Search

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.

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.

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.

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.

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.