Saturday, 15 July 2006

Frost Action in the Mountain Soils of Central Europe (Tatra Mts.) - Relict or Contemporary Processes.

Marek Drewnik Sr., Jagiellonian University, Gronostajowa 7, Krakow, 30387, Poland

Tatra Mountains are the highest part of the Carpathians (2655 m a.s.l.). These mountains have well developed alpine relief and geoecological zonality from lower montane zone to alpine zone. The Tatra Mts are not glaciated and the presence of permafrost has not been found. However, these mountains are subject to intense morphogenetic processes (rock falls, rock slides, debris and grain flows, solifluction, and others). Hitherto research has not proved the contemporary occurrence of the frost sorting processes in the soils and soil cover of the Tatra Mts. The clear polygonal structures can be interpreted as relict Pleistocene forms. This paper presents research data concerning the connection of the soil forming with the morphogenetic processes. The standard soil research methods together with the geomorphological analysis methods have been used. Micromorphological analysis on thin sections prepared from undisturbed soil material played a crucial role in the research. The soils studied have been localized in the alpine zone (1800-2200 m a.s.l.). The bedrock of the research soils consists of granitoides. The soils studied are shallow and contain a considerable amount of clast. They are very acidic and of sandy loam and loamy sand texture. They are subject to podzolisation process and they can be characterized by thick humus horizons (both ecto- and endohumus). The research shows the presence of the frost structures in micro scale. During the mineral observations structures typical for frost weathering, both mechanic and chemical, have been found. A typical platy structures (connected to the formation of ice lenses) with silt cappings, micropan and sometimes link-capping have also been found. However, those structures are disturbed by the contemporary soil and morphodynamic processes. First of all soil processes like humus accumulation and podzolisation are secondary to the traces of the frost sorting processes. In the relatively old soils frost structures prevail over the typically soil features when researched on bigger depths. In younger soils well formed frost structures do not occur. On the other hand the described above frost structures support the soil forming processes. It is so due to big porosity and low bulk density caused by the frost action, which phenomenon does not occur in the other areas (except for the Tatra Mts) of this part of Europe. Geochemical research shows high chemical weathering ratio in those young soils together with considerable common and lateral podzolisation processes. Secondly, morphogenetic processes cause the mixing of the soil material that destroys the frost structures. It takes place in the case of catastrophic processes when a uniform soil mass is formed and this soil mass provides a base for the initial soils. Solifluction does not transport the soil material in big distances. Ectohumus horizon overgrown with grass and herb roots plays a stabilising role in the soil cover. There were cases observed when this horizon was disconnected from the independently moving parent material. Micromorphological analysis shows that the solifluction processes occur as short periods of active transport that take place in between relatively longer stabilisation periods. Well formed silt cappings on grains in various different positions provide a good evidence for that. Frost structures occurrence can be one of the factors influencing the catastrophic processes like debris and grain flows. The intensity of these processes during some seasons can be interpreted as a result of climatic changes but also as a result of a long soil weathering process. This might lead to a considerable energy accumulation, which can be released only by a strong impulse. The areas of the frost structures occurrence are identical with the zones of e.g. debris flows. Concluding, it has to be said that most of the frost action traces in the Tatra Mts soils are a relict as it is also in the case of the polygonal structures. Contemporary frost sorting processes take place in micro scale and they are strongly modified by syngenetic soil and morphogenetic processes. Yet they are not to be forgotten because of the fact that those processes clearly influence soil forming and morphogenetic processes. They are also a factor influencing considerable dynamics of the soil cover in the alpine zones of the Central European mountains. This work was supported by the Polish State Committee for Scientific Research - under grant no 3 P04G 095 24.

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