Search

Snow cover has significant impacts on geoecological dynamics as well as on socio-economical systems. An accurate quantification of snow precipitation patterns in mountain regions is needed to better understand the spatio-temporal implications of snow cover. The objective of this work is to characterize the patterns of solid precipitation and snow cover in two high Mediterranean massifs. To this purpose, we analyse instrumental data series of snowfall and snow depth of Port del Comte (2316 m a.s.l.) and Cadí-Nord (2134 m). Both stations are situated in the eastern Pre-Pyrenees and include 14 consecutive snow seasons from November to May, allowing to (i) explore the dependence of the main drivers of snowpack: temperature and snowfall; (ii) find out the most frequent circulation weather types associated with high intensity snowfall events, and finally (iii) investigate the role of the North Atlantic Oceanic (NAO) teleconnection pattern explaining snow cover evolution during the winter season. Data show that snowfall is controlled by similar weather types in both stations that resulted in similar snowfall averages: 205 cm and 258 cm at Port del Comte and Cadí-Nord, respectively. Nevertheless, local factors interfere with the amount of snow depth recorded, which is moderately different between stations. Whereas Cadí-Nord records a seasonal mean of 66 cm, Port del Comte records a smaller quantity of 25 cm with a high interannual and seasonal variability. In fact, snowfall recurrence, snow amount or duration in the ground is considerably variable among years (CV>20). In these stations, snow cover duration is determined by the precipitation in the form of snow falling during the previous months. Snowfalls in moderate to severe episodes (>15 cm in 24 h) are mainly driven by Atlantic flows, mostly from NW. In addition, NAO pattern is negatively correlated with snowfall in November and December months (R>-0.50), showing a weaker and not statistically significant correlation during the rest of the winter season.

The rock glacier of Corral del Veleta is located in the southwest of the Mediterranean basin, in the Sierra Nevada mountain range (Spain), being the highest in the Iberian Peninsula. It is located in the Quaternary circus of Guarnón at an altitude of 3,100 m, below the peak of Veleta at 3,398 m and facing northeast. The monitoring carried out during the 2001-2019 period has been carried out through different geomatic techniques: Topography, Photogrammetry, GNSS, TLS, UAV & GPR. Thermal measurements of the active layer have been added to these techniques. The analysis and results of the monitoring carried out show that it is in an accelerated process of immobilization and the relict glacial ice and permafrost on which it sits show a continuous degradation. The origin of the changes can be related to the variations in the dominant climate in the high mountains of the Sierra Nevada, particularly since the last third of the 20th century and the beginning of the 21st century.

The Southeastern Pyrenees extend eastward along the north-south line that the Segre River traces with its Andorran tributary, the Valira River. The main massifs correspond to the Tossa Plana de Lles-Calmquerdos-Carlit to the west, the Puigmal-Bastiments-Costabona in the center—both within the Cerdanya basin (Upper Segre Valley)—and the Ripolles district (headwaters of the Ter Valley) to the east. The discovery and analysis of the glacial landforms existing in these massifs started at the end of the 19th century, but it was not until the end of the 20th century when remarkable advances were made, complemented in the early 21st century with the establishment of the glacial chronology. Glacial landforms are limited to the mountain regions and include a great variety of landforms, ranging from extensive areas in the higher massifs modeled by ice field, valley glaciers >10 km long, and small glacial cirques in the lower mountains of the Pre-Pyrenean massifs. The main glacial advance in the Southeastern Pyrenees took place between 80 and 35 ka. Moreover, the glacial advance occurred during the global Last Glacial Maximum (gLGM) and reached almost the same extent as the previous advance. After a massive retreat at 19–20 ka, the glaciers readvanced at c. 17–16 ka. Most of the cirques were deglaciated at c. 15 ka, and rock glaciers formed afterward. Only in the highest cirques (2800 to 2900 m), north- and east-exposed, small glaciers were formed during the Younger Dryas. No glacial activity has been detected during the Holocene. This glacial evolution is very similar to that occurred in the northeastern slope of the Pyrenees but the spatiotemporal pattern of glacial oscillations since the Last Glacial Maximum is significantly different than in the Central Pyrenees, where the climate was more influenced by the Atlantic Ocean.

