Introduction

Knowledge of mountain permafrost in SouthernCarpathians is very recent and is based on relativelyfew investigations (Urdea, 1992a, 1993a, 1993b, 1993c).Permafrost phenomena in this mountain area are afunction of: mean annual air temperature, a function ofaltitude; direct solar radiation, a function of local reliefand tophography; and snow cover thickness and dura-tion, a function of wind drift and avalanche activity,(Haeberli, 1992; King, 1983). Rock glaciers are amongthe few geomorphological features diagnostic of alpinepermafrost (Barsch,1978; Haeberli,1985). In theSouthern Carpathians, relict rock glaciers are found inareas which had discontinuous permafrost during thelast part of the Pleistocene glaciation (Ichim, 1978;Urdea, 1988, 1992a, 1993b) and therefore are regardedas useful paleoenvironmental indicators.Geomorphological mapping of these landforms maytherefore be applied to the study of altitudinal and lati-tudinal limits of mountain permafrost (Dramis andKotarba, 1994).

Study area

The Southern Carpathians form the most massive andhighest part of the Romanian Carpathians, (Figure 1A)having 10 peaks above 2500 m and a maximum eleva-tion of 2544 m in Moldoveanu Peak (Fgras Mountains).Ten percent of the mountain area lies above 2000 m.

Pleistocene glaciers reached elevation of 1100-1200 mduring their maximum extension, and carved an exten-sive suite of alpine glacial landforms (Figures 1B and1C). The interaction of paraglacial processes andperiglacial phenomena produced a variety ofperiglacial forms (rock glaciers, talus cones and screeslopes, block fields, rock streams, cryoplanation terracesand solifluction forms). The mean annual air tempera-ture is Ð0.5¡C at Tarcu (2180 m) and -2.6¡C at Omu (2505 m) with an absolute minimum of -3 ¡C. The num-ber of days with frost is 200-254 and the number offreeze-thaw cycles is more than 125, with frost possibleat any time of the year. The mean annual precipitations 1180 mm at Tarcu and 1280 at Omu. The thickness ofthe snow layer can be between 50 and 370 cm and ishighly variable acording to wind action. The upperlimit of the forest is generally betwen 1750 and 1800 m.The crystalline rock of the Southern Carpathiansincludes granites and granodiorites especially in theRetezat, Parg and Tarcu Mountains.

Alpine areas of the Southern Carpathians containmany periglacial features. Perhaps the most distinctivemezo-forms are the rock glaciers. As indicators of dis-continuous permafrost, they can be used in the recon-struction of the development of mountain permafrostfrom the Late Pleistocene up to the present, especiallyin the most representative areas of the Retezat andFgras Mountains (Figures 1B and 1C). Following therecession of the Pleistocene glaciers in the Carpathian

Abstract

Rock glaciers are indicators of discontinuous permafrost which permits them to be used in the reconstructionof the development of mountain permafrost. The mapping of rock glaciers in the Southern Carpathians alloweda clear differentiation between talus rock glaciers and debris rock glaciers, as well as their spatial and morpho-logical relations with glacial deposits. Given the significance of rock glaciers in the glacial-periglacial landscapecontinuum, geomorphological analysis has led to the outlining of three evolutionary models.

Two major periods of development of rock glaciers were recognised: Wurm III - Older Dryas for forms below1600-1750 m, and the Medium and Younger Dryas for features over 1800 m a.s.l.. During the Little Ice Age, fea-tures located above 2050 m were reactivated. Calculations were also made of the volume of mountain per-mafrost represented by the rock glaciers and the volume of ground-ice, as well as the evolution in time of thelower limits of continuous permafrost and widespread and patchy discontinuous permafrost in the SouthernCarpathians.

Petru Urdea 1063

ROCK GLACIERS AND PERMAFROST RECONSTRUCTION IN THE SOUTHERN CARPATHIAN MOUNTAINS, ROMANIA

Petru Urdea

University of Timisoara, Department of Geography, Pestalozzi Str., Nr. 16, 1900 - Timisoara, Romaniae-mail: urdea@cbg.uvt.ro

