The geomorphological role of snow since the Little Ice Age in the Sierra de Ancares (NW Spain)

P Carrera-Gómez,M Valcárcel

doi:10.18172/cig.3379

Abstract

On the Pico Cuiña cirque, Sierra de Ancares (León, Spain), the seasonal snow cover undergoes both slow and rapid mass displacements. Push associated with moving snow is responsible for an intense geomorphological activity, which is characterised by the plucking and transport of fragments of the bedrock, the abrasion of rock surfaces and the deposition of the mobilized material. Pronival ramparts are the most characteristic accumulation geoform created by pushing snow. Its study enabled us to verify the functionality of the nival processes and to prove the relative antiquity of some of them. The use of lichenometric techniques, based on the prior construction of a growth curve for lichens of the Rhizocarpon subgenus, has made possible to date sectors of the pronival ramparts. Lichenometric dates show a series of events of geomorphic activity of the snow cover fitting chronologically within the so-called Little Ice Age. It can be deduced from the observation of the current geomorphic dynamics of the snow cover that, although Little Ice Age temperature decrease might be important, particularly in the summer, the role of the variations in snow precipitation must be also taken into consideration.

Highlights

Snow plays a very important role in the current morphological evolution of the rock slopes of the Sierra de Ancares and, undoubtedly, in other sectors of the Cantabrian Mountains where its significance has gone unnoticed (Valcárcel et al, 2005; Carrera Gómez et al, 2006; Carrera Gómez et al, 2010; Santos González et al, 2010)
The combined pushing action of snow slide and full-depth avalanches cause intense erosion on the underlying rock surfaces, as well as accumulative processes at the lower sector of the area, which are directly responsible for the occurrence of debris accumulations similar to those termed by Shakesby et al (1999) as pronival ramparts (Valcárcel, 1998)
The lichenometrical dating of the different sectors of the pronival ramparts associated to the late-lying snow patch of Pico Cuiña indicate early snow-push activity coinciding, broadly speaking, with the beginning of the Little Ice Age (LIA) in Europe

Summary

Introduction

Snow plays a very important role in the current morphological evolution of the rock slopes of the Sierra de Ancares and, undoubtedly, in other sectors of the Cantabrian Mountains where its significance has gone unnoticed (Valcárcel et al, 2005; Carrera Gómez et al, 2006; Carrera Gómez et al, 2010; Santos González et al, 2010). In favourable locations where a deep snowpack is developed, snow cover can last almost half a year, attaining sufficiently large thicknesses to generate erosion and accumulation processes (Carrera Gómez and Valcárcel, 2010). Over much of this time period, mass displacements may occur, affecting the rock substrate. The combined pushing action of snow slide and full-depth avalanches cause intense erosion on the underlying rock surfaces, as well as accumulative processes at the lower sector of the area, which are directly responsible for the occurrence of debris accumulations similar to those termed by Shakesby et al (1999) as pronival (protalus) ramparts (Valcárcel, 1998).

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