The mountain range of Sierra Nevada is c. 90 km long and located in the southeast of the Iberian Peninsula. Its highest peak, the Mulhacen (3479 m; 37o 03′ 12″ N, 3o 18′ 41″ W), is also the highest in the Iberian Peninsula. Sierra Nevada is part of the Betic Range, which crosses the southeastern part of the peninsula from southwest to northeast. It is composed of metamorphic and crystalline rocks that folded and fractured during the Alpine orogeny. The average annual temperature is 4.4°C, and the recorded precipitation at an altitude of 2500 m is 710 mm. The Pleistocene glaciers of the Sierra Nevada, the southernmost in Europe, were enclosed in the headwaters of ancient valleys, and their maximum lengths ranged between 6 and 9 km. Some moraines from the previous glacial cycle (130 ka) can be found here, but most of them belong to the Last Glacial Cycle, whose maximum advance occurred at c. 30 ka. An advance of almost similar proportions took place at approximately 20–19 ka, followed by a massive deglaciation until a new advance occurred in the Oldest Dryas. After the probable almost total disappearance of the glaciers, small cirque glaciers formed during the Younger Dryas. The glaciers melted away at the beginning of the Holocene, but rock glaciers formed simultaneously in numerous cirques. Later, during the Late Holocene, small glaciers formed only under the northern walls of the highest peaks (Mulhacen and Veleta), but disappeared at the end of the Little Ice Age, favoring the development of incipient rock glaciers.

The COVID-19 pandemic is having an enormous negative impact on human health, with more than 4.44 million deaths worldwide; on the economy, with an unprecedented deep and abrupt crisis; and on society, with millions of people facing unemployment and dependent, in the best-case scenario, on public welfare or social aid systems. Home confinement, measures to limit non-essential economic activity and travel restrictions in many countries during the spring of 2020 led to rapid air quality improvements in cities. A detailed analysis of Barcelona's daily immissions of seven pollutants (CO, SO2, NO, NO2, NOx, PM10 and O3) shows a clear decrease from mid-March to June, with the peak in April and the nitrogen oxides. For these pollutants the reduction of traffic density is very likely the main cause of their immissions decrease. On another note, the global reduction of CO2 emissions derived from the use of fossil fuels was estimated at approximately 8 % in 2020, which, despite constituting an unprecedented drop, will have little impact on concentrations of CO2 and other greenhouse gases in the atmosphere. The current situation must be seen as an opportunity to push, without delay, for a drastic change in the energy and economy models towards a socio-environmental paradigm based on sustainability, economic efficiency and solidarity between peoples. Resumen. La pandemia de la COVID-19 está teniendo un enorme impacto negativo en la salud humana, con más de 4,44 millones de muertos en todo el mundo; en la economía, con una profunda y abrupta crisis sin precedentes; y en la sociedad, con millones de personas en situación de desempleo y dependientes, en el mejor de los casos, de los sistemas de asistencia social o de bienestar público. El confinamiento domiciliario, las medidas para limitar la actividad económica no esencial y las restricciones de los viajes en muchos países durante la primavera de 2020 llevaron a mejoras rápidas en la calidad del aire de las ciudades. Un análisis detallado de las inmisiones diarias de Barcelona de siete contaminantes (CO, SO2, NO, NO2, NOx, PM10 y O3) muestra una clara disminución desde mediados de marzo hasta junio, con el pico en abril y en los óxidos de nitrógeno. Para estos contaminantes, la reducción de la densidad del tráfico es muy probablemente la principal causa de la disminución de sus inmisiones. Por otro lado, la reducción global de las emisiones de CO2 derivadas del uso de combustibles fósiles se estimó en aproximadamente un 8 % en 2020, lo que, a pesar de constituir una caída sin precedentes, tendrá poco impacto en las concentraciones de CO2 y de otros gases de efecto invernadero en la atmósfera. La situación actual debe ser vista como una oportunidad para impulsar, sin demora, un cambio drástico en los modelos energético y económico hacia un paradigma socioambiental basado en la sostenibilidad, la eficiencia económica y la solidaridad entre los pueblos.

