OCCURRENCE IN THE ALPINE ZONE OF THE TATRA MOUNTAINS,

Wojciech Dobinski

Department of Geomorphology, Faculty of Earth Sciences, University of Silesia, ul. Bedzinska 60, 41-200 Sosnowiec, Poland, e-mail: [email protected]

Abstract

At an altitude of 1990 m a.s.l., the mean annual air temperature in the Tatra Mountains of southern Poland is -1¡C. The values of the freezing and thawing indices suggest that, at such an altitude, the depth of ground thaw ought to be smaller than that of ground freezing. Geophysical methods were used to try to confirm that per- mafrost is present. The most common result for electroresistivity soundings is about 300 kOhm-m. Seismic soundings indicate velocities from 2260 to 2670 m/s at the depths of 9 m or so. Several hundred BTS measure- ments have also been made in the study area and temperatures from 0 to -4.8¡C have been recorded. The results strongly suggest the presence of discontinuous permafrost in the Tatra Mountains and it appears that it under- lies an area of the order of 100 km2 .

Introduction Previously unsuspected cases of permafrost have recently been reported in the Apennines, the Alps, the The Tatra Mountains represent an area where the Jura Mountains and the highest southern Carpathian alpine and cold-climate zones are contiguous (Hess, Mountains, even at altitudes where the annual average 1965; 1974). The periglacial zone is also represented and air temperature is as high as +2¡C (Dramis and Kotarba many typical periglacial forms and processes are still 1992; Hoelzle, 1992; Urdea, 1992; 1993). active (Jahn, 1958; Klimaszewski, 1988; Kotarba, 1992). Geomorphological features such as rock glaciers and The initial study in this project was the determination active below an altitude of 1600 m of freezing and thawing indices for the area (Harris, a.s.l. (Jahn, 1970) strongly suggest that permafrost may 1981); these then guided the field studies in respect of be present above the . Recent discoveries of per- determination of the potential for permafrost occur- mafrost zones in similar mountain situations elsewhere rence. Traditionally, investigations of mountain per- have been the stimulus for the present research. mafrost normally involve electroresistivity sounding,

Figure 1. Location of research area: a - Piec Staw—w Polskich valley b - Piarzysta valley, c - Dzika valley, d - Za Mnichem valley, e - Gasienicowa valley and Kasprowy summit, f - Lomnicky summit

Wojciech Dobinski 231 temperature measurements at the base of the snow freezing and thawing. The results from the Kasprowy cover (BTS) and seismic soundings (Hoelzle et al.. 1993; Wierch (E) and £omnicki Szczyt (F) summits show that King 1990; King et al.. 1990); a similar approach has these lie above the altitude where average freezing been adopted here. depth is balanced by average thawing depth. These val- ues are good for theoretical sites, where the snow cover Physical setting is less than 50 cm in thickness; this is considered to be a requirement for the successful application of this The Tatra Mountains, situated between latitude 49¡05' method. and 49¡15' N, represent the highest massif of the west- ern Carpathians (Figure 1). They originated in the RESULTS OF INVESTIGATIONS USING THE BTS METHOD Alpine orogenesis. Their alpine landscape is essentially This method was developed and applied by Haeberli one inherited from the Pleistocene, when local moun- (1973) in the Alps. It measures heat flow at the ground tain glaciation occurred. The total area of the massif is surface. Heat flow here depends mainly on the occur- rence or absence of permafrost below, and also on the about 750 km2 but the so-called "High Tatras", the high- amount of heat which is present in the cover above, est peaks of which exceed 2600 m a.s.l., occupy only which is derived principally from solar radiation in the about one-third of the total. The main crest of the High summer (Haeberli, 1985). The influence of geothermal Tatras, which is 26.5 km long and averages 2280 m a.s.l. heat is considered to be so small in the heat budget at in elevation, runs more or less W-E (Klimaszewski, the ground surface that it is normally insignificant in 1988; Luknis, 1973). Two climatic zones are recognised respect to the origin and preservation of permafrost; it in this area, namely "cold" and "moderately cold". In the may, however, affect its thickness. The heat input from moderately cold zone, zero mean annual air tempera- solar radiation is considered to be about 6000 times ture (MAAT) occurs on the northern slopes at an alti- greater than that supplied by geothermal sources tude of 1850 m a.s.l. whereas, on the southern slopes, it (Judge, 1973; Gold and Lachenbruch 1973). occurs at 2050 m (Hess, 1965). At these altitudes, there are 135 days of frost a year. The amount of precipitation The measurements made by the BTS method not only in the Tatras shows that they are to be regarded as a indicate the probability of permafrost but they also "wet" type; part of this precipitation becomes a snow enable us to determine the average annual ground tem- cover which normally varies in thickness between 115 perature (King, 1990; King et al.. 1992). The method can and 230 cm (Hess, 1965; 1974). The tree-line is at an alti- also, therefore, be used to make a more detailed estima- tude where the MAAT is zero, while on the highest tion of permafrost distribution. In alpine permafrost, Tatra summits, the average air temperature is -3.8¡C. the depth of perenially frozen ground (i.e. the top of ice-bonded permafrost) may be determined from the Results empirical relationship between the BTS values and the depth of an (which may be determined by CLIMATIC ANALYSIS seismic methods) (Haeberli and Epifani, 1986). The The data used to determine the thawing and freezing intervals for permafrost occurrence estimated in this indices were collected from six meteorological stations way are as follows: in the High Tatras at altitudes between 1,408 and 2,632 m a.s.l. The thawing indices (TI) and freezing 1. <-3¡C: a probability of permafrost indices (FI) were calculated for each year and each site. 2. from -3 to -2¡C: a possibility of permafrost The 5- and 10-year average values are shown in 3. >-2¡C: permafrost unlikely. Figure 2 (cf. Harris, 1981). Also, the depths of freezing and thawing were calculated using the following for- Thus, BTS values which are lower than -3¡C indicate mula: the presence of frozen ground whereas values higher Df= a FI than -2¡C exclude the possibility of frozen ground at a depth of between 4 and 6 m; in the middle interval it is Dt= b TI simply not possible to make any reliable interpretations (Haeberli and Epifani 1986). The fieldwork in the Polish part of the Tatra Mountains, which comprised 320 mea- where a and b are parameters defined empirically and surements, was carried out at the end of winter over a TI and FI are the thawing and freezing indices (Sone, three-season period, 1994-6, at altitudes of between 1992; Urdea, 1993). Figure 3 shows the calculated 1550 and 2100 m a.s.l. depths of ground thawing and freezing relative to ele- vation in the study area. An indication of the boundary In almost all of the area studied, the BTS results fall of potential permafrost at 1930 m a.s.l. relates to the into each of the three groups. Thus it is possible, to intersections of the lines showing the depths of ground define areas of possible permafrost occurrence and the

