Luis M. Tanarro

Talus Instability in a Recent Deglaciation Area and Its Relationship to Buried Ice and Snow Cover Evolution (Picacho Del Veleta, Sierra Nevada, Spain)

Abstract The southernmost glacier in Europe formed during the Little Ice Age at the foot of the north wall of Picacho del Veleta (3 398 m) in Sierra Nevada, in the southeast region of the Iberian Peninsula (lat. 37δ03‘N, long. 3δ22‘W). The glacier gradually retreated during the last century, leaving a large talus slope at the base of the wall. The unconsolidated material covering the ice masses acted as a thermal insulator. Recent bottom temperature of snow (BTS) analyses and drillings indicate that the ice still exists within the talus. Evidence from field observations made during the period 1995–2001, revealed that large mass movements occurred during the driest summers (1998 and especially, 1999 and 2000) when the talus was snow free. These conditions suggest a direct relationship between talus stability and thermal insulation from the snow cover in areas where buried ice or decaying marginal permafrost exists.

Inexistence of permafrost at the top of the Veleta peak (Sierra Nevada, Spain).

A 114.5m deep drilling was carried out in August 2000 in the bedrock of the Veleta peak, at 3380m in the massif of Sierra Nevada, Southern Spain. The objective of this work is to analyse temperatures at the first 60m depth of this drilling from September 2002 to August 2013 based on 11 UTL-1 thermal loggers located at different depths, together with air temperatures at the summit of the Veleta peak. Permanent negative temperatures have not been detected in the borehole, which shows evidence of the absence of widespread permafrost conditions nowadays in the highest lands of this massif. Bedrock temperatures oscillated between 3.2°C at 0.6m depth and 2°C at 20m below the surface. The largest temperature ranges were recorded on the most external sensors until 1.2m depth, where values reached 22.3°C. Seasonal temperature variations were significant until 10m depth. The thickness of the seasonal frozen layer was highly variable (0.6-2m) and dependent on annual climate conditions. The mean air temperature at the Veleta peak increased by 0.12°C during the study period. Bedrock temperatures followed diverging trends: a drop of 0.3-0.4°C down to 0.6m depth, a decrease of up to 0.7°C between 4 and 10m, thermal stability at 20m and a rise of 0.2°C that occurred in 2009 at the deepest sensor at 60m. The calculation of the thermal wave damping in the subsoil of the Veleta peak has allowed for quantifying the thermal diffusivity of the rock as (7.05±0.03)10(-7)m(2)/s, which means that the external climate signal arrives with an 8.5-year lag to the sensor at 60m deep. This allows to deduce a trend change in the climate of the area, moving from warmer conditions towards a trend of cooling from 2006 to 2007.

Unchanged surface morphology in debris-covered glaciers and rock glaciers in Tröllaskagi peninsula (northern Iceland)

Abstract This paper analyses changes in the surface morphology of rock and debris-covered glaciers in the Holadalsjokull and Fremri-Grjotardalur cirques near Holar village in the Trollaskagi peninsula (northern Iceland) (65°43′55″N; 19°06′49″W, 160 m), to understand the dynamics and climatic significance of these landforms. The study includes an analysis of historical aerial photographs from 1946 to 2000. The aim was to evaluate surface changes in these landforms and obtain the horizontal displacement and elevation changes of large boulders and linear features (ridges and furrows) at each date. In addition, the surface elevation differences between 1980 and 1994 were obtained from digital elevation models. The horizontal displacement results obtain a mean velocity of 0.33 m yr−1 and an average elevation difference of −0.72 m for the boulders, with the linear features advancing 14.84 m during the period 1946–2000. Except for this slow mobility, no changes occurred in the surface morphology of these landforms during the 54 years. The low displacement rates of boulders and linear features, together with the surface lowering processes observed in these landforms, indicate that widespread melting is the most important activity in the debris-covered and rock glaciers in Trollaskagi. This is confirmed by the recent formation of collapse depressions.

Geomorphology of glaciated gorges in a granitic massif (Gredos range, central Spain)

ABSTRACT A detailed geomorphological map on a 1:10,000 scale is presented for a high mountain area in Gredos range (Iberian Central System). Only few detailed geomorphological maps of the range are available despite the wide diversity of landforms. The map was created with the aid of aerial photographs, satellite images, and 3D images and verified with field surveys. The landforms resulting were classified using the IGUL (Institute of Geography, University of Lausanne) legend system combined with the legend proposed by Peña et al. (1997). As a result, 40 landforms distributed over an area of 40 km2 have been identified. The map shows the spatial distribution of different geomorphological processes that have modeled a wide variety of landforms. This variety of processes and landforms identified demonstrated that geomorphological cartography obtained by combining traditional image interpretation and GIS technology facilitates the production of geomorphological maps and the obtaining of valuable data for identify and understand surface processes and landforms.