Czy najwyższe partie Sudetów powyżej górnej granicy lasu są domeną peryglacjalną?
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CG_2010_1_2-79.pdf (6.78 MB)
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2010
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Polskie Towarzystwo Geograficzne
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Abstract
W artykule omówiono problematykę zasięgu występowania form peryglacjalnych w czeskiej części Sudetów powyżej górnej granicy lasu oraz obecności i charakteru współczesnej domeny peryglacjalnej. Dokonano klasyfikacji genetycznej form peryglacjalnych, omówiono ich rozprzestrzenienie, cechy morfologiczne, aktywność, a w odniesieniu do kopczyków ziemnych – sezonowość występowania procesów mrozowych. Na podstawie tych cech, skonfrontowanych z literaturą przedmiotu, poddano krytycznej analizie dotychczasowe poglądy odnośnie występowania i zasięgu współczesnej domeny peryglacjalnej w Sudetach. W znacznej części w artykule wykorzystano oryginalne materiały zgromadzone przez autorów w trakcie wieloletnich obserwacji. W odniesieniu do najwyższych partii Sudetów można wykazać istnienie domeny peryglacjalnej, ale nie jest ona tożsama z całym obszarem położonym powyżej górnej granicy lasu. Ma ona charakter wyspowy i jest przede wszystkim zależna od lokalnych warunków mikroi topoklimatycznych.The summit areas of the High Sudetes are unique relief and landscape within the Bohemian Massif for their composition of fossil and active periglacial landforms. Jeník & Sekyra (1995) knew it and defined a model of artic-alpine tundra in the Giant Mts. It is certain that permafrost has not large area expansion in the High Sudetes. It can not be excluded that some shaded blockfields with great thickness of boulders might fulfil a climatic definition of permafrost local occurrence such as block accumulations in the České středohoří Mts. and in the Lužické hory Mts. (Zachara, Gude, Růžička, 2007). Thus it is not possible to define a periglacial zone within the meaningof a permafrost occurrence in the High Sudetes. Consequently existence of processes bounded to permafrost (especially frost cracking) must be excluded and in this sense recent origin of sorted polygons cannot be considered. On the other hand the areas of the High Sudetes which are located in the highest altitudes correspond with French (2007) climatic definition of the periglacial zone. It is also clear that there is an indisputable activity of some periglacial landforms and processes above the alpine timberline in the High Sudetes. It includes: solifluction, ploughing blocks, sorted cirques, nivation hollows and mainly earth hummocks with soil horizons affected by cryoturbation, with cryoexpulsion features, with long-term persisting segregated ice, with specific thermal regime which differentiates them from their neighborhood, with regelation activity which runs episodically mainly in spring time. Besides we can recognize effect of needle ice, frost heaving and frost sorting and horizontal and vertical movement of soil horizons and clasts. The above mentioned active periglacial landforms do not occur continuously in the whole area above timberline but only in the climatically most extreme localities whereas these landforms are characteristic for lower part of mountain periglacial zones defined by Williams (1961), Furrer (in Wasburn, 1979) or Leser (in Embleton /ed./, 1984). Based on these criteria we can talk about periglacial zone in the summit part of the High Sudetes. The question is how to define the area which can be designated as „periglacial“ in other words how to define the particular part of area above alpine timberline in the High Sudetes where the activity of at least part of the periglacial landforms is undeniable and characteristic. Seeing that position of the alpine timberline is not influenced by climatic factors only but also by relief and anthropogenic factors and since active periglacial landforms are linked to altitudes above 1 400 m a.s.l. the lower border of current „soft periglacial area“ of the High Sudetes can be found between 1300 and 1400 m a.s.l., and its course can still be modified depending on local conditions. Such characterized boundary of periglacial zone of the High Sudetes corresponds with definition of articalpine tundra in the Giant Mts. (sensu Jeník & Sekyra, 1995). In any case, it is necessary to realize that the current „soft periglacial area“ has a completely different quality than that which existed there during the last glacial age, and after which well-developed cryoplanation terraces, tors or sorted polygons, that can be found below the current alpine timberline, were left here. The current „soft periglacial area“ of the High Sudetes cannot be taken as continuous zone above the alpine timberline from the spatial point of view but more like a complex of islands with favorable local conditions mainly microclimatic ones; in case of earth hummocks also lithological conditions (large content of fine soil with high rate of organic matter) where the less climatically demanding periglacial landforms are active. On the other hand it appears (tab. 4) that an occurrence of all groups of periglacial landforms (active and fossil – non active ones) is and was bound to similar topographic and morphologic criteria (altutude, inclination of slopes and aspect) which have influence even today. The time period of origin of earth hummocks in the Hrubý Jeseník Mts. was determinated to turn of the Sub-Boreal/Sub-Atlantic based on pollen analysis and dating of hummocks´ base by method AMS 14C (2090±35 year BP, non-calibrated age) (Treml, Křížek, Engel, 2005). The age of peatbog basement on the Bílá louka Meadow in the Giant Mts., where peat humocks can be found, is 2340±35 years BP /non-calibrated 14C AMS age/. The age of peat hummocks base is 1587±295 year BP /non-calibrated 14C LSC age/ (Treml, Křížek, Engel, Petr, 2006).
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Křížek M., Treml V., Engel Z., 2010, Czy najwyższe partie Sudetów powyżej górnej granicy lasu są domeną peryglacjalną?,Czasopismo Geograficzne, 81(1–2): 75–102.