Holocene environmental changes in Sierra Nevada

Investigators: Lothar Schulte, Marc Oliva, Antonio Gómez-Ortiz, Javier de Marcos, David Palacios, Felipe Carvalho, Ramon Julià, Francesc Burjachs
Period: 1995 - ongoing
Funding: from diverse projects of the Spanish Ministry of Education and Science (BS02250-0745, PI = Antonio Gómez-Ortiz, CGL2006-01111, PI = Lothar Schulte) and the European Commission (EN4V-CT97-0492, PI = David Palacios).

Scientific highlights

High mountain natural archives as glaciers, lakes, fens and solifluction lobes provide useful tools for the understanding of paleoclimate variability at higher altitudes. Our research focuses on the reconstruction of Late Glacial and Holocene changes of alpine environments in Sierra Nevada, the southernmost range of the Iberian Peninsula and European continent.

Holocene glacier fluctuations in the Veleta cirque as an indicator for Holocene climatic changes

The most outstanding site in southern Spain for studying Holocene glacier shifts is the Veleta cirque in Sierra Nevada, where the southernmost glacier of Europe persisted during the Little Ice Age.

Based on detailed morphological mapping of the Veleta cirque, up to 5 Holocene moraine units were identified. Figure 1 shows a map of the location of the moraine arches. The age of the outermost and highest moraine LGM (= Late Glacial period moraine) is assumed as the Late Glacial period (Messerli, 1965) although no radiometric dating was obtained. Morphological evidence on the other hand points to a pre-Holocene age. The topographical configuration of the western lateral moraine permits the reconstruction of the glacier´s dimensions, which by far exceeds the ice mass of the younger (Holocene) glacier stands.

Map of the Holocene moraines of the Veleta cirque

Figure 1: Map of the Holocene moraines of the Veleta cirque according to Schulte (2002).

So far, only the age of the two youngest moraines can be determined. The youngest moraine HM4b (HM = Holocene moraine), located at an altitude of 3060 m, corresponds to the extension of the glacier in 1876, as reported by Hellmann (1881) and represents the latest glacier advances at the end of the Little Ice Age.

The approximate age of the second youngest moraine HM4a can be estimated by 210Pb-dating undertaken in lacustrine sediments located between both glacier stillstands. Figure 2 shows the sedimentological structure and the 210Pb-activity profile of the lacustrine sands and silts. The sample taken from a depth of 7 cm revealed an age of 1908 ± 3 A.D..

210Pb activity profile of lacustrine sediments located between the Holocene moraines HM4a and HM4b in the Veleta cirque (Sierra Nevada, Spain) at 3086 m a.s.l. 1 = Ground moraine, 2,3 and 4 = Layered lacustrine silts with intercalated fine sand layers.

Figure 2: 210Pb activity profile of lacustrine sediments located between the Holocene moraines HM4a and HM4b in the Veleta cirque (Sierra Nevada, Spain) at 3086 m a.s.l. 1 = Ground moraine, 2,3 and 4 = Layered lacustrine silts with intercalated fine sand layers. See location of profile in Fig. 1. (Schulte, 2002).

Extrapolation of 210Pb dates provide only poor approximate ages, primarily due to the possible presence of discontinuities as pointed out in figure 2. However, the obtained data indicate that the base of unit IV could be between 200 and 250 years old. Both the underlying lacustrine sediments (units III and II) and the ground moraine are older. According to these findings, the moraine HM4a represents an earlier advance of the glacier, probably at the beginning of the Little Ice Age. A much earlier accumulation of the coarsely grained moraine is not very plausible. This moraine has been altered very little compared to the older Holocene moraines (HM1, HM2 and HM3) which are rich in fine material.

Late Glacial Deglaciation and Subsequent Expansion of Periglacial Processes in the Mulhacen Cirque

Semiarid Mediterranean mountains are in general very sensitive to global climate warming in terms of deglaciation and permafrost degradation. In the context of the PACE-Project (Permafrost and Climate in Europe) the aim of the undertaken research is to gain a better understanding of late Pleistocene and Holocene glacial and periglacial history of Sierra Nevada, the southernmost European range with subrecent glacial features and recent permafrost. Furthermore, research is focused on the complex relationship between the deglaciation and the subsequent expansion of periglacial processes in the Mulhacen cirque.

Detailed morphological mapping on a scale of 1:5000 and morphometrical analysis of glacial and periglacial deposits along several cross sections were carried out in the Mulhacen cirque situated at an altitude between 2863 m (lowest area of the cirque bottom) and 3478 m a.s.l. (highest point of the headwall). High-resolution geophysical surveys were undertaken close to the Mulhacen peak (Fig. 3).

Model resistivity tomography with topography (Schulte et al., 2002)

Figure 3: Model resistivity tomography with topography (Schulte et al., 2002).

