Classification of Andean Permafrost, an attempt

DARIO TROMBOTTO LIAUDAT

Göttingen, Alemania

Congreso; International Lateinamerika_Kollokium 2009; 2009

Geowissentschafliches Zentrum der Universität Göttingen

This is an attempt to present a classification of permafrost types with the help of different examples and study cases of mountain permafrost in the Andes, which may be applied for permafrost mapping and which would express periglacial geomorphology as well as physical cryogenic characteristics of mountain permafrost. This classification is different from the classification presently applied to Arctic regions. According to the MAAT map the area with Andean permafrost in South America represents an important area which is considered in the present work. It constitutes an enormous water supply and is of crucial hydrological and economic importance for human settlements near the Andes. At first glance mountain permafrost may be divided into two large environments, one with permafrost  in situ and the other associated with the movement of frozen cryosediments and ice, known as creeping phenomena, and the landforms identified as rockglaciers, or glaciares de escombros or litoglaciares as regional names. Both environments are completely different one from the other and the rockglaciers, in form of creeping permafrost, may reach down to heights in the mountaineous systems where permafrost in a paraperiglacial environment does not exist anymore. A detailed analysis of mountain permafrost however, allows to identify particular and exceptional situations which are different from the ones mentioned before. The occurrence of Andean permafrost up to the high frozen summits and following the altitudinal curves is of „discontinuous“ character and is optimized in a permafrost type called "„quasi-continuous permafrost“ by some authors. This kind of permafrost is influenced mainly by topography, geomorphology, exposition, petrology and surface energy balance, and is the most reliable and outstanding representative of frozen ground to be mapped. Scarce meteorological data, poor topographical maps and the inaccessability of some areas by land or air complicate the task. Nevertheless, applying classical geomorphological and geophysical methods, modeling of ground thermal state as well as direct observations through superficial drillings and temperature measurings pilot areas may be selected to identify the permafrost types that will be characterized. Certain thermal soil conditions also cause zonal or azonal permafrost in a type considered to be insular. On the other hand the absence of visible ice (or soils with very little ice content) reminds of a variety of dry permafrost which also appears in certain sites with quasi-continuous permafrost. On the other hand, looking at the „rockglacier or creeping permafrost pattern“ of the Central Andes of Mendoza, it becomes obvious that the area is one of the most significant areas of this kind on our planet. In this last case degraded permafrost may also be identified through the activation and enlargement of ancient thermokarst forms. These landforms do not only create a characteristic landscape, they are also most significant for the climatic and palaeoclimatic history of the region.