). In contrast, when the snow cover abruptly melts during summer time, the shear strength of
the slope decreases leading to large slope movements (Strömquist, 1985; Rapp & Nyberg, 1988).
Every year since 1995 we have monitored the residence time of the snow cover and the
geomorphological processes in order to understand the relationship between snow cover dynamics
and slope movements (table 6 and figure 18). The monitoring has been carried out by oblique
aerial photographs in September when snow cover is minimum. Slope movements and snow
cover have been mapped and the photographs have been georeferenced using a 5 m resolution
digital elevation model (DEM).
Interation 5 RMS error = 4.5
High Velocity (3600 m/s)
from seismic Line D
Elevation
-2.0
-4.0
-6.0
-8.0
-10.0 0.0
-12.0
-14.0
-16.0 W est
40.0
30.0
Very High Resistivity Zone
20.0
10.0
East
3431
5150
7730 11603 17418 26146 39247
Resistivity in Ohm.m
Vertical exaggeration in model section display= 1.0
First electrode is located = 0.0 m.
Last electrode is located = 40.0 m.
58914
Unit Electrode Spacing = 2.5 m.
Source: TerraDat & ETH (1998)
Figure 18. Topography and Electrical D-log in the Corral del Veleta cirque.
Evolution of the snow cover (1995/2004)
In 1995 the climate was dry and only some snow patches remained. In contrast, during 1996 and
1997 the bottom of the Corral del Veleta cirque was covered of snow all the time. In 1998 the
snow occupied 65 per cent of the slope. In 1999 the climate was very dry and the snow
disappeared at all. In 2000 the slope was almost uncovered. In 2001 as in 1998 the snow covered
60 per cent of the slope. In 2002 as in 2000 rainfalls were scarce and only some snow patches
occurred at the head of the eastern talus cones. In 2003 the situation was better than in 2002 and
the snow remained in the contact between the slope and the cental and eastern cirque walls and in
different points of the western zone. In 2004 the extension of the snow cover was greater than in
previous years and it occupied the bottom of several basins (table 6 and figure 20).
30
Iteration 5 RMS error = 11.2
Elevation (m)
0.0
30.0
Very High Resistivity Zone
Rock fall talus
20.0
40.0
10.0
Low Resistivity
Moraine Material
High Velocity (3600m/s)
from seismic Line C
Ice-creep tngue
160
120
80.0
0.0
-10.0
South West
North East
-20.0
150
486
1575
5102
16530
53557 173525
562220
Resistivity in Ohm.m
Unit electrode spacing= 5.0 m
Vertical exaggeration in model section display= 1.0
First electrode is located = 0.0 m.
Last electrode is located = 200.0 m.
Source: TerraDat & ETH (1998)
Figure 19. Topography and Electrical C-log in the Corral del Veleta cirque.
We can distinguish three areas depending on the snow residence time. The first one is located
between the debris-mantled slope and the eastern and central walls of the cirque. There snow can
be found all the year. The second one is situated in creeks and between the debris-mantled slope
and the western wall of the cirque. In these places the snow only remains in very wet years.
Finally, the third one covers the central zone of the debris-mantled slope and the western side of
the cirque. Here, the snow tends to disappear every summer.
467.5
468.0
Very low summer snow-cover remain
Low summer snow-cover remain
Medium summer snow-cover remain
High summer snow-cover remain
Maximum summer snow-cover remain
4.102.0
2.900
4.102.0
2.950
3.000
3.0
50
3.10
0
3.053,5
3.073,0
3.065,5
3.095,5
3.15
3.072,5
0
3.200
3.137,0
3.250
3.3
4.101.5
3.250
3.319,5
3.298,5
467.5
Elaborated by Luis Tanarro
3.299,0
os M
eL
ro d
C er
3.323,5
3.350
3.300
3.352,5
Pico del Veleta
3.398
00
4.101.5
os
a ch
3.324,5
468.0
Rockwall
Rocky outcrops
Scarps in bedrock
Lake
Figure 20. Evolution of the snow cover in the Corral del Veleta area in summer (from 1998 to 2004).