According to the obtained geomorphological data up to five principal moraine complexes at different altitudes (2863 - 2940 m a.s.l.) were identified (Fig. 4). Based on morphological criteria, E.L.A. calculations and correlation with the glacial records or the Veleta cirque we propose a late glacial age for the different moraine stands. The small differences in altitude and geographical distribution of the end moraine arches indicate the high sensibility of the glacier to past climate changes. However, the Mulhacen cirque and the Valdecasillas valley offer one of the most complex moraine sequences in southern Iberian Peninsula.

Chronostratigraphy of the Sierra Nevada according to Schulte et al. (2002)

Figure 4: Chronostratigraphy of the Sierra Nevada according to Schulte et al. (2002).

With regard to the periglacial dynamics rockfalls, debris flows, rock glaciers, protalus rampart, block fields, stone rivers and gelifluction lobes were identified and mapped. In the southwestern sector of the cirque the youngest moraine is nearly completely buried by younger rockglaciers and rock streams indicating the high efficiency of the periglacial processes during the Holocene. These processes are mostly controlled by the Holocene climatic conditions (cycles of freezing and thawing), topographical configuration and fragility of the outcropping schist related also to the postglacial release of the cirque headwall. Resistivity tomography data obtained from the southern slope of the Mulhacen peak may evidence discontinues permafrost (Fig. 3).

Solifluction Lobes in Sierra Nevada (Southern Spain)

A morphometric and spatial approach aims to classify solifluction lobes in Sierra Nevada in southern Iberian Peninsula, to understand the involved geomorphic processes and to reconstruct their evolution during the Late Holocene. Under the present climatic conditions, solifluction dynamics are very punctual in this massif. According to our findings, water availability in the semiarid environment of Sierra Nevada is the main factor controlling solifluidal dynamics. Only lobes near water channels and those influenced by water supply from late-lying snow patches show displacements. By contrast, thermal and topographic monitoring of a solifluction lobe in the Rio Seco valley showed that despite a seasonal frozen layer of 70 cm thickness solifluction processes remain inactive. However, sedimentological studies on solifluction lobes indicate that during the Late Holocene, periods of increased solifluction processes (e.g. Little Ice Age) alternated with periods of geomorphic stability (e.g. Medieval Warm Period). Present climate may not be cold and/or wet enough to trigger important solifluction processes from 2500 to 3000 m altitude.

Different generations of solifluction lobes at 2800 m a.s.l., northern slope of Sierra Nevada

Figure 5: Different generations of solifluction lobes at 2800 m a.s.l., northern slope of Sierra Nevada.

References

Gómez, A., Schulte, L., Salvador, F., Palacios, D., Sanz de Galdeano, C., Sanjosé, J.J., Tanarro, L.M., Atkinson, A., 2005. Field trip to Sierra Nevada Massif Glacial Geomorphology and Present Cold Processes. In: Sixth International Conference on Geomorphology. September 7-11, 2005 Zaragoza (Spain). Field trip guides, Vol. II, Zaragoza. pp. 309-354.

Oliva, M., Schulte, L., Gómez Ortiz, A, 2008. Solifluction Lobes in Sierra Nevada (Southern Spain): Morphometry, Process Monitoring and Palaeoenvironmental Changes. Proceedings 9th Internacional Conference on Permafrost. in press.

Schulte, L., 2002. Climatic and human influence on river systems and glacier fluctuations in southeast Spain. Quaternary International 93-94, 85-100.

Relevant publications

L. Schulte1, J. C. Peña, F. Carvalho, T. Schmidt, R. Julià, J. Llorca, and H. Veit, 2015.

A 2600-year history of floods in the Bernese Alps, Switzerland: frequencies, mechanisms and climate forcing

Hydrol. Earth Syst. Sci., 19, 3047-3072, 2015


J. C. Peña1, L. Schulte, A. Badoux, M. Barriendos, and A. Barrera-Escoda, 2015.

Influence of solar forcing, climate variability and modes of low-frequency atmospheric variability on summer floods in Switzerland

Hydrol. Earth Syst. Sci., 19, 3807-3827, 2015


L. Schulte, J.C. Peña, R. Julià, F. Carvalho, J. Llorca, J. Losada, F. Burjachs, T. Schmidt, P. Rubio, H. Veit, 2014.

CLIMATE FORCING OF PALEOFLOODS IN THE SWISS ALPS

Avances de la Geomorfología en España 2012-2014. Editores: Susanne Schnabel y Álvaro Gómez Gutiérrez. XIII Reunión Nacional de Geomorfología, Cáceres, 2014. pp. 143-146

Universitat de BarcelonaICREA - Institució Catalana de Recerca i Estudis AvançatsUniversität BernServei Meteorològic de CatalunyaGobierno de España - Ministerio de Educación y CienciaAlexander von Humboldt Foundation