Glacial history - Mediterranean Mountain Environments - page 42

(Vidal-Romanı et al. , 1999; Fernandez-Mosquera et al. , 2000; Vidal-Romanı and
Fernandez-Mosquera 2006).
In the Serra da Estrela, the highest mountains of Portugal (1991 m asl), glaciation
during the last cold stage was characterized by a plateau ice cap that fed diffluent
glaciers. The ice cap covered a total area of 66 km 2 with an average equilibrium
line altitude of 1650 m. The ice cap and its outlet glaciers have produced impressive
erosional landforms including deep glacial troughs formed by ice more than 300 m
thick in some places (Vieira, 2007). Thermoluminescence dates from glaciofluvial
sediments of between 16.6 ± 2.5 and 10.6 ± 1.6 ka suggest glacial activity during
the Late-glacial (Vieira et al. , 2001). These were the first radiometric ages to be
published on the Estrela glaciations, although the precise timing of the largest phase
of ice cap glaciation in this region has not yet been established.
Jimenez-Sanchez and Farias Arquer (2002) used radiocarbon dating to establish
the timing of glacial phases in the Redes Natural Park of the Cantabrian Moun-
tains. The most extensive glacial phase was characterized by an ice field with outlet
glaciers extending up to 5 km in length, descending to c. 950 m asl with snowlines
at c. 1550 m asl. A radiocarbon date of 29

0.5 cal. ka) was
obtained for this glacial phase from a core retrieved from ice-dammed lacustrine de-
posits that formed when drainage was blocked by a lateral moraine. This provides
a minimum age for the presence of glacier ice. In the nearby Comella basin of the
Picos de Europa, Moreno et al. (2009) demonstrated that the Enol glacier retreated
from its maximum extent prior to 40 000 years ago as demonstrated by the onset of
proglacial lacustrine sedimentation in two glaciated depressions: the Comella hol-
low to the north (before 40 cal. ka) and the Lago Enol (before 38 cal. ka). These
results, from the Redes Natural Park and the Picos de Europa, imply that the max-
imum phase of glaciation during the last glacial stage took place much earlier than
the global LGM. However, in other massifs of Spain such as the Sierra de Gredos
and Sierra de Guadarrama, 36 Cl exposure ages from glacial landforms suggest that
glaciers reached their maximum extent close to the global LGM (Palacios et al. ,
2010, 2011). A similar dichotomy of geochronologies has also occurred in the
Pyrenees (see below).

± 0.2 ka 14 C BP (34.2 ±

3.2.3 Pyrenees

The Pyrenees were extensively glaciated during the Pleistocene and some of the
first glacial geomorphological research was undertaken in the nineteenth century
by Penck (1885). Former glaciations have been attributed to at least two Pleistocene
cold stages, the oldest deposits to the Rissian Stage and a second, higher suite of
deposits to the Wurmian Stage (Barrere, 1963). However, the deposits of the older
glaciation are poorly preserved and the glaciers of the last cold stage were close in
size to the most extensive glaciations. The largest Pleistocene glaciers formed on
the northern slopes of the Pyrenees in France (Delmas et al ., 2011). For example, in