Mountains, the postglacial period has been dominatedby periglacial and fluvio-torrential processes. In thedeglaciated spaces during the so-called paraglacial pe-riod (c.f. Johnson, 1984) a quick adjustment of physicalsystems took place resulting in some relief meso-formssuch as the rock glaciers. The large spreading rock gla-ciers in the Southern Carpathians are found in thealpine glacial landscape area, where they achieve a den-sity of 76/100 km2 in the Retezat Mountains and36/100 km2 in the Fgras Mountains. This high frequen-cy of rock glaciers is explained by the fact that the wallsof glacial cirques and valleys surrounding peaks pro-vided large quantities of frost-shattered debris, favour-ing rock glacier formation. The great production ofdebris, incorporated either in rock glaciers or in taluscones and scree slopes in the immediate postglacialperiod, is due to the presence of rock sensitive to frostweathering, namely jointed granite, granodiorite,gneisses, amphibolites. The relative ease of joint-blockseparation is a function of pressure release as a result ofliberation from the ice mass (cf. Summerfield,1991) andis partly controlled by structural elements such asfaults, joints, schistosity and bedding (Evin, 1987).

Relation of rock glaciers to glacial deposits

Mapping of rock glaciers in the Southern Carpathiansallowed a clear differentiation between talus rock gla-ciers and debris rock glaciers, and clarified their spatialand morphological relationships with glacial deposits.

In many cases, the detailed topography of the valleyfloors and glacial cirques in Retezat, Fgras and ParngMountains allowed the following evolutionarysequence of the latest glaciers to be identified: ablationcomplexes, ice-cored rock glaciers, debris rock glaciers,secondary rock glaciers (Corte, 1976), or ablation com-plex rock glaciers (Evin, 1987), like those in the Galesu(Figure 2), Valea Rea, Pietrele, Stevia in RetezatMountains, Slveiu in Parng, or Arpsel, Cldarea Pietroasa Arpasului, Izvorul Grohotisului, Cltun, Litel, BurianuMare, Podeiu, Cldarea Pietroas a Doamnei, Podrgel,Hrtopu Ursului, Smbta, Fundu Mogosului, Belia Mare,etc. in Fgras Mountains. For example in the CldareaGrohotisului cirque, two generations of rock glaciersare present, both known to be coeval with stadialmoraines in other areas. Here, the rock glacier develop-ment was curtailed at the debris-covered glacier stage.Three typical environments are found for rock glacierformation. The first involves glacial cirques and valleys

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Figure 1. Geographical locations of research sites described in this paper.

surrounded by high peaks, which provide significantquantities of frost-shattered blocks. The second involvesglacial cirques and valleys cut into plateau margins,e.g., the cirques Bulzul, Vlsia Mic, Mocirliu, Stna Marede Est from Godeanu Mountains. These areas are cha-racterized by hummocky dead-ice topography, withirregular hummocks, arcuate ridges and convex fur-rows, separated by small lakes and/or hollows. In thethird case, the evolutionary sequence was as follows:rockfall cones and/or avalanche cones, scree slope, pro-talus rampart, talus rock glaciers (lobate rock glaciers),and finally tongue-shaped rock glaciers. This evolutionis possible because at the bottom of the walls of glacialcirques and valleys, the mixture of rock debris and ice

derived from refreezing of meltwater, was favourablefor the deve-lopment of talus rock glaciers (Barsch,1988). There are deposits of lateral moraines here,pushed to the axis of the valleys. A typical situationoccurs within Vsiel cirque, where under the southernwall of the cirque corresponding on a fault-line escarp-ment, there is a 1.5 km long zone containing a series oflobate-linear type rock glaciers. The lobate part of theserock glaciers overlies the median zone of the lateralmoraine from the Vsiel stage (Older Dryas), which pro-vides some constraint on their age.

Results

The inventory of rock glaciers was based on fieldmapping and aerial photograph interpretation of 116rock glaciers in the Fgras Mountains between 1680 andover 2300 m.a.s.l., and 93 cases from the RetezatMountains between 1690 and over 2200 m.a.s.l. This

Petru Urdea 1065

Figure 2. Debris rock glaciers Galesu (Retezat Mountains) and their spatialrelations with stadial moraines of Older Dryas (ODM) and Middle Dryas(MDM).

Figure 3. Talus rock glaciers in Papusii cirque (Retezat Mountains) and fossil debris rock glaciers B�rlogu Ursului.

