Cirques in the Sierra de Guadarrama and Somosierra Mountains (Iberian Central System): Shape, size and controlling factors

Abstract

The Guadarrama and Somosierra mountain ranges form the eastern sector of the Iberian Central System and hosted numerous glaciers during the Late Pleistocene (MIS2). Glaciation was of low intensity with glaciers of small sizes, strongly controlled by the climatic context and the topography. This study analyses the shape, size, distribution and location of 96 cirques existing in these mountain ranges. In addition to the standard morphometric parameters and controlling factors (altitude, aspect and lithology) used in most studies, additional factors were considered here in relation to the pre-glacial relief and fracture network. The data were obtained and processed using ArcGIS 10.4 and relations between the parameters and controlling factors were evaluated using statistical methods. The results indicate that most are simple cirques, tending to isometry, with low vertical incision capacity, considerable variation in size and predominantly east-facing. In the context of the Iberian Peninsula and other European mountains, these cirques are among the most isometric, the lowest in height and present the least overdeepening. The development of these cirques has generally been the result of random combination of various factors. Thus: (i) the largest cirques are located at intermediate altitudes, with the headwall located on the main divides, at former torrential valley heads or at the headwalls of fracture corridor valleys, and are north-facing; (ii) the longest cirques are located at former torrential valley heads, on metamorphic bedrock (i.e. schists, slates) and on uniform slopes. Finally, the prevailing eastern aspects are explained by topoclimatic factors and are in agreement with previous studies, which have proposed a Circulation Weather Type (CWT) model throughout the Iberian Peninsula during the Last Glacial Period, similar to its current configuration.