Pleistocene glaciers shaped the highest lands of the National Park of Sierra Nevada, South Spain. Alpine glaciers filled the western valleys of the massif with hundreds of meters of ice. Surface exposure dating shows evidence of glacial expansion during the Younger Dryas and the subsequent disappearance of glaciers of the massif during the Early Holocene. Since then, glacial records and lake sediments reveal that the massif has been ice-free for the most part of the Holocene, with the development of small glaciers during the coldest phases inside the highest northern cirques. This occurred at 2.8–2.7, 1.4–1.2 cal. ka BP and during the Little Ice Age (1300–1850 CE), when documentary sources confirm also the existence of some glaciers at the foot of the highest summits. This historical period was probably the coldest and wettest phase of the Holocene in the massif and recorded the largest glaciers of the current interglacial. Those glaciers finally melted away during the mid-20th century.

Outside the Alps, the Sierra Nevada is probably the best studied European massif with respect to its past and current environmental dynamics. A multi‐approach research program started in the early 2000s focused on the monitoring of frozen ground conditions in this National Park. Here, we present data on the thermal state and distribution of permafrost and seasonal frozen ground in different sites across the highest areas of the massif. New results confirm the absence of widespread permafrost conditions, with seasonal frost prevailing above 2500 m. Small permafrost patches have been only detected in glaciated areas of the Veleta and Mulhacen cirques during the Little Ice Age at elevations of 3000–3100 m. The remnants of those glaciers are still preserved under the thick debris layer covering the cirque floors. Geomatic and geophysical surveying of a rock glacier existing in the Veleta cirque, together with the monitoring of soil temperature at different depths, have revealed permanently frozen conditions undergoing a process of degradation. In the rest of the massif, a seasonal frost regime prevails, even at the highest plateaus at 3300–3400 m, where annual soil temperatures average 2.5°C. The monitoring of soil temperatures in other different periglacial features has also revealed positive average values ranging between 2°C (inactive sorted‐circles) and 3–4°C (inactive and weakly active solifluction lobes). Consequently, we conclude that the present‐day climatic regime does not allow the existence of permafrost in the Sierra Nevada, and environmental dynamics is controlled by the intensity and duration of seasonal frost in the ground.

Historical documents have shown their potential to infer the origin and evolution of the glacier existing in the Veleta cirque, in the massif of Sierra Nevada (Spain). This information encompasses written sources spanning from the 17th to the mid-20th centuries, and provides valuable knowledge about the Little Ice Age. These new data complement the already existing geomorphological knowledge about the natural system and landscape evolution in Sierra Nevada, particularly with regards to glacial geomorphic events in the summit areas. From a transdisciplinary methodological approach, the results show that the Veleta glacier was a singular geomorphic event that owed its existence to the particular environmental conditions of the high lands of Sierra Nevada, besides the favourable morpho-topographical setting, altitude, aspect as well as microclimate conditions prevailing in this area.

International audience; An accurate review of the literature on surface exposure dating methods shows evidence of the difficulty in applying cosmogenic dating methods to old moraines because of the intensity of Late Quaternary erosion processes. Moreover, as in some previous cases, we found also special difficulties in applying these methods to LIA moraines, due to the intensity of current paraglacial processes. The objective of this study is to apply cosmogenic dating methods to very old and very young moraines, which in both cases have been or are being affected intensively by erosion. With this purpose, we collected samples of boulders from moraines corresponding to: (a) the penultimate glaciation, and (b) the Little Ice Age (LIA), both from Sierra Nevada, in the south of the Iberian Peninsula. The sampling strategy was based on a preliminary accurate analysis of the geomorphological settings of two valley sites that Manuscript with line numbering and double line spacing Click here to view linked References resulted in the collection of only four boulder samples from an old moraine and three more from a very recent moraine. Using in situ produced cosmogenic 10 Be to date these boulders, the old samples yielded an age of ca. 130-135 ka for moraine stabilization. The younger samples indicate that the LIA moraine accretion probably occurred between the 14 th and 17 th centuries, with a subsequent stage of accumulation during the 19 th century as suggested by historical documents. Both, dating a glaciation that occurred prior to the last Pleistocene glacial cycle and dating LIA glacial stages are novel in the context of Iberian glaciations and agree with other palaeoenvironmental studies in Iberian and in other European mountains. The limited number of boulders adequate for cosmic-ray exposure dating prevents statistical methods to be applied, and therefore highlights the need to improve geomorphological criteria in sample selection.

