Dedradation of buried ice and permafrost in the Veleta Cirque (Sierra Nevada, Spain) from 2006–2013

Abstract

Abstract. 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.

Monitoring permafrost and periglacial processes in Sierra Nevada (Spain) from 2001 to 2016

“…The central aim of this work is to provide a review and new data regarding present‐day activity of periglacial processes and their relationship with the ground thermal regime in different landforms across the Sierra Nevada (Table ). We update data and provide the most extensive and complete review of the thermal regime of a southern massif in Europe, complementing previous works …”

“…Glacial activity reached maximum development in the high areas of the valleys, in their headwaters and slopes above 2500 m. Large cirques were carved by Quaternary glaciers, which deposited sediments in the valley bottoms forming different moraine systems above 1900–2000 m. According to 10 Be cosmogenic dates, sedimentary and erosive records show ages of glacial phases ranging from 135 ka to 300 years . This indicates the occurrence of glacial activity since phases prior to the Last Glaciation up until the LIA, when those summits intensely affected by periglacial processes included small glaciers in sheltered areas of the highest glacial cirques, in some of which remnants of ice still persist under a thick debris cover . According to historical documents, the lower limit of the periglacial processes in the mid‐19th century was probably located at around 2435 m, ca.…”

“…This includes the basin of the Guarnón cirque, which is affected by active paraglacial processes. During the LIA it included a small glacier, from which some relict ice and permafrost still remain under debris cover Rio Seco cirque (3000–3050 m) and headwaters of the San Juan valley (2800–2900 m) …”

“…In the Veleta geomorphological unit, the rock glacier located in the Veleta cirque was monitored by tracking and controlling fixed monitors installed on its surface, which also allowed us to analyze the volumetric changes taking place there. The values were obtained based on different geomatics techniques, including classic total station topography, Global Navigation Satellite System and photogrammetry and Terrestrial Laser Scanner, which have been described in detail by Gómez‐Ortiz et al This was complemented with tracking of summer snow cover in the Veleta cirque obtained through geo‐referenced oblique and vertical digital photographs taken from fixed points . Monitoring of the displacement rates of solifluction lobes in the Rio Seco and San Juan valleys was carried out following the procedures described by Oliva and Oliva et al…”

“…In the Sierra Nevada, due to its latitudinal position and geographical characteristics, changes resulting from the end of the LIA still have a significant impact on ecosystem dynamics typical of high semi‐arid Mediterranean mountains. This is particularly relevant at summit level where periglacial processes are the main driver of environmental dynamics . From this perspective, since the early 2000s we have been monitoring different landforms of the Sierra Nevada's current periglacial belt that are located in cirque floors, headwaters of valleys and summit plateaus.…”