Uwagi o roli murów w modelowaniu rzeźby Karpat

Abstract

During the recent twenty years the Carpathians suffered from several floods which in some Carpathian basins were of a disastrous nature. They have not only resulted in relief re-modelling, but caused also enormous damages of the technical site infrastructure. Morphological effects of the floods have been worked out many times and T. Ziętara (1968) has not only compiled earlier investigations of the violent rain-storms and floods course in the Flysch Carpathians, but he has also presented (1972 and 1974) erosion and denudation rates, as well as the forecasts of the Flysch Carpathians modelling during floods. The site investigations conducted during the freshets and floods by the members of the Department of Geography of Cracov Paedagogical College discovered some processes and forms which had not been included in the earlier scientific bibliography concerning Carpathians relief. These Alps, Caucasus, Tiań-Szań or Pamyr. The author has got to know these processes during his mountain expeditions in Tiań-Szań, Caucasus and Alps. Comparative investigations and observations have been also conducted in Slovakian and Roumanian Carpathians. During the investigations the interpreting of air-pictures has been utilized. In the first part of his paper the authors discusses a morphological sense of erosion. Later he passes to a relation of energy distribution to transfer intensity, whilst in the third part, which is the most comprehensive one, he discusses the mudflows (mura) effect on Carpathians relief modelling. T. Ziętara was the first to observe and to describe these processes in 1958—60 and he called them stone-mudflows or mud-stoneflows according to the prevalent material (rubble or mud) which is displaced down the slopes and then down the valleys. The author discerns four Carpathian levels where these processes occur, i.e. the highest, the intermediate, the middle and the lowest one. The highest level (above 1800 m) principally coincides with the moderate — cold and cold horizon of cooms and crags. The intermediate level (1400 to 2200 m) is situated on various heights in each mountain group) the High and Low Tatras, Babia Góra Mountain, Big and Small Fatra, the Gorgany and Czarnohora, the Fagaroskie Mountains). Weathering gravity (agradation) as well as weathering-scree slopes occur mostly in this level. Huge packedrock landslides and rocky brashes are also encountered. The level includes also a big accumulation of moraine deposit in mountain ranges locally glaciated in Pleistocene. In the intermediate level there is the biggest accumulation of loose deposits susceptible to the displacement by mudflows. The middle level (from 800 to 1800 m) is covered by lower and higher prealpine forests. In Polish Carpathians, the birthplace of the mura in this level (the Beskidy) are mostly steep valley closures digitally cut by V-shaped valleys covered by colluvial deposits, rubbles and rock brashes which had arisen due to a mechanical weathering or to a development of packed-rock lanslides. The lowest level slope inclination ranges from 20 to 45°. The slopes are covered by weathering crusts of solifluction, colluvial and proluvial origin. In general, the clay material is prevailing over the rubble one in the crusts. The mura appear in this level only occasionally and as mudflows mainly. In the plateau and foreland level (up to 500 m) the mura do not appear, since they are not favoured by small slope inclinations. Two types of mura occur in the Carpathians: turbulence and structural. Turbulence mura are more frequent. Liquid phase is then prevailing over a solid one. Structural mura appear seldom in the Carpathians and their formation is associated to disastrous rainfalls only. A moving mass behaves like a plastic or semi-plastic body. Only 30 to 40 per cent of this mass is water, the other 60 to 70 per cent being clay and rock-blocks. Three displacement stages are identified by the author within structural mura: 1. Preliminary stage where water reanimates the movement of a plastic-liquid mass along an inclined plane. 2. Proper displacement stage where water acts as a catalyst of the movement of solid body and makes it behave like a plastic mass which is not only able to overcome friction on the subgrade but has also an enormous destroying force. 3. Final stage where accumulation is caused by the slope decrease and not by a lack of proper water amount. In the Carpathian Mountains, mura occur occasionally, primarily during disastrous rain-storms and floods. They may appear occasionally in the mountain zone during a sudden melting of the snow cover. They are modelling steep weathering slopes, as well as weathering-gravity (agradation), weathering scree, solifluction, and colluvial slopes and higher parts of considerably inclined valleys, the inclination often exceeding 100 per cent. Wide flat — bottomed valleys inclined more than 30 per cent are modelled by turbulence mass only exceptionally (the Southern Carpathians), while structural mura do not appear in these valleys. Mura arise mostly in the intermediate level where the biggest accumulations of displacement-susceptible sediments are deposited along steep slopes and mountain-sides. Mura are an intermediate link between landsliding and fluvial processes. Although the frequency of their occurrence is rather occasional, their effect is enormous, often disastrous. One more question arises. Perhaps the deposits in higher valley parts in the stream-bed zone having a structure and texture much alike to a material accumulated by the mura, which are believed to be solifluction crusts and thus described on geomorphological maps, can be really attributed to mura activity in Holocene climatic optimum?