The Veleta cirque is located at the foot of the Veleta peak, one of the highest summits of the Sierra Nevada National Park (southern Spain). This cirque was the source of a glacier valley during the Quaternary cold periods. During the Little Ice Age it sheltered a small glacier, the most southerly in Europe, about which we have possessed written records since the 17th century. This glacier still had ice residues until the mid-20th century. This ice is no longer visible, but a residue persists along with discontinuous permafrost trapped under strata of rock blocks that make up an incipient rock glacier. From 2006 to 2013, this rock glacier was monitored by measurement of the temperature of the active layer, the degree of snow cover on the ground, movements of the body of the rock glacier and geophysical prospection inside it. The results show that the relict ice and trapped permafrost have been steadily declining. The processes that explain this degradation occur in chain, starting from the external radiation that affects the ground in summer, which is when the temperatures are higher. In effect, when this radiation steadily melts the snow on the ground, the thermal expansive wave advances into the heart of the active layer, reaching the ceiling of the frozen mass, which it then degrades and melts. In this entire linked process, the circulation of meltwaters fulfils a highly significant function, as they act as heat transmitters. The complementary nature of these processes explains the subsidence and continuous changes in the entire clastic pack and the melting of the frozen ceiling on which it rests. This happens in summer in just a few weeks. All these events, in particular the geomorphological ones, take place on the Sierra Nevada peaks within certain climate conditions that are at present unfavourable to the maintenance of snow on the ground in summer. These conditions could be related to recent variations in the climate, starting in the mid-19th century and most markedly since the second half of the 20th century. The work and results highlight the climate sensitivity of the peaks of the Sierra Nevada to the effect of climate change and its impact on the dynamics of ecosystems, which is a benchmark for evaluating the current evolution of landscapes of Mediterranean high mountains., We are grateful to the research projects 018/2007 of the Autonomous Organisation of National Parks and CSO2012-30681 from the Ministry of Economy and Competition.

Our knowledge of the Quaternary landscape evolution in the high mountain areas of the Iberian Peninsula has substantially improved over the last decades. The Sierra Nevada is one of the most studied mountain ranges in southern Europe regarding its environmental evolution. The purpose of the present paper is to integrate and summarize all the studies focused on the reconstruction of the palaeoenvironmental history in this massif since the Last Glaciation. Research has focused both on different sedimentary records and historical sources. A wide range of geomorphological, sedimentological and geochronological techniques have been used to characterize the glacial, periglacial, wetland and lacustrine records for palaeoenvironmental purposes. For the last nine centuries tens of descriptions, maps and sketches describe the landscape of the summit area of the Sierra Nevada, providing evidences of the historical environmental events. Based on a multi-proxy approach, five periods have been identified: Last Glaciation, deglaciation, Holocene, Little Ice Age and recent evolution. Recent studies have detected the maximum expansion of glaciers in the Sierra Nevada around 30–32 ka BP, predating the global temperature minimum. No data about the environmental evolution is available between 20–30 ka BP. Around 19–20 ka BP glaciers advanced significantly. The process of deglaciation was rapid and around 14–15 ka BP the massif was almost free of ice. The Late Glacial promoted the formation of small glaciers in the highest northern cirques and widespread active periglacial processes (i.e. rock glaciers). During the Holocene there has been an alternation of colder/warmer periods and changing moisture conditions. Periglacial processes have been generally widespread in the summit area, with an increasing or decreasing activity depending on climate conditions. Ephemeral reappearance of small glacial cirques occurred in the highest northern cirques during the coldest and wettest phases. This is the case of the Little Ice Age, as revealed by historical documents and sedimentary records. Since the last decades of the XIX century the temperature has increased ∼0.93°C leading to a decrease of the intensity of periglacial processes in the high lands of the Sierra Nevada.

