Hohe Tauern National Park (Austria)

Debris flows in the mountain permafrost zone: Hohe Tauern national park (Austria)

M. Hirschmugl Institute of Geography and Regional Sciences, University of Graz, Austria

ABSTRACT: The existence of permafrost and its degradation can have an important influence on the evolution of debris flows in high mountain areas. Areas have been selected by visual interpretation of remote sensing data, which show an interrelation between permafrost and debris flows. Their hazard potential has been estimated in relation to threat to humans and infrastructure. The investigation area comprises the Carinthian parts of the Hohe Tauern national park. Moreover the work should provide data for further research on permanent debris flow- monitoring in a highly sensitive ecosystem.

1 INTRODUCTION traditionally cultivated area with settlements and Alpine farming up to high altitude. According to a case Debris flows occur in mountainous environments study in this area (“Seebachtal”), the upper borderline throughout the world and may cause devastating effects of extensive seasonal pasture farming is between 2400 on the people who live nearby. Beside the main factor and 2700 m a.s.l., depending on aspect (Egger 1996). of precipitation, the amounts of water released from In 1984, a large national park has been established the melting of snow and ice can affect the formation of debris flows (Zimmermann 1990). Perennially frozen slopes occurring in the Alps above the timberline often consists of ice-rich debris or morainic material with temperatures close to the melting point. Therefore, Vienna these localities, especially those near the lower boundary of permafrost, are expected to be the most sensitive to degradation processes (Haeberli 1992, Veit & Höfner 1993). Salzburg Thus, the occurrence of debris flows arising due to East melting permafrost seems to be related to the amount Tyrol Carinthia of water stored within a previously frozen slope (Zimmermann & Haeberli 1992). Figure 1a. Study area (Austria). This study was carried out within the scope of a sem- inar and is based on a visual interpretation of remote sensing data. It should give a birdseye view of a larger Fusch Rauris area by using a low cost method. Zones have been detected, which show an interrelationship between per- Hüttschlag mafrost, debris flows and human infrastructure. In Salzburg Badgastein consequence, a closer look will be given to these rela- Muhr tions in the particular region. The main goals of the Großglockner Gr. Hafner Heiligen-Sonnblick Ankogel investigation are to focus on the situation in the Matrei blut Carinthian part of the Hohe Tauern national park in Kals Grosskirch- Mallnitz Malta heim Austria and to provide data for further research. East- Mörtschach Hopf- Tyrol garten Winklern 2 STUDY AREA AND GENERAL Nussdorf- Debant Iselsberg- Stronach Carinthia CONDITIONS Lienz N 5 km Dölsach Spittal The study area, part of the Hohe Tauern range, is Study area regional borders national park outside the Study area rivers located in the northwestern part of Carinthia and belongs to the Central Alps (Fig. 1a). It concerns a Figure 1b. Study area in detail.

413 within this region to protect this particular mountainous area (Fig. 1b). Nevertheless, the development of tourism and the use of hydroelectric power increased the number of visitors, and resulted in higher infrastructural facili- ties within the area. Therefore, natural hazards, such as debris flows can nowadays have more grave effects on human beings than in former times. The study area stretches from about 1100 m up to 3797 m a.s.l. In general, the region mainly consists of crystalline parent rocks. Figure 1b shows the area of the national park Hohe Tauern, the investigated part has been shaded and consists of two sections:

– parts of the Ankogel-Mountains (ca. 303 km2), and – parts of the Großglockner- and Schober-Mountains (ca. 301 km2). Figure 2. Visual interpretation of remote sensing data Recently, this region has also been involved in other with numbered debris flows. investigations concerning permafrost, which have been carried out at the University of Graz (Lieb 1998, Table 1. Construction of the table with important Krobath et al. 2003). With altitudes up to 3797 m a.s.l., parameters. the region investigated belongs to a high mountain H_catchment area, where both permafrost and debris flows are likely H_min H_max area to occur. In Switzerland, where the population in the Flow No. (m a.s.l.) (m a.s.l) (m a.s.l) Pf Alpine environments is quite dense, debris flows can cause much damage and even loss of life. Hence, the 200 2010 2320 2880 x potential for instability of Alpine permafrost has been 201 2050 2320 2820 x identified as being an issue of natural importance 202 2200 2600 2800 y (Haeberli et al. 1999). In this paper it will be shown 203 2180 2660 2800 x 204 2220 2560 2800 n how the hazard of debris flows connected with permafrost can have an influence on human beings or infrastructure. the basic question of possible hazards in these critical zones.

