Introduction

The Tatra Mountains represent an area where thealpine and cold-climate zones are contiguous (Hess,1965; 1974). The periglacial zone is also represented andmany typical periglacial forms and processes are stillactive (Jahn, 1958; Klimaszewski, 1988; Kotarba, 1992).Geomorphological features such as rock glaciers andactive patterned ground below an altitude of 1600 ma.s.l. (Jahn, 1970) strongly suggest that permafrost maybe present above the tree line. Recent discoveries of per-mafrost zones in similar mountain situations elsewherehave been the stimulus for the present research.

Previously unsuspected cases of permafrost haverecently been reported in the Apennines, the Alps, theJura Mountains and the highest southern CarpathianMountains, even at altitudes where the annual averageair temperature is as high as +2¡C (Dramis and Kotarba1992; Hoelzle, 1992; Urdea, 1992; 1993).

The initial study in this project was the determinationof freezing and thawing indices for the area (Harris,1981); these then guided the field studies in respect ofdetermination of the potential for permafrost occur-rence. Traditionally, investigations of mountain per-mafrost normally involve electroresistivity sounding,

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 thawought 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. Seismicsoundings 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 resultsstrongly 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 .

Wojciech Dobinski 231

PERMAFROST OCCURRENCE IN THE ALPINE ZONE OF THE TATRAMOUNTAINS, POLAND

Wojciech Dobinski

Department of Geomorphology, Faculty of Earth Sciences, University of Silesia, ul. Bedzinska 60, 41-200 Sosnowiec, Poland, e-mail: dobin@ultra.cto.us.edu.pl

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

temperature measurements at the base of the snowcover (BTS) and seismic soundings (Hoelzle et al.. 1993;King 1990; King et al.. 1990); a similar approach hasbeen adopted here.

Physical setting

The Tatra Mountains, situated between latitude 49¡05'and 49¡15' N, represent the highest massif of the west-ern Carpathians (Figure 1). They originated in theAlpine orogenesis. Their alpine landscape is essentiallyone inherited from the Pleistocene, when local moun-tain glaciation occurred. The total area of the massif isabout 750 km2 but the so-called "High Tatras", the high-est peaks of which exceed 2600 m a.s.l., occupy onlyabout one-third of the total. The main crest of the HighTatras, which is 26.5 km long and averages 2280 m a.s.l.in elevation, runs more or less W-E (Klimaszewski,1988; Luknis, 1973). Two climatic zones are recognisedin this area, namely "cold" and "moderately cold". In themoderately cold zone, zero mean annual air tempera-ture (MAAT) occurs on the northern slopes at an alti-tude of 1850 m a.s.l. whereas, on the southern slopes, itoccurs at 2050 m (Hess, 1965). At these altitudes, thereare 135 days of frost a year. The amount of precipitationin the Tatras shows that they are to be regarded as a"wet" type; part of this precipitation becomes a snowcover which normally varies in thickness between 115and 230 cm (Hess, 1965; 1974). The tree-line is at an alti-tude where the MAAT is zero, while on the highestTatra summits, the average air temperature is -3.8¡C.

Results

CLIMATIC ANALYSIS

The data used to determine the thawing and freezingindices were collected from six meteorological stationsin the High Tatras at altitudes between 1,408 and 2,632 m a.s.l. The thawing indices (TI) and freezingindices (FI) were calculated for each year and each site.The 5- and 10-year average values are shown in Figure 2 (cf. Harris, 1981). Also, the depths of freezingand thawing were calculated using the following for-mula:

where a and b are parameters defined empirically andTI and FI are the thawing and freezing indices (Sone,1992; Urdea, 1993). Figure 3 shows the calculateddepths of ground thawing and freezing relative to ele-vation in the study area. An indication of the boundaryof potential permafrost at 1930 m a.s.l. relates to theintersections of the lines showing the depths of ground

freezing and thawing. The results from the KasprowyWierch (E) and £omnicki Szczyt (F) summits show thatthese lie above the altitude where average freezingdepth is balanced by average thawing depth. These val-ues are good for theoretical sites, where the snow coveris less than 50 cm in thickness; this is considered to be arequirement for the successful application of thismethod.

