Pleistocene and Holocene Periglacial Forms in the

Pleistocene and Holocene Periglacial Forms in the Cantabrian Mountains (NW Spain)
Darío Trombotto Liaudat * & Victoria Alonso **
Ninth International Conference
On Permafrost
* IANIGLA, CONICET, 5500 Mendoza, Argentina. E-mail: dtrombot@lab.cricyt.edu.ar
* * D E PA R TA M E N TO D E G E O L O G Í A . U N I V E R S I D A D D E O V I E D O . C / J e s ú s A r i a s d e Ve l a s c o s / n . 3 3 0 0 5 O v i e d o , S p a i n . E - m a i l : v a l o n s o @ g e o l . u n i o v i . e s
IAN I GLA
Universidad de Oviedo
6° W
1a
Teverga
6º W
44° N
C a n t a b r i a n
42° N
Py
re
Cantabrian
Mountains
ne
es
Puerto de
Somiedo
Cornón
2188
15
1500
1923
S P A I N
PORTUGAL
Peña Chana
2068
S
6º 12´
6º 08´
General features of the relief of the CM,
considered as an extension of the Pyrenees
to the west, were set during the Alpine
Orogeny, when the Variscan basement was
uplifted. Ever since, dominating denudation
processes have been eroding this mountain
chain.
The CM show a great variety of glacial
erosional forms related to a Pleistocene
alpine glaciation with valley glaciers and
small ice fields; during its maximum, ice
fronts reached altitudes around 900-800 m
in many of the valleys. In the Somiedo-Babia
ice field, distribution of erratics, till and
glacially abraded surfaces indicate a
minimum ice thickness up to 400 m in some
areas (Figs. 1a and 1b; Alonso & Suárez
Rodríguez, 2004). Glacial deposits, as
primary or reworked tills, cover most of
the cold slopes with N or E aspect, although
moraines are usually not well preserved.
Double ridges and antiscarps are widespread
landforms in deglaciated valleys. Recent
instabilities removed glacial and periglacial
deposits in the glaciated valleys as mass
movements, and paraglacial alluvial fans
were formed in some of the valleys.
However, the former fluvial landscape was
not completely destroyed; erosional
preglacial surfaces are irregularly
preserved close to the divides (Fig. 11).
N
Lago
del Valle
Piedrafita
de Babia
l
u n
a
00
15 00
i
6º 16´
43º N
Montihuero
2180
L
Villablino
Peña Ubiña
2417
Main glacial features of the Babia Region
18
a s
I b i
1b
2182
Muxivén
2027
00
15 00
Cueto Arbás
2007
Degaña
A detailed geomorphological map of an
alpine deglaciated environment, in the
Cantabrian Mountains (CM), has revealed a
great variety of periglacial forms that have
been ascribed to different cryomeres during
and following deglaciation.
N
S e a
Asturias
León
Bárzana
1500
300
Sena de Luna
El Miro
1985
00
20
Puerto de
Somiedo
1600
160
Cañada
2154
Nevadín
2082
1600
0
1500
00
18
Páramo
del Sil
Catoute
2111
43º
Montihuero
2180 m
00´
10 km
00
1600
18
220
14
1600
00
0
160
1800
Muxivén
2027 m
400
16
00
260
200
L E G E N D
Nivation and Periglacial Processes
and Forms (fossil, inactive and active)
Glacial Forms and Deposits
Main peak
Arête
Glacial cirque
Rockglacier
Permanent stream
Till (undiferenciated
glacial deposit)
Protalus
Lineal channel
Moraine crest
Stone stripes
Rock threshold
Slope change
in glacial valley
Solifluction
Abraded and/or glacially
eroded rock surface
Striae
Nivation hollow
Erratic or subglacially
transported boulder
Roche moutonee
Whaleback
260
13
150
42º
00
14
0
140
Fractures and faults
Mountain
lake
Boulder slope
Slope break
Glacier difluence zone
200
260
Villaseca
de Laciana
65 Bed strike and dip
River
Luna
56´
100
14
00
Rill runoff in permanent
and non-permanent
streams
Furrows
Trough limit
Structural Features
San Félix
de Arce
0
Piedrafita
Laguna de
Villaseca
Fluvial and
Lacustrine Forms
Ridges
140
Sil River
200
120
140
Gravitational Forms
Alluvial cone
150
Avalanche
Boulder lobe
Mixed landslide
16
00
Slided
block
Province limit
Ice thickness during
glacial maximum
Landslide scar
0
1
2
3 km
1600
Based on Alonso & Suárez Rodríguez, 2004
El Miro
Peña Baquín
2
12
s l o p e s
Warm
E n v i r o n m e n t a l
-
glacial and periglacial
environments
-
13. The Babia intramountainous plain was covered by a small ice
field during the LGM. Moraines formed by stabilizations during
glacier retreat, in the Luna valley, are marked by dotted lines.
