Post‐little ice age paraglacial processes and landforms in the high Iberian mountains: A review

Abstract

Three Iberian mountain ranges encompassed glaciers during the Little Ice Age (LIA):the Pyrenees, Cantabrian Mountains, and Sierra Nevada. The gradual warming trend initiated during the second half of the 19th century promoted the progressive shrinking of these glaciers, which completely melted during the first half of the 20th century in the Cantabrian mountains and Sierra Nevada and reduced by 80% of their LIA extent in the Pyrenees. In these formerly glaciated environments, the transition between glacial and periglacial conditions results in an accelerated paraglacial readjustment, with very active geomorphic processes. Cirque walls generate a large amount of sediments through rock-falls and slides. LIA moraines, devoid of vegetation and composed of highly unstable sediments, are being intensely mobilized by slope processes. Inside the moraines, the shrinking of LIA glaciers favoured the development of buried ice patches, with permafrost-related landforms, small periglacial features generated by solifluction, and cryoturbation processes and remarkable hydrological changes. Present-day morphodynamics is mostly related to seasonal frost, though patches of permafrost have formed in contact with the buried ice, undergoing a process of degradation because it is not balanced with present-day climate. This is reflected in the occurrence of multiple collapses and subsidence of the debris cover where the frozen bodies sit. Next to the small glaciated environments in the highest Pyrenean massifs, there is a permafrost belt undergoing also rapid geomorphic changes. Based on the observed processes, we discuss spatio-temporal patterns of paraglacial readjustment in Iberian mountains and compare it with other midlatitude mountain environments.

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

“…The degradation of relict ice and permafrost has been also detected in other Iberian high mountain environments glaciated during the LIA, such as in the Pyrenees and the Cantabrian Mountains . Similarly, evidence of degradation of perennial ice deep in the ground has also been reported in several karstic environments across the Mediterranean region: recent studies have reported shrinkage of the ice volume stored in ice caves as well as a decrease in the extent of permanently frozen ground existing in these sporadic permafrost environments in the Cantabrian Mountains, Pyrenees, Italy, Croatia and Greece, among others.…”

“…Lanjarón, Rio Seco and Dílar valleys) . As occurred during the post‐LIA phase in the rock glacier that exists in the Veleta cirque, the formation of permafrost‐related features – including rock glaciers and protalus lobes – must have been conditioned by highly active paraglacial processes, with very unstable rock walls that produced large quantities of sediment, which must have trapped ice that no longer featured glacial dynamics . This process has also been detected in other environments of the Iberian mountains, such as the Central and Eastern Pyrenees .…”

“…As in other Iberian mountains such as the central sector of the Cantabrian Mountains in the Picos de Europa, the occurrence of permafrost is strongly conditioned by past geomorphological processes, namely the existence of glaciers during the LIA . This is also the case in several massifs in the Central Pyrenees …”

“…This facilitated slow displacement of the surface blocks, deformation of the frozen mass and the formation of an incipient rock glacier . In the nearby Mulhacén cirque, where a small glacier disappeared around 1710 towards the end of the Maunder Minimum, the paraglacial processes associated with the deglaciation of the enclave fostered the development of a protalus lobe at the foot of the steep northern face of Mulhacén peak …”

“…This temperature increase since the end of the LIA is much more pronounced in the mountain areas than in the lowlands, which has led to changes in the intensity and spatial distribution of cold geomorphological processes . It has also resulted in an intensification of the paraglacial response, an accelerated degradation of alpine permafrost, and alterations in biogeographic dynamics in European high mountain environments, with a geographic redistribution of some plant species that tend to move up to higher altitudes . 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.…”