31
Table 6. Snow cover in the debris-mantled slope of the Corral del Veleta cirque during September
________________________________________________________________________________
Time of residence
Percentage of covered area
Years
………………………………………………………………………………………………………………………
Maximum time
>65 %
1996, 1997
Intermediate time
25/65 %
1998, 2001, 2004
Minimum time
<25 % to 0 %
1995, 199, 2000, 2002, 2003
________________________________________________________________________________
Geomorphological dynamics of the debris-mantled slope (1995/2004)
A talus cone situated in the eastern side of the cirque is undergoing the most important slope
movements. In 1995 several debris flows formed (60 cm long and 50 cm wide). The largest blocks
moved towards the surface and they were stacked at their toes while fine-grained sediments
occurred in the core of the deposit. In the accumulation zone, they showed low-gradient surfaces
with transverse ridges. Their toes were irregular and they presented vertical throws of 1 m high.
During the same year, the slope was affected by an important landslide. The depleted mass was
more than 6m long, 4 m wide and 2.5 m high. Three years later, in 1998, when the talus cone was
uncovered of snow again these landforms had already disappeared. During this year, the snow
melting led to new debris flows that displayed similar features to the ones formed in 1995. In 1999
two large rotational landslides affected the eastern and central zone of the talus cone. The one
formed in the central part evolved to a debris flow. Apart from the landslide, many gelifluction
lobes broke the slope topography. Slope movements affected 40 per cent of the eastern and central
sectors and 15 per cent of the western sector of the talus cone. In September 2000, the preexisting
movements became blurred due to the formation of three debris flows whose failure surfaces were
above the 1999 landslide scarps. These flows were from 10 m to 25 m long and 0.5 m to 1.5 m
wide. In 2001, many superficial debris flows broke the topography of the debris-mantled slope.
They were between 5 and 10 m long. In addition, at the end of the spring a huge rockfall covered
50 per cent of the talus central zone. The snow that was trapped by the fallen rocks remained all
the year. In 2002, the melting of the trapped snow led to thermokarstic collapse structures.
Besides, very plastic debris flows formed at the head of the debris-mantled slope. They were
between 20 m and 50 m long and from 8 m to 15 m wide. In 2003, a few debris flows occurred and
the central zone affected by the 2001 rockfall became blurred. The changes observed in 2004 were
few and they were associated with meltwater runoff.
Conclusions
After 10 years of study it seems that the increase in the number of slope movements is related to
the absence of snow cover during summer time although there are differences depending on the
zone of the debris-mantled slope (picture 9). The existence of frozen layers within the substratum
and the amount of fine-grained sediments are also important factors for the development of slope
movements.
The debris-mantled slope that connects the bottom and the vertical walls of the cirque can be
divided into three zones depending on the activity of the slope processes. The western zone is not
affected by slope movements except for the bed of the creeks where snow tend to remain. Slope
movements, especially debris flows and landslides, often take place in the central zone. Processes
in the eastern zone aren’t as active as the ones that happen in the central zone. The movements
tend to be slow and they are associated with frost heaving, thermokarstic collapses and solifluction
flows.
32
Picture 9. Debris-mantled slope in the Corral del Veleta cirque
The obtained data indicate that the northern wall of the Corral del Veleta cirque is undergoing a
transition from an old glacial period to a present deglaciated paraglacial period. In the former,
cirque walls were affected by unloading and gelifraction processes that supplied a big amount of
debris. The material was evacuated by the glacier forming moraine ridges. During the latter, a
debris-mantled slope was generated.
At the beginning of the XX century, during this transition period we can distinguish a post-glacial
stage in which the Corral de la Veleta glacier mass balance became negative. As a result, the
glacier was unable to transport the supplied materials that came from the cirque walls leading to an
incipient debris-mantled slope. The thickness of the debris was minimum in comparison with the
thickness of the ice mass. Solar radiation at the toe of the cirque walls was minimum. Therefore,
the ice melted at a slower rate than at the top of the cirque walls. The slope was affected by slow
slope movements and processes such as frost heaving, thermokarstic collapses and solifluction
flows.
In a later period, the debris-mantled slope already appeared but in an early phase of development.
Although the debris layer was thicker, there were important frozen beds very close to the surface.
As a result, their permanence or melting depended on the snow cover variation. Slope movements
were fast, catastrophic and they had a very irregular distribution.
In the last period the frozen layers disappeared and the slope reached its mature phase. The slope
became a real accumulation area and its morphogenetic activity was controlled by the debris
supply and the snow cover.