3 PROCEDURE 3.2 Debris flows

3.1 General remarks Debris flows generally occur on steep slopes and have been described as rapid viscous flows of granular Air-borne remote sensing data, namely 103 already solids, water and air. The flows consistency resembles pre-processed true-colour images (scale 1:5000) from a fast moving mixture of loose sediment and, mostly August 1998, have been visually interpreted. Initially, rather small amounts of water (Haeberli 1991). The all visually recognizable debris flows in the study area driving forces of slope stability include self-weight were digitized by using the GIS software ArcView. gravity, shear resistance and high pore water pressure. Figure 2 shows a sample area with five numbered The presence of water in slope materials is an debris flows. important cause of their stability or instability, In the next phase, a table including appropriate because water causes various forces in the soil. If the attribute data was created. The characteristics of every pore spaces in the soil matrix are not completely filled flow, such as the highest point of the catchment area, with water – the soil is unsaturated – and a suction the minimum and maximum altitude of the debris force is exerted, which tends to draw the soil grains flow itself, as well as a figure for the estimated more closely together. This suction is caused by a permafrost occurrence were included in this table process called capillary tension. However, if the pore (Table 1). spaces are completely filled with water, then the soil Finally, the possible hazard to all kind of human is said to be saturated. In this state, the water exerts a installations was estimated and combined with the other pressure within the pore spaces that tends to produce data to lead to a summarizing statement concerning forces that push the grains apart. Since the effective

414 stresses acting between the soil particles directly frozen slopes (Haeberli 1990, 1991, 1992). Therefore, influence the shear strength of the soil, if pore water a melting of underground ice can lead to higher insta- pressures reach high levels in the slopes, these materi- bility of the slopes mentioned above. als may become unstable. Based on various classifica- Concerning the occurrence of permafrost, latest tion schemes, the causes of mass movements can be investigation results from the study region have been grouped into the following two categories: taken into consideration. In general, discontinuous permafrost can be expected above 2500 m a.s.l. in the 1. So-called permanent factors: central section of the Austrian Alps, which covers the Tectonics, changes in stress and strain, weathering, Hohe Tauern range (Lieb 1998). However, the altitude changes in vegetation, root pressure as well as frost of permafrost occurrence strongly varies with aspect. and ice with the connected freezing and thawing Referring to other studies (Haeberli 1975, Lieb processes. 1998) surfaces without vegetation can in a first approx- 2. Induction factors: imation be considered as areas of potential permafrost Long term and intense precipitation, snow melt, occurrence in the Alps. This fact has also been proven undercuts, wash-outs, joint water or ground water, by current large-scale permafrost investigations (BTS earthquakes or human intervention, e.g. construc- measurements) in the Doesen Valley (Lieb 1998) and a tion (Buchroithner & Granica 1995). modelling of permafrost distribution in the Reisseck So the major causes for the triggering of flows tend to mountain range (Krobath et al. 2003). be the presence of abnormally high amounts of water. Simultaneously with altitude and aspect, vegetation As mentioned above, freezing and thawing processes cover has been used as the most important indicator as well as snow melt can be important to provide the for the assessment of the occurrence of permafrost in critical amount of water (Arenson & Springman 2000). the adjacent areas of debris flows. Beside the availability of water, large amounts of Three categories were established as permafrost material and the factor of mobilization could be the probable (y), no permafrost (n) and occurrence unsure causes for movements, too. The factor of mobilization (x). For further projects, small-scale permafrost mod- depends on some parameters, such as grain size and elling of the entire region, based on an exact digital looseness of the detritus, presence of water leakage, terrain model would doubtless lead to a higher accuracy presence and type of vegetation and steepness of the of differentiation. slope. Steep slopes mainly consisting of debris with inclination higher than about 35% tend to instability 3.4 Danger (Stötter 1994). This is a function of the soil and the groundwater conditions (Arenson et al. 2002). Slopes A hazard evaluation has been performed for every containing permafrost are still stable even if the inclina- single debris flow and added to the table (Table 2). tion is far above this threshold. The investigated debris Two different types of danger could be identified: flows occurring in summer 1987 in the Swiss Alps showed inclinations between 23 and 65%, whereby in – Column “Danger 1” represents danger to all kinds of most of the cases the theoretical minimal inclination of human infrastructure, such as huts and forest trails, 27% was far exceeded (Haeberli et al. 1991). in the immediate environment of the debris flow. – Column “Danger 2” concerns debris flows, which could reach and destroy permanent settlements or 3.3 Permafrost traffic life-lines. Two possibilities are provided for both columns: (y) The occurrence of permafrost in the Alps is continu- for existing danger and (n) for no danger. To estimate ous above 3300 m a.s.l., and discontinuous down to the possible presence of a danger, following factors 2400 m a.s.l. (Dramis et al. 1995). Perennially frozen, have been taken into consideration. Firstly, the distance loose deposits, often situated on steep slopes are usu- ally supersaturated with ice (Haeberli et al. 1990). In addition, these high amounts of underground ice exist Table 2. Estimation of the potential danger & additional at temperatures, which are rather close to the melting information. point. The combination of relatively warm temperatures Flow no. Danger 1 Danger 2 Information and high ice contents on steep slopes makes Alpine permafrost vulnerable to even small climatic changes. 200 y n long, flat valley The atmospheric warming during the 20th century has 201 y n long, flat valley probably induced a shifting in altitude of the lower 202 y n long, flat valley boundary of Alpine permafrost, causing degradation 203 y n long, flat valley 204 y n long, flat valley of underground ice and destabilization of formerly