RESULTS OF INVESTIGATIONS USING THE BTS METHOD

This method was developed and applied by Haeberli(1973) in the Alps. It measures heat flow at the groundsurface. Heat flow here depends mainly on the occur-rence or absence of permafrost below, and also on theamount of heat which is present in the cover above,which is derived principally from solar radiation in thesummer (Haeberli, 1985). The influence of geothermalheat is considered to be so small in the heat budget atthe ground surface that it is normally insignificant inrespect to the origin and preservation of permafrost; itmay, however, affect its thickness. The heat input fromsolar radiation is considered to be about 6000 timesgreater than that supplied by geothermal sources(Judge, 1973; Gold and Lachenbruch 1973).

The measurements made by the BTS method not onlyindicate the probability of permafrost but they alsoenable us to determine the average annual ground tem-perature (King, 1990; King et al.. 1992). The method canalso, therefore, be used to make a more detailed estima-tion of permafrost distribution. In alpine permafrost,the depth of perenially frozen ground (i.e. the top ofice-bonded permafrost) may be determined from theempirical relationship between the BTS values and thedepth of an active layer (which may be determined byseismic methods) (Haeberli and Epifani, 1986). Theintervals for permafrost occurrence estimated in thisway are as follows:

1. <-3¡C: a probability of permafrost2. from -3 to -2¡C: a possibility of permafrost3. >-2¡C: permafrost unlikely.

Thus, BTS values which are lower than -3¡C indicatethe presence of frozen ground whereas values higherthan -2¡C exclude the possibility of frozen ground at adepth of between 4 and 6 m; in the middle interval it issimply not possible to make any reliable interpretations(Haeberli and Epifani 1986). The fieldwork in the Polishpart of the Tatra Mountains, which comprised 320 mea-surements, was carried out at the end of winter over athree-season period, 1994-6, at altitudes of between1550 and 2100 m a.s.l.

In almost all of the area studied, the BTS results fallinto each of the three groups. Thus it is possible, todefine areas of possible permafrost occurrence and the

The 7th International Permafrost Conference232

Df a FI

Dt b TI

=

=

results show that it may be present in both the PiecStaw�w and Gasiencowa valleys. In respect of theamount of solar radiation gained in the system, it is alsolikely that the permafrost is conditioned by generalslope disposition (Funk and Hoelzle, 1992; Hoelzle,1992; Keller, 1992). Presumably, it also depends on localtopographic conditions such as the degree of exposureon slopes below high mountain summits, in cirques andin valleys situated high between summits, which canhave their own specific microclimate. There, BTS valuesare coldest and can reach as low as -4.8.¡C. Certainly, itmay be assumed with some confidence that, above 1900 m a.s.l., the geomorphological boundaries of per-

mafrost occurrence are conditioned by the prominentW-E-trending high ridges. The results obtained fromthe BTS method are generally in accord with the thaw-ing and freezing index determinations.

ELECTRORESISTIVITY SOUNDINGS

Electroresistivity soundings were carried out at select-ed sites, with the objective of obtaining the widest pos-sible spectrum of results i.e. they were carried out bothin areas where permafrost was considered to be veryprobable and in areas where it was considered improb-able. This work, comprising 38 soundings, concentratedon areas where BTS measurements had previously been

Wojciech Dobinski 233

Figure 2. Freezing and thawing index in High Tatra on Harris (1981) diagram (see text).

made. The soundings were carried out at altitudesvarying from 1535 to 2105 m a.s.l. in a variety of topog-raphy. Since the method has never before been used inPoland to investigate permafrost occurrence, it was con-sidered appropriate also to include some soundings inthe permanent snow patch in the Dzika valley(Slovakia). This is situated at an altitude of 2045-2085 ma.s.l.; its length is about 115 m and inclination about 20¡.The density of the ice in the snow patch is in the range0.50-0.51 g/cm3. This sounding was made in the sameconfiguration as in the other surveys, the aim being todetermine the resistance of the local firn and ice and tocalibrate the equipment used in terms of these resis-tance values.

The results obtained show that the first layer, thethickness of which was determined to be ca. 1 m, has aresistance of 500 kOhm-m.

Excavations show this to be a compact wet snowwhich is partly transformed into firn. The second layerhad a resistance of 6 MOhm-m, i.e. one typical of gla-cier ice. Below, the third layer appears to comprisefrozen rubble with voids caused by drainage below thesnow patch. The plot of resistance values is shown inFigure 4, together with its interpretation. The results ofthe resistivity soundings were compared with studiescarried out at Ponteressina-Schafberg, and rockglacierMurt(l 1 (Haeberli, 1990; Vonder M�hll, 1993; VonderM�hll and Holub, 1992.).