3.5. Dynamics of the Lagunilla del Corral rock glacier
It is an active rock glacier situated in the western zone of the Corral del Veleta cirque (Gómez
Ortiz et al., 1999, 2004). It descends from the debris slope at an altitude of 3174 m to the altitude
of 3100 m in the vicinity of the Lagunilla del Corral pond. It is a 120 m long, L-shaped rock
glacier with an average width of 30 m and an average topographical gradient of 23º. The boulders
33
and stones that constitute its surface may reach 10 m thick. It occupies an area of 3700-4000 m2.
Its central and frontal parts are characterized by the existence of arcuate ridges and lobes. Its
origin, present morphology and dynamics are associated with the continuous supply of rock debris
from the eastern wall of the Corral del Veleta cirque, the intervention of cold processes in the
debris and the successive and different slope movements that affect it. We are especially
interested in its evolution, movement, geometric configuration, the temperature of its layers and
the temperature of the permafrost top (picture 10).
Picture 10. Corral del Veleta cirque and Corral del Veleta rock glacier.
Table 7. Straight rods average displacement (cm/year)
___________________________________________________________________________________________________
Rod number
rock glacier zone
1995-1999*
2001-2004**
__________________________________________________________
H
V
H
…………………………………………………………………………………………………………………………………
B1
Front
--5,9
B2
--8,8
B3
--12,8
B4
--4,8
……………………………………………………………………………………………………………………………………
B5
Back front
--4,5
B6
--4,1
B7
--6,3
B8
12,4
-8,6
3,7
B9
--6,6
…………………………………………………………………………………………………………………………………..
B10
Main body
1,9
-9,8
1,7
B11
6,1
-15,5
4,2
B12
--2,7
B13
--4,0
B14
--6,5
B15
--4,4
B22
--2,0
B23
14,5
-27,1
24,9
B24
5,7
-44,8
7,1
B25
--12,9
____________________________________________________________________________________________________
* Topographical measurement; ** Measurements using topographical, geodetic and photogrammetric techniques.
H. Horizontal displacement (advance), V. vertical displacement (subsidence)
____________________________________________________________________________________________________
V
-19,3
-24,8
-22,6
-20,9
-17,7
-16,5
-19,0
-14,6
-19,4
-19,3
-21,4
-16,9
-18,7
-13,2
-12,8
-44,7
-39,6
-25,7
-18,2
34
We have used Sanjosé Blasco (2003) and Sanjosé Blasco et al. (2004) methodology and
techniques (Geodetic, topographical and photogrammetric monitoring) in the central and frontal
parts of the rock glacier in order to determine its movement (figure 21). The installation of
straight rods in its perimeter, transverse lines and points allow us to measure vertical (subsidence)
and horizontal (advance) topographical variations once a year since 1995 (table 7). The average
subsidence of the glacier indicates that during 2002-2003 and 2003-2004 the volume-loss was
1500 m3 and 336 m3 respectively.
In 1999, a drillhole were carried out in the rock glacier front at an altitude of 3.107 m reaching the
permafrost top. Thermal sensors of the datalogger tiny-talk type (-35º/+70ºC temperature range,
and in past years UTL-1) were installed inside at depths of 0m, -0.15 m, -0.40 m, -0.9 m and 1.9
m. We used Ramos’ (1998) methodology for data capture (table 8 and figure 22).
3130
lagoon
31
20
10
31
31
90
30
00
4.101,6
1
2
4
3
5
6
7
8
9
SCV
10
25
11
24
0
10
20
30 m
12
13
23
Perimeter
22
Transect
14
15
Resistivity
Reference bar
4.101,5
Borehole and thermal control
Topographical base
467,7
Figure 21. Topography and measurement points of the Corral del Veleta rock glacier.
The research of the Corral del Veleta rock glacier demonstrates the relationship between the
thermal evolution of the ground (with or without snow cover) and the instability of the rock
debris. The dynamics of the rock glacier is deduced by the vertical and horizontal displacement of
the rock debris layer and the volume balance. The different mechanical response of the debris
layer to canges in the superficial and internal temperature may explain its dynamics.
35
Temperature (ºC)
Extreme min.
-30
-20
-10
-5
Mean
0
Extreme Max.