415 between the deposition area of the respective debris 2751-2850 17 flow and the possibly endangered area is a major input 2651-2750 30 parameter. Secondly, there is a strong interaction 2551-2650 between distance and slope: in general, the steeper the 54 slope, the farther the runout of the flow. Vegetation 2451-2550 64 cover in the lower parts of the debris flow and the pos- 2351-2450 47 sibility of sediment storage can also play important flow) 2251-2350 35 roles. The latter, i.e. a lake, a reservoir, a long, flat val- 2151-2250 7 ley or a large hollow, proved to be decisive factors for 2051-2150 11 the assessment, because these possibilities of sediment 1951-2050 8 storage reduce the danger. Altitude in m above sea level (highest point of the visible debris 1850-1950 7 The “Information” field in the table reveals the most 010203040506070 important and finally decisive factor for the estimation No. of debris flows of each debris flow. In addition to this, the kind of endangered things can also be mentioned in this column. Figure 3. Distribution of the 296 debris flows in terms Figure 2, Table 1 and Table 2 show the whole procedure of altitude levels. of data capture, whereby Table 2 shows examples of the just described danger estimation process. Table 3. Distribution of danger-classified debris flows After the interpretation of 103 images, 296 debris connected with the existence of permafrost. flows and their attributes were integrated into the data- base. At this point, it has to be emphasized that visual Number of debris flows interpretation is always a subjective process, whereby Permafrost occurence Danger 1 Danger 2 the quality of the results highly depend on the experi- ence of the interpreter. In consequence, there is defi- Permafrost probable (y) 35 6 nitely a need for the development of automatic and Permafrost possible/unsure (x) 44 6 semi-automatic methods, which would lead to more No permafrost expected (n) 60 30 objective results. Sum 139 42