From these results, it is believed that if the upper lay-ers comprise fine- or coarse-grained rubble, the resis-tance values do not support the presence of permafrosthere. However, there are exceptions, such as those car-

ried out where there was a particularly favourablemicroclimate; these showed resistance of as much as170 kOhm-m.

The results from the middle layer suggest the occur-rence of permafrost here (values of 350-600 kOhm-m).After mature analysis of the results, the value of 50 kOhm-m was assumed to be the limiting resistancefor permafrost in this layer. The large differences in theresistance of the middle layer (from 20 kOhm-m to 6 MOhm-m) show either that the ice in the permafrostlayer is very variable or the permafrost temperature isitself very variable, or both. The ice of the Tatra per-mafrost is probably of the nature of a cementing, pore-filling ice (denoted by low resistance values) or is segre-gated into lenses or discontinuous layers (this is alsoindicated by the large dispersion of measurement sites,despite a good contact of electrodes in the field). In geo-morphological features, e.g. rock glaciers, electroresis-tivity values were high. This would suggest large vol-umes of ice which is interpreted as an ice core under thecover of frozen rubble. In the case of pore or segregatedice, the origin is presumably associated with the cryo-genic processes which occur in the periglacial zone,rather than any surface process. The ice cores whichpossibly occur in cirques or rock glaciers are usuallyassociated with glacier ice. The third layer usually rep-resents bedrock, which is often slightly weathered andis not normally frozen; in places where permafrost hasnot formed, its moisture content is normally quite high.

SEISMIC SOUNDINGS

The sounding site was located on a debris cone at analtitude of ca. 1800 m a.s.l. A Terraloc Mk3 24-channel

The 7th International Permafrost Conference234

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

recorder with mega-frequency geophones was used.The distance between the geophones along the profilewas 2.5 m. Vibrations were induced by blows from a 5-kg hammer. The shape of the hodographs indicates atwo-layer structure here. In the first layer, the velocityvaries within the range 600-900 m/s; in the secondlayer, it is 2260-2670 m/s. The boundary between thetwo layers lies at a depth of ca 8 m and is almost paral-lel with the ground surface. The velocity of the refract-ed wave in the Tatra granodiorite is about 3500 m/s sothe velocities obtained are more similar to that of ice,i.e. ca 2500 m/s (M�ller, 1961). It may be assumed,therefore, that this horizon represents the top of theperennialy frozen zone or the surface where it plungesbeneath the debris cone ice. Scott et al.. (1979) opinedthat the velocity of seismic waves decreases commensu-rately with an increase in the permafrost temperature.Vonder M�hll (1993) gives the value of 2200 m/s forpermafrost which has a temperature close to zero.Apparently, the limiting velocity for permafrost is 2000m/s (Vonder M�hll, 1993).

Conclusions

With respect to the results of the fieldwork, it may beassumed that the area underlain by permafrost in theTatra Mountains is about 100 km2 i.e. about 13.2% of

the entire area. This estimate assumes that the tempera-ture of the permafrost ranges from 0 to -5¡C and it alsodepends on the altitude and local conditions of micro-climate and slope disposition. Ice in the permafrostwhich has a temperature close to zero was also deter-mined by seismic surveying. Such a temperature sug-gests that the permafrost in such places may havebecome degraded and this is why it does not show highresistance or low BTS temperature values. Based on theresults obtained from the indirect methods used in thisresearch, it is suggested that the content of ice in theTatra permafrost ranges from zero (in the relativelyunfissured parts of the granodiorites which crop out onthe highest summits of the Tatras) to more than 90% (inthe ice cores which are present under the thick covers ofweathered material in the highest cirques).

Both seismic and resistance investigations show that itis possible for ice to occur in rock glaciers and in thehighest cirques. It is assumed, therefore, that the per-mafrost present in these places must be relict from thePleistocene. By contrast, the ice present in the debriscones deposits probably originated in the periglacialconditions which prevailed here in the Holocene.

Wojciech Dobinski 235

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 trueresistance and layer thickness.

Acknowledgments

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

The 7th International Permafrost Conference236

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