5
10
20
30
40
800
800
400
400
0
Thermal sample level (cm)
0
-15
-15
-40
-50
-40
-50
-90
-90
-190
-30
-190
-20
-10
-5
0
5
10
20
30
TMR (1999 - 2000)
TMR (2001 - 2002)
PV (2003 - 2004)
GR (1999 - 2000)
GR (2001 - 2002)
GR (2003 - 2004)
40
Figure 22. Sub-surface temperatures of the Corral del Veleta rock glacier and Verro de los Machos pass and air
temperatures of the Veleta summit.
4. Cerro de los Machos pass
Cerro de los Machos pass (3299 m) connects the Picacho del Veleta peak (3398 m) and the Cerro
de los Machos peak (3327 m). The pass is the remain of an old quaternary cryoplanation terrace
cut into bedrock, limited by cirques and characterized by the existence of patterned grounds.
Nowadays, the pass has become a place where cold processes are effective and significant due to
repetitive snow melting (picture 11).
Picture 11. Cerro de los Machos pass and Picacho del Veleta peak
36
xT
eMT
1999-2000 (Nov-august)
emT
eA
TMR (air)
3.095 m asl
-20.7
0.4
15.9
36.6
(-2)
-22.2
-1.3
36.5
58.7
(-50)
-7.5
-0.8
15.0
22.5
CV-rg (-2)
3.107 m asl
-19.6
2.2
23.0
42.6
(-15)
-4.0
-1.1
20.6
24.6
(-40)
-4.0
-1.1
14.2
18.2
(-90)
-4.0
-1.4
8.4
12.4
(-190)
-3.1
-1.5
-0.6
2.5
CM-pg (-10)
3.297 m asl
-13.4
1.4
28.1
41.5
(-50)
-7.2
1.0
14.5
21.7
TMR: micrometeorological reference station (PACE Project) (3095 m)
PV: Veleta Peak
CV-rg: Corral del Veleta rock glacier borehole
CM-pg: Collado de los Machos patterned ground
(--): no data
Site
-16.5
-22.3
-7.3
--5.0
-4.9
--4.3
---
emT
0.2
-1.1
-1.7
--1.3
-1.8
--3.2
---
xT
32.2
57.4
18.0
-33.9
20.6
-2.2
---
eA
PV(air)
---CV-rg (-15)
-(-90)
-CM-pg (-5)
(-50)
3.297 m asl
3.107 m asl
3.395 m asl
emT: extreme minimum temperature
xT: mean temperature
eMT: :extreme maximum temperature
eA: extreme thermal amplitude
15.7
35.1
10.7
-28.9
15.7
--2.1
---
eMT
-21.5
----2.8
--2.5
--12.9
-7.4
emT
0.4
----0.6
--0.8
-0.6
0.4
xT
28.6
---12.9
-8.2
-29.3
12.1
eMT
eA
50.1
---15.7
-10.7
-42.2
19.5
Table 8. Extreme and average temperatura values for air and ground surface, in the Corral del Veleto cirque, Collado de los Machos Peak and meteorological reference
sites
37
4.1. Cryoplanation and patterned grounds
It seems that Sierra Nevada summits didn’t host fjeld type glaciers (Sánchez Gómez, 1990). The
reason is that snow deflaction inhibited the development of ice sheets. This is evidenced by the
absence of striated, polished and grooved rock surfaces. Under these conditions periglacial
processes (gelifraction, geliturbation and gelifluction) were important forming cryoplanation or
altiplanation terraces.
The altiplanation terraces of Sierra Nevada are highly eroded, individualized and isolated due to
the later retreatment of glacial cirque walls. The Machos cryoplanation terrace that is limited by
Valdeinfierno and Corral del Veleta cirques is a good example. In addition, this surface host the
most interesting patterned ground of Sierra Nevada and the best ones of the Iberian Peninsula. The
patterned ground occupies 0.5 ha and it includes different forms depending on the topographical
gradient. Sorted circles and stone roses occur when the slope angle is less than 3º. If it is between
3º and 6º the circles deform and become sorted stripes. All of them resulted from frost heaving
(Tricart & Cailleux, 1967). The stones that constitute them are metric and decimetric size (picture
12). The surroundings of patterned grounds show terraces, vegetation stripes, stone lobes and
block fields at slope angles between 6º and 9º. When the slope increases the previous forms grade
into block lobes. When the slope angle exceeds 20º the resulted forms are closely associated to
gravitational processes as it occurs in the boundaries between the terrace and Valdeinfierno and
Veleta cirques.