4 RESULTS catchment area and the danger to human infrastructure. Before focusing on this topic, the general classi- First results of the investigations are presented in the fication of the debris flows investigated according to following section. As research has just started, only permafrost occurrence should be mentioned. Almost some basic figures can be given. One example of a half of the flows definitely have no connection to per- debris flow is representative for these results. Further mafrost. Nearly 30% show signs of permafrost occur- analysis has not been performed recently. rence in adjacent areas. No distinct statements can be made for the remaining cases. 4.1 Distribution above sea level Table 3 shows how many debris flows are classified as hazardous and how they are distributed over the per- One of the basic results, the distribution of the debris mafrost areas. As the figures demonstrate, 47% of the flows (highest point of the visible debris flow) above debris flows (139) in the investigated area can endanger sea level, is shown in Figure 3. human infrastructure. Less than a third of these (42) As shown in this figure, the majority of the debris can be regarded as being hazardous to the built envi- flows in the observed area occur in altitudes between ronment according to the meaning of “Danger 2”. 2250 and 2750 m a.s.l. Below 2250 m a.s.l., only few Figure 4 displays the distribution of the 42 have been investigated, because in principle, the study “Danger 2” evaluated debris flows, in terms of whether is focused on high mountainous areas. permafrost is expected at the location. Above a boundary of about 2750 m a.s.l., glaciers Most of these cases (30 debris flows, i.e. 72%) are and rock faces in these very high altitudes do not give debris flows without any connection to permafrost, much space or many loose deposits for the formation because of their occurrence in lower altitudes. Popula- of debris flows. tion is denser and there is more human infrastructure in these areas. For the categories “existing per- 4.2 Permafrost and hazardous debris flows mafrost” (y) and “possible permafrost” (x) six debris flows fall in each of them. In conclusion, it can be One of the most interesting issues is the correlation stated that permanent settlements and roads are hardly between possible permafrost occurrence in the threatened by debris flows coming from the “possibly

416 Figure 4. Distribution of the 42 “Danger 2” – classified debris flows in terms of existence of permafrost. permafrost zone”. This case was counted only 12 times, which corresponds to 4%. Figure 5. Aerial image data (1998): Debris flows near the On the other hand, the investigation also showed Pasterze glacier, south of the “Sandersee”. that there is a risk for seasonal settlements and other human infrastructure in high mountain regions. Table 3 records that 139 out of 296 debris flows can be regarded as hazardous, analogous to “Danger 1”. This number still includes debris flows from the region, where no permafrost can be expected. But even after subtracting the latter, there remain 79 cases, possibly originating from the permafrost zone. From this, it follows, that the danger for seasonal settlements, forest trails or huts is quite high: 27% of the debris flows were counted in this category.

4.3 Example: Debris flow near the Pasterze glacier Figure 6. View South-East: Debris flows below the “Schwert-eckkees” glacier, south of the “Sandersee”. One debris flow has been selected for illustration. This flow is situated on a north-facing slope close to the Pasterze glacier in the Großglockner moun- This example demonstrates the complexity of the tains, with a starting zone at about 2500 m a.s.l. The relations between permafrost, debris flows and haz- missing vegetation cover and the nearby glaciers ard, which will lead to significant economic loss. (“Schwerteckkees”) lead to the assumption that this debris flow is definitely originating in the permafrost zone. Figure 5 shows the interpreted image data in this 5 CONCLUSIONS particular area, Figure 6 displays the surroundings of the concerned debris flow. Areas near the permafrost boundary, especially steep Permafrost degradation in this area can therefore slopes, are most sensitive to degradation processes partly become a trigger for debris flows. The danger and corresponding destabilization (Haeberli 1992). can be considered as rather low because of the capacity Based on the visual interpretation of the air-borne of the “Sandersee” lake for sediment storage. Neverthe- remote sensing data in this study, the assumption was less, the high sediment input from all of the debris confirmed that permafrost degradation can lead to an flows in this area and from the Pasterze glacier to the increasing number of debris flows in mountainous “Sandersee” and further to the “Margaritzenstausee” regions at high altitudes. has been shown to be a problem for the hydropower According to this investigation, it could be shown company. Some years ago, this company tried to solve that huts and forest roads are mostly endangered at the sediment difficulties by opening the floodgates to these high altitudes. In some cases the occurrence of allow large quantities of mud to flow out of the reser- debris flows increases proportionally with the melting voir. This measure caused an ecological disaster in of underground ice and degradation of formerly frozen the “Möll”-river. slopes, which could endanger settlements or roads.

