Mountain Hazards associated with Permafrost Degradation

Term Paper (Advanced seminar) , 2008 , 13 Pages , Grade: 1,3

Geography / Earth Science - Physical Geography, Geomorphology, Environmental Studies

Permafrost degradation due to global warming is a widespread phenomenon in recent dec-ades (Lemke et al. 2007), latitudinal as well as altitudinal. Dealing with permafrost related mountain hazards requires knowledge on the exact permafrost distribution throughout mountain areas. Therefore, a monitoring project on European permafrost distribution will be discussed. Furthermore, it has to be determined, what mountain hazards exist in general and which of them could be affected by permafrost degradation in terms of frequency and/or intensity. Two different types of mountain hazards will be examined in detail: rockfall and outburst flood of permafrost dammed lakes.
Moreover, the impact of mountain hazards on the society will be marked. The focus will be on investigations which can be done, before undertaking engineering projects. After that a brief overview on perspectives in terms of climate scenarios and their possible impact on permafrost degradation and mountain hazards will be given. Finally, some concluding statements will be made.

Outline

1. Introduction

2. Permafrost distribution and monitoring in mountain areas

3. Permafrost related hazards
3.1 Mass movements/ Rockfall
3.2 Outburst floods

4. Hazard and risk assessment

5. Perspective

6. Conclusion

References

1. Introduction

Permafrost degradation due to global warming is a widespread phenomenon in recent decades (Lemke et al. 2007), latitudinal as well as altitudinal. Dealing with permafrost related mountain hazards requires knowledge on the exact permafrost distribution throughout mountain areas. Therefore, a monitoring project on European permafrost distribution will be discussed. Furthermore, it has to be determined, what mountain hazards exist in general and which of them could be affected by permafrost degradation in terms of frequency and/or intensity. Two different types of mountain hazards will be examined in detail: rockfall and outburst flood of permafrost dammed lakes.

Moreover, the impact of mountain hazards on the society will be marked. The focus will be on investigations which can be done, before undertaking engineering projects. After that a brief overview on perspectives in terms of climate scenarios and their possible impact on permafrost degradation and mountain hazards will be given. Finally, some concluding statements will be made.

2. Permafrost in mountain areas

The distribution of permafrost is the result of the interaction of a number of factors: Altitude, slope aspect, mean air temperature, solar radiation, snow cover, snow redistribution, wind and avalanches.

The occurrence of permafrost in middle latitudes is limited to mountain chains. Most research is done in Europe (Harris et al. 2001a; 2001b; 2003; 2005). The data density outside of Europe is markedly lower. Even the recent IPCC (Lemke et al. 2007) report concentrates mainly on data from European and some Asian mountain chains. A study by Li et al.( 2008) revealed permafrost trends for China, which are similar to Europe.

The lower altitudinal limits of permafrost in Europe span a range from 1500 m in southern Norway to 2500 m in the southern Swiss Alps. Looking at the spatial distribution of permafrost, there is no continuous permafrost in mid-latitude Europe. This is caused by the steep terrain, the high solar radiation throughout summer and relatively high mean annual temperatures. Therefore, the spatial distribution of permafrost is discontinuous or sporadic. Another striking feature of permafrost in European mid-latitude mountains is that the permafrost temperature is just a few degrees below 0°C. Hence, even slight climatic shifts can cause major changes in the depth of seasonal thawing and finally permafrost degradation.

The Permafrost and Climate in Europe (PACE) Project

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The PACE (Harris et al. 2001b) consists of a transect of instrumented permafrost boreholes across the higher mountains of Europe (fig.1). The transect starts in Svalbard, includes the Scandinavian mountains, the Alps and ends in the Sierra Nevada in southern Spain. The aim of the project is to improve the knowledge on permafrost and, finally, the assessment of related hazards.

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Fig. 1: Sites included in the PACE project. Harris et al. 2003

The project contains several complementary investigations like geophysical surveys, microclimatic investigations, numerical modeling of permafrost distribution and physical modeling of permafrost related slope instability. The first results (Harris et al. 2003) showed that the thermal permafrost gradients are consistent with the 20th century surface warming. Important to notice is further the uniqueness of the thermal profile at each site (fig.2), which has a huge impact on risk assessment and related investigations required for determining the site specific features. For example, each thermal profile in fig. 2 indicates a site specific depth of the lowest temperature as well as different permafrost temperatures and active layer depths. Factors influencing the thermal profiles are geothermal heat flux (warming the permafrost at its bottom), variations in lithology, the ground surface temperature and past changes of surface temperatures as well (Harris et al. 2003). Therefore, a big difficulty in predicting future permafrost changes is that the permafrost/thermal relationship is not in equilibrium, rather it is in part a function of the climate over the last decades and centuries (Harris et al. 2005).

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Fig.2: Thermal profiles measured at several sites of the PACE project borehole network. Numbers on the profiles refer to fig.1. Harris et al. 2003

3. Permafrost related hazards

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Figure 3 summarizes some of the most common hazards occurring in mountain areas. This includes storms, volcanic eruptions, earthquakes, glacier advance, snow avalanches, lake outburst floods and mass movements. However, only two of them are directly related to permafrost degradation: mass movement and outburst floods.

Mass movements can be further subdivided into rockfall, debris flow, landslides and rock avalanches; outburst floods into floods resulting due to thermokarst or due to failure of moraine-dammed lakes. An important point is that chain reactions of different hazards (e.g. rock fall in lakes causing floods) illustrate another issue, which has to be taken into account.

3.1 Mass movements/ Rockfall

Mass movements occur on different temporal and spatial scales. They span a range from solifluction and rock glacier movement with slow velocities to debris flows or rockfall marked by very high velocities.

The thawing reduces the strength of ice-rich sediment and bedrock. That leads to thaw consolidation in ice-rich soils. The slope failure ranges from shallow translational landslides in finer-grained sediment to rapid mudflows and debris flows (Harris 2005). Thereby, the critical issue is the ice-content of the frozen ground (Harris et al. 2001). Slope failure can even dam rivers. This results in the potential of floods as a consequence of sudden release of huge amounts of water in the course of dam failure.

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• College: University of Kent (Department of Geography)
• Course: Cryospheric Processes and climate change
• Grade: 1,3
• Author: Eric Petermann (Author)
• Publication Year: 2008
• Pages: 13
• Catalog Number: V119367
• ISBN (eBook): 9783640239313
• ISBN (Book): 9783640239504
• Language: English
• Tags: Mountain, Hazards, Permafrost, Degradation, Cryospheric, Processes