Ponencia presentada en: X Congreso de la Asociación Española de Climatología celebrado en Alicante entre el 5 y el 8 de octubre de 2016. [ES]A partir de los datos diarios de precipitación, permanencia y espesor de nieve, se han calculado los valores más significativos de nivosidad e innivación en La Molina (1.703 m, extremo oriental del Pirineo), durante 38 temporadas nivales (de noviembre a mayo, de 1956/57 a 1995/96). Su rasgo más destacado es la acusada irregularidad de todas las variables nivoclimáticas estudiadas, tanto las relacionadas con la cuantía y frecuencia de la precipitación nivosa, como las relacionadas con la permanencia y espesor del manto de nieve. [EN]Daily snow data in La Molina (1.703 m asl, eastern Pyrenees) is analysed during 38 nival seasons (November to May; 1956/57 to 1995/96), from which the most significant values of snowfall and snow cover are calculated. It should be pointed the accused irregularity of all climatic characteristics studied: the amount and frequency of snow precipitation, as well as the persistence and thickness of the mantle of snow. Este trabajo se inscribe dentro de las actividades del Grupo de Investigación consolidado SGR2014-0373 Paisatge i paleoambients a la muntanya mediterrània (Generalitat de Catalunya).

El Hierro es la isla más occidental del archipiélago canario y se halla en latitudes subtropicales (27,5ºN). El clima subtopical/tropical canario de la isla se caracteriza por tener gran diversidad de microclimas debido a la importante influencia de algunos factores geográficos. El objetivo principal de este trabajo es analizar los datos de temperatura y humedad relativa del aire, registrados a resolución horaria por sensores instalados en sabinares de El Hierro, a lo largo de tres ciclos anuales (de septiembre de 2012 a agosto de 2015) y estudiar episodios extremos de termohigrométricos. Los datos provienen de dos enclaves con orientación y altitud contrastadas: El Júlan (996 m, en la vertiente sur y en el interior) y Sabinosa (258 m, en la cara norte y cerca de la línea de costa). Los resultados obtenidos muestran ciclos termohigrométricos muy similares entre ambas áreas de estudio, pero presentan grandes diferencias en el rango de sus valores a pesar de hallarse a menos de 4 km de distancia horizontal. Los contrastes extremos de temperatura acontecen en julio y agosto cuando El Júlan registra hasta 21ºC más que Sabinosa a la misma hora. Son situaciones sinópticas en que los alisios soplan fuerte y dejan Sabinosa bajo el mar de nubes. Los contrastes extremos de humedad tienen lugar también en verano, sobre todo en agosto, bajo advecciones del este de origen sahariano, donde los valores de El Júlan pueden caer por debajo del 5% y los de Sabinosa mantenerse por encima del 90%. El Hierro is the westernmost island of Canary Isles and it is located in the north subtropic (27.5ºN). The subtropical-tropical Canary climate is featured by multiple microclimates due to geographical factors. The main objective of the present study is to analyse air temperature and relative humidity data of Juniperus turbinata forests and study extreme events of thermohygrometric differences. Sensors in the branches of Juniperus turbinata trees hourly recorded these data along three annual cycles (from September 2012 to August 2015). Data come from two locations with different aspect and altitude: El Júlan (996 masl, in the south face and inland) and Sabinosa (258 masl, in the north face and next to the sea). The results show similar thermohygrometric cycles in both locations. Despite these two points are very close (horizontally separated by 4 km), a large difference is found between their respective ranges of values. The largest temperature differences take place in July and August. El Júlan can record 21ºC more than Sabinosa at the same time in summer. Trade winds contribute to this large temperature difference because they form orographic clouds over the north face of the island (Sabinosa is to windward). The largest differences of relative humidity take place in summer too, above all, in August. Easterly winds from Sahara Desert reduce humidity in El Júlan below 5%, whereas humidity in Sabinosa can keep over 90%. Este estudio ha sido financiado por los proyectos de investigación JUNITUR (CSO2011-24425, 2012-2015) y JUNITUR+ (CSO2015-68500- R, 2016-2019) de la Secretaría de Investigación, Desarrollo e Innovación del Ministerio de Economía y Competitividad.