417 It is foreseen, that semi-automatic methods should Internationale Fachtagung von 11. Mai 1990. be adopted in future, necessitating further research in Mitteilungen der Versuchsanstalt für Wasserbau, the meantime. These methods should at least include a Hydrologie und Glaziologie 108: 71–88. permafrost map of the territory based on a digital ele- Haeberli, W., Rickenmann, D., Zimmermann, M. & Rösli, U. vation model, which so far only exists for some parts 1991. Murgänge. In: Ursachenanalyse der Hochwasser 1987 – Ergebnisse der Untersuchungen. Mitteilungen of the entire study area (Krobath et al. 2003). First des Bundesamtes für Wasserwirtschaft 4: 77–88. investigations on the automatic detection of the debris Haeberli, W. 1991. Permafrost und Murgänge in der alpinen flows have been started, but so far they have not Periglazialstufe. Bündner Wald 44(6): 59–65. yielded the expected results. Haeberli, W. 1992. Possible Effects of Climatic Change on This project can be seen as a first step to provide the Evolution of Alpine Permafrost. Catena data for further research for permanent monitoring, Supplement 22: 23–33. forecasting and modelling of debris flows within the Haeberli, W., Kääb, A., Hoelzle, M., Bösch, H., Funk, M., permafrost zone in this particular region. Vonder Mühll, D. & Keller, F. 1999. Eisschwund und Naturkatastrophen im Hochgebirge. Zürich: vdf, Hochschulverlag an der ETH. REFERENCES Krobath, M., Lieb, G.K. & Pertl, A. 2003. Permafrost in the Reisseck mountains (Austria) – a case study. In Arenson, L. & Springman, S.M. 2000. Slope stability and Proceedings of the 8th International Conference on related problems of Alpine permafrost. In Proceedings Permafrost, Zurich: this issue. of the International Workshop on Permafrost Engineer- Lieb, G.K. 1996: Permafrost und Blockgletscher in den ing, Longyearbyen, Svalbard, Norway: 185–196. österreichischen Alpen. Beiträge zur Permafrost- Arenson, L., Hoelzle, M. & Springman, S. 2002. Borehole forschung in Österreich. Arbeiten aus dem Institut für Deformation Measurements and Internal Structure of Geographie und Raumforschung der Karl-Franzens- some Rock Glaciers in Switzerland. Permafrost and UniversitätGraz33: 9–125. Periglacial Processes 13: 117–135. Lieb, G.K. 1998. High-Mountain Permafrost in the Austrian Buchroithner, M.F. & Granica, K. 1997. Applications of Alps (Europe). In Proceedings of the 7th International Imaging Radar in Hydro-Geological Disaster Manage- Conference on Permarost, Yellowknife: 663–668. ment: A Review. Amsterdam: OPA. Stötter, J. 1994. Veränderungen der Kryosphäre in Vergan- Dramis, F., Govi, M., Guglielmin, M. & Mortara, G. 1995. genheit und Zukunft sowie Folgeerscheinungen. Short Communication: Mountain Permafrost and Slope München. Instability in the Italian Alps: the Val Pola Landslide. Veit, H. & Höfner, T. 1993. Permafrost, Gelifluction and Permafrost and Periglacial Processes 6: 73–82. Fluvial Sediment Transfer in the Alpine/Subnival Egger, G. 1996: Vegetationsökologische Untersuchung Ecotone, Central Alps, Austria: Present, Past and Seebachtal, Nationalpark Hohe Tauern. Klagenfurt. Future. Zeitschrift für Geomorphologie 92: 71–84. Haeberli, W. 1975. Untersuchungen zur Verbreitung von Zimmermann, M. 1990. Periglaziale Murgänge In: Schnee, Permafrost zwischen Flüelapaß und Piz Grialetsch Eis und Wasser der Alpen in einer wärmeren (Graubünden). Mitteilungen der Versuchsanstalt für Atmosphäre – Internationale Fachtagung von 11. Mai Wasserbau, Hydrologie und Glaziologie 17: ETH 1990: Mitteilungen der Versuchsanstalt für Wasserbau, Zürich. Hydrologie und Glaziologie 108: 89–107. Haeberli, W., Rickenmann, D., Zimmermann, M. & Rösli, Zimmermann, M. & Haeberli, W. 1992. Climatic Change U. 1990. Investigation of 1987 debris flows in Swiss and Debris Flow Activity in High- Mountain Areas – Alps: general concept and geophysical soundings. IAHS A Case Study in the Swiss Alps. In M. Boer & E. Publications 194: 303–310. Koster (eds) Greenhouse-Impact on Cold-Climate Haeberli, W. 1990. Permafrost. In: Schnee, Eis und Ecosystems and Landscapes. Catena Supplement 22: Wasser der Alpen in einer wärmeren Atmosphäre. 59–72.

418