In contrast to other cryoplanation terraces of Sierra Nevada, lichen and psicroxerophite grass have
settled on Macho terrace patterned grounds. Therefore, they are inherited forms that were
generated in cirques and headwaters during the last phases of the Pleistocene glaciarism.
Picture 12. Detailed picture of Machos cryoplanation terrace patterned ground field
4.2. Geophysics and thermometry
Thanks to Pace Project, a vertical electrical sounding survey was carried out in the Cerro de los
Machos peak in 1999 in order to determine the existence of permafrost. The electric logs points
38
out the probable existence of discontinuous permafrost between 1 m and 4 m deep. The maximum
values of resistivity were 100.000 Ohm/m (Terradat & ETH, 1998-99) (figura 23). Datalogger
type thermal sensors (NTC100 thermistor Tiny-Talk model and TMC-1T thermistor UTL-1
model) were installed at -5 cm, -10 cm and -50 cm deep. We only have the continuous and daily
data of the 1999-2000 and 2003-2004 field surveys from November to August (table 8). We
observed in the table that the thermal profiles show a constant and positive mean temperature of
0.4ºC. This value may be in agreement with the existence of permafrost 1 m under the surface.
Other important data are the large number of days in which the temperature was negative or it
ranged around 0ºC during the 2003-2004 survey (table 9 and figure 24).
Depth
Teration 8 RMS error -4.0%
6.0
0.0
24.0
16.0
32.0
40.0
M.
0.5
2.5
5.0
Inverse Model Resistivity Section
7000
15000
30000
50000
Figure 23. Resistivity tomography in pass Cerro de los Machos pass.
We can see from the table 9 that the air temperature was 102 days bellow 0º C and 115 days
ranging around 0º C. For the same period, ground temperature shows negative values 195 days at
-50 cm deep and 162 days at -10 cm deep. In addition, freeze and thaw cycles occurred 2 days at 50 cm deep and 47 days at -10 cm deep. These temperature data demonstrate that the ground
freezes while there is a snow cover and it melts during the postnival period. On the other hand, the
fluctuation of temperature values around 0º C (47 days at -10 cm deep and 2 days at -50 cm deep)
suggests that the snow cover does not exert an insulating effect probably due to the deflaction of
the snow cover.
Table 9. Freezing days and freeze/thaw cycles (Period 2003-2004, Nov-August)
__________________________________________________________________
Sampling site
D+
D+/D__________________________________________________________________
PV (air) 3095 m
88
115
102
………………………………………………………………………………………
CV-rg (-15 cm)
23
1
279
CV-rg (-50 cm)
23
1
279
………………………………………………………………………………………
CM-pg (-10 cm)
89
47
162
CM-pg (-50 cm)
102
2
195
__________________________________________________________________
PV: air temperature in the Veleta peak (3396 m) 4 m over the ground; CV-rg: bore-hole in the Corral del Veleta rock
glacier (3107 m); CM-pg: Paterned ground in Cerro de los Machos pass (3297 m).
39
Temperature (ºC)
Extreme min.
Thermal sample level (cm)
-30
-20
-10
-5
Mean
0
Extreme Max.
5
10
20
30
40
800
800
400
400
0
0
-10
-10
-50
-50
-30
-20
-10
-5
0
5
10
20
TMR (1999 - 2000)
PV (2003 - 2004)
CM (1999 - 2000)
CM (2003 - 2004)
30
40
Figure 24. Sub-surface temperatures of the Cerro de los Machos pass and air temperatures of the Veleta summit.
All these data do not allow ensuring the existence of permafrost in the Cerro de los Machos peak.
Therefore, we will need to control the temperature at deeper layers in the coming future.
Acknowledgements
We are sincerely grateful to E.U. ENV4-Ct97-0492 and Spanish Government BSO0745 research
projects and to David Serrano Giné for his graphical support. Servei de Paisatge from Universitat
de Barcelona is thanked for it special collaboration, as well as Parque Nacional de Sierra Nevada
for it stakeholder.
40
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44

sierra nevada massif glacial geomorphology and present cold

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