232 The 7th International Permafrost Conference Figure 2. Freezing and thawing index in High Tatra on Harris (1981) diagram (see text). results show that it may be present in both the Piec mafrost occurrence are conditioned by the prominent Staw—w and Gasiencowa valleys. In respect of the W-E-trending high ridges. The results obtained from amount of solar radiation gained in the system, it is also the BTS method are generally in accord with the thaw- likely that the permafrost is conditioned by general ing and freezing index determinations. slope disposition (Funk and Hoelzle, 1992; Hoelzle, 1992; Keller, 1992). Presumably, it also depends on local ELECTRORESISTIVITY SOUNDINGS topographic conditions such as the degree of exposure Electroresistivity soundings were carried out at select- on slopes below high mountain summits, in cirques and ed sites, with the objective of obtaining the widest pos- in valleys situated high between summits, which can sible spectrum of results i.e. they were carried out both have their own specific microclimate. There, BTS values in areas where permafrost was considered to be very are coldest and can reach as low as -4.8.¡C. Certainly, it probable and in areas where it was considered improb- may be assumed with some confidence that, above able. This work, comprising 38 soundings, concentrated 1900 m a.s.l., the geomorphological boundaries of per- on areas where BTS measurements had previously been

Wojciech Dobinski 233 made. The soundings were carried out at altitudes ried out where there was a particularly favourable varying from 1535 to 2105 m a.s.l. in a variety of topog- microclimate; these showed resistance of as much as raphy. Since the method has never before been used in 170 kOhm-m. Poland to investigate permafrost occurrence, it was con- sidered appropriate also to include some soundings in The results from the middle layer suggest the occur- the permanent snow patch in the Dzika valley rence of permafrost here (values of 350-600 kOhm-m). (). This is situated at an altitude of 2045-2085 m After mature analysis of the results, the value of a.s.l.; its length is about 115 m and inclination about 20¡. 50 kOhm-m was assumed to be the limiting resistance The density of the ice in the snow patch is in the range for permafrost in this layer. The large differences in the resistance of the middle layer (from 20 kOhm-m to 0.50-0.51 g/cm3. This sounding was made in the same 6 MOhm-m) show either that the ice in the permafrost configuration as in the other surveys, the aim being to layer is very variable or the permafrost temperature is determine the resistance of the local firn and ice and to itself very variable, or both. The ice of the Tatra per- calibrate the equipment used in terms of these resis- mafrost is probably of the nature of a cementing, pore- tance values. filling ice (denoted by low resistance values) or is segre- The results obtained show that the first layer, the gated into lenses or discontinuous layers (this is also thickness of which was determined to be ca. 1 m, has a indicated by the large dispersion of measurement sites, resistance of 500 kOhm-m. despite a good contact of electrodes in the field). In geo- morphological features, e.g. rock glaciers, electroresis- Excavations show this to be a compact wet snow tivity values were high. This would suggest large vol- which is partly transformed into firn. The second layer umes of ice which is interpreted as an ice core under the had a resistance of 6 MOhm-m, i.e. one typical of gla- cover of frozen rubble. In the case of pore or segregated cier ice. Below, the third layer appears to comprise ice, the origin is presumably associated with the cryo- frozen rubble with voids caused by drainage below the genic processes which occur in the periglacial zone, snow patch. The plot of resistance values is shown in rather than any surface process. The ice cores which Figure 4, together with its interpretation. The results of possibly occur in cirques or rock glaciers are usually the resistivity soundings were compared with studies associated with glacier ice. The third layer usually rep- carried out at Ponteressina-Schafberg, and rockglacier resents bedrock, which is often slightly weathered and Murt(l 1 (Haeberli, 1990; Vonder MŸhll, 1993; Vonder is not normally frozen; in places where permafrost has MŸhll and Holub, 1992.). not formed, its moisture content is normally quite high.