Cosmogenic 36 Cl surface exposure dating was carried out on 19 samples from glacially polished bedrock, rock glaciers and moraines of four glaciated valleys with different orientations in the Sierra Nevada (Spain) around Pico del Veleta (37° 3′N 3° 21′W, 3398 m asl). Remains of moraines older than the global Last Glacial Maximum exist, but their poor preservation makes them an unreliable subject for surface exposure dating. Results show that the last local glacial maximum advance took place earlier than the global Last Glacial Maximum, but within the MIS 2, although additional dating is needed to confirm this. Exposure ages from bedrock steps show a general glacier retreat in progress by 15–14 ka. Shortly afterwards an extensive system of rock glaciers formed at the base of the valley headwalls, with the most recent rock glacier lasting until 7 ka ago. From their location, morphology and analysis of other proxies, we interpret their origin as related to the deglaciation process and marked instability of cirque headwalls, rather than to extreme periglacial conditions. A recent similar occurrence was the transformation of the Little Ice Age glacier on the north face of the Pico del Veleta into a rock glacier under temperate high mountain climatic conditions.

The Sierra Nevada is the highest mountain system on the Iberian Peninsula (Mulhacen 3482 m; Veleta 3308 m) and is located in the extreme SE region of Spain (lat 37°N, long 3°W). Bibliographic resou...

A 114.5m deep drilling was carried out in August 2000 in the bedrock of the Veleta peak, at 3380m in the massif of Sierra Nevada, Southern Spain. The objective of this work is to analyse temperatures at the first 60m depth of this drilling from September 2002 to August 2013 based on 11 UTL-1 thermal loggers located at different depths, together with air temperatures at the summit of the Veleta peak. Permanent negative temperatures have not been detected in the borehole, which shows evidence of the absence of widespread permafrost conditions nowadays in the highest lands of this massif. Bedrock temperatures oscillated between 3.2°C at 0.6m depth and 2°C at 20m below the surface. The largest temperature ranges were recorded on the most external sensors until 1.2m depth, where values reached 22.3°C. Seasonal temperature variations were significant until 10m depth. The thickness of the seasonal frozen layer was highly variable (0.6-2m) and dependent on annual climate conditions. The mean air temperature at the Veleta peak increased by 0.12°C during the study period. Bedrock temperatures followed diverging trends: a drop of 0.3-0.4°C down to 0.6m depth, a decrease of up to 0.7°C between 4 and 10m, thermal stability at 20m and a rise of 0.2°C that occurred in 2009 at the deepest sensor at 60m. The calculation of the thermal wave damping in the subsoil of the Veleta peak has allowed for quantifying the thermal diffusivity of the rock as (7.05±0.03)10(-7)m(2)/s, which means that the external climate signal arrives with an 8.5-year lag to the sensor at 60m deep. This allows to deduce a trend change in the climate of the area, moving from warmer conditions towards a trend of cooling from 2006 to 2007.

This paper examines glacial evolution in the La Pera and Malniu cirques, and Aranser, La Llosa and Duran valleys, in the Cerdanya massifs on the south-facing slopes of the eastern Pyrenees. A geomorphologic analysis and dating of moraine boulders, glacially polished bedrock and rock glacier blocks were carried out by means of cosmogenic 36Cl surface exposure dating. The maximum ice advance was contemporary with the Last Glacial Maximum at 23 ka ago, and it was of greater or only slightly lesser magnitude than for previous Quaternary advances. The termini of glaciers remained close to maximum positions, with minor advances and retreats until 18–17 ka when the glacial tongues disappeared from the valleys. Depending on the previous topography, these glaciers left behind a single polygenic moraine, in the case of confined valleys, or multiple moraines next to each other in the case of flat, more open areas. A final glacial advance is detected during the Oldest Dryas close to the cirque headwalls, and the glaciers finally disappeared during the Bolling interstadial. The glaciers were then replaced by rock glaciers, whose front immediately became inactive, although their activity continued near their source area until the early Holocene.

