Cristina García-Hernández

Spatial characterization of glacial and periglacial landforms in the highlands of Sierra Nevada (Spain)

Sierra Nevada constitutes the southernmost and highest massif in the Iberian Peninsula, with elevations exceeding 3000m. Two large glacial advances were recorded during the Last Glaciation and several minor advances occurred until the Early Holocene. Since then, periglacial activity has prevailed above 2500m. Here, we present a new and more accurate geomorphological map of the highlands of Sierra Nevada, integrating in a GIS environment i) high resolution satellite imagery, ii) topographic data, and iii) field observations. This approach has allowed a better characterization of the spatial extent of cold-climate morphogenic processes and associated landforms formed during the Last Glaciation and subsequent deglaciation. Despite its extension and high altitude, the steep relief of Sierra Nevada and its southern location conditioned a significantly lower glaciated surface (104.6km2) with respect to other Iberian massifs. We have also inferred the paleoclimatic conditions of the study area through the calculation of Equilibrium Line Altitudes (ELAs). The distribution of the lowest moraines suggests an ELA for the maximum glacial extent at 2525m in the northern slope and 2650m in the southern side, increasing towards the east. Local ELA differences are related to: (i) the influence of the warmer Mediterranean Sea in contrast to the cooler Atlantic Ocean, (ii) the climate with more continental characteristics on the northern slope, and (iii) the microscale control of the local topography. Mean annual air temperatures in the ice-free summit plateaus were between -4/-6°C during the maximum local glacial extent, determining permafrost conditions with intense periglacial dynamics. Rock glaciers and protalus lobes developed until 2500m, the lowest boundary for permafrost regime. The distribution of other glacial and periglacial landforms within the limits of the maximum ice extent provides evidence to better understand the extent of subsequent glacial stages and post-glacial landscape evolution in Sierra Nevada.

Topographic and geomorphologic controls on the distribution of vegetation formations in Elephant Point (Livingston Island, Maritime Antarctica)

This article focuses on the spatial distribution of vegetation formations in Elephant Point, an ice-free area of 1.16km2 located in Livingston Island (South Shetland Islands, Antarctica). Fieldwork carried out in January 2014 consisted of floristic surveys and designation of a vegetation map. We have examined these data in a GIS environment together with topographical and geomorphological features existing in the peninsula in order to infer the factors controlling vegetation distribution. This has allowed quantifying the total area covered by the four different vegetation formations distributed across the peninsula, proliferating mainly on bedrock plateaus and Holocene raised beaches. Grass formation is essentially composed of Deschampsia antarctica, distributed almost exclusively on raised beaches, and covering 4.1% of the ice-free surface. The remaining three formations are fundamentally composed of cryptogam species. The first of which is fruticose lichen and moss formation, present on high bedrock plateaus and principally formed by lichens such as Usnea aurantiaco-atra. The next is the crustose lichen formation, spreading on bedrock plateaus near the coast populated by bird colonies. In this case, ornitocoprophilous lichens such as Caloplaca regalis, Xanthoria elegans and Haematomma erythromma are predominant. Together, both formations have colonised 5.1% of the peninsula. The last variety, moss carpet and moss cushion formation, occupies 1.4% of the deglaciated surface, spreading primarily in flooded areas, stabilised talus slopes, and bedrock plateaus as well. Therefore, the total surface colonised by vegetation is 12.2ha, which comprises 10.5% of the peninsula. Due to the retreat of the Rotch Dome glacier, 20.1ha remain ice-free since 1956 (17.3% of the deglaciated area). Ever since, even though the Antarctic Peninsula has registered one of the most significant temperature rises on Earth, vegetation has only colonised 0.04ha of this new space, which merely represents 0.3% of the vegetated area in Elephant Point.