From these results, it is believed that if the upper lay- SEISMIC SOUNDINGS ers comprise fine- or coarse-grained rubble, the resis- The sounding site was located on a debris cone at an tance values do not support the presence of permafrost altitude of ca. 1800 m a.s.l. A Terraloc Mk3 24-channel here. However, there are exceptions, such as those -

Figure 3. Theoretical thickness of the ground thawing and freezing in the Tatra Mountains, as calculated from the thawing and freezing indices for the area where the snow cover is less than 50 cm thick.

234 The 7th International Permafrost Conference Figure 4. Plots of typical resistance sounding curves from the Tatra Mountains and their interpretation. A. Sounding at a site where permafrost does not occur, B. Sounding at a site where permafrost probably occurs, C. Sounding on the permanent snow patch (Dzika Valley). The table shows an interpretation of the true resistance and layer thickness. recorder with mega-frequency geophones was used. the entire area. This estimate assumes that the tempera- The distance between the geophones along the profile ture of the permafrost ranges from 0 to -5¡C and it also was 2.5 m. Vibrations were induced by blows from a depends on the altitude and local conditions of micro- 5-kg hammer. The shape of the hodographs indicates a climate and slope disposition. Ice in the permafrost two-layer structure here. In the first layer, the velocity which has a temperature close to zero was also deter- varies within the range 600-900 m/s; in the second mined by seismic surveying. Such a temperature sug- layer, it is 2260-2670 m/s. The boundary between the gests that the permafrost in such places may have two layers lies at a depth of ca 8 m and is almost paral- become degraded and this is why it does not show high lel with the ground surface. The velocity of the refract- resistance or low BTS temperature values. Based on the ed wave in the Tatra granodiorite is about 3500 m/s so results obtained from the indirect methods used in this the velocities obtained are more similar to that of ice, research, it is suggested that the content of ice in the i.e. ca 2500 m/s (MŸller, 1961). It may be assumed, Tatra permafrost ranges from zero (in the relatively therefore, that this horizon represents the top of the unfissured parts of the granodiorites which crop out on perennialy frozen zone or the surface where it plunges the highest summits of the Tatras) to more than 90% (in beneath the debris cone ice. Scott et al.. (1979) opined the ice cores which are present under the thick covers of that the velocity of seismic waves decreases commensu- weathered material in the highest cirques). rately with an increase in the permafrost temperature. Vonder MŸhll (1993) gives the value of 2200 m/s for Both seismic and resistance investigations show that it permafrost which has a temperature close to zero. is possible for ice to occur in rock glaciers and in the Apparently, the limiting velocity for permafrost is 2000 highest cirques. It is assumed, therefore, that the per- m/s (Vonder MŸhll, 1993). mafrost present in these places must be relict from the Pleistocene. By contrast, the ice present in the debris Conclusions cones deposits probably originated in the periglacial conditions which prevailed here in the Holocene. With respect to the results of the fieldwork, it may be assumed that the area underlain by permafrost in the Tatra Mountains is about 100 km2 i.e. about 13.2% of

Wojciech Dobinski 235 Acknowledgments

I am grateful to Professor Dr. Jacek Jania and Professor Dr. Adam Kotarba for discussions and criti- cism of my work, and to Professor Dr. Wilfried Haeberli for introducing me to problems of active permafrost. I wish to acknowledge Professor Dr. S. A. Harris and Professor Dr. R. van Everdingen and Professor A. Lewkowicz for their assistance in reviewing and editing my manuscript. This research was financially support- ed by University of Silesia and KBN research grant No. 6 PO 4 E 01908.

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