The Veleta cirque is located at the foot of the Veleta peak, one of the highest summits of the Sierra Nevada National Park (Southern Spain). This cirque was the source of a glacier valley during the Quaternary cold periods. During the Little Ice Age it sheltered a small glacier, the most southerly in Europe, about which we have possessed written records since the XVII century. This glacier still had ice residues until the mid-XX century. This ice is no longer visible, but a residue persists along with discontinuous permafrost trapped under strata of rock blocks that make up an incipient rock glacier. From 2006 to 2013, this rock glacier was monitored by measurement of the temperature of the active layer, the degree of snow cover on the ground, movements of the body of the rock glacier and geophysical prospection inside it. The results show that the relict ice and trapped permafrost have been steadily declining. The processes that explain this degradation occur in chain, starting from the external radiation that affects the ground in summer, which is when the temperatures are higher. In effect, when this radiation steadily melts the snow on the ground, the thermal expansive wave advances into the heart of the active layer, reaching the ceiling of the frozen mass, which it then degrades and melts. In this entire linked process, the circulation of melt waters fulfil a highly significant function, as they act as heat transmitters. The complementary nature of these processes explains the subsidence and continuous changes in the entire clastic pack and the melting of the frozen ceiling on which it rests. This happens in summer in just a few weeks. All these events, in particular the geomorphological ones, take place on the Sierra Nevada peaks within certain climate conditions that are at present unfavourable to the maintenance of snow on the ground in summer. These conditions could be related to recent variations in the climate, starting in the mid-XIX century and most markedly since the second half of the XX century. The work and results highlight the climate sensitivity of the peaks of the Sierra Nevada to the effect of climate change and its impact on the dynamics of ecosystems, which is a benchmark for evaluating the current evolution of landscapes Mediterranean high mountain.

In the highest land of the Sierra Nevada National Park, an experiment to monitor solifluction rates together with the thermal regime of the ground was implemented during the period 2005–2011. Data show evidence of the low activity of solifluction processes in the present-day periglacial belt of Sierra Nevada. Annual displacement rates were lower than 1 cm yr-1 both in northern and southern slopes. Solifluction was more active near snow patches and streams. Rates were also higher during snowier years. Soil temperatures showed seasonal frost occurrence, though the depth and duration of the frozen layer is strongly conditioned by the annual snow cover. Water availability appears to be a crucial factor for solifluction processes in this semiarid environment.

Soil temperatures play a key role on the dynamics of geomorphological processes in periglacial environments. However, little is known about soil thermal dynamics in periglacial environments of semiarid mid-latitude mountains, where seasonal frost is dominant. From September 2006 to August 2012 we have monitored soil temperatures at different depths (2, 10, 20, 50 and 100 cm) in a solifluction landform located at 3005 m.a.s.l. in the summit area of the Sierra Nevada (South Spain). Mean annual temperatures in the first meter of the soil ranged from 3.6 to 3.9 °C while the mean annual air temperature at the nearby Veleta peak was 0.08 °C. Therefore, these data point out the inexistence of widespread permafrost conditions today in this massif. Seasonal frost controls the geomorphodynamics even in the highest lands. Climate conditions have shown a large interannual variability, as it is characteristic in a high mountainous Mediterranean environment. These variations are reflected in the patterns of soil thermal dynamics. The depth and duration of the frozen layer are strongly conditioned by the thickness of the snow cover. The date of the first significant snowfalls conditioned the beginning and rhythm of freezing of the soil. Wet years resulted in a thick snow cover which insulated the ground from external climate oscillations and favored a shallow frost layer (2008–2009, 2009–2010 and 2010–2011). On the other hand, years with low precipitations promoted deeper freezing of the soil down to 60–70 cm extending until late May or early June (2006–2007, 2007–2008 and 2011–2012). When snow melted a high increase of temperatures of 10–12 °C in few weeks was recorded at all depths. At this time of the year, periglacial activity is enhanced due to higher water availability and the existence of freeze–thaw cycles. These were recorded mostly in spring and autumn in the first 50 cm depth of the soil, ranging from 9.8 days (at 2 cm) to 3.7 days (at 50 cm). However, the inactivity of solifluction landforms suggests that the combination of present-day soil temperatures together with moisture conditions is not favorable to promote solifluction activity in the periglacial belt of the Sierra Nevada. Future climate scenarios point to a temperature increase and precipitation decrease in the area, which would entail deeper but shorter frozen soil layers. These conditions would not be favorable for active periglacial slope processes in the Sierra Nevada.