almost continuous permafrost
in ice free areas,
creeping permafrost
-
local
-
periglacial processes
without glaciers
-
considerable creeping
permafrost
-
less
-
nivation
Note the glacially abraded limestones. Location shown in Fig. 1b.
glacial
freezing
processes
and
-
covered
-
mountain
-
perennial and
patches
by
glaciers
for
less
time
Geomorphological Map of El Miro
500 m
0
temporary
snow
in
areas
of
thawing
gelifluction
-
more
-
nivation
6º 32´
and
freezing
solifluction
and
thawing
cycles
cycles
-
rockglaciers
-
felsenmeer
-
embryonal periglacial forms
within glacial/periglacial
domain
-
boulder
-
gelifluction
-
nivation
l a n d f o r m s
-
giant sorted
streams
-
solifluction
-
boulder
-
small
stripes
and
rock
lobes
slopes
of
cryosediment
slopes
lobes
nivation
hollows
hollows
42º
55´
1700
1908
Alto del Bigardón
(1939)
3. Block field with longitudinal and transverse ridges and furrows.
1929
Note partially reworked glacier moraines at north and south ends
to the south.
1915
Fana del
Coronxo(1836)
1858
17
00
64
18
00
(indicated by arrows) and boulder lobes on the talus slope. View
11
Peña Ubiña
2417 m
1700
4
1884
11
3
1800
65
1700
0
160
Cornón de
Busmori
(1932)
160
0
75
8
73
4
00
15
1829
58
65
1593
16
00
5
4. Tongue-shaped rockglacier at the bottom of north El Miro
valley developed between 1540 and 1655 m. The root is
disconnected from the cirque floor. Blocks in the lower zone are
up to 8.5 m in length.
11. In the foreground on the left, boulder lobes on talus deposits
at 1725 m with a south aspect. Partially eroded pre-quaternary
surfaces are frequently preserved in the main water divide. View
64
6
t o t h e e a s t ; P e ñ a U b i ñ a l o c a t i o n i s s h o w n i n F i g . 1 a.
1800
7
00
17
160
42º
58
0
54´
1500
5
Peña Baquín
(1986)
10
1833
2
9
1800
71
El Miro
(1985)
1937
80
18
00
00
19
00
vegetation cover indicate a younger age than the tongue-shaped
1800
17
with the front at 1725 m and a northeast aspect. Location and
form shown in Fig. 4.
6
8
7
*
6. Well developed protalus at 1775 m and a north aspect. In the
7. Small protalus at the foot of talus slopes with a northwest
8. Boulder deposits and curved fractures at the top of warm
9 and 10. Giant sorted stone stripes on warm slopes to the west of El Miro. Lower zones
background on the left, glacially abraded bedrock in the north-
aspect. Asterisk marks the same position in Fig. 6.
slopes. The lower half shows the beginning of the giant stone
are usually affected by mixed landslides. In undisturbed zones, a lower limit for the stripes
stripes partially deformed by mixed landslides.
is calculated at 1700-1650 m.
rockglacier in Fig. 5; asterisk marks the same position in Fig. 7.
We propose that conditions during
deglaciation were probably similar to those
of the Pyrenees, where continuous
permafrost and important cryogenic
landforms with glacier ice at the same time
are represented in the Climex Map of 2002
for the Last Glacial Maximum.
The peak of the periglacial environment
in the CM, however, must have occurred
after the LGM, with predominantly much
drier climatic conditions and benefitting
from vaster areas uncovered by ice;
discontinuous permafrost, expressed by
rockglaciers during the Late Pleistocene or
Early Holocene is likely to have reached
1540 m a.s.l.
