Introduction

This chapter provides an introduction to mountain permafrost and a review of recent scientific progress. In it, we use rather few references to the scientific literature in order to make the text more easily readable. For further reading, we recommend, Haeberli et al. (2006), and Gruber and Haeberli (2007), two recent reviews in which the current state of the art is discussed in depth and in which extensive references can be found.

Permafrost is lithosphere material that permanently remains at or below 0°C. In this context, "permanence" is often defined to be two or more consecutive years, in order to establish a minimum value for avoiding the effect of only one cold and long winter being considered permafrost. By this definition, permafrost can - but does not need to - contain water or ice. Based on this purely thermal definition, every substrate is permafrost when subject to certain temperature conditions. By definition, glaciers are not permafrost. Most permafrost areas experience seasonal thaw, during which surface temperatures rise above the melting point and a certain volume of material directly beneath the surface is thawed. The material that is subject to seasonal temperature changes crossing 0°C is termed the "active layer", and has a typical thickness of 0.5-8 m.

Mountain permafrost is simply permafrost in mountain areas. It can be situated at low or at high latitudes and in the Arctic or Antarctic - we define mountain permafrost based on the influence that mountain topography has on its properties. Many other terms that are commonly used to classify certain types of permafrost, such as Arctic, Antarctic, polar, or plateau, can be applicable at the same time. These qualifying terms are useful to describe properties, but not to sharply dissect geographic or scientific space. The dominating characteristic of mountain areas and mountain permafrost is their extreme spatial variability with respect to nearly all surface and near-surface characteristics and properties. Examples of this are:

Stephan Gruber

Glaciology, Geomorphodynamics & Geochronology, Department of Geography, University of

Zurich, Winterthurerstr. 190, CH-8057 Zurich, Switzerland

[email protected]

R. Margesin (ed.) Permafrost Soils, Soil Biology 16,

DOI: 10.1007/978-3-540-69371-0, © Springer-Verlag Berlin Heidelberg 2009

(a) Elevation itself, as well as other geometric measures such as slope, aspect, curvature, or roughness

(b) Surface micro-climatology, which is dominated by differences in elevation (strongly affecting long-wave radiation and turbulent fluxes) and in short-wave solar irradiance due to shading and variable angles of insolation

(c) Subsurface material thickness and composition, which is dominated by diverse processes of erosion, grain-size fractionation, and deposition

(d) Water availability, which is affected by contributing area, surface shape, and subsurface material

(e) Snow cover, which is influenced by surface micro-climatology, precipitation patterns, wind drift and avalanches.

All these properties affect ground temperature and, as a consequence, permafrost occurrence and characteristics. Water in mountain permafrost areas drains quickly, and the water content of mountain permafrost soils is usually small when compared to the often-waterlogged substrates found in Arctic lowland areas. Data on mountain permafrost are often sparse and biased to areas with existing infrastructure, because access and measurements on most mountain slopes are difficult and expensive. This is especially true for mountain areas outside Europe, where access infrastructure is sparse.

Permafrost is invisible because it is a thermal phenomenon. It is difficult to assess at the ground surface, because it usually lies beneath an active layer. Furthermore, its reliable detection requires temperature measurements spanning at least 2 years in order to understand the seasonal temperature evolution or, alternatively, measurements at greater depths. The depth of zero annual amplitude (ZAA), where the seasonal temperature fluctuation is damped to less than 0.1°C, is usually about 10-15 m below the surface. Below this depth, single measurements can establish the presence or absence of permafrost. However, great care has to be taken to minimize the thermal disturbance caused by drilling or measuring. The difficulty in detecting permafrost, together with expensive access and extreme lateral variability, makes permafrost research in mountain areas a difficult endeavor. Understanding and predicting spatial patterns of permafrost occurrence and characteristics needs to be based on a combination of measurements and models, because the systematic variability caused by topography dominates spatial patterns already over short distances.

The scientific and practical relevance of mountain permafrost has many facets. Permafrost is an important element of landscape evolution because of the characteristic landforms such as rock glaciers, push-moraines, ice faces and hanging glaciers, which are connected to its existence, and because it affects long-term sediment transfer mechanisms. This alteration of sediment transfer systems (Fig. 3.1) leads to changing regimes of natural hazards, such as rock avalanches and debris flows. Here, permafrost warming and thaw has the potential to alter frequency and magnitude of events, and to affect geographic areas that have previously been considered safe based on historical evidence. The safe construction and maintenance of infrastructure in mountain permafrost requires special techniques for the handling of thermal perturbations and ground movement. Furthermore, in some areas, land cover and land use are connected to the presence of water tables perched on permafrost.

Fig. 3.1 North-exposed steep bedrock containing permafrost beneath the top station of the Corvatsch cable car, Switzerland. The debris on the small glacier is almost exclusively due to strong rock fall activity during 2003-2006. Most likely this is caused by permafrost degradation
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