Table 1. Distribution (%) of area occupied by rock glaciersin (a) Retezat and (b) Fagaras Mountains

Table 2. Altitudinal distribution (%) of rock glaciers in (a) Retezat and (b) Fagaras Mountains

Table 3. Altitudinal distribution (%) of area occupied byrock glaciers in Retezat and Fagaras Mountains

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Figure 4. Orientation of rock glaciers (azimuth of median axis) in Retezat and Fagaras Mountains for: a - total area; b - northern slope; c - southern slope.

distribution gives an impression of the zone of discon-tinuous permafrost within these mountain areas. Toclarify the time evolution of the limits of discontinuouspermafrost, it is necessary to establish the major periodswithin which rock glaciers formed. We consider thatduring the W�rm III - Younger Dryas period ofdeglaciation in the Southern Carpathians up to theBoreal period, climatic conditions favoured the deve-lopment of rock glaciers. This is documented by palino-logical data (Ciobanu et al., 1967; Diaconeasa, 1968; Popet al., 1971; Boscaiu and Lupsa, 1984). Taking intoaccount the spatial relations with the moraines and thepalynological data, we consider there to be two majorperiods of rock glacier development: W�rm III - Older

Dryas for the forms located below 1600-1750 m, andMiddle and Younger Dryas for the forms located over1800 m. Most recently, during the Little Ice Age, rockglaciers located above 2050 m.a.s.l. were reactivated, asshown by dendrochrological and dendroecological data(Soran et al., 1981; Urdea, 1998).

During the Younger Dryas, the permafrost area, asrepresented by the rock glaciers, is estimated to havebeen 15 km2 in Fgras Mountains and 6.1 km2 in RetezatMountains These areas are 4.6 % and 5%, respectively,of the highest parts of the two mountains areas. It isworth underlining the present differences between thenorth- and south-facing slopes (Table 1, Figures 4 and5). The percentage of the total rock glacier areas foundon the north-facing slope is 62% in Retezat Mountainsand 59% in Fgras Mountains. These figures represent10% and 3%, respectively, of the total surface alpinezone. Also notable is the altitudinal spread of the rockglaciers and therefore of discontinuous permafrost,indicating differences between the two researchedmountain areas (Tables 2 and 3).

Assuming a mean thickness for rock glaciers of 20 mand a mean ice content of 40% (cf. Barsch, 1996), thevolume of the permafrost and its ice volume was calcu-lated (Table 4). Including the Parng Mountains, whererock glaciers occupy a surface of about 3.1 km2, andother small rock glacier areas in Tarcu and GodeanuMountains, the total permafrost area in the alpine beltof the Southern Carpathians is about 26-28 km2, or 1.1%of the total alpine area.

The results of the reconstruction of the developmentof Quaternary glaciations in the Retezat Mountains(Urdea, 1993a), and the postglacial development of thesame mountain area (Urdea, 1992a), have been used tosketch the evolution of the lower limits of the conti-nuous, widespread and patchy discontinuous permafrost (Table 5). The lower limit of continuous per-

Petru Urdea 1067

Figure 5. Distribution of area occupied by rock glaciers in Retezat and Fagaras Mountains.

Table 4. Estimated permafrost volume (PV) and ground ice(VPI) (40%) for Retezat and Fagaras Mountains at

theYounger Dryas level

Table 5. Evolution of lower limits of continuous, wide-spread and patchy discontinuous permafrost in the

Southern Carpathians

mafrost is situated at the altitude of the -6¡C isothermof the MAAT, the limit between the widespread andpatchy discontinuous permafrost at the level of Ð4.5¡Cisotherm, and the lower limit of the discontinuous per-mafrost at the elevation of the Ð1.5¡C isotherm (King,1983, 1986). The values obtained for the lower limit ofdiscontinuous permafrost and the limit of perennialsnowcover involve an average altitude difference of 431 m, a value close to the 460 m figure typical of theBernina zone (Belloni et al., 1993).

Today the presence of segregation and cementationice, BTS (the bottom temperature of winter snow cover;cf. Haeberli, 1973) results and the summer temperaturesof springs situated at the front of rock glaciers and atthe foot of talus cones, indicate the existence of patchyand sporadic permafrost in the Southern Carpathiansabove 2100-2200 m.a.s.l. (Urdea, 1993b, 1993c). This pre-sent distribution of permafrost is closely related totopographic and microclimatic conditions. Segregationand cementation ice have both been documented

within debris rock glaciers and with talus rock glaciers(Urdea, 1993b). In the case of debris rock glaciers, it islikely relict permafrost, while within the talus rock gla-ciers situated in shady places, it is regarded as modernpermafrost. We believe that the model of rock glacierevolution and permafrost reconstruction in the mostrepresentative parts of Southern Carpathians, theRetezat and Fgras Mountains, may be applicable to theremainder of the Carpathians alpine belt.

Acknowledgments

The author wishes to thank Dr. Michael Bovis and twoanonymous reviewers for their constructive commentsand suggestions and for assistance with the Englishediting of the manuscript.

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