This article discusses the methodology and techniques used in observations of permafrost, which is confined to a small enclave in south-east Spain (Corral del Veleta, Sierra Nevada, 3398 m altitude, 37°03′ N, and 3°22′ W). Several geophysical, geothermal and geomorphologic prospecting techniques were used to locate the permafrost at Corral del Veleta, an area highly sensitive to slight climatic variations, and to study its evolution under marginal conditions. The results from the application of this methodology confirm the location of Europe's southernmost permafrost remnant. Copyright © 2001 John Wiley & Sons, Ltd. RESUME Le present article discute la methodologie et les techniques utilisees pour observer le pergelisol qui se trouve dans un petit territoire du sud-est de I'Espagne (Corral del Veleta, Sierra Nevada, 3.398 m d'altitude, 37° 03′ N, 3°22′ W). Differentes techniques de prospection geophysiques, geothermiques et geomorphologiques ont ete utilisees pour localiser le pergelisol dans le site de Corral del Veleta, un endroit hautement sensible aux variations climatiques et favorables a l'etude de son evolution sous des conditions marginales. Les resultats de l'application de cette methodologie confirment qu'il s'agit du lambeau le plus meridional de pergelisol europeen. Copyright © 2001 John Wiley & Sons, Ltd.

Texto resumen.

Sierra Nevada is a protected mountain in the Iberian Peninsula classified as a Biosphere Reserve (1986), Natural Park (1989) and National Park (1999). All these environmental protection programmers are a consequence of its unique landscape in the context of the mid-latitude semiarid mountains, with enclaves of exceptional scientific and cultural value. Thanks to its high altitude, Sierra Nevada held the southernmost Quaternary glaciers in Europe, as well as it happened during the Little Ice Age. In turn, Sierra Nevada is also singular thanks to its vast cultural heritage, since very early societies settled on its slopes and valleys and accommodate their lifestyles and economy to the characteristics of this mountain environment. Currently, Sierra Nevada has become an important tourist centre and receives a large amount of visitors. This process of change has conditioned the implementation of a different economic model: it brings benefits to the populations but it involves changes in the landscape as well, sometimes questionable. From this perspective, a critical revision of the legislation is required balancing the sustainable economic development of the population and the preservation and safeguarding of the heritage values of the landscape. With this goal, we suggest creating and implementing the Sites of Geomorphological Interest.

The large number of studies of Sierra Nevada’s environmental history since the Last Pleistocene glacial period makes it one of the most intensively analysed massifs in the Iberian Peninsula. The early geomorphological descriptions have been complemented in recent decades with absolute dating techniques that have allocated in time the sequence of environmental events occurred in Sierra Nevada during the last millennia. The maximum expansion of the glaciers during the Last Glaciation took place around 30-32 ka, with a subsequent re-advance by 19-20 ka. The process of deglaciation was very fast, and around 14-15 ka the ice had almost completely retreated from the massif. Since then, with greater or less intensity and extent, periglacial processes have driven the environmental change in the massif. The coldest and wettest phases during the Holocene have favoured the development of small glaciers in the highest northern cirques. The last of these phases was the Little Ice Age, where abundant historical sources and sedimentary records exist. During the mid XX century the last glaciers melted, resulting in the complete deglaciation of the massif.

In spite of considerable advances in the knowledge and understanding of the glacial chronology of southern Europe, some very significant mountains still have to be studied. These include the Sierra Nevada, the highest mountain range in the Iberian Peninsula, located in the extreme south-east, only 170 km from Africa, where the last glaciers disappeared last century. The aim of this paper is to present a chronology of deglaciation from the Sierra Nevada based on geomorphological analysis of glacial and periglacial landforms and on 36Cl surface exposure dating, then to relate it to the historical Little Ice Age (LIA) deglaciation process reconstructed from field data and historical documentary sources.