9
*
south main valley. White arrow indicates the front of the lobate
Altitude, aspect, preservation degree and
soil development of cryogenic forms around
El Miro indicate more than one cryomere,
although the lack of datable material has
not allowed us to determine a precise time
for these cryomeres. A tongue-shaped
rockglacier in a cold and low position (Fig.
4) and giant sorted stripes on warm slopes
(Figs. 9 and 10), both proposed to be coeval
with cirque glaciers, suggest a continuous
mountain permafrost in ice free areas during
deglaciation, when the most important
indicators were cryogenic periglacial and
not glacigenic.
At higher altitudes, sparsely vegetated
small forms with scarce or none development
of soil –lobate rockglaciers, protalus and
boulder lobes- would correspond to more
recent times; some of these landforms were
probably active during the LIA, when cirque
glaciers developed in Picos de Europa. The
rockglacier fronts end at 1730 m a.s.l.
approximately.
68
5. Lobate rockglacier at the bottom of the north El Miro valley
Most of these forms are fossil features;
at present, meteorological data indicate
important cryogenic activity approximately
above 2000 m. Solifluction in relation with
nival processes is still active.
Deglaciation in this zone of the CM was
dated to have occurred before 34 000±1400
C -14 y r B P i n L a g u n a d e V i l l a s e c a , a t 1 3 0 5
m a.s.l. (Jalut et al., 2004; see Fig. 1b for
location). But terminal moraine complexes
at lower altitudes, formed when glaciers
still were 11 km in length in areas with
calculated previous ice thicknesses up to
260 m (Figs. 1b and 13), suggest a long
evolution between the beginning of
deglaciation and stabilization phases during
retreat. Other data worth mentioning (Pallàs
et al., 2006) about the close region of the
Pyrenees, where an early maximum glacier
extent during the last glacial cycle is not
excluded, indicate an extensive glaciation
at ca 18-20 ka (MIS 2), coinciding with the
global LGM.
permafrost
-
A c t i ve c r y o g e n i c
3
6º 33´
This zone, as many others in the CM,
shows a strong asymmetry in processes and
forms (Figs. 1c and 2). Rockglaciers,
felsenmeer, protalus, boulder lobes,
solifluction forms and talus deposits,
formed by glacially derived material or by
cryosediment, are frequent on cold slopes
(Figs. 2 to 7). Warm slopes, slighter or even
non glaciated and with a more regular
gradient, developed giant sorted stone
stripes, boulder lobes and stone-banked
lobes from cryosediment (Figs. 8 to 11).
C o n d i t i o n s
P r o c e s s e s
1c
Analysis of the map, made in a regional
context, indicates that, during and after
deglaciation, permafrost and periglacial
processes affected to a great extent the
highest parts of the deglaciated areas.
slopes
2. View to the southeast of El Miro showing asymmetry between
facing slopes with a more regular gradient to the top.
The geomorphological map, at a 1:5000
scale, was made for a sector around El Miro
peak (1895 m), located to the south of the
main divide and characterized by a
homogeneous bedrock formed mainly by
cambro-ordovician quartzites (Figs. 1a and
1c).
Hypothetical Conditions, Processes and Landforms during Recent Cryomeres
(Greenland stadial 1/ Lower Holocene, Neoglacial phases, Little Ice Age)
C o l d
east facing slopes, with glacier cirques, and non-glaciated west
Today, Picos de Europa, to the east, contain
small ice bodies from the LIA in glaciokarst
depressions (González Suárez & Alonso,
1994).
Conditions, processes and landforms
distribution during recent cryomeres have
been summarized in a table (Fig. 12).
13
Cornón
2188 m
CONICET
REFERENCES: V. Alonso & A. Suárez
Rodríguez (2004) Revista de la Sociedad
Geológica de España, 17: 61-70; CLIMEX
World Maps (2002) N. Petit-Maire, Ph.
Bouysse (Scientific editors), CCGM, CGMW
& ANDRA, France; J.J. González Suárez &
V. Alonso (1994) J. Glaciology, 40: 198-199;
G. Jalut, et al. (2004) Geo-Temas, 6: 105108; Pallàs et al. (2006) Quaternary Science
Reviews, 25: 2937-2963.