PERMAFROST OCCURRENCE IN THE ALPINE ZONE OF THE TATRA MOUNTAINS, POLAND 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 patterned ground 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